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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

- enum RecordType { None, A, Aaaa, Mx, Srv, Cname, Ptr, Txt }
- QDns ()
- QDns ( const QString & label, RecordType rr = A )
- QDns ( const QHostAddress & address, RecordType rr = Ptr )
- virtual ~QDns ()
- virtual void setLabel ( const QString & label )
- virtual void setLabel ( const QHostAddress & address )
- QString label () const
- virtual void setRecordType ( RecordType rr = A )
- RecordType recordType () const
- bool isWorking () const
- QValueList<QHostAddress> addresses () const
- QValueList<MailServer> mailServers () const
- QValueList<Server> servers () const
- QStringList hostNames () const
- QStringList texts () const
- QString canonicalName () const
- QStringList qualifiedNames () const

## Signals

- void resultsReady ()

## Detailed Description

The QDns class provides asynchronous DNS lookups.

Both Windows and UNIX provides synchronous DNS lookups; Windows provides some asynchronous support too. Neither OS provides asynchronous support for anything other than hostname-to-address mapping.

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

The class is a bit hard to use (although much simpler than the native APIs); QSocket provides much simpler TCP connection facilities. The aim of QDns is to provide a correct and small API to the DNS: Nothing more. (Correctness implies that the DNS information is correctly cached, and correctly timed out.)

The API is made up of a constructor, functions to set the DNS node (the domain in DNS terminology) and record type (setLabel() and setRecordType()), the corresponding getters, an isWorking() function to determine whether QDns is working or reading, a resultsReady() signal, and finally 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() return the name you'll presumably end up using (the exact meaning of that 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:

- `None` - no information. This exists only so that QDns can have a default.
- `A` - IPv4 addresses. By far the most common type.
- `Aaaa` - Ipv6 addresses. So far mostly unused.
- `Mx` - Mail eXchanger names. Used for mail delivery.
- `Srv` - SeRVer names. Generic record type for finding servers. So far mostly unused.
- `Cname` - canonical name. Maps from nicknames to the true name (the canonical name) for a host.
- `Ptr` - name PoinTeR. Maps from IPv4 or IPv6 addresses to hostnames.
- `Txt` - arbitrary text for domains.

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 both for the label and the search type.

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

Constructs a DNS query object that will return rr information about address. The label is set to the IN-ADDR.ARPA domain name. This is useful in combination with the Ptr record type (i.e. 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 emmitted.

rr defaults to `Ptr,` that maps addresses to hostnames.

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

Constructs a DNS query object that will return 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 emmitted.

rr defaults to `A,` IPv4 addresses.

### QDns::~QDns () `[virtual]`

Destroys the query object and frees its allocated resources.

### QValueList<QHostAddress> QDns::addresses () const

Returns a list of the addresses for this name if this QDns object has a recordType() of QDns::A or QDns::Aaaa and the answer is available, or an empty list else.

As a special case, if label() is a valid numeric IP address, this function returns that address.

### QString QDns::canonicalName () const

Returns the canonical name for this DNS node. (This works regardless of what recordType() is set to.)

If the canonical name isn't known, this function returns a null string.

The canonical name of a DNS node is its full name, or the full name of the target of its CNAME. For example, if l.trolltech.com is a CNAME to lupinella.troll.no, and the search path for QDns is "trolltech.com", then the canonical name for all of "lupinella", "l", "lupinella.troll.no." and "l.trolltech.com" is "lupinella.troll.no.".

### QStringList QDns::hostNames () const

Returns a list of host names if the record type is `Ptr.`

### bool QDns::isWorking () const

Returns TRUE if QDns is doing a lookup for this object, and FALSE if this object has the information it wants.

QDns emits the resultsReady() signal when the status changes to FALSE.

### QString QDns::label () const

Returns the domain name for which this object returns information.

See also setLabel().

### QValueList<MailServer> QDns::mailServers () const

Returns a list of mail servers if the record type is `Mx.` The struct `QDns::MailServer` contains the following variables:

- `QString` QDns::MailServer::name
- `Q_UINT16` QDns::MailServer::priority

### QStringList QDns::qualifiedNames () const

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

### QDns::RecordType QDns::recordType() const

Returns the record type of this query object.

See also setRecordType() and RecordType.

### void QDns::resultsReady () `[signal]`

This signal is emitted when results are available for one of the qualifiedNames().

### QValueList<Server> QDns::servers () const

Returns a list of servers if the record type is `Srv.` The struct `QDns::Server` contains the following variables:

- `QString` QDns::Server::name
- `Q_UINT16` QDns::Server::priority
- `Q_UINT16` QDns::Server::weight
- `Q_UINT16` QDns::Server::port

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

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

This does not change the recordType(), but its isWorking() most likely changes 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 emmitted.

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

Sets this query object to query for information about label.

This does not change the recordType(), but its isWorking() most likely changes 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 emmitted.

### void QDns::setRecordType ( RecordType rr = A )

Sets this object to query for 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 emmitted.

See also RecordType.

### QStringList QDns::texts () const

Returns a list of texts if the record type is `Txt.`

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