From c16e192e2f9970cc62adfd758034244631968102 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Tue, 5 Nov 2019 15:49:43 +0000
Subject: [PATCH] Fix caching devices for remote servers in worker.

When the `/keys/query` API is hit on client_reader worker Synapse may
decide that it needs to resync some remote deivces. Usually this happens
on master, and then gets cached. However, that fails on workers and so
it falls back to fetching devices from remotes directly, which may in
turn fail if the remote is down.
---
 synapse/handlers/e2e_keys.py         | 19 ++++++--
 synapse/replication/http/__init__.py | 10 +++-
 synapse/replication/http/devices.py  | 69 ++++++++++++++++++++++++++++
 3 files changed, 94 insertions(+), 4 deletions(-)
 create mode 100644 synapse/replication/http/devices.py

diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index f09a0b73c8..28c12753c1 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -30,6 +30,7 @@ from twisted.internet import defer
 from synapse.api.errors import CodeMessageException, Codes, NotFoundError, SynapseError
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.logging.opentracing import log_kv, set_tag, tag_args, trace
+from synapse.replication.http.devices import ReplicationUserDevicesResyncRestServlet
 from synapse.types import (
     UserID,
     get_domain_from_id,
@@ -53,6 +54,12 @@ class E2eKeysHandler(object):
 
         self._edu_updater = SigningKeyEduUpdater(hs, self)
 
+        self._is_master = hs.config.worker_app is None
+        if not self._is_master:
+            self._user_device_resync_client = ReplicationUserDevicesResyncRestServlet.make_client(
+                hs
+            )
+
         federation_registry = hs.get_federation_registry()
 
         # FIXME: switch to m.signing_key_update when MSC1756 is merged into the spec
@@ -191,9 +198,15 @@ class E2eKeysHandler(object):
                 # probably be tracking their device lists. However, we haven't
                 # done an initial sync on the device list so we do it now.
                 try:
-                    user_devices = yield self.device_handler.device_list_updater.user_device_resync(
-                        user_id
-                    )
+                    if self._is_master:
+                        user_devices = yield self.device_handler.device_list_updater.user_device_resync(
+                            user_id
+                        )
+                    else:
+                        user_devices = yield self._user_device_resync_client(
+                            user_id=user_id
+                        )
+
                     user_devices = user_devices["devices"]
                     for device in user_devices:
                         results[user_id] = {device["device_id"]: device["keys"]}
diff --git a/synapse/replication/http/__init__.py b/synapse/replication/http/__init__.py
index 81b85352b1..28dbc6fcba 100644
--- a/synapse/replication/http/__init__.py
+++ b/synapse/replication/http/__init__.py
@@ -14,7 +14,14 @@
 # limitations under the License.
 
 from synapse.http.server import JsonResource
-from synapse.replication.http import federation, login, membership, register, send_event
+from synapse.replication.http import (
+    devices,
+    federation,
+    login,
+    membership,
+    register,
+    send_event,
+)
 
 REPLICATION_PREFIX = "/_synapse/replication"
 
@@ -30,3 +37,4 @@ class ReplicationRestResource(JsonResource):
         federation.register_servlets(hs, self)
         login.register_servlets(hs, self)
         register.register_servlets(hs, self)
+        devices.register_servlets(hs, self)
diff --git a/synapse/replication/http/devices.py b/synapse/replication/http/devices.py
new file mode 100644
index 0000000000..795ca7b65e
--- /dev/null
+++ b/synapse/replication/http/devices.py
@@ -0,0 +1,69 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# 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.
+
+import logging
+
+from synapse.replication.http._base import ReplicationEndpoint
+
+logger = logging.getLogger(__name__)
+
+
+class ReplicationUserDevicesResyncRestServlet(ReplicationEndpoint):
+    """Notifies that a user has joined or left the room
+
+    Request format:
+
+        POST /_synapse/replication/user_device_resync/:user_id
+
+        {}
+
+    Response is equivalent to ` /_matrix/federation/v1/user/devices/:user_id`
+    response, e.g.:
+
+        {
+            "user_id": "@alice:example.org",
+            "devices": [
+                {
+                    "device_id": "JLAFKJWSCS",
+                    "keys": { ... },
+                    "device_display_name": "Alice's Mobile Phone"
+                }
+            ]
+        }
+    """
+
+    NAME = "user_device_resync"
+    PATH_ARGS = ("user_id",)
+    CACHE = False
+
+    def __init__(self, hs):
+        super(ReplicationUserDevicesResyncRestServlet, self).__init__(hs)
+
+        self.device_list_updater = hs.get_device_handler().device_list_updater
+        self.store = hs.get_datastore()
+        self.clock = hs.get_clock()
+
+    @staticmethod
+    def _serialize_payload(user_id):
+        return {}
+
+    async def _handle_request(self, request, user_id):
+        user_devices = await self.device_list_updater.user_device_resync(user_id)
+
+        return 200, user_devices
+
+
+def register_servlets(hs, http_server):
+    ReplicationUserDevicesResyncRestServlet(hs).register(http_server)