1 /****************************************************************************
3 ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
4 ** All rights reserved.
5 ** Contact: Nokia Corporation (qt-info@nokia.com)
7 ** This file is part of the documentation of the Qt Toolkit.
9 ** $QT_BEGIN_LICENSE:FDL$
10 ** GNU Free Documentation License
11 ** Alternatively, this file may be used under the terms of the GNU Free
12 ** Documentation License version 1.3 as published by the Free Software
13 ** Foundation and appearing in the file included in the packaging of
17 ** Alternatively, this file may be used in accordance with the terms
18 ** and conditions contained in a signed written agreement between you
26 ****************************************************************************/
30 \title Network Programming API
31 \brief Classes for Network Programming
37 \page network-programming.html
38 \title Network Programming
40 \brief An Introduction to Network Programming with Qt
42 The QtNetwork module offers classes that allow you to write TCP/IP clients
43 and servers. It offers classes such as QFtp that implement specific
44 application-level protocols, lower-level classes such as QTcpSocket,
45 QTcpServer and QUdpSocket that represent low level network concepts,
46 and high level classes such as QNetworkRequest, QNetworkReply and
47 QNetworkAccessManager to perform network operations using common protocols.
48 It also offers classes such as QNetworkConfiguration,
49 QNetworkConfigurationManager and QNetworkSession that implement bearer
54 \section1 Qt's Classes for Network Programming
56 The following classes provide support for network programming in Qt.
58 \annotatedlist network
60 \section1 High Level Network Operations for HTTP and FTP
62 The Network Access API is a collection of classes for performing
63 common network operations. The API provides an abstraction layer
64 over the specific operations and protocols used (for example,
65 getting and posting data over HTTP), and only exposes classes,
66 functions, and signals for general or high level concepts.
68 Network requests are represented by the QNetworkRequest class,
69 which also acts as a general container for information associated
70 with a request, such as any header information and the encryption
71 used. The URL specified when a request object is constructed
72 determines the protocol used for a request.
73 Currently HTTP, FTP and local file URLs are supported for uploading
76 The coordination of network operations is performed by the
77 QNetworkAccessManager class. Once a request has been created,
78 this class is used to dispatch it and emit signals to report on
79 its progress. The manager also coordinates the use of
80 \l{QNetworkCookieJar}{cookies} to store data on the client,
81 authentication requests, and the use of proxies.
83 Replies to network requests are represented by the QNetworkReply
84 class; these are created by QNetworkAccessManager when a request
85 is dispatched. The signals provided by QNetworkReply can be used
86 to monitor each reply individually, or developers may choose to
87 use the manager's signals for this purpose instead and discard
88 references to replies. Since QNetworkReply is a subclass of
89 QIODevice, replies can be handled synchronously or asynchronously;
90 i.e., as blocking or non-blocking operations.
92 Each application or library can create one or more instances of
93 QNetworkAccessManager to handle network communication.
95 \section1 Writing FTP Clients with QFtp
97 FTP (File Transfer Protocol) is a protocol used almost exclusively
98 for browsing remote directories and for transferring files.
100 \image httpstack.png FTP Client and Server
102 FTP uses two network connections, one for sending
103 commands and one for transferring data. The
104 FTP protocol has a state and requires the client to send several
105 commands before a file transfer takes place.
106 FTP clients establish a connection
107 and keeps it open throughout the session. In each session, multiple
110 The QFtp class provides client-side support for FTP.
111 It has the following characteristics:
114 \o \e{Non-blocking behavior.} QFtp is asynchronous.
115 You can schedule a series of commands which are executed later,
116 when control returns to Qt's event loop.
118 \o \e{Command IDs.} Each command has a unique ID number that you
119 can use to follow the execution of the command. For example, QFtp
120 emits the \l{QFtp::commandStarted()}{commandStarted()} and
121 \l{QFtp::commandFinished()}{commandFinished()} signal with the
122 command ID for each command that is executed.
124 \o \e{Data transfer progress indicators.} QFtp emits signals
125 whenever data is transferred (QFtp::dataTransferProgress(),
126 QNetworkReply::downloadProgress(), and
127 QNetworkReply::uploadProgress()). You could connect these signals
128 to QProgressBar::setProgress() or QProgressDialog::setProgress(),
131 \o \e{QIODevice support.} The class supports convenient
132 uploading from and downloading to \l{QIODevice}s, in addition to a
133 QByteArray-based API.
137 There are two main ways of using QFtp. The most common
138 approach is to keep track of the command IDs and follow the
139 execution of every command by connecting to the appropriate
140 signals. The other approach is to schedule all commands at once
141 and only connect to the done() signal, which is emitted when all
142 scheduled commands have been executed. The first approach
143 requires more work, but it gives you more control over the
144 execution of individual commands and allows you to initiate new
145 commands based on the result of a previous command. It also
146 enables you to provide detailed feedback to the user.
148 The \l{network/qftp}{FTP} example
149 illustrates how to write an FTP client.
150 Writing your own FTP (or HTTP) server is possible using the
151 lower-level classes QTcpSocket and QTcpServer.
153 \section1 Using TCP with QTcpSocket and QTcpServer
155 TCP (Transmission Control Protocol) is a low-level network
156 protocol used by most Internet protocols, including HTTP and FTP,
157 for data transfer. It is a reliable, stream-oriented,
158 connection-oriented transport protocol. It is particularly well
159 suited to the continuous transmission of data.
161 \image tcpstream.png A TCP Stream
163 The QTcpSocket class provides an interface for TCP. You can use
164 QTcpSocket to implement standard network protocols such as POP3,
165 SMTP, and NNTP, as well as custom protocols.
167 A TCP connection must be established to a remote host and port
168 before any data transfer can begin. Once the connection has been
169 established, the IP address and port of the peer are available
170 through QTcpSocket::peerAddress() and QTcpSocket::peerPort(). At
171 any time, the peer can close the connection, and data transfer
172 will then stop immediately.
174 QTcpSocket works asynchronously and emits signals to report status
175 changes and errors, just like QNetworkAccessManager and QFtp. It
176 relies on the event loop to detect incoming data and to
177 automatically flush outgoing data. You can write data to the
178 socket using QTcpSocket::write(), and read data using
179 QTcpSocket::read(). QTcpSocket represents two independent streams
180 of data: one for reading and one for writing.
182 Since QTcpSocket inherits QIODevice, you can use it with
183 QTextStream and QDataStream. When reading from a QTcpSocket, you
184 must make sure that enough data is available by calling
185 QTcpSocket::bytesAvailable() beforehand.
187 If you need to handle incoming TCP connections (e.g., in a server
188 application), use the QTcpServer class. Call QTcpServer::listen()
189 to set up the server, and connect to the
190 QTcpServer::newConnection() signal, which is emitted once for
191 every client that connects. In your slot, call
192 QTcpServer::nextPendingConnection() to accept the connection and
193 use the returned QTcpSocket to communicate with the client.
195 Although most of its functions work asynchronously, it's possible
196 to use QTcpSocket synchronously (i.e., blocking). To get blocking
197 behavior, call QTcpSocket's waitFor...() functions; these suspend
198 the calling thread until a signal has been emitted. For example,
199 after calling the non-blocking QTcpSocket::connectToHost()
200 function, call QTcpSocket::waitForConnected() to block the thread
201 until the \l{QTcpSocket::connected()}{connected()} signal has
204 Synchronous sockets often lead to code with a simpler flow of
205 control. The main disadvantage of the waitFor...() approach is
206 that events won't be processed while a waitFor...() function is
207 blocking. If used in the GUI thread, this might freeze the
208 application's user interface. For this reason, we recommend that
209 you use synchronous sockets only in non-GUI threads. When used
210 synchronously, QTcpSocket doesn't require an event loop.
212 The \l{network/fortuneclient}{Fortune Client} and
213 \l{network/fortuneserver}{Fortune Server} examples show how to use
214 QTcpSocket and QTcpServer to write TCP client-server
215 applications. See also \l{network/blockingfortuneclient}{Blocking
216 Fortune Client} for an example on how to use a synchronous
217 QTcpSocket in a separate thread (without using an event loop),
218 and \l{network/threadedfortuneserver}{Threaded Fortune Server}
219 for an example of a multithreaded TCP server with one thread per
222 \section1 Using UDP with QUdpSocket
224 UDP (User Datagram Protocol) is a lightweight, unreliable,
225 datagram-oriented, connectionless protocol. It can be used when
226 reliability isn't important. For example, a server that reports
227 the time of day could choose UDP. If a datagram with the time of
228 day is lost, the client can simply make another request.
230 \image udppackets.png UDP Packets
232 The QUdpSocket class allows you to send and receive UDP
233 datagrams. It inherits QAbstractSocket, and it therefore shares
234 most of QTcpSocket's interface. The main difference is that
235 QUdpSocket transfers data as datagrams instead of as a continuous
236 stream of data. In short, a datagram is a data packet of limited
237 size (normally smaller than 512 bytes), containing the IP address
238 and port of the datagram's sender and receiver in addition to the
239 data being transferred.
241 QUdpSocket supports IPv4 broadcasting. Broadcasting is often used
242 to implement network discovery protocols, such as finding which
243 host on the network has the most free hard disk space. One host
244 broadcasts a datagram to the network that all other hosts
245 receive. Each host that receives a request then sends a reply
246 back to the sender with its current amount of free disk space.
247 The originator waits until it has received replies from all
248 hosts, and can then choose the server with most free space to
249 store data. To broadcast a datagram, simply send it to the
250 special address QHostAddress::Broadcast (255.255.255.255), or
251 to your local network's broadcast address.
253 QUdpSocket::bind() prepares the socket for accepting incoming
254 datagrams, much like QTcpServer::listen() for TCP servers.
255 Whenever one or more datagrams arrive, QUdpSocket emits the
256 \l{QUdpSocket::readyRead()}{readyRead()} signal. Call
257 QUdpSocket::readDatagram() to read the datagram.
259 The \l{network/broadcastsender}{Broadcast Sender} and
260 \l{network/broadcastreceiver}{Broadcast Receiver} examples show how to
261 write a UDP sender and a UDP receiver using Qt.
263 QUdpSocket also supports multicasting. The
264 \l{network/multicastsender}{Multicast Sender} and
265 \l{network/multicastreceiver}{Multicast Receiver} examples show how to use
266 write UDP multicast clients.
268 \section1 Resolving Host Names using QHostInfo
270 Before establishing a network connection, QTcpSocket and
271 QUdpSocket perform a name lookup, translating the host name
272 you're connecting to into an IP address. This operation is
273 usually performed using the DNS (Domain Name Service) protocol.
275 QHostInfo provides a static function that lets you perform such a
276 lookup yourself. By calling QHostInfo::lookupHost() with a host
277 name, a QObject pointer, and a slot signature, QHostInfo will
278 perform the name lookup and invoke the given slot when the
279 results are ready. The actual lookup is done in a separate
280 thread, making use of the operating system's own methods for
281 performing name lookups.
283 QHostInfo also provides a static function called
284 QHostInfo::fromName() that takes the host name as argument and
285 returns the results. In this case, the name lookup is performed
286 in the same thread as the caller. This overload is useful for
287 non-GUI applications or for doing name lookups in a separate,
288 non-GUI thread. (Calling this function in a GUI thread may cause
289 your user interface to freeze while the function blocks as
290 it performs the lookup.)
292 \section1 Support for Network Proxies
294 Network communication with Qt can be performed through proxies,
295 which direct or filter network traffic between local and remote
298 Individual proxies are represented by the QNetworkProxy class,
299 which is used to describe and configure the connection to a proxy.
300 Proxy types which operate on different levels of network communication
301 are supported, with SOCKS 5 support allowing proxying of network
302 traffic at a low level, and HTTP and FTP proxying working at the
303 protocol level. See QNetworkProxy::ProxyType for more information.
305 Proxying can be enabled on a per-socket basis or for all network
306 communication in an application. A newly opened socket can be
307 made to use a proxy by calling its QAbstractSocket::setProxy()
308 function before it is connected. Application-wide proxying can
309 be enabled for all subsequent socket connections through the use
310 of the QNetworkProxy::setApplicationProxy() function.
312 Proxy factories are used to create policies for proxy use.
313 QNetworkProxyFactory supplies proxies based on queries for specific
314 proxy types. The queries themselves are encoded in QNetworkProxyQuery
315 objects which enable proxies to be selected based on key criteria,
316 such as the purpose of the proxy (TCP, UDP, TCP server, URL request),
317 local port, remote host and port, and the protocol in use (HTTP, FTP,
320 QNetworkProxyFactory::proxyForQuery() is used to query the factory
321 directly. An application-wide policy for proxying can be implemented
322 by passing a factory to QNetworkProxyFactory::setApplicationProxyFactory()
323 and a custom proxying policy can be created by subclassing
324 QNetworkProxyFactory; see the class documentation for details.
326 \section1 Bearer Management Support
328 Bearer Management controls the connectivity state of the device such that
329 the application can start or stop network interfaces and roam
330 transparently between access points.
332 The QNetworkConfigurationManager class manages the list of network
333 configurations known to the device. A network configuration describes the
334 set of parameters used to start a network interface and is represented by
335 the QNetworkConfiguration class.
337 A network interface is started by openning a QNetworkSession based on a
338 given network configuration. In most situations creating a network session
339 based on the platform specified default network configuration is
340 appropriate. The default network configuration is returned by the
341 QNetworkConfigurationManager::defaultConfiguration() function.
343 On some platforms it is a platform requirement that the application open a
344 network session before any network operations can be performed. This can be
345 tested by the presents of the
346 QNetworkConfigurationManager::NetworkSessionRequired flag in the value
347 returned by the QNetworkConfigurationManager::capabilities() function.
349 \sa {Bearer Management}