Add a /replication API for extracting the updates that happened on

synapse

This is necessary for replicating the data in synapse to be visible to a
separate service because presence and typing notifications aren't stored
in a database so won't be visible to another process.

This API can be used to either get the raw data by requesting the tables
themselves or to just receive notifications for updates by following the
streams meta-stream.

Returns updates for each table requested a JSON array of arrays with a
row for each row in the table.

Each table is prefixed by a header row with the: name of the table,
current stream_id position for the table, number of rows, number of
columns and the names of the columns.
This is followed by the rows that have been added to the server since
the requester last asked.

The API has a timeout and is hooked up to the notifier so that a slave
can long poll for updates.

synapse/storage/tags.py

@@ -58,6 +58,59 @@ class TagsStore(SQLBaseStore):
 
         return deferred
 
+    @defer.inlineCallbacks
+    def get_all_updated_tags(self, last_id, current_id, limit):
+        """Get all the client tags that have changed on the server
+        Args:
+            last_id(int): The position to fetch from.
+            current_id(int): The position to fetch up to.
+        Returns:
+            A deferred list of tuples of stream_id int, user_id string,
+            room_id string, tag string and content string.
+        """
+        def get_all_updated_tags_txn(txn):
+            sql = (
+                "SELECT stream_id, user_id, room_id"
+                " FROM room_tags_revisions as r"
+                " WHERE ? < stream_id AND stream_id <= ?"
+                " ORDER BY stream_id ASC LIMIT ?"
+            )
+            txn.execute(sql, (last_id, current_id, limit))
+            return txn.fetchall()
+
+        tag_ids = yield self.runInteraction(
+            "get_all_updated_tags", get_all_updated_tags_txn
+        )
+
+        def get_tag_content(txn, tag_ids):
+            sql = (
+                "SELECT tag, content"
+                " FROM room_tags"
+                " WHERE user_id=? AND room_id=?"
+            )
+            results = []
+            for stream_id, user_id, room_id in tag_ids:
+                txn.execute(sql, (user_id, room_id))
+                tags = []
+                for tag, content in txn.fetchall():
+                    tags.append(json.dumps(tag) + ":" + content)
+                tag_json = "{" + ",".join(tags) + "}"
+                results.append((stream_id, user_id, room_id, tag_json))
+
+            return results
+
+        batch_size = 50
+        results = []
+        for i in xrange(0, len(tag_ids), batch_size):
+            tags = yield self.runInteraction(
+                "get_all_updated_tag_content",
+                get_tag_content,
+                tag_ids[i:i + batch_size],
+            )
+            results.extend(tags)
+
+        defer.returnValue(results)
+
     @defer.inlineCallbacks
     def get_updated_tags(self, user_id, stream_id):
         """Get all the tags for the rooms where the tags have changed since the