From fb35b258ebb6c674d59cce75ddb38f463bcdc746 Mon Sep 17 00:00:00 2001
From: "Gustavo J. A. M. Carneiro" <gjcarneiro@gmail.com>
Date: Sat, 26 Oct 2019 10:08:51 +0100
Subject: [PATCH] Preserve view handler function attributes across middlewares
 (#4195)

---
 CHANGES/4174.bugfix          |  1 +
 aiohttp/web_app.py           |  6 ++--
 tests/test_web_middleware.py | 66 ++++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 2 deletions(-)
 create mode 100644 CHANGES/4174.bugfix

diff --git a/CHANGES/4174.bugfix b/CHANGES/4174.bugfix
new file mode 100644
index 00000000000..5a50eb8249f
--- /dev/null
+++ b/CHANGES/4174.bugfix
@@ -0,0 +1 @@
+Preserve view handler function attributes across middlewares
diff --git a/aiohttp/web_app.py b/aiohttp/web_app.py
index a5d5b92b49a..fe0f343746f 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
+from functools import partial, update_wrapper
 from typing import (  # noqa
     TYPE_CHECKING,
     Any,
@@ -327,7 +327,9 @@ async def _handle(self, request: Request) -> StreamResponse:
                 for app in match_info.apps[::-1]:
                     assert app.pre_frozen, "middleware handlers are not ready"
                     for m in app._middlewares_handlers:  # noqa
-                        handler = partial(m, handler=handler)
+                        handler = update_wrapper(
+                            partial(m, handler=handler), handler
+                        )
 
             resp = await handler(request)
 
diff --git a/tests/test_web_middleware.py b/tests/test_web_middleware.py
index fa434c74549..79359a46ef2 100644
--- a/tests/test_web_middleware.py
+++ b/tests/test_web_middleware.py
@@ -49,8 +49,18 @@ async def test_middleware_chain(loop, aiohttp_client) -> None:
     async def handler(request):
         return web.Response(text='OK')
 
+    handler.annotation = "annotation_value"
+
+    async def handler2(request):
+        return web.Response(text='OK')
+
+    middleware_annotation_seen_values = []
+
     def make_middleware(num):
         async def middleware(request, handler):
+            middleware_annotation_seen_values.append(
+                getattr(handler, "annotation", None)
+            )
             resp = await handler(request)
             resp.text = resp.text + '[{}]'.format(num)
             return resp
@@ -60,11 +70,67 @@ async def middleware(request, handler):
     app.middlewares.append(make_middleware(1))
     app.middlewares.append(make_middleware(2))
     app.router.add_route('GET', '/', handler)
+    app.router.add_route('GET', '/r2', handler2)
     client = await aiohttp_client(app)
     resp = await client.get('/')
     assert 200 == resp.status
     txt = await resp.text()
     assert 'OK[2][1]' == txt
+    assert middleware_annotation_seen_values == [
+        'annotation_value', 'annotation_value'
+    ]
+
+    # check that attributes from handler are not applied to handler2
+    resp = await client.get('/r2')
+    assert 200 == resp.status
+    assert middleware_annotation_seen_values == [
+        'annotation_value', 'annotation_value', None, None
+    ]
+
+
+async def test_middleware_subapp(loop, aiohttp_client) -> None:
+    async def sub_handler(request):
+        return web.Response(text='OK')
+
+    sub_handler.annotation = "annotation_value"
+
+    async def handler(request):
+        return web.Response(text='OK')
+
+    middleware_annotation_seen_values = []
+
+    def make_middleware(num):
+        async def middleware(request, handler):
+            annotation = getattr(handler, "annotation", None)
+            if annotation is not None:
+                middleware_annotation_seen_values.append(
+                    "{}/{}".format(annotation, num)
+                )
+            return await handler(request)
+        return middleware
+
+    app = web.Application()
+    app.middlewares.append(make_middleware(1))
+    app.router.add_route('GET', '/r2', handler)
+
+    subapp = web.Application()
+    subapp.middlewares.append(make_middleware(2))
+    subapp.router.add_route('GET', '/', sub_handler)
+    app.add_subapp("/sub", subapp)
+
+    client = await aiohttp_client(app)
+    resp = await client.get('/sub/')
+    assert 200 == resp.status
+    await resp.text()
+    assert middleware_annotation_seen_values == [
+        'annotation_value/1', 'annotation_value/2'
+    ]
+
+    # check that attributes from sub_handler are not applied to handler
+    del middleware_annotation_seen_values[:]
+    resp = await client.get('/r2')
+    assert 200 == resp.status
+    assert middleware_annotation_seen_values == []
 
 
 @pytest.fixture