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+****************************************************************************/
+
+/*!
+ \page qt4-network.html
+ \title The Network Module in Qt 4
+
+ \contentspage {What's New in Qt 4}{Home}
+ \previouspage The Qt 4 Database GUI Layer
+ \nextpage The Qt 4 Style API
+
+ The network module in Qt 4 provides some new features, such as
+ support for internationalized domain names, better IPv6 support,
+ and better performance. And since Qt 4 allows us to break binary
+ compatibility with previous releases, we took this opportunity to
+ improve the class names and API to make them more intuitive to
+ use.
+
+ \tableofcontents
+
+ \section1 General Overview
+
+ Compared to Qt 3, the network module in Qt 4 brings the following
+ benefits:
+
+ \list
+ \o The Qt 4 network classes have more intuitive names and APIs.
+ For example, QServerSocket has been renamed QTcpServer.
+ \o The entire network module is \l{reentrant}, making it
+ possible to use them simultaneously from multiple threads.
+ \o It is now possible to send and receive UDP datagrams and to
+ use synchronous (i.e., blocking) sockets without having to
+ use a low-level API (QSocketDevice in Qt 3).
+ \o QHostAddress and QHostInfo support internationalized domain names
+ (RFC 3492).
+ \o QUrl is more lightweight and fully supports the latest URI
+ specification draft.
+ \o UDP broadcasting is now supported.
+ \endlist
+
+ The Qt 4 network module provides fundamental classes for writing
+ TCP and UDP applications, as well as higher-level classes that
+ implement the client side of the HTTP and FTP protocols.
+
+ Here's an overview of the TCP and UDP classes:
+
+ \list
+ \o QTcpSocket encapsulates a TCP socket. It inherits from
+ QIODevice, so you can use QTextStream and QDataStream to read
+ or write data. It is useful for writing both clients and
+ servers.
+ \o QTcpServer allows you to listen on a certain port on a
+ server. It emits a
+ \l{QTcpServer::newConnection()}{newConnection()} signal every
+ time a client tries to connect to the server. Once the
+ connection is established, you can talk to the client using
+ QTcpSocket.
+ \o QUdpSocket is an API for sending and receiving UDP datagrams.
+ \endlist
+
+ QTcpSocket and QUdpSocket inherit most of their functionality
+ from QAbstractSocket. You can also use QAbstractSocket directly
+ as a wrapper around a native socket descriptor.
+
+ By default, the socket classes work asynchronously (i.e., they
+ are non-blocking), emitting signals to notify when data has
+ arrived or when the peer has closed the connection. In
+ multithreaded applications and in non-GUI applications, you also
+ have the opportunity of using blocking (synchronous) functions on
+ the socket, which often results in a more straightforward style
+ of programming, with the networking logic concentrated in one or
+ two functions instead of spread across multiple slots.
+
+ QFtp and QNetworkAccessManager and its associated classes use
+ QTcpSocket internally to implement the FTP and HTTP protocols. The
+ classes work asynchronously and can schedule (i.e., queue)
+ requests.
+
+ The network module contains four helper classes: QHostAddress,
+ QHostInfo, QUrl, and QUrlInfo. QHostAddress stores an IPv4 or IPv6
+ address, QHostInfo resolves host names into addresses, QUrl stores a
+ URL, and QUrlInfo stores information about a resource pointed to
+ by a URL, such as the file size and modification date. (Because
+ QUrl is used by QTextBrowser, it is part of the QtCore library and
+ not of QtNetwork.)
+
+ See the \l QtNetwork module overview for more information.
+
+ \section1 Example Code
+
+ All the code snippets presented here are quoted from
+ self-contained, compilable examples located in Qt's \c
+ examples/network directory.
+
+ \section2 TCP Client
+
+ The first example illustrates how to write a TCP client using
+ QTcpSocket. The client talks to a fortune server that provides
+ fortune to the user. Here's how to set up the socket:
+
+ \snippet examples/network/fortuneclient/client.cpp 1
+ \codeline
+ \snippet examples/network/fortuneclient/client.cpp 2
+ \snippet examples/network/fortuneclient/client.cpp 4
+
+ When the user requests a new fortune, the client establishes a
+ connection to the server:
+
+ \snippet examples/network/fortuneclient/client.cpp 7
+
+ When the server answers, the following code is executed to read
+ the data from the socket:
+
+ \snippet examples/network/fortuneclient/client.cpp 9
+
+ The server's answer starts with a \e size field (which we store
+ in \c blockSize), followed by \e size bytes of data. If the
+ client hasn't received all the data yet, it waits for the server
+ to send more.
+
+ An alternative approach is to use a blocking socket. The code can
+ then be concentrated in one function:
+
+ \snippet examples/network/blockingfortuneclient/fortunethread.cpp 7
+
+ \section2 TCP Server
+
+ The following code snippets illustrate how to write a TCP server
+ using QTcpServer and QTcpSocket. Here's how to set up a TCP
+ server:
+
+ \snippet examples/network/fortuneserver/server.cpp 0
+ \codeline
+ \snippet examples/network/fortuneserver/server.cpp 3
+
+ When a client tries to connect to the server, the following code
+ in the sendFortune() slot is executed:
+
+ \snippet examples/network/fortuneserver/server.cpp 5
+
+ \section2 UDP Senders and Receivers
+
+ Here's how to broadcast a UDP datagram:
+
+ \snippet examples/network/broadcastsender/sender.cpp 0
+ \snippet examples/network/broadcastsender/sender.cpp 1
+
+ Here's how to receive a UDP datagram:
+
+ \snippet examples/network/broadcastreceiver/receiver.cpp 0
+ \codeline
+ \snippet examples/network/broadcastreceiver/receiver.cpp 1
+
+ Then in the processPendingDatagrams() slot:
+
+ \snippet examples/network/broadcastreceiver/receiver.cpp 2
+
+ \section1 Comparison with Qt 3
+
+ The main difference between Qt 3 and Qt 4 is that the very high
+ level QNetworkProtocol and QUrlOperator abstraction has been
+ eliminated. These classes attempted the impossible (unify FTP and
+ HTTP under one roof), and unsurprisingly failed at that. Qt 4
+ still provides QFtp, and it also provides the QNetworkAccessManager.
+
+ The QSocket class in Qt 3 has been renamed QTcpSocket. The new
+ class is reentrant and supports blocking. It's also easier to
+ handle closing than with Qt 3, where you had to connect to both
+ the QSocket::connectionClosed() and the
+ QSocket::delayedCloseFinished() signals.
+
+ The QServerSocket class in Qt 3 has been renamed QTcpServer. The
+ API has changed quite a bit. While in Qt 3 it was necessary to
+ subclass QServerSocket and reimplement the newConnection() pure
+ virtual function, QTcpServer now emits a
+ \l{QTcpServer::newConnection()}{newConnection()} signal that you
+ can connect to a slot.
+
+ The QHostInfo class has been redesigned to use the operating system's
+ getaddrinfo() function instead of implementing the DNS protocol.
+ Internally, QHostInfo simply starts a thread and calls getaddrinfo()
+ in that thread. This wasn't possible in Qt 3 because
+ getaddrinfo() is a blocking call and Qt 3 could be configured
+ without multithreading support.
+
+ The QSocketDevice class in Qt 3 is no longer part of the public
+ Qt API. If you used QSocketDevice to send or receive UDP
+ datagrams, use QUdpSocket instead. If you used QSocketDevice
+ because it supported blocking sockets, use QTcpSocket or
+ QUdpSocket instead and use the blocking functions
+ (\l{QAbstractSocket::waitForConnected()}{waitForConnected()},
+ \l{QAbstractSocket::waitForConnected()}{waitForReadyRead()},
+ etc.). If you used QSocketDevice from a non-GUI thread because it
+ was the only reentrant networking class in Qt 3, use QTcpSocket,
+ QTcpServer, or QUdpSocket instead.
+
+ Internally, Qt 4 has a class called QSocketLayer that provides a
+ cross-platform low-level socket API. It resembles the old
+ QSocketDevice class. We might make it public in a later release
+ if users ask for it.
+
+ As an aid to porting to Qt 4, the \l{Qt3Support}
+ library includes Q3Dns, Q3ServerSocket, Q3Socket, and Q3SocketDevice
+ classes.
+*/