test(fastapi): added tests for custom api route implementation fix

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.

Author: lannuttia

instrumentation/opentelemetry-instrumentation-fastapi/tests/test_fastapi_instrumentation.py

@@ -22,7 +22,10 @@
 import fastapi
 from fastapi.middleware.httpsredirect import HTTPSRedirectMiddleware
 from fastapi.responses import JSONResponse
+from fastapi.routing import APIRoute
 from fastapi.testclient import TestClient
+from starlette.routing import Match
+from starlette.types import Receive, Scope, Send
 
 import opentelemetry.instrumentation.fastapi as otel_fastapi
 from opentelemetry import trace
@@ -38,9 +41,7 @@
 from opentelemetry.instrumentation.auto_instrumentation._load import (
     _load_instrumentors,
 )
-from opentelemetry.instrumentation.dependencies import (
-    DependencyConflict,
-)
+from opentelemetry.instrumentation.dependencies import DependencyConflict
 from opentelemetry.sdk.metrics.export import (
     HistogramDataPoint,
     NumberDataPoint,
@@ -123,6 +124,23 @@
 )
 
 
+class CustomMiddleware:
+    def __init__(self, app: fastapi.FastAPI) -> None:
+        self.app = app
+
+    async def __call__(
+        self, scope: Scope, receive: Receive, send: Send
+    ) -> None:
+        scope["nonstandard_field"] = "here"
+        await self.app(scope, receive, send)
+
+
+class CustomRoute(APIRoute):
+    def matches(self, scope: Scope) -> tuple[Match, Scope]:
+        assert "nonstandard_field" in scope
+        return super().matches(scope)
+
+
 class TestBaseFastAPI(TestBase):
     def _create_app(self):
         app = self._create_fastapi_app()
@@ -183,6 +201,7 @@ def setUp(self):
         self._instrumentor = otel_fastapi.FastAPIInstrumentor()
         self._app = self._create_app()
         self._app.add_middleware(HTTPSRedirectMiddleware)
+        self._app.add_middleware(CustomMiddleware)
         self._client = TestClient(self._app, base_url="https://testserver:443")
         # run the lifespan, initialize the middleware stack
         # this is more in-line with what happens in a real application when the server starts up
@@ -202,6 +221,7 @@ def tearDown(self):
     def _create_fastapi_app():
         app = fastapi.FastAPI()
         sub_app = fastapi.FastAPI()
+        custom_router = fastapi.APIRouter(route_class=CustomRoute)
 
         @sub_app.get("/home")
         async def _():
@@ -227,6 +247,12 @@ async def _():
         async def _():
             raise UnhandledException("This is an unhandled exception")
 
+        @custom_router.get("/success")
+        async def _():
+            return None
+
+        app.include_router(custom_router, prefix="/custom-router")
+
         app.mount("/sub", app=sub_app)
 
         return app
@@ -304,6 +330,14 @@ def test_sub_app_fastapi_call(self):
             span.attributes[HTTP_URL],
         )
 
+    def test_custom_api_router(self):
+        """
+        This test is to ensure that custom API routers the OpenTelemetryMiddleware does not cause issues with
+        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)
+
 
 class TestBaseAutoFastAPI(TestBaseFastAPI):
     @classmethod
@@ -988,6 +1022,7 @@ def test_metric_uninstrument(self):
     def _create_fastapi_app():
         app = fastapi.FastAPI()
         sub_app = fastapi.FastAPI()
+        custom_router = fastapi.APIRouter(route_class=CustomRoute)
 
         @sub_app.get("/home")
         async def _():
@@ -1013,6 +1048,12 @@ async def _():
         async def _():
             raise UnhandledException("This is an unhandled exception")
 
+        @custom_router.get("/success")
+        async def _():
+            return None
+
+        app.include_router(custom_router, prefix="/custom-router")
+
         app.mount("/sub", app=sub_app)
 
         return app