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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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4 ** All rights reserved. |
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5 ** Contact: Nokia Corporation (qt-info@nokia.com) |
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6 ** |
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7 ** This file is part of the documentation of the Qt Toolkit. |
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8 ** |
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9 ** $QT_BEGIN_LICENSE:LGPL$ |
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10 ** No Commercial Usage |
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11 ** This file contains pre-release code and may not be distributed. |
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12 ** You may use this file in accordance with the terms and conditions |
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13 ** contained in the Technology Preview License Agreement accompanying |
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14 ** this package. |
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15 ** |
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16 ** GNU Lesser General Public License Usage |
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17 ** Alternatively, this file may be used under the terms of the GNU Lesser |
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18 ** General Public License version 2.1 as published by the Free Software |
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19 ** Foundation and appearing in the file LICENSE.LGPL included in the |
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20 ** packaging of this file. Please review the following information to |
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21 ** ensure the GNU Lesser General Public License version 2.1 requirements |
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22 ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. |
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23 ** |
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24 ** In addition, as a special exception, Nokia gives you certain additional |
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25 ** rights. These rights are described in the Nokia Qt LGPL Exception |
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29 ** Nokia at qt-info@nokia.com. |
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31 ** |
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32 ** |
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33 ** |
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34 ** |
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35 ** |
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36 ** |
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37 ** |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \example network/fortuneclient |
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44 \title Fortune Client Example |
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45 |
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46 The Fortune Client example shows how to create a client for a simple |
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47 network service using QTcpSocket. It is intended to be run alongside the |
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48 \l{network/fortuneserver}{Fortune Server} example or |
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49 the \l{network/threadedfortuneserver}{Threaded Fortune Server} example. |
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50 |
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51 \image fortuneclient-example.png Screenshot of the Fortune Client example |
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52 |
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53 This example uses a simple QDataStream-based data transfer protocol to |
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54 request a line of text from a fortune server (from the |
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55 \l{network/fortuneserver}{Fortune Server} example). The client requests a |
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56 fortune by simply connecting to the server. The server then responds with |
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57 a 16-bit (quint16) integer containing the length of the fortune text, |
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58 followed by a QString. |
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59 |
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60 QTcpSocket supports two general approaches to network programming: |
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61 |
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62 \list |
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63 |
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64 \o \e{The asynchronous (non-blocking) approach.} Operations are scheduled |
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65 and performed when control returns to Qt's event loop. When the operation |
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66 is finished, QTcpSocket emits a signal. For example, |
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67 QTcpSocket::connectToHost() returns immediately, and when the connection |
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68 has been established, QTcpSocket emits |
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69 \l{QTcpSocket::connected()}{connected()}. |
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70 |
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71 \o \e{The synchronous (blocking) approach.} In non-GUI and multithreaded |
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72 applications, you can call the \c waitFor...() functions (e.g., |
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73 QTcpSocket::waitForConnected()) to suspend the calling thread until the |
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74 operation has completed, instead of connecting to signals. |
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75 |
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76 \endlist |
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77 |
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78 In this example, we will demonstrate the asynchronous approach. The |
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79 \l{network/blockingfortuneclient}{Blocking Fortune Client} example |
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80 illustrates the synchronous approach. |
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81 |
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82 Our class contains some data and a few private slots: |
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83 |
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84 \snippet examples/network/fortuneclient/client.h 0 |
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85 |
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86 Other than the widgets that make up the GUI, the data members include a |
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87 QTcpSocket pointer, a copy of the fortune text currently displayed, and |
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88 the size of the packet we are currently reading (more on this later). |
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89 |
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90 The socket is initialized in the Client constructor. We'll pass the main |
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91 widget as parent, so that we won't have to worry about deleting the |
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92 socket: |
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93 |
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94 \snippet examples/network/fortuneclient/client.cpp 0 |
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95 \dots |
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96 \snippet examples/network/fortuneclient/client.cpp 1 |
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97 |
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98 The only QTcpSocket signals we need in this example are |
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99 QTcpSocket::readyRead(), signifying that data has been received, and |
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100 QTcpSocket::error(), which we will use to catch any connection errors: |
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101 |
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102 \dots |
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103 \snippet examples/network/fortuneclient/client.cpp 3 |
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104 \dots |
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105 \snippet examples/network/fortuneclient/client.cpp 5 |
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106 |
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107 Clicking the \gui{Get Fortune} button will invoke the \c |
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108 requestNewFortune() slot: |
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109 |
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110 \snippet examples/network/fortuneclient/client.cpp 6 |
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111 |
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112 In this slot, we initialize \c blockSize to 0, preparing to read a new block |
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113 of data. Because we allow the user to click \gui{Get Fortune} before the |
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114 previous connection finished closing, we start off by aborting the |
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115 previous connection by calling QTcpSocket::abort(). (On an unconnected |
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116 socket, this function does nothing.) We then proceed to connecting to the |
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117 fortune server by calling QTcpSocket::connectToHost(), passing the |
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118 hostname and port from the user interface as arguments. |
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119 |
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120 As a result of calling \l{QTcpSocket::connectToHost()}{connectToHost()}, |
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121 one of two things can happen: |
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122 |
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123 \list |
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124 \o \e{The connection is established.} In this case, the server will send us a |
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125 fortune. QTcpSocket will emit \l{QTcpSocket::readyRead()}{readyRead()} |
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126 every time it receives a block of data. |
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127 |
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128 \o \e{An error occurs.} We need to inform the user if the connection |
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129 failed or was broken. In this case, QTcpSocket will emit |
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130 \l{QTcpSocket::error()}{error()}, and \c Client::displayError() will be |
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131 called. |
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132 \endlist |
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133 |
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134 Let's go through the \l{QTcpSocket::error()}{error()} case first: |
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135 |
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136 \snippet examples/network/fortuneclient/client.cpp 13 |
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137 |
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138 We pop up all errors in a dialog using |
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139 QMessageBox::information(). QTcpSocket::RemoteHostClosedError is silently |
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140 ignored, because the fortune server protocol ends with the server closing |
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141 the connection. |
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142 |
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143 Now for the \l{QTcpSocket::readyRead()}{readyRead()} alternative. This |
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144 signal is connected to \c Client::readFortune(): |
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145 |
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146 \snippet examples/network/fortuneclient/client.cpp 8 |
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147 \codeline |
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148 \snippet examples/network/fortuneclient/client.cpp 10 |
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149 |
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150 The protocol is based on QDataStream, so we start by creating a stream |
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151 object, passing the socket to QDataStream's constructor. We then |
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152 explicitly set the protocol version of the stream to QDataStream::Qt_4_0 |
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153 to ensure that we're using the same version as the fortune server, no |
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154 matter which version of Qt the client and server use. |
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155 |
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156 Now, TCP is based on sending a stream of data, so we cannot expect to get |
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157 the entire fortune in one go. Especially on a slow network, the data can |
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158 be received in several small fragments. QTcpSocket buffers up all incoming |
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159 data and emits \l{QTcpSocket::readyRead()}{readyRead()} for every new |
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160 block that arrives, and it is our job to ensure that we have received all |
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161 the data we need before we start parsing. The server's response starts |
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162 with the size of the packet, so first we need to ensure that we can read |
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163 the size, then we will wait until QTcpSocket has received the full packet. |
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164 |
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165 \snippet examples/network/fortuneclient/client.cpp 11 |
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166 \codeline |
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167 \snippet examples/network/fortuneclient/client.cpp 12 |
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168 |
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169 We proceed by using QDataStream's streaming operator to read the fortune |
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170 from the socket into a QString. Once read, we can call QLabel::setText() |
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171 to display the fortune. |
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172 |
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173 \sa {Fortune Server Example}, {Blocking Fortune Client Example} |
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174 */ |