connection.cpp Example File

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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;

 /*
  * Protocol is defined as follows, using the CBOR Data Definition Language:
  *
  *  protocol    = [
  *     greeting,        ; must start with a greeting command
  *     * command        ; zero or more regular commands after
  *  ]
  *  command     = plaintext / ping / pong / greeting
  *  plaintext   = { 0 => text }
  *  ping        = { 1 => null }
  *  pong        = { 2 => null }
  *  greeting    = { 3 => text }
  */

 Connection::Connection(QObject *parent)
     : QTcpSocket(parent), writer(this)
 {
     greetingMessage = tr("undefined");
     username = tr("unknown");
     state = WaitingForGreeting;
     currentDataType = Undefined;
     transferTimerId = -1;
     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()));
 }

 Connection::Connection(qintptr socketDescriptor, QObject *parent)
     : Connection(parent)
 {
     setSocketDescriptor(socketDescriptor);
     reader.setDevice(this);
 }

 Connection::~Connection()
 {
     if (isGreetingMessageSent) {
         // Indicate clean shutdown.
         writer.endArray();
         waitForBytesWritten(2000);
     }
 }

 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;

     writer.startMap(1);
     writer.append(PlainText);
     writer.append(message);
     writer.endMap();
     return true;
 }

 void Connection::timerEvent(QTimerEvent *timerEvent)
 {
     if (timerEvent->timerId() == transferTimerId) {
         abort();
         killTimer(transferTimerId);
         transferTimerId = -1;
     }
 }

 void Connection::processReadyRead()
 {
     // we've got more data, let's parse
     reader.reparse();
     while (reader.lastError() == QCborError::NoError) {
         if (state == WaitingForGreeting) {
             if (!reader.isArray())
                 break;                  // protocol error

             reader.enterContainer();    // we'll be in this array forever
             state = ReadingGreeting;
         } else if (reader.containerDepth() == 1) {
             // Current state: no command read
             // Next state: read command ID
             if (!reader.hasNext()) {
                 reader.leaveContainer();
                 disconnectFromHost();
                 return;
             }

             if (!reader.isMap() || !reader.isLengthKnown() || reader.length() != 1)
                 break;                  // protocol error
             reader.enterContainer();
         } else if (currentDataType == Undefined) {
             // Current state: read command ID
             // Next state: read command payload
             if (!reader.isInteger())
                 break;                  // protocol error
             currentDataType = DataType(reader.toInteger());
             reader.next();
         } else {
             // Current state: read command payload
             if (reader.isString()) {
                 auto r = reader.readString();
                 buffer += r.data;
                 if (r.status != QCborStreamReader::EndOfString)
                     continue;
             } else if (reader.isNull()) {
                 reader.next();
             } else {
                 break;                   // protocol error
             }

             // Next state: no command read
             reader.leaveContainer();
             if (transferTimerId != -1) {
                 killTimer(transferTimerId);
                 transferTimerId = -1;
             }

             if (state == ReadingGreeting) {
                 if (currentDataType != Greeting)
                     break;              // protocol error
                 processGreeting();
             } else {
                 processData();
             }
         }
     }

     if (reader.lastError() != QCborError::EndOfFile)
         abort();       // parse error

     if (transferTimerId != -1 && reader.containerDepth() > 1)
         transferTimerId = startTimer(TransferTimeout);
 }

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

     writer.startMap(1);
     writer.append(Ping);
     writer.append(nullptr);     // no payload
     writer.endMap();
 }

 void Connection::sendGreetingMessage()
 {
     writer.startArray();        // this array never ends

     writer.startMap(1);
     writer.append(Greeting);
     writer.append(greetingMessage);
     writer.endMap();
     isGreetingMessageSent = true;

     if (!reader.device())
         reader.setDevice(this);
 }

 void Connection::processGreeting()
 {
     username = buffer + '@' + peerAddress().toString() + ':'
             + QString::number(peerPort());
     currentDataType = Undefined;
     buffer.clear();

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

     if (!isGreetingMessageSent)
         sendGreetingMessage();

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

 void Connection::processData()
 {
     switch (currentDataType) {
     case PlainText:
         emit newMessage(username, buffer);
         break;
     case Ping:
         writer.startMap(1);
         writer.append(Pong);
         writer.append(nullptr);     // no payload
         writer.endMap();
         break;
     case Pong:
         pongTime.restart();
         break;
     default:
         break;
     }

     currentDataType = Undefined;
     buffer.clear();
 }