Move client command handling out of TCP protocol (#7185)

The aim here is to move the command handling out of the TCP protocol classes and to also merge the client and server command handling (so that we can reuse them for redis protocol). This PR simply moves the client paths to the new `ReplicationCommandHandler`, a future PR will move the server paths too.

1 files changed, 31 insertions, 166 deletions

diff --git a/synapse/replication/tcp/protocol.py b/synapse/replication/tcp/protocol.py
index dae246825f..f2a37f568e 100644
--- a/synapse/replication/tcp/protocol.py
+++ b/synapse/replication/tcp/protocol.py
@@ -46,12 +46,11 @@ 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
 from collections import defaultdict
-from typing import Any, DefaultDict, Dict, List, Set
+from typing import TYPE_CHECKING, DefaultDict, List
 
 from six import iteritems
 
@@ -78,13 +77,12 @@ from synapse.replication.tcp.commands import (
     SyncCommand,
     UserSyncCommand,
 )
-from synapse.replication.tcp.streams import STREAMS_MAP, Stream
 from synapse.types import Collection
 from synapse.util import Clock
 from synapse.util.stringutils import random_string
 
-MYPY = False
-if MYPY:
+if TYPE_CHECKING:
+    from synapse.replication.tcp.handler import ReplicationCommandHandler
     from synapse.server import HomeServer
 
 
@@ -475,71 +473,6 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
         self.streamer.lost_connection(self)
 
 
-class AbstractReplicationClientHandler(metaclass=abc.ABCMeta):
-    """
-    The interface for the handler that should be passed to
-    ClientReplicationStreamProtocol
-    """
-
-    @abc.abstractmethod
-    async def on_rdata(self, stream_name, token, rows):
-        """Called to handle a batch of replication data with a given stream token.
-
-        Args:
-            stream_name (str): name of the replication stream for this batch of rows
-            token (int): stream token for this batch of rows
-            rows (list): a list of Stream.ROW_TYPE objects as returned by
-                Stream.parse_row.
-        """
-        raise NotImplementedError()
-
-    @abc.abstractmethod
-    async def on_position(self, stream_name, token):
-        """Called when we get new position data."""
-        raise NotImplementedError()
-
-    @abc.abstractmethod
-    def on_sync(self, data):
-        """Called when get a new SYNC command."""
-        raise NotImplementedError()
-
-    @abc.abstractmethod
-    async def on_remote_server_up(self, server: str):
-        """Called when get a new REMOTE_SERVER_UP command."""
-        raise NotImplementedError()
-
-    @abc.abstractmethod
-    def get_streams_to_replicate(self):
-        """Called when a new connection has been established and we need to
-        subscribe to streams.
-
-        Returns:
-            map from stream name to the most recent update we have for
-            that stream (ie, the point we want to start replicating from)
-        """
-        raise NotImplementedError()
-
-    @abc.abstractmethod
-    def get_currently_syncing_users(self):
-        """Get the list of currently syncing users (if any). This is called
-        when a connection has been established and we need to send the
-        currently syncing users."""
-        raise NotImplementedError()
-
-    @abc.abstractmethod
-    def update_connection(self, connection):
-        """Called when a connection has been established (or lost with None).
-        """
-        raise NotImplementedError()
-
-    @abc.abstractmethod
-    def finished_connecting(self):
-        """Called when we have successfully subscribed and caught up to all
-        streams we're interested in.
-        """
-        raise NotImplementedError()
-
-
 class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
     VALID_INBOUND_COMMANDS = VALID_SERVER_COMMANDS
     VALID_OUTBOUND_COMMANDS = VALID_CLIENT_COMMANDS
@@ -550,7 +483,7 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
         client_name: str,
         server_name: str,
         clock: Clock,
-        handler: AbstractReplicationClientHandler,
+        command_handler: "ReplicationCommandHandler",
     ):
         BaseReplicationStreamProtocol.__init__(self, clock)
 
@@ -558,20 +491,7 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
 
         self.client_name = client_name
         self.server_name = server_name
-        self.handler = handler
-
-        self.streams = {
-            stream.NAME: stream(hs) for stream in STREAMS_MAP.values()
-        }  # type: Dict[str, Stream]
-
-        # Set of stream names that have been subscribe to, but haven't yet
-        # caught up with. This is used to track when the client has been fully
-        # connected to the remote.
-        self.streams_connecting = set(STREAMS_MAP)  # type: Set[str]
-
-        # Map of stream to batched updates. See RdataCommand for info on how
-        # batching works.
-        self.pending_batches = {}  # type: Dict[str, List[Any]]
+        self.handler = command_handler
 
     def connectionMade(self):
         self.send_command(NameCommand(self.client_name))
@@ -589,89 +509,39 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
 
         # We've now finished connecting to so inform the client handler
         self.handler.update_connection(self)
+        self.handler.finished_connecting()
 
-    async def on_SERVER(self, cmd):
-        if cmd.data != self.server_name:
-            logger.error("[%s] Connected to wrong remote: %r", self.id(), cmd.data)
-            self.send_error("Wrong remote")
-
-    async def on_RDATA(self, cmd):
-        stream_name = cmd.stream_name
-        inbound_rdata_count.labels(stream_name).inc()
-
-        try:
-            row = STREAMS_MAP[stream_name].parse_row(cmd.row)
-        except Exception:
-            logger.exception(
-                "[%s] Failed to parse RDATA: %r %r", self.id(), stream_name, cmd.row
-            )
-            raise
-
-        if cmd.token is None or stream_name in self.streams_connecting:
-            # I.e. this is part of a batch of updates for this stream. Batch
-            # until we get an update for the stream with a non None token
-            self.pending_batches.setdefault(stream_name, []).append(row)
-        else:
-            # Check if this is the last of a batch of updates
-            rows = self.pending_batches.pop(stream_name, [])
-            rows.append(row)
-            await self.handler.on_rdata(stream_name, cmd.token, rows)
-
-    async def on_POSITION(self, cmd: PositionCommand):
-        stream = self.streams.get(cmd.stream_name)
-        if not stream:
-            logger.error("Got POSITION for unknown stream: %s", cmd.stream_name)
-            return
-
-        # Find where we previously streamed up to.
-        current_token = self.handler.get_streams_to_replicate().get(cmd.stream_name)
-        if current_token is None:
-            logger.warning(
-                "Got POSITION for stream we're not subscribed to: %s", cmd.stream_name
-            )
-            return
-
-        # Fetch all updates between then and now.
-        limited = True
-        while limited:
-            updates, current_token, limited = await stream.get_updates_since(
-                current_token, cmd.token
-            )
-
-            # Check if the connection was closed underneath us, if so we bail
-            # rather than risk having concurrent catch ups going on.
-            if self.state == ConnectionStates.CLOSED:
-                return
-
-            if updates:
-                await self.handler.on_rdata(
-                    cmd.stream_name,
-                    current_token,
-                    [stream.parse_row(update[1]) for update in updates],
-                )
+    async def handle_command(self, cmd: Command):
+        """Handle a command we have received over the replication stream.
 
-        # We've now caught up to position sent to us, notify handler.
-        await self.handler.on_position(cmd.stream_name, cmd.token)
+        Delegates to `command_handler.on_<COMMAND>`, which must return an
+        awaitable.
 
-        self.streams_connecting.discard(cmd.stream_name)
-        if not self.streams_connecting:
-            self.handler.finished_connecting()
+        Args:
+            cmd: received command
+        """
+        handled = False
 
-        # Check if the connection was closed underneath us, if so we bail
-        # rather than risk having concurrent catch ups going on.
-        if self.state == ConnectionStates.CLOSED:
-            return
+        # First call any command handlers on this instance. These are for TCP
+        # specific handling.
+        cmd_func = getattr(self, "on_%s" % (cmd.NAME,), None)
+        if cmd_func:
+            await cmd_func(cmd)
+            handled = True
 
-        # Handle any RDATA that came in while we were catching up.
-        rows = self.pending_batches.pop(cmd.stream_name, [])
-        if rows:
-            await self.handler.on_rdata(cmd.stream_name, rows[-1].token, rows)
+        # Then call out to the handler.
+        cmd_func = getattr(self.handler, "on_%s" % (cmd.NAME,), None)
+        if cmd_func:
+            await cmd_func(cmd)
+            handled = True
 
-    async def on_SYNC(self, cmd):
-        self.handler.on_sync(cmd.data)
+        if not handled:
+            logger.warning("Unhandled command: %r", cmd)
 
-    async def on_REMOTE_SERVER_UP(self, cmd: RemoteServerUpCommand):
-        self.handler.on_remote_server_up(cmd.data)
+    async def on_SERVER(self, cmd):
+        if cmd.data != self.server_name:
+            logger.error("[%s] Connected to wrong remote: %r", self.id(), cmd.data)
+            self.send_error("Wrong remote")
 
     def replicate(self):
         """Send the subscription request to the server
@@ -768,8 +638,3 @@ tcp_outbound_commands = LaterGauge(
         for k, count in iteritems(p.outbound_commands_counter)
     },
 )
-
-# number of updates received for each RDATA stream
-inbound_rdata_count = Counter(
-    "synapse_replication_tcp_protocol_inbound_rdata_count", "", ["stream_name"]
-)