Qt 4.8: Q3SocketDevice Class Reference

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# Q3SocketDevice Class Reference

The Q3SocketDevice class provides a platform-independent low-level socket API. More...

     #include <Q3SocketDevice>

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.

Inherits: QIODevice.

Note: All functions in this class are reentrant.

- List of all members, including inherited members

## Public Types

enum | Error { NoError, AlreadyBound, Inaccessible, NoResources, ..., UnknownError }
enum | Protocol { IPv4, IPv6, Unknown }
enum | Type { Stream, Datagram }

## Public Functions

| Q3SocketDevice ( Type type = Stream )
| Q3SocketDevice ( Type type, Protocol protocol, int dummy )
| Q3SocketDevice ( int socket, Type type )
virtual | ~Q3SocketDevice ()
virtual int | accept ()
QHostAddress | address () const
bool | addressReusable () const
Offset | at () const
bool | at ( Offset offset )
virtual bool | bind ( const QHostAddress & address, Q_UINT16 port )
bool | blocking () const
virtual bool | connect ( const QHostAddress & addr, Q_UINT16 port )
Error | error () const
bool | flush ()
bool | isValid () const
virtual bool | listen ( int backlog )
bool | open ( int mode )
QHostAddress | peerAddress () const
Q_UINT16 | peerPort () const
Q_UINT16 | port () const
Protocol | protocol () const
qint64 | readBlock ( char * data, Q_ULONG maxlen )
int | receiveBufferSize () const
int | sendBufferSize () const
virtual void | setAddressReusable ( bool enable )
virtual void | setBlocking ( bool enable )
virtual void | setReceiveBufferSize ( uint size )
virtual void | setSendBufferSize ( uint size )
virtual void | setSocket ( int socket, Type type )
int | socket () const
Type | type () const
Q_LONG | waitForMore ( int msecs, bool * timeout = 0 ) const
Q_LONG | writeBlock ( const char * data, Q_ULONG len )
virtual Q_LONG | writeBlock ( const char * data, Q_ULONG len, const QHostAddress & host, Q_UINT16 port )

## Reimplemented Public Functions

virtual bool | atEnd () const
virtual qint64 | bytesAvailable () const
virtual void | close ()
virtual bool | open ( OpenMode mode )
virtual Offset | size () const

- 33 public functions inherited from QIODevice
- 29 public functions inherited from QObject

## Protected Functions

void | setError ( Error err )

## Reimplemented Protected Functions

virtual qint64 | readData ( char * data, qint64 maxlen )
virtual qint64 | writeData ( const char * data, qint64 len )

- 5 protected functions inherited from QIODevice
- 8 protected functions inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 4 signals inherited from QIODevice
- 1 signal inherited from QObject
- 7 static public members inherited from QObject

## Detailed Description

The Q3SocketDevice class provides a platform-independent low-level socket API.

This class provides a low level API for working with sockets. Users of this class are assumed to have networking experience. For most users the Q3Socket class provides a much easier and high level alternative, but certain things (like UDP) can't be done with Q3Socket and if you need a platform-independent API for those, Q3SocketDevice is the right choice.

The essential purpose of the class is to provide a QIODevice that works on sockets, wrapped in a platform-independent API.

When calling connect() or bind(), Q3SocketDevice detects the protocol family (IPv4, IPv6) automatically. Passing the protocol family to Q3SocketDevice's constructor or to setSocket() forces creation of a socket device of a specific protocol. If not set, the protocol will be detected at the first call to connect() or bind().

See also Q3Socket, QSocketNotifier, and QHostAddress.

## Member Type Documentation

### enum Q3SocketDevice::Error

This enum type describes the error states of Q3SocketDevice.

Constant | Value | Description
--- | --- | ---
`Q3SocketDevice::NoError` | `0` | No error has occurred.
`Q3SocketDevice::AlreadyBound` | `1` | The device is already bound, according to bind().
`Q3SocketDevice::Inaccessible` | `2` | The operating system or firewall prohibited the action.
`Q3SocketDevice::NoResources` | `3` | The operating system ran out of a resource.
`Q3SocketDevice::InternalError` | `4` | An internal error occurred in Q3SocketDevice.
`Q3SocketDevice::Impossible` | ? | An attempt was made to do something which makes no sense. For example:
     ::close( sd->socket() );
     sd->writeBlock( someData, 42 );

The libc ::close() closes the socket, but Q3SocketDevice is not aware of this. So when you call writeBlock(), the impossible happens.

Constant | Value | Description
--- | --- | ---
`Q3SocketDevice::NoFiles` | ? | The operating system will not let Q3SocketDevice open another file.
`Q3SocketDevice::ConnectionRefused` | ? | A connection attempt was rejected by the peer.
`Q3SocketDevice::NetworkFailure` | ? | There is a network failure.
`Q3SocketDevice::UnknownError` | ? | The operating system did something unexpected.

### enum Q3SocketDevice::Protocol

This enum type describes the protocol family of the socket. Possible values are:

Constant | Value | Description
--- | --- | ---
`Q3SocketDevice::IPv4` | `0` | The socket is an IPv4 socket.
`Q3SocketDevice::IPv6` | `1` | The socket is an IPv6 socket.
`Q3SocketDevice::Unknown` | `2` | The protocol family of the socket is not known. This can happen if you use Q3SocketDevice with an already existing socket; it tries to determine the protocol family, but this can fail if the protocol family is not known to Q3SocketDevice.

See also protocol() and setSocket().

### enum Q3SocketDevice::Type

This enum type describes the type of the socket:

Constant | Value | Description
--- | --- | ---
`Q3SocketDevice::Stream` | `0` | a stream socket (TCP, usually)
`Q3SocketDevice::Datagram` | `1` | a datagram socket (UDP, usually)

## Member Function Documentation

### Q3SocketDevice::Q3SocketDevice ( Type type = Stream )

Creates a Q3SocketDevice object for a stream or datagram socket.

The type argument must be either Q3SocketDevice::Stream for a reliable, connection-oriented TCP socket, or `Q3SocketDevice::Datagram` for an unreliable UDP socket.

The socket is created as an IPv4 socket.

See also blocking() and protocol().

### Q3SocketDevice::Q3SocketDevice ( Type type, Protocol protocol, int dummy )

Creates a Q3SocketDevice object for a stream or datagram socket.

The type argument must be either Q3SocketDevice::Stream for a reliable, connection-oriented TCP socket, or `Q3SocketDevice::Datagram` for an unreliable UDP socket.

The protocol indicates whether the socket should be of type IPv4 or IPv6. Passing `Unknown` is not meaningful in this context and you should avoid using (it creates an IPv4 socket, but your code is not easily readable).

The argument dummy is necessary for compatibility with some compilers.

See also blocking() and protocol().

### Q3SocketDevice::Q3SocketDevice ( int socket, Type type )

Creates a Q3SocketDevice object for the existing socket socket.

The type argument must match the actual socket type; use `Q3SocketDevice::Stream` for a reliable, connection-oriented TCP socket, or Q3SocketDevice::Datagram for an unreliable, connectionless UDP socket.

### Q3SocketDevice::~Q3SocketDevice ()`[virtual]`

Destroys the socket device and closes the socket if it is open.

### int Q3SocketDevice::accept ()`[virtual]`

Extracts the first connection from the queue of pending connections for this socket and returns a new socket identifier. Returns -1 if the operation failed.

See also bind() and listen().

### QHostAddress Q3SocketDevice::address () const

Returns the address of this socket device. This may be 0.0.0.0 for a while, but is set to something sensible as soon as a sensible value is available.

### bool Q3SocketDevice::addressReusable () const

Returns true if the address of this socket can be used by other sockets at the same time, and false if this socket claims exclusive ownership.

See also setAddressReusable().

### Offset Q3SocketDevice::at () const

The read/write index is meaningless for a socket, therefore this function returns 0.

### bool Q3SocketDevice::at ( Offset offset )

The read/write index is meaningless for a socket, therefore this function does nothing and returns true.

The offset parameter is ignored.

### bool Q3SocketDevice::atEnd () const`[virtual]`

Reimplemented from QIODevice::atEnd().

Returns true if no data is currently available at the socket; otherwise returns false.

### bool Q3SocketDevice::bind ( const QHostAddress & address, Q_UINT16 port )`[virtual]`

Assigns a name to an unnamed socket. The name is the host address address and the port number port. If the operation succeeds, bind() returns true; otherwise it returns false without changing what port() and address() return.

bind() is used by servers for setting up incoming connections. Call bind() before listen().

### bool Q3SocketDevice::blocking () const

Returns true if the socket is valid and in blocking mode; otherwise returns false.

Note that this function does not set error().

Warning: On Windows, this function always returns true since the ioctlsocket() function is broken.

See also setBlocking() and isValid().

### qint64 Q3SocketDevice::bytesAvailable () const`[virtual]`

Reimplemented from QIODevice::bytesAvailable().

Returns the number of bytes available for reading, or -1 if an error occurred.

Warning: On Microsoft Windows, we use the ioctlsocket() function to determine the number of bytes queued on the socket. According to Microsoft (KB Q125486), ioctlsocket() sometimes returns an incorrect number. The only safe way to determine the amount of data on the socket is to read it using readBlock(). QSocket has workarounds to deal with this problem.

### void Q3SocketDevice::close ()`[virtual]`

Reimplemented from QIODevice::close().

Closes the socket and sets the socket identifier to -1 (invalid).

(This function ignores errors; if there are any then a file descriptor leakage might result. As far as we know, the only error that can arise is EBADF, and that would of course not cause leakage. There may be OS-specific errors that we haven't come across, however.)

See also open().

### bool Q3SocketDevice::connect ( const QHostAddress & addr, Q_UINT16 port )`[virtual]`

Connects to the IP address and port specified by addr and port. Returns true if it establishes a connection; otherwise returns false. If it returns false, error() explains why.

Note that error() commonly returns NoError for non-blocking sockets; this just means that you can call connect() again in a little while and it'll probably succeed.

### Error Q3SocketDevice::error () const

Returns the first error seen.

See also setError().

### bool Q3SocketDevice::flush ()

The current Q3SocketDevice implementation does not buffer at all, so this is a no-op. This function always returns true.

### bool Q3SocketDevice::isValid () const

Returns true if this is a valid socket; otherwise returns false.

See also socket().

### bool Q3SocketDevice::listen ( int backlog )`[virtual]`

Specifies how many pending connections a server socket can have. Returns true if the operation was successful; otherwise returns false. A backlog value of 50 is quite common.

The listen() call only applies to sockets where type() is `Stream`, i.e. not to `Datagram` sockets. listen() must not be called before bind() or after accept().

See also bind() and accept().

### bool Q3SocketDevice::open ( OpenMode mode )`[virtual]`

Reimplemented from QIODevice::open().

Opens the socket using the specified QIODevice file mode. This function is called from the Q3SocketDevice constructors and from the setSocket() function. You should not call it yourself.

See also close().

### bool Q3SocketDevice::open ( int mode )

This is an overloaded function.

### QHostAddress Q3SocketDevice::peerAddress () const

Returns the address of the port this socket device is connected to. This may be 0.0.0.0 for a while, but is set to something sensible as soon as a sensible value is available.

Note that for Datagram sockets, this is the source port of the last packet received.

### Q_UINT16 Q3SocketDevice::peerPort () const

Returns the port number of the port this socket device is connected to. This may be 0 for a while, but is set to something sensible as soon as a sensible value is available.

Note that for Datagram sockets, this is the source port of the last packet received, and that it is in native byte order.

### Q_UINT16 Q3SocketDevice::port () const

Returns the port number of this socket device. This may be 0 for a while, but is set to something sensible as soon as a sensible value is available.

Note that Qt always uses native byte order, i.e. 67 is 67 in Qt; there is no need to call htons().

### Protocol Q3SocketDevice::protocol () const

Returns the socket's protocol family, which is one of `Unknown`, `IPv4`, or `IPv6`.

Q3SocketDevice either creates a socket with a well known protocol family or it uses an already existing socket. In the first case, this function returns the protocol family it was constructed with. In the second case, it tries to determine the protocol family of the socket; if this fails, it returns `Unknown`.

See also Protocol and setSocket().

### qint64 Q3SocketDevice::readBlock ( char * data, Q_ULONG maxlen )

Reads maxlen bytes from the socket into data and returns the number of bytes read. Returns -1 if an error occurred. Returning 0 is not an error. For Stream sockets, 0 is returned when the remote host closes the connection. For Datagram sockets, 0 is a valid datagram size.

### qint64 Q3SocketDevice::readData ( char * data, qint64 maxlen )`[virtual protected]`

Reimplemented from QIODevice::readData().

Reads maxlen bytes from the socket into data and returns the number of bytes read. Returns -1 if an error occurred.

### int Q3SocketDevice::receiveBufferSize () const

Returns the size of the operating system receive buffer.

See also setReceiveBufferSize().

### int Q3SocketDevice::sendBufferSize () const

Returns the size of the operating system send buffer.

See also setSendBufferSize().

### void Q3SocketDevice::setAddressReusable ( bool enable )`[virtual]`

Sets the address of this socket to be usable by other sockets too if enable is true, and to be used exclusively by this socket if enable is false.

When a socket is reusable, other sockets can use the same port number (and IP address), which is generally useful. Of course other sockets cannot use the same (address,port,peer-address,peer-port) 4-tuple as this socket, so there is no risk of confusing the two TCP connections.

See also addressReusable().

### void Q3SocketDevice::setBlocking ( bool enable )`[virtual]`

Makes the socket blocking if enable is true or nonblocking if enable is false.

Sockets are blocking by default, but we recommend using nonblocking socket operations, especially for GUI programs that need to be responsive.

Warning: On Windows, this function should be used with care since whenever you use a QSocketNotifier on Windows, the socket is immediately made nonblocking.

See also blocking() and isValid().

### void Q3SocketDevice::setError ( Error err )`[protected]`

Allows subclasses to set the error state to err.

See also error().

### void Q3SocketDevice::setReceiveBufferSize ( uint size )`[virtual]`

Sets the size of the operating system receive buffer to size.

The operating system receive buffer size effectively limits two things: how much data can be in transit at any one moment, and how much data can be received in one iteration of the main event loop.

The default is operating system-dependent. A socket that receives large amounts of data is probably best with a buffer size of 49152.

See also receiveBufferSize().

### void Q3SocketDevice::setSendBufferSize ( uint size )`[virtual]`

Sets the size of the operating system send buffer to size.

The operating system send buffer size effectively limits how much data can be in transit at any one moment.

The default is operating system-dependent. A socket that sends large amounts of data is probably best with a buffer size of 49152.

See also sendBufferSize().

### void Q3SocketDevice::setSocket ( int socket, Type type )`[virtual]`

Sets the socket device to operate on the existing socket socket.

The type argument must match the actual socket type; use `Q3SocketDevice::Stream` for a reliable, connection-oriented TCP socket, or Q3SocketDevice::Datagram for an unreliable, connectionless UDP socket.

Any existing socket is closed.

See also socket(), isValid(), and close().

### Offset Q3SocketDevice::size () const`[virtual]`

Reimplemented from QIODevice::size().

The size is meaningless for a socket, therefore this function returns 0.

### int Q3SocketDevice::socket () const

Returns the socket number, or -1 if it is an invalid socket.

See also setSocket(), isValid(), and type().

### Type Q3SocketDevice::type () const

Returns the socket type which is either Q3SocketDevice::Stream or Q3SocketDevice::Datagram.

See also socket().

### Q_LONG Q3SocketDevice::waitForMore ( int msecs, bool * timeout = 0 ) const

Wait up to msecs milliseconds for more data to be available. If msecs is -1 the call will block indefinitely.

Returns the number of bytes available for reading, or -1 if an error occurred.

If timeout is non-null and no error occurred (i.e. it does not return -1): this function sets *timeout to true, if the reason for returning was that the timeout was reached; otherwise it sets *timeout to false. This is useful to find out if the peer closed the connection.

Warning: This is a blocking call and should be avoided in event driven applications.

See also bytesAvailable().

### Q_LONG Q3SocketDevice::writeBlock ( const char * data, Q_ULONG len )

Writes len bytes to the socket from data and returns the number of bytes written. Returns -1 if an error occurred.

This is used for Q3SocketDevice::Stream sockets.

### Q_LONG Q3SocketDevice::writeBlock ( const char * data, Q_ULONG len, const QHostAddress & host, Q_UINT16 port )`[virtual]`

This is an overloaded function.

Writes len bytes to the socket from data and returns the number of bytes written. Returns -1 if an error occurred.

This is used for Q3SocketDevice::Datagram sockets. You must specify the host and port of the destination of the data.

### qint64 Q3SocketDevice::writeData ( const char * data, qint64 len )`[virtual protected]`

Reimplemented from QIODevice::writeData().

Writes len bytes to the socket from data and returns the number of bytes written. Returns -1 if an error occurred.

This is used for Q3SocketDevice::Stream sockets.