Add timestamp lookup API

synapse/rest/client/v1/room.py

@@ -830,6 +830,30 @@ class JoinedRoomsRestServlet(ClientV1RestServlet):
         defer.returnValue((200, {"joined_rooms": list(room_ids)}))
 
 
+class TimestampLookupRestServlet(ClientV1RestServlet):
+    PATTERNS = client_path_patterns("/rooms/(?P<room_id>[^/]*)/timestamp_to_event$")
+
+    def __init__(self, hs):
+        super(TimestampLookupRestServlet, self).__init__(hs)
+        self.store = hs.get_datastore()
+
+    @defer.inlineCallbacks
+    def on_GET(self, request, room_id):
+        requester = yield self.auth.get_user_by_req(request)
+        yield self.auth.check_joined_room(room_id, requester.user.to_string())
+
+        timestamp = parse_integer(request, "ts")
+        thread_id = parse_integer(request, "thread_id", 0)
+
+        event_id = yield self.store.get_event_for_timestamp(
+            room_id, thread_id, timestamp,
+        )
+
+        defer.returnValue((200, {
+            "event_id": event_id,
+        }))
+
+
 def register_txn_path(servlet, regex_string, http_server, with_get=False):
     """Registers a transaction-based path.
 
@@ -879,6 +903,7 @@ def register_servlets(hs, http_server):
     JoinedRoomsRestServlet(hs).register(http_server)
     RoomEventServlet(hs).register(http_server)
     RoomEventContextServlet(hs).register(http_server)
+    TimestampLookupRestServlet(hs).register(http_server)
 
 
 def register_deprecated_servlets(hs, http_server):

synapse/storage/events_worker.py

@@ -528,3 +528,43 @@ class EventsWorkerStore(SQLBaseStore):
             return res
 
         return self.runInteraction("get_rejection_reasons", f)
+
+    def get_event_for_timestamp(self, room_id, thread_id, timestamp):
+        sql_template = """
+            SELECT event_id, origin_server_ts FROM events
+            WHERE
+                origin_server_ts %s ?
+                AND room_id = ?
+                AND thread_id = ?
+            ORDER BY origin_server_ts
+            LIMIT 1;
+        """
+
+        def f(txn):
+            txn.execute(sql_template % ("<=",), (timestamp, room_id, thread_id))
+            row = txn.fetchone()
+            if row:
+                event_id_before, ts_before = row
+            else:
+                event_id_before, ts_before = None, None
+
+            txn.execute(sql_template % (">=",), (timestamp, room_id, thread_id))
+            row = txn.fetchone()
+            if row:
+                event_id_after, ts_after = row
+            else:
+                event_id_after, ts_after = None, None
+
+            if event_id_before and event_id_before:
+                # Return the closest one
+                if (timestamp - ts_before) < (ts_after - timestamp):
+                    return event_id_before
+                else:
+                    return event_id_after
+
+            if event_id_before:
+                return event_id_before
+
+            return event_id_after
+
+        return self.runInteraction("get_event_for_timestamp", f)

synapse/storage/schema/delta/52/add_threa_index.sql

@@ -0,0 +1,16 @@
+/* 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.
+ */
+
+CREATE INDEX event_room_thread_ts ON events (room_id, thread_id, origin_server_ts);