Getting errors from asyncio when ui.run(reload=True)

[eitama]

Question

Hi,

Context

I got slow internet connection, and a few PCs that download game updates from Steam/Epic.

I implemented a client/server python app (two entry points, client.py and server.py) to only download updates on one PC, and copy the new/changed files to other PCs through LAN - On demand.

It works by comparing MD5s across computers and only copying different files. Copying uses httpx.post with large timeouts, over lan at 1Gbps.

It all works very nicely.

The problem

Sometimes I get these errors (below) in stdout:

When they show, it's millions of them very quick.

Since I am a python noob, and don't really understand threads / asyncio, it's hard for me to drill into this efficiently.
I spent 3 days trying to pinpoint the issue.

I looked into nicegui code and saw it extends uvicorn.Server, and calls the super().run function.
There are 3 flavors there, one without sockets. I noticed it is related to the reload flag, so I disabled reload, and problem went away.

Would appreciate help.

All the code is in github: https://github.com/eitama/folder-sync

The error happens when files are uploaded, but not every time, and even if it's just 1 file it still may happen.
Upload is triggered here: https://github.com/eitama/folder-sync/blob/master/client.py#L84

Thanks!

  File "<string>", line 1, in <module>
  File "C:\Users\eitama\miniconda3\Lib\multiprocessing\spawn.py", line 122, in spawn_main
    exitcode = _main(fd, parent_sentinel)
  File "C:\Users\eitama\miniconda3\Lib\multiprocessing\spawn.py", line 135, in _main
    return self._bootstrap(parent_sentinel)
  File "C:\Users\eitama\miniconda3\Lib\multiprocessing\process.py", line 314, in _bootstrap
    self.run()
  File "C:\Users\eitama\miniconda3\Lib\multiprocessing\process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "D:\Projects\folder-sync\.venv\Lib\site-packages\uvicorn\_subprocess.py", line 80, in subprocess_started
    target(sockets=sockets)
  File "D:\Projects\folder-sync\.venv\Lib\site-packages\nicegui\server.py", line 36, in run
    super().run(sockets=sockets)
  File "D:\Projects\folder-sync\.venv\Lib\site-packages\uvicorn\server.py", line 65, in run
    return asyncio.run(self.serve(sockets=sockets))
  File "C:\Users\eitama\miniconda3\Lib\asyncio\runners.py", line 194, in run
    return runner.run(main)
  File "C:\Users\eitama\miniconda3\Lib\asyncio\runners.py", line 118, in run
    return self._loop.run_until_complete(task)
  File "C:\Users\eitama\miniconda3\Lib\asyncio\base_events.py", line 674, in run_until_complete
    self.run_forever()
  File "C:\Users\eitama\miniconda3\Lib\asyncio\base_events.py", line 641, in run_forever
    self._run_once()
  File "C:\Users\eitama\miniconda3\Lib\asyncio\base_events.py", line 1988, in _run_once
    handle._run()
  File "C:\Users\eitama\miniconda3\Lib\asyncio\events.py", line 88, in _run
    traceback.print_stack(file=sys.stdout)
Exception!!: Data should not be empty
Traceback (most recent call last):
  File "C:\Users\eitama\miniconda3\Lib\asyncio\events.py", line 90, in _run
    self._context.run(self._callback, *self._args)
  File "C:\Users\eitama\miniconda3\Lib\asyncio\selector_events.py", line 1139, in _write_send
    assert self._buffer, 'Data should not be empty'
           ^^^^^^^^^^^^
AssertionError: Data should not be empty

[falkoschindler]

Hi @eitama,

Unfortunately it is very hard and time-consuming for us to debug your code in its current form. Can you, please, try to create a minimum reproducible code example? This would allow us and the community to help more efficiently. Thanks!
Why is it important to provide a minimal reproducible example?

[rodja]

Are you sure it ist NiceGUI related? The stack trace indicates that it might also happen with a plain FastAPI App and uvicorn running with reload=True.

[eitama]

Hi @falkoschindler and @rodja,

• I'm trying to reproduce it with a minimal implementation but with no luck so far.
• @rodja , the side that suffers this error is the client which does not use FastAPI at all, just NiceGUI and HTTPX (and uvicorn under the hood I guess)

I don't really understand what kind of data uvicorn was looking for and it was empty, so don't know how to make progress on reproduction.

When I googled, I saw some issue in DAP 1.2 having the same exception:

https://community.canvaslms.com/t5/Data-and-Analytics-Group/CD2-dap-issues/m-p/602559

I'd feel better if I can figure it out hehe.