Fix domain matching being lower priority than path matching (#11673)

Author: Dreamsorcerer

CHANGES/11673.bugfix.rst

@@ -0,0 +1,2 @@
+Fixed routing to a sub-application added via ``.add_domain()`` not working
+if the same path exists on the parent app. -- by :user:`Dreamsorcerer`.

aiohttp/web_urldispatcher.py

@@ -977,6 +977,21 @@ async def resolve(self, request: Request) -> UrlMappingMatchInfo:
         resource_index = self._resource_index
         allowed_methods: set[str] = set()
 
+        # MatchedSubAppResource is primarily used to match on domain names
+        # (though custom rules could match on other things). This means that
+        # the traversal algorithm below can't be applied, and that we likely
+        # need to check these first so a sub app that defines the same path
+        # as a parent app will get priority if there's a domain match.
+        #
+        # For most cases we do not expect there to be many of these since
+        # currently they are only added by `.add_domain()`.
+        for resource in self._matched_sub_app_resources:
+            match_dict, allowed = await resource.resolve(request)
+            if match_dict is not None:
+                return match_dict
+            else:
+                allowed_methods |= allowed
+
         # Walk the url parts looking for candidates. We walk the url backwards
         # to ensure the most explicit match is found first. If there are multiple
         # candidates for a given url part because there are multiple resources
@@ -994,21 +1009,6 @@ async def resolve(self, request: Request) -> UrlMappingMatchInfo:
                 break
             url_part = url_part.rpartition("/")[0] or "/"
 
-        #
-        # We didn't find any candidates, so we'll try the matched sub-app
-        # resources which we have to walk in a linear fashion because they
-        # have regex/wildcard match rules and we cannot index them.
-        #
-        # For most cases we do not expect there to be many of these since
-        # currently they are only added by `add_domain`
-        #
-        for resource in self._matched_sub_app_resources:
-            match_dict, allowed = await resource.resolve(request)
-            if match_dict is not None:
-                return match_dict
-            else:
-                allowed_methods |= allowed
-
         if allowed_methods:
             return MatchInfoError(HTTPMethodNotAllowed(request.method, allowed_methods))
 

docs/web_reference.rst

@@ -1539,6 +1539,14 @@ Application and Router
       matches the pattern *domain* then
       further resolving is passed to *subapp*.
 
+      .. warning::
+
+         Registering many domains using this method may cause performance
+         issues with handler routing. If you have a substantial number of
+         applications for different domains, you may want to consider
+         using a reverse proxy (such as Nginx) to handle routing to
+         different apps, rather that registering them as sub-applications.
+
       :param str domain: domain or mask of domain for the resource.
 
       :param Application subapp: nested application.

tests/test_web_urldispatcher.py

@@ -951,8 +951,8 @@ async def get(self) -> web.Response:
         assert r.status == 200
 
 
-@pytest.mark.xfail(reason="https://github.com/aio-libs/aiohttp/issues/11665")
 async def test_subapp_domain_routing_same_path(aiohttp_client: AiohttpClient) -> None:
+    """Regression test for #11665."""
     app = web.Application()
     sub_app = web.Application()