Remove no-op send_command for Redis replication. (#15274)

With Redis commands do not need to be re-issued by the main
process (they fan-out to all processes at once) and thus it is no
longer necessary to worry about them reflecting recursively forever.

4 files changed, 3 insertions, 89 deletions

diff --git a/changelog.d/15272.misc b/changelog.d/15272.misc
index 7a3ef323e9..f7c0276ecc 100644
--- a/changelog.d/15272.misc
+++ b/changelog.d/15272.misc
@@ -1 +1 @@
-Remove unused class `DirectTcpReplicationClientFactory`.
+Clean-up direct TCP replication code.
diff --git a/changelog.d/15274.misc b/changelog.d/15274.misc
new file mode 100644
index 0000000000..f7c0276ecc
--- /dev/null
+++ b/changelog.d/15274.misc
@@ -0,0 +1 @@
+Clean-up direct TCP replication code.
diff --git a/synapse/replication/tcp/handler.py b/synapse/replication/tcp/handler.py
index d03a53d764..2290b3e6fe 100644
--- a/synapse/replication/tcp/handler.py
+++ b/synapse/replication/tcp/handler.py
@@ -625,23 +625,6 @@ class ReplicationCommandHandler:
 
         self._notifier.notify_remote_server_up(cmd.data)
 
-        # We relay to all other connections to ensure every instance gets the
-        # notification.
-        #
-        # When configured to use redis we'll always only have one connection and
-        # so this is a no-op (all instances will have already received the same
-        # REMOTE_SERVER_UP command).
-        #
-        # For direct TCP connections this will relay to all other connections
-        # connected to us. When on master this will correctly fan out to all
-        # other direct TCP clients and on workers there'll only be the one
-        # connection to master.
-        #
-        # (The logic here should also be sound if we have a mix of Redis and
-        # direct TCP connections so long as there is only one traffic route
-        # between two instances, but that is not currently supported).
-        self.send_command(cmd, ignore_conn=conn)
-
     def new_connection(self, connection: IReplicationConnection) -> None:
         """Called when we have a new connection."""
         self._connections.append(connection)
@@ -689,21 +672,14 @@ class ReplicationCommandHandler:
         """
         return bool(self._connections)
 
-    def send_command(
-        self, cmd: Command, ignore_conn: Optional[IReplicationConnection] = None
-    ) -> None:
+    def send_command(self, cmd: Command) -> None:
         """Send a command to all connected connections.
 
         Args:
             cmd
-            ignore_conn: If set don't send command to the given connection.
-                Used when relaying commands from one connection to all others.
         """
         if self._connections:
             for connection in self._connections:
-                if connection == ignore_conn:
-                    continue
-
                 try:
                     connection.send_command(cmd)
                 except Exception:
diff --git a/tests/replication/tcp/test_remote_server_up.py b/tests/replication/tcp/test_remote_server_up.py
deleted file mode 100644
index b75fc05fd5..0000000000
--- a/tests/replication/tcp/test_remote_server_up.py
+++ /dev/null
@@ -1,63 +0,0 @@
-# Copyright 2020 The Matrix.org Foundation C.I.C.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from typing import Tuple
-
-from twisted.internet.address import IPv4Address
-from twisted.internet.interfaces import IProtocol
-from twisted.test.proto_helpers import MemoryReactor, StringTransport
-
-from synapse.replication.tcp.resource import ReplicationStreamProtocolFactory
-from synapse.server import HomeServer
-from synapse.util import Clock
-
-from tests.unittest import HomeserverTestCase
-
-
-class RemoteServerUpTestCase(HomeserverTestCase):
-    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
-        self.factory = ReplicationStreamProtocolFactory(hs)
-
-    def _make_client(self) -> Tuple[IProtocol, StringTransport]:
-        """Create a new direct TCP replication connection"""
-
-        proto = self.factory.buildProtocol(IPv4Address("TCP", "127.0.0.1", 0))
-        transport = StringTransport()
-        proto.makeConnection(transport)
-
-        # We can safely ignore the commands received during connection.
-        self.pump()
-        transport.clear()
-
-        return proto, transport
-
-    def test_relay(self) -> None:
-        """Test that Synapse will relay REMOTE_SERVER_UP commands to all
-        other connections, but not the one that sent it.
-        """
-
-        proto1, transport1 = self._make_client()
-
-        # We shouldn't receive an echo.
-        proto1.dataReceived(b"REMOTE_SERVER_UP example.com\n")
-        self.pump()
-        self.assertEqual(transport1.value(), b"")
-
-        # But we should see an echo if we connect another client
-        proto2, transport2 = self._make_client()
-        proto1.dataReceived(b"REMOTE_SERVER_UP example.com\n")
-
-        self.pump()
-        self.assertEqual(transport1.value(), b"")
-        self.assertEqual(transport2.value(), b"REMOTE_SERVER_UP example.com\n")