QUdpSocket: sending and receiving on the same socket?

[mhoover]

Hi,

I'm trying to implement a command client / command server architecture using QUdpSocket. So far I can send QStrings and the server gets them, but when I try to send status responses back nothing happens.

So when I send the command: "HADRONCOLLIDER5 GENERATE_STRANGELETS AMOUNT=DELUGE"

I'd like to get back: "0 0 0 GENERATE_STRANGELETS AMOUNT=DELUGE EXTREME_DANGER".

But I never get that return string.

Can I send the commands to the server and read responses from the server over the same port? Or is this crazy?

The command client is waiting for a readyRead() signal from the QUdpSocket.

[mhoover]

Ah ha.

I forgot that if you are *receiving* data, you have to bind to the port.

I added the .bind() and everything seems to be working.

Except one of our buildings seems to be turning into strange matter.

[mhoover]

Oops, it isn't working after all.

I thought I was getting a response, but what I was actually getting was the command I was sending the first time.

In other words, if I'm listening for a command when I send it, I get the command that I send. Is there anyway around this?

I tried disconnecting the readyRead() signal and reconnecting immediately after I send it, but it doesn't seem to fix it.

[wysota]

How exactly do you send the datagrams? And to what address?

[mhoover]

I've tried sending the datagrams a couple ways.

1) From a class that is waiting for a readReady() response, but if it was the first one to bind to the port it catches its own response. If it was the second class to bind to the port, it sends the command, but it cannot get the response. Sounds like a turf war.

2) From a class that sends udpSocket.write() and then immediately calls a waitForReadyRead() but never gets the response. Again, depending on whether the server binds first, it either sends the command and gets no response or the response fails to reach the server.

For the bind() I am using QUdpSocket::ShareAddress | QUdpSocket::ReuseAddressHint. For the datastreams I am using QIODevice::ReadWrite.

[mhoover]

It would be nice if there were a udp "echo" example.


I have seen this one (not using Qt classes):

http://gnosis.cx/publish/programming/sockets2.html

And this Qt example, but I haven't been able to find all the code:

http://www.archivum.info/qt-interest.../msg00367.html

[mhoover]

Dang, I've tried using the QAbstractSockets and that doesn't help either.

I was thinking that if I avoided a 'bind' neither side would lock the readyRead() signals all for itself.

[wysota]

Can we see your actual code?

[mhoover]

I realize this is not the best way to structure the code. I should use returns instead of nesting the if's more. I've been in kind of a hurry.

client side:

QUdpSocket udpSocket;
    QByteArray datagram;
   QDataStream out( &datagram, QIODevice::ReadWrite );
   out.setVersion( QDataStream::Qt_4_5 );
   out << ui.command_lineEdit->text();
    udpSocket.connectToHost( QHostAddress::LocalHost, 5825 );
    cout << "sending manual command: " << ui.command_lineEdit->text().toAscii().data() << endl;
    bool result = udpSocket.waitForConnected( 3000 );
    if ( result != false ) {
        qint64 writtenSize = udpSocket.write( datagram );       // send command
        if ( writtenSize != -1 ) {
            result = udpSocket.waitForReadyRead( 3000 );
            if ( result != false ) {
                cout << "found a response." << endl;
                while ( udpSocket.hasPendingDatagrams() ) {
                    QByteArray datagram(command_socket_device.bytesAvailable(), '0' );
                    command_socket_device.readDatagram(datagram.data(), datagram.size());
                    QString the_return;
 
                    QDataStream in( &datagram, QIODevice::ReadWrite);
                    in.setVersion( QDataStream::Qt_4_5 );
                    in >> the_return;
                    this->statusBar()->showMessage( the_return );
 
                }
            } else {
                cout << "No response." << endl;
            }
        }
    }

QUdpSocket udpSocket;
    QByteArray datagram;
   QDataStream out( &datagram, QIODevice::ReadWrite );
   out.setVersion( QDataStream::Qt_4_5 );
   out << ui.command_lineEdit->text();
    udpSocket.connectToHost( QHostAddress::LocalHost, 5825 );
    cout << "sending manual command: " << ui.command_lineEdit->text().toAscii().data() << endl;
    bool result = udpSocket.waitForConnected( 3000 );
    if ( result != false ) {
        qint64 writtenSize = udpSocket.write( datagram );       // send command
        if ( writtenSize != -1 ) {
            result = udpSocket.waitForReadyRead( 3000 );
            if ( result != false ) {
                cout << "found a response." << endl;
                while ( udpSocket.hasPendingDatagrams() ) {
                    QByteArray datagram(command_socket_device.bytesAvailable(), '0' );
                    command_socket_device.readDatagram(datagram.data(), datagram.size());
                    QString the_return;

                    QDataStream in( &datagram, QIODevice::ReadWrite);
                    in.setVersion( QDataStream::Qt_4_5 );
                    in >> the_return;
                    this->statusBar()->showMessage( the_return );

                }
            } else {
                cout << "No response." << endl;
            }
        }
    }

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server side:
(called in the constructuor after a 1 sec delay)

while ( !done ) {
 
            if ( command_socket_device.hasPendingDatagrams() == true ) {
                cout << "found something to read." << endl;
                QString command( "" );
 
                QByteArray datagram(command_socket_device.bytesAvailable(), '0' );
 
                command_socket_device.read(datagram.data(), datagram.size());
 
                QDataStream in( &datagram, QIODevice::ReadWrite);
                in.setVersion( QDataStream::Qt_4_5 );
                in >> command;
 
                cout << "Received: " << command.toAscii().data() << endl;
                ui.log_textEdit->append( command );
 
                if ( command == "HADRON_STARTUP" ) {
                    command.prepend( "0 0 0 " );
                    QByteArray datagram2;
                    QDataStream out( &datagram2, QIODevice::ReadWrite );
                    out.setVersion( QDataStream::Qt_4_5 );
                    out << command;
                    cout << "sending response: " << command.toAscii().data() << endl;
                    command_socket_device.write( datagram2 );
                    ui.log_textEdit->append( command );
                }
                cout << "Should have logged something." << endl;
            }
            qApp->processEvents();
        }

while ( !done ) {

            if ( command_socket_device.hasPendingDatagrams() == true ) {
                cout << "found something to read." << endl;
                QString command( "" );

                QByteArray datagram(command_socket_device.bytesAvailable(), '0' );

                command_socket_device.read(datagram.data(), datagram.size());

                QDataStream in( &datagram, QIODevice::ReadWrite);
                in.setVersion( QDataStream::Qt_4_5 );
                in >> command;

                cout << "Received: " << command.toAscii().data() << endl;
                ui.log_textEdit->append( command );

                if ( command == "HADRON_STARTUP" ) {
                    command.prepend( "0 0 0 " );
                    QByteArray datagram2;
                    QDataStream out( &datagram2, QIODevice::ReadWrite );
                    out.setVersion( QDataStream::Qt_4_5 );
                    out << command;
                    cout << "sending response: " << command.toAscii().data() << endl;
                    command_socket_device.write( datagram2 );
                    ui.log_textEdit->append( command );
                }
                cout << "Should have logged something." << endl;
            }
            qApp->processEvents();
        }

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I've tried a lot of combinations binding and not binding to the port.

Also, this is the blocking version I tried. I've also tried a version based on the more normal "readyRead".

[wysota]

What if you don't call connectToHost()?

[mhoover]

If I don't call connectToHost() on the server side, the client still catches it's own datagrams (regardless of which comes up first -client or server).

If I don't call connectToHost() on the client side, the server never gets the datagram (regardless of which comes up first).

If I don't call connectToHost() on either client or server, the server never receives the messages and the client doesn't get a response (regardless of which comes up first).

No bind() calls were made in these classes either.