[Interest] Problem transfering bigger data amounts over Websockets on iOS

[Markus Steinhilber]

Hi,

I currently have a problem with websockets on iOS. I'm using a
websocket connection to send commands and files over a network (WiFi)
between 2 devices. The server is a Windows CE device with Qt5.3 and
the client can be an iPad or Windows PC, using a program compiled with
Qt 5.7.1. The files are transfered by breaking them into smaller parts
(~20-300KB, depending on the speed of the last part) and sending them
as a websocket message. There is a small protocol implemented to
coordinate the parts.

Especially when transfering bigger files(>200MB) over the network, at
some point i always run into a disconnect of the socket with the
closeReason "Timeout when reading data from socket." on the Client.
The server then gives a normal disconnect without closeReason.

My first question is: Is this a normal closeReason for a disconnect in
case of a bad WiFi connection or could it be a bug in my software or
even in Qt's Websocket implementation? I did force some disconnects by
powering off the server device while transfering data and I did not
get the same error on the client.

I also found the QTBUG-14975 which very much sounds like my issue. The
closeReason is set in qwebsocketframe.cpp after a
waitForReadyRead(5000). But the main differences are that this bug is
only reported as happening on Windows and about every 4-5GB
transmitted. In my case it's happening only on iOS and about every
200-300 MB.

Since the problem only happens on iOS(iPad and simulator) but not with
a Windows PC as client, i am also thinking about, if this could be an
OS related problem. Like iOS detecting a Wifi disconnect earlier when
a Windows PC maybe waits a bit longer and the connections get better
again.

Would it be a solution to change the timeout of the
waitForReadyRead(5000) in qwebsocketframe.cpp and compile a custom Qt?
Is it likely that this will help?

Thanks for any help on that topic. I'm investigating this problem for
days and don't find any solution.