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<title>Qt 4.8: Fortune Server Example</title>
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<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
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<h1 class="title">Fortune Server Example</h1>
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<p>Files:</p>
<ul>
<li><a href="network-fortuneserver-server-cpp.html">network/fortuneserver/server.cpp</a></li>
<li><a href="network-fortuneserver-server-h.html">network/fortuneserver/server.h</a></li>
<li><a href="network-fortuneserver-main-cpp.html">network/fortuneserver/main.cpp</a></li>
<li><a href="network-fortuneserver-fortuneserver-pro.html">network/fortuneserver/fortuneserver.pro</a></li>
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<p>The Fortune Server example shows how to create a server for a simple network service.<p>The example is intended to be run alongside the <a href="network-fortuneclient.html">Fortune Client</a> example or the <a href="network-blockingfortuneclient.html">Blocking Fortune Client</a> example.</p>
<p class="centerAlign"><img src="images/fortuneserver-example.png" alt="Screenshot of the Fortune Server example" /></p><p>This example uses <a href="qtcpserver.html">QTcpServer</a> to accept incoming TCP connections, and a simple <a href="qdatastream.html">QDataStream</a> based data transfer protocol to write a fortune to the connecting client (from the <a href="network-fortuneclient.html">Fortune Client</a> example), before closing the connection.</p>
<pre class="cpp"> <span class="keyword">class</span> Server : <span class="keyword">public</span> <span class="type"><a href="qdialog.html">QDialog</a></span>
{
Q_OBJECT
<span class="keyword">public</span>:
Server(<span class="type"><a href="qwidget.html">QWidget</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>);
<span class="keyword">private</span> <span class="keyword">slots</span>:
<span class="type">void</span> sessionOpened();
<span class="type">void</span> sendFortune();
<span class="keyword">private</span>:
<span class="type"><a href="qlabel.html">QLabel</a></span> <span class="operator">*</span>statusLabel;
<span class="type"><a href="qpushbutton.html">QPushButton</a></span> <span class="operator">*</span>quitButton;
<span class="type"><a href="qtcpserver.html">QTcpServer</a></span> <span class="operator">*</span>tcpServer;
<span class="type"><a href="qstringlist.html">QStringList</a></span> fortunes;
<span class="type"><a href="qnetworksession.html">QNetworkSession</a></span> <span class="operator">*</span>networkSession;
};</pre>
<p>The server is implemented using a simple class with only one slot, for handling incoming connections.</p>
<pre class="cpp"> tcpServer <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qtcpserver.html">QTcpServer</a></span>(<span class="keyword">this</span>);
<span class="keyword">if</span> (<span class="operator">!</span>tcpServer<span class="operator">-</span><span class="operator">></span>listen()) {
<span class="type"><a href="qmessagebox.html">QMessageBox</a></span><span class="operator">::</span>critical(<span class="keyword">this</span><span class="operator">,</span> tr(<span class="string">"Fortune Server"</span>)<span class="operator">,</span>
tr(<span class="string">"Unable to start the server: %1."</span>)
<span class="operator">.</span>arg(tcpServer<span class="operator">-</span><span class="operator">></span>errorString()));
close();
<span class="keyword">return</span>;
}
<span class="type"><a href="qstring.html">QString</a></span> ipAddress;
<span class="type"><a href="qlist.html">QList</a></span><span class="operator"><</span><span class="type"><a href="qhostaddress.html">QHostAddress</a></span><span class="operator">></span> ipAddressesList <span class="operator">=</span> <span class="type"><a href="qnetworkinterface.html">QNetworkInterface</a></span><span class="operator">::</span>allAddresses();
<span class="comment">// use the first non-localhost IPv4 address</span>
<span class="keyword">for</span> (<span class="type">int</span> i <span class="operator">=</span> <span class="number">0</span>; i <span class="operator"><</span> ipAddressesList<span class="operator">.</span>size(); <span class="operator">+</span><span class="operator">+</span>i) {
<span class="keyword">if</span> (ipAddressesList<span class="operator">.</span>at(i) <span class="operator">!</span><span class="operator">=</span> <span class="type"><a href="qhostaddress.html">QHostAddress</a></span><span class="operator">::</span>LocalHost <span class="operator">&</span><span class="operator">&</span>
ipAddressesList<span class="operator">.</span>at(i)<span class="operator">.</span>toIPv4Address()) {
ipAddress <span class="operator">=</span> ipAddressesList<span class="operator">.</span>at(i)<span class="operator">.</span>toString();
<span class="keyword">break</span>;
}
}
<span class="comment">// if we did not find one, use IPv4 localhost</span>
<span class="keyword">if</span> (ipAddress<span class="operator">.</span>isEmpty())
ipAddress <span class="operator">=</span> <span class="type"><a href="qhostaddress.html">QHostAddress</a></span>(<span class="type"><a href="qhostaddress.html">QHostAddress</a></span><span class="operator">::</span>LocalHost)<span class="operator">.</span>toString();
statusLabel<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"The server is running on\n\nIP: %1\nport: %2\n\n"</span>
<span class="string">"Run the Fortune Client example now."</span>)
<span class="operator">.</span>arg(ipAddress)<span class="operator">.</span>arg(tcpServer<span class="operator">-</span><span class="operator">></span>serverPort()));</pre>
<p>In its constructor, our Server object calls <a href="qtcpserver.html#listen">QTcpServer::listen</a>() to set up a <a href="qtcpserver.html">QTcpServer</a> to listen on all addresses, on an arbitrary port. In then displays the port <a href="qtcpserver.html">QTcpServer</a> picked in a label, so that user knows which port the fortune client should connect to.</p>
<pre class="cpp"> fortunes <span class="operator"><</span><span class="operator"><</span> tr(<span class="string">"You've been leading a dog's life. Stay off the furniture."</span>)
<span class="operator"><</span><span class="operator"><</span> tr(<span class="string">"You've got to think about tomorrow."</span>)
<span class="operator"><</span><span class="operator"><</span> tr(<span class="string">"You will be surprised by a loud noise."</span>)
<span class="operator"><</span><span class="operator"><</span> tr(<span class="string">"You will feel hungry again in another hour."</span>)
<span class="operator"><</span><span class="operator"><</span> tr(<span class="string">"You might have mail."</span>)
<span class="operator"><</span><span class="operator"><</span> tr(<span class="string">"You cannot kill time without injuring eternity."</span>)
<span class="operator"><</span><span class="operator"><</span> tr(<span class="string">"Computers are not intelligent. They only think they are."</span>);</pre>
<p>Our server generates a list of random fortunes that is can send to connecting clients.</p>
<pre class="cpp"> connect(tcpServer<span class="operator">,</span> SIGNAL(newConnection())<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(sendFortune()));</pre>
<p>When a client connects to our server, <a href="qtcpserver.html">QTcpServer</a> will emit <a href="qtcpserver.html#newConnection">QTcpServer::newConnection</a>(). In turn, this will invoke our sendFortune() slot:</p>
<pre class="cpp"> <span class="type">void</span> Server<span class="operator">::</span>sendFortune()
{
<span class="type"><a href="qbytearray.html">QByteArray</a></span> block;
<span class="type"><a href="qdatastream.html">QDataStream</a></span> out(<span class="operator">&</span>block<span class="operator">,</span> <span class="type"><a href="qiodevice.html">QIODevice</a></span><span class="operator">::</span>WriteOnly);
out<span class="operator">.</span>setVersion(<span class="type"><a href="qdatastream.html">QDataStream</a></span><span class="operator">::</span>Qt_4_0);</pre>
<p>The purpose of this slot is to select a random line from our list of fortunes, encode it into a <a href="qbytearray.html">QByteArray</a> using <a href="qdatastream.html">QDataStream</a>, and then write it to the connecting socket. This is a common way to transfer binary data using <a href="qtcpsocket.html">QTcpSocket</a>. First we create a <a href="qbytearray.html">QByteArray</a> and a <a href="qdatastream.html">QDataStream</a> object, passing the bytearray to <a href="qdatastream.html">QDataStream</a>'s constructor. We then explicitly set the protocol version of <a href="qdatastream.html">QDataStream</a> to <a href="qdatastream.html#Version-enum">QDataStream::Qt_4_0</a> to ensure that we can communicate with clients from future versions of Qt. (See <a href="qdatastream.html#setVersion">QDataStream::setVersion</a>().)</p>
<pre class="cpp"> out <span class="operator"><</span><span class="operator"><</span> (<span class="type"><a href="qtglobal.html#quint16-typedef">quint16</a></span>)<span class="number">0</span>;
out <span class="operator"><</span><span class="operator"><</span> fortunes<span class="operator">.</span>at(qrand() <span class="operator">%</span> fortunes<span class="operator">.</span>size());
out<span class="operator">.</span>device()<span class="operator">-</span><span class="operator">></span>seek(<span class="number">0</span>);
out <span class="operator"><</span><span class="operator"><</span> (<span class="type"><a href="qtglobal.html#quint16-typedef">quint16</a></span>)(block<span class="operator">.</span>size() <span class="operator">-</span> <span class="keyword">sizeof</span>(<span class="type"><a href="qtglobal.html#quint16-typedef">quint16</a></span>));</pre>
<p>At the start of our <a href="qbytearray.html">QByteArray</a>, we reserve space for a 16 bit integer that will contain the total size of the data block we are sending. We continue by streaming in a random fortune. Then we seek back to the beginning of the <a href="qbytearray.html">QByteArray</a>, and overwrite the reserved 16 bit integer value with the total size of the array. By doing this, we provide a way for clients to verify how much data they can expect before reading the whole packet.</p>
<pre class="cpp"> <span class="type"><a href="qtcpsocket.html">QTcpSocket</a></span> <span class="operator">*</span>clientConnection <span class="operator">=</span> tcpServer<span class="operator">-</span><span class="operator">></span>nextPendingConnection();
connect(clientConnection<span class="operator">,</span> SIGNAL(disconnected())<span class="operator">,</span>
clientConnection<span class="operator">,</span> SLOT(deleteLater()));</pre>
<p>We then call QTcpServer::newPendingConnection(), which returns the <a href="qtcpsocket.html">QTcpSocket</a> representing the server side of the connection. By connecting <a href="qabstractsocket.html#disconnected">QTcpSocket::disconnected</a>() to <a href="qobject.html#deleteLater">QObject::deleteLater</a>(), we ensure that the socket will be deleted after disconnecting.</p>
<pre class="cpp"> clientConnection<span class="operator">-</span><span class="operator">></span>write(block);
clientConnection<span class="operator">-</span><span class="operator">></span>disconnectFromHost();
}</pre>
<p>The encoded fortune is written using <a href="qiodevice.html#write">QTcpSocket::write</a>(), and we finally call <a href="qabstractsocket.html#disconnectFromHost">QTcpSocket::disconnectFromHost</a>(), which will close the connection after <a href="qtcpsocket.html">QTcpSocket</a> has finished writing the fortune to the network. Because <a href="qtcpsocket.html">QTcpSocket</a> works asynchronously, the data will be written after this function returns, and control goes back to Qt's event loop. The socket will then close, which in turn will cause <a href="qobject.html#deleteLater">QObject::deleteLater</a>() to delete it.</p>
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<p><b>See also </b><a href="network-fortuneclient.html">Fortune Client Example</a> and <a href="network-threadedfortuneserver.html">Threaded Fortune Server Example</a>.</p>
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