Surface non-Connect handler exceptions to user by anuraaga · Pull Request #219 · connectrpc/connect-python

anuraaga · 2026-04-17T02:38:43Z

Fixes #217

Ended up folding WSGI in too. Could confirm servers render the exceptions

❯ uv run pyvoy example.eliza_service:app
pyvoy listening on 127.0.0.1:8000
Exception in ASGI application
Traceback (most recent call last):
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/applications.py", line 107, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/middleware/errors.py", line 186, in __call__
    raise exc
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/middleware/errors.py", line 164, in __call__
    await self.app(scope, receive, _send)
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/middleware/exceptions.py", line 63, in __call__
    await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    raise exc
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
    await app(scope, receive, sender)
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/routing.py", line 716, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/routing.py", line 736, in app
    await route.handle(scope, receive, send)
  File "/Users/anuraag/git/connect-python/.venv/lib/python3.14/site-packages/starlette/routing.py", line 462, in handle
    await self.app(scope, receive, send)
  File "/Users/anuraag/git/connect-python/src/connectrpc/_server_async.py", line 224, in __call__
    return await self._handle_unary_connect(
  File "/Users/anuraag/git/connect-python/src/connectrpc/_server_async.py", line 264, in _handle_unary_connect
    response_data = await endpoint.function(request, ctx)
  File "/Users/anuraag/git/connect-python/example/example/eliza_service.py", line 36, in say
    raise TypeError("FOO")
TypeError: FOO
^CShutting down pyvoy...

❯ uv run gunicorn  example.eliza_service_sync:app
[2026-04-17 12:19:27 +0900] [23456] [INFO] Starting gunicorn 25.3.0
[2026-04-17 12:19:27 +0900] [23456] [INFO] Listening at: http://127.0.0.1:8000 (23456)
[2026-04-17 12:19:27 +0900] [23456] [INFO] Using worker: sync
[2026-04-17 12:19:27 +0900] [23457] [INFO] Booting worker with pid: 23457
[2026-04-17 12:19:27 +0900] [23456] [INFO] Control socket listening at /Users/anuraag/.gunicorn/gunicorn.ctl
Exception in WSGI application
Traceback (most recent call last):
  File "/Users/anuraag/git/connect-python/src/connectrpc/_server_sync.py", line 249, in __call__
    return self._handle_unary(
           ~~~~~~~~~~~~~~~~~~^
        environ, start_response, http_method, endpoint, ctx, headers
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/Users/anuraag/git/connect-python/src/connectrpc/_server_sync.py", line 277, in _handle_unary
    response = endpoint.function(request, ctx)
  File "/Users/anuraag/git/connect-python/example/example/eliza_service_sync.py", line 35, in say
    raise TypeError("Foo")
TypeError: Foo

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

anuraaga · 2026-04-17T04:03:37Z

                        "more_trailers": False,
                    }
                )
+            if error and not isinstance(error, ConnectError):


We only raise HTTPExceptions before negotiating a response so don't worry here

valentimarco · 2026-04-17T07:40:13Z

-            return await self._handle_error(e, ctx, send)
+            await self._handle_error(e, ctx, send)
+            if not isinstance(e, (ConnectError, HTTPException)):
+                raise


This should be raise e , isn't it?

When inside an except block, raise is actually enough to reraise the active exception. This is exercised in the test_async_unhandled_exception_reraised test

stefanvanburen

looks good, just some nits / questions

stefanvanburen · 2026-04-17T13:11:04Z

+    if isinstance(exc, (ConnectError, HTTPException)):
+        return
+    errors: ErrorStream = environ["wsgi.errors"]
+    errors.write(


nit: not sure, but should we errors.flush() after this?: https://peps.python.org/pep-3333/#input-and-error-streams. Still understanding WSGI's idioms 😅. I'm assuming we ought to as we're the "portable application"...?

Good diligence. I'm leaning towards leaving it out though since I can't imagine a server not writing error messages directly, but also the following For example, to minimize intermingling of data from multiple processes writing to the same error log. doesn't even make sense to me. Preventing intermingling requires passing a chunk of data in a single write call, flush doesn't seem to matter. So I interpret it as a PEP bug, which happens some times

stefanvanburen · 2026-04-17T13:12:49Z

+    class RaisingHaberdasher(Haberdasher):
+        def make_similar_hats(
+            self, request: Size, ctx: RequestContext
+        ) -> AsyncIterator[Hat]:


nit: should this be NoReturn typed? (also not async def)

stefanvanburen · 2026-04-17T13:13:06Z

+    class RaisingHaberdasher(Haberdasher):
+        def make_similar_hats(
+            self, request: Size, ctx: RequestContext
+        ) -> AsyncIterator[Hat]:


same nit as above

stefanvanburen · 2026-04-17T13:14:38Z

  "Typing :: Typed",
 ]
-dependencies = ["protobuf>=5.28", "pyqwest>=0.4.1"]
+dependencies = ["protobuf>=5.28", "pyqwest>=0.5.1"]


assuming we need this for https://github.com/curioswitch/pyqwest/releases/tag/v0.5.1:

WSGI testing transport registers and exposes wsgi.errors to allow testing handlers that use it

Assuming the transparent wheel change in https://github.com/curioswitch/pyqwest/releases/tag/v0.5.0 doesn't need to be called out on our end?

I don't think so - we never really called out the native aspect clearly before I think, at least in compatibility terms. The perf aspect is probably too much detail on the consumer side (it's pretty small)

stefanvanburen

lgtm after force-push w/ DCO

anuraaga requested a review from a team April 17, 2026 02:38

anuraaga force-pushed the reraise-exception-asgi branch from fa73a27 to 73b011d Compare April 17, 2026 02:40

anuraaga added 2 commits April 17, 2026 11:58

Reraise non-connect exceptions in ASGI

3e0e886

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

Don't reraise for HTTP exception

485b5d9

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

anuraaga force-pushed the reraise-exception-asgi branch from 73b011d to 485b5d9 Compare April 17, 2026 03:02

WSGI

373f9f1

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

anuraaga changed the title ~~Reraise non-connect exceptions in ASGI~~ Surface non-Connect handler exceptions to user Apr 17, 2026

anuraaga commented Apr 17, 2026

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valentimarco reviewed Apr 17, 2026

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stefanvanburen approved these changes Apr 17, 2026

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Surface non-Connect handler exceptions to user#219

Surface non-Connect handler exceptions to user#219
anuraaga wants to merge 4 commits intoconnectrpc:mainfrom
anuraaga:reraise-exception-asgi

anuraaga commented Apr 17, 2026 •

edited

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anuraaga commented Apr 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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anuraaga commented Apr 17, 2026 •

edited

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