QSocketDevice Class

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# QSocketDevice Class Reference
[network module]

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

`#include <qsocketdevice.h>`

Inherits QIODevice.

List of all member functions.

## Public Members

- enum Type { Stream, Datagram }
- QSocketDevice ( Type type = Stream )
- QSocketDevice ( int socket, Type type )
- virtual ~QSocketDevice ()
- bool isValid () const
- Type type () const
- int socket () const
- virtual void setSocket ( int socket, Type type )
- bool blocking () const
- virtual void setBlocking ( bool enable )
- bool addressReusable () const
- virtual void setAddressReusable ( bool enable )
- int receiveBufferSize () const
- virtual void setReceiveBufferSize ( uint size )
- int sendBufferSize () const
- virtual void setSendBufferSize ( uint size )
- virtual bool connect ( const QHostAddress & addr, Q_UINT16 port )
- virtual bool bind ( const QHostAddress & address, Q_UINT16 port )
- virtual bool listen ( int backlog )
- virtual int accept ()
- Q_LONG bytesAvailable () const
- Q_LONG waitForMore ( int msecs, bool * timeout = 0 ) const
- virtual Q_LONG readBlock ( char * data, Q_ULONG maxlen )
- virtual 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 )
- Q_UINT16 port () const
- Q_UINT16 peerPort () const
- QHostAddress address () const
- QHostAddress peerAddress () const
- enum Error { NoError, AlreadyBound, Inaccessible, NoResources, InternalError, Bug = InternalError, Impossible, NoFiles, ConnectionRefused, NetworkFailure, UnknownError }
- Error error () const

## Protected Members

- void setError ( Error err )

## Detailed Description

The QSocketDevice 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 QSocket class provides a much easier and high level alternative, but certain thing (like UDP) can't be done with QSocket and if you need a platform-independent API for those, QSocketDevice 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.

See also QSocket, QSocketNotifier, QHostAddress, and Input/Output and Networking.

## Member Type Documentation

### QSocketDevice::Error

This enum type describes the error states of QSocketDevice.

- `QSocketDevice::NoError` - No error has occurred.
- `QSocketDevice::AlreadyBound` - The device is already bound, according to bind().
- `QSocketDevice::Inaccessible` - The operating system or firewall prohibited the action.
- `QSocketDevice::NoResources` - The operating system ran out of a resource.
- `QSocketDevice::InternalError` - An internal error occurred in QSocketDevice.
- `QSocketDevice::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 QSocketDevice is not aware of this. So when you call writeBlock(), the impossible happens.
- `QSocketDevice::NoFiles` - The operating system will not let QSocketDevice open another file.
- `QSocketDevice::ConnectionRefused` - A connection attempt was rejected by the peer.
- `QSocketDevice::NetworkFailure` - There is a network failure.
- `QSocketDevice::UnknownError` - The operating system did something unexpected.

### QSocketDevice::Type

This enum type describes the type of the socket:

- `QSocketDevice::Stream` - a stream socket (TCP, usually)
- `QSocketDevice::Datagram` - a datagram socket (UDP, usually)

## Member Function Documentation

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

Creates a QSocketDevice object for a stream or datagram socket.

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

See also blocking().

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

Creates a QSocketDevice object for the existing socket socket.

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

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

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

### int QSocketDevice::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 QSocketDevice::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 QSocketDevice::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().

### bool QSocketDevice::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 QSocketDevice::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().

### Q_LONG QSocketDevice::bytesAvailable () const

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.

### bool QSocketDevice::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 QSocketDevice::error () const

Returns the first error seen.

### bool QSocketDevice::isValid () const

Returns TRUE if this is a valid socket; otherwise returns FALSE.

See also socket().

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

Specifies how many pending connections a server socket can have. Returns TRUE if the operation was successful; otherwise returns FALSE.

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(). It is common to use a backlog value of 50 on most Unix systems.

See also bind() and accept().

### QHostAddress QSocketDevice::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 QSocketDevice::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 QSocketDevice::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().

### Q_LONG QSocketDevice::readBlock ( char * data, Q_ULONG maxlen )`[virtual]`

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

Reimplemented from QIODevice.

### int QSocketDevice::receiveBufferSize () const

Returns the size of the operating system receive buffer.

See also setReceiveBufferSize().

### int QSocketDevice::sendBufferSize () const

Returns the size of the operating system send buffer.

See also setSendBufferSize().

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

Allows subclasses to set the error state to err.

### void QSocketDevice::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.

### void QSocketDevice::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.

### void QSocketDevice::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 QSocketDevice::Stream for a reliable, connection-oriented TCP socket, or QSocketDevice::Datagram for an unreliable, connectionless UDP socket.

Any existing socket is closed.

See also isValid() and close().

### int QSocketDevice::socket () const

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

See also isValid() and type().

### Type QSocketDevice::type () const

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

See also socket().

### Q_LONG QSocketDevice::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 QSocketDevice::writeBlock ( const char * data, Q_ULONG len )`[virtual]`

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 QSocketDevice::Stream sockets.

Reimplemented from QIODevice.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above 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 QSocketDevice::Datagram sockets. You must specify the host and port of the destination of the data.

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