[Qt-interest] QTcpSocket::waitForReadyRead() "loses" data in a QThread with an event loop

[FD]

Dear all,

Sorry if it's longer, tried to keep it as succint as possible.

I have a QThread with an event loop running which does the network handling. 
Communication with the thread is through signal/slots, which works as 
expected.

What I am doing now is signaling the thread to do some network communication, 
which consists of sending a command, then reading and parsing the results sent 
by the server. Reading the data consists of issuing a waitForReadyRead() and 
when that returns true, read()ing 50 bytes at a time as long as read returns 
some bytes (or the buffer is filled by read()). I repeat this until the server 
response is complete. Of course read() will return 0 bytes read at some point, 
even though the server response is not complete.

Problem: Parsing/processing is quite fast, so it will go back quickly to 
waitForReadyRead() if more data is expected. This call to waitForReadyRead() 
(as well as a read() without waitForReadyRead()) will often return nothing (in 
the case of waitForReadyRead(), it will wait the default timeout of 30 
seconds, read() will just return 0), even though tcpdump shows, that the 
server sent more data. This data cannot be retrieved. Having delays/longer 
waits before waitForReadyRead() or read() sometimes helps and I can retrieve 
more data, but not all. It this happens, this data can never be read, even if 
trying to do so forever.

Why would waitForReadyRead() "never" return, even though the server sent data 
in the meantime? Or why would read() not be able to get data from the socket, 
even though there's clearly more data available? Or is there some major flaw 
in the logic in how I'm using the socket?

I know that many say doing the network stuff in a thread isn't necessary, but 
the overall code would be less complicated if it could be done in separate 
threads using asynchronous signal/slots.

Thanks for bearing with me and for any help. ;-)


Greetings...