QAbstractSocket::UnknownSocketError

Question

What could be cause of QAbstractSocket::UnknownSocketError when using QTcpSocket?

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CODE

I'm getting this error code with the following code:

this->connect(socket, SIGNAL(socketError(QAbstractSocket::SocketError)), SLOT(handleSocketError(QAbstractSocket::SocketError)));
...
void MyClass::handleSocketError(QAbstractSocket::SocketError error)
{
    qDebug() << error;
}

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MORE INFO

The QTcpSocket is trying to connect to some remote host. And it fails with mentioned error code.

Answer 1

Possibly you called the error() function when there is no error.

Answer 2

Looking for AbstractSocketError in the Qt sources gives quite some hits. Maybe fire up a debugger and look into the backtrace when you get the error() signal. Possibly an exotic error condition occured in the underlying socket engine (which is a Qt internal class).

Answer 3

Does remote host require ssl connection? It may be problem if your Qt copy can't load libssl. I had same problem (UnkownSocketError) when Qt couldn't find libssl

Answer 4

If you read the code, you'll see that this error means exactly what it says: "something bad happened and I don't know why". There had to be exceptions, of course:

• The socket is not connected to a server and you try to write to it (src/network/socket/qabstractsocket.cpp on line 2025)
• An SSL error occurred (src/network/ssl/qsslsocket_openssl.cpp in a lot of places)

In both situations the errorString is set to an appropriate message.