Add support for via query parameter from MSC4156 (#17322)

This adds support for the `via` query parameter from
https://github.com/matrix-org/matrix-spec-proposals/pull/4156.

1 files changed, 8 insertions, 0 deletions

diff --git a/synapse/rest/client/room.py b/synapse/rest/client/room.py
index 61fdf71a27..c98241f6ce 100644
--- a/synapse/rest/client/room.py
+++ b/synapse/rest/client/room.py
@@ -417,6 +417,7 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, TransactionRestServlet):
         super().__init__(hs)
         super(ResolveRoomIdMixin, self).__init__(hs)  # ensure the Mixin is set up
         self.auth = hs.get_auth()
+        self._support_via = hs.config.experimental.msc4156_enabled
 
     def register(self, http_server: HttpServer) -> None:
         # /join/$room_identifier[/$txn_id]
@@ -435,6 +436,13 @@ class JoinRoomAliasServlet(ResolveRoomIdMixin, TransactionRestServlet):
         # twisted.web.server.Request.args is incorrectly defined as Optional[Any]
         args: Dict[bytes, List[bytes]] = request.args  # type: ignore
         remote_room_hosts = parse_strings_from_args(args, "server_name", required=False)
+        if self._support_via:
+            remote_room_hosts = parse_strings_from_args(
+                args,
+                "org.matrix.msc4156.via",
+                default=remote_room_hosts,
+                required=False,
+            )
         room_id, remote_room_hosts = await self.resolve_room_id(
             room_identifier,
             remote_room_hosts,