Subscription message not being received in Qt

xxxcucus

I am testing a STOMP communication between a Spring Boot server and a Qt desktop program.
The server implementation looks as follows:

@Controller
class GreetingController {

     @MessageMapping("/hello")
     @SendTo("/topic/greetings")
     @Throws(Exception::class)
     fun greeting(@RequestBody message : HelloMessage) : Greeting  {
         Thread.sleep(1000); // simulated delay
         return Greeting("Hello, " + HtmlUtils.htmlEscape(message.getName()) + "!")
     }
}

The Qt program looks as follows:

bool StompClient::sendFrame(std::shared_ptr<StompFrame> stompFrame) {
     if (!stompFrame->isBinaryBody()) {
         QString str = stompFrame->convertToQString();
         m_Socket.sendTextMessage(str);
         qDebug() << "Send stomp frame " << str;
         return true;
    }

    QByteArray ba = stompFrame->convertToByteArray();
    m_Socket.sendBinaryMessage(ba);
    return true;
 }

 std::shared_ptr<StompFrame> StompFrameCreator::createSubscribeFrame(const QString&   destination) {
     auto stompFrame = std::make_shared<StompFrame>();
     stompFrame->setCommand(StompFrame::HeaderTypes::SUBSCRIBE);
     stompFrame->addHeader("destination", destination);
     return stompFrame;
}

std::shared_ptr<StompFrame> StompFrameCreator::createSendTextFrame(const QString& destination, const QString& message) {
     auto stompFrame = std::make_shared<StompFrame>();
     stompFrame->setCommand(StompFrame::HeaderTypes::SEND);
     stompFrame->addHeader("destination", destination);
     stompFrame->addHeader("content-type", "application/json");
     stompFrame->addTextBody(message);
     return stompFrame;
 }

void StompDemoView::sendGreeting() {
     qDebug() << "Send greeting";
     StompFrameCreator stompFrameCreator;

     QJsonObject jsonObject;
     jsonObject.insert("name", QJsonValue::fromVariant(m_NameLineEdit->text()));
     QJsonDocument doc(jsonObject);

     auto publishFrame = stompFrameCreator.createSendTextFrame("/app/hello", doc.toJson());
     qDebug() << "Sending " << doc.toJson();
     m_StompClient.sendFrame(publishFrame);
 }

void StompDemoView::clientConnected() {
    StompFrameCreator stompFrameCreator;
    qDebug() << "Subscribe to topic";
    auto subscribeFrame = stompFrameCreator.createSubscribeFrame(0, "/topic/greetings", "auto");
    m_StompClient.sendFrame(subscribeFrame);
}

When the client connects to the server I am sending a subscribe request. This is being received by the server:

 Decoded SUBSCRIBE {id=[0], destination=[/topic/greetings], ack=[auto]} session=null
 From client: SUBSCRIBE /topic/greetings id=0 session=6cc3a2b6-48a5-1c1c-2366-d746224d60e8
 Processing SUBSCRIBE /topic/greetings id=0 session=6cc3a2b6-48a5-1c1c-2366-d746224d60e8

Then when a user performs a specific action in the GUI I am sending the message to the Greeting controller which should send back a message to the subscribing client:

  Decoded SEND {destination=[/app/hello], content-type=[application/json]} session=null         application/json payload={
"name": "Cris"

}

  From client: SEND /app/hello session=6cc3a2b6-48a5-1c1c-2366-d746224d60e8 application/json payload={
 "name": "Cris"

}

  Searching methods to handle SEND /app/hello session=6cc3a2b6-48a5-1c1c-2366-d746224d60e8 application/json payload={
"name": "Cris"

}
, lookupDestination='/hello'
Found 1 handler methods: [{[MESSAGE],[/hello]}]
Invoking GreetingController#greeting[1 args]
Arguments: [HelloMessage@3903b632]
Processing return value with SendToMethodReturnValueHandler [annotationRequired=true]
Processing MESSAGE destination=/topic/greetings session=6cc3a2b6-48a5-1c1c-2366-d746224d60e8 payload={"content":"Hello, Cris!"}
Broadcasting to 1 sessions.

But I am not receiving anything on the client. I created slots for the signals binaryMessageReceived, textMessageReceived, binaryFrameReceived, textFrameReceived, errorOccured for the QWebSocket used in the communication.

Can anyone point me please in the right direction here ?

xxxcucus

After using wireshark and a javascript stomp client to compare the websocket messages exchanged between the clients and the server I reached the conclusion that the Qt client did not send a CONNECT Stomp Frame to the server. That is why the server did not send a message corresponding to the subscription, although the client had previously sent a SUBSCRIBE package.

Here is the code in the slot connect to the socketConnected slot of the QWebSocket:

 StompFrameCreator stompFrameCreator;
 auto connectFrame = stompFrameCreator.createConnectFrame("1.2", "", "", "", 10000, 10000);
 m_StompClient.sendFrame(connectFrame);

After adding that before sending the subscription to the server, the client receives messages pertaining to the subscription from the server.

SGaist

Hi,

You should also add the setup code you use for the web socket.

In the absolute, have a minimal compilable example triggering the issue would be even better.

xxxcucus

@SGaist
This is the code used for the opening the QWebSocket:

void StompDemoView::connectToServer() {
qDebug() << "Connect to server";
m_StompClient.setUrl("ws://localhost:8080/gs-guide-websocket");
m_StompClient.connectToServer();
}

void StompClient::setUrl(const QString& url) {
m_Url = url;
}

void StompClient::connectToServer() {
if (m_Url.isEmpty())
return;

qDebug() << "Connect to " << m_Url;
m_Socket.open(m_Url);

}

I could add an archive with the whole project but I am not sure how to do this on this forum.

SGaist

Did you also connect the error management related signals ?

xxxcucus

@SGaist
I connected errorOccured. Are there other signals for error management ? I see there are some other error messages concerning handshake and authorization. I will connect those as well and see what I receive.

xxxcucus

@SGaist
I connected the following signals to slots in my class:
errorOccurred, alertReceived, authenticationRequired, handshakeInterruptedOnError, peerVerifyError, proxyAuthenticationRequired,sslErrors, stateChanged,

Except for the obvious state changes when connecting and closing the connection and the connect and disconnect signals I am not receiving anything.

For me it seems that the server (running on localhost as well) is sending the messages but somehow they do not arrive to the socket. Is there a way how I can debug this ?

SGaist

The next step would be to use Wireshark to check what happens between your server and client.

xxxcucus

@SGaist
I used wireshark to view the websocket packages exchanged between the Spring Boot server and the Qt client. It seems that the server does not send a qwebsocket message to the subscribing Qt client.

xxxcucus

After using wireshark and a javascript stomp client to compare the websocket messages exchanged between the clients and the server I reached the conclusion that the Qt client did not send a CONNECT Stomp Frame to the server. That is why the server did not send a message corresponding to the subscription, although the client had previously sent a SUBSCRIBE package.

Here is the code in the slot connect to the socketConnected slot of the QWebSocket:

 StompFrameCreator stompFrameCreator;
 auto connectFrame = stompFrameCreator.createConnectFrame("1.2", "", "", "", 10000, 10000);
 m_StompClient.sendFrame(connectFrame);

After adding that before sending the subscription to the server, the client receives messages pertaining to the subscription from the server.

SGaist

Nice !

Glad you found out and thanks for sharing :-)

Don't forget to mark the thread as solved :-)