Further improvements to requesting the public rooms list on a homeserver which has it set to private (#7368)

changelog.d/7368.bugfix

@@ -0,0 +1 @@
+Improve error responses when accessing remote public room lists.

synapse/federation/federation_client.py

@@ -883,18 +883,37 @@ class FederationClient(FederationBase):
 
     def get_public_rooms(
         self,
-        destination,
-        limit=None,
-        since_token=None,
-        search_filter=None,
-        include_all_networks=False,
-        third_party_instance_id=None,
+        remote_server: str,
+        limit: Optional[int] = None,
+        since_token: Optional[str] = None,
+        search_filter: Optional[Dict] = None,
+        include_all_networks: bool = False,
+        third_party_instance_id: Optional[str] = None,
     ):
-        if destination == self.server_name:
-            return
+        """Get the list of public rooms from a remote homeserver
 
+        Args:
+            remote_server: The name of the remote server
+            limit: Maximum amount of rooms to return
+            since_token: Used for result pagination
+            search_filter: A filter dictionary to send the remote homeserver
+                and filter the result set
+            include_all_networks: Whether to include results from all third party instances
+            third_party_instance_id: Whether to only include results from a specific third
+                party instance
+
+        Returns:
+            Deferred[Dict[str, Any]]: The response from the remote server, or None if
+            `remote_server` is the same as the local server_name
+
+        Raises:
+            HttpResponseException: There was an exception returned from the remote server
+            SynapseException: M_FORBIDDEN when the remote server has disallowed publicRoom
+                requests over federation
+
+        """
         return self.transport_layer.get_public_rooms(
-            destination,
+            remote_server,
             limit,
             since_token,
             search_filter,

synapse/federation/transport/client.py

@@ -15,13 +15,14 @@
 # limitations under the License.
 
 import logging
-from typing import Any, Dict
+from typing import Any, Dict, Optional
 
 from six.moves import urllib
 
 from twisted.internet import defer
 
 from synapse.api.constants import Membership
+from synapse.api.errors import Codes, HttpResponseException, SynapseError
 from synapse.api.urls import (
     FEDERATION_UNSTABLE_PREFIX,
     FEDERATION_V1_PREFIX,
@@ -326,18 +327,25 @@ class TransportLayerClient(object):
     @log_function
     def get_public_rooms(
         self,
-        remote_server,
-        limit,
-        since_token,
-        search_filter=None,
-        include_all_networks=False,
-        third_party_instance_id=None,
+        remote_server: str,
+        limit: Optional[int] = None,
+        since_token: Optional[str] = None,
+        search_filter: Optional[Dict] = None,
+        include_all_networks: bool = False,
+        third_party_instance_id: Optional[str] = None,
     ):
+        """Get the list of public rooms from a remote homeserver
+
+        See synapse.federation.federation_client.FederationClient.get_public_rooms for
+        more information.
+        """
         if search_filter:
             # this uses MSC2197 (Search Filtering over Federation)
             path = _create_v1_path("/publicRooms")
 
-            data = {"include_all_networks": "true" if include_all_networks else "false"}
+            data = {
+                "include_all_networks": "true" if include_all_networks else "false"
+            }  # type: Dict[str, Any]
             if third_party_instance_id:
                 data["third_party_instance_id"] = third_party_instance_id
             if limit:
@@ -347,9 +355,19 @@ class TransportLayerClient(object):
 
             data["filter"] = search_filter
 
+            try:
                 response = yield self.client.post_json(
                     destination=remote_server, path=path, data=data, ignore_backoff=True
                 )
+            except HttpResponseException as e:
+                if e.code == 403:
+                    raise SynapseError(
+                        403,
+                        "You are not allowed to view the public rooms list of %s"
+                        % (remote_server,),
+                        errcode=Codes.FORBIDDEN,
+                    )
+                raise
         else:
             path = _create_v1_path("/publicRooms")
 
@@ -363,9 +381,19 @@ class TransportLayerClient(object):
             if since_token:
                 args["since"] = [since_token]
 
+            try:
                 response = yield self.client.get_json(
                     destination=remote_server, path=path, args=args, ignore_backoff=True
                 )
+            except HttpResponseException as e:
+                if e.code == 403:
+                    raise SynapseError(
+                        403,
+                        "You are not allowed to view the public rooms list of %s"
+                        % (remote_server,),
+                        errcode=Codes.FORBIDDEN,
+                    )
+                raise
 
         return response