From bf022b390ee97172d20c0f554b87868d0ef4d938 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Tue, 17 Sep 2024 17:22:28 +0200
Subject: [PATCH] Cache construction of middleware handlers (#9158)

---
 CHANGES/9158.misc.rst        |  3 +++
 aiohttp/web_app.py           | 25 +++++++++++++++++++------
 tests/test_web_middleware.py | 22 ++++++++++++++--------
 3 files changed, 36 insertions(+), 14 deletions(-)
 create mode 100644 CHANGES/9158.misc.rst

diff --git a/CHANGES/9158.misc.rst b/CHANGES/9158.misc.rst
new file mode 100644
index 00000000000..8d87623c056
--- /dev/null
+++ b/CHANGES/9158.misc.rst
@@ -0,0 +1,3 @@
+Significantly improved performance of middlewares -- by :user:`bdraco`.
+
+The construction of the middleware wrappers is now cached and is built once per handler instead of on every request.
diff --git a/aiohttp/web_app.py b/aiohttp/web_app.py
index 516d5e619b5..dd13ea00714 100644
--- a/aiohttp/web_app.py
+++ b/aiohttp/web_app.py
@@ -1,7 +1,7 @@
 import asyncio
 import logging
 import warnings
-from functools import partial, update_wrapper
+from functools import cache, partial, update_wrapper
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -16,6 +16,7 @@
     MutableMapping,
     Optional,
     Sequence,
+    Tuple,
     Type,
     TypeVar,
     Union,
@@ -30,7 +31,7 @@
 from . import hdrs
 from .helpers import AppKey
 from .log import web_logger
-from .typedefs import Middleware
+from .typedefs import Handler, Middleware
 from .web_exceptions import NotAppKeyWarning
 from .web_middlewares import _fix_request_current_app
 from .web_request import Request
@@ -69,6 +70,18 @@
 _Resource = TypeVar("_Resource", bound=AbstractResource)
 
 
+@cache
+def _build_middlewares(
+    handler: Handler, apps: Tuple["Application", ...]
+) -> Callable[[Request], Awaitable[StreamResponse]]:
+    """Apply middlewares to handler."""
+    for app in apps:
+        assert app.pre_frozen, "middleware handlers are not ready"
+        for m in app._middlewares_handlers:
+            handler = update_wrapper(partial(m, handler=handler), handler)
+    return handler
+
+
 @final
 class Application(MutableMapping[Union[str, AppKey[Any]], Any]):
     __slots__ = (
@@ -186,6 +199,9 @@ def __len__(self) -> int:
     def __iter__(self) -> Iterator[Union[str, AppKey[Any]]]:
         return iter(self._state)
 
+    def __hash__(self) -> int:
+        return id(self)
+
     @overload  # type: ignore[override]
     def get(self, key: AppKey[_T], default: None = ...) -> Optional[_T]: ...
 
@@ -380,10 +396,7 @@ async def _handle(self, request: Request) -> StreamResponse:
             handler = match_info.handler
 
             if self._run_middlewares:
-                for app in match_info.apps[::-1]:
-                    assert app.pre_frozen, "middleware handlers are not ready"
-                    for m in app._middlewares_handlers:
-                        handler = update_wrapper(partial(m, handler=handler), handler)
+                handler = _build_middlewares(handler, match_info.apps[::-1])
 
             resp = await handler(request)
 
diff --git a/tests/test_web_middleware.py b/tests/test_web_middleware.py
index 1e5b75ce2f6..57f4670c8fa 100644
--- a/tests/test_web_middleware.py
+++ b/tests/test_web_middleware.py
@@ -23,10 +23,13 @@ async def middleware(request, handler: Handler):
     app.middlewares.append(middleware)
     app.router.add_route("GET", "/", handler)
     client = await aiohttp_client(app)
-    resp = await client.get("/")
-    assert 201 == resp.status
-    txt = await resp.text()
-    assert "OK[MIDDLEWARE]" == txt
+
+    # Call twice to verify cache works
+    for _ in range(2):
+        resp = await client.get("/")
+        assert 201 == resp.status
+        txt = await resp.text()
+        assert "OK[MIDDLEWARE]" == txt
 
 
 async def test_middleware_handles_exception(loop: Any, aiohttp_client: Any) -> None:
@@ -42,10 +45,13 @@ async def middleware(request, handler: Handler):
     app.middlewares.append(middleware)
     app.router.add_route("GET", "/", handler)
     client = await aiohttp_client(app)
-    resp = await client.get("/")
-    assert 501 == resp.status
-    txt = await resp.text()
-    assert "Error text[MIDDLEWARE]" == txt
+
+    # Call twice to verify cache works
+    for _ in range(2):
+        resp = await client.get("/")
+        assert 501 == resp.status
+        txt = await resp.text()
+        assert "Error text[MIDDLEWARE]" == txt
 
 
 async def test_middleware_chain(loop: Any, aiohttp_client: Any) -> None: