Commands JSON content mangled

[gagern]

Commands JSON content mangled

[gagern]

Using IPython.core.debugger.set_trace I've traced the synchronous call stack through ipywidgets and comm to ipykernel.iostream.BackgroundSocket.send_multipart and found that the data is still in order at that point. Even monkey-patching the method to pass bytes objects instead of the (potentially mutable) memoryview didn't change things, so it doesn't seem to be due to asynchronous mutation of the memory area, and it does seem to be nested fairly deeply in the communication stack. I don't have a good idea for how to trace the asynchronous communication, though, since it's harder to get a pdb attached to a background thread.

[martinRenou]

Thanks for opening an issue and for the thorough debugging.

My gut feeling would be that tornado has a web socket message size limit that you are reaching, and tornado may be cutting your message. But this hypothesis does not match with the diff you are seeing I suppose.

[gagern]

Plain size limitation doesn't match with the buffer size being the same on both sides of the channel. Must be at least somewhat more subtle to allow length to be passed independently.

Have you been able to reproduce? I'm having a hard time reproducing just now. I could reproduce with near certainty yesterday. Today when I wanted to explore other browsers (original report was using Chrome) and using Wireshark to observe the data over the wire, and suddenly I can't reproduce with any browser. Will try again, wondering what other aspects could come into this, including system load, network connectivity, or perhaps actually bad hardware.