Anyio errors (only) on automatic reload

[kleynjan]

This is not really a bug, more of an inconvenience - and primarily caused by starlette/fastapi, I think [EDIT: aiosqlite, in fact]. While debugging I have a number of browser windows open. When I have edited the source and the app automatically reloads, I get a long "flag" of errors that is apparently caused by the server side trying to handle websocket database connections that have gone stale. See below.

When I interrupt the console and manually restart (or if I close all browser windows!), this is clean.

Anyone have a suggestion how to do a "clean" reload, ie get rid of the old state when doing ui.run?

Cheers, -Peter

fastapi==0.97.0
starlette==0.27.0
nicegui==1.3.7

(Btw, it's hard to post a "minimal" app to reproduce this. Not sure what triggers this behavior. Multiple browser sessions is certainly one factor.)

ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File ".../site-packages/anyio/streams/memory.py", line 98, in receive
    return self.receive_nowait()
           ^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/anyio/streams/memory.py", line 93, in receive_nowait
    raise WouldBlock
anyio.WouldBlock

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ".../site-packages/starlette/middleware/base.py", line 78, in call_next
    message = await recv_stream.receive()
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/anyio/streams/memory.py", line 118, in receive
    raise EndOfStream
anyio.EndOfStream

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ".../site-packages/uvicorn/protocols/http/httptools_impl.py", line 435, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/uvicorn/middleware/proxy_headers.py", line 78, in __call__
    return await self.app(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/fastapi/applications.py", line 282, in __call__
    await super().__call__(scope, receive, send)
  File ".../site-packages/starlette/applications.py", line 122, in __call__
    await self.middleware_stack(scope, receive, send)
  File ".../site-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File ".../site-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File ".../site-packages/starlette/middleware/sessions.py", line 86, in __call__
    await self.app(scope, receive, send_wrapper)
  File ".../site-packages/starlette/middleware/base.py", line 108, in __call__
    response = await self.dispatch_func(request, call_next)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/nicegui/storage.py", line 69, in dispatch
    response = await call_next(request)
               ^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/starlette/middleware/base.py", line 84, in call_next
    raise app_exc
  File ".../site-packages/starlette/middleware/base.py", line 70, in coro
    await self.app(scope, receive_or_disconnect, send_no_error)
  File ".../site-packages/starlette/middleware/gzip.py", line 24, in __call__
    await responder(scope, receive, send)
  File ".../site-packages/starlette/middleware/gzip.py", line 44, in __call__
    await self.app(scope, receive, self.send_with_gzip)
  File ".../site-packages/starlette/middleware/exceptions.py", line 79, in __call__
    raise exc
  File ".../site-packages/starlette/middleware/exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File ".../site-packages/fastapi/middleware/asyncexitstack.py", line 20, in __call__
    raise e
  File ".../site-packages/fastapi/middleware/asyncexitstack.py", line 17, in __call__
    await self.app(scope, receive, send)
  File ".../site-packages/starlette/routing.py", line 718, in __call__
    await route.handle(scope, receive, send)
  File ".../site-packages/starlette/routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File ".../site-packages/starlette/routing.py", line 66, in app
    response = await func(request)
               ^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/fastapi/routing.py", line 241, in app
    raw_response = await run_endpoint_function(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/fastapi/routing.py", line 167, in run_endpoint_function
    return await dependant.call(**values)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/nicegui/page.py", line 98, in decorated
    result = task.result() if task.done() else None
             ^^^^^^^^^^^^^
ValueError: Connection closed

[rodja]

While debugging I have a number of browser windows open.

Do you attach a debugger?

I'm not able to reproduce the error. Does it also happen with a minimal app (eg "hello world")? Is it always happening if you have multiple browser tabs open or only sometimes?

[kleynjan]

Hi Rodja, thank you for taking a look. Your questions prompted me to take a closer look, and I've narrowed it down to the interface with Tortoise ORM and aiosqlite: both ValueErrors (below and above) originate in aiosqlite.core.py.

To reproduce, take the sqlite example in the repo and comment out the generate_schemas in the init (after first creating the db):

register_tortoise(
    app,
    db_url="sqlite://db.sqlite3",
    modules={"models": ["models"]},  # tortoise will look for models in this main module
    # generate_schemas=True,  # in production you should use version control migrations instead
)

Open two browser sessions, not sharing cookies (eg, one should be incognito). Then make a trivial edit in main.py, causing a reload. You should see this error:

 ....
  File ".../site-packages/fastapi/routing.py", line 167, in run_endpoint_function
    return await dependant.call(**values)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/nicegui/page.py", line 98, in decorated
    result = task.result() if task.done() else None
             ^^^^^^^^^^^^^
ValueError: no active connection 

I have added the generate_schemas call to my own init code and I no longer get the 'Connection closed' error when reloading. So for me, the issue is resolved.

It does feel a bit shaky that these errors in underlying coroutines (?) cannot be surfaced properly, but it's totally up to you how deep you want to get into this, of course. Cheers, -Peter

[rodja]

It would be good to dig deeper and try to find a even more minimal reproduction without NiceGUI to post the issue in the Tortoise repo. Thanks to your analysis I think it is not really something caused by NiceGUI, so I'll close the issue. Thanks!