Fix sendmessage (#46)

* Fix send message example

If a secondary instance sends a message immediately after connecting, the
message follows the init message. This causes the slotConnectionEstablished to
read and consume the tail of the message and interpret it as the checksum. The
checksum fails and the connection becomes invalid.

To avoid this race, we prefix the init message with its length. This way, we
consume only the data relevant to the init message.

This patch fixes the sending_arguments example.

Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>

* Fix include file case

Signed-off-by: Francis Giraldeau <francis.giraldeau@nrc-cnrc.gc.ca>

examples/basic/main.cpp

@@ -1,4 +1,4 @@
-#include <SingleApplication.h>
+#include <singleapplication.h>
 
 int main(int argc, char *argv[])
 {

examples/calculator/main.cpp

@@ -50,7 +50,7 @@
 
 #include <QApplication>
 
-#include <SingleApplication.h>
+#include <singleapplication.h>
 
 #include "calculator.h"
 

examples/sending_arguments/main.cpp

@@ -1,4 +1,4 @@
-#include <SingleApplication.h>
+#include <singleapplication.h>
 #include "messagereceiver.h"
 
 int main(int argc, char *argv[])

singleapplication.cpp

@@ -216,6 +216,13 @@ void SingleApplicationPrivate::connectToPrimary( int msecs, ConnectionType conne
         quint16 checksum = qChecksum(initMsg.constData(), static_cast<quint32>(initMsg.length()));
         writeStream << checksum;
 
+        // The header indicates the message length that follows
+        QByteArray header;
+        QDataStream headerStream(&header, QIODevice::WriteOnly);
+        headerStream.setVersion(QDataStream::Qt_5_6);
+        headerStream << (quint64) initMsg.length();
+
+        socket->write( header );
         socket->write( initMsg );
         socket->flush();
         socket->waitForBytesWritten( msecs );
@@ -274,33 +281,43 @@ void SingleApplicationPrivate::slotConnectionEstablished()
     quint32 instanceId = 0;
     ConnectionType connectionType = InvalidConnection;
     if( nextConnSocket->waitForReadyRead( 100 ) ) {
-        // read all data from message in same order/format as written
+        // read the fields in same order and format as written
-        QByteArray msgBytes = nextConnSocket->read(nextConnSocket->bytesAvailable() - static_cast<qint64>(sizeof(quint16)));
+        QDataStream headerStream(nextConnSocket);
-        QByteArray checksumBytes = nextConnSocket->read(sizeof(quint16));
+        headerStream.setVersion(QDataStream::Qt_5_6);
+
+        // Read the header to know the message length
+        quint64 msgLen = 0;
+        headerStream >> msgLen;
+
+        if (msgLen >= sizeof(quint16)) {
+           // Read the message body
+           QByteArray msgBytes = nextConnSocket->read(msgLen);
            QDataStream readStream(msgBytes);
            readStream.setVersion(QDataStream::Qt_5_6);
 
            // server name
            QByteArray latin1Name;
            readStream >> latin1Name;
-        // connectioon type
+
+           // connection type
            quint8 connType = InvalidConnection;
            readStream >> connType;
            connectionType = static_cast<ConnectionType>(connType);
+
            // instance id
            readStream >> instanceId;
+
            // checksum
            quint16 msgChecksum = 0;
-        QDataStream checksumStream(checksumBytes);
+           readStream >> msgChecksum;
-        checksumStream.setVersion(QDataStream::Qt_5_6);
-        checksumStream >> msgChecksum;
 
-        const quint16 actualChecksum = qChecksum(msgBytes.constData(), static_cast<quint32>(msgBytes.length()));
+           const quint16 actualChecksum = qChecksum(msgBytes.constData(), static_cast<quint32>(msgBytes.length() - sizeof(quint16)));
 
            if (readStream.status() != QDataStream::Ok || QLatin1String(latin1Name) != blockServerName || msgChecksum != actualChecksum) {
              connectionType = InvalidConnection;
            }
         }
+    }
 
     if( connectionType == InvalidConnection ) {
         nextConnSocket->close();