Fix FastAPI issue with APIRoute subclasses #3681
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Fixes: open-telemetry#3671 When an APIRoute subclass would overwrite the matches method with an implementation that depended on non-standard fields existing on the HTTP connection scope, this would cause a failure when the OpenTelemetryMiddleware tried to get the default span details for the incoming request. This has been fixed by using the matches implementation on the Route class for any subclass of Route. This should be sufficient since the only information we are trying to get from that method is the path for the request.
This commit adds tests that illustrate the original issue that was being experienced for custom api route implementations when they depended on non-standard fields existing on the ASGI HTTP connection scope. Before the fix was implemented, the inclusion of a custom API route in the FastAPI application would cause an exception to be raised inside the OpenTelemetryMiddleware since the non-standard fields do not exist on the ASGI HTTP connection scope until after the subsequent middleware runs and adds the expected fields.
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emdneto
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Oct 2, 2025
| custom API routers that depend on non-standard fields on the ASGI scope. | ||
| """ | ||
| resp = self._client.get("/custom-router/success") | ||
| self.assertEqual(resp.status_code, 200) |
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Can you assert spans and it's attributes as well?
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I added some asserts for spans and it's attributes.
| match, _ = starlette_route.matches(scope) | ||
| match, _ = ( | ||
| Route.matches(starlette_route, scope) | ||
| if isinstance(starlette_route, Route) |
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This will be true for almost everything no? Maybe check if type(starlette_route).matches is Route.matches
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It's been a while since I wrote this so I forget why I did this specifically. I would have thought that your suggestion would work but when I made that change and ran the test suite, it appears that that change makes several tests fail.
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Description
When an APIRoute subclass would overwrite the matches method with an implementation that depended on non-standard fields existing on the HTTP connection scope, this would cause a failure when the OpenTelemetryMiddleware tried to get the default span details for the incoming request. This has been fixed by using the matches implementation on the Route class for any subclass of Route. This should be sufficient since the only information we are trying to get from that method is the path for the request.
Fixes #3671
Type of change
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How Has This Been Tested?
This has been validated with automated tests that are included in this pull request.
Does This PR Require a Core Repo Change?
Checklist:
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