2 files changed, 60 insertions, 7 deletions
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 25ed1257f1..6e03ce21af 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -993,3 +993,39 @@ class FederationClient(FederationBase):
                 )
 
         raise RuntimeError("Failed to send to any server.")
+
+    @defer.inlineCallbacks
+    def get_room_complexity(self, destination, room_id):
+        """
+        Fetch the complexity of a remote room from another server.
+
+        Args:
+            destination (str): The remote server
+            room_id (str): The room ID to ask about.
+
+        Returns:
+            Deferred[dict] or Deferred[None]: Dict contains the complexity
+            metric versions, while None means we could not fetch the complexity.
+        """
+        try:
+            complexity = yield self.transport_layer.get_room_complexity(
+                destination=destination, room_id=room_id
+            )
+            defer.returnValue(complexity)
+        except CodeMessageException as e:
+            # We didn't manage to get it -- probably a 404. We are okay if other
+            # servers don't give it to us.
+            logger.debug(
+                "Failed to fetch room complexity via %s for %s, got a %d",
+                destination,
+                room_id,
+                e.code,
+            )
+        except Exception:
+            logger.exception(
+                "Failed to fetch room complexity via %s for %s", destination, room_id
+            )
+
+        # If we don't manage to find it, return None. It's not an error if a
+        # server doesn't give it to us.
+        defer.returnValue(None)
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 2a6709ff48..0cea0d2a10 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -21,7 +21,11 @@ from six.moves import urllib
 from twisted.internet import defer
 
 from synapse.api.constants import Membership
-from synapse.api.urls import FEDERATION_V1_PREFIX, FEDERATION_V2_PREFIX
+from synapse.api.urls import (
+    FEDERATION_UNSTABLE_PREFIX,
+    FEDERATION_V1_PREFIX,
+    FEDERATION_V2_PREFIX,
+)
 from synapse.logging.utils import log_function
 
 logger = logging.getLogger(__name__)
@@ -935,6 +939,23 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
+    def get_room_complexity(self, destination, room_id):
+        """
+        Args:
+            destination (str): The remote server
+            room_id (str): The room ID to ask about.
+        """
+        path = _create_path(FEDERATION_UNSTABLE_PREFIX, "/rooms/%s/complexity", room_id)
+
+        return self.client.get_json(destination=destination, path=path)
+
+
+def _create_path(federation_prefix, path, *args):
+    """
+    Ensures that all args are url encoded.
+    """
+    return federation_prefix + path % tuple(urllib.parse.quote(arg, "") for arg in args)
+
 
 def _create_v1_path(path, *args):
     """Creates a path against V1 federation API from the path template and
@@ -951,9 +972,7 @@ def _create_v1_path(path, *args):
     Returns:
         str
     """
-    return FEDERATION_V1_PREFIX + path % tuple(
-        urllib.parse.quote(arg, "") for arg in args
-    )
+    return _create_path(FEDERATION_V1_PREFIX, path, *args)
 
 
 def _create_v2_path(path, *args):
@@ -971,6 +990,4 @@ def _create_v2_path(path, *args):
     Returns:
         str
     """
-    return FEDERATION_V2_PREFIX + path % tuple(
-        urllib.parse.quote(arg, "") for arg in args
-    )
+    return _create_path(FEDERATION_V2_PREFIX, path, *args)