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# connection.cpp Example File
network/chat/connection.cpp

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     #include "connection.h"

     #include <QtNetwork>

     static const int TransferTimeout = 30 * 1000;
     static const int PongTimeout = 60 * 1000;
     static const int PingInterval = 5 * 1000;
     static const char SeparatorToken = ' ';

     Connection::Connection(QObject *parent)
         : QTcpSocket(parent)
     {
         greetingMessage = tr("undefined");
         username = tr("unknown");
         state = WaitingForGreeting;
         currentDataType = Undefined;
         numBytesForCurrentDataType = -1;
         transferTimerId = 0;
         isGreetingMessageSent = false;
         pingTimer.setInterval(PingInterval);

         QObject::connect(this, SIGNAL(readyRead()), this, SLOT(processReadyRead()));
         QObject::connect(this, SIGNAL(disconnected()), &pingTimer, SLOT(stop()));
         QObject::connect(&pingTimer, SIGNAL(timeout()), this, SLOT(sendPing()));
         QObject::connect(this, SIGNAL(connected()),
                          this, SLOT(sendGreetingMessage()));
     }

     QString Connection::name() const
     {
         return username;
     }

     void Connection::setGreetingMessage(const QString &message)
     {
         greetingMessage = message;
     }

     bool Connection::sendMessage(const QString &message)
     {
         if (message.isEmpty())
             return false;

         QByteArray msg = message.toUtf8();
         QByteArray data = "MESSAGE " + QByteArray::number(msg.size()) + " " + msg;
         return write(data) == data.size();
     }

     void Connection::timerEvent(QTimerEvent *timerEvent)
     {
         if (timerEvent->timerId() == transferTimerId) {
             abort();
             killTimer(transferTimerId);
             transferTimerId = 0;
         }
     }

     void Connection::processReadyRead()
     {
         if (state == WaitingForGreeting) {
             if (!readProtocolHeader())
                 return;
             if (currentDataType != Greeting) {
                 abort();
                 return;
             }
             state = ReadingGreeting;
         }

         if (state == ReadingGreeting) {
             if (!hasEnoughData())
                 return;

             buffer = read(numBytesForCurrentDataType);
             if (buffer.size() != numBytesForCurrentDataType) {
                 abort();
                 return;
             }

             username = QString(buffer) + "@" + peerAddress().toString() + ":"
                        + QString::number(peerPort());
             currentDataType = Undefined;
             numBytesForCurrentDataType = 0;
             buffer.clear();

             if (!isValid()) {
                 abort();
                 return;
             }

             if (!isGreetingMessageSent)
                 sendGreetingMessage();

             pingTimer.start();
             pongTime.start();
             state = ReadyForUse;
             emit readyForUse();
         }

         do {
             if (currentDataType == Undefined) {
                 if (!readProtocolHeader())
                     return;
             }
             if (!hasEnoughData())
                 return;
             processData();
         } while (bytesAvailable() > 0);
     }

     void Connection::sendPing()
     {
         if (pongTime.elapsed() > PongTimeout) {
             abort();
             return;
         }

         write("PING 1 p");
     }

     void Connection::sendGreetingMessage()
     {
         QByteArray greeting = greetingMessage.toUtf8();
         QByteArray data = "GREETING " + QByteArray::number(greeting.size()) + " " + greeting;
         if (write(data) == data.size())
             isGreetingMessageSent = true;
     }

     int Connection::readDataIntoBuffer(int maxSize)
     {
         if (maxSize > MaxBufferSize)
             return 0;

         int numBytesBeforeRead = buffer.size();
         if (numBytesBeforeRead == MaxBufferSize) {
             abort();
             return 0;
         }

         while (bytesAvailable() > 0 && buffer.size() < maxSize) {
             buffer.append(read(1));
             if (buffer.endsWith(SeparatorToken))
                 break;
         }
         return buffer.size() - numBytesBeforeRead;
     }

     int Connection::dataLengthForCurrentDataType()
     {
         if (bytesAvailable() <= 0 || readDataIntoBuffer() <= 0
                 || !buffer.endsWith(SeparatorToken))
             return 0;

         buffer.chop(1);
         int number = buffer.toInt();
         buffer.clear();
         return number;
     }

     bool Connection::readProtocolHeader()
     {
         if (transferTimerId) {
             killTimer(transferTimerId);
             transferTimerId = 0;
         }

         if (readDataIntoBuffer() <= 0) {
             transferTimerId = startTimer(TransferTimeout);
             return false;
         }

         if (buffer == "PING ") {
             currentDataType = Ping;
         } else if (buffer == "PONG ") {
             currentDataType = Pong;
         } else if (buffer == "MESSAGE ") {
             currentDataType = PlainText;
         } else if (buffer == "GREETING ") {
             currentDataType = Greeting;
         } else {
             currentDataType = Undefined;
             abort();
             return false;
         }

         buffer.clear();
         numBytesForCurrentDataType = dataLengthForCurrentDataType();
         return true;
     }

     bool Connection::hasEnoughData()
     {
         if (transferTimerId) {
             QObject::killTimer(transferTimerId);
             transferTimerId = 0;
         }

         if (numBytesForCurrentDataType <= 0)
             numBytesForCurrentDataType = dataLengthForCurrentDataType();

         if (bytesAvailable() < numBytesForCurrentDataType
                 || numBytesForCurrentDataType <= 0) {
             transferTimerId = startTimer(TransferTimeout);
             return false;
         }

         return true;
     }

     void Connection::processData()
     {
         buffer = read(numBytesForCurrentDataType);
         if (buffer.size() != numBytesForCurrentDataType) {
             abort();
             return;
         }

         switch (currentDataType) {
         case PlainText:
             emit newMessage(username, QString::fromUtf8(buffer));
             break;
         case Ping:
             write("PONG 1 p");
             break;
         case Pong:
             pongTime.restart();
             break;
         default:
             break;
         }

         currentDataType = Undefined;
         numBytesForCurrentDataType = 0;
         buffer.clear();
     }