# $ +Windows Sockets
An Open Interface for
Network Programming under
Microsoft Windows

Version 1.1
20 January 1993

Authors and Copyright
Acknowledgements
Introduction
Programming with Sockets
Socket Library Overview
Socket Library Reference
Appendices
Error Codes and Header Files
Error Codes
Header Files
Notes for Windows Sockets Suppliers
For Further Reference
Background Information
Origins of Windows Sockets
Legal Status of Windows Sockets
The Story Behind the Windows Socket Icon
Windows Sockets in Windows Help

# This Windows Help version of the Windows Socket 1.1 Specification is provided by InfoMagic, Inc.  It may be freely redistributed, either as provided or in modified form.  Winsock providers may integrate it into their product documentation without incurring any obligation to InfoMagic, Inc.  The source .rtf file is available from microdyne.com via anonymous FTP along with the other WIndows Sockets material.

#Martin Hall
Mark Towfiq
Geoff Arnold
David Treadwell
Henry Sanders

Copyright  1992 by Martin Hall, Mark Towfiq
Geoff Arnold, David Treadwell and Henry Sanders

All rights reserved.

This document may be freely redistributed in any form, electronic or otherwise, provided that it is distributed in its entirety and that the copyright and this notice are included.  Comments or questions may be submitted via electronic mail to winsock@microdyne.com.  Requests to be added to the Windows Sockets mailing list should be addressed to winsock-request@microdyne.com.  This specification, archives of the mailing list, and other information on Windows Sockets are available via anonymous FTP from the host microdyne.com, directory /pub/winsock.  Questions about products conforming to this specification should be addressed to the vendors of the products.

# $ + K Windows Sockets
Acknowledgments

The authors would like to thank their companies for allowing them the time and resources to make this specification possible:  JSB Corporation, Microdyne Corporation, FTP Software, Sun Microsystems, and Microsoft Corporation.

Special thanks should also be extended to the other efforts contributing to the success of Windows Sockets. The original draft was heavily influenced by existing specifications offered and detailed by JSB Corporation and Net Manage, Inc. The "version 1.0 debate" hosted by Microsoft in Seattle allowed many of the members of the working group to hash out final details for 1.0 vis-a-vis. 

Sun Microsystems was kind enough to allow first time implementors to "plug and play" beta software during the first Windows Sock-A-Thon of  Windows Sockets applications and implementations at Interop Fall '92.  Microsoft has shared WSAT (the Windows Sockets API Tester) with other Windows Sockets implementors as a standard Windows Sockets test suite to aid in testing their implementations. Finally, Sun Microsystems and FTP Software plan to host the Windows Sock-A-Thon II in Boston February '93. 

Without the contributions of the individuals and corporations involved in the working group, Windows Sockets would never have been as thoroughly reviewed and completed as quickly. In just one year, several competitors in the networking business developed a useful specification with something to show for it! Many thanks to all which participated, either in person or on e-mail to the Windows Sockets effort. The authors would like to thank everyone who participated in any way, and apologize in advance for anyone we have omitted. 

List of contributors:

Martin Hall 	(Chairman)	JSB Corporation	martinh@jsbus.com
Mark Towfiq 	(Coordinator)	Microdyne Corporation	towfiq@microdyne.com
Geoff Arnold 	(Editor 1.0)	Sun Microsystems	geoff@east.sun.com
David Treadwell	(Editor 1.1)	Microsoft Corporation	davidtr@microsoft.com
Henry Sanders		Microsoft Corporation	henrysa@microsoft.com

J. Allard	Microsoft Corporation	jallard@microsoft.com
Chris Arap-Bologna	Distinct	chris@distinct.com
Larry Backman	FTP Software	backman@ftp.com
Alistair Banks	Microsoft Corporation	alistair@microsoft.com
Rob Barrow	JSB Corporation	robb@jsb.co.uk
Carl Beame	Beame & Whiteside	beame@mcmaster,ca
Dave Beaver	Microsoft Corporation	dbeaver@microsoft.com
Amatzia BenArtzi	NetManage, Inc.	amatzia@netmanage.com
Mark Beyer	Ungermann-Bass	mbeyer@ub.com
Nelson Bolyard	Silicon Graphics, Inc.	nelson@sgi.com
Pat Bonner	Hewlett-Packard	p_bonner@cnd.hp.com
Derek Brown	FTP Software	db@wco.ftp.com
Malcolm Butler	ICL	mcab@oasis.icl.co.uk
Mike Calbaum	Fronteir Technologies	mike@frontiertech.com
Isaac Chan	Microsoft Corporation	isaacc@microsoft.com
Khoji Darbani	Informix	khoji@informix.com
Nestor Fesas	Hughes LAN Systems	nestor@hls.com
Karanja Gakio	FTP Software	karanja@ftp.com
Vikas Garg	Distinct	vikas@distinct.com
Gary Gere	Gupta	ggere@gupta.com
Jim Gilroy	Microsoft Corporation	jamesg@microsoft.com
Bill Hayes	Hewlett-Packard	billh@hpchdpc.cnd.hp.com
Paul Hill	MIT	pbh@athena.mit.edu
Tmima Koren	Net Manage, Inc.	tmima@netmanage.com
Hoek Law	Citicorp	law@dcc.tti.com
Graeme Le Roux	Moresdawn P/L	-
Kevin Lewis	Novell	kevinl@novell.com
Roger Lin	3Com	roger_lin@3mail.3com.com
Terry Lister	Hewlett-Packard	tel@cnd.hp.com
Jeng Long Jiang	Wollongong	long@twg.com
Lee Murach	Network Research	lee@nrc.com
Pete Ostenson	Microsoft Corporation	peteo@microsoft.com
David Pool	Spry, Inc.	dave@spry.com
Bob Quinn	FTP Software	rcq@ftp.com
Glenn Reitsma	Hughes LAN Systems	glennr@hls.com
Brad Rice	Age	rice@age.com
Allen Rochkind	3Com	-
Jonathan Rosen	IBM	jrosen@vnet.ibm.com
Steve Stokes	Novell	stoke@novell.com
Joseph Tsai	3Com	joe_tsai@3mail.3com.com
James Van Bokkelen	FTP Software	jbvb@ftp.com
Miles Wu	Wollongong	wu@twg.com
Boris Yanovsky	NetManage, Inc.	boris@netmanage.com

# $ + K Windows Sockets
Introduction
What is Windows Sockets
Berkeley Sockets
Microsoft Windows and Windows-specific extensions
The Status of this Specification
Revision History

# $ + Introduction

What is Windows Sockets
The Windows Sockets specification defines a network programming interface for Microsoft Windows which is based on the "socket" paradigm popularized in the Berkeley Software Distribution (BSD) from the University of California at Berkeley.  It encompasses both familiar Berkeley socket style routines and a set of Windows-specific extensions designed to allow the programmer to take advantage of the message-driven nature of Windows.

The Windows Sockets Specification is intended to provide a single API to which application developers can program and multiple network software vendors can conform.  Furthermore, in the context of a particular version of Microsoft Windows, it defines a binary interface (ABI) such that an application written to the Windows Sockets API can work with a conformant protocol implementation from any network software vendor.  This specification thus defines the library calls and associated semantics to which an application developer can program and which a network software vendor can implement.

Network software which conforms to this Windows Sockets specification will be considered "Windows Sockets Compliant".  Suppliers of interfaces which are "Windows Sockets Compliant" shall be referred to as "Windows Sockets Suppliers".  To be Windows Sockets Compliant, a vendor must implement 100% of this Windows Sockets specification.

Applications which are capable of operating with any "Windows Sockets Compliant" protocol implementation will be considered as having a "Windows Sockets Interface" and will be referred to as "Windows Sockets Applications".

This version of the Windows Sockets specification defines and documents the use of the API in conjunction with the Internet Protocol Suite (IPS, generally referred to as TCP/IP).  Specifically, all Windows Sockets implementations support both stream (TCP) and datagram (UDP) sockets.

While the use of this API with alternative protocol stacks is not precluded (and is expected to be the subject of future revisions of the specification), such usage is beyond the scope of this version of the specification.

# $ + K Introduction

Berkeley Sockets
The Windows Sockets Specification has been built upon the Berkeley Sockets programming model which is the de facto standard for TCP/IP networking.  It is intended to provide a high degree of familiarity for programmers who are used to programming with sockets in UNIX and other environments, and to simplify the task of porting existing sockets-based source code.  The Windows Sockets API is consistent with release 4.3 of the Berkeley Software Distribution (4.3BSD).

Portions of the Windows Sockets specification are derived from material which is Copyright (c) 1982-1986 by the Regents of the University of California.  All rights are reserved.  The Berkeley Software License Agreement specifies the terms and conditions for redistribution.

# $ + Introduction

Microsoft Windows and Windows-specific extensions
This API is intended to be usable within all implementations and versions of Microsoft Windows from Microsoft Windows Version 3.0 onwards.  It thus provides for Windows Sockets implementations and Windows Sockets applications in both 16 and 32 bit operating environments.  

Windows Sockets makes provisions for multithreaded Windows processes.  A process contains one or more threads of execution.  In the Windows 3.1 non-multithreaded world, a task corresponds to a process with a single thread.  All references to threads in this document refer to actual "threads" in multithreaded Windows environments.  In non multithreaded environments (such as Windows 3.0), use of the term thread refers to a Windows process.

The Microsoft Windows extensions included in Windows Sockets are provided to allow application developers to create software which conforms to the Windows programming model.  It is expected that this will facilitate the creation of robust and high-performance applications, and will improve the cooperative multitasking of applications within non-preemptive versions of Windows.  With the exception of WSAStartup() and WSACleanup() their use is not mandatory.

# $ + K Introduction
The Status of this Specification
Windows Sockets is an independent specification which was created and exists for the benefit of application developers and network vendors and, indirectly, computer users. Each published (non-draft) version of this specification  represents a fully workable API for implementation by network vendors and programming use by application developers. Discussion of this specification and  suggested improvements continue and are welcomed. Such discussion occurs mainly via the Internet electronic mail forum winsock@microdyne.com. Meetings of  interested parties occur on an irregular basis. Details of these meetings are publicized to the electronic mail forum.

# $ + K Introduction
Revision History
Windows Sockets Version 1.0
Windows Sockets Version 1.0 represented the results of considerable work within  the vendor and user community as discussed in "Origins of Windows Sockets". This version of  the specification was released in order that network software suppliers and  application developers could begin to construct implementations and applications  which conformed to the Windows Sockets standard.

Windows Sockets Version 1.1
Windows Sockets Version 1.1 follows the guidelines and structure laid out by version 1.0, making changes only where absolutely necessary as indicated by the experiences of a number of companies that created Windows Sockets implementations based on the version 1.0 specification.  Version 1.1 contains several clarifications and minor fixes to version 1.0.  Additionally, the following more significant changes were incorporated into version 1.1:

	Inclusion of the gethostname() routine to simplify retrieval of the host's name and address.

	Definition of DLL ordinal values below 1000 as reserved for Windows Sockets and ordinals above 1000 as unrestricted.  This allows Windows Sockets vendors to include private interfaces to their DLLs without risking that the ordinals choosen will conflict with a future version of Windows Sockets.

	Addition of a reference count to WSAStartup() and WSACleanup(), requiring correspondences between the calls.  This allows applications and third-party DLLs to make use of a Windows Sockets implementation without being concerned about the calls to these APIs made by the other.

	Change of return type of inet_addr() from struct in_addr to unsigned long.  This was required due to different handling of four-byte structure returns between the Microsoft and Borland C compilers.

	Change of WSAAsyncSelect() semantics from "edge-triggerred" to "level-triggerred".  The level-triggerred semantics significantly simplify an application's use of this routine.

	Change the ioctlsocket() FIONBIO semantics to fail if a WSAAsyncSelect() call is outstanding on the socket.

	Addition of the TCP_NODELAY socket option for RFC 1122 conformance.

# $ + Windows Sockets
Programming with Sockets
Windows Sockets Stack Installation Checking
Sockets
Byte Ordering
Socket Options
Database Files
Deviation from Berkeley Sockets
Windows Sockets in Multithreaded Versions of Windows

# $ + K Programming with Sockets
Windows Sockets Stack Installation Checking
To detect the presence of one (or many) Windows Sockets implementations on a system, an application which has been linked with the Windows Sockets Import Library may simply call the WSAStartup() routine.  If an application wishes to be a little more sophisticated it can examine the $PATH environment variable and search for instances of Windows Sockets implementations (WINSOCK.DLL).  For each instance it can issue a LoadLibrary() call and use the WSAStartup() routine to discover implementation specific data.

This version of the Windows Sockets specification does not attempt to address explicitly the issue of multiple concurrent Windows Sockets implementations.  Nothing in the specification should be interpreted as restricting multiple Windows Sockets DLLs from being present and used concurrently by one or more Windows Sockets applications.

For further details of where to obtain Windows Sockets components, see "Windows Sockets Components".

# $ + K K Programming with Sockets
Sockets
The following material is derived from the document "An Advanced 4.3BSD Interprocess Communication Tutorial" by Samuel J. Leffler, Robert S. Fabry, William N. Joy, Phil Lapsley, Steve Miller, and Chris Torek.

Basic concepts
Client-server model
Out-of-band data
Broadcasting

# $ + K Sockets
Basic concepts
The basic building block for communication is the socket.  A socket is an endpoint of communication to which a name may be bound.  Each socket in use has a type and an associated process.  Sockets exist within communication domains.  A communication domain is an abstraction introduced to bundle common properties of threads communicating through sockets.  Sockets normally exchange data only with sockets in the same domain (it may be possible to cross domain boundaries, but only if some translation process is performed).  The Windows Sockets facilities support a single communication domain: the Internet domain, which is used by processes which communicate using the Internet Protocol Suite.  (Future versions of this specification may include additional domains.) 

Sockets are typed according to the communication properties visible to a user.  Applications are presumed to communicate only between sockets of the same type, although there is nothing that prevents communication between sockets of different types should the underlying communication protocols support this.  

Two types of sockets currently are available to a user.  A stream socket provides for the bi-directional, reliable, sequenced, and unduplicated flow of data without record boundaries.  

A datagram socket supports bi-directional flow of data which is not promised to be sequenced, reliable, or unduplicated.  That is, a process receiving messages on a datagram socket may find messages duplicated, and, possibly, in an order different from the order in which it was sent.  An important characteristic of a datagram socket is that record boundaries in data are preserved.  Datagram sockets closely model the facilities found in many contemporary packet switched networks such as Ethernet.  

# $ + K Sockets
Client-server model
The most commonly used paradigm in constructing distributed applications is the client/server model.  In this scheme client applications request services from a server application.  This implies an asymmetry in establishing communication between the client and server.  

The client and server require a well-known set of conventions before service may be rendered (and accepted).  This set of conventions comprises a protocol which must be implemented at both ends of a connection.  Depending on the situation, the protocol may be symmetric or asymmetric.  In a symmetric protocol, either side may play the master or slave roles.  In an asymmetric protocol, one side is immutably recognized as the master, with the other as the slave.  An example of a symmetric protocol is the TELNET protocol used in the Internet for remote terminal emulation.  An example of an asymmetric protocol is the Internet file transfer protocol, FTP.  No matter whether the specific protocol used in obtaining a service is symmetric or asymmetric, when accessing a service there is a "client process'' and a "server process''.  

A server application normally listens at a well-known address for service requests.  That is, the server process remains dormant until a connection is requested by a client's connection to the server's address.  At such a time the server process "wakes up'' and services the client, performing whatever appropriate actions the client requests of it.  While connection-based services are the norm, some services are based on the use of datagram sockets.  

# $ + K Sockets
Out-of-band data
Note: The following discussion of out-of-band data, also referred to as TCP Urgent data,  follows the model used in the Berkeley software distribution.  Users and implementors should be aware of the fact that there are at present two conflicting interpretations of RFC 793 (in which the concept is introduced), and that the implementation of out-of-band data in the Berkeley Software Distribution does not conform to the Host Requirements laid down in RFC 1122.  To minimize interoperability problems, applications writers are advised not to use out-of-band data unless this is required in order to interoperate with an existing service.  Windows Sockets suppliers are urged to document the out-of-band semantics (BSD or RFC 1122) which their product implements.  It is beyond the scope of this specification to mandate a particular set of semantics for out-of-band data handling.

The stream socket abstraction includes the notion of "out of band'' data.  Out-of-band data is a logically independent transmission channel associated with each pair of connected stream sockets.  Out-of-band data is delivered to the user independently of normal data.  The abstraction defines that the out-of-band data facilities must support the reliable delivery of at least one out-of-band message at a time.  This message may contain at least one byte of data, and at least one message may be pending delivery to the user at any one time.  For communications protocols which support only in-band signaling (i.e.  the urgent data is delivered in sequence with the normal data), the system normally extracts the data from the normal data stream and stores it separately.  This allows users to choose between receiving the urgent data in order and receiving it out of sequence without having to buffer all the intervening data.  It is possible to "peek'' at out-of-band data.  

An application may prefer to process out-of-band data "in-line", as part of the normal data stream.  This is achieved by setting the socket option SO_OOBINLINE (see setsockopt()).  In this case, the application may wish to determine whether any of the unread data is "urgent" (the term usually applied to in-line out-of-band data).  To facilitate this, the Windows Sockets implementation will maintain a logical "mark" in the data stream to indicate the point at which the out-of-band data was sent.  An application can use the SIOCATMARK ioctlsocket() command to determine whether there is any unread data preceding the mark.  For example, it might use this to resynchronize with its peer by ensuring that all data up to the mark in the data stream is discarded when appropriate.

The WSAAsyncSelect() routine is particularly well suited to handling notification of the presence of out-of-band-data.

# $ + K Sockets
Broadcasting
By using a datagram socket, it is possible to send broadcast packets on many networks supported by the system.  The network itself must support broadcast: the system provides no simulation of broadcast in software.  Broadcast messages can place a high load on a network, since they force every host on the network to service them.  Consequently, the ability to send broadcast packets has been limited to sockets which are explicitly marked as allowing broadcasting.  Broadcast is typically used for one of two reasons: it is desired to find a resource on a local network without prior knowledge of its address, or important functions such as routing require that information be sent to all accessible neighbors.

The destination address of the message to be broadcast depends on the network(s) on which the message is to be broadcast.  The Internet domain supports a shorthand notation for broadcast on the local network, the address INADDR_BROADCAST.  Received broadcast messages contain the senders address and port, as datagram sockets must be bound before use.

Some types of network support the notion of different types of broadcast.  For example, the IEEE 802.5 token ring architecture supports the use of link-level broadcast indicators, which control whether broadcasts are forwarded by bridges.  The Windows Sockets specification does not provide any mechanism whereby an application can determine the type of underlying network, nor any way to control the semantics of broadcasting.

# $ + K Programming with Sockets
Byte Ordering
The Intel byte ordering is like that of the DEC VAX, and therefore differs from the Internet and 68000-type processor byte ordering.  Thus care must be taken to ensure correct orientation.

Any reference to IP addresses or port numbers passed to or from a Windows Sockets routine must be in network order.  This includes the IP address and port fields of a struct sockaddr_in (but not the sin_family field).

Consider an application which normally contacts a server on the TCP port corresponding to the "time" service, but which provides a mechanism for the user to specify that an alternative port is to be used.  The port number returned by getservbyname() is already in network order, which is the format required constructing an address, so no translation is required.  However if the user elects to use a different port, entered as an integer, the application must convert this from host to network order (using the htons() function) before using it to construct an address.  Conversely, if the application wishes to display the number of the port within an address (returned via, e.g., getpeername()), the port number must be converted from network to host order (using ntohs()) before it can be displayed.

Since the Intel and Internet byte orders are different, the conversions described above are unavoidable.  Application writers are cautioned that they should use the standard conversion functions provided as part of the Windows Sockets API rather than writing their own conversion code, since future implementations of Windows Sockets are likely to run on systems for which the host order is identical to the network byte order.  Only applications which use the standard conversion functions are likely to be portable.

# $ + K Programming with Sockets
Socket Options
The socket options supported by Windows Sockets are listed in the pages describing setsockopt() and getsockopt().  A Windows Sockets implementation must recognize all of these options, and (for getsockopt()) return plausible values for each.  The default value for each option is shown in the following table.

Value	Type	Meaning	Default	Note
SO_ACCEPTCON	BOOL	Socket is listen()ing.	FALSE unless
			a listen() has
			been performed	
SO_BROADCAST	BOOL	Socket is configured	FALSE
		for the transmission of
		broadcast messages.	
SO_DEBUG	BOOL	Debugging is enabled.  	FALSE	(i)
SO_DONTLINGER	BOOL	If true, the SO_LINGER	TRUE
		option is disabled..		
SO_DONTROUTE	BOOL	Routing is disabled.	FALSE	(i)
SO_ERROR	int	Retrieve error status	0
		and clear.	
SO_KEEPALIVE	BOOL	Keepalives are being	FALSE
		sent.	
SO_LINGER	struct linger FAR *	Returns the current	l_onoff is 0
		linger options.	
SO_OOBINLINE	BOOL	Out-of-band data is	FALSE
		being received in the
		normal data stream.	
SO_RCVBUF	int	Buffer size for receives	Implementation
			dependant.	(i)
SO_REUSEADDR	BOOL	The address to which	FALSE
		this socket is bound
		can be used by others.	
SO_SNDBUF	int	Buffer size for sends	Implementation
			dependant.	(i)
SO_TYPE	int	The type of the socket	As created
		(e.g. SOCK_STREAM). via socket()	
TCP_NODELAY	BOOL	Disables the Nagle	Implementation
			dependant.
		algorithm for send
		coalescing.

Notes:
(i)	An implementation may silently ignore this option on setsockopt() and return a constant value for getsockopt(), or it may accept a value for setsockopt() and return the corresponding value in getsockopt() without using the value in any way.

# $ + K K Programming with Sockets
Database Files
The getXbyY() and WSAAsyncGetXByY() classes of routines are provided for retrieving network specific information.  The getXbyY() routines were originally designed (in the first Berkeley UNIX releases) as mechanisms for looking up information in text databases.  Although the information may be retrieved by the Windows Sockets implementation in different ways, a Windows Sockets application requests such information in a consistent manner through either the getXbyY() or the WSAAsyncGetXByY() class of routines.

# $ + K Programming with Sockets
Deviation from Berkeley Sockets
There are a few limited instances where the Windows Sockets API has had to divert from strict adherence to the Berkeley conventions, usually because of difficulties of implementation in a Windows environment.

socket data type and error values
select() and FD_*
Error codes - errno, h_errno & WSAGetLastError()
Pointers
Renamed functions
Blocking routines & EINPROGRESS
Maximum number of sockets supported
Include files
Return values on API failure

# $ + K Deviation from Berkeley Sockets
socket data type and error values
A new data type, SOCKET, has been defined.  The definition of this type was necessary for future enhancements to the Windows Sockets specification, such as being able to use sockets as file handles in Windows NT.  Definition of this type also facilitates porting of applications to a Win/32 environment, as the type will automatically be promoted from 16 to 32 bits.

In UNIX, all handles, including socket handles, are small, non-negative intergers, and some applications make assumptions that this will be true.  Windows Sockets handles have no restrictions, other than that the value INVALID_SOCKET is not a valid socket.  Socket handles may take any value in the range 0 to INVALID_SOCKET-1.

Because the SOCKET type is unsigned, compiling existing source code from, for example, a UNIX environment may lead to compiler warnings about signed/unsigned data type mismatches.

This means, for example, that checking for errors when the socket() and accept() routines return should not be done by comparing the return value with -1, or seeing if the value is negative (both common, and legal, approaches in BSD).  Instead, an application should use the manifest constant INVALID_SOCKET as defined in winsock.h.  For example:
	TYPICAL BSD STYLE:
s = socket(...);
if (s == -1)	/* or s < 0 */
	{...}

	PREFERRED STYLE:
s = socket(...);
if (s == INVALID_SOCKET)
	{...}

# $ + K Deviation from Berkeley Sockets
select() and FD_*
Because a SOCKET is no longer represented by the UNIX-style "small non-negative integer", the implementation of the select() function was changed in the Windows Sockets API.  Each set of descriptors is still represented by the fd_set type, but instead of being stored as a bitmask the set is implemented as an array of SOCKETs..  To avoid potential problems, applications must adhere to the use of the FD_XXX macros to set, initialize, clear, and check the fd_set structures.

# $ + K Deviation from Berkeley Sockets
Error codes - errno, h_errno & WSAGetLastError()
Error codes set by the Windows Sockets implementation are NOT made available via the errno variable.  Additionally, for the getXbyY() class of functions, error codes are NOT made available via the h_errno variable.  Instead, error codes are accessed by using the WSAGetLastError() API.  This function is provided in Windows Sockets as a precursor (and eventually an alias) for the Win32 function GetLastError().  This is intended to provide a reliable way for a thread in a multi-threaded process to obtain per-thread error information.

For compatibility with BSD, an application may choose to include a line of the form:

#define errno WSAGetLastError()

This will allow networking code which was written to use the global errno to work correctly in a single-threaded environment.  There are, obviously, some drawbacks.  If a source file includes code which inspects errno for both socket and non-socket functions, this mechanism cannot be used.  Furthermore, it is not possible for an application to assign a new value to errno.  (In Windows Sockets the function WSASetLastError() may be used for this purpose.)

	TYPICAL BSD STYLE:
r = recv(...);
if (r == -1
    && errno == EWOULDBLOCK)
	{...}

	PREFERRED STYLE:
r = recv(...);
if (r == -1       /* (but see below) */
    && WSAGetLastError() == EWOULDBLOCK)
	{...}

Although error constants consistent with 4.3 Berkeley Sockets are provided for compatibility purposes, applications should, where possible, use the "WSA" error code definitions.  For example, a more accurate version of the above source code fragment is:

r = recv(...);
if (r == -1
    && WSAGetLastError() == WSAEWOULDBLOCK)
	{...}

# $ + K Deviation from Berkeley Sockets
Pointers
All pointers used by applications with Windows Sockets should be FAR.  To facilitate this, data type definitions such as LPHOSTENT are provided.

# $ + K Deviation from Berkeley Sockets
Renamed functions
In two cases it was necessary to rename functions which are used in Berkeley Sockets in order to avoid clashes with other APIs.

close() & closesocket()
In Berkeley Sockets, sockets are represented by standard file descriptors, and so the close() function can be used to close sockets as well as regular files.  While nothing in the Windows Sockets API prevents an implementation from using regular file handles to identify sockets, nothing requires it either.  Socket descriptors are not presumed to correspond to regular file handles, and file operations such as read(), write(), and close() cannot be assumed to work correctly when applied to socket descriptors..  Sockets must be closed by using the closesocket() routine.  Using the close() routine to close a socket is incorrect and the effects of doing so are undefined by this specification.

ioctl() & ioctlsocket()
Various C language run-time systems use the ioctl() routine for purposes unrelated to Windows Sockets.  For this reason we have defined the routine ioctlsocket() which is used to handle socket functions which in the Berkeley Software Distribution are performed using ioctl() and fcntl().

# $ + K Deviation from Berkeley Sockets
Blocking routines & EINPROGRESS
Although blocking operations on sockets are supported under Windows Sockets, their use is strongly discouraged.  Programmers who are constrained to use blocking mode - for example, as part of an existing application which is to be ported - should be aware of the semantics of blocking operations in Windows Sockets.  See Blocking/Non blocking & Data Volatility for more details.

# $ + K Deviation from Berkeley Sockets
Maximum number of sockets supported
The maximum number of sockets supported by a particular Windows Sockets supplier is implementation specific.  An application should make no assumptions about the availability of a certain number of sockets.  This topic is addressed further in the section on WSAStartup().  However, independent of the number of sockets supported by a particular implementation is the issue of the maximum number of sockets which an application can actually make use of.

The maximum number of sockets which a Windows Sockets application can make use of is determined at compile time by the manifest constant FD_SETSIZE.  This value is used in constructing the fd_set structures used in select().  The default value in winsock.h is 64.  If an application is designed to be capable of working with more than 64 sockets, the implementor should define the manifest FD_SETSIZE in every source file before including winsock.h.  One way of doing this may be to include the definition within the compiler options in the makefile, for example adding -DFD_SETSIZE=128 as an option to the compiler command line for Microsoft C.  It must be emphasized that defining FD_SETSIZE as a particular value has no effect on the actual number of sockets provided by a Windows Sockets implementation.

# $ + K Deviation from Berkeley Sockets
Include files
For ease of portability of existing Berkeley sockets based source code, a number of standard Berkeley include files are supported.  However, these Berkeley header files merely include the winsock.h include file, and it is therefore sufficient (and recommended) that Windows Sockets application source files should simply include winsock.h.

# $ + K Deviation from Berkeley Sockets
Return values on API failure
The manifest constant SOCKET_ERROR is provided for checking API failure.  Although use of this constant is not mandatory, it is recommended.  The following example illustrates the use of the SOCKET_ERROR constant:

	TYPICAL BSD STYLE:
r = recv(...);
if (r == -1     /* or r < 0 */
    && errno == EWOULDBLOCK)
	{...}
	PREFERRED STYLE:
r = recv(...);
if (r == SOCKET_ERROR
    && WSAGetLastError() == WSAEWOULDBLOCK)
	{...}

# $ + K Programming with Sockets
Raw Sockets
The Windows Sockets specification does not mandate that a Windows Sockets DLL support raw sockets, that is, sockets opened with SOCK_RAW.  However, a Windows Sockets DLL is allowed and encouraged to supply raw socket support.  A Windows Sockets-compliant application that wishes to use raw sockets should attempt to open the socket with the socket() call (see section 4.1.23), and if it fails either attempt to use another socket type or indicate the failure to the user.

# $ + K Programming with Sockets
Windows Sockets in Multithreaded Versions of Windows
The Windows Sockets interface is designed to work for both single-threaded versions of Windows (such as Windows 3.1) and future multithreaded versions of Windows (such as Windows NT).  In a multithreaded environment the sockets interface is basically the same, but the author of a multithreaded application must be aware that it is the responsibility of the application, not the Windows Sockets implementation, to synchronize access to a socket between threads.  This is the same rule as applies to other forms of I/O such as file I/O.  Failure to synchronize calls on a socket leads to unpredictable results; for example if there are two simultaneous calls to send(), there is no guarantee as to the order in which the data will be sent.  

Closing a socket in one thread that has an outstanding blocking call on the same socket in another thread will cause the blocking call to fail with WSAEINTR, just as if the operation were cancelled.  This also applies if there is a select() call outstanding and the application closes one of the sockets being selected.

There is no default blocking hook installed in preemptive multithreaded versions of Windows.  This is because the machine will not be blocked if a single application is waiting for an operation to complete and hence not calling PeekMessage() or GetMessage() which cause the application to yield in nonpremptive Windows.  However, for backwards compatibility the WSASetBlockingHook() call is implemented in multithreaded versions of Windows, and any application whose behavior depends on the default blocking hook may install their own blocking hook which duplicates the default hook's semantics, if desired.

# $ + Windows Sockets
Socket Library Overview

Socket Functions
Blocking/Non blocking & Data Volatility
Database Functions
Microsoft Windows-specific Extension Functions

# $ + K Socket Library Overview
Socket Functions
The Windows Sockets specification includes the following Berkeley-style socket routines:

accept()	An incoming connection is acknowledged and associated with an immediately created socket.  The original socket is returned to the listening state.
bind()	Assign a local name to an unnamed socket.
closesocket()	Remove a socket descriptor from the per-process object reference table.  Only blocks if SO_LINGER is set.
connect()	Initiate a connection on the specified socket.
getpeername()	Retrieve the name of the peer connected to the specified socket descriptor.
getsockname()	Retrieve the current name for the specified socket
getsockopt()	Retrieve options associated with the specified socket descriptor.
htonl()	Convert a 32-bit quantity from host byte order to network byte order.
htons()	Convert a 16-bit quantity from host byte order to network byte order.
inet_addr()	Converts a character string representing a number in the Internet standard ".'' notation to an Internet address value.
inet_ntoa()	Converts an Internet address value to an ASCII string in ".'' notation i.e.  "a.b.c.d''.
ioctlsocket()	Provide control for descriptors.
listen()	Listen for incoming connections on a specified socket.
ntohl()	Convert a 32-bit quantity from network byte order to host byte order.
ntohs()	Convert a 16-bit quantity from network byte order to host byte order.
recv()*	Receive data from a connected socket.
recvfrom()*	Receive data from either a connected or unconnected socket.
select()*	Perform synchronous I/O multiplexing.
send()*	Send data to a connected socket.
sendto()*	Send data to either a connected or unconnected socket.
setsockopt()	Store options associated with the specified socket descriptor.
shutdown()	Shut down part of a full-duplex connection.
socket()	Create an endpoint for communication and return a socket descriptor.

* The routine can block if acting on a blocking socket.

# $ + K Socket Library Overview
Blocking/Non blocking & Data Volatility
One major issue in porting applications from a Berkeley sockets environment to a Windows environment involves "blocking"; that is, invoking a function which does not return until the associated operation is completed.  The problem arises when the operation may take an arbitrarily long time to complete: an obvious example is a recv() which may block until data has been received from the peer system.  The default behavior within the Berkeley sockets model is for a socket to operate in a blocking mode unless the programmer explicitly requests that operations be treated as non-blocking.  It is strongly recommended that programmers use the nonblocking (asynchronous) operations if at all possible, as they work significantly better within the nonpreemptive Windows environment.  Use blocking operations only if absolutely necessary, and carefully read and understand this section if you must use blocking operations.

Even on a blocking socket, some operations (e.g. bind(), getsockopt(), getpeername()) can be completed immediately.  For such operations there is no difference between blocking and non-blocking operation.  Other operations (e.g. recv()) may be completed immediately or may take an arbitrary time to complete, depending on various transport conditions.  When applied to a blocking socket, these operations are referred to as blocking operations.  All routines which can block are listed with an asterisk in the tables above and below.

Within a Windows Sockets implementation, a blocking operation which cannot be completed immediately is handled as follows.  The DLL initiates the operation, and then enters a loop in which it dispatches any Windows messages (yielding the processor to another thread if necessary) and then checks for the completion of the Windows Sockets function.  If the function has completed, or if WSACancelBlockingCall() has been invoked, the blocking function completes with an appropriate result.  Refer to  WSASetBlockingHook(), for a complete description of this mechanism, including pseudocode for the various functions.

If a Windows message is received for a process for which a blocking operation is in progress, there is a risk that the application will attempt to issue another Windows Sockets call.  Because of the difficulty of managing this condition safely, the Windows Sockets specification does not support such application behavior.  Two functions are provided to assist the programmer in this situation.  WSAIsBlocking() may be called to determine whether or not a blocking Windows Sockets call is in progress.  WSACancelBlockingCall() may be called to cancel an in-progress blocking call, if any.  Any other Windows Sockets function which is called in this situation will fail with the error WSAEINPROGRESS.  It should be emphasized that this restriction applies to both blocking and non-blocking operations.

Although this mechanism is sufficient for simple applications, it cannot support the complex message-dispatching requirements of more advanced applications (for example, those using the MDI model).  For such applications, the Windows Sockets API includes the function WSASetBlockingHook(), which allows the programmer to define a special routine which will be called instead of the default message dispatch routine described above.

The Windows Sockets DLL will call the blocking hook function only if all of the following are true: the routine is one which is defined as being able to block, the specified socket is a blocking socket, and the request cannot be completed immediately.  (A socket is set to blocking by default, but the IOCTL FIONBIO and  WSAAsyncSelect() both set a socket to nonblocking mode.)  If an application uses only non-blocking sockets and uses the WSAAsyncSelect() and/or the WSAAsyncGetXByY() routines instead of select() and the getXbyY() routines, then the blocking hook will never be called and the application does not need to be concerned with the reentrancy issues the blocking hook can introduce.

If an application invokes an asynchronous or non-blocking operation which takes a pointer to a memory object (e.g. a buffer, or a global variable) as an argument, it is the responsibility of the application to ensure that the object is available to the Windows Sockets implementation throughout the operation.  The application must not invoke any Windows function which might affect the mapping or addressability of the memory involved.  In a multithreaded system, the application is also responsible for coordinating access to the object using appropriate synchronization mechanisms.  A Windows Sockets implementation cannot, and will not, address these issues.  The possible consequences of failing to observe these rules are beyond the scope of this specification.

# $ + K K Socket Library Overview
Database Functions
The Windows Sockets specification defines the following "database" routines.  As noted earlier, a Windows Sockets supplier may choose to implement these in a manner which does not depend on local database files.  The pointer returned by certain database routines such as gethostbyname() points to a structure which is allocated by the Windows Sockets library.  The data which is pointed to is volatile and is good only until the next Windows Sockets API call from that thread.  Additionally, the application must never attempt to modify this structure or to free any of its components.  Only one copy of this structure is allocated for a thread, and so the application should copy any information which it needs before issuing any other Windows Sockets API calls.

gethostbyaddr()*	Retrieve the name(s) and address corresponding to a network address.
gethostname()	Retrieve the name of the local host.
gethostbyname()*	Retrieve the name(s) and address corresponding to a host name.
getprotobyname()*	Retrieve the protocol name and number corresponding to a protocol name.
getprotobynumber()*	Retrieve the protocol name and number corresponding to a protocol number.
getservbyname()*	Retrieve the service name and port corresponding to a service name.
getservbyport()*	Retrieve the service name and port corresponding to a port.

* The routine can block under some circumstances.

# $ + K K Socket Library Overview
Microsoft Windows-specific Extension Functions
The Windows Sockets specification provides a number of extensions to the standard set of Berkeley Sockets routines.  Principally, these extended APIs allow message-based, asynchronous access to network events.  While use of this extended API set is not mandatory for socket-based programming (with the exception of WSAStartup() and WSACleanup()), it is recommended for conformance with the Microsoft Windows programming paradigm.

Asynchronous select() Mechanism
Asynchronous Support Routines
Hooking Blocking Methods
Error Handling
Accessing a Windows Sockets DLL from an Intermediate DLL
Internal Use of Messages by Windows Sockets Implementations
Private API Interfaces

WSAAsyncGetHostByAddr()	A set of functions which provide asynchronous
WSAAsyncGetHostByName()	versions of the standard Berkeley
WSAAsyncGetProtoByName()	getXbyY() functions.  For example, the
WSAAsyncGetProtoByNumber()	WSAAsyncGetHostByName() function provides an asynchronous message based
WSAAsyncGetServByName()	implementation of the standard Berkeley
WSAAsyncGetServByPort()	gethostbyname() function.
WSAAsyncSelect()	Perform asynchronous version of select()
WSACancelAsyncRequest()	Cancel an outstanding instance of a WSAAsyncGetXByY() function.
WSACancelBlockingCall()	Cancel an outstanding "blocking" API call
WSACleanup()	Sign off from the underlying Windows Sockets DLL.
WSAGetLastError()	Obtain details of last Windows Sockets API error
WSAIsBlocking()	Determine if the underlying Windows Sockets DLL is already blocking an existing call for this thread
WSASetBlockingHook()	"Hook" the blocking method used by the underlying Windows Sockets implementation
WSASetLastError()	Set the error to be returned by a subsequent WSAGetLastError()
WSAStartup()	Initialize the underlying Windows Sockets DLL.
WSAUnhookBlockingHook()	Restore the original blocking function

# $ + K K Microsoft Windows Extension Functions
Asynchronous select() Mechanism
The WSAAsyncSelect() API allows an application to register an interest in one or many network events.  This API is provided to supersede the need to do polled network I/O.  Any situation in which select() or non-blocking I/O routines (such as send() and recv()) are either already used or are being considered is usually a candidate for the WSAAsyncSelect() API.  When declaring interest in such condition(s), you supply a window handle to be used for notification.  The corresponding window then receives message-based notification of the conditions in which you declared an interest.

WSAAsyncSelect() allows interest to be declared in the following conditions for a particular socket:
	Socket readiness for reading
	Socket readiness for writing
	Out-of-band data ready for reading
	Socket readiness for accepting incoming connection
	Completion of non-blocking connect()
	Connection closure

# $ + K K Microsoft Windows Extension Functions
Asynchronous Support Routines
The asynchronous "database" functions allow applications to request information in an asynchronous manner.  Some network implementations and/or configurations perform network based operations to resolve such requests.  The WSAAsyncGetXByY() functions allow application developers to request services which would otherwise block the operation of the whole Windows environment if the standard Berkeley function were used.  The WSACancelAsyncRequest() function allows an application to cancel any outstanding asynchronous request.

# $ + K Microsoft Windows Extension Functions
Hooking Blocking Methods
As noted in Blocking/Non blocking & Data Volatility, Windows Sockets implements blocking operations in such a way that Windows message processing can continue, which may result in the application which issued the call receiving a Windows message.  In certain situations an application may want to influence or change the way in which this pseudo-blocking process is implemented.  The WSASetBlockingHook() provides the ability to substitute a named routine which the Windows Sockets implementation is to use when relinquishing the processor during a "blocking" operation.

# $ + K Microsoft Windows Extension Functions
Error Handling
For compatibility with thread-based environments, details of API errors are obtained through the WSAGetLastError() API.  Although the accepted "Berkeley-Style" mechanism for obtaining socket-based network errors is via "errno", this mechanism cannot guarantee the integrity of an error ID in a multi-threaded environment.  WSAGetLastError() allows you to retrieve an error code on a per thread basis.

WSAGetLastError() returns error codes which avoid conflict with standard Microsoft C error codes.  Certain error codes returned by certain Windows Sockets routines fall into the standard range of error codes as defined by Microsoft C.  If you are NOT using an application development environment which defines error codes consistent with Microsoft C, you are advised to use the Windows Sockets error codes prefixed by "WSA" to ensure accurate error code detection.

Note that this specification defines a recommended set of error codes, and lists the possible errors which may be returned as a result of each function.  It may be the case in some implementations that other Windows Sockets error codes will be returned in addition to those listed, and applications should be prepared to handle errors other than those enumerated under each API description.  However a Windows Sockets implementation must not return any value which is not enumerated in the table of legal Windows Sockets errors given in Error Codes.

# $ + K Microsoft Windows Extension Functions
Accessing a Windows Sockets DLL from an Intermediate DLL
A Windows Sockets DLL may be accessed both directly from an application and through an "intermediate" DLL.  An example of such an intermediate DLL would be a virtual network API layer that supports generalized network functionality for applications and uses Windows Sockets.  Such a DLL could be used by several applications simultaneously, and the DLL must take special precautions with respect to the WSAStartup() and WSACleanup() calls to ensure that these routines are called in the context of each task that will make Windows Sockets calls.  This is because the Windows Sockets DLL will need a call to WSAStartup() for each task in order to set up task-specific data structures, and a call to WSACleanup() to free any resources allocated for the task.  

There are (at least) two ways to accomplish this.  The simplest method is for the intermediate DLL to have calls similiar to WSAStartup() and WSACleanup() that applications call as appropriate.  The DLL would then call WSAStartup() or WSACleanup()  from within these routines.  Another mechanism is for the intermediate DLL to build a table of task handles, which are obtained from the GetCurrentTask() Windows API, and at each entry point into the intermediate DLL check whether WSAStartup() has been called for the current task, then call WSAStartup() if necessary.

If a DLL makes a blocking call and does not install its own blocking hook, then the DLL author must be aware that control may be returned to the application either by an application-installed blocking hook or by the default blocking hook.  Thus, it is possible that the application will cancel the DLL's blocking operation via WSACancelBlockingCall().  If this occurs, the DLL's blocking operation will fail with the error code WSAEINTR, and the DLL must return control to the calling task as quickly as possible, as the used has likely pressed a cancel or close button and the task has requested control of the CPU.  It is recommended that DLLs which make blocking calls install their own blocking hooks with WSASetBlockingHook() to prevent unforeseen interactions between the application and the DLL.

Note that this is not necessary for DLLs in Windows NT because of its different process and DLL structure.  Under Windows NT, the intermediate DLL could simply call WSAStartup() in its DLL initialization routine, which is called whenever a new process which uses the DLL starts.

# $ + K Microsoft Windows Extension Functions
3.3.6 Internal use of Messages by Windows Sockets Implementations
In order to implement Windows Sockets purely as a DLL, it may be necessary for the DLL to post messages internally for communication and timing.  This is perfectly legal; however, a Windows Sockets DLL must not post messages to a window handle opened by a client application except for those messages requested by the application.  A Windows Sockets DLL that needs to use messages for its own purposes must open a hidden window and post any necessary messages to the handle for that window.

# $ + K Microsoft Windows Extension Functions
3.3.7 Private API Interfaces
The winsock.def file lists the ordinals defined for the Windows Sockets APIs.  In addition to the ordinal values listed, all ordinals 999 and below are reserved for future Windows Sockets use.  It may be convenient for a Windows Sockets implementation to export additional, private interfaces from the Windows Sockets DLL.  This is perfectly acceptable, as long as the ordinals for these exports are above 1000.  Note that any application that uses a particular Windows Sockets DLL's private APIs will most likely not work on any other vendor's Windows Sockets implementation.  Only the APIs defined in this document are guaranteed to be present in every Windows Sockets implementation.

If an application uses private interfaces of a particular vendor's Windows Sockets DLL, it is recommended that the DLL not be statically linked with the application but rather dynamically loaded with the Windows routines LoadLibrary() and GetProcAddress().  This allows the application to give an informative error message if it is run on a system with a Windows Sockets DLL that does not support the same set of extended functionality.

# $ + K Windows Sockets
Socket Library Reference
Socket Routines
Database Routines
Microsoft Windows-specific Extensions

# $ + Socket Library Reference
Socket Routines

This chapter presents the socket library routines in alphabetical order, and describes each routine in detail.  

In each routine it is indicated that the header file winsock.h must be included.  Header Files lists the Berkeley-compatible header files which are supported.  These are provided for compatibility purposes only, and each of them will simply include winsock.h.  The Windows header file windows.h is also needed, but winsock.h will include it if necessary.

accept()
bind()
closesocket()
connect()
getpeername()
getsockname()
getsockopt()
htonl()
htons()
inet_addr()
inet_ntoa()
ioctlsocket()
listen()
ntohl()
ntohs()
recv()
recvfrom()
select()
send()
sendto()
setsockopt()
shutdown()
socket()

# $ + K Windows Sockets - Socket Routines
accept()
Description	Accept a connection on a socket.

 	#include <winsock.h>

 	SOCKET PASCAL FAR accept ( SOCKET s, struct sockaddr FAR * addr, int FAR * addrlen );

s	A descriptor identifying a socket which is listening for connections after a listen().

addr	An optional pointer to a buffer which receives the address of the connecting entity, as known to the communications layer.  The exact format of the addr argument is determined by the address family established when the socket was created.

addrlen	A optional pointer to an integer which contains the length of the address addr.

Remarks	This routine extracts the first connection on the queue of pending connections on s, creates a new socket with the same properties as s and returns a handle to the new socket.  If no pending connections are present on the queue, and the socket is not marked as non-blocking, accept() blocks the caller until a connection is present.  If the socket is marked non-blocking and no pending connections are present on the queue, accept() returns an error as described below.  The accepted socket may not be used to accept more connections.  The original socket remains open.

The argument addr is a result parameter that is filled in with the address of the connecting entity, as known to the communications layer.  The exact format of the addr parameter is determined by the address family in which the communication is occurring.  The addrlen is a value-result parameter; it should initially contain the amount of space pointed to by addr; on return it will contain the actual length (in bytes) of the address returned.  This call is used with connection-based socket types such as SOCK_STREAM.  If addr and/or addrlen are equal to NULL, then no information about the remote address of the accepted socket is returned.

Return Value	If no error occurs, accept() returns a value of type SOCKET which is a descriptor for the accepted packet.  Otherwise, a value of INVALID_SOCKET is returned, and a specific error code may be retrieved by calling WSAGetLastError().

The integer referred to by addrlen initially contains the amount of space pointed to by addr.  On return it will contain the actual length in bytes of the address returned.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEFAULT	The addrlen argument is too small (less than the sizeof a struct sockaddr).

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets call is in progress.

WSAEINVAL	listen() was not invoked prior to accept().

WSAEMFILE	The queue is empty upon entry to accept() and there are no descriptors available.

WSAENOBUFS	No buffer space is available.

WSAENOTSOCK	The descriptor is not a socket.

WSAEOPNOTSUPP	The referenced socket is not a type that supports connection-oriented service.

WSAEWOULDBLOCK	The socket is marked as non-blocking and no connections are present to be accepted.

See Also	bind(), connect(), listen(), select(), socket(), WSAAsyncSelect().

# $ + K Windows Sockets - Socket Routines
bind()
Description	Associate a local address with a socket.

 	#include <winsock.h>

 	int PASCAL FAR bind ( SOCKET s, const struct sockaddr FAR * name, int namelen );

s	A descriptor identifying an unbound socket.

name	The address to assign to the socket.  The sockaddr structure is defined as follows:

	struct sockaddr {
		u_short	sa_family;
		char	sa_data[14];
	};

namelen	The length of the name.

Remarks	This routine is used on an unconnected datagram or stream socket, before subsequent connect()s or listen()s.  When a socket is created with socket(), it exists in a name space (address family), but it has no name assigned.  bind() establishes the local association (host address/port number) of the socket by assigning a local name to an unnamed socket.

In the Internet address family, a name consists of several components.  For SOCK_DGRAM and SOCK_STREAM, the name consists of three parts: a host address, the protocol number (set implicitly to UDP or TCP, respectively), and a port number which identifies the application.  If an application does not care what address is assigned to it, it may specify an Internet address equal to INADDR_ANY, a port equal to 0, or both.  If the Internet address is equal to INADDR_ANY, any appropriate network interface will be used; this simplifies application programming in the presence of multi-homed hosts.  If the port is specified as 0, the Windows Sockets implementation will assign a unique port to the application with a value between 1024 and 5000.  The application may use getsockname() after bind() to learn the address that has been assigned to it, but note that getsockname() will not necessarily fill in the Internet address until the socket is connected, since several Internet addresses may be valid if the host is multi-homed.

If an application desires to bind to an arbitrary port outside of the range 1024 to 5000, such as the case of rsh which must bind to any reserved port, code similar to the following may be used:

    SOCKADDR_IN sin;
    SOCKET s;
    u_short alport = IPPORT_RESERVED;

    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = 0;
    for (;;) {
        sin.sin_port = htons(alport);
        if (bind(s, (LPSOCKADDR)&sin, sizeof (sin)) == 0) {
            /* it worked */
        }
        if ( GetLastError() != WSAEADDRINUSE) {
            /* fail */
        }
        alport--;
        if (alport == IPPORT_RESERVED/2 ) {
            /* fail--all unassigned reserved ports are */
            /* in use. */
        }
    }

Return Value	If no error occurs, bind() returns 0.  Otherwise, it returns SOCKET_ERROR, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEADDRINUSE 	The specified address is already in use.  (See the SO_REUSEADDR socket option under setsockopt().)

WSAEFAULT	The namelen argument is too small (less than the size of a struct sockaddr).

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets call is in progress.

WSAEAFNOSUPPORT	The specified address family is not supported by 
this protocol.

WSAEINVAL	The socket is already bound to an address.

WSAENOBUFS	Not enough buffers available, too many connections.

WSAENOTSOCK	The descriptor is not a socket.

See Also	connect(), listen(), getsockname(), setsockopt(), socket(), WSACancelBlockingCall().

# $ + K Windows Sockets - Socket Routines
closesocket()
Description	Close a socket.

 	#include <winsock.h>

 	int FAR PASCAL closesocket ( SOCKET s );

s	A descriptor identifying a socket.

Remarks	This function closes a socket.  More precisely, it releases the socket descriptor s, so that further references to s will fail with the error WSAENOTSOCK.  If this is the last reference to the underlying socket, the associated naming information and queued data are discarded.

The semantics of closesocket() are affected by the socket options SO_LINGER and SO_DONTLINGER as follows:

Option		Interval	Type of close	Wait for close?
SO_DONTLINGER	Don't care	Graceful		No
SO_LINGER		Zero		Hard			No
SO_LINGER		Non-zero	Graceful		Yes

If SO_LINGER is set (i.e. the l_onoff field of the linger structure is non-zero; see Socket Options, getsockopt() and setsockopt()) with a zero timeout interval (l_linger is zero), closesocket() is not blocked even if queued data has not yet been sent or acknowledged.  This is called a "hard" close, because the socket is closed immediately, and any unsent data is lost.  Any recv() call on the remote side of the circuit can fail with WSAECONNRESET.

If SO_LINGER is set with a non-zero timeout interval, the closesocket() call blocks until the remaining data has been sent or until the timeout expires.  This is called a graceful disconnect.  Note that if the socket is set to non-blocking and SO_LINGER is set to a non-zero timeout, the call to closesocket() will fail with an error of WSAEWOULDBLOCK.

If SO_DONTLINGER is set on a stream socket (i.e. the l_onoff field of the linger structure is zero; see Socket Options, getsockopt() and setsockopt()), the closesocket() call will return immediately.  However, any data queued for transmission will be sent if possible before the underlying socket is closed.  This is also called a graceful disconnect.  Note that in this case the Windows Sockets implementation may not release the socket and other resources for an arbitrary period, which may affect applications which expect to use all available sockets.

Return Value	If no error occurs, closesocket() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOTSOCK	The descriptor is not a socket.

WSAEINPROGRESS	A blocking Windows Sockets call is in progress.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall().

WSAEWOULDBLOCK	The socket is marked as nonblocking and SO_LINGER is set to a nonzero timeout value.

See Also	accept(), socket(), ioctlsocket(), setsockopt(), WSAAsyncSelect().

# $ + K Windows Sockets - Socket Routines
connect()
Description	Establish a connection to a peer.

 	#include <winsock.h>

 	int PASCAL FAR connect ( SOCKET s, const struct sockaddr FAR * name, int namelen );

s	A descriptor identifying an unconnected socket.

name	The name of the peer to which the socket is to be connected.

namelen	The length of the name.

Remarks	This function is used to create a connection to the specified foreign association.  The parameter s specifies an unconnected datagram or stream socket  If the socket is unbound, unique values are assigned to the local association by the system, and the socket is marked as bound.  Note that if the address field of the name structure is all zeroes, connect() will return the error WSAEADDRNOTAVAIL.

For stream sockets (type SOCK_STREAM), an active connection is initiated to the foreign host using name (an address in the name space of the socket).  When the socket call completes successfully, the socket is ready to send/receive data.  

For a datagram socket (type SOCK_DGRAM), a default destination is set, which will be used on subsequent send() and recv() calls.

On a non-blocking socket, if the return value is SOCKET_ERROR an application should call WSAGetLastError().  If this indicates an error code of WSAEWOULDBLOCK, then your application can either:

1. Use select() to determine the completion of the connection request by checking if the socket is writeable,  or

2. If your application is using the message-based WSAAsyncSelect() to indicate interest in connection events, then your application will receive an FD_CONNECT message when the connect operation is complete.

Return Value	If no error occurs, connect() returns 0.  Otherwise, it returns SOCKET_ERROR, and a specific error code may be retrieved by calling WSAGetLastError().

	On a blocking socket, the return value indicates success or failure of the connection attempt.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEADDRINUSE	The specified address is already in use.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets call is in progress.

WSAEADDRNOTAVAIL	The specified address is not available from the local machine.

WSAEAFNOSUPPORT	Addresses in the specified family cannot be used with this socket.

WSAECONNREFUSED	The attempt to connect was forcefully rejected.

WSAEDESTADDREQ	A destination address is required.

WSAEFAULT	The namelen argument is incorrect.

WSAEINVAL	The socket is not already bound to an address.

WSAEISCONN	The socket is already connected.

WSAEMFILE	No more file descriptors are available.

WSAENETUNREACH	The network can't be reached from this host at this time.

WSAENOBUFS	No buffer space is available.  The socket cannot be connected.

WSAENOTSOCK	The descriptor is not a socket.

WSAETIMEDOUT	Attempt to connect timed out without establishing a connection

WSAEWOULDBLOCK 	The socket is marked as non-blocking and the connection cannot be completed immediately.  It is possible to select() the socket while it is connecting by select()ing it for writing.

See Also	accept(), bind(), getsockname(), socket(), and WSAAsyncSelect.

# $ + K Windows Sockets - Socket Routines
getpeername()
Description	Get the address of the peer to which a socket is connected.

 	#include <winsock.h>

 	int PASCAL FAR getpeername(SOCKET s, struct sockaddr FAR * name, int FAR * namelen);

s	A descriptor identifying a connected socket.

name	The structure which is to receive the name of the peer.

namelen	A pointer to the size of the name structure.

Remarks	getpeername() retrieves the name of the peer connected to the socket s and stores it in the struct sockaddr identified by name.  It is used on a connected datagram or stream socket.

On return, the namelen argument contains the actual size of the name returned in bytes.

Return Value	If no error occurs, getpeername() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEFAULT	The namelen argument is not large enough.

WSAEINPROGRESS	A blocking Windows Sockets call is in progress.

WSAENOTCONN	The socket is not connected.

WSAENOTSOCK	The descriptor is not a socket.

See Also	bind(), socket(), getsockname().

# $ + K Windows Sockets - Socket Routines
getsockname()
Description	Get the local name for a socket.

 	#include <winsock.h>

 	int PASCAL FAR getsockname(SOCKET s, struct sockaddr FAR * name, int FAR * namelen);

s	A descriptor identifying a bound socket.

name	Receives the address (name) of the socket.

namelen	 The size of the name buffer.

Remarks	getsockname() retrieves the current name for the specified socket descriptor in name.  It is used on a bound and/or connected socket specified by the s parameter.  The local association is returned.  This call is especially useful when a connect() call has been made without doing a bind() first; this call provides the only means by which you can determine the local association which has been set by the system.

	On return, the namelen argument contains the actual size of the name returned in bytes.

If a socket was bound to INADDR_ANY, indicating that any of the host's IP addresses should be used for the socket, getsockname() will not necessarily return information about the host IP address, unless the socket has been connected with connect() or accept().  A Windows Sockets application must not assume that the IP address will be changed from INADDR_ANY unless the socket is connected.  This is because for a multi-homed host the IP address that will be used for the socket is unknown unless the socket is connected.

Return Value	If no error occurs, getsockname() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEFAULT	The namelen argument is not large enough.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAENOTSOCK	The descriptor is not a socket.

WSAEINVAL	The socket has not been bound to an address with bind().

See Also	bind(), socket(), getpeername().

# $ + K Windows Sockets - Socket Routines
getsockopt()
Description	Retrieve a socket option.

 	#include <winsock.h>

 	int PASCAL FAR getsockopt ( SOCKET s, int level, int optname, char FAR * optval, int FAR * optlen );

s	A descriptor identifying a socket.

level	The level at which the option is defined; the only supported levels are SOL_SOCKET and IPPROTO_TCP.

optname	The socket option for which the value is to be retrieved.

optval	A pointer to the buffer in which the value for the requested option is to be returned.

optlen	A pointer to the size of the optval buffer.

Remarks	getsockopt() retrieves the current value for a socket option associated with a socket of any type, in any state, and stores the result in optval.  Options may exist at multiple protocol levels, but they are always present at the uppermost "socket'' level.  Options affect socket operations, such as whether an operation blocks or not, the routing of packets, out-of-band data transfer, etc.

The value associated  with the selected option is returned in the buffer optval.  The integer pointed to by  optlen should originally contain the size of this buffer; on return, it will be set to the size of the value returned.  For SO_LINGER, this will be the size of  a struct linger; for all other options it will be the size of an integer.

If the option was never set with setsockopt(), then getsockopt() returns the default value for the option.

The following options are supported for getsockopt().  The Type identifies the type of data addressed by optval.  The TCP_NODELAY option uses level IPPROTO_TCP, all other options use level SOL_SOCKET.

Value	Type	Meaning
SO_ACCEPTCONN	BOOL	Socket is listen()ing.
SO_BROADCAST	BOOL	Socket is configured for the transmission of broadcast messages.
SO_DEBUG	BOOL	Debugging is enabled.  
SO_DONTLINGER	BOOL	If true, the SO_LINGER option is disabled..
SO_DONTROUTE	BOOL	Routing is disabled.
SO_ERROR	int	Retrieve error status and clear.
SO_KEEPALIVE	BOOL	Keepalives are being sent.
SO_LINGER	struct linger FAR *	Returns the current linger options.
SO_OOBINLINE	BOOL	Out-of-band data is being received in the normal data stream.  
SO_RCVBUF	int	Buffer size for receives
SO_REUSEADDR	BOOL	The socket may be bound to an address which is already in use.
SO_SNDBUF	int	Buffer size for sends
SO_TYPE	int	The type of the socket (e.g. SOCK_STREAM).  
TCP_NODELAY	BOOL	Disables the Nagle algorithm for send coalescing.

BSD options not supported for getsockopt() are:

Value	Type	Meaning
SO_RCVLOWAT	int	Receive low water mark
SO_RCVTIMEO	int	Receive timeout
SO_SNDLOWAT	int	Send low water mark
SO_SNDTIMEO	int	Send timeout
IP_OPTIONS		Get options in IP header.
TCP_MAXSEG	int	Get TCP maximum segment size.

Calling getsockopt() with an unsupported option will result in an error code of WSAENOPROTOOPT being returned from WSAGetLastError().

Return Value	If no error occurs, getsockopt() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEFAULT	The optlen argument was invalid.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAENOPROTOOPT	The option is unknown or unsupported.  In particular, SO_BROADCAST is not supported on sockets of type SOCK_STREAM, while SO_ACCEPTCON, SO_DONTLINGER, SO_KEEPALIVE, SO_LINGER and SO_OOBINLINE are not supported on sockets of type SOCK_DGRAM.

WSAENOPROTOOPT	The option is unknown or unsupported.  In particular, SO_BROADCAST is not supported on sockets of type SOCK_STREAM, while SO_ACCEPTCONN, SO_DONTLINGER, SO_KEEPALIVE, SO_LINGER and SO_OOBINLINE are not supported on sockets of type SOCK_DGRAM.

WSAENOTSOCK	The descriptor is not a socket.

See Also	setsockopt(), WSAAsyncSelect(), socket().

# $ + K Windows Sockets - Socket Routines
htonl()
Description	Convert a u_long from host to network byte order.

 	#include <winsock.h>

 	u_long PASCAL FAR htonl ( u_long hostlong );

hostlong	A 32-bit number in host byte order.

Remarks	This routine takes a 32-bit number in host byte order and returns a 32-bit number in network byte order.

Return Value	htonl() returns the value in network byte order.

See Also	htons(), ntohl(), ntohs().

# $ + K Windows Sockets - Socket Routines
htons()
Description	Convert a u_short from host to network byte order.

 	#include <winsock.h>

 	u_short PASCAL FAR htons ( u_short hostshort );

hostshort	A 16-bit number in host byte order.

Remarks	This routine takes a 16-bit number in host byte order and returns a 16-bit number in network byte order.

Return Value	htons() returns the value in network byte order.

See Also	htonl(), ntohl(), ntohs().

# $ + K Windows Sockets - Socket Routines
inet_addr()
Description	Convert a string containing a dotted address into an in_addr.

 	#include <winsock.h>

 	unsigned long PASCAL FAR inet_addr ( const char FAR * cp );

cp	A character string representing a number expressed in the Internet standard ".'' notation.

Remarks	This function interprets the character string specified by the cp parameter.  This string represents a numeric Internet address expressed in the Internet standard ".'' notation.  The value returned is a number suitable for use as an Internet address.  All Internet addresses are returned in network order (bytes ordered from left to right).

Internet Addresses

Values specified using the ".'' notation take one of the following forms:

a.b.c.d	a.b.c	a.b	a

When four parts are specified, each is interpreted as a byte of data and assigned, from left to right, to the four bytes of an Internet address.  Note that when an Internet address is viewed as a 32-bit integer quantity on the Intel architecture, the bytes referred to above appear as "d.c.b.a''.  That is, the bytes on an Intel processor are ordered from right to left.

Note: The following notations are only used by Berkeley, and nowhere else on the Internet.  In the interests of compatibility with their software, they are supported as specified.

When a three part address is specified, the last part is interpreted as a 16-bit quantity and placed in the right most two bytes of the network address.  This makes the three part address format convenient for specifying Class B network addresses as "128.net.host''.

When a two part address is specified, the last part is interpreted as a 24-bit quantity and placed in the right most three bytes of the network address.  This makes the two part address format convenient for specifying Class A network addresses as "net.host''.

When only one part is given, the value is stored directly in the network address without any byte rearrangement.

Return Value	If no error occurs, inet_addr() returns an unsigned long containing a suitable binary representation of the Internet address given.  If the passed-in string does not contain a legitimate Internet address, for example if a portion of an "a.b.c.d" address exceeds 255, inet_addr() returns the value INADDR_NONE.

See Also	inet_ntoa().

# $ + K Windows Sockets - Socket Routines
inet_ntoa()
Description	Convert a network address into a string in dotted format.

 	#include <winsock.h>

 	char FAR * PASCAL FAR inet_ntoa ( struct in_addr in );

in	A structure which represents an Internet host address.

Remarks	This function takes an Internet address structure specified by the in parameter.  It returns an ASCII string representing the address in ".''  notation as "a.b.c.d''.  Note that the string returned by inet_ntoa() resides in memory which is allocated by the Windows Sockets implementation.  The application should not make any assumptions about the way in which the memory is allocated.  The data is guaranteed to be valid until the next Windows Sockets API call within the same thread, but no longer.

Return Value	If no error occurs, inet_ntoa() returns a char pointer to a static buffer containing the text address in standard ".'' notation.  Otherwise, it returns NULL.  The data should be copied before another Windows Sockets call is made.

See Also	inet_addr().

# $ + K Windows Sockets - Socket Routines
ioctlsocket()
Description	Control the mode of a socket.

 	#include <winsock.h>

 	int PASCAL FAR ioctlsocket ( SOCKET s, long cmd, u_long FAR * argp );

s	A descriptor identifying a socket.

cmd	The command to perform on the socket s.

argp	A pointer to a parameter for cmd.

Remarks	This routine may be used on any socket in any state.  It is used to get or retrieve operating parameters associated with the socket, independent of the protocol and communications subsystem.  The following commands are supported:

Command	Semantics
FIONBIO	Enable or disable non-blocking mode on the socket s.  argp points at an unsigned long, which is non-zero if non-blocking mode is to be enabled and zero if it is to be disabled.  When a socket is created, it operates in blocking mode (i.e. non-blocking mode is disabled).  This is consistent with BSD sockets.
	The WSAAsyncSelect() routine automatically sets a socket to nonblocking mode.  If WSAAsyncSelect() has been issued on a socket, then any attempt to use ioctlsocket() to set the socket back to blocking mode will fail with WSAEINVAL.  To set the socket back to blocking mode, an application must first disable WSAAsyncSelect() by calling WSAAsyncSelect() with the lEvent parameter equal to 0.

FIONREAD	Determine the amount of data which can be read atomically from socket s.  argp points at an unsigned long in which ioctlsocket() stores the result.  If s is of type SOCK_STREAM, FIONREAD returns the total amount of data which may be read in a single recv(); this is normally the same as the total amount of data queued on the socket.  If s is of type SOCK_DGRAM, FIONREAD returns the size of the first datagram queued on the socket.

SIOCATMARK	Determine whether or not all out-of-band data has been read.  This applies only to a socket of type SOCK_STREAM which has been configured for in-line reception of any out-of-band data (SO_OOBINLINE).  If no out-of-band data is waiting to be read,  the operation returns TRUE.  Otherwise it returns FALSE, and the next recv() or recvfrom() performed on the socket will retrieve some or all of the data preceding the "mark"; the application should use the SIOCATMARK operation to determine whether any remains.  If there is any normal data preceding the "urgent" (out of band) data, it will be received in order.  (Note that a recv() or recvfrom() will never mix out-of-band and normal data in the same call.)  argp points at a BOOL in which ioctlsocket() stores the result.

Compatibility	This function is a subset of ioctl() as used in Berkeley sockets.  In particular, there is no command which is equivalent to FIOASYNC, while SIOCATMARK is the only socket-level command which is supported.

Return Value	Upon successful completion, the ioctlsocket() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINVAL	cmd is not a valid command, or argp is not an acceptable parameter for cmd, or the command is not applicable to the type of socket supplied

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAENOTSOCK	The descriptor s is not a socket.

See Also	socket(), setsockopt(), getsockopt(), WSAAsyncSelect().

# $ + K Windows Sockets - Socket Routines
listen()
Description	Establish a socket to listen for incoming connection.

 	#include <winsock.h>

 	int PASCAL FAR listen(SOCKET s, int backlog );

s	A descriptor identifying a bound, unconnected socket.

backlog	The maximum length to which the queue of pending connections may grow.

Remarks	To accept connections, a socket is first created with socket(), a backlog for incoming connections is specified with listen(), and then the connections are accepted with accept().  listen() applies only to sockets that support connections, i.e. those of type SOCK_STREAM.  The socket s is put into "passive'' mode where incoming connections are acknowledged and queued pending acceptance by the process.

This function is typically used by servers that could have more than one connection request at a time: if a connection request arrives with the queue full, the client will receive an error with an indication of WSAECONNREFUSED.

listen() attempts to continue to function rationally when there are no available descriptors.  It will accept connections until the queue is emptied.  If descriptors become available, a later call to listen() or accept() will re-fill the queue to the current or most recent "backlog'', if possible, and resume listening for incoming connections.

Compatibility	backlog is currently limited (silently) to 5.  As in 4.3BSD, illegal values (less than 1 or greater than 5) are replaced by the nearest legal value.

Return Value	If no error occurs, listen() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEADDRINUSE	An attempt has been made to listen() on an address in use.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEFAULT	An invalid argument was given.

WSAEINVAL	The socket has not been bound with bind() or is already connected.

WSAEISCONN	The socket is already connected.

WSAEMFILE	No more file descriptors are available.

WSAENOBUFS	No buffer space is available.

WSAENOTSOCK	The descriptor is not a socket.

WSAEOPNOTSUPP	The referenced socket is not of a type that supports the listen() operation.

See Also	accept(),  connect(), socket().

# $ + K Windows Sockets - Socket Routines
ntohl()
Description	Convert a u_long from network to host byte order.

 	#include <winsock.h>

 	u_long PASCAL FAR ntohl ( u_long netlong );

netlong	A 32-bit number in network byte order.

Remarks	This routine takes a 32-bit number in network byte order and returns a 32-bit number in host byte order.

Return Value	ntohl() returns the value in host byte order.

See Also	htonl(), htons(), ntohs().

# $ + K Windows Sockets - Socket Routines
ntohs()
Description	Convert a u_short from network to host byte order.

 	#include <winsock.h>

 	u_short PASCAL FAR ntohs ( u_short netshort );

netshort	A 16-bit number in network byte order.

Remarks	This routine takes a 16-bit number in network byte order and returns a 16-bit number in host byte order.

Return Value	ntohs() returns the value in host byte order.

See Also	htonl(), htons(), ntohl().

# $ + K Windows Sockets - Socket Routines
recv()
Description	Receive data from a socket.

 	#include <winsock.h>

 	int PASCAL FAR recv ( int s, char FAR * buf, int len, int flags );

s	A descriptor identifying a connected socket.

buf	A buffer for the incoming data.

len	The length of buf.

flags	Specifies the way in which the call is made.

Remarks	This function is used on connected datagram or stream sockets specified by the s parameter and is used to read incoming data.

For sockets of type SOCK_STREAM, as much information as is currently available up to the size of the buffer supplied is returned.  If the socket has been configured for in-line reception of out-of-band data (socket option SO_OOBINLINE) and out-of-band data is unread, only out-of-band data will be returned.  The application may use the ioctlsocket() SIOCATMARK to determine whether any more out-of-band data remains to be read.

For datagram sockets, data is extracted from the first enqueued datagram, up to the size of the size of the buffer supplied.  If the datagram is larger than the buffer supplied, the excess data is lost, and recv() returns the error WSAEMSGSIZE.

If no incoming data is available at the socket, the recv() call waits for data to arrive unless the socket is non-blocking.  In this case a value of SOCKET_ERROR is returned with the error code set to WSAEWOULDBLOCK.  The select() or WSAAsyncSelect() calls may be used to determine when more data arrives.

If the socket is of type SOCK_STREAM and the remote side has shut down the connection gracefully, a recv() will complete immediately with 0 bytes received.  If the connection has been abortively disconnected, a recv() will fail with the error WSAECONNRESET.

Flags may be used to influence the behavior of the function invocation beyond the options specified for the associated socket.  That is, the semantics of this function are determined by the socket options and the flags parameter.  The latter is constructed by or-ing any of the following values:

Value	Meaning
MSG_PEEK	Peek at the incoming data.  The data is copied into the buffer but is not removed from the input queue.

MSG_OOB	Process out-of-band data (See Out of Band Data for a discussion of this topic.)

Return Value	If no error occurs, recv() returns the number of bytes received.  If the connection has been closed, it returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOTCONN	The socket is not connected.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAENOTSOCK	The descriptor is not a socket.

WSAEOPNOTSUPP	MSG_OOB was specified, but the socket is not of type SOCK_STREAM.

WSAESHUTDOWN	The socket has been shutdown; it is not possible to recv() on a socket after shutdown() has been invoked with how set to 0 or 2.

WSAEWOULDBLOCK	The socket is marked as non-blocking and the receive operation would block.

WSAEMSGSIZE	The datagram was too large to fit into the specified buffer and was truncated.

WSAEINVAL	The socket has not been bound with bind().

WSAECONNABORTED	The virtual circuit was aborted due to timeout or other failure.

WSAECONNRESET	The virtual circuit was reset by the remote side.

See Also	recvfrom(), send(), select(), WSAAsyncSelect(), socket().

# $ + K Windows Sockets - Socket Routines
recvfrom()
Description	Receive a datagram and store the source address.

 	#include <winsock.h>

 	int PASCAL FAR recvfrom ( int s, char FAR * buf, int len, int flags, struct sockaddr FAR * from, int FAR * fromlen );

s	A descriptor identifying a bound socket.

buf	A buffer for the incoming data.

len	The length of buf.

flags	Specifies the way in which the call is made.

from	An optional pointer to a buffer which will hold the source address upon return.

fromlen	An optional pointer to the size of the from buffer.

Remarks	This function is used to read incoming data on a (possibly connected) socket and capture the address from which the data was sent.

For sockets of type SOCK_STREAM, as much information as is currently available up to the size of the buffer supplied is returned.  If the socket has been configured for in-line reception of out-of-band data (socket option SO_OOBINLINE) and out-of-band data is unread, only out-of-band data will be returned.  The application may use the ioctlsocket() SIOCATMARK to determine whether any more out-of-band data remains to be read.  The from and fromlen parameters are ignored for SOCK_STREAM sockets.

For datagram sockets, data is extracted from the first enqueued datagram, up to the size of the size of the buffer supplied.  If the datagram is larger than the buffer supplied, the buffer is filled with the first part of the message, the excess data is lost, and recvfrom() returns the error code WSAEMSGSIZE.

If from is non-zero, and the socket is of type SOCK_DGRAM, the network address of the peer which sent the data is copied to the corresponding struct sockaddr.  The value pointed to by fromlen is initialized to the size of this structure, and is modified on return to indicate the actual size of the address stored there.

If no incoming data is available at the socket, the recvfrom() call waits for data to arrive unless the socket is non-blocking.  In this case a value of SOCKET_ERROR is returned with the error code set to WSAEWOULDBLOCK.  The select() or WSAAsyncSelect() calls may be used to determine when more data arrives.

If the socket is of type SOCK_STREAM and the remote side has shut down the connection gracefully, a recvfrom() will complete immediately with 0 bytes received.  If the connection has been abortively disconnected, a recvfrom() will fail with the error WSAECONNRESET.

Flags may be used to influence the behavior of the function invocation beyond the options specified for the associated socket.  That is, the semantics of this function are determined by the socket options and the flags parameter.  The latter is constructed by or-ing any of the following values:

Value	Meaning
MSG_PEEK	Peek at the incoming data.  The data is copied into the buffer but is not removed from the input queue.

MSG_OOB	Process out-of-band data (See Out of Band Data for a discussion of this topic.)

Return Value	If no error occurs, recvfrom() returns the number of bytes received.  If the connection has been closed, it returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEFAULT	The fromlen argument was invalid: the from buffer was too small to accommodate the peer address.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINVAL	The socket has not been bound with bind().

WSAENOTCONN	The socket is not connected (SOCK_STREAM only).

WSAENOTSOCK	The descriptor is not a socket.

WSAEOPNOTSUPP	MSG_OOB was specified, but the socket is not of type SOCK_STREAM.

WSAESHUTDOWN	The socket has been shutdown; it is not possible to recvfrom() on a socket after shutdown() has been invoked with how set to 0 or 2.

WSAEWOULDBLOCK	The socket is marked as non-blocking and the recvfrom() operation would block.

WSAEMSGSIZE	The datagram was too large to fit into the specified buffer and was truncated.

WSAECONNABORTED	The virtual circuit was aborted due to timeout or other failure.

WSCONNRESET	The virtual circuit was reset by the remote side.

See Also	recv(), send(), socket(), WSAAsyncSelect().

# $ + K Windows Sockets - Socket Routines
select()
Description	Determine the status of one or more sockets, waiting if necessary.

 	#include <winsock.h>

 	long PASCAL FAR select ( int nfds, fd_set FAR * readfds, fd_set FAR * writefds, fd_set FAR * exceptfds, const struct timeval FAR * timeout );

nfds	This argument is ignored and included only for the sake of compatibility.

readfds	An optional pointer to a set of sockets to be checked for readability.

writefds	An optional pointer to a set of sockets to be checked for writeability

exceptfds	An optional pointer to a set of sockets to be checked for errors.

timeout	The maximum time for select() to wait, or NULL for blocking operation.

Remarks	This function is used to determine the status of one or more sockets.  For each socket, the caller may request information on read, write or error status.  The set of sockets for which a given status is requested is indicated by an fd_set structure.  Upon return, the structure is updated to reflect the subset of these sockets which meet the specified condition, and select() returns the number of sockets meeting the conditions.  A set of macros is provided for manipulating an fd_set.  These macros are compatible with those used in the Berkeley software, but the underlying representation is completely different.  

The parameter readfds identifies those sockets which are to be checked for readability.  If the socket is currently listen()ing, it will be marked as readable if an incoming connection request has been received, so that an accept() is guaranteed to complete without blocking.  For other sockets, readability means that queued data is available for reading or,  for sockets of type SOCK_STREAM, that the virtual socket corresponding to the socket has been closed, so that a recv() or recvfrom() is guaranteed to complete without blocking.  If the virtual circuit was closed gracefully, then a recv() will return immediately with 0 bytes read; if the virtual circuit was closed abortively, then a recv() will complete immediately with the error code WSAECONNRESET.  The presence of out-of-band data will be checked if the socket option SO_OOBINLINE has been enabled (see setsockopt()).

The parameter writefds identifies those sockets which are to be checked for writeability.  If a socket is connect()ing (non-blocking), writeability means that the connection establishment is complete.  For other sockets, writeability means that a send() or sendto() will complete without blocking.  [It is not specified how long this guarantee can be assumed to be valid, particularly in a multithreaded environment.]

The parameter exceptfds identifies those sockets which are to be checked for the presence of out-of-band data or any exceptional error conditions.  Note that out-of-band data will only be reported in this way if the option SO_OOBINLINE is FALSE.  For a SOCK_STREAM, the breaking of the connection by the peer or due to KEEPALIVE failure will be indicated as an exception.  This specification does not define which other errors will be included.  If a socket is connect()ing (non-blocking), failure of the connect attempt is indicated in exceptfds.

Any of readfds, writefds, or exceptfds may be given as NULL if no descriptors are of interest.

Four macros are defined in the header file winsock.h for manipulating the descriptor sets.  The variable FD_SETSIZE determines the maximum number of descriptors in a set.  (The default value of FD_SETSIZE is 64, which may be modified by #defining FD_SETSIZE to another value before #including winsock.h.)  Internally, an fd_set is represented as an array of SOCKETs; the last valid entry is followed by an element set to INVALID_SOCKET.  The macros are:

FD_CLR(s, *set)	Removes the descriptor s from set.

FD_ISSET(s, *set)	Nonzero if s is a member of the set, zero otherwise.

FD_SET(s, *set)		Adds descriptor s to set.

FD_ZERO(*set)		Initializes the set to the NULL set.

The parameter timeout controls how long the select() may take to complete.  If timeout is a null pointer, select() will block indefinitely until at least one descriptor meets the specified criteria.  Otherwise, timeout points to a struct timeval which specifies the maximum time that select() should wait before returning.  If the timeval is initialized to {0, 0}, select() will return immediately; this is used to "poll" the state of the selected sockets.  If this is the case, then the select() call is considered nonblocking and the standard assumptions for nonblocking calls apply.  For example, the blocking hook must not be called, and the Windows Sockets implementation must not yield.

Return Value	select() returns the total number of descriptors which are ready and contained in the fd_set structures, or 0 if the time limit expired, or SOCKET_ERROR if an error occurred.  If the return value is SOCKET_ERROR, WSAGetLastError() may be used to retrieve a specific error code.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINVAL	The timeout value is not valid.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAENOTSOCK	One of the descriptor sets contains an entry which is not a socket.

See Also	WSAAsyncSelect(), accept(), connect(), recv(), recvfrom(), send().

# $ + K Windows Sockets - Socket Routines
send()
Description	Send data on a connected socket.

 	#include <winsock.h>

 	int PASCAL FAR send ( SOCKET s, const char FAR * buf, int len, int flags );

s	A descriptor identifying a connected socket.

buf	A buffer containing the data to be transmitted.

len	The length of the data in buf.

flags	Specifies the way in which the call is made.

Remarks	send() is used on connected datagram or stream sockets and is used to write outgoing data on a socket.  For datagram sockets, care must be taken not to exceed the maximum IP packet size of the underlying subnets, which is given by the iMaxUdpDg element in the WSAData structure returned by WSAStartup().  If the data is too long to pass atomically through the underlying protocol the error WSAEMSGSIZE is returned, and no data is transmitted.

Note that the successful completion of a send() does not indicate that the data was successfully delivered.

If no buffer space is available within the transport system to hold the data to be transmitted, send() will block unless the socket has been placed in a non-blocking I/O mode.  On non-blocking SOCK_STREAM sockets, the number of bytes written may be between 1 and the requested length, depending on buffer availability on both the local and foreign hosts.  The select() call may be used to determine when it is possible to send more data.

Flags may be used to influence the behavior of the function invocation beyond the options specified for the associated socket.  That is, the semantics of this function are determined by the socket options and the flags parameter.  The latter is constructed by or-ing any of the following values:

Value	Meaning
MSG_DONTROUTE
Specifies that the data should not be subject to routing.  A Windows Sockets supplier may choose to ignore this flag; see also the discussion of the SO_DONTROUTE option in Socket Options.

MSG_OOB	Send out-of-band data (SOCK_STREAM only; see also Out of Band Data)

Return Value	If no error occurs, send() returns the total number of characters sent.  (Note that this may be less than the number indicated by len.) Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEACCES	The requested address is a broadcast address, but the appropriate flag was not set.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEFAULT	The buf is not in a valid part of the user address space.

WSAENETRESET	The connection must be reset because the Windows Sockets implementation dropped it.

WSAENOBUFS	The Windows Sockets implementation reports a buffer deadlock.

WSAENOTCONN	The socket is not connected.

WSAENOTSOCK	The descriptor is not a socket.

WSAEOPNOTSUPP	MSG_OOB was specified, but the socket is not of type SOCK_STREAM.

WSAESHUTDOWN	The socket has been shutdown; it is not possible to send() on a socket after shutdown() has been invoked with how set to 1 or 2.

WSAEWOULDBLOCK	The socket is marked as non-blocking and the requested operation would block.

WSAEMSGSIZE	The socket is of type SOCK_DGRAM, and the datagram is larger than the maximum supported by the Windows Sockets implementation.

WSAEINVAL	The socket has not been bound with bind().

WSAECONNABORTED	The virtual circuit was aborted due to timeout or other failure.

WSAECONNRESET	The virtual circuit was reset by the remote side.

See Also	recv(), recvfrom(), socket(), sendto(), WSAStartup().

# $ + K Windows Sockets - Socket Routines
sendto()
Description	Send data to a specific destination.

 	#include <winsock.h>

 	int PASCAL FAR sendto ( SOCKET s, const char FAR * buf, int len, int flags, const struct sockaddr FAR * to, int tolen );

s	A descriptor identifying a socket.

buf	A buffer containing the data to be transmitted.

len	The length of the data in buf.

flags	Specifies the way in which the call is made.

to	A optional pointer to the address of the target socket.

tolen	The size of the address in to.

Remarks	sendto() is used on datagram or stream sockets and is used to write outgoing data on a socket.  For datagram sockets, care must be taken not to exceed the maximum IP packet size of the underlying subnets, which is given by the iMaxUdpDg element in the WSAData structure returned by WSAStartup().  If the data is too long to pass atomically through the underlying protocol the error WSAEMSGSIZE is returned, and no data is transmitted.

Note that the successful completion of a sendto() does not indicate that the data was successfully delivered.

sendto() is normally used on a SOCK_DGRAM socket to send a datagram to a specific peer socket identified by the to parameter.  On a SOCK_STREAM socket, the to and tolen parameters are ignored; in this case the sendto() is equivalent to send().

To send a broadcast (on a SOCK_DGRAM only), the address in the to parameter should be constructed using the special IP address INADDR_BROADCAST (defined in winsock.h) together with the intended port number.  It is generally inadvisable for a broadcast datagram to exceed the size at which fragmentation may occur, which implies that the data portion of the datagram (excluding headers) should not exceed 512 bytes.

If no buffer space is available within the transport system to hold the data to be transmitted, sendto() will block unless the socket has been placed in a non-blocking I/O mode.  On non-blocking SOCK_STREAM sockets, the number of bytes written may be between 1 and the requested length, depending on buffer availability on both the local and foreign hosts.  The select() call may be used to determine when it is possible to send more data.

Flags may be used to influence the behavior of the function invocation beyond the options specified for the associated socket.  That is, the semantics of this function are determined by the socket options and the flags parameter.  The latter is constructed by or-ing any of the following values:

Value	Meaning
MSG_DONTROUTE
Specifies that the data should not be subject to routing.  A Windows Sockets supplier may choose to ignore this flag; see also the discussion of the SO_DONTROUTE option in Socket Options.

MSG_OOB	Send out-of-band data (SOCK_STREAM only; see also Out of Band Data)

Return Value	If no error occurs, sendto() returns the total number of characters sent.  (Note that this may be less than the number indicated by len.) Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEACCES	The requested address is a broadcast address, but the appropriate flag was not set.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEFAULT	The buf or to are not in a valid part of the user address space, or the to argument is too small (less than the sizeof a struct sockaddr).

WSAENETRESET	The connection must be reset because the Windows Sockets implementation dropped it.

WSAENOBUFS	The Windows Sockets implementation reports a buffer deadlock.

WSAENOTCONN	The socket is not connected (SOCK_STREAM only).

WSAENOTSOCK	The descriptor is not a socket.

WSAEOPNOTSUPP	MSG_OOB was specified, but the socket is not of type SOCK_STREAM.

WSAESHUTDOWN	The socket has been shutdown; it is not possible to sendto() on a socket after shutdown() has been invoked with how set to 1 or 2.

WSAEWOULDBLOCK	The socket is marked as non-blocking and the requested operation would block.

WSAEMSGSIZE	The socket is of type SOCK_DGRAM, and the datagram is larger than the maximum supported by the Windows Sockets implementation.

WSAECONNABORTED	The virtual circuit was aborted due to timeout or other failure.

WSAECONNRESET	The virtual circuit was reset by the remote side.

WSAEADDRNOTAVAIL	The specified address is not available from the local machine.

WSAEAFNOSUPPORT	Addresses in the specified family cannot be used with this socket.

WSAEDESTADDRREQ	A destination address is required.

WSAENETUNREACH	The network can't be reached from this host at this time.

See Also	recv(), recvfrom(), socket(), send(), WSAStartup().

# $ + K Windows Sockets - Socket Routines
setsockopt()
Description	Set a socket option.

 	#include <winsock.h>

 	int PASCAL FAR setsockopt ( SOCKET s, int level, int optname, const char FAR * optval, int optlen );

s	A descriptor identifying a socket.

level	The level at which the option is defined; the only supported levels are SOL_SOCKET and IPPROTO_TCP.

optname	The socket option for which the value is to be set.

optval	A pointer to the buffer in which the value for the requested option is supplied.

optlen	The size of the optval buffer.

Remarks	setsockopt() sets the current value for a socket option associated with a socket of any type, in any state.  Although options may exist at multiple protocol levels, this specification only defines options that exist at the uppermost "socket'' level.  Options affect socket operations, such as whether expedited data is received in the normal data stream, whether broadcast messages may be sent on the socket, etc.  

There are two types of socket options: Boolean options that enable or disable a feature or behavior, and options which require an integer value or structure.  To enable a Boolean option, optval points to a nonzero integer.  To disable the option optval points to an integer equal to zero.  optlen should be equal to sizeof(int) for Boolean options.  For other options, optval points to the an integer or structure that contains the desired value for the option, and optlen is the length of the integer or structure.

SO_LINGER controls the action taken when unsent data is queued on a socket and a closesocket() is performed.  See closesocket() for a description of the way in which the SO_LINGER settings affect the semantics of closesocket().  The application sets the desired behavior by creating a struct linger (pointed to by the optval argument) with the following elements:

struct linger {
	int	l_onoff;
	int	l_linger;
}

To enable SO_LINGER, the application should set l_onoff to a non-zero value, set l_linger to 0 or the desired timeout (in seconds), and call setsockopt().  To enable SO_DONTLINGER (i.e. disable SO_LINGER) l_onoff should be set to zero and setsockopt() should be called.

By default, a socket may not be bound (see bind()) to a local address which is already in use.  On occasions, however, it may be desirable to "re-use" an address in this way.  Since every connection is uniquely identified by the combination of local and remote addresses, there is no problem with having two sockets bound to the same local address as long as the remote addresses are different.  To inform the Windows Sockets implementation that a bind() on a socket should not be disallowed because the desired address is already in use by another socket, the application should set the SO_REUSEADDR socket option for the socket before issuing the bind().  Note that the option is interpreted only at the time of the bind(): it is therefore unnecessary (but harmless) to set the option on a socket which is not to be bound to an existing address, and setting or resetting the option after the bind() has no effect on this or any other socket..

An application may request that the Windows Sockets implementation enable the use of "keep-alive" packets on TCP connections by turning on the SO_KEEPALIVE socket option.  A Windows Sockets implementation need not support the use of keep-alives: if it does, the precise semantics are implementation-specific but should conform to section 4.2.3.6 of RFC 1122: Requirements for Internet Hosts -- Communication Layers.  If a connection is dropped as the result of "keep-alives" the error code WSAENETRESET is returned to any calls in progress on the socket, and any subsequent calls will fail with WSAENOTCONN.  

The TCP_NODELAY option disables the Nagle algorithm.  The Nagle algorithm is used to reduce the number of small packets sent by a host by buffering unacknowledged send data until a full-size packet can be sent.  However, for some applications this algorithm can impede performance, and TCP_NODELAY may be used to turn it off.  Application writers should not set TCP_NODELAY unless the impact of doing so is well-understood and desired, since setting TCP_NODELAY can have a significant negative impact of network performance.  TCP_NODELAY is the only supported socket option which uses level IPPROTO_TCP; all other options use level SOL_SOCKET.

Windows Sockets suppliers are encouraged (but not required) to supply output debug information if the SO_DEBUG option is set by an application.  The mechanism for generating the debug information and the form it takes are beyond the scope of this specification.

The following options are supported for setsockopt().  The Type identifies the type of data addressed by optval.

Value	Type	Meaning
SO_BROADCAST	BOOL	Allow transmission of broadcast messages on the socket.
SO_DEBUG	BOOL	Record debugging information.  
SO_DONTLINGER	BOOL	Don't block close waiting for unsent data to be sent.  Setting this option is equivalent to setting SO_LINGER with l_onoff set to zero.
SO_DONTROUTE	BOOL	Don't route: send directly to interface.
SO_KEEPALIVE	BOOL	Send keepalives
SO_LINGER	struct linger FAR *	Linger on close if unsent data is present
SO_OOBINLINE	BOOL	Receive out-of-band data in the normal data stream.  
SO_RCVBUF	int	Specify buffer size for receives
SO_REUSEADDR	BOOL	Allow the socket to be bound to an address which is already in use.  (See bind().) 
SO_SNDBUF	int	Specify buffer size for sends
TCP_NODELAY	BOOL	Disables the Nagle algorithm for send coalascing.

BSD options not supported for setsockopt() are:

Value	Type	Meaning
SO_ACCEPTCON	BOOL	Socket is listening
SO_ERROR	int	Get error status and clear
SO_RCVLOWAT	int	Receive low water mark
SO_RCVTIMEO	int	Receive timeout
SO_SNDLOWAT	int	Send low water mark
SO_SNDTIMEO	int	Send timeout
SO_TYPE	int	Type of the socket
IP_OPTIONS		Set options field in IP header.

Return Value	If no error occurs, setsockopt() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEFAULT	optval is not in a valid part of the process address  space.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINVAL	level is not valid, or the information in optval is not valid.

WSAENETRESET	Connection has timed out when SO_KEEPALIVE is set.

WSAENOPROTOOPT	The option is unknown or unsupported.  In particular, SO_BROADCAST is not supported on sockets of type SOCK_STREAM, while SO_DONTLINGER, SO_KEEPALIVE, SO_LINGER and SO_OOBINLINE are not supported on sockets of type SOCK_DGRAM.

WSAENOTCONN	Connection has been reset when SO_KEEPALIVE is set.

WSAENOTSOCK	The descriptor is not a socket.

See Also	bind(), getsockopt(), ioctlsocket(), socket(), WSAAsyncSelect().

# $ + K Windows Sockets - Socket Routines
shutdown()
Description	Disable sends and/or receives on a socket.

 	#include <winsock.h>

 	int PASCAL FAR shutdown ( SOCKET s, int how );

s	A descriptor identifying a socket.

how	A flag that describes what types of operation will no longer be allowed.

Remarks	shutdown() is used on all types of sockets to disable reception, transmission, or both.

If how is 0, subsequent receives on the socket will be disallowed.  This has no effect on the lower protocol layers.  For TCP, the TCP window is not changed and incoming data will be accepted (but not acknowledged) until the window is exhausted.  For UDP, incoming datagrams are accepted and queued.  In no case will an ICMP error packet be generated.

If how is 1, subsequent sends are disallowed.  For TCP sockets, a FIN will be sent.

Setting how to 2 disables both sends and receives as described above.

Note that shutdown() does not close the socket, and resources attached to the socket will not be freed until closesocket() is invoked.

Comments	shutdown() does not block regardless of the SO_LINGER setting on the socket.

An application should not rely on being able to re-use a socket after it has been shut down.  In particular, a Windows Sockets implementation is not required to support the use of connect() on such a socket.

Return Value	If no error occurs, shutdown() returns 0.  Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINVAL	how is not valid.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAENOTCONN	The socket is not connected (SOCK_STREAM only).

WSAENOTSOCK	The descriptor is not a socket.

See Also	connect(), socket().

# $ + K Windows Sockets - Socket Routines
socket()
Description	Create a socket.

 	#include <winsock.h>

 	SOCKET PASCAL FAR socket ( int af, int type, int protocol );

af	An address format specification.  The only format currently supported is PF_INET, which is the ARPA Internet address format.

type	A type specification for the new socket.

protocol	A particular protocol to be used with the socket, or 0 if the caller does not wish to specify a protocol.

Remarks	socket() allocates a socket descriptor of the specified address family, data type and protocol, as well as related resources.  If a protocol is not specified (i.e. equal to 0), the default for the specified connection mode is used.

Only a single protocol exists to support a particular socket type using a given address format.  However, the address family may be given as AF_UNSPEC (unspecified), in which case the protocol parameter must be specified.  The protocol number to use is particular to the "communication domain'' in which communication is to take place.

The following type specifications are supported:

Type	Explanation
SOCK_STREAM	Provides sequenced, reliable, two-way, connection-based byte streams with an out-of-band data transmission mechanism.  Uses TCP for the Internet address family.

SOCK_DGRAM	Supports datagrams, which are connectionless, unreliable buffers of a fixed (typically small) maximum length.  Uses UDP for the Internet address family.

Sockets of type SOCK_STREAM are full-duplex byte streams.  A stream socket must be in a connected state before any data may be sent or received on it.  A connection to another socket is created with a connect() call.  Once connected, data may be transferred using send() and recv() calls.  When a session has been completed, a closesocket() must be performed.  Out-of-band data may also be transmitted as described in send() and received as described in recv().

The communications protocols used to implement a SOCK_STREAM ensure that data is not lost or duplicated.  If data for which the peer protocol has buffer space cannot be successfully transmitted within a reasonable length of time,  the connection is considered broken and subsequent calls will fail with the error code set to WSAETIMEDOUT.

SOCK_DGRAM sockets allow sending and receiving of datagrams to and from arbitrary peers using sendto() and recvfrom().  If such a socket is connect()ed to a specific peer, datagrams may be send to that peer send() and may be received from (only) this peer using recv().

Return Value	If no error occurs, socket() returns a descriptor referencing the new socket.  Otherwise, a value of INVALID_SOCKET is returned, and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEAFNOSUPPORT	The specified address family is not supported..

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEMFILE	No more file descriptors are available.

WSAENOBUFS	No buffer space is available.  The socket cannot be created.

WSAEPROTONOSUPPORT	The specified protocol is not supported.

WSAEPROTOTYPE	The specified protocol is the wrong type for this socket.

WSAESOCKTNOSUPPORT	The specified socket type is not supported in this address family.

See Also	accept(), bind(), connect(), getsockname(), getsockopt(), setsockopt(), listen(), recv(), recvfrom(), select(), send(), sendto(), shutdown(), ioctlsocket().

# $ + K Socket Library Reference
Database Routines
gethostbyaddr()
gethostbyname()
gethostname()
getprotobyname()
getprotobynumber()
getservbyname()
getservbyport()

# $ + K Database Routines
gethostbyaddr()
Description	Get host information corresponding to an address.

 	#include <winsock.h>

 	struct hostent FAR * PASCAL FAR gethostbyaddr ( const char FAR * addr, int len, int type );

addr	A pointer to an address in network byte order.

len	The length of the address, which must be 4 for PF_INET addresses.

type	The type of the address, which must be PF_INET.

Remarks	gethostbyaddr() returns a pointer to the following structure which contains the name(s) and address which correspond to the given address.  

struct hostent {
	char FAR *	h_name;
	char FAR * FAR *	h_aliases;
	short	h_addrtype;
	short	h_length;
	char FAR * FAR *	h_addr_list;
};

The members of this structure are:
Element	Usage
h_name	Official name of the host (PC).
h_aliases	A NULL-terminated array of alternate names.
h_addrtype	The type of address being returned; for Windows Sockets this is always PF_INET.
h_length	The length, in bytes, of each address; for PF_INET, this is always 4.
h_addr_list	A NULL-terminated list of addresses for the host.  Addresses are returned in network byte order.

The macro h_addr is defined to be h_addr_list[0] for compatibility with older software.

The pointer which is returned points to a structure which is allocated by the Windows Sockets implementation.  The application must never attempt to modify this structure or to free any of its components.  Furthermore, only one copy of this structure is allocated per thread, and so the application should copy any information which it needs before issuing any other Windows Sockets API calls.

Return Value	If no error occurs, gethostbyaddr() returns a pointer to the hostent structure described above.  Otherwise it returns a NULL pointer and a specific error number may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

See Also	WSAAsyncGetHostByAddr(), gethostbyname(),

# $ + K Database Routines
gethostbyname()
Description	Get host information corresponding to a hostname.

 	#include <winsock.h>

 	struct hostent FAR * PASCAL FAR gethostbyname ( const char FAR * name );

name	A pointer to the name of the host.

Remarks	gethostbyname() returns a pointer to a hostent structure as described under gethostbyaddr().  The contents of this structure correspond to the hostname name.

The pointer which is returned points to a structure which is allocated by the Windows Sockets implementation.  The application must never attempt to modify this structure or to free any of its components.  Furthermore, only one copy of this structure is allocated per thread, and so the application should copy any information which it needs before issuing any other Windows Sockets API calls.

A gethostbyname() implementation must not resolve IP address strings passed to it.  Such a request should be treated exactly as if an unknown host name were passed.  An application with an IP address string to resolve should use inet_addr() to convert the string to an IP address, then gethostbyaddr() to obtain the hostent structure.

Return Value	If no error occurs, gethostbyname() returns a pointer to the hostent structure described above.  Otherwise it returns a NULL pointer and a specific error number may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

See Also	WSAAsyncGetHostByName(), gethostbyaddr()

# $ + K Database Routines
gethostname()
Description	Return the standard host name for the local machine.

	#include <winsock.h>

	int PASCAL FAR gethostname ( char FAR * name, int namelen );

name	A pointer to a buffer that will receive the host name.

namelen	The length of the buffer.

Remarks	This routine returns the name of the local host into the buffer specified by the name parameter.  The host name is returned as a null-terminated string.  The form of the host name is dependent on the Windows Sockets implementation--it may be a simple host name, or it may be a fully qualified domain name.  However, it is guaranteed that the name returned will be successfully parsed by gethostbyname() and WSAAsyncGetHostByName().

Return Value	If no error occurs, gethostname() reutrns 0, otherwise it returns SOCKET_ERROR and a specific error code may be retrieved by calling WSAGetLastError().

Error Codes	WSAEFAULT	The namelen parameter is too small

	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

	WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

	WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

See Also	gethostbyname(), WSAAsyncGetHostByName().

# $ + K Database Routines
getprotobyname()
Description	Get protocol information corresponding to a protocol name.

 	#include <winsock.h>

 	struct protoent FAR * PASCAL FAR getprotobyname ( const char FAR * name );

name	A pointer to a protocol name.

Remarks	getprotobyname() returns a pointer to the following structure which contains the name(s) and protocol number which correspond to the given protocol name.  

struct protoent {
	char FAR *	p_name;
	char FAR * FAR *	p_aliases;
	short	p_proto;
};

The members of this structure are:
Element	Usage
p_name	Official name of the protocol.
p_aliases	A NULL-terminated array of alternate names.
p_proto	The protocol number, in host byte order.

The pointer which is returned points to a structure which is allocated by the Windows Sockets library.  The application must never attempt to modify this structure or to free any of its components.  Furthermore only one copy of this structure is allocated per thread, and so the application should copy any information which it needs before issuing any other Windows Sockets API calls.

Return Value	If no error occurs, getprotobyname() returns a pointer to the protoent structure described above.  Otherwise it returns a NULL pointer and a specific error number may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

See Also	WSAAsyncGetProtoByName(), getprotobynumber().

# $ + K Database Routines
getprotobynumber()
Description	Get protocol information corresponding to a protocol number.

 	#include <winsock.h>

 	struct protoent FAR * PASCAL FAR getprotobynumber ( int number );

number	A protocol number, in host byte order.

Remarks	This function returns a pointer to a protoent structure as described above in getprotobyname().  The contents of the structure correspond to the given protocol number.

The pointer which is returned points to a structure which is allocated by the Windows Sockets implementation.  The application must never attempt to modify this structure or to free any of its components.  Furthermore, only one copy of this structure is allocated per thread, and so the application should copy any information which it needs before issuing any other Windows Sockets API calls.

Return Value	If no error occurs, getprotobynumber() returns a pointer to the protoent structure described above.  Otherwise it returns a NULL pointer and a specific error number may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

See Also	WSAAsyncGetProtoByNumber(), getprotobyname()

# $ + K Database Routines
getservbyname()
Description	Get service information corresponding to a service name and protocol.

 	#include <winsock.h>

 	struct servent FAR * PASCAL FAR getservbyname ( const char FAR * name, const char FAR * proto );

name	A pointer to a service name.

proto	An optional pointer to a protocol name.  If this is NULL, getservbyname() returns the first service entry for which the name matches the s_name or one of the s_aliases.  Otherwise getservbyname() matches both the name and the proto.

Remarks	getservbyname() returns a pointer to the following structure which contains the name(s) and service number which correspond to the given service name.  

struct servent {
	char FAR *	s_name;
	char FAR * FAR *	s_aliases;
	short	s_port;
	char FAR *	s_proto;
};

The members of this structure are:
Element	Usage
s_name	Official name of the service.
s_aliases	A NULL-terminated array of alternate names.
s_port	The port number at which the service may be contacted.  Port numbers are returned in network byte order.
s_proto	The name of the protocol to use when contacting the service.

The pointer which is returned points to a structure which is allocated by the Windows Sockets library.  The application must never attempt to modify this structure or to free any of its components.  Furthermore only one copy of this structure is allocated per thread, and so the application should copy any information which it needs before issuing any other Windows Sockets API calls.

Return Value	If no error occurs, getservbyname() returns a pointer to the servent structure described above.  Otherwise it returns a NULL pointer and a specific error number may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

See Also	WSAAsyncGetServByName(), getservbyport()

# $ + K Database Routines
getservbyport()
Description	Get service information corresponding to a port and protocol.

 	#include <winsock.h>

 	struct servent FAR * PASCAL FAR getservbyport ( int port, const char FAR * proto );

port	The port for a service, in network byte order.

proto	An optional pointer to a protocol name.  If this is NULL, getservbyport() returns the first service entry for which the port matches the s_port.  Otherwise getservbyport() matches both the port and the proto.

Remarks	getservbyport() returns a pointer a servent structure as described above for getservbyname().

The pointer which is returned points to a structure which is allocated by the Windows Sockets implementation.  The application must never attempt to modify this structure or to free any of its components.  Furthermore, only one copy of this structure is allocated per thread, and so the application should copy any information which it needs before issuing any other Windows Sockets API calls.

Return Value	If no error occurs, getservbyport() returns a pointer to the servent structure described above.  Otherwise it returns a NULL pointer and a specific error number may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEINTR	The (blocking) call was canceled via WSACancelBlockingCall()

See Also	WSAAsyncGetServByPort(), getservbyname()

# $ + K Socket Library Reference
Microsoft Windows-specific Extensions
WSAAsyncGetHostByAddr()
WSAAsyncGetHostByName()
WSAAsyncGetProtoByName()
WSAAsyncGetProtoByNumber()
WSAAsyncGetServByName()
WSAAsyncGetServByPort()
WSAAsyncSelect()
WSACancelAsyncRequest()
WSACancelBlockingCall()
WSACleanup()
WSAGetLastError()
WSAIsBlocking()
WSASetBlockingHook()
WSASetLastError()
WSAStartup()
WSAUnhookBlockingHook()

# $ + K Microsoft Windows Specific Extensions
WSAAsyncGetHostByAddr()
Description	Get host information corresponding to an address - asynchronous version.

 	#include <winsock.h>

 	HANDLE PASCAL FAR WSAAsyncGetHostByAddr ( HWND hWnd, unsigned int wMsg, const char FAR * addr, int len, int type, char FAR * buf, int buflen );

hWnd	The handle of the window which should receive a message when the asynchronous request completes.

wMsg	The message to be received when the asynchronous request completes.

addr	A pointer to the network address for the host.  Host addresses are stored in network byte order.

len	The length of the address, which must be 4 for PF_INET.

type	The type of the address, which must be PF_INET.

buf	A pointer to the data area to receive the hostent data.  Note that this must be larger than the size of a hostent structure.  This is because the data area supplied is used by the Windows Sockets implementation to contain not only a hostent structure but any and all of the data which is referenced by members of the hostent structure.  It is recommended that you supply a buffer of MAXGETHOSTSTRUCT bytes.

buflen	The size of data area buf above.

Remarks	This function is an asynchronous version of gethostbyaddr(), and is used to retrieve host n`me and address information corresponding to a network address.  The Windows Sockets implementation initiates the operation and returns to the caller immediately, passing back an asynchronous task handle which the application may use to identify the operation.  When the operation is completed, the results (if any) are copied into the buffer provided by the caller and a message is sent to the application's window.

When the asynchronous operation is complete the application's window hWnd receives message wMsg.  The wParam argument contains the asynchronous task handle as returned by the original function call.  The high 16 bits of lParam contain any error code.  The error code may be any error as defined in winsock.h.  An error code of zero indicates successful completion of the asynchronous operation.  On successful completion, the buffer supplied to the original function call contains a hostent structure.  To access the elements of this structure, the original buffer address should be cast to a hostent structure pointer and accessed as appropriate.

Note that if the error code is WSAENOBUFS, it indicates that the size of the buffer specified by buflen in the original call was too small to contain all the resultant information.  In this case, the low 16 bits of lParam contain the size of buffer required to supply ALL the requisite information.  If the application decides that the partial data is inadequate, it may reissue the WSAAsyncGetHostByAddr() function call with a buffer large enough to receive all the desired  information (i.e.  no smaller than the low 16 bits of lParam).

The error code and buffer length should be extracted from the lParam using the macros  WSAGETASYNCERROR and WSAGETASYNCBUFLEN, defined in winsock.h as:

#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

The use of these macros will maximize the portability of the source code for the application.  

Return Value	The return value specifies whether or not the asynchronous operation was successfully initiated.  Note that it does not imply success or failure of the operation itself.

If the operation was successfully initiated, WSAAsyncGetHostByAddr() returns a nonzero value of type HANDLE which is the asynchronous task handle for the request.  This value can be used in two ways.  It can be used to cancel the operation using WSACancelAsyncRequest().  It can also be used to match up asynchronous operations and completion messages, by examining the wParam message argument.

If the asynchronous operation could not be initiated, WSAAsyncGetHostByAddr() returns a zero value, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	The buffer supplied to this function is used by the Windows Sockets implementation to construct a hostent structure together with the contents of data areas referenced by members of the same hostent structure.  To avoid the WSAENOBUFS error noted above, the application should provide a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in winsock.h).

Notes For
Windows Sockets
Suppliers	It is the responsibility of the Windows Sockets implementation to ensure that messages are successfully posted to the application.  If a PostMessage() operation fails, the Windows Sockets implementation must re-post that message as long as the window exists.

Windows Sockets suppliers should use the WSAMAKEASYNCREPLY macro when constructing the lParam in the message.

Error Codes	The following error codes may be set when an application window receives a message.  As described above, they may be extracted from the lParam in the reply message using the WSAGETASYNCERROR macro.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOBUFS	No/insufficient buffer space is available

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

The following errors may occur at the time of the function call, and indicate that the asynchronous operation could not be initiated.

WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEWOULDBLOCK	The asynchronous operation cannot be scheduled at this time due to resource or other constraints within the Windows Sockets implementation.

See Also	gethostbyaddr(), WSACancelAsyncRequest()

# $ + K Microsoft Windows Specific Extensions
WSAAsyncGetHostByName()
Description	Get host information corresponding to a hostname - asynchronous version.

 	#include <winsock.h>

 	HANDLE PASCAL FAR WSAAsyncGetHostByName ( HWND hWnd, unsigned int wMsg, const char FAR * name, char FAR * buf, int buflen );

hWnd	The handle of the window which should receive a message when the asynchronous request completes.

wMsg	The message to be received when the asynchronous request completes.

name	A pointer to the name of the host.

buf	A pointer to the data area to receive the hostent data.  Note that this must be larger than the size of a hostent structure.  This is because the data area supplied is used by the Windows Sockets implementation to contain not only a hostent structure but any and all of the data which is referenced by members of the hostent structure.  It is recommended that you supply a buffer of MAXGETHOSTSTRUCT bytes.

buflen	The size of data area buf above.

Remarks	This function is an asynchronous version of gethostbyname(), and is used to retrieve host name and address information corresponding to a hostname.  The Windows Sockets implementation initiates the operation and returns to the caller immediately, passing back an asynchronous task handle which the application may use to identify the operation.  When the operation is completed, the results (if any) are copied into the buffer provided by the caller and a message is sent to the application's window.

When the asynchronous operation is complete the application's window hWnd receives message wMsg.  The wParam argument contains the asynchronous task handle as returned by the original function call.  The high 16 bits of lParam contain any error code.  The error code may be any error as defined in winsock.h.  An error code of zero indicates successful completion of the asynchronous operation.  On successful completion, the buffer supplied to the original function call contains a hostent structure.  To access the elements of this structure, the original buffer address should be cast to a hostent structure pointer and accessed as appropriate.

Note that if the error code is WSAENOBUFS, it indicates that the size of the buffer specified by buflen in the original call was too small to contain all the resultant information.  In this case, the low 16 bits of lParam contain the size of buffer required to supply ALL the requisite information.  If the application decides that the partial data is inadequate, it may reissue the WSAAsyncGetHostByName() function call with a buffer large enough to receive all the desired  information (i.e. no smaller than the low 16 bits of lParam).

The error code and buffer length should be extracted from the lParam using the macros  WSAGETASYNCERROR and WSAGETASYNCBUFLEN, defined in winsock.h as:

#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

The use of these macros will maximize the portability of the source code for the application.  

Return Value	The return value specifies whether or not the asynchronous operation was successfully initiated.  Note that it does not imply success or failure of the operation itself.

If the operation was successfully initiated, WSAAsyncGetHostByName() returns a nonzero value of type HANDLE which is the asynchronous task handle for the request.  This value can be used in two ways.  It can be used to cancel the operation using WSACancelAsyncRequest().  It can also be used to match up asynchronous operations and completion messages, by examining the wParam message argument.

If the asynchronous operation could not be initiated, WSAAsyncGetHostByName() returns a zero value, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	The buffer supplied to this function is used by the Windows Sockets implementation to construct a hostent structure together with the contents of data areas referenced by members of the same hostent structure.  To avoid the WSAENOBUFS error noted above, the application should provide a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in winsock.h).

Notes For
Windows Sockets
Suppliers	It is the responsibility of the Windows Sockets implementation to ensure that messages are successfully posted to the application.  If a PostMessage() operation fails, the Windows Sockets implementation must re-post that message as long as the window exists.

Windows Sockets suppliers should use the WSAMAKEASYNCREPLY macro when constructing the lParam in the message.

Error Codes	The following error codes may be set when an application window receives a message.  As described above, they may be extracted from the lParam in the reply message using the WSAGETASYNCERROR macro.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOBUFS	No/insufficient buffer space is available

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

The following errors may occur at the time of the function call, and indicate that the asynchronous operation could not be initiated.

WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEWOULDBLOCK	The asynchronous operation cannot be scheduled at this time due to resource or other constraints within the Windows Sockets implementation.

See Also	gethostbyname(), WSACancelAsyncRequest()

# $ + K Microsoft Windows Specific Extensions
WSAAsyncGetProtoByName()
Description	Get protocol information corresponding to a protocol name - asynchronous version.

 	#include <winsock.h>

 	HANDLE PASCAL FAR WSAAsyncGetProtoByName ( HWND hWnd, unsigned int wMsg, const char FAR * name, char FAR * buf, int buflen );

hWnd	The handle of the window which should receive a message when the asynchronous request completes.

wMsg	The message to be received when the asynchronous request completes.

name	A pointer to the protocol name to be resolved.

buf	A pointer to the data area to receive the protoent data.  Note that this must be larger than the size of a protoent structure.  This is because the data area supplied is used by the Windows Sockets implementation to contain not only a protoent structure but any and all of the data which is referenced by members of the protoent structure.  It is recommended that you supply a buffer of MAXGETHOSTSTRUCT bytes.

buflen	The size of data area buf above.

Remarks	This function is an asynchronous version of getprotobyname(), and is used to retrieve the protocol name and number corresponding to a protocol name.  The Windows Sockets implementation initiates the operation and returns to the caller immediately, passing back an asynchronous task handle which the application may use to identify the operation.  When the operation is completed, the results (if any) are copied into the buffer provided by the caller and a message is sent to the application's window.

When the asynchronous operation is complete the application's window hWnd receives message wMsg.  The wParam argument contains the asynchronous task handle as returned by the original function call.  The high 16 bits of lParam contain any error code.  The error code may be any error as defined in winsock.h.  An error code of zero indicates successful completion of the asynchronous operation.  On successful completion, the buffer supplied to the original function call contains a protoent structure.  To access the elements of this structure, the original buffer address should be cast to a protoent structure pointer and accessed as appropriate.

Note that if the error code is WSAENOBUFS, it indicates that the size of the buffer specified by buflen in the original call was too small to contain all the resultant information.  In this case, the low 16 bits of lParam contain the size of buffer required to supply ALL the requisite information.  If the application decides that the partial data is inadequate, it may reissue the WSAAsyncGetProtoByName() function call with a buffer large enough to receive all the desired  information (i.e.  no smaller than the low 16 bits of lParam).

The error code and buffer length should be extracted from the lParam using the macros  WSAGETASYNCERROR and WSAGETASYNCBUFLEN, defined in winsock.h as:

#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

The use of these macros will maximize the portability of the source code for the application.  

Return Value	The return value specifies whether or not the asynchronous operation was successfully initiated.  Note that it does not imply success or failure of the operation itself.

If the operation was successfully initiated, WSAAsyncGetProtoByName() returns a nonzero value of type HANDLE which is the asynchronous task handle for the request.  This value can be used in two ways.  It can be used to cancel the operation using WSACancelAsyncRequest().  It can also be used to match up asynchronous operations and completion messages, by examining the wParam message argument.

If the asynchronous operation could not be initiated, WSAAsyncGetProtoByName() returns a zero value, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	The buffer supplied to this function is used by the Windows Sockets implementation to construct a protoent structure together with the contents of data areas referenced by members of the same protoent structure.  To avoid the WSAENOBUFS error noted above, the application should provide a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in winsock.h).

Notes For
Windows Sockets
Suppliers	It is the responsibility of the Windows Sockets implementation to ensure that messages are successfully posted to the application.  If a PostMessage() operation fails, the Windows Sockets implementation must re-post that message as long as the window exists.

Windows Sockets suppliers should use the WSAMAKEASYNCREPLY macro when constructing the lParam in the message.

Error Codes	The following error codes may be set when an application window receives a message.  As described above, they may be extracted from the lParam in the reply message using the WSAGETASYNCERROR macro.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOBUFS	No/insufficient buffer space is available

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

The following errors may occur at the time of the function call, and indicate that the asynchronous operation could not be initiated.

WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEWOULDBLOCK	The asynchronous operation cannot be scheduled at this time due to resource or other constraints within the Windows Sockets implementation.

See Also	getprotobyname(), WSACancelAsyncRequest()

# $ + K Microsoft Windows Specific Extensions
WSAAsyncGetProtoByNumber()
Description	Get protocol information corresponding to a protocol number - asynchronous version.

 	#include <winsock.h>

 	HANDLE PASCAL FAR WSAAsyncGetProtoByNumber ( HWND hWnd, unsigned int wMsg, int number, char FAR * buf, int buflen );

hWnd	The handle of the window which should receive a message when the asynchronous request completes.

wMsg	The message to be received when the asynchronous request completes.

number	The protocol number to be resolved, in host byte order.

buf	A pointer to the data area to receive the protoent data.  Note that this must be larger than the size of a protoent structure.  This is because the data area supplied is used by the Windows Sockets implementation to contain not only a protoent structure but any and all of the data which is referenced by members of the protoent structure.  It is recommended that you supply a buffer of MAXGETHOSTSTRUCT bytes.

buflen	The size of data area buf above.

Remarks	This function is an asynchronous version of getprotobynumber(), and is used to retrieve the protocol name and number corresponding to a protocol number.  The Windows Sockets implementation initiates the operation and returns to the caller immediately, passing back an asynchronous task handle which the application may use to identify the operation.  When the operation is completed, the results (if any) are copied into the buffer provided by the caller and a message is sent to the application's window.

When the asynchronous operation is complete the application's window hWnd receives message wMsg.  The wParam argument contains the asynchronous task handle as returned by the original function call.  The high 16 bits of lParam contain any error code.  The error code may be any error as defined in winsock.h.  An error code of zero indicates successful completion of the asynchronous operation.  On successful completion, the buffer supplied to the original function call contains a protoent structure.  To access the elements of this structure, the original buffer address should be cast to a protoent structure pointer and accessed as appropriate.

Note that if the error code is WSAENOBUFS, it indicates that the size of the buffer specified by buflen in the original call was too small to contain all the resultant information.  In this case, the low 16 bits of lParam contain the size of buffer required to supply ALL the requisite information.  If the application decides that the partial data is inadequate, it may reissue the WSAAsyncGetProtoByNumber() function call with a buffer large enough to receive all the desired  information (i.e. no smaller than the low 16 bits of lParam).

The error code and buffer length should be extracted from the lParam using the macros  WSAGETASYNCERROR and WSAGETASYNCBUFLEN, defined in winsock.h as:

#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

The use of these macros will maximize the portability of the source code for the application.  

Return Value	The return value specifies whether or not the asynchronous operation was successfully initiated.  Note that it does not imply success or failure of the operation itself.

If the operation was successfully initiated, WSAAsyncGetProtoByNumber() returns a nonzero value of type HANDLE which is the asynchronous task handle for the request.  This value can be used in two ways.  It can be used to cancel the operation using WSACancelAsyncRequest().  It can also be used to match up asynchronous operations and completion messages, by examining the wParam message argument.

If the asynchronous operation could not be initiated, WSAAsyncGetProtoByNumber() returns a zero value, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	The buffer supplied to this function is used by the Windows Sockets implementation to construct a protoent structure together with the contents of data areas referenced by members of the same protoent structure.  To avoid the WSAENOBUFS error noted above, the application should provide a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in winsock.h).

Notes For
Windows Sockets
Suppliers	It is the responsibility of the Windows Sockets implementation to ensure that messages are successfully posted to the application.  If a PostMessage() operation fails, the Windows Sockets implementation must re-post that message as long as the window exists.

Windows Sockets suppliers should use the WSAMAKEASYNCREPLY macro when constructing the lParam in the message.

Error Codes	The following error codes may be set when an application window receives a message.  As described above, they may be extracted from the lParam in the reply message using the WSAGETASYNCERROR macro.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOBUFS	No/insufficient buffer space is available

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

The following errors may occur at the time of the function call, and indicate that the asynchronous operation could not be initiated.

WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEWOULDBLOCK	The asynchronous operation cannot be scheduled at this time due to resource or other constraints within the Windows Sockets implementation.
See Also	getprotobynumber(), WSACancelAsyncRequest()

# $ + K Microsoft Windows Specific Extensions
WSAAsyncGetServByName()
Description	Get service information corresponding to a service name and port - asynchronous version.

 	#include <winsock.h>

 	HANDLE PASCAL FAR WSAAsyncGetServByName ( HWND hWnd, unsigned int wMsg, const char FAR * name, const char FAR * proto, char FAR * buf, int buflen );

hWnd	The handle of the window which should receive a message when the asynchronous request completes.

wMsg	The message to be received when the asynchronous request completes.

name	A pointer to a service name.

proto	A pointer to a protocol name.  This may be NULL, in which case WSAAsyncGetServByName() will search for the first service entry for which s_name or one of the s_aliases matches the given name.  Otherwise WSAAsyncGetServByName() matches both name and proto.

buf	A pointer to the data area to receive the servent data.  Note that this must be larger than the size of a servent structure.  This is because the data area supplied is used by the Windows Sockets implementation to contain not only a servent structure but any and all of the data which is referenced by members of the servent structure.  It is recommended that you supply a buffer of MAXGETHOSTSTRUCT bytes.

buflen	The size of data area buf above.

Remarks	This function is an asynchronous version of getservbyname(), and is used to retrieve service information corresponding to a service name.  The Windows Sockets implementation initiates the operation and returns to the caller immediately, passing back an asynchronous task handle which the application may use to identify the operation.  When the operation is completed, the results (if any) are copied into the buffer provided by the caller and a message is sent to the application's window.

When the asynchronous operation is complete the application's window hWnd receives message wMsg.  The wParam argument contains the asynchronous task handle as returned by the original function call.  The high 16 bits of lParam contain any error code.  The error code may be any error as defined in winsock.h.  An error code of zero indicates successful completion of the asynchronous operation.  On successful completion, the buffer supplied to the original function call contains a hostent structure.  To access the elements of this structure, the original buffer address should be cast to a hostent structure pointer and accessed as appropriate.

Note that if the error code is WSAENOBUFS, it indicates that the size of the buffer specified by buflen in the original call was too small to contain all the resultant information.  In this case, the low 16 bits of lParam contain the size of buffer required to supply ALL the requisite information.  If the application decides that the partial data is inadequate, it may reissue the WSAAsyncGetServByName() function call with a buffer large enough to receive all the desired  information (i.e. no smaller than the low 16 bits of lParam).

The error code and buffer length should be extracted from the lParam using the macros  WSAGETASYNCERROR and WSAGETASYNCBUFLEN, defined in winsock.h as:

#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

The use of these macros will maximize the portability of the source code for the application.  

Return Value	The return value specifies whether or not the asynchronous operation was successfully initiated.  Note that it does not imply success or failure of the operation itself.

If the operation was successfully initiated, WSAAsyncGetServByName() returns a nonzero value of type HANDLE which is the asynchronous task handle for the request.  This value can be used in two ways.  It can be used to cancel the operation using WSACancelAsyncRequest().  It can also be used to match up asynchronous operations and completion messages, by examining the wParam message argument.

If the asynchronous operation could not be initiated, WSAAsyncGetHostByAddr() returns a zero value, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	The buffer supplied to this function is used by the Windows Sockets implementation to construct a hostent structure together with the contents of data areas referenced by members of the same hostent structure.  To avoid the WSAENOBUFS error noted above, the application should provide a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in winsock.h).

Notes For
Windows Sockets
Suppliers	It is the responsibility of the Windows Sockets implementation to ensure that messages are successfully posted to the application.  If a PostMessage() operation fails, the Windows Sockets implementation must re-post that message as long as the window exists.

Windows Sockets suppliers should use the WSAMAKEASYNCREPLY macro when constructing the lParam in the message.

Error Codes	The following error codes may be set when an application window receives a message.  As described above, they may be extracted from the lParam in the reply message using the WSAGETASYNCERROR macro.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOBUFS	No/insufficient buffer space is available

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

The following errors may occur at the time of the function call, and indicate that the asynchronous operation could not be initiated.

WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEWOULDBLOCK	The asynchronous operation cannot be scheduled at this time due to resource or other constraints within the Windows Sockets implementation.

See Also	getservbyname(), WSACancelAsyncRequest()

# $ + K Microsoft Windows Specific Extensions
WSAAsyncGetServByPort()
Description	Get service information corresponding to a port and protocol - asynchronous version.

 	#include <winsock.h>

 	HANDLE PASCAL FAR WSAAsyncGetServByPort ( HWND hWnd, unsigned int wMsg, int port, const char FAR * proto, char FAR * buf, int buflen );

hWnd	The handle of the window which should receive a message when the asynchronous request completes.

wMsg	The message to be received when the asynchronous request completes.

port	The port for the service, in network byte order.

proto	A pointer to a protocol name.  This may be NULL, in which case WSAAsyncGetServByPort() will search for the first service entry for which s_port match the given port.  Otherwise WSAAsyncGetServByPort() matches both port and proto.

buf	A pointer to the data area to receive the servent data.  Note that this must be larger than the size of a servent structure.  This is because the data area supplied is used by the Windows Sockets implementation to contain not only a servent structure but any and all of the data which is referenced by members of the servent structure.  It is recommended that you supply a buffer of MAXGETHOSTSTRUCT bytes.

buflen	The size of data area buf above.

Remarks	This function is an asynchronous version of getservbyport(), and is used to retrieve service information corresponding to a port number.  The Windows Sockets implementation initiates the operation and returns to the caller immediately, passing back an asynchronous task handle which the application may use to identify the operation.  When the operation is completed, the results (if any) are copied into the buffer provided by the caller and a message is sent to the application's window.

When the asynchronous operation is complete the application's window hWnd receives message wMsg.  The wParam argument contains the asynchronous task handle as returned by the original function call.  The high 16 bits of lParam contain any error code.  The error code may be any error as defined in winsock.h.  An error code of zero indicates successful completion of the asynchronous operation.  On successful completion, the buffer supplied to the original function call contains a servent structure.  To access the elements of this structure, the original buffer address should be cast to a servent structure pointer and accessed as appropriate.

Note that if the error code is WSAENOBUFS, it indicates that the size of the buffer specified by buflen in the original call was too small to contain all the resultant information.  In this case, the low 16 bits of lParam contain the size of buffer required to supply ALL the requisite information.  If the application decides that the partial data is inadequate, it may reissue the WSAAsyncGetServByPort() function call with a buffer large enough to receive all the desired  information (i.e. no smaller than the low 16 bits of lParam).

The error code and buffer length should be extracted from the lParam using the macros  WSAGETASYNCERROR and WSAGETASYNCBUFLEN, defined in winsock.h as:

#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

The use of these macros will maximize the portability of the source code for the application.  

Return Value	The return value specifies whether or not the asynchronous operation was successfully initiated.  Note that it does not imply success or failure of the operation itself.

If the operation was successfully initiated, WSAAsyncGetServByPort() returns a nonzero value of type HANDLE which is the asynchronous task handle for the request.  This value can be used in two ways.  It can be used to cancel the operation using WSACancelAsyncRequest().  It can also be used to match up asynchronous operations and completion messages, by examining the wParam message argument.

If the asynchronous operation could not be initiated, WSAAsyncGetServByPort() returns a zero value, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	The buffer supplied to this function is used by the Windows Sockets implementation to construct a servent structure together with the contents of data areas referenced by members of the same servent structure.  To avoid the WSAENOBUFS error noted above, the application should provide a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in winsock.h).

Notes For
Windows Sockets
Suppliers	It is the responsibility of the Windows Sockets implementation to ensure that messages are successfully posted to the application.  If a PostMessage() operation fails, the Windows Sockets implementation must re-post that message as long as the window exists.

Windows Sockets suppliers should use the WSAMAKEASYNCREPLY macro when constructing the lParam in the message.

Error Codes	The following error codes may be set when an application window receives a message.  As described above, they may be extracted from the lParam in the reply message using the WSAGETASYNCERROR macro.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAENOBUFS	No/insufficient buffer space is available

WSAHOST_NOT_FOUND	Authoritative Answer Host not found.

WSATRY_AGAIN	Non-Authoritative Host not found, or SERVERFAIL.

WSANO_RECOVERY	Non recoverable errors, FORMERR, REFUSED, NOTIMP.

WSANO_DATA	Valid name, no data record of requested type.

The following errors may occur at the time of the function call, and indicate that the asynchronous operation could not be initiated.

WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEWOULDBLOCK	The asynchronous operation cannot be scheduled at this time due to resource or other constraints within the Windows Sockets implementation.

See Also	getservbyport(), WSACancelAsyncRequest()

# $ + K Microsoft Windows Specific Extensions
WSAAsyncSelect()
Description	Request event notification for a socket.

 	#include <winsock.h>

 	 int PASCAL FAR WSAAsyncSelect ( SOCKET s, HWND hWnd, unsigned int wMsg, long lEvent );

s	A descriptor identifying the socket for which event notification is required.

hWnd	A handle identifying the window which should receive a message when a network event occurs.

wMsg	The message to be received when a network event occurs.

lEvent	A bitmask which specifies a combination of network events in which the application is interested.

Remarks	This function is used to request that the Windows Sockets DLL should send a message to the window hWnd whenever it detects any of the network events specified by the lEvent parameter.  The message which should be sent is specified by the wMsg parameter.  The socket for which notification is required is identified by s.

The lEvent parameter is constructed by or'ing any of the values specified in the following list.

Value	Meaning
FD_READ	Want to receive notification of readiness for reading
FD_WRITE	Want to receive notification of readiness for writing
FD_OOB	Want to receive notification of the arrival of out-of-band data
FD_ACCEPT	Want to receive notification of incoming connections
FD_CONNECT	Want to receive notification of completed connection
FD_CLOSE	Want to receive notification of socket closure

Issuing a WSAAsyncSelect() for a socket cancels any previous WSAAsyncSelect() for the same socket.  For example, to receive notification for both reading and writing, the application must call WSAAsyncSelect() with both FD_READ and FD_WRITE, as follows:

rc = WSAAsyncSelect(s, hWnd, wMsg, FD_READ|FD_WRITE);

It is not possible to specify different messages for different events.  The following code will not work; the second call will cancel the effects of the first, and only FD_WRITE events will be reported with message wMsg2:

rc = WSAAsyncSelect(s, hWnd, wMsg1, FD_READ);
rc = WSAAsyncSelect(s, hWnd, wMsg2, FD_WRITE);

To cancel all notification - i.e., to indicate that the Windows Sockets implementation should send no further messages related to network events on the socket - lEvent should be set to zero.  

rc = WSAAsyncSelect(s, hWnd, 0, 0);

Although in this instance WSAAsyncSelect() immediately disables event message posting for the socket, it is possible that messages may be waiting in the application's message queue.  The application must therefore be prepared to receive network event messages even after cancellation.  Closing a socket with closesocket() also cancels WSAAsyncSelect() message sending, but the same caveat about messages in the queue prior to the closesocket() still applies.

Since an accept()'ed socket has the same properties as the listening socket used to accept it, any WSAAsyncSelect() events set for the listening socket apply to the accepted socket.  For example, if a listening socket has WSAAsyncSelect() events FD_ACCEPT, FD_READ, and FD_WRITE, then any socket accepted on that listening socket will also have FD_ACCEPT, FD_READ, and FD_WRITE events with the same wMsg value used for messages.  If a different wMsg or events are desired, the application should call WSAAsyncSelect(), passing the accepted socket and the desired new information.

[Note: There is a timing window between the accept() call and the call to WSAAsyncSelect() to change the events or wMsg.  An application which desires a different wMsg for the listening and accept()'ed sockets should ask for only FD_ACCEPT events on the listening socket, then set appropriate events after the accept().  Since FD_ACCEPT is never sent for a connected socket and FD_READ, FD_WRITE, FD_OOB, and FD_CLOSE are never sent for listening sockets, this will not impose difficulties.]

When one of the nominated network events occurs on the specified socket s, the application's window hWnd receives message wMsg.  The wParam argument identifies the socket on which a network event has occurred.  The low word of lParam specifies the network event that has occurred.  The high word of lParam contains any error code.  The error code be any error as defined in winsock.h.

The error and event codes may be extracted from the lParam using the macros WSAGETSELECTERROR and WSAGETSELECTEVENT, defined in winsock.h as:

#define WSAGETSELECTERROR(lParam)            HIWORD(lParam)
#define WSAGETSELECTEVENT(lParam)            LOWORD(lParam)

The use of these macros will maximize the portability of the source code for the application.  

The possible network event codes which may be returned are as follows:

Value	Meaning
FD_READ	Socket s ready for reading
FD_WRITE	Socket s ready for writing
FD_OOB	Out-of-band data ready for reading on socket s.
FD_ACCEPT	Socket s ready for accepting a new incoming connection
FD_CONNECT	Connection on socket s completed
FD_CLOSE	Connection identified by socket s has been closed

Return Value	The return value is 0 if the application's declaration of interest in the network event set was successful.  Otherwise the value SOCKET_ERROR is returned, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	Although WSAAsyncSelect() can be called with interest in multiple events, the application window will receive a single message for each network event.

As in the case of the select() function, WSAAsyncSelect() will frequently be used to determine when a data transfer operation (send() or recv()) can be issued with the expectation of immediate success.  Nevertheless, a robust application must be prepared for the possibility that it may receive a message and issue a Windows Sockets API call which returns WSAEWOULDBLOCK immediately.  For example, the following sequence of events is possible:

(i)	data arrives on socket s; Windows Sockets posts WSAAsyncSelect message
(ii)	application processes some other message
(iii)	while processing, application issues an ioctlsocket(s, FIONREAD...) and notices that there is data ready to be read
(iv)	application issues a recv(s,...) to read the data
(v)	application  loops to process next message, eventually reaching the WSAAsyncSelect message indicating that data is ready to read
(vi)	application issues recv(s,...), which fails with the error WSAEWOULDBLOCK.

Other sequences are possible.  

The Windows Sockets DLL will not continually flood an application with messages for a particular network event.  Having successfully posted notification of a particular event to an application window, no further message(s) for that network event will be posted to the application window until the application makes the function call which implicitly re-enables notification of that network event.

Event	Re-enabling function
FD_READ	recv() or recvfrom()
FD_WRITE	send() or sendto()
FD_OOB	recv()
FD_ACCEPT	accept()
FD_CONNECT	NONE
FD_CLOSE	NONE

Any call to the reenabling routine, even one which fails, results in reenabling of message posting for the relevent event.

For FD_READ, FD_OOB, and FD_ACCEPT events, message posting is "level-triggerred."  This means that if the reenabling routine is called and the relevent event is still valid after the call, a WSAAsyncSelect() message is posted to the application.  This allows an application to be event-driven and not concern itself with the amount of data that arrives at any one time.  Consider the following sequence:

(i)	Windows Sockets DLL receives 100 bytes of data on socket s and posts an FD_READ message.
(ii)	The application issues recv( s, buffptr, 50, 0) to read 50 bytes.
(iii)	The Windows Sockets DLL posts another FD_READ message since there is still data to be read.

With these semantics, an application need not read all available data in response to an FD_READ message--a single recv() in response to each FD_READ message is appropriate.  If an application issues multiple recv() calls in response to a single FD_READ, it may receive multiple FD_READ messages.  Such an application may wish to disable FD_READ messages before starting the recv() calls by calling WSAAsyncSelect() with the FD_READ event not set.

If an event is true when the application initially calls WSAAsyncSelect() or when the reenabling function is called, then a message is posted as appropriate.  For example, if an application calls listen(), a connect attempt is made, then the application calls WSAAsyncSelect() specifying that it wants to receive FD_ACCEPT messages for the socket, the Windows Sockets implementation posts an FD_ACCEPT message immediately.

The FD_WRITE event is handled slightly differently.  An FD_WRITE message is posted when a socket is first connected with connect() or accepted with accept(), and then after a send() or sendto() fails with WSAEWOULDBLOCK and buffer space becomes available.  Therefore, an application can assume that sends are possible starting from the first FD_WRITE message and lasting until a send returns WSAEWOULDBLOCK.  After such a failure the application will be notified that sends are again possible with an FD_WRITE message.

The FD_OOB event is used only when a socket is configured to receive out-of-band data separately.  If the socket is configured to receive out-of-band data in-line, the out-of-band (expedited) data is treated as normal data and the application should register an interest in, and will  receive, FD_READ events, not FD_OOB events.  An application may set or inspect the way in which out-of-band data is to be handled by using setsockopt() or getsockopt for the SO_OOBINLINE option.

The error code in an FD_CLOSE message indicates whether the socket close was graceful or abortive.  If the error code is 0, then the close was graceful; if the error code is WSAECONNRESET, then the socket's virtual socket was abortively disconnected.  This only applies to sockets of type SOCK_STREAM.  

The FD_CLOSE message is posted when a close indication is received for the virtual circuit corresponding to the socket.  In TCP terms, this means that the FD_CLOSE is posted when the connection goes into the FIN WAIT or CLOSE WAIT states.  This results from the remote end performing a shutdown() on the send side or a closesocket().

Please note your application will receive ONLY an FD_CLOSE message to indicate closure of a virtual circuit. It will NOT receive an FD_READ message to indicate this condition.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINVAL	Indicates that one of the specified parameters was invalid

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

Additional error codes may be set when an application window receives a message.  This error code is extracted from the lParam in the reply message using the WSAGETSELECTERROR macro.  Possible error codes for each network event are:
Event: FD_CONNECT
Error Code		Meaning
WSAEADDRINUSE	The specified address is already in use.

WSAEADDRNOTAVAIL	The specified address is not available from the local machine.

WSAEAFNOSUPPORT	Addresses in the specified family cannot be used with this socket.

WSAECONNREFUSED	The attempt to connect was forcefully rejected.

WSAEDESTADDRREQ	A destination address is required.

WSAEFAULT	The namelen argument is incorrect.

WSAEINVAL	The socket is already bound to an address.

WSAEISCONN	The socket is already connected.

WSAEMFILE	No more file descriptors are available.

WSAENETUNREACH	The network can't be reached from this host at this time.

WSAENOBUFS	No buffer space is available.  The socket cannot be connected.

WSAENOTCONN	The socket is not connected.

WSAENOTSOCK	The descriptor is a file, not a socket.

WSAETIMEDOUT	Attempt to connect timed out without establishing a connection

Event: FD_CLOSE
Error Code		Meaning
WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAECONNRESET	The connection is reset by the remote side.

WSAECONNABORTED	The connection was aborted due to timeout or other failure.

Event: FD_READ
Event: FD_WRITE
Event: FD_OOB
Event: FD_ACCEPT
Error Code		Meaning
WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

Notes For
Windows Sockets
Suppliers	It is the responsibility of the Windows Sockets Supplier to ensure that messages are successfully posted to the application.  If a PostMessage() operation fails, the Windows Sockets implementation must re-post that message as long as the window exists.

Windows Sockets suppliers should use the WSAMAKESELECTREPLY macro when constructing the lParam in the message.

When a socket is closed, the Windows Sockets Supplier should purge any messages remaining for posting to the application window.  However the application must be prepared to receive, and discard, any messages which may have been posted prior to the closesocket().

See Also	select()

# $ + K Microsoft Windows Specific Extensions
WSACancelAsyncRequest()
Description	Cancel an incomplete asynchronous operation.

 	#include <winsock.h>

 	int PASCAL FAR WSACancelAsyncRequest ( HANDLE hAsyncTaskHandle );

hAsyncTaskHandle	Specifies the asynchronous operation to be canceled.

Remarks	The WSACancelAsyncRequest() function is used to cancel an asynchronous operation which was initiated by one of the WSAAsyncGetXByY() functions such as WSAAsyncGetHostByName().  The operation to be canceled is identified by the hAsyncTaskHandle parameter, which should be set to the asynchronous task handle as returned by the initiating function.

Return Value	The value returned by WSACancelAsyncRequest() is 0 if the operation was successfully canceled.  Otherwise the value SOCKET_ERROR is returned, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	An attempt to cancel an existing asynchronous WSAAsyncGetXByY() operation can fail with an error code of WSAEALREADY for two reasons.  Firstly, the original operation has already completed and the application has dealt with the resultant message.  Secondly, the original operation has already completed but the resultant message is still waiting in the application window queue.

Notes For
Windows Sockets
Suppliers	It is unclear whether the application can usefully distinguish between WSAEINVAL and WSAEALREADY, since in both cases the error indicates that there is no asynchronous operation in progress with the indicated handle.  [Trivial exception: 0 is always an invalid asynchronous task handle.]  The Windows Sockets specification does not prescribe how a conformant Windows Sockets implementation should distinguish between the two cases.  For maximum portability, a Windows Sockets application should treat the two errors as equivalent.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINVAL	Indicates that the specified asynchronous task handle was invalid

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

WSAEALREADY	The asynchronous routine being canceled has already completed.

See Also	WSAAsyncGetHostByAddr(), WSAAsyncGetHostByName(), WSAAsyncGetProtoByNumber(), WSAAsyncGetProtoByName(), WSAAsyncGetHostByName(), WSAAsyncGetServByPort(), WSAAsyncGetServByName().

# $ + K Microsoft Windows Specific Extensions
WSACancelBlockingCall()
Description	Cancel a blocking call which is currently in progress.

 	#include <winsock.h>

 	int PASCAL FAR WSACancelBlockingCall ( void );

Remarks	This function cancels any outstanding blocking operation for this task.  It is normally used in two situations:

(1) An application is processing a message which has been received while a blocking call is in progress.  In this case, WSAIsBlocking() will be true.

(2) A blocking call is in progress, and Windows Sockets has called back to the application's "blocking hook" function (as established by WSASetBlockingHook()).

In each case, the original blocking call will terminate as soon as possible with the error WSAEINTR.  (In (1), the termination will not take place until Windows message scheduling has caused control to revert to the blocking routine in Windows Sockets.  In (2), the blocking call will be terminated as soon as the blocking hook function completes.)

In the case of a blocking connect() operation, the Windows Sockets implementation will terminate the blocking call as soon as possible, but it may not be possible for the socket resources to be released until the connection has completed (and then been reset) or timed out.  This is likely to be noticeable only if the application immediately tries to open a new socket (if no sockets are available), or to connect() to the same peer.

Cancelling an accept() or a select() call does not adversely impact the sockets passed to these calls.  Only the particular call fails; any operation that was legal before the cancel is legal after the cancel, and the state of the socket is not affected in any way.

Cancelling any operation other than accept() and select() can leave the socket in an indeterminate state.  If an application cancels a blocking operation on a socket, the only operation that the application can depend on being able to perform on the socket is a call to closesocket(), although other operations may work on some Windows Sockets implementations.  If an application desires maximum portability, it must be careful not to depend on performing operations after a cancel.  An application may reset the connection by setting the timeout on SO_LINGER to 0.

If a cancel operation comprimised the integrity of a SOCK_STREAM's data stream in any way, the Windows Sockets implementation must reset the connection and fail all future operations other than closesocket() with WSAECONNABORTED.

Return Value	The value returned by WSACancelBlockingCall() is 0 if the operation was successfully canceled.  Otherwise the value SOCKET_ERROR is returned, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	Note that it is possible that the network operation completes before the WSACancelBlockingCall()  is processed, for example if data is received into the user buffer at interrupt time while the application is in a blocking hook.  In this case, the blocking operation will return successfully as if WSACancelBlockingCall() had never been called.  Note that the WSACancelBlockingCall() still succeeds in this case; the only way to know with certainty that an operation was actually cancelled is to check for a return code of WSAEINTR from the blocking call.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINVAL	Indicates that there is no outstanding blocking call.

# $ + K Microsoft Windows Specific Extensions
WSACleanup()
Description	Terminate use of the Windows Sockets DLL.

	 #include <winsock.h>

 	int PASCAL FAR WSACleanup ( void );

Remarks	An application is required to perform a (successful) WSAStartup() call before it can use Windows Sockets services.  When it has completed the use of Windows Sockets, the application must call WSACleanup() to deregister itself from a Windows Sockets implementation and allow the implementation to free any resources allocated on behalf of the application or DLL.  Any open SOCK_STREAM sockets that are connected when WSACleanup() is called are reset; sockets which have been closed with closesocket() but which still have pending data to be sent are not affected--the pending data is still sent.

	There must be a call to WSACleanup() for every call to WSAStartup() made by a task.  Only the final WSACleanup() does the actual cleanup; the preceding calls simply decrement an internal reference count in the Windows Sockets DLL.  A naive application may ensure that WSACleanup() was called enough times by calling WSACleanup() in a loop until it returns WSANOTINITIALISED.

Return Value	The return value is 0 if the operation was successful.  Otherwise the value SOCKET_ERROR is returned, and a specific error number may be retrieved by calling WSAGetLastError().

Comments	Attempting to call WSACleanup() from within a blocking hook and then failing to check the return code is a common Windows Sockets programming error.  If an application needs to quit while a blocking call is outstanding, the application must first cancel the blocking call with WSACancelBlockingCall() then issue the WSACleanup() call once control has been returned to the application.

Notes For
Windows Sockets
Suppliers	Well-behaved Windows Sockets applications will make a WSACleanup() call to indicate deregistration from a Windows Sockets implementation.  This function can thus, for example, be utilized to free up resources allocated to the specific application.

A Windows Sockets implementation must be prepared to deal with an application which terminates without invoking WSACleanup() - for example, as a result of an error.

In a multithreaded environment, WSACleanup() terminates Windows Sockets operations for all threads. 

A Windows Sockets implementation must ensure that WSACleanup() leaves things in a state in which the application can invoke WSAStartup() to re-establish Windows Sockets usage.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

See Also	WSAStartup()

# $ + K Microsoft Windows Specific Extensions
WSAGetLastError()
Description	Get the error status for the last operation which failed.

 	#include <winsock.h>

 	int PASCAL FAR WSAGetLastError ( void );

Remarks	This function returns the last network error that occurred.  When a particular Windows Sockets API function indicates that an error has occurred, this function should be called to retrieve the appropriate error code.

Return Value	The return value indicates the error code for the last Windows Sockets API routine performed by this thread.

Notes For
Windows Sockets
Suppliers	The use of the WSAGetLastError() function to retrieve the last error code, rather than relying on a global error variable (cf. errno), is required in order to provide compatibility with future multi-threaded environments.  

Note that in a Win16 environment WSAGetLastError() is used to retrieve only Windows Sockets API errors.  In a Win32 environment, WSAGetLastError() will invoke GetLastError(), which is used to retrieve the error status for all Win32 API functions on a per-thread basis.  For portability, an application should use WSAGetLastError() immediately after the Windows Sockets API function which failed.

See Also	WSASetLastError()

# $ + K Microsoft Windows Specific Extensions
WSAIsBlocking()
Description	Determine if a blocking call is in progress.

 	#include <winsock.h>

 	BOOL PASCAL FAR WSAIsBlocking ( void );

Remarks	This function allows a task to determine if it is executing while waiting for a previous blocking call to complete.

Return Value	The return value is TRUE if there is an outstanding blocking function awaiting completion.  Otherwise, it is FALSE.

Comments	Although a call issued on a blocking socket appears to an application program as though it "blocks", the Windows Sockets DLL has to relinquish the processor to allow other applications to run.  This means that it is possible for the application which issued the blocking call to be re-entered, depending on the message(s) it receives.  In this instance, the WSAIsBlocking() function can be used to ascertain whether the task has been re-entered while waiting for an outstanding blocking call to complete.  Note that Windows Sockets prohibits more than one outstanding call per thread.

Notes For
Windows Sockets
Suppliers	A Windows Sockets implementation must prohibit more than one outstanding blocking call per thread.

# $ + K Microsoft Windows Specific Extensions
WSASetBlockingHook()
Description	Establish an application-specific blocking hook function.

	#include <winsock.h>

 	FARPROC PASCAL FAR WSASetBlockingHook ( FARPROC lpBlockFunc );

lpBlockFunc	A pointer to the procedure instance address of the blocking function to be installed.

Remarks	This function installs a new function which a Windows Sockets implementation should use to implement blocking socket function calls.

A Windows Sockets implementation includes a default mechanism by which blocking socket functions are implemented.  The function WSASetBlockingHook() gives the application the ability to execute its own function at "blocking" time in place of the default function.

When an application invokes a blocking Windows Sockets API operation, the Windows Sockets implementation initiates the operation and then enters a loop which is equivalent to the following pseudocode:

for(;;) {
     /* flush messages for good user response */
     while(BlockingHook())
          ;
     /* check for WSACancelBlockingCall() */
     if(operation_cancelled())
          break;
     /* check to see if operation completed */
     if(operation_complete())
          break;     /* normal completion */
}

Note that Windows Sockets implementations may perform the above steps in a different order; for example, the check for operation complete may occur before calling the blocking hook.  The default BlockingHook() function is equivalent to:

BOOL DefaultBlockingHook(void) {
     MSG msg;
     BOOL ret;
     /* get the next message if any */
     ret = (BOOL)PeekMessage(&msg,NULL,0,0,PM_REMOVE);
     /* if we got one, process it */
     if (ret) {
          TranslateMessage(&msg);
          DispatchMessage(&msg);
     }
     /* TRUE if we got a message */
     return ret;
}

The WSASetBlockingHook() function is provided to support those applications which require more complex message processing - for example, those employing the MDI (multiple document interface) model.  It is not intended as a mechanism for performing general applications functions.  In particular, the only Windows Sockets API function which may be issued from a custom blocking hook function is WSACancelBlockingCall(), which will cause the blocking loop to terminate.

This function must be implemented on a per-task basis for non-multithreaded versions of Windows and on a per-thread basis for multithreaded versions of Windows such as Windows NT.  It thus provides for a particular task or thread to replace the blocking mechanism without affecting other tasks or threads.

In multithreaded versions of Windows, there is no default blocking hook--blocking calls block the thread that makes the call.  However, an application may install a specific blocking hook by calling WSASetBlockingHook().  
This allows easy portability of applications that depend on the blocking hook behavior.

Return Value	The return value is a pointer to the procedure-instance of the previously installed blocking function.  The application or library that calls the WSASetBlockingHook() function should save this return value so that it can be restored if necessary.  (If "nesting" is not important, the application may simply discard the value returned by WSASetBlockingHook() and eventually use WSAUnhookBlockingHook() to restore the default mechanism.)  If the operation fails, a NULL pointer is returned, and a specific error number may be retrieved by calling WSAGetLastError().

Notes For
Windows Sockets
Suppliers	This function must be implemented on a per-thread basis.  It thus provides for a particular thread to replace the blocking mechanism without affecting other threads.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

WSAENETDOWN	The Windows Sockets implementation has detected that the network subsystem has failed.

WSAEINPROGRESS	A blocking Windows Sockets operation is in progress.

See Also	WSAUnhookBlockingHook()

# $ + K Microsoft Windows Specific Extensions
WSASetLastError()
Description	Set the error code which can be retrieved by WSAGetLastError().

	#include <winsock.h>

 	void PASCAL FAR WSASetLastError ( int iError );

Remarks	This function allows an application to set the error code to be returned by a subsequent WSAGetLastError() call for the current thread.  Note that any subsequent Windows Sockets routine called by the application will override the error code as set by this routine.

iError	Specifies the error code to be returned by a subsequent WSAGetLastError() call.

Notes For
Windows Sockets
Suppliers	In a Win32 environment, this function will invoke SetLastError().

Return Value	None.

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

See Also	WSAGetLastError()

# $ + K Microsoft Windows Specific Extensions
WSAStartup()
Description	

 	#include <winsock.h>

 	int PASCAL FAR WSAStartup ( WORD wVersionRequired, LPWSADATA lpWSAData );

wVersionRequired	The highest version of Windows Sockets API support that the caller can use.  The high order byte specifies the minor version (revision) number; the low-order byte specifies the major version number.

lpWSAData	A pointer to the WSADATA data structure that is to receive details of the Windows Sockets implementation.

Remarks	This function must be the first Windows Sockets function called by an application or DLL.  It allows an application to specify the version of Windows Sockets API required and to retrieve details of the specific Windows Sockets implementation.  The application may only issue further Windows Sockets API functions after a successful WSAStartup() invocation.

In order to support future Windows Sockets implementations and applications which may have functionality differences from Windows Sockets 1.1, a negotiation takes place in WSAStartup().  The caller of WSAStartup() and the Windows Sockets DLL indicate to each other the highest version that they can support, and each confirms that the other's highest version is acceptable.  Upon entry to WSAStartup(), the Windows Sockets DLL examines the version requested by the application.  If this version is higher than the lowest version supported by the DLL, the call succeeds and the DLL returns in wHighVersion the highest version it supports and in wVersion the minimum of its high version and wVersionRequested.  The Windows Sockets DLL then assumes that the application will use wVersion.  If the wVersion field of the WSADATA structure is unacceptable to the caller, it should call WSACleanup() and either search for another Windows Sockets DLL or fail to initialize.

This negotiation allows both a Windows Sockets DLL and a Windows Sockets application to support a range of Windows Sockets versions.  An application can successfully utilize a Windows Sockets DLL if there is any overlap in the version ranges.  The following chart gives examples of how WSAStartup() works in conjunction with different application and Windows Sockets DLL versions: 
 
App versions	DLL Versions	wVersionRequested	wVersion	wHighVersion	End Result 
1.1	1.1	1.1	1.1	1.1	use 1.1
1.0 1.1	1.0	1.1	1.0	1.0	use 1.0 
1.0	1.0 1.1	1.0	1.0	1.1		use 1.0
1.1	1.0 1.1	1.1	1.1	1.1	use 1.1
1.1	1.0	1.1	1.0	1.0	App fails
1.0	1.1	1.0	---	---	NotSupp
1.0 1.1	1.0 1.1	1.1	1.1	1.1	use 1.1
1.1 2.0	1.1	2.0	1.1	1.1	use 1.1
2.0	1.1	2.0	1.1	1.1		App fails

The following code fragment demonstrates how an application which supports only version 1.1 of Windows Sockets makes a WSAStartup() call:

WORD wVersionRequested;
WSADATA wsaData;
int err;

wVersionRequested = MAKEWORD( 1, 1 );

err = WSAStartup( wVersionRequested, &wsaData );
if ( err != 0 ) {
    /* Tell the user that we couldn't find a useable */
    /* winsock.dll.                                  */
    return;
}

/* Confirm that the Windows Sockets DLL supports 1.1.*/
/* Note that if the DLL supports versions greater    */
/* than 1.1 in addition to 1.1, it will still return */
/* 1.1 in wVersion since that is the version we      */
/* requested.                                        */

if ( LOBYTE( wsaData.wVersion ) != 1 ||
         HIBYTE( wsaData.wVersion ) != 1 ) {
    /* Tell the user that we couldn't find a useable */
    /* winsock.dll.                                  */
    WSACleanup( );
    return;   
}

/* The Windows Sockets DLL is acceptable.  Proceed.  */

And this code fragment demonstrates how a Windows Sockets DLL which supports only version 1.1 performs the WSAStartup() negotiation:

/* Make sure that the version requested is >= 1.1.   */
/* The low byte is the major version and the high    */
/* byte is the minor version.                        */

if ( LOBYTE( wVersionRequested ) < 1 ||
     ( LOBYTE( wVersionRequested ) == 1 &&
       HIBYTE( wVersionRequested ) < 1 ) {
    return WSAVERNOTSUPPORTED;
}

/* Since we only support 1.1, set both wVersion and  */
/* wHighVersion to 1.1.                              */

lpWsaData->wVersion = MAKEWORD( 1, 1 );
		lpWsaData->wHighVersion = MAKEWORD( 1, 1 );

Once an application has made a successful WSAStartup() call, it may proceed to make other Windows Sockets API calls as needed.  When it has finished using the services of the Windows Sockets DLL, the application must call WSACleanup() in order to allow the DLL to free any resources allocated by the Windows Sockets DLL for the application.

Details of the actual Windows Sockets implementation are described in the WSAData structure defined as follows:

struct WSAData {
	WORD			wVersion;
	WORD			wHighVersion;
	char 			szDescription[WSADESCRIPTION_LEN+1];
	char			szSystemStatus[WSASYSSTATUS_LEN+1];
	unsigned short	iMaxSockets;
	unsigned short	iMaxUdpDg;
	char FAR *		lpVendorInfo
};

The members of this structure are:
Element	Usage
wVersion	The version of the Windows Sockets specification that the Windows Sockets DLL expects the caller to use.
wHighVersion	The highest version of the Windows Sockets specification that this DLL can support (also encoded as above).  Normally this will be the same as wVersion.
szDescription	A null-terminated ASCII string into which the Windows Sockets DLL copies a description of the Windows Sockets implementation, including vendor identification.  The text (up to 256 characters in length) may contain any characters, but vendors are cautioned against including control and formatting characters: the most likely use that an application will put this to is to display it (possibly truncated) in a status message.
szSystemStatus	A null-terminated ASCII string into which the Windows Sockets DLL copies relevant status or configuration information.  The Windows Sockets DLL should use this field only if the information might be useful to the user or  support staff: it should not be considered as an extension of the szDescription field.
iMaxSockets	The maximum number of sockets which a single process can potentially open.  A Windows Sockets implementation may provide a global pool of sockets for allocation to any process; alternatively it may allocate per-process resources for sockets.  The number may well reflect the way in which the Windows Sockets DLL or the networking software was configured.  Application writers may use this number as a crude indication of whether the Windows Sockets implementation is usable by the application.  For example, an X Windows server might check iMaxSockets when first started: if it is less than 8, the application would display an error message instructing the user to reconfigure the networking software.  (This is a situation in which the szSystemStatus text might be used.)  Obviously there is no guarantee that a particular application can actually allocate iMaxSockets sockets, since there may be other Windows Sockets applications in use.
iMaxUdpDg	The size in bytes of the largest UDP datagram that can be sent or received by a Windows Sockets application.  If the implementation imposes no limit, iMaxUdpDg is zero.  In many implementations of Berkeley sockets, there is an implicit limit of 8192 bytes on UDP datagrams (which are fragmented if necessary).  A Windows Sockets implementation may impose a limit based, for instance, on the allocation of fragment reassembly buffers.  The minimum value of iMaxUdpDg for a compliant Windows Sockets implementation is 512.  Note that regardless of the value of iMaxUdpDg, it is inadvisable to attempt to send a broadcast datagram which is larger than the Maximum Transmission Unit (MTU) for the network.  (The Windows Sockets API does not provide a mechanism to discover the MTU, but it must be no less than 512 bytes.)
lpVendorInfo	A far pointer to a vendor-specific data structure.  The definition of this structure (if supplied) is beyond the scope of this specification.

An application may call WSAStartup() more than once if it needs to obtain the WSAData structure information more than once.  However, the wVersionRequired parameter is assumed to be the same on all calls to WSAStartup(); that is, an application cannot change the version of Windows Sockets it expects after the initial call to WSAStartup().  

There must be one WSACleanup() call corresponding to every WSAStartup() call to allow third-party DLLs to make use of a Windows Sockets DLL on behalf of an application.  This means, for example, that if an application calls WSAStartup() three times, it must call WSACleanup() three times.  The first two calls to WSACleanup() do nothing except decrement an internal counter; the final WSACleanup() call does all necessary resource deallocation for the task.

Return Value	WSAStartup() returns zero if successful.  Otherwise it returns one of the error codes listed below.  Note that the normal mechanism whereby the application calls WSAGetLastError() to determine the error code cannot be used, since the Windows Sockets DLL may not have established the client data area where the "last error" information is stored.

Notes For
Windows Sockets
Suppliers	Each Windows Sockets application must make a WSAStartup() call before issuing any other Windows Sockets API calls.  This function can thus be utilized for initialization purposes.

Further issues are discussed in the notes for WSACleanup().

Error Codes	WSASYSNOTREADY	Indicates that the underlying network subsystem is not ready for network communication.

WSAVERNOTSUPPORTED
The version of Windows Sockets API support requested is not provided by this particular Windows Sockets implementation.

WSAEINVAL	The Windows Sockets version specified by the application is not supported by this DLL.

See Also	send(), sendto(), WSACleanup()

# $ + K Microsoft Windows Specific Extensions
WSAUnhookBlockingHook()
Description	Restore the default blocking hook function.

	#include <winsock.h>

 	int PASCAL FAR WSAUnhookBlockingHook ( void );

Remarks	This function removes any previous blocking hook that has been installed and reinstalls the default blocking mechanism.  

WSAUnhookBlockingHook() will always install the default mechanism, not the previous mechanism.  If an application wish to nest blocking hooks - i.e. to establish a temporary blocking hook function and then revert to the previous mechanism (whether the default or one established by an earlier WSASetBlockingHook()) - it must save and restore the value returned by WSASetBlockingHook(); it cannot use WSAUnhookBlockingHook().

In multithreaded versions of Windows such as Windows NT, there is no default blocking hook.  Calling WSAUnhookBlockingHook() disables any blocking hook installed by the application and any blocking calls made block the thread which made the call.

Return Value	The return value is 0 if the operation was successful.  Otherwise the value SOCKET_ERROR is returned, and a specific error number may be retrieved by calling WSAGetLastError().

Error Codes	WSANOTINITIALISED	A successful WSAStartup() must occur before using this API.

See Also	WSASetBlockingHook()

# $ + K Windows Sockets
Error Codes
The following is a list of possible error codes returned by the WSAGetLastError() call, along with their explanations.  The error numbers are consistently set across all Windows Sockets-compliant implementations.

Windows Sockets code	Berkeley equivalent	Error	Interpretation
WSAEINTR	EINTR	10004	As in standard C
WSAEBADF	EBADF	10009	As in standard C
WSEACCES	EACCES	10013	As in standard C
WSAEFAULT	EFAULT	10014	As in standard C
WSAEINVAL	EINVAL	10022	As in standard C
WSAEMFILE	EMFILE	10024	As in standard C
WSAEWOULDBLOCK	EWOULDBLOCK	10035	As in BSD
WSAEINPROGRESS	EINPROGRESS	10036	This error is returned if anyWindows Sockets API function is called while a blocking function is in progress.
WSAEALREADY	EALREADY	10037	As in BSD
WSAENOTSOCK	ENOTSOCK	10038	As in BSD
WSAEDESTADDRREQ	EDESTADDRREQ	10039	As in BSD
WSAEMSGSIZE	EMSGSIZE	10040	As in BSD
WSAEPROTOTYPE	EPROTOTYPE	10041	As in BSD
WSAENOPROTOOPT	ENOPROTOOPT	10042	As in BSD
WSAEPROTONOSUPPORT	EPROTONOSUPPORT	10043	As in BSD
WSAESOCKTNOSUPPORT	ESOCKTNOSUPPORT	10044	As in BSD
WSAEOPNOTSUPP	EOPNOTSUPP	10045	As in BSD
WSAEPFNOSUPPORT	EPFNOSUPPORT	10046	As in BSD
WSAEAFNOSUPPORT	EAFNOSUPPORT	10047	As in BSD
WSAEADDRINUSE	EADDRINUSE	10048	As in BSD
WSAEADDRNOTAVAIL	EADDRNOTAVAIL	10049	As in BSD
WSAENETDOWN	ENETDOWN	10050	As in BSD.  This error may be reported at any time if the Windows Sockets implementation detects an underlying failure.
WSAENETUNREACH	ENETUNREACH	10051	As in BSD
WSAENETRESET	ENETRESET	10052	As in BSD
WSAECONNABORTED	ECONNABORTED	10053	As in BSD
WSAECONNRESET	ECONNRESET	10054	As in BSD
WSAENOBUFS	ENOBUFS	10055	As in BSD
WSAEISCONN	EISCONN	10056	As in BSD
WSAENOTCONN	ENOTCONN	10057	As in BSD
WSAESHUTDOWN	ESHUTDOWN	10058	As in BSD
WSAETOOMANYREFS	ETOOMANYREFS	10059	As in BSD
WSAETIMEDOUT	ETIMEDOUT	10060	As in BSD
WSAECONNREFUSED	ECONNREFUSED	10061	As in BSD
WSAELOOP	ELOOP	10062	As in BSD
WSAENAMETOOLONG	ENAMETOOLONG	10063	As in BSD
WSAEHOSTDOWN	EHOSTDOWN	10064	As in BSD
WSAEHOSTUNREACH	EHOSTUNREACH	10065	As in BSD
WSASYSNOTREADY		10091	Returned by WSAStartup() 
indicating that the network subsystem is unusable.
WSAVERNOTSUPPORTED		10092	Returned by WSAStartup() 
indicating that the Windows Sockets
DLL cannot support this app.
WSANOTINITIALISED		10093	Returned by any function except WSAStartup() indicating that a successful WSAStartup() has not yet been performed.
WSAHOST_NOT_FOUND	HOST_NOT_FOUND	11001	As in BSD.
WSATRY_AGAIN	TRY_AGAIN	11002	As in BSD
WSANO_RECOVERY	NO_RECOVERY	11003	As in BSD
WSANO_DATA	NO_DATA	11004	As in BSD

The first set of definitions is present to resolve contentions between standard C error codes which may be defined inconsistently between various C compilers.

The second set of definitions provides Windows Sockets versions of regular Berkeley Sockets error codes.

The third set of definitions consists of extended Windows Sockets-specific error codes.

The fourth set of errors are returned by Windows Sockets getXbyY() and WSAAsyncGetXByY() functions, and correspond to the errors which in Berkeley software would be returned in the h_errno variable.  They correspond to various failures which may be returned by the Domain Name Service.  If the Windows Sockets implementation  does not use the DNS, it will use the most appropriate code.  In general, a Windows Sockets application should interpret WSAHOST_NOT_FOUND and WSANO_DATA as indicating that the key (name, address, etc.) was not found,, while WSATRY_AGAIN and WSANO_RECOVERY suggest that the name service itself is non-operational.

The error numbers are derived from the winsock.h header file, and are based on the fact that Windows Sockets error numbers are computed by adding 10000 to the "normal" Berkeley error number.

Note that this table does not include all of the error codes defined in winsock.h.  This is because it includes only errors which might reasonably be returned by a Windows Sockets implementation: winsock.h, on the other hand, includes a full set of BSD definitions to ensure compatibility with ported software.

# $ + K Windows Sockets
Header Files
Berkeley Header Files
Windows Sockets Header File - winsock.h

# $ + K Windows Sockets Header Files
Berkeley Header Files
A Windows Sockets supplier who provides a development kit to support the development of Windows Sockets applications must supply a set of vestigial header files with names that match a number of the header files in the Berkeley software distribution.  These files are provided for source code compatibility only, and each consists of three lines:

#ifndef _WINSOCKAPI_
#include <winsock.h>
#endif

The header files provided for compatibility are:
netdb.h
arpa/inet.h
sys/time.h
sys/socket.h
netinet/in.h

The file winsock.h contains all of the type and structure definitions, constants, macros, and function prototypes used by the Windows Sockets specification.  An application writer may choose to ignore the compatibility headers and include winsock.h in each source file.

# $ + K Windows Sockets Header Files
Windows Sockets Header File - winsock.h

The winsock.h header file includes a number of types and definitions from the standard Windows header file windows.h.  The windows.h in the Windows 3.0 SDK (Software Developer's Kit) lacks a #include guard, so if you need to include windows.h as well as winsock.h, you should define the symbol _INC_WINDOWS before #including winsock.h, as follows:
#include <windows.h>
#define _INC_WINDOWS
#include <winsock.h>

Users of the SDK for Windows 3.1 and later need not do this.

A Windows Sockets DLL vendor MUST NOT make any modifications to this header file which could impact binary compatibility of Windows Sockets applications.  The constant values, function parameters and return codes, and the like must remain consistent across all Windows Sockets DLL vendors.

/* WINSOCK.H--definitions to be used with the WINSOCK.DLL
 *
 * This header file corresponds to version 1.1 of the Windows Sockets specification.
 *
 * This file includes parts which are Copyright (c) 1982-1986 Regents
 * of the University of California.  All rights reserved.  The
 * Berkeley Software License Agreement specifies the terms and
 * conditions for redistribution.
 */

#ifndef _WINSOCKAPI_
#define _WINSOCKAPI_

/*
 * Pull in WINDOWS.H if necessary
 */
#ifndef _INC_WINDOWS
#include <windows.h>
#endif /* _INC_WINDOWS */

/*
 * Basic system type definitions, taken from the BSD file sys/types.h.
 */
typedef unsigned char   u_char;
typedef unsigned short  u_short;
typedef unsigned int    u_int;
typedef unsigned long   u_long;

/*
 * The new type to be used in all
 * instances which refer to sockets.
 */
typedef u_int           SOCKET;

/*
 * Select uses arrays of SOCKETs.  These macros manipulate such
 * arrays.  FD_SETSIZE may be defined by the user before including
 * this file, but the default here should be >= 64.
 *
 * CAVEAT IMPLEMENTOR and USER: THESE MACROS AND TYPES MUST BE
 * INCLUDED IN WINSOCK.H EXACTLY AS SHOWN HERE.
 */
#ifndef FD_SETSIZE
#define FD_SETSIZE      64
#endif /* FD_SETSIZE */

typedef struct fd_set {
        u_short fd_count;               /* how many are SET? */
        SOCKET  fd_array[FD_SETSIZE];   /* an array of SOCKETs */
} fd_set;

extern int PASCAL FAR __WSAFDIsSet(SOCKET, fd_set FAR *);

#define FD_CLR(fd, set) do { \
    u_int __i; \
    for (__i = 0; __i < ((fd_set FAR *)(set))->fd_count ; __i++) { \
        if (((fd_set FAR *)(set))->fd_array[__i] == fd) { \
            while (__i < ((fd_set FAR *)(set))->fd_count-1) { \
                ((fd_set FAR *)(set))->fd_array[__i] = \
                    ((fd_set FAR *)(set))->fd_array[__i+1]; \
                __i++; \
            } \
            ((fd_set FAR *)(set))->fd_count--; \
            break; \
        } \
    } \
} while(0)

#define FD_SET(fd, set) do { \
    if (((fd_set FAR *)(set))->fd_count < FD_SETSIZE) \
        ((fd_set FAR *)(set))->fd_array[((fd_set FAR *)(set))->fd_count++]=fd;\
} while(0)

#define FD_ZERO(set) (((fd_set FAR *)(set))->fd_count=0)

#define FD_ISSET(fd, set) __WSAFDIsSet((SOCKET)fd, (fd_set FAR *)set)

/*
 * Structure used in select() call, taken from the BSD file sys/time.h.
 */
struct timeval {
        long    tv_sec;         /* seconds */
        long    tv_usec;        /* and microseconds */
};

/*
 * Operations on timevals.
 *
 * NB: timercmp does not work for >= or <=.
 */
#define timerisset(tvp)         ((tvp)->tv_sec || (tvp)->tv_usec)
#define timercmp(tvp, uvp, cmp) \
        ((tvp)->tv_sec cmp (uvp)->tv_sec || \
         (tvp)->tv_sec == (uvp)->tv_sec && (tvp)->tv_usec cmp (uvp)->tv_usec)
#define timerclear(tvp)         (tvp)->tv_sec = (tvp)->tv_usec = 0

/*
 * Commands for ioctlsocket(),  taken from the BSD file fcntl.h.
 *
 *
 * Ioctl's have the command encoded in the lower word,
 * and the size of any in or out parameters in the upper
 * word.  The high 2 bits of the upper word are used
 * to encode the in/out status of the parameter; for now
 * we restrict parameters to at most 128 bytes.
 */
#define IOCPARM_MASK    0x7f            /* parameters must be < 128 bytes */
#define IOC_VOID        0x20000000      /* no parameters */
#define IOC_OUT         0x40000000      /* copy out parameters */
#define IOC_IN          0x80000000      /* copy in parameters */
#define IOC_INOUT       (IOC_IN|IOC_OUT)
                                        /* 0x20000000 distinguishes new &
                                           old ioctl's */
#define _IO(x,y)        (IOC_VOID|(x<<8)|y)

#define _IOR(x,y,t)     (IOC_OUT|(((long)sizeof(t)&IOCPARM_MASK)<<16)|(x<<8)|y)

#define _IOW(x,y,t)     (IOC_IN|(((long)sizeof(t)&IOCPARM_MASK)<<16)|(x<<8)|y)

#define FIONREAD    _IOR('f', 127, u_long) /* get # bytes to read */
#define FIONBIO     _IOW('f', 126, u_long) /* set/clear non-blocking i/o */
#define FIOASYNC    _IOW('f', 125, u_long) /* set/clear async i/o */

/* Socket I/O Controls */
#define SIOCSHIWAT  _IOW('s',  0, u_long)  /* set high watermark */
#define SIOCGHIWAT  _IOR('s',  1, u_long)  /* get high watermark */
#define SIOCSLOWAT  _IOW('s',  2, u_long)  /* set low watermark */
#define SIOCGLOWAT  _IOR('s',  3, u_long)  /* get low watermark */
#define SIOCATMARK  _IOR('s',  7, u_long)  /* at oob mark? */

/*
 * Structures returned by network data base library, taken from the
 * BSD file netdb.h.  All addresses are supplied in host order, and
 * returned in network order (suitable for use in system calls).
 */

struct  hostent {
        char    FAR * h_name;           /* official name of host */
        char    FAR * FAR * h_aliases;  /* alias list */
        short   h_addrtype;             /* host address type */
        short   h_length;               /* length of address */
        char    FAR * FAR * h_addr_list; /* list of addresses */
#define h_addr  h_addr_list[0]          /* address, for backward compat */
};

/*
 * It is assumed here that a network number
 * fits in 32 bits.
 */
struct  netent {
        char    FAR * n_name;           /* official name of net */
        char    FAR * FAR * n_aliases;  /* alias list */
        short   n_addrtype;             /* net address type */
        u_long  n_net;                  /* network # */
};

struct  servent {
        char    FAR * s_name;           /* official service name */
        char    FAR * FAR * s_aliases;  /* alias list */
        short   s_port;                 /* port # */
        char    FAR * s_proto;          /* protocol to use */
};

struct  protoent {
        char    FAR * p_name;           /* official protocol name */
        char    FAR * FAR * p_aliases;  /* alias list */
        short   p_proto;                /* protocol # */
};

/*
 * Constants and structures defined by the internet system,
 * Per RFC 790, September 1981, taken from the BSD file netinet/in.h.
 */

/*
 * Protocols
 */
#define IPPROTO_IP              0               /* dummy for IP */
#define IPPROTO_ICMP            1               /* control message protocol */
#define IPPROTO_GGP             2               /* gateway^2 (deprecated) */
#define IPPROTO_TCP             6               /* tcp */
#define IPPROTO_PUP             12              /* pup */
#define IPPROTO_UDP             17              /* user datagram protocol */
#define IPPROTO_IDP             22              /* xns idp */
#define IPPROTO_ND              77              /* UNOFFICIAL net disk proto */

#define IPPROTO_RAW             255             /* raw IP packet */
#define IPPROTO_MAX             256

/*
 * Port/socket numbers: network standard functions
 */
#define IPPORT_ECHO             7
#define IPPORT_DISCARD          9
#define IPPORT_SYSTAT           11
#define IPPORT_DAYTIME          13
#define IPPORT_NETSTAT          15
#define IPPORT_FTP              21
#define IPPORT_TELNET           23
#define IPPORT_SMTP             25
#define IPPORT_TIMESERVER       37
#define IPPORT_NAMESERVER       42
#define IPPORT_WHOIS            43
#define IPPORT_MTP              57

/*
 * Port/socket numbers: host specific functions
 */
#define IPPORT_TFTP             69
#define IPPORT_RJE              77
#define IPPORT_FINGER           79
#define IPPORT_TTYLINK          87
#define IPPORT_SUPDUP           95

/*
 * UNIX TCP sockets
 */
#define IPPORT_EXECSERVER       512
#define IPPORT_LOGINSERVER      513
#define IPPORT_CMDSERVER        514
#define IPPORT_EFSSERVER        520

/*
 * UNIX UDP sockets
 */
#define IPPORT_BIFFUDP          512
#define IPPORT_WHOSERVER        513
#define IPPORT_ROUTESERVER      520
                                        /* 520+1 also used */

/*
 * Ports < IPPORT_RESERVED are reserved for
 * privileged processes (e.g. root).
 */
#define IPPORT_RESERVED         1024

/*
 * Link numbers
 */
#define IMPLINK_IP              155
#define IMPLINK_LOWEXPER        156
#define IMPLINK_HIGHEXPER       158

/*
 * Internet address (old style... should be updated)
 */
struct in_addr {
        union {
                struct { u_char s_b1,s_b2,s_b3,s_b4; } S_un_b;
                struct { u_short s_w1,s_w2; } S_un_w;
                u_long S_addr;
        } S_un;
#define s_addr  S_un.S_addr
                                /* can be used for most tcp & ip code */
#define s_host  S_un.S_un_b.s_b2
                                /* host on imp */
#define s_net   S_un.S_un_b.s_b1
                                /* network */
#define s_imp   S_un.S_un_w.s_w2
                                /* imp */
#define s_impno S_un.S_un_b.s_b4
                                /* imp # */
#define s_lh    S_un.S_un_b.s_b3
                                /* logical host */
};

/*
 * Definitions of bits in internet address integers.
 * On subnets, the decomposition of addresses to host and net parts
 * is done according to subnet mask, not the masks here.
 */
#define IN_CLASSA(i)            (((long)(i) & 0x80000000) == 0)
#define IN_CLASSA_NET           0xff000000
#define IN_CLASSA_NSHIFT        24
#define IN_CLASSA_HOST          0x00ffffff
#define IN_CLASSA_MAX           128

#define IN_CLASSB(i)            (((long)(i) & 0xc0000000) == 0x80000000)
#define IN_CLASSB_NET           0xffff0000
#define IN_CLASSB_NSHIFT        16
#define IN_CLASSB_HOST          0x0000ffff
#define IN_CLASSB_MAX           65536

#define IN_CLASSC(i)            (((long)(i) & 0xc0000000) == 0xc0000000)
#define IN_CLASSC_NET           0xffffff00
#define IN_CLASSC_NSHIFT        8
#define IN_CLASSC_HOST          0x000000ff

#define INADDR_ANY              (u_long)0x00000000
#define INADDR_LOOPBACK         0x7f000001
#define INADDR_BROADCAST        (u_long)0xffffffff    
#define INADDR_NONE             0xffffffff

/*
 * Socket address, internet style.
 */
struct sockaddr_in {
        short   sin_family;
        u_short sin_port;
        struct  in_addr sin_addr;
        char    sin_zero[8];
};

#define WSADESCRIPTION_LEN      256
#define WSASYS_STATUS_LEN       128

typedef struct WSAData {
        WORD                    wVersion;
        WORD                    wHighVersion;
        char                    szDescription[WSADESCRIPTION_LEN+1];
        char                    szSystemStatus[WSASYS_STATUS_LEN+1];
        unsigned short          iMaxSockets;
        unsigned short          iMaxUdpDg;
        char FAR *              lpVendorInfo;
} WSADATA;

typedef WSADATA FAR *LPWSADATA;

/*
 * Options for use with [gs]etsockopt at the IP level.
 */
#define IP_OPTIONS      1               /* set/get IP per-packet options */

/*
 * Definitions related to sockets: types, address families, options,
 * taken from the BSD file sys/socket.h.
 */

/*
 * This is used instead of -1, since the
 * SOCKET type is unsigned.
 */
#define INVALID_SOCKET  (SOCKET)(~0)
#define SOCKET_ERROR            (-1)

/*
 * Types
 */
#define SOCK_STREAM     1               /* stream socket */
#define SOCK_DGRAM      2               /* datagram socket */
#define SOCK_RAW        3               /* raw-protocol interface */
#define SOCK_RDM        4               /* reliably-delivered message */
#define SOCK_SEQPACKET  5               /* sequenced packet stream */

/*
 * Option flags per-socket.
 */
#define SO_DEBUG        0x0001          /* turn on debugging info recording */
#define SO_ACCEPTCONN   0x0002          /* socket has had listen() */
#define SO_REUSEADDR    0x0004          /* allow local address reuse */
#define SO_KEEPALIVE    0x0008          /* keep connections alive */
#define SO_DONTROUTE    0x0010          /* just use interface addresses */
#define SO_BROADCAST    0x0020          /* permit sending of broadcast msgs */
#define SO_USELOOPBACK  0x0040          /* bypass hardware when possible */
#define SO_LINGER       0x0080          /* linger on close if data present */
#define SO_OOBINLINE    0x0100          /* leave received OOB data in line */

#define SO_DONTLINGER   (u_int)(~SO_LINGER)

/*
 * Additional options.
 */
#define SO_SNDBUF       0x1001          /* send buffer size */
#define SO_RCVBUF       0x1002          /* receive buffer size */
#define SO_SNDLOWAT     0x1003          /* send low-water mark */
#define SO_RCVLOWAT     0x1004          /* receive low-water mark */
#define SO_SNDTIMEO     0x1005          /* send timeout */
#define SO_RCVTIMEO     0x1006          /* receive timeout */
#define SO_ERROR        0x1007          /* get error status and clear */
#define SO_TYPE         0x1008          /* get socket type */

/*
 * TCP options.
 */
#define TCP_NODELAY     0x0001

/*
 * Address families.
 */
#define AF_UNSPEC       0               /* unspecified */
#define AF_UNIX         1               /* local to host (pipes, portals) */
#define AF_INET         2               /* internetwork: UDP, TCP, etc. */
#define AF_IMPLINK      3               /* arpanet imp addresses */
#define AF_PUP          4               /* pup protocols: e.g. BSP */
#define AF_CHAOS        5               /* mit CHAOS protocols */
#define AF_NS           6               /* XEROX NS protocols */
#define AF_ISO          7               /* ISO protocols */
#define AF_OSI          AF_ISO          /* OSI is ISO */
#define AF_ECMA         8               /* european computer manufacturers */
#define AF_DATAKIT      9               /* datakit protocols */
#define AF_CCITT        10              /* CCITT protocols, X.25 etc */
#define AF_SNA          11              /* IBM SNA */
#define AF_DECnet       12              /* DECnet */
#define AF_DLI          13              /* Direct data link interface */
#define AF_LAT          14              /* LAT */
#define AF_HYLINK       15              /* NSC Hyperchannel */
#define AF_APPLETALK    16              /* AppleTalk */
#define AF_NETBIOS      17              /* NetBios-style addresses */

#define AF_MAX          18

/*
 * Structure used by kernel to store most
 * addresses.
 */
struct sockaddr {
        u_short sa_family;              /* address family */
        char    sa_data[14];            /* up to 14 bytes of direct address */
};

/*
 * Structure used by kernel to pass protocol
 * information in raw sockets.
 */
struct sockproto {
        u_short sp_family;              /* address family */
        u_short sp_protocol;            /* protocol */
};

/*
 * Protocol families, same as address families for now.
 */
#define PF_UNSPEC       AF_UNSPEC
#define PF_UNIX         AF_UNIX
#define PF_INET         AF_INET
#define PF_IMPLINK      AF_IMPLINK
#define PF_PUP          AF_PUP
#define PF_CHAOS        AF_CHAOS
#define PF_NS           AF_NS
#define PF_ISO          AF_ISO
#define PF_OSI          AF_OSI
#define PF_ECMA         AF_ECMA
#define PF_DATAKIT      AF_DATAKIT
#define PF_CCITT        AF_CCITT
#define PF_SNA          AF_SNA
#define PF_DECnet       AF_DECnet
#define PF_DLI          AF_DLI
#define PF_LAT          AF_LAT
#define PF_HYLINK       AF_HYLINK
#define PF_APPLETALK    AF_APPLETALK

#define PF_MAX          AF_MAX

/*
 * Structure used for manipulating linger option.
 */
struct  linger {
        u_short l_onoff;                /* option on/off */
        u_short l_linger;               /* linger time */
};

/*
 * Level number for (get/set)sockopt() to apply to socket itself.
 */
#define SOL_SOCKET      0xffff          /* options for socket level */

/*
 * Maximum queue length specifiable by listen.
 */
#define SOMAXCONN       5

#define MSG_OOB         0x1             /* process out-of-band data */
#define MSG_PEEK        0x2             /* peek at incoming message */
#define MSG_DONTROUTE   0x4             /* send without using routing tables */

#define MSG_MAXIOVLEN   16

/*
 * Define constant based on rfc883, used by gethostbyxxxx() calls.
 */
#define MAXGETHOSTSTRUCT        1024

/*
 * Define flags to be used with the WSAAsyncSelect() call.
 */
#define FD_READ         0x01
#define FD_WRITE        0x02
#define FD_OOB          0x04
#define FD_ACCEPT       0x08
#define FD_CONNECT      0x10
#define FD_CLOSE        0x20

/*
 * All Windows Sockets error constants are biased by WSABASEERR from
 * the "normal"
 */
#define WSABASEERR              10000
/*
 * Windows Sockets definitions of regular Microsoft C error constants
 */
#define WSAEINTR                (WSABASEERR+4)
#define WSAEBADF                (WSABASEERR+9)
#define WSAEACCES               (WSABASEERR+13)
#define WSAEFAULT               (WSABASEERR+14)
#define WSAEINVAL               (WSABASEERR+22)
#define WSAEMFILE               (WSABASEERR+24)

/*
 * Windows Sockets definitions of regular Berkeley error constants
 */
#define WSAEWOULDBLOCK          (WSABASEERR+35)
#define WSAEINPROGRESS          (WSABASEERR+36)
#define WSAEALREADY             (WSABASEERR+37)
#define WSAENOTSOCK             (WSABASEERR+38)
#define WSAEDESTADDRREQ         (WSABASEERR+39)
#define WSAEMSGSIZE             (WSABASEERR+40)
#define WSAEPROTOTYPE           (WSABASEERR+41)
#define WSAENOPROTOOPT          (WSABASEERR+42)
#define WSAEPROTONOSUPPORT      (WSABASEERR+43)
#define WSAESOCKTNOSUPPORT      (WSABASEERR+44)
#define WSAEOPNOTSUPP           (WSABASEERR+45)
#define WSAEPFNOSUPPORT         (WSABASEERR+46)
#define WSAEAFNOSUPPORT         (WSABASEERR+47)
#define WSAEADDRINUSE           (WSABASEERR+48)
#define WSAEADDRNOTAVAIL        (WSABASEERR+49)
#define WSAENETDOWN             (WSABASEERR+50)
#define WSAENETUNREACH          (WSABASEERR+51)
#define WSAENETRESET            (WSABASEERR+52)
#define WSAECONNABORTED         (WSABASEERR+53)
#define WSAECONNRESET           (WSABASEERR+54)
#define WSAENOBUFS              (WSABASEERR+55)
#define WSAEISCONN              (WSABASEERR+56)
#define WSAENOTCONN             (WSABASEERR+57)
#define WSAESHUTDOWN            (WSABASEERR+58)
#define WSAETOOMANYREFS         (WSABASEERR+59)
#define WSAETIMEDOUT            (WSABASEERR+60)
#define WSAECONNREFUSED         (WSABASEERR+61)
#define WSAELOOP                (WSABASEERR+62)
#define WSAENAMETOOLONG         (WSABASEERR+63)
#define WSAEHOSTDOWN            (WSABASEERR+64)
#define WSAEHOSTUNREACH         (WSABASEERR+65)
#define WSAENOTEMPTY            (WSABASEERR+66)
#define WSAEPROCLIM             (WSABASEERR+67)
#define WSAEUSERS               (WSABASEERR+68)
#define WSAEDQUOT               (WSABASEERR+69)
#define WSAESTALE               (WSABASEERR+70)
#define WSAEREMOTE              (WSABASEERR+71)

/*
 * Extended Windows Sockets error constant definitions
 */
#define WSASYSNOTREADY          (WSABASEERR+91)
#define WSAVERNOTSUPPORTED      (WSABASEERR+92)
#define WSANOTINITIALISED       (WSABASEERR+93)

/*
 * Error return codes from gethostbyname() and gethostbyaddr()
 * (when using the resolver). Note that these errors are
 * retrieved via WSAGetLastError() and must therefore follow
 * the rules for avoiding clashes with error numbers from
 * specific implementations or language run-time systems.
 * For this reason the codes are based at WSABASEERR+1001.
 * Note also that [WSA]NO_ADDRESS is defined only for
 * compatibility purposes.
 */

#define h_errno         WSAGetLastError()

/* Authoritative Answer: Host not found */
#define WSAHOST_NOT_FOUND       (WSABASEERR+1001)
#define HOST_NOT_FOUND          WSAHOST_NOT_FOUND

/* Non-Authoritative: Host not found, or SERVERFAIL */
#define WSATRY_AGAIN            (WSABASEERR+1002)
#define TRY_AGAIN               WSATRY_AGAIN

/* Non recoverable errors, FORMERR, REFUSED, NOTIMP */
#define WSANO_RECOVERY          (WSABASEERR+1003)
#define NO_RECOVERY             WSANO_RECOVERY

/* Valid name, no data record of requested type */
#define WSANO_DATA              (WSABASEERR+1004)
#define NO_DATA                 WSANO_DATA

/* no address, look for MX record */
#define WSANO_ADDRESS           WSANO_DATA
#define NO_ADDRESS              WSANO_ADDRESS

/*
 * Windows Sockets errors redefined as regular Berkeley error constants
 */
#define EWOULDBLOCK             WSAEWOULDBLOCK
#define EINPROGRESS             WSAEINPROGRESS
#define EALREADY                WSAEALREADY
#define ENOTSOCK                WSAENOTSOCK
#define EDESTADDRREQ            WSAEDESTADDRREQ
#define EMSGSIZE                WSAEMSGSIZE
#define EPROTOTYPE              WSAEPROTOTYPE
#define ENOPROTOOPT             WSAENOPROTOOPT
#define EPROTONOSUPPORT         WSAEPROTONOSUPPORT
#define ESOCKTNOSUPPORT         WSAESOCKTNOSUPPORT
#define EOPNOTSUPP              WSAEOPNOTSUPP
#define EPFNOSUPPORT            WSAEPFNOSUPPORT
#define EAFNOSUPPORT            WSAEAFNOSUPPORT
#define EADDRINUSE              WSAEADDRINUSE
#define EADDRNOTAVAIL           WSAEADDRNOTAVAIL
#define ENETDOWN                WSAENETDOWN
#define ENETUNREACH             WSAENETUNREACH
#define ENETRESET               WSAENETRESET
#define ECONNABORTED            WSAECONNABORTED
#define ECONNRESET              WSAECONNRESET
#define ENOBUFS                 WSAENOBUFS
#define EISCONN                 WSAEISCONN
#define ENOTCONN                WSAENOTCONN
#define ESHUTDOWN               WSAESHUTDOWN
#define ETOOMANYREFS            WSAETOOMANYREFS
#define ETIMEDOUT               WSAETIMEDOUT
#define ECONNREFUSED            WSAECONNREFUSED
#define ELOOP                   WSAELOOP
#define ENAMETOOLONG            WSAENAMETOOLONG
#define EHOSTDOWN               WSAEHOSTDOWN
#define EHOSTUNREACH            WSAEHOSTUNREACH
#define ENOTEMPTY               WSAENOTEMPTY
#define EPROCLIM                WSAEPROCLIM
#define EUSERS                  WSAEUSERS
#define EDQUOT                  WSAEDQUOT
#define ESTALE                  WSAESTALE
#define EREMOTE                 WSAEREMOTE

/* Socket function prototypes */

#ifdef __cplusplus
extern "C" {
#endif

SOCKET PASCAL FAR accept (SOCKET s, struct sockaddr FAR *addr,
                          int FAR *addrlen);

int PASCAL FAR bind (SOCKET s, const struct sockaddr FAR *addr, int namelen);

int PASCAL FAR closesocket (SOCKET s);

int PASCAL FAR connect (SOCKET s, const struct sockaddr FAR *name, int namelen);

int PASCAL FAR ioctlsocket (SOCKET s, long cmd, u_long FAR *argp);

int PASCAL FAR getpeername (SOCKET s, struct sockaddr FAR *name,
                            int FAR * namelen);

int PASCAL FAR getsockname (SOCKET s, struct sockaddr FAR *name,
                            int FAR * namelen);

int PASCAL FAR getsockopt (SOCKET s, int level, int optname,
                           char FAR * optval, int FAR *optlen);

u_long PASCAL FAR htonl (u_long hostlong);

u_short PASCAL FAR htons (u_short hostshort);

unsigned long PASCAL FAR inet_addr (const char FAR * cp);

char FAR * PASCAL FAR inet_ntoa (struct in_addr in);

int PASCAL FAR listen (SOCKET s, int backlog);

u_long PASCAL FAR ntohl (u_long netlong);

u_short PASCAL FAR ntohs (u_short netshort);

int PASCAL FAR recv (SOCKET s, char FAR * buf, int len, int flags);

int PASCAL FAR recvfrom (SOCKET s, char FAR * buf, int len, int flags,
                         struct sockaddr FAR *from, int FAR * fromlen);

int PASCAL FAR select (int nfds, fd_set FAR *readfds, fd_set FAR *writefds,
                       fd_set FAR *exceptfds, const struct timeval FAR *timeout);

int PASCAL FAR send (SOCKET s, const char FAR * buf, int len, int flags);

int PASCAL FAR sendto (SOCKET s, const char FAR * buf, int len, int flags,
                       const struct sockaddr FAR *to, int tolen);

int PASCAL FAR setsockopt (SOCKET s, int level, int optname,
                           const char FAR * optval, int optlen);

int PASCAL FAR shutdown (SOCKET s, int how);

SOCKET PASCAL FAR socket (int af, int type, int protocol);

/* Database function prototypes */

struct hostent FAR * PASCAL FAR gethostbyaddr(const char FAR * addr,
                                              int len, int type);

struct hostent FAR * PASCAL FAR gethostbyname(const char FAR * name);

int PASCAL FAR gethostname (char FAR * name, int namelen);

struct servent FAR * PASCAL FAR getservbyport(int port, const char FAR * proto);

struct servent FAR * PASCAL FAR getservbyname(const char FAR * name,
                                              const char FAR * proto);

struct protoent FAR * PASCAL FAR getprotobynumber(int proto);

struct protoent FAR * PASCAL FAR getprotobyname(const char FAR * name);

/* Microsoft Windows Extension function prototypes */

int PASCAL FAR WSAStartup(WORD wVersionRequired, LPWSADATA lpWSAData);

int PASCAL FAR WSACleanup(void);

void PASCAL FAR WSASetLastError(int iError);

int PASCAL FAR WSAGetLastError(void);

BOOL PASCAL FAR WSAIsBlocking(void);

int PASCAL FAR WSAUnhookBlockingHook(void);

FARPROC PASCAL FAR WSASetBlockingHook(FARPROC lpBlockFunc);

int PASCAL FAR WSACancelBlockingCall(void);

HANDLE PASCAL FAR WSAAsyncGetServByName(HWND hWnd, u_int wMsg,
                                        const char FAR * name, 
                                        const char FAR * proto,
                                        char FAR * buf, int buflen);

HANDLE PASCAL FAR WSAAsyncGetServByPort(HWND hWnd, u_int wMsg, int port,
                                        const char FAR * proto, char FAR * buf,
                                        int buflen);

HANDLE PASCAL FAR WSAAsyncGetProtoByName(HWND hWnd, u_int wMsg,
                                         const char FAR * name, char FAR * buf,
                                         int buflen);

HANDLE PASCAL FAR WSAAsyncGetProtoByNumber(HWND hWnd, u_int wMsg,
                                           int number, char FAR * buf,
                                           int buflen);

HANDLE PASCAL FAR WSAAsyncGetHostByName(HWND hWnd, u_int wMsg,
                                        const char FAR * name, char FAR * buf,
                                        int buflen);

HANDLE PASCAL FAR WSAAsyncGetHostByAddr(HWND hWnd, u_int wMsg,
                                        const char FAR * addr, int len, int type,
                                        const char FAR * buf, int buflen);

int PASCAL FAR WSACancelAsyncRequest(HANDLE hAsyncTaskHandle);

int PASCAL FAR WSAAsyncSelect(SOCKET s, HWND hWnd, u_int wMsg,
                               long lEvent);

#ifdef __cplusplus
}
#endif

/* Microsoft Windows Extended data types */
typedef struct sockaddr SOCKADDR;
typedef struct sockaddr *PSOCKADDR;
typedef struct sockaddr FAR *LPSOCKADDR;

typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr_in *PSOCKADDR_IN;
typedef struct sockaddr_in FAR *LPSOCKADDR_IN;

typedef struct linger LINGER;
typedef struct linger *PLINGER;
typedef struct linger FAR *LPLINGER;

typedef struct in_addr IN_ADDR;
typedef struct in_addr *PIN_ADDR;
typedef struct in_addr FAR *LPIN_ADDR;

typedef struct fd_set FD_SET;
typedef struct fd_set *PFD_SET;
typedef struct fd_set FAR *LPFD_SET;

typedef struct hostent HOSTENT;
typedef struct hostent *PHOSTENT;
typedef struct hostent FAR *LPHOSTENT;

typedef struct servent SERVENT;
typedef struct servent *PSERVENT;
typedef struct servent FAR *LPSERVENT;

typedef struct protoent PROTOENT;
typedef struct protoent *PPROTOENT;
typedef struct protoent FAR *LPPROTOENT;

typedef struct timeval TIMEVAL;
typedef struct timeval *PTIMEVAL;
typedef struct timeval FAR *LPTIMEVAL;

/*
 * Windows message parameter composition and decomposition
 * macros.
 *
 * WSAMAKEASYNCREPLY is intended for use by the Windows Sockets implementation
 * when constructing the response to a WSAAsyncGetXByY() routine.
 */
#define WSAMAKEASYNCREPLY(buflen,error)     MAKELONG(buflen,error)
/*
 * WSAMAKESELECTREPLY is intended for use by the Windows Sockets implementation
 * when constructing the response to WSAAsyncSelect().
 */
#define WSAMAKESELECTREPLY(event,error)     MAKELONG(event,error)
/*
 * WSAGETASYNCBUFLEN is intended for use by the Windows Sockets application
 * to extract the buffer length from the lParam in the response
 * to a WSAGetXByY().
 */
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)
/*
 * WSAGETASYNCERROR is intended for use by the Windows Sockets application
 * to extract the error code from the lParam in the response
 * to a WSAGetXByY().
 */
#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
/*
 * WSAGETSELECTEVENT is intended for use by the Windows Sockets application
 * to extract the event code from the lParam in the response
 * to a WSAAsyncSelect().
 */
#define WSAGETSELECTEVENT(lParam)           LOWORD(lParam)
/*
 * WSAGETSELECTERROR is intended for use by the Windows Sockets application
 * to extract the error code from the lParam in the response
 * to a WSAAsyncSelect().
 */
#define WSAGETSELECTERROR(lParam)           HIWORD(lParam)

#endif  /* _WINSOCKAPI_ */

$ # + K Windows Sockets
Notes for Windows Sockets Suppliers
Introduction
Windows Sockets Components
Multithreadedness and blocking routines.
Database Files
FD_ISSET
Error Codes
DLL Ordinal Numbers
Validation Suite

# $ + K Notes for Windows Sockets Suppliers
Introduction
A Windows Sockets implementation must implement ALL the functionality described in the Windows Sockets documentation.  Validation of compliance is discussed in Validation Suite.

Windows Sockets Version 1.1 implementations must support both TCP and UDP type sockets.  An implementation may support raw sockets (of type SOCK_RAW), but their use is deprecated.

Certain APIs documented above have special notes for Windows Sockets implementors.  A Windows Sockets implementation should pay special attention to conforming to the API as documented.  The Special Notes are provided for assistance and clarification.

# $ + K Notes for Windows Sockets Suppliers
Windows Sockets Components
Development Components
The Windows Sockets development components for use by Windows Sockets application developers will be provided by each Windows Sockets supplier.  These Windows Sockets development components are:

Component	Description
Windows Sockets Documentation	This document
WINSOCK.LIB file	Windows Sockets API Import Library
WINSOCK.H file	Windows Sockets Header File
NETDB.H file	Berkeley Compatible Header File
ARPA/INET.H file	Berkeley Compatible Header File
SYS/TIME.H file	Berkeley Compatible Header File
SYS/SOCKET.H file	Berkeley Compatible Header File
NETINET/IN.H file	Berkeley Compatible Header File

Run Time Components
The run time component provided by each Windows Sockets supplier is:

Component	Description
WINSOCK.DLL	The Windows Sockets API implementation DLL

# $ + K Notes for Windows Sockets Suppliers
Multithreadedness and blocking routines.
Data areas returned by, for example, the getXbyY() routines MUST be on a per thread basis.

Note that an application MUST be prevented from making multiple nested Windows Sockets function calls.  Only one outstanding function call will be allowed for a particular task.  Any Windows Sockets call performed when an existing blocking call is already outstanding will fail with an error code of WSAEINPROGRESS.  There are two exceptions to this restriction: WSACancelBlockingCall() and WSAIsBlocking() may be called at any time.  Windows Sockets suppliers should note that although preliminary drafts of this specification indicated that the restriction only applied to blocking function calls, and that it would be permissible to make non-blocking calls while a blocking call was in progress, this is no longer true.

Regarding the implementation of blocking routines, the solution in Windows Sockets is to simulate the blocking mechanism by having each routine call PeekMessage() as it waits for the completion of its operation.  In anticipation of this, the function WSASetBlockingHook() is provided to allow the programmer to define a special routine to be called instead of the default PeekMessage() loop.  The blocking hook functions are discussed in more detail in WSASetBlockingHook().

# $ + K Notes for Windows Sockets Suppliers
Database Files
The database routines in the getXbyY() family (gethostbyaddr(), etc.) were originally designed (in the first Berkeley UNIX releases) as mechanisms for looking up information in text databases.  A Windows Sockets supplier may choose to employ local files OR a name service to provide some or all of this information.  If local files exist, the format of the files must be identical to that used in BSD UNIX, allowing for the differences in text file formats.  

# $ + K Notes for Windows Sockets Suppliers
FD_ISSET
It is necessary to implement the FD_ISSET Berkeley macro using a supporting function: __WSAFDIsSet().  It is the responsibility of a Windows Sockets implementation to make this available as part of the Windows Sockets API.  Unlike the other functions exported by a Windows Sockets DLL, however, this function is not intended to be invoked directly by Windows Sockets applications: it should be used only to support the FD_ISSET macro.  The source code for this function is listed below:

int FAR
__WSAFDIsSet(SOCKET fd, fd_set FAR *set)
{
    int i = set->count;

    while (i--)
	if (set->fd_array[i] == fd)
	    return 1;

    return 0;
}

# $ + K Notes for Windows Sockets Suppliers
Error Codes
In order to avoid conflict between various compiler environments Windows Sockets implementations MUST return the error codes listed in the API specification, using the manifest constants beginning with "WSA".  The Berkeley-compatible error code definitions are provided solely for compatibility purposes for applications which are being ported from other platforms.

# $ + K Notes for Windows Sockets Suppliers
DLL Ordinal Numbers
The winsock.def file for use by every Windows Sockets implementation is as follows.  Ordinal values starting at 1000 are reserved for Windows Sockets implementors to use for exporting private interfaces to their DLLs.  A Windows Sockets implementation must not use any ordinals 999 and below except for those APIs listed below.  An application which wishes to work with any Windows Sockets DLL must use only those routines listed below; using a private export makes an application dependent on a particular Windows Sockets implementation.

;  
;         File: winsock.def 
;       System: MS-Windows 3.x 
;      Summary: Module definition file for Windows Sockets DLL.  
;  

LIBRARY         WINSOCK         ; Application's module name 

DESCRIPTION     'BSD Socket API for Windows' 

EXETYPE         WINDOWS         ; required for all windows applications 

STUB            'WINSTUB.EXE'   ; generates error message if application 
                                ; is run without Windows 

;CODE can be FIXED in memory because of potential upcalls 
CODE            PRELOAD         FIXED 

;DATA must be SINGLE and at a FIXED location since this is a DLL 
DATA            PRELOAD         FIXED           SINGLE

HEAPSIZE        1024 
STACKSIZE       16384 

; All functions that will be called by any Windows routine 
; must be exported.  Any additional exports beyond those defined
; here must have ordinal numbers 1000 or above. 

EXPORTS 
        accept                         @1 
        bind                           @2 
        closesocket                    @3 
        connect                        @4 
        getpeername                    @5 
        getsockname                    @6 
        getsockopt                     @7 
        htonl                          @8 
        htons                          @9 
        inet_addr                      @10 
        inet_ntoa                      @11 
        ioctlsocket                    @12 
        listen                         @13 
        ntohl                          @14 
        ntohs                          @15 
        recv                           @16 
        recvfrom                       @17 
        select                         @18 
        send                           @19 
        sendto                         @20 
        setsockopt                     @21 
        shutdown                       @22 
        socket                         @23 

        gethostbyaddr                  @51 
        gethostbyname                  @52 
        getprotobyname                 @53 
        getprotobynumber               @54 
        getservbyname                  @55 
        getservbyport                  @56 
        gethostname                    @57

        WSAAsyncSelect                 @101 
        WSAAsyncGetHostByAddr          @102 
        WSAAsyncGetHostByName          @103 
        WSAAsyncGetProtoByNumber       @104 
        WSAAsyncGetProtoByName         @105 
        WSAAsyncGetServByPort          @106 
        WSAAsyncGetServByName          @107 
        WSACancelAsyncRequest          @108 
        WSASetBlockingHook             @109 
        WSAUnhookBlockingHook          @110 
        WSAGetLastError                @111 
        WSASetLastError                @112 
        WSACancelBlockingCall          @113 
        WSAIsBlocking                  @114 
        WSAStartup                     @115 
        WSACleanup                     @116 

        __WSAFDIsSet                   @151 

        WEP                            @500    RESIDENTNAME 

;eof 

# $ + K Notes for Windows Sockets Suppliers
Validation Suite
The Windows Sockets API Tester (WSAT) to ensure Windows Sockets compatibility between Windows Sockets DLL implementations is currently in beta test.  This beta version includes functionality testing of the Windows Sockets interface and is supported by a comprehensive scripting language.  The final version of WSAT will be available in Spring 1993.  If you wish to receive the tester or more information on the beta, send email to wsat@microsoft.com. 

# $ + K Notes for Windows Sockets Suppliers
For Further Reference

This specification is intended to cover the Windows Sockets interface to TCP/IP in detail.  Many details of TCP/IP and Windows, however, are intentionally omitted in the interest of brevity, and this specification often assumes background knowledge of these topics.  For more information, the following references may be helpful:

Braden, R.[1989], RFC 1122, Requirements for Internet Hosts--Communication Layers, Internet Engineering Task Force.

Comer, D. [1991], Internetworking with TCP/IP Volume I: Principles, Protocols, and Architecture, Prentice Hall, Englewood Cliffs, New Jersey.

Comer, D. and Stevens, D. [1991], Internetworking with TCP/IP Volume II: Design, Implementation, and Internals, Prentice Hall, Englewood Cliffs, New Jersey.

Comer, D. and Stevens, D. [1991], Internetworking with TCP/IP Volume III: Client-Server Programming and Applications, Prentice Hall, Englewood Cliffs, New Jersey.

Leffler, S. et al., An Advanced 4.3BSD Interprocess Communication Tutorial.

Petzold, C. [1992], Programming Windows 3.1, Microsoft Press, Redmond, Washington.

Stevens, W.R. [1990], Unix Network Programming, Prentice Hall, Englewood Cliffs, New Jersey.

# $ + K Background Information
Origins of Windows Sockets
The Windows Sockets project had its origins in a Birds Of A Feather session held at Interop '91 in San Jose on October 10, 1991.  A committee was established, and an intensive debate via email resulted in the creation of a first draft specification, which was largely based on submissions from JSB and NetManage.  This draft, and issues arising from it, were debated at a committee meeting hosted by Microsoft in Redmond, WA on December 9, 1991.  Following further email discussions, a working group was established to develop the specification into its current form.

The following people participated in the process as committee members, in working meetings, or in email review.  The authors would like to thank everyone who participated in any way, and apologize in advance if we have omitted anyone.

Martin Hall (Moderator)	JSB Corporation	martinh@jsbus.com
Mark Towfiq (Coordinator)	Microdyne Corporation	towfiq@microdyne.com
Geoff Arnold	Sun Microsystems, Inc.	geoff@east.sun.com
Alistair Banks	Microsoft	alistair@microsoft.com
Carl Beame	Beame & Whiteside	beame@mcmaster,ca
David Beaver	Microsoft	dbeaver@microsoft.com
Amatzia BenArtzi	NetManage, Inc.	amatzia@netmanage.com
Mark Beyer	Ungermann-Bass	mbeyer@ub.com
James Van Bokkelen	FTP Software	jbvb@ftp.com
Nelson Bolyard	Silicon Graphics, Inc.	nelson@sgi.com
Pat Bonner	Hewlett-Packard	p_bonner@cnd.hp.com
Isaac Chan	Microsoft	isaacc@microsoft.com
Nestor Fesas	Hughes LAN Systems	nestor@hls.com
Gary Gere	Gupta	ggere@gupta.com
Bill Hayes	Hewlett-Packard	billh@hpchdpc.cnd.hp.com
Hoek Law	Citicorp	law@dcc.tti.com
Paul Hill	MIT	pbh@athena.mit.edu
Graeme Le Roux	Moresdawn P/L	-
Terry Lister	Hewlett-Packard	tel@cnd.hp.com
Lee Murach	Network Research	lee@nrc.com
David Pool	Spry, Inc.	dave@spry.com
Brad Rice	Age	rice@age.com
Allen Rochkind	3Com	-
Henry Sanders	Microsoft	henrysa@microsoft.com
David Treadwell	Microsoft	davidtr@microsoft.com
Miles Wu	Wollongong	wu@twg.com
Boris Yanovsky	NetManage, Inc.	boris@netmanage.com
J Allard	Microsoft Corporation	jallard@microsoft.com

# $ + K Background Information
Legal Status of Windows Sockets
The copyright for the Windows Sockets specification is owned by the specification authors listed on the title page.  Permission is granted to redistribute this specification in any form, provided that the contents of the specification are not modified.  Windows Sockets implementors are encouraged to include this specification with their product documentation.

The Windows Sockets logo on the title page of this document is meant for use on both Windows Sockets implementations and for applications that use the Windows Sockets interface.  Use of the logo is encouraged on packaging, documentation, collateral, and advertising.  The logo is 
available on microdyne.com in pub/winsock as winsock.bmp.  The suggested color for the logo's title bar is blue, the electrical socket grey, and the text and outline black.  

# $ + K Background Information
The Story Behind the Windows Sockets Icon
(by Alistair Banks, Microsoft Corporation)

We thought we'd do a "Wind Sock" at one stage--but you try to get that into 32x32 bits! It would have had to look wavy and colorful, and... well, it just didn't work. Also, our graphics designers have "opinions" about the icons truly representing what they are--people would have thought this was "The colorful wavy tube specification 1.0!"

I tried to explain "API" "Programming Interface" to the artist--we ended up with toolbox icons with little flying windows

Then we came to realise that we should be going after the shortened form of the name, rather the name in full... Windows Sockets... And so we went for that - so she drew (now remember I'm English and you're probably American) "Windows Spanner", a.k.a. a socket wrench.  In the U.S. you'd have been talking about the "Windows Socket spec" OK, but in England that would have been translatated as "Windows Spanner Spec 1.0" - so we went to Electrical sockets - well the first ones came out looking like "Windows Pignose Spec 1.0"!!!!

So how do you use 32x32, get an international electrical socket! You take the square type (American & English OK, Europe & Australia are too rounded)--you choose the American one, because it's on the wall in front of you (and it's more compact (but less safe, IMHO) and then you turn it upside down, thereby compromising its nationality!

[IMHO = "In My Humble Opinion"--ed.]

{bmc winsock.bmp}