Path of Mount() being the initial substring of WebSocketRoute()'s blocks websocket with AssertionError: assert scope["type"] == "http"

[TrulyBright]

Panicking code (uvicorn panicking:app):

# panicking.py
from starlette.applications import Starlette
from starlette.routing import WebSocketRoute, Mount
from starlette.websockets import WebSocket, WebSocketDisconnect
from starlette.staticfiles import StaticFiles

async def endpoint(ws: WebSocket):
    await ws.accept()
    try:
        while msg := await ws.receive():
            ws._raise_on_disconnect(msg)
            print(msg)
    except WebSocketDisconnect:
        pass
    finally:
        await ws.close()

app = Starlette(debug=True, routes=[
    Mount("/", StaticFiles(directory="dist")),
    WebSocketRoute("/foo", endpoint),
])

The raised error log when I tried connecting to ws://localhost:8000/foo:

  File "C:@@@\.venv\lib\site-packages\uvicorn\protocols\websockets\websockets_impl.py", line 184, in run_asgi
    result = await self.app(self.scope, self.asgi_receive, self.asgi_send)
  File "C:@@@\.venv\lib\site-packages\uvicorn\middleware\proxy_headers.py", line 75, in __call__
    return await self.app(scope, receive, send)
  File "C:@@@\.venv\lib\site-packages\starlette\applications.py", line 119, in __call__
    await self.middleware_stack(scope, receive, send)
  File "C:@@@\.venv\lib\site-packages\starlette\middleware\errors.py", line 146, in __call__
    await self.app(scope, receive, send)
  File "C:@@@\.venv\lib\site-packages\starlette\exceptions.py", line 66, in __call__
    await self.app(scope, receive, send)
  File "C:@@@\.venv\lib\site-packages\starlette\routing.py", line 666, in __call__
    await route.handle(scope, receive, send)
  File "C:@@@\.venv\lib\site-packages\starlette\routing.py", line 418, in handle
    await self.app(scope, receive, send)
    assert scope["type"] == "http"
AssertionError

Working code where the path of WebSocketRoute no longer starts with that of Mount (uvicorn working:app):

# panicking.py
from starlette.applications import Starlette
from starlette.routing import WebSocketRoute, Mount
from starlette.websockets import WebSocket, WebSocketDisconnect
from starlette.staticfiles import StaticFiles

async def endpoint(ws: WebSocket):
    await ws.accept()
    try:
        while msg := await ws.receive():
            ws._raise_on_disconnect(msg)
            print(msg)
    except WebSocketDisconnect:
        pass
    finally:
        await ws.close()

app = Starlette(debug=True, routes=[
    Mount("/bar", StaticFiles(directory="dist")),
    WebSocketRoute("/foo", endpoint),
])

So the raised error is not clear enough to figure out the actual problem.
Version:

• uvicorn: 0.17.6 with CPython 3.10.2 on Windows
• starlette: 0.19.0

[TrulyBright]

It solves the error to insert all WebSocketRoute()s before Mount() into routes, without modifying their paths, though the actual problem is the unclearness of the raised error.

app = Starlette(debug=True, routes=[
    WebSocketRoute("/foo", endpoint),
    Mount("/", StaticFiles(directory="dist")),
]) # works fine

[Kludex]

Your client is trying to access the wrong route.

Check https://www.starlette.io/routing/#route-priority for more details.

Suggestions to improve the error message are welcome, but in this case, I can't think of a useful message considering the cause.