BaseHTTPMiddleware: Exception displayed twice in logs

[phihung]

Reproduction

class MyMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request: Request, call_next) -> Response:
        return await call_next(request)

def homepage(request): raise Exception("Very bad")

app = Starlette(routes=[Route("/", homepage)])
app.add_middleware(MyMiddleware)  # No more problem if we remove this line

Exception is shown twice in the logs

ERROR:    Exception in ASGI application
  + Exception Group Traceback (most recent call last):
     ...
  |   File ".venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 736, in __aexit__
  |     raise BaseExceptionGroup(
  | exceptiongroup.ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
          ...
    |   File "a.py", line 15, in homepage
    |     raise Exception("Very bad")
    | Exception: Very bad
    +------------------------------------

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  ...
  File "a.py", line 15, in homepage
    raise Exception("Very bad")
Exception: Very bad

Full stack trace

ERROR:    Exception in ASGI application
  + Exception Group Traceback (most recent call last):
  |   File ".venv/lib/python3.10/site-packages/starlette/_utils.py", line 77, in collapse_excgroups
  |     yield
  |   File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 186, in __call__
  |     async with anyio.create_task_group() as task_group:
  |   File ".venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 736, in __aexit__
  |     raise BaseExceptionGroup(
  | exceptiongroup.ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File ".venv/lib/python3.10/site-packages/uvicorn/protocols/http/httptools_impl.py", line 401, in run_asgi
    |     result = await app(  # type: ignore[func-returns-value]
    |   File ".venv/lib/python3.10/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
    |     return await self.app(scope, receive, send)
    |   File ".venv/lib/python3.10/site-packages/starlette/applications.py", line 113, in __call__
    |     await self.middleware_stack(scope, receive, send)
    |   File ".venv/lib/python3.10/site-packages/starlette/middleware/errors.py", line 187, in __call__
    |     raise exc
    |   File ".venv/lib/python3.10/site-packages/starlette/middleware/errors.py", line 165, in __call__
    |     await self.app(scope, receive, _send)
    |   File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 185, in __call__
    |     with collapse_excgroups():
    |   File "...uv/python/cpython-3.10.0-macos-aarch64-none/lib/python3.10/contextlib.py", line 153, in __exit__
    |     self.gen.throw(typ, value, traceback)
    |   File ".venv/lib/python3.10/site-packages/starlette/_utils.py", line 83, in collapse_excgroups
    |     raise exc
    |   File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 187, in __call__
    |     response = await self.dispatch_func(request, call_next)
    |   File "a.py", line 11, in dispatch
    |     return await call_next(request)
    |   File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 163, in call_next
    |     raise app_exc
    |   File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 149, in coro
    |     await self.app(scope, receive_or_disconnect, send_no_error)
    |   File ".venv/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
    |     await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
    |   File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 62, in wrapped_app
    |     raise exc
    |   File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 51, in wrapped_app
    |     await app(scope, receive, sender)
    |   File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 715, in __call__
    |     await self.middleware_stack(scope, receive, send)
    |   File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 735, in app
    |     await route.handle(scope, receive, send)
    |   File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 288, in handle
    |     await self.app(scope, receive, send)
    |   File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 76, in app
    |     await wrap_app_handling_exceptions(app, request)(scope, receive, send)
    |   File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 62, in wrapped_app
    |     raise exc
    |   File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 51, in wrapped_app
    |     await app(scope, receive, sender)
    |   File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 73, in app
    |     response = await f(request)
    |   File ".venv/lib/python3.10/site-packages/starlette/concurrency.py", line 39, in run_in_threadpool
    |     return await anyio.to_thread.run_sync(func, *args)
    |   File ".venv/lib/python3.10/site-packages/anyio/to_thread.py", line 56, in run_sync
    |     return await get_async_backend().run_sync_in_worker_thread(
    |   File ".venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 2405, in run_sync_in_worker_thread
    |     return await future
    |   File ".venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 914, in run
    |     result = context.run(func, *args)
    |   File "a.py", line 15, in homepage
    |     raise Exception("Very bad")
    | Exception: Very bad
    +------------------------------------

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ".venv/lib/python3.10/site-packages/uvicorn/protocols/http/httptools_impl.py", line 401, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
  File ".venv/lib/python3.10/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
    return await self.app(scope, receive, send)
  File ".venv/lib/python3.10/site-packages/starlette/applications.py", line 113, in __call__
    await self.middleware_stack(scope, receive, send)
  File ".venv/lib/python3.10/site-packages/starlette/middleware/errors.py", line 187, in __call__
    raise exc
  File ".venv/lib/python3.10/site-packages/starlette/middleware/errors.py", line 165, in __call__
    await self.app(scope, receive, _send)
  File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 185, in __call__
    with collapse_excgroups():
  File ".../uv/python/cpython-3.10.0-macos-aarch64-none/lib/python3.10/contextlib.py", line 153, in __exit__
    self.gen.throw(typ, value, traceback)
  File ".venv/lib/python3.10/site-packages/starlette/_utils.py", line 83, in collapse_excgroups
    raise exc
  File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 187, in __call__
    response = await self.dispatch_func(request, call_next)
  File "a.py", line 11, in dispatch
    return await call_next(request)
  File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 163, in call_next
    raise app_exc
  File ".venv/lib/python3.10/site-packages/starlette/middleware/base.py", line 149, in coro
    await self.app(scope, receive_or_disconnect, send_no_error)
  File ".venv/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
    await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 62, in wrapped_app
    raise exc
  File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 51, in wrapped_app
    await app(scope, receive, sender)
  File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 715, in __call__
    await self.middleware_stack(scope, receive, send)
  File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 735, in app
    await route.handle(scope, receive, send)
  File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 288, in handle
    await self.app(scope, receive, send)
  File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 76, in app
    await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 62, in wrapped_app
    raise exc
  File ".venv/lib/python3.10/site-packages/starlette/_exception_handler.py", line 51, in wrapped_app
    await app(scope, receive, sender)
  File ".venv/lib/python3.10/site-packages/starlette/routing.py", line 73, in app
    response = await f(request)
  File ".venv/lib/python3.10/site-packages/starlette/concurrency.py", line 39, in run_in_threadpool
    return await anyio.to_thread.run_sync(func, *args)
  File ".venv/lib/python3.10/site-packages/anyio/to_thread.py", line 56, in run_sync
    return await get_async_backend().run_sync_in_worker_thread(
  File ".venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 2405, in run_sync_in_worker_thread
    return await future
  File ".venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 914, in run
    result = context.run(func, *args)
  File "a.py", line 15, in homepage
    raise Exception("Very bad")
Exception: Very bad

[Kludex]

What's your Starlette version?

[phihung]

Starlette 0.38.6
Uvicorn 0.31.0
Python 3.10.0

[Kludex]

Does it reproduce in the last Starlette?

[phihung]

Yes. Same problem with

• Starlette 0.39.2, python 3.11.10, Mac osx
• Starlette main commit e116840

[phihung]

Hi. Do you think I should create an issue for this?
It is just in the logs, so nothing urgent.