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QDns Class Reference
[network module]

The QDns class provides asynchronous DNS lookups. More...

#include <qdns.h>

Inherits QObject.

List of all member functions.

Public Members

Signals


Detailed Description

The QDns class provides asynchronous DNS lookups.

Both Windows and Unix provide synchronous DNS lookups; Windows provides some asynchronous support too. At the time of writing neither operating system provides asynchronous support for anything other than hostname-to-address mapping.

QDns rectifies this shortcoming, by providing asynchronous caching lookups for the record types that we expect modern GUI applications to need in the near future.

The class is not straightforward to use (although it is much simpler than the native APIs); QSocket provides much easier to use TCP connection facilities. The aim of QDns is to provide a correct and small API to the DNS and nothing more. (We use "correctness" to mean that the DNS information is correctly cached, and correctly timed out.)

The API comprises a constructor, functions to set the DNS node (the domain in DNS terminology) and record type (setLabel() and setRecordType()), the corresponding get functions, an isWorking() function to determine whether QDns is working or reading, a resultsReady() signal and query functions for the result.

There is one query function for each RecordType, namely addresses(), mailServers(), servers(), hostNames() and texts(). There are also two generic query functions: canonicalName() returns the name you'll presumably end up using (the exact meaning of this depends on the record type) and qualifiedNames() returns a list of the fully qualified names label() maps to.

See also QSocket.


Member Type Documentation

QDns::RecordType

This enum type defines the record types QDns can handle. The DNS provides many more; these are the ones we've judged to be in current use, useful for GUI programs and important enough to support right away:

We expect that some support for the RFC-2535 extensions will be added in future versions.


Member Function Documentation

QDns::QDns ()

Constructs a DNS query object with invalid settings for both the label and the search type.

QDns::QDns ( const QString & label, RecordType rr = A )

Constructs a DNS query object that will return record type rr information about label.

The DNS lookup is started the next time the application enters the event loop. When the result is found the signal resultsReady() is emitted.

rr defaults to A, IPv4 addresses.

QDns::QDns ( const QHostAddress & address, RecordType rr = Ptr )

Constructs a DNS query object that will return record type rr information about host address address. The label is set to the IN-ADDR.ARPA domain name. This is useful in combination with the Ptr record type (e.g. if you want to look up a hostname for a given address).

The DNS lookup is started the next time the application enters the event loop. When the result is found the signal resultsReady() is emitted.

rr defaults to Ptr, that maps addresses to hostnames.

QDns::~QDns () [virtual]

Destroys the DNS query object and frees its allocated resources.

QString QDns::label () const

Returns the domain name for which this object returns information.

See also setLabel().

QStringList QDns::qualifiedNames () const

Returns a list of the fully qualified names label() maps to.

void QDns::setLabel ( const QString & label ) [virtual]

Sets this DNS query object to query for information about label.

This does not change the recordType(), but its isWorking() status will probably change as a result.

The DNS lookup is started the next time the application enters the event loop. When the result is found the signal resultsReady() is emitted.

void QDns::setLabel ( const QHostAddress & address ) [virtual]

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Sets this DNS query object to query for information about the host address address. The label is set to the IN-ADDR.ARPA domain name. This is useful in combination with the Ptr record type (e.g. if you want to look up a hostname for a given address).

This does not change the recordType(), but its isWorking() status will probably change as a result.

The DNS lookup is started the next time the application enters the event loop. When the result is found the signal resultsReady() is emitted.

void QDns::setRecordType ( RecordType rr = A ) [virtual]

Sets this object to query for record type rr records.

The DNS lookup is started the next time the application enters the event loop. When the result is found the signal resultsReady() is emitted.

See also RecordType.


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