Support federation in the new spaces summary API (MSC2946). (#10569)

3 files changed, 132 insertions, 0 deletions

diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 2eefac04fd..0af953a5d6 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -1290,6 +1290,88 @@ class FederationClient(FederationBase):
             failover_on_unknown_endpoint=True,
         )
 
+    async def get_room_hierarchy(
+        self,
+        destinations: Iterable[str],
+        room_id: str,
+        suggested_only: bool,
+    ) -> Tuple[JsonDict, Sequence[JsonDict], Sequence[str]]:
+        """
+        Call other servers to get a hierarchy of the given room.
+
+        Performs simple data validates and parsing of the response.
+
+        Args:
+            destinations: The remote servers. We will try them in turn, omitting any
+                that have been blacklisted.
+            room_id: ID of the space to be queried
+            suggested_only:  If true, ask the remote server to only return children
+                with the "suggested" flag set
+
+        Returns:
+            A tuple of:
+                The room as a JSON dictionary.
+                A list of children rooms, as JSON dictionaries.
+                A list of inaccessible children room IDs.
+
+        Raises:
+            SynapseError if we were unable to get a valid summary from any of the
+               remote servers
+        """
+
+        async def send_request(
+            destination: str,
+        ) -> Tuple[JsonDict, Sequence[JsonDict], Sequence[str]]:
+            res = await self.transport_layer.get_room_hierarchy(
+                destination=destination,
+                room_id=room_id,
+                suggested_only=suggested_only,
+            )
+
+            room = res.get("room")
+            if not isinstance(room, dict):
+                raise InvalidResponseError("'room' must be a dict")
+
+            # Validate children_state of the room.
+            children_state = room.get("children_state", [])
+            if not isinstance(children_state, Sequence):
+                raise InvalidResponseError("'room.children_state' must be a list")
+            if any(not isinstance(e, dict) for e in children_state):
+                raise InvalidResponseError("Invalid event in 'children_state' list")
+            try:
+                [
+                    FederationSpaceSummaryEventResult.from_json_dict(e)
+                    for e in children_state
+                ]
+            except ValueError as e:
+                raise InvalidResponseError(str(e))
+
+            # Validate the children rooms.
+            children = res.get("children", [])
+            if not isinstance(children, Sequence):
+                raise InvalidResponseError("'children' must be a list")
+            if any(not isinstance(r, dict) for r in children):
+                raise InvalidResponseError("Invalid room in 'children' list")
+
+            # Validate the inaccessible children.
+            inaccessible_children = res.get("inaccessible_children", [])
+            if not isinstance(inaccessible_children, Sequence):
+                raise InvalidResponseError("'inaccessible_children' must be a list")
+            if any(not isinstance(r, str) for r in inaccessible_children):
+                raise InvalidResponseError(
+                    "Invalid room ID in 'inaccessible_children' list"
+                )
+
+            return room, children, inaccessible_children
+
+        # TODO Fallback to the old federation API and translate the results.
+        return await self._try_destination_list(
+            "fetch room hierarchy",
+            destinations,
+            send_request,
+            failover_on_unknown_endpoint=True,
+        )
+
 
 @attr.s(frozen=True, slots=True, auto_attribs=True)
 class FederationSpaceSummaryEventResult:
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 90a7c16b62..8b247fe206 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -1177,6 +1177,28 @@ class TransportLayerClient:
             destination=destination, path=path, data=params
         )
 
+    async def get_room_hierarchy(
+        self,
+        destination: str,
+        room_id: str,
+        suggested_only: bool,
+    ) -> JsonDict:
+        """
+        Args:
+            destination: The remote server
+            room_id: The room ID to ask about.
+            suggested_only: if True, only suggested rooms will be returned
+        """
+        path = _create_path(
+            FEDERATION_UNSTABLE_PREFIX, "/org.matrix.msc2946/hierarchy/%s", room_id
+        )
+
+        return await self.client.get_json(
+            destination=destination,
+            path=path,
+            args={"suggested_only": "true" if suggested_only else "false"},
+        )
+
 
 def _create_path(federation_prefix: str, path: str, *args: str) -> str:
     """
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index 640f46fff6..79a2e1afa0 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -1936,6 +1936,33 @@ class FederationSpaceSummaryServlet(BaseFederationServlet):
         )
 
 
+class FederationRoomHierarchyServlet(BaseFederationServlet):
+    PREFIX = FEDERATION_UNSTABLE_PREFIX + "/org.matrix.msc2946"
+    PATH = "/hierarchy/(?P<room_id>[^/]*)"
+
+    def __init__(
+        self,
+        hs: HomeServer,
+        authenticator: Authenticator,
+        ratelimiter: FederationRateLimiter,
+        server_name: str,
+    ):
+        super().__init__(hs, authenticator, ratelimiter, server_name)
+        self.handler = hs.get_space_summary_handler()
+
+    async def on_GET(
+        self,
+        origin: str,
+        content: Literal[None],
+        query: Mapping[bytes, Sequence[bytes]],
+        room_id: str,
+    ) -> Tuple[int, JsonDict]:
+        suggested_only = parse_boolean_from_args(query, "suggested_only", default=False)
+        return 200, await self.handler.get_federation_hierarchy(
+            origin, room_id, suggested_only
+        )
+
+
 class RoomComplexityServlet(BaseFederationServlet):
     """
     Indicates to other servers how complex (and therefore likely
@@ -1999,6 +2026,7 @@ FEDERATION_SERVLET_CLASSES: Tuple[Type[BaseFederationServlet], ...] = (
     FederationVersionServlet,
     RoomComplexityServlet,
     FederationSpaceSummaryServlet,
+    FederationRoomHierarchyServlet,
     FederationV1SendKnockServlet,
     FederationMakeKnockServlet,
 )