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# Q3Dns Class Reference
[Qt3Support module]

The Q3Dns class provides asynchronous DNS lookups. More...

     #include <Q3Dns>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

Note to Qt Desktop Light Edition users: This class is only available in the Qt Desktop Edition.

Inherits QObject.

- List of all members, including inherited members

### Public Types

- enum RecordType { None, A, Aaaa, Mx, ..., Txt }

### Public Functions

- Q3Dns ()
- Q3Dns ( const QString & label, RecordType rr = A )
- Q3Dns ( const QHostAddress & address, RecordType rr = Ptr )
- virtual ~Q3Dns ()
- Q3ValueList<QHostAddress> addresses () const
- QString canonicalName () const
- QStringList hostNames () const
- bool isWorking () const
- QString label () const
- Q3ValueList<MailServer> mailServers () const
- QStringList qualifiedNames () const
- RecordType recordType () const
- Q3ValueList<Server> servers () const
- virtual void setLabel ( const QString & label )
- virtual void setLabel ( const QHostAddress & address )
- virtual void setRecordType ( RecordType rr = A )
- QStringList texts () const

- 29 public functions inherited from QObject

### Signals

- void resultsReady ()

- 1 signal inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 5 static public members inherited from QObject
- 7 protected functions inherited from QObject

## Detailed Description

The Q3Dns 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.

Q3Dns 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); Q3Socket provides much easier to use TCP connection facilities. The aim of Q3Dns 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 Q3Dns 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 Q3Socket.

## Member Type Documentation

### enum Q3Dns::RecordType

This enum type defines the record types Q3Dns 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:

Constant | Value | Description
--- | --- | ---
`Q3Dns::None` | `0` | No information. This exists only so that Q3Dns can have a default.
`Q3Dns::A` | `1` | IPv4 addresses. By far the most common type.
`Q3Dns::Aaaa` | `2` | IPv6 addresses. So far mostly unused.
`Q3Dns::Mx` | `3` | Mail eXchanger names. Used for mail delivery.
`Q3Dns::Srv` | `4` | SeRVer names. Generic record type for finding servers. So far mostly unused.
`Q3Dns::Cname` | `5` | Canonical names. Maps from nicknames to the true name (the canonical name) for a host.
`Q3Dns::Ptr` | `6` | name PoinTeRs. Maps from IPv4 or IPv6 addresses to hostnames.
`Q3Dns::Txt` | `7` | arbitrary TeXT for domains.

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

## Member Function Documentation

### Q3Dns::Q3Dns ()

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

### Q3Dns::Q3Dns ( 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.

### Q3Dns::Q3Dns ( 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.

### Q3Dns::~Q3Dns () `[virtual]`

Destroys the DNS query object and frees its allocated resources.

### Q3ValueList<QHostAddress> Q3Dns::addresses () const

Returns a list of the addresses for this name if this Q3Dns object has a recordType() of Q3Dns::A or Q3Dns::Aaaa and the answer is available; otherwise returns an empty list.

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

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

     Q3ValueList<QHostAddress> list = myDns.addresses();
     Q3ValueList<QHostAddress>::Iterator it = list.begin();
     while( it != list.end() ) {
         myProcessing( *it );
         ++it;
     }

### QString Q3Dns::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 lillian.troll.no, and the search path for Q3Dns is "trolltech.com", then the canonical name for all of "lillian", "l", "lillian.troll.no." and "l.trolltech.com" is "lillian.troll.no.".

### QStringList Q3Dns::hostNames () const

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

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

     QStringList list = myDns.hostNames();
     QStringList::Iterator it = list.begin();
     while( it != list.end() ) {
         myProcessing( *it );
         ++it;
     }

### bool Q3Dns::isWorking () const

Returns true if Q3Dns is doing a lookup for this object (i.e. if it does not already have the necessary information); otherwise returns false.

Q3Dns emits the resultsReady() signal when the status changes to false.

### QString Q3Dns::label () const

Returns the domain name for which this object returns information.

See also setLabel().

### Q3ValueList<MailServer> Q3Dns::mailServers () const

Returns a list of mail servers if the record type is `Mx`. The class Q3Dns::MailServer contains the following public variables:

- QString Q3Dns::MailServer::name
- Q_UINT16 Q3Dns::MailServer::priority

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

     Q3ValueList<Q3Dns::MailServer> list = myDns.mailServers();
     Q3ValueList<Q3Dns::MailServer>::Iterator it = list.begin();
     while( it != list.end() ) {
         myProcessing( *it );
         ++it;
     }

### QStringList Q3Dns::qualifiedNames () const

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

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

     QStringList list = myDns.qualifiedNames();
     QStringList::Iterator it = list.begin();
     while( it != list.end() ) {
         myProcessing( *it );
         ++it;
     }

### RecordType Q3Dns::recordType () const

Returns the record type of this DNS query object.

See also setRecordType() and RecordType.

### void Q3Dns::resultsReady () `[signal]`

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

### Q3ValueList<Server> Q3Dns::servers () const

Returns a list of servers if the record type is `Srv`. The class Q3Dns::Server contains the following public variables:

- QString Q3Dns::Server::name
- Q_UINT16 Q3Dns::Server::priority
- Q_UINT16 Q3Dns::Server::weight
- Q_UINT16 Q3Dns::Server::port

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

     Q3ValueList<Q3Dns::Server> list = myDns.servers();
     Q3ValueList<Q3Dns::Server>::Iterator it = list.begin();
     while( it != list.end() ) {
         myProcessing( *it );
         ++it;
     }

### void Q3Dns::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.

See also label().

### void Q3Dns::setLabel ( const QHostAddress & address ) `[virtual]`

This is an overloaded member function, provided for convenience.

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).

### void Q3Dns::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() and RecordType.

### QStringList Q3Dns::texts () const

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

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

     QStringList list = myDns.texts();
     QStringList::Iterator it = list.begin();
     while( it != list.end() ) {
         myProcessing( *it );
         ++it;
     }