perf: skip the WebSocket handshake probe without an Upgrade header

docs/adr/0002-scope-follows-the-handshake-probe.md

@@ -7,7 +7,8 @@ Both connection providers bind `web.Request`
 passing the chosen provider to `integrations.bind` for the child's scope and context. The probe is
 aiohttp's own handshake check rather than a reimplementation that can drift from it: on a fresh
 response object it cannot raise, it is synchronous, and it neither consumes the request nor starts
-the handshake. dishka's `Connection == "Upgrade"` header comparison was rejected as brittle, missing
+the handshake. The probe is skipped when the request has no `Upgrade` header, because aiohttp's
+handshake rejects that case first, so the outcome is the same without the probe's cost. dishka's `Connection == "Upgrade"` header comparison was rejected as brittle, missing
 the legal `keep-alive, Upgrade` form and casing variants, and dispatching on the route was
 unavailable because scope selection runs before routing has produced a handler. The boundary is that
 scope follows the handshake headers and nothing else, so a request advertising a valid upgrade to a

modern_di_aiohttp/main.py

@@ -5,7 +5,7 @@
 import typing
 
 import aiohttp.abc
-from aiohttp import web
+from aiohttp import hdrs, web
 from modern_di import Container, Scope, integrations, providers
 
 
@@ -64,9 +64,8 @@ async def _di_middleware(
     # bind `web.Request`, so `integrations.classify_connection`'s isinstance
     # dispatch can't tell them apart — this probe is what picks the provider;
     # `integrations.bind` only derives the scope+context once it's picked.
-    provider = (
-        aiohttp_websocket_provider if web.WebSocketResponse().can_prepare(request).ok else aiohttp_request_provider
-    )
+    is_websocket = hdrs.UPGRADE in request.headers and web.WebSocketResponse().can_prepare(request).ok
+    provider = aiohttp_websocket_provider if is_websocket else aiohttp_request_provider
     match = integrations.bind(provider, request)
     async with fetch_di_container(request.app).build_child_container(
         scope=match.scope, context=match.context

tests/test_middleware.py

@@ -1,7 +1,9 @@
 import collections.abc
 import gc
 import http
+from unittest import mock
 
+import pytest
 from aiohttp import web
 from aiohttp.test_utils import TestClient
 from modern_di import Container, Scope
@@ -26,6 +28,22 @@ async def endpoint(request: web.Request) -> web.Response:
     assert (await client.get("/")).status == http.HTTPStatus.OK
 
 
+async def test_a_request_without_an_upgrade_header_skips_the_handshake_probe(
+    aiohttp_client: AiohttpClient, app: web.Application, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    async def endpoint(request: web.Request) -> web.Response:
+        assert request[_CONTAINER_REQUEST_KEY].scope is Scope.REQUEST
+        return web.Response(text="ok")
+
+    app.router.add_get("/", endpoint)
+    client = await aiohttp_client(app)
+    websocket_response = mock.Mock(wraps=web.WebSocketResponse)
+    monkeypatch.setattr(web, "WebSocketResponse", websocket_response)
+
+    assert (await client.get("/")).status == http.HTTPStatus.OK
+    assert websocket_response.call_count == 0
+
+
 async def test_middleware_opens_session_scoped_child_for_websocket(
     aiohttp_client: AiohttpClient, app: web.Application
 ) -> None: