Fix Starlette/FastAPI middleware for non-http scopes (#1187)

* Don't raise exceptions on non-http scopes

Instead just don't process non-http scopes

* CHANGELOG

* Add missing return

* Add a websocket test to exercise non-http scope

Author: basepi

CHANGELOG.asciidoc

@@ -30,6 +30,20 @@ endif::[]
 //===== Bug fixes
 //
 
+=== Unreleased
+
+// Unreleased changes go here
+// When the next release happens, nest these changes under the "Python Agent version 6.x" heading
+[float]
+===== Features
+
+
+[float]
+===== Bug fixes
+
+* Fix handling of non-http scopes in Starlette/FastAPI middleware {pull}1187[#1187]
+
+
 [[release-notes-6.x]]
 === Python Agent version 6.x
 

elasticapm/contrib/starlette/__init__.py

@@ -130,9 +130,10 @@ async def __call__(self, scope, receive, send):
             receive: receive awaitable callable
             send: send awaitable callable
         """
-        # we only handle the http scope, raise an exception for anything else
-        # see https://www.uvicorn.org/#the-asgi-interface
-        assert scope["type"] == "http"
+        # we only handle the http scope, skip anything else.
+        if scope["type"] != "http":
+            await self.app(scope, receive, send)
+            return
 
         @functools.wraps(send)
         async def wrapped_send(message):

tests/contrib/asyncio/starlette_tests.py

@@ -104,6 +104,12 @@ async def hi_from_sub(request):
     async def hi_from_sub(request):
         return PlainTextResponse(request.path_params["name"])
 
+    @app.websocket_route("/ws")
+    async def ws(websocket):
+        await websocket.accept()
+        await websocket.send_text("Hello, world!")
+        await websocket.close()
+
     app.add_middleware(ElasticAPM, client=elasticapm_client)
 
     yield app
@@ -457,3 +463,12 @@ def test_make_client_without_config():
         c = make_apm_client(client_cls=TempStoreClient)
         c.close()
         assert c.config.service_name == "foo"
+
+
+def test_websocket(app, elasticapm_client):
+    client = TestClient(app)
+    with client.websocket_connect("/ws") as websocket:
+        data = websocket.receive_text()
+        assert data == "Hello, world!"
+
+    assert len(elasticapm_client.events[constants.TRANSACTION]) == 0