Return JSON errors for unknown resources under /matrix/client. (#11602)

Instead of returning 404 errors with HTML bodies when an unknown
prefix was requested (e.g. /matrix/client/v1 before Synapse v1.49.0).

changelog.d/11602.bugfix

@@ -0,0 +1 @@
+Fix a long-standing bug that some unknown endpoints would return HTML error pages instead of JSON `M_UNRECOGNIZED` errors.

synapse/app/homeserver.py

@@ -27,6 +27,7 @@ import synapse
 import synapse.config.logger
 from synapse import events
 from synapse.api.urls import (
+    CLIENT_API_PREFIX,
     FEDERATION_PREFIX,
     LEGACY_MEDIA_PREFIX,
     MEDIA_R0_PREFIX,
@@ -192,13 +193,7 @@ class SynapseHomeServer(HomeServer):
 
             resources.update(
                 {
-                    "/_matrix/client/api/v1": client_resource,
-                    "/_matrix/client/r0": client_resource,
-                    "/_matrix/client/v1": client_resource,
-                    "/_matrix/client/v3": client_resource,
-                    "/_matrix/client/unstable": client_resource,
-                    "/_matrix/client/v2_alpha": client_resource,
-                    "/_matrix/client/versions": client_resource,
+                    CLIENT_API_PREFIX: client_resource,
                     "/.well-known": well_known_resource(self),
                     "/_synapse/admin": AdminRestResource(self),
                     **build_synapse_client_resource_tree(self),

synapse/http/server.py

@@ -530,7 +530,7 @@ class RootRedirect(resource.Resource):
     """Redirects the root '/' path to another path."""
 
     def __init__(self, path: str):
-        resource.Resource.__init__(self)
+        super().__init__()
         self.url = path
 
     def render_GET(self, request: Request) -> bytes:
@@ -539,7 +539,7 @@ class RootRedirect(resource.Resource):
     def getChild(self, name: str, request: Request) -> resource.Resource:
         if len(name) == 0:
             return self  # select ourselves as the child to render
-        return resource.Resource.getChild(self, name, request)
+        return super().getChild(name, request)
 
 
 class OptionsResource(resource.Resource):
@@ -556,7 +556,7 @@ class OptionsResource(resource.Resource):
     def getChildWithDefault(self, path: str, request: Request) -> resource.Resource:
         if request.method == b"OPTIONS":
             return self  # select ourselves as the child to render
-        return resource.Resource.getChildWithDefault(self, path, request)
+        return super().getChildWithDefault(path, request)
 
 
 class RootOptionsRedirectResource(OptionsResource, RootRedirect):