connection.cpp Example File
network/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();
 }