Add MSC4040 matrix-fed service lookups (#16137)

scripts-dev/federation_client.py

@@ -329,6 +329,17 @@ class MatrixConnectionAdapter(HTTPAdapter):
                 raise ValueError("Invalid host:port '%s'" % (server_name,))
             return out[0], port, out[0]
 
+        # Look up SRV for Matrix 1.8 `matrix-fed` service first
+        try:
+            srv = srvlookup.lookup("matrix-fed", "tcp", server_name)[0]
+            print(
+                f"SRV lookup on _matrix-fed._tcp.{server_name} gave {srv}",
+                file=sys.stderr,
+            )
+            return srv.host, srv.port, server_name
+        except Exception:
+            pass
+        # Fall back to deprecated `matrix` service
         try:
             srv = srvlookup.lookup("matrix", "tcp", server_name)[0]
             print(
@@ -337,6 +348,7 @@ class MatrixConnectionAdapter(HTTPAdapter):
             )
             return srv.host, srv.port, server_name
         except Exception:
+            # Fall even further back to just port 8448
             return server_name, 8448, server_name
 
     @staticmethod