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+** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
+** Contact:
+** This file is part of the documentation of the Qt Toolkit.
+** GNU Free Documentation License
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file.
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms
+** and conditions contained in a signed written agreement between you
+** and Nokia.
+ \group network
+ \title Network Programming API
+ \brief Classes for Network Programming
+ \ingroup groups
+ \page network-programming.html
+ \title Network Programming
+ \ingroup qt-network
+ \brief An Introduction to Network Programming with Qt
+ The QtNetwork module offers classes that allow you to write TCP/IP clients
+ and servers. It offers lower-level classes such as QTcpSocket,
+ QTcpServer and QUdpSocket that represent low level network concepts,
+ and high level classes such as QNetworkRequest, QNetworkReply and
+ QNetworkAccessManager to perform network operations using common protocols.
+ It also offers classes such as QNetworkConfiguration,
+ QNetworkConfigurationManager and QNetworkSession that implement bearer
+ management.
+ \tableofcontents
+ \section1 Qt's Classes for Network Programming
+ The following classes provide support for network programming in Qt.
+ \annotatedlist network
+ \section1 High Level Network Operations for HTTP and FTP
+ The Network Access API is a collection of classes for performing
+ common network operations. The API provides an abstraction layer
+ over the specific operations and protocols used (for example,
+ getting and posting data over HTTP), and only exposes classes,
+ functions, and signals for general or high level concepts.
+ Network requests are represented by the QNetworkRequest class,
+ which also acts as a general container for information associated
+ with a request, such as any header information and the encryption
+ used. The URL specified when a request object is constructed
+ determines the protocol used for a request.
+ Currently HTTP, FTP and local file URLs are supported for uploading
+ and downloading.
+ The coordination of network operations is performed by the
+ QNetworkAccessManager class. Once a request has been created,
+ this class is used to dispatch it and emit signals to report on
+ its progress. The manager also coordinates the use of
+ \l{QNetworkCookieJar}{cookies} to store data on the client,
+ authentication requests, and the use of proxies.
+ Replies to network requests are represented by the QNetworkReply
+ class; these are created by QNetworkAccessManager when a request
+ is dispatched. The signals provided by QNetworkReply can be used
+ to monitor each reply individually, or developers may choose to
+ use the manager's signals for this purpose instead and discard
+ references to replies. Since QNetworkReply is a subclass of
+ QIODevice, replies can be handled synchronously or asynchronously;
+ i.e., as blocking or non-blocking operations.
+ Each application or library can create one or more instances of
+ QNetworkAccessManager to handle network communication.
+ \section1 Using TCP with QTcpSocket and QTcpServer
+ TCP (Transmission Control Protocol) is a low-level network
+ protocol used by most Internet protocols, including HTTP and FTP,
+ for data transfer. It is a reliable, stream-oriented,
+ connection-oriented transport protocol. It is particularly well
+ suited to the continuous transmission of data.
+ \image tcpstream.png A TCP Stream
+ The QTcpSocket class provides an interface for TCP. You can use
+ QTcpSocket to implement standard network protocols such as POP3,
+ SMTP, and NNTP, as well as custom protocols.
+ A TCP connection must be established to a remote host and port
+ before any data transfer can begin. Once the connection has been
+ established, the IP address and port of the peer are available
+ through QTcpSocket::peerAddress() and QTcpSocket::peerPort(). At
+ any time, the peer can close the connection, and data transfer
+ will then stop immediately.
+ QTcpSocket works asynchronously and emits signals to report status
+ changes and errors, just like QNetworkAccessManager. It
+ relies on the event loop to detect incoming data and to
+ automatically flush outgoing data. You can write data to the
+ socket using QTcpSocket::write(), and read data using
+ QTcpSocket::read(). QTcpSocket represents two independent streams
+ of data: one for reading and one for writing.
+ Since QTcpSocket inherits QIODevice, you can use it with
+ QTextStream and QDataStream. When reading from a QTcpSocket, you
+ must make sure that enough data is available by calling
+ QTcpSocket::bytesAvailable() beforehand.
+ If you need to handle incoming TCP connections (e.g., in a server
+ application), use the QTcpServer class. Call QTcpServer::listen()
+ to set up the server, and connect to the
+ QTcpServer::newConnection() signal, which is emitted once for
+ every client that connects. In your slot, call
+ QTcpServer::nextPendingConnection() to accept the connection and
+ use the returned QTcpSocket to communicate with the client.
+ Although most of its functions work asynchronously, it's possible
+ to use QTcpSocket synchronously (i.e., blocking). To get blocking
+ behavior, call QTcpSocket's waitFor...() functions; these suspend
+ the calling thread until a signal has been emitted. For example,
+ after calling the non-blocking QTcpSocket::connectToHost()
+ function, call QTcpSocket::waitForConnected() to block the thread
+ until the \l{QTcpSocket::connected()}{connected()} signal has
+ been emitted.
+ Synchronous sockets often lead to code with a simpler flow of
+ control. The main disadvantage of the waitFor...() approach is
+ that events won't be processed while a waitFor...() function is
+ blocking. If used in the GUI thread, this might freeze the
+ application's user interface. For this reason, we recommend that
+ you use synchronous sockets only in non-GUI threads. When used
+ synchronously, QTcpSocket doesn't require an event loop.
+ The \l{network/fortuneclient}{Fortune Client} and
+ \l{network/fortuneserver}{Fortune Server} examples show how to use
+ QTcpSocket and QTcpServer to write TCP client-server
+ applications. See also \l{network/blockingfortuneclient}{Blocking
+ Fortune Client} for an example on how to use a synchronous
+ QTcpSocket in a separate thread (without using an event loop),
+ and \l{network/threadedfortuneserver}{Threaded Fortune Server}
+ for an example of a multithreaded TCP server with one thread per
+ active client.
+ \section1 Using UDP with QUdpSocket
+ UDP (User Datagram Protocol) is a lightweight, unreliable,
+ datagram-oriented, connectionless protocol. It can be used when
+ reliability isn't important. For example, a server that reports
+ the time of day could choose UDP. If a datagram with the time of
+ day is lost, the client can simply make another request.
+ \image udppackets.png UDP Packets
+ The QUdpSocket class allows you to send and receive UDP
+ datagrams. It inherits QAbstractSocket, and it therefore shares
+ most of QTcpSocket's interface. The main difference is that
+ QUdpSocket transfers data as datagrams instead of as a continuous
+ stream of data. In short, a datagram is a data packet of limited
+ size (normally smaller than 512 bytes), containing the IP address
+ and port of the datagram's sender and receiver in addition to the
+ data being transferred.
+ QUdpSocket supports IPv4 broadcasting. Broadcasting is often used
+ to implement network discovery protocols, such as finding which
+ host on the network has the most free hard disk space. One host
+ broadcasts a datagram to the network that all other hosts
+ receive. Each host that receives a request then sends a reply
+ back to the sender with its current amount of free disk space.
+ The originator waits until it has received replies from all
+ hosts, and can then choose the server with most free space to
+ store data. To broadcast a datagram, simply send it to the
+ special address QHostAddress::Broadcast (, or
+ to your local network's broadcast address.
+ QUdpSocket::bind() prepares the socket for accepting incoming
+ datagrams, much like QTcpServer::listen() for TCP servers.
+ Whenever one or more datagrams arrive, QUdpSocket emits the
+ \l{QUdpSocket::readyRead()}{readyRead()} signal. Call
+ QUdpSocket::readDatagram() to read the datagram.
+ The \l{network/broadcastsender}{Broadcast Sender} and
+ \l{network/broadcastreceiver}{Broadcast Receiver} examples show how to
+ write a UDP sender and a UDP receiver using Qt.
+ QUdpSocket also supports multicasting. The
+ \l{network/multicastsender}{Multicast Sender} and
+ \l{network/multicastreceiver}{Multicast Receiver} examples show how to use
+ write UDP multicast clients.
+ \section1 Resolving Host Names using QHostInfo
+ Before establishing a network connection, QTcpSocket and
+ QUdpSocket perform a name lookup, translating the host name
+ you're connecting to into an IP address. This operation is
+ usually performed using the DNS (Domain Name Service) protocol.
+ QHostInfo provides a static function that lets you perform such a
+ lookup yourself. By calling QHostInfo::lookupHost() with a host
+ name, a QObject pointer, and a slot signature, QHostInfo will
+ perform the name lookup and invoke the given slot when the
+ results are ready. The actual lookup is done in a separate
+ thread, making use of the operating system's own methods for
+ performing name lookups.
+ QHostInfo also provides a static function called
+ QHostInfo::fromName() that takes the host name as argument and
+ returns the results. In this case, the name lookup is performed
+ in the same thread as the caller. This overload is useful for
+ non-GUI applications or for doing name lookups in a separate,
+ non-GUI thread. (Calling this function in a GUI thread may cause
+ your user interface to freeze while the function blocks as
+ it performs the lookup.)
+ \section1 Support for Network Proxies
+ Network communication with Qt can be performed through proxies,
+ which direct or filter network traffic between local and remote
+ connections.
+ Individual proxies are represented by the QNetworkProxy class,
+ which is used to describe and configure the connection to a proxy.
+ Proxy types which operate on different levels of network communication
+ are supported, with SOCKS 5 support allowing proxying of network
+ traffic at a low level, and HTTP and FTP proxying working at the
+ protocol level. See QNetworkProxy::ProxyType for more information.
+ Proxying can be enabled on a per-socket basis or for all network
+ communication in an application. A newly opened socket can be
+ made to use a proxy by calling its QAbstractSocket::setProxy()
+ function before it is connected. Application-wide proxying can
+ be enabled for all subsequent socket connections through the use
+ of the QNetworkProxy::setApplicationProxy() function.
+ Proxy factories are used to create policies for proxy use.
+ QNetworkProxyFactory supplies proxies based on queries for specific
+ proxy types. The queries themselves are encoded in QNetworkProxyQuery
+ objects which enable proxies to be selected based on key criteria,
+ such as the purpose of the proxy (TCP, UDP, TCP server, URL request),
+ local port, remote host and port, and the protocol in use (HTTP, FTP,
+ etc.).
+ QNetworkProxyFactory::proxyForQuery() is used to query the factory
+ directly. An application-wide policy for proxying can be implemented
+ by passing a factory to QNetworkProxyFactory::setApplicationProxyFactory()
+ and a custom proxying policy can be created by subclassing
+ QNetworkProxyFactory; see the class documentation for details.
+ \section1 Bearer Management Support
+ Bearer Management controls the connectivity state of the device such that
+ the application can start or stop network interfaces and roam
+ transparently between access points.
+ The QNetworkConfigurationManager class manages the list of network
+ configurations known to the device. A network configuration describes the
+ set of parameters used to start a network interface and is represented by
+ the QNetworkConfiguration class.
+ A network interface is started by openning a QNetworkSession based on a
+ given network configuration. In most situations creating a network session
+ based on the platform specified default network configuration is
+ appropriate. The default network configuration is returned by the
+ QNetworkConfigurationManager::defaultConfiguration() function.
+ On some platforms it is a platform requirement that the application open a
+ network session before any network operations can be performed. This can be
+ tested by the presents of the
+ QNetworkConfigurationManager::NetworkSessionRequired flag in the value
+ returned by the QNetworkConfigurationManager::capabilities() function.
+ \sa {Bearer Management}