Add MSC4040 matrix-fed service lookups (#16137)

matrix-org · Sep 5, 2023 · b1d71c6 · b1d71c6
1 parent c9cec2d
commit b1d71c6
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Showing 4 changed files with 331 additions and 34 deletions.
diff --git a/changelog.d/16137.feature b/changelog.d/16137.feature
@@ -0,0 +1 @@
+Support resolving homeservers using `matrix-fed` DNS SRV records from [MSC4040](https://github.com/matrix-org/matrix-spec-proposals/pull/4040).
diff --git a/scripts-dev/federation_client.py b/scripts-dev/federation_client.py
@@ -329,6 +329,17 @@ def _lookup(server_name: str) -> Tuple[str, int, str]:
                 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 @@ def _lookup(server_name: str) -> Tuple[str, int, str]:
             )
             return srv.host, srv.port, server_name
         except Exception:
+            # Fall even further back to just port 8448
             return server_name, 8448, server_name
 
     @staticmethod

diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
@@ -399,15 +399,34 @@ async def _resolve_server(self) -> List[Server]:
         if port or _is_ip_literal(host):
             return [Server(host, port or 8448)]
 
+        # Check _matrix-fed._tcp SRV record.
         logger.debug("Looking up SRV record for %s", host.decode(errors="replace"))
+        server_list = await self._srv_resolver.resolve_service(
+            b"_matrix-fed._tcp." + host
+        )
+
+        if server_list:
+            if logger.isEnabledFor(logging.DEBUG):
+                logger.debug(
+                    "Got %s from SRV lookup for %s",
+                    ", ".join(map(str, server_list)),
+                    host.decode(errors="replace"),
+                )
+            return server_list
+
+        # No _matrix-fed._tcp SRV record, fallback to legacy _matrix._tcp SRV record.
+        logger.debug(
+            "Looking up deprecated SRV record for %s", host.decode(errors="replace")
+        )
         server_list = await self._srv_resolver.resolve_service(b"_matrix._tcp." + host)
 
         if server_list:
-            logger.debug(
-                "Got %s from SRV lookup for %s",
-                ", ".join(map(str, server_list)),
-                host.decode(errors="replace"),
-            )
+            if logger.isEnabledFor(logging.DEBUG):
+                logger.debug(
+                    "Got %s from deprecated SRV lookup for %s",
+                    ", ".join(map(str, server_list)),
+                    host.decode(errors="replace"),
+                )
             return server_list
 
         # No SRV records, so we fallback to host and 8448