1 files changed, 18 insertions, 15 deletions
diff --git a/synapse/replication/tcp/protocol.py b/synapse/replication/tcp/protocol.py
index e0b4ad314d..825900f64c 100644
--- a/synapse/replication/tcp/protocol.py
+++ b/synapse/replication/tcp/protocol.py
@@ -46,7 +46,6 @@ indicate which side is sending, these are *not* included on the wire::
     > ERROR server stopping
     * connection closed by server *
 """
-import abc
 import fcntl
 import logging
 import struct
@@ -54,8 +53,10 @@ from inspect import isawaitable
 from typing import TYPE_CHECKING, List, Optional
 
 from prometheus_client import Counter
+from zope.interface import Interface, implementer
 
 from twisted.internet import task
+from twisted.internet.tcp import Connection
 from twisted.protocols.basic import LineOnlyReceiver
 from twisted.python.failure import Failure
 
@@ -121,6 +122,14 @@ class ConnectionStates:
     CLOSED = "closed"
 
 
+class IReplicationConnection(Interface):
+    """An interface for replication connections."""
+
+    def send_command(cmd: Command):
+        """Send the command down the connection"""
+
+
+@implementer(IReplicationConnection)
 class BaseReplicationStreamProtocol(LineOnlyReceiver):
     """Base replication protocol shared between client and server.
 
@@ -137,6 +146,10 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
     (if they send a `PING` command)
     """
 
+    # The transport is going to be an ITCPTransport, but that doesn't have the
+    # (un)registerProducer methods, those are only on the implementation.
+    transport = None  # type: Connection
+
     delimiter = b"\n"
 
     # Valid commands we expect to receive
@@ -181,6 +194,7 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
 
         connected_connections.append(self)  # Register connection for metrics
 
+        assert self.transport is not None
         self.transport.registerProducer(self, True)  # For the *Producing callbacks
 
         self._send_pending_commands()
@@ -205,6 +219,7 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
                 logger.info(
                     "[%s] Failed to close connection gracefully, aborting", self.id()
                 )
+                assert self.transport is not None
                 self.transport.abortConnection()
         else:
             if now - self.last_sent_command >= PING_TIME:
@@ -294,6 +309,7 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
     def close(self):
         logger.warning("[%s] Closing connection", self.id())
         self.time_we_closed = self.clock.time_msec()
+        assert self.transport is not None
         self.transport.loseConnection()
         self.on_connection_closed()
 
@@ -391,6 +407,7 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
     def connectionLost(self, reason):
         logger.info("[%s] Replication connection closed: %r", self.id(), reason)
         if isinstance(reason, Failure):
+            assert reason.type is not None
             connection_close_counter.labels(reason.type.__name__).inc()
         else:
             connection_close_counter.labels(reason.__class__.__name__).inc()
@@ -495,20 +512,6 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
         self.send_command(ReplicateCommand())
 
 
-class AbstractConnection(abc.ABC):
-    """An interface for replication connections."""
-
-    @abc.abstractmethod
-    def send_command(self, cmd: Command):
-        """Send the command down the connection"""
-        pass
-
-
-# This tells python that `BaseReplicationStreamProtocol` implements the
-# interface.
-AbstractConnection.register(BaseReplicationStreamProtocol)
-
-
 # The following simply registers metrics for the replication connections
 
 pending_commands = LaterGauge(