QWebSocket::textMessageReceived() emitted after the socked is disconnected

[Alvein]

Hello.

I am connecting to a chat server through web sockets. Everything is nice, but when I close the connection, the QWebSocket signals keep arriving for some while, even if I forcefully delete the object.

Why is this happening and how should I "cut" the communication instead?

This is the class definition:

class Chatbot:public QObject {
    Q_OBJECT
public:
    Chatbot();
    ~Chatbot();
    bool         enterChat();
    void         leaveChat();
private:
    QString      sChatURL;
    QWebSocket   *wsChat;
    CBChatStatus cbcsStatus;
private slots:
    void on_connected();
    void on_disconnected();
    void on_textMessageReceived(QString);
signals:
    void logEvent(QString);
};

And these are the methods, simplified for the sample:

bool Chatbot::enterChat() {
    bool bEC=false;
    if(cbcsStatus==CBChatStatus::CBCS_DISCONNECTED) {
        emit logEvent(QStringLiteral("Connecting..."));
        wsChat=new QWebSocket;
        QObject::connect(wsChat,SIGNAL(connected()),this,SLOT(on_connected()));
        QObject::connect(wsChat,SIGNAL(disconnected()),this,SLOT(on_disconnected()));
        QObject::connect(wsChat,SIGNAL(textMessageReceived(QString)),this,SLOT(on_textMessageReceived(QString)));
        cbcsStatus=CBChatStatus::CBCS_CONNECTING; // EDIT
        wsChat->open(QUrl(sChatURL));
        bEC=true;
    }
    return bEC;
}

void Chatbot::leaveChat() {
    if(cbcsStatus!=CBChatStatus::CBCS_DISCONNECTED) {
        wsChat->close();
        wsChat->disconnect(); // EDIT
        delete wsChat;
        wsChat=nullptr;
    }
}

void Chatbot::on_connected() {
    emit logEvent(QStringLiteral("** Connected **"));
    cbcsStatus=CBChatStatus::CBCS_CONNECTED;
}

void Chatbot::on_disconnected() {
    emit logEvent(QStringLiteral("** Disconnected **"));
    cbcsStatus=CBChatStatus::CBCS_DISCONNECTED;
}

void Chatbot::on_textMessageReceived(QString sMessage) {
    emit logEvent(QStringLiteral("Message received: %1").arg(sMessage));
    // ...
}

*The logEvent() signal is just my way of registering events.

So, after hitting some "End chat" button, which calls leaveChat(), I get the following in my log:

** Disconnected **
Message received: <some server response>
Message received: <some server response>
Message received: <some server response>
...

It seems that after some seconds, the server detects the connection is idle and finally closes it itself, but I should not be getting those messages in first place!

Does anybody have an idea about what's happening?

Thanks.

[Christian Ehrlicher]

I would guess there is a second socket around otherwise I don't see why you would get the disconnected() debug output at all since you already disconnected the signals/slots. Simply inrt out the pointer of wsChat / sender() in the approriate functions.

Also don't use disconnect(wsChat) but wsChat->disconnect(this) since you for sure won't disconnect all (also internal) signals wsChat is emitting.

[Alvein]

@Christian-Ehrlicher:

I would guess there is a second socket around otherwise I don't see why you would get the disconnected() debug output at all since you already disconnected the signals/slots. Simply inrt out the pointer of wsChat / sender() in the approriate functions.

I only use a single QWebSocket.

And I close it right before QObject::disconnect().
I have no idea if this close() method is synchronous, but it should be or if not, why is disconnected() being fired?

I've logged wsChat in on_textMessageReceived() and it shows 0x0 !!

And when the server finally closes the connection itself, on_disconnected() is triggered again, showing that wsChat is 0x0 as well.

Just for testing, I've removed the wsChat=nullptr line inside leaveChat() (because it's worth nothing), and after that the debug line in on_textMessageReceived() crashes because wsChat is -1.

That's insane.

@Christian-Ehrlicher:

Also don't use disconnect(wsChat) but wsChat->disconnect(this) since you for sure won't disconnect all (also internal) signals wsChat is emitting.

Nothing else should fire my custom slot on_textMessageReceived() after disconnecting it.

But I used wsChat->disconnect(this), and the result is the same.

[nagesh]

@Alvein Just a suggestion
In leaveChat() function call disconnectFromHost() which will trigger disconnected signal,
In on_disconnected() slot perform cleanup task

[Alvein]

@nagesh

There's no such thing as disconnectFromHost() in QWebSocket.

Previously, I tried abort(), but the resulting behavior is the same.

Deleting wsChat in on_disconnected() raises an exception in on_textMessageReceived(), because the textMessageReceived() signal keeps being triggered.

...

At this point I don't care if the socket remains open forever. I just want to remove the wsChat object signal/slot connections inside leaveChat() or on_disconnected(). Seems like an impossible task, though.

...

EDIT:

Found the problem. The posted snippet was basically good. It's hard to tell in a few words but the CALLER was not having into account that cbcsStatus can take a little while going from CBChatStatus::CBCS_DISCONNECTED to CBChatStatus::CBCS_CONNECTED.

A Chatbot instance is intended to be created multiple times, and the routine which does this decides if it's OK to invoke enterChat() according to the given instance status (CBCS_DISCONNECTED or not).

So, enterChat() was being executed twice, even if a single bot was being used, overwriting the previous wsChat value. Boom.

Solution? Just setting a new status, CBCS_CONNECTING, right before wsChat->open().

Also, once wsChat is freed, there's no need of disconnecting signals/slots, BUT:

I was wrong.

This fails

QObject::disconnect(wsChat);

This works:

wsChat->disconnect(this);
// or
QObject::disconnect(wsChat,nullptr,this,nullptr);

This also works (a little more general:

wsChat->disconnect();
// or
QObject::disconnect(wsChat,nullptr,nullptr,nullptr);

I've done the modifications in the original snippet.

Thanks to everyone for giving me ideas.