class QLocalServer

The QLocalServer class provides a local socket based server. More…

Inheritance diagram of PySide6.QtNetwork.QLocalServer

Synopsis

Properties

Methods

Virtual methods

Signals

Static functions

Note

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Detailed Description

This class makes it possible to accept incoming local socket connections.

Call listen() to have the server start listening for incoming connections on a specified key. The newConnection() signal is then emitted each time a client connects to the server.

Call nextPendingConnection() to accept the pending connection as a connected QLocalSocket . The function returns a pointer to a QLocalSocket that can be used for communicating with the client.

If an error occurs, serverError() returns the type of error, and errorString() can be called to get a human readable description of what happened.

When listening for connections, the name which the server is listening on is available through serverName() .

Calling close() makes QLocalServer stop listening for incoming connections.

Although QLocalServer is designed for use with an event loop, it’s possible to use it without one. In that case, you must use waitForNewConnection() , which blocks until either a connection is available or a timeout expires.

class SocketOption

(inherits enum.Flag) This enum describes the possible options that can be used to create the socket. This changes the access permissions on platforms (Linux, Windows) that support access permissions on the socket. Both GroupAccess and OtherAccess may vary slightly in meanings depending on the platform. On Linux and Android it is possible to use sockets with abstract addresses; socket permissions have no meaning for such sockets.

Constant

Description

QLocalServer.NoOptions

No access restrictions have been set.

QLocalServer.UserAccessOption

Access is restricted to the same user as the process that created the socket.

QLocalServer.GroupAccessOption

Access is restricted to the same group but not the user that created the socket on Linux. Access is restricted to the primary group of the process on Windows

QLocalServer.OtherAccessOption

Access is available to everyone but the user and group that created the socket on Linux. Access is available to everyone on Windows.

QLocalServer.WorldAccessOption

No access restrictions.

QLocalServer.AbstractNamespaceOption

The listening socket will be created in the abstract namespace. This flag is specific to Linux. In case of other platforms, for the sake of code portability, this flag is equivalent to WorldAccessOption.

See also

socketOptions

Note

Properties can be used directly when from __feature__ import true_property is used or via accessor functions otherwise.

property socketOptionsᅟ: Combination of QLocalServer.SocketOption

This property holds the socket options that control how the socket operates..

For example, the socket may restrict access to what user ids can connect to the socket.

These options must be set before listen() is called.

In some cases, such as with Unix domain sockets on Linux, the access to the socket will be determined by file system permissions, and are created based on the umask. Setting the access flags will override this and will restrict or permit access as specified.

Other Unix-based operating systems, such as macOS, do not honor file permissions for Unix domain sockets and by default have WorldAccess and these permission flags will have no effect.

On Windows, UserAccessOption is sufficient to allow a non elevated process to connect to a local server created by an elevated process run by the same user. GroupAccessOption refers to the primary group of the process (see TokenPrimaryGroup in the Windows documentation). OtherAccessOption refers to the well known “Everyone” group.

On Linux platforms it is possible to create a socket in the abstract namespace, which is independent of the filesystem. Using this kind of socket implies ignoring permission options. On other platforms AbstractNamespaceOption is equivalent to WorldAccessOption .

By default none of the flags are set, access permissions are the platform default.

See also

listen()

Access functions:
__init__([parent=None])
Parameters:

parent – QObject

Create a new local socket server with the given parent.

See also

listen()

addPendingConnection(socket)
Parameters:

socket – QLocalSocket

This function is called by incomingConnection() to add the socket to the list of pending incoming connections.

Note

Don’t forget to call this member from reimplemented incomingConnection() if you do not want to break the Pending Connections mechanism. This function emits the newConnection() signal after the socket has been added.

See also

incomingConnection() newConnection()

close()

Stop listening for incoming connections. Existing connections are not affected, but any new connections will be refused.

errorString()
Return type:

str

Returns the human-readable message appropriate to the current error reported by serverError() . If no suitable string is available, an empty string is returned.

See also

serverError()

fullServerName()
Return type:

str

Returns the full path that the server is listening on.

Note: This is platform specific

hasPendingConnections()
Return type:

bool

Returns true if the server has a pending connection; otherwise returns false.

incomingConnection(socketDescriptor)
Parameters:

socketDescriptor – quintptr

This virtual function is called by QLocalServer when a new connection is available. socketDescriptor is the native socket descriptor for the accepted connection.

The base implementation creates a QLocalSocket , sets the socket descriptor and then stores the QLocalSocket in an internal list of pending connections. Finally newConnection() is emitted.

Reimplement this function to alter the server’s behavior when a connection is available.

isListening()
Return type:

bool

Returns true if the server is listening for incoming connections otherwise false.

See also

listen() close()

listen(name)
Parameters:

name – str

Return type:

bool

Tells the server to listen for incoming connections on name. If the server is currently listening then it will return false. Return true on success otherwise false.

name can be a single name and QLocalServer will determine the correct platform specific path. serverName() will return the name that is passed into listen.

Usually you would just pass in a name like “foo”, but on Unix this could also be a path such as “/tmp/foo” and on Windows this could be a pipe path such as “\\.\pipe\foo”

Note

On Unix if the server crashes without closing listen will fail with AddressInUseError. To create a new server the file should be removed. On Windows two local servers can listen to the same pipe at the same time, but any connections will go to one of the server.

See also

serverName() isListening() close()

listen(socketDescriptor)
Parameters:

socketDescriptor – qintptr

Return type:

bool

Instructs the server to listen for incoming connections on socketDescriptor. The property returns false if the server is currently listening. It returns true on success; otherwise, it returns false. The socket must be ready to accept new connections with no extra platform-specific functions called. The socket is set into non-blocking mode.

serverName() , fullServerName() may return a string with a name if this option is supported by the platform; otherwise, they return an empty QString. In particular, the addresses of sockets in the abstract namespace supported by Linux will not yield useful names if they contain unprintable characters.

listenBacklogSize()
Return type:

int

Returns the backlog queue size of to be accepted connections.

maxPendingConnections()
Return type:

int

Returns the maximum number of pending accepted connections. The default is 30.

newConnection()

This signal is emitted every time a new connection is available.

nextPendingConnection()
Return type:

QLocalSocket

Returns the next pending connection as a connected QLocalSocket object.

The socket is created as a child of the server, which means that it is automatically deleted when the QLocalServer object is destroyed. It is still a good idea to delete the object explicitly when you are done with it, to avoid wasting memory.

None is returned if this function is called when there are no pending connections.

static removeServer(name)
Parameters:

name – str

Return type:

bool

Removes any server instance that might cause a call to listen() to fail and returns true if successful; otherwise returns false. This function is meant to recover from a crash, when the previous server instance has not been cleaned up.

On Windows, this function does nothing; on Unix, it removes the socket file given by name.

Warning

Be careful to avoid removing sockets of running instances.

serverError()
Return type:

SocketError

Returns the type of error that occurred last or NoError .

See also

errorString()

serverName()
Return type:

str

Returns the server name if the server is listening for connections; otherwise returns QString()

setListenBacklogSize(size)
Parameters:

size – int

Sets the backlog queue size of to be accepted connections to size. The operating system might reduce or ignore this value. By default, the queue size is 50.

Note

This property must be set prior to calling listen() .

See also

listenBacklogSize()

setMaxPendingConnections(numConnections)
Parameters:

numConnections – int

Sets the maximum number of pending accepted connections to numConnections. QLocalServer will accept no more than numConnections incoming connections before nextPendingConnection() is called.

Note: Even though QLocalServer will stop accepting new connections after it has reached its maximum number of pending connections, the operating system may still keep them in queue which will result in clients signaling that it is connected.

setSocketOptions(options)
Parameters:

options – Combination of SocketOption

See also

socketOptions()

Setter of property socketOptionsᅟ .

socketDescriptor()
Return type:

qintptr

Returns the native socket descriptor the server uses to listen for incoming instructions, or -1 if the server is not listening.

The type of the descriptor depends on the platform:

  • On Windows, the returned value is a Winsock 2 Socket Handle.

  • On INTEGRITY, the returned value is the QTcpServer socket descriptor and the type is defined by socketDescriptor .

  • On all other UNIX-like operating systems, the type is a file descriptor representing a listening socket.

See also

listen()

socketOptions()
Return type:

Combination of SocketOption

Returns the socket options set on the socket.

Getter of property socketOptionsᅟ .

waitForNewConnection(msec)
Parameters:

msec – int

Return type:

(retval, timedOut)

Waits for at most msec milliseconds or until an incoming connection is available. Returns true if a connection is available; otherwise returns false. If the operation timed out and timedOut is not None, *timedOut will be set to true.

This is a blocking function call. Its use is ill-advised in a single-threaded GUI application, since the whole application will stop responding until the function returns. waitForNewConnection() is mostly useful when there is no event loop available.

The non-blocking alternative is to connect to the newConnection() signal.

If msec is -1, this function will not time out.