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 }
enum Protocol { IPv4, IPv6, Unknown }
QSocketDevice ( Type type = Stream )
QSocketDevice ( Type type, Protocol protocol, int dummy )
QSocketDevice ( int socket, Type type )
virtual ~QSocketDevice ()
bool isValid () const
Type type () const
Protocol protocol () 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 things (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.

When calling connect() or bind(), QSocketDevice detects the protocol family (IPv4, IPv6) automatically. Passing the protocol family to QSocketDevice'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().

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::Protocol

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

QSocketDevice::IPv4 - The socket is an IPv4 socket.
QSocketDevice::IPv6 - The socket is an IPv6 socket.
QSocketDevice::Unknown - The protocol family of the socket is not known. This can happen if you use QSocketDevice with an already existing socket; it tries to determine the protocol family, but this can fail if the protocol family is not known to QSocketDevice.

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.

The socket is created as an IPv4 socket.

QSocketDevice::QSocketDevice ( Type type, Protocol protocol, int dummy )

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.

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.

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.

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.

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.

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.

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. 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().

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().

Protocol QSocketDevice::protocol () const

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

QSocketDevice 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.

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. 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.

Reimplemented from QIODevice.

int QSocketDevice::receiveBufferSize () const

Returns the size of the operating system receive buffer.

int QSocketDevice::sendBufferSize () const

Returns the size of the operating system send buffer.

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.

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.

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.

Any existing socket is closed.

int QSocketDevice::socket () const

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

Type QSocketDevice::type () const

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

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.

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.