Include the original event in /relations (#5626)

When asking for the relations of an event, include the original event in the response. This will mostly be used for efficiently showing edit history, but could be useful in other circumstances.

4 files changed, 12 insertions, 4 deletions

diff --git a/changelog.d/5626.feature b/changelog.d/5626.feature
new file mode 100644
index 0000000000..5ef793b943
--- /dev/null
+++ b/changelog.d/5626.feature
@@ -0,0 +1 @@
+Include the original event when asking for its relations.
diff --git a/synapse/rest/client/v2_alpha/relations.py b/synapse/rest/client/v2_alpha/relations.py
index 8e362782cc..458afd135f 100644
--- a/synapse/rest/client/v2_alpha/relations.py
+++ b/synapse/rest/client/v2_alpha/relations.py
@@ -145,9 +145,9 @@ class RelationPaginationServlet(RestServlet):
             room_id, requester.user.to_string()
         )
 
-        # This checks that a) the event exists and b) the user is allowed to
-        # view it.
-        yield self.event_handler.get_event(requester.user, room_id, parent_id)
+        # This gets the original event and checks that a) the event exists and
+        # b) the user is allowed to view it.
+        event = yield self.event_handler.get_event(requester.user, room_id, parent_id)
 
         limit = parse_integer(request, "limit", default=5)
         from_token = parse_string(request, "from")
@@ -173,10 +173,12 @@ class RelationPaginationServlet(RestServlet):
         )
 
         now = self.clock.time_msec()
+        original_event = yield self._event_serializer.serialize_event(event, now)
         events = yield self._event_serializer.serialize_events(events, now)
 
         return_value = result.to_dict()
         return_value["chunk"] = events
+        return_value["original_event"] = original_event
 
         defer.returnValue((200, return_value))
 
diff --git a/synapse/storage/relations.py b/synapse/storage/relations.py
index 1b01934c19..9954bc094f 100644
--- a/synapse/storage/relations.py
+++ b/synapse/storage/relations.py
@@ -60,7 +60,7 @@ class PaginationChunk(object):
 class RelationPaginationToken(object):
     """Pagination token for relation pagination API.
 
-    As the results are order by topological ordering, we can use the
+    As the results are in topological order, we can use the
     `topological_ordering` and `stream_ordering` fields of the events at the
     boundaries of the chunk as pagination tokens.
 
diff --git a/tests/rest/client/v2_alpha/test_relations.py b/tests/rest/client/v2_alpha/test_relations.py
index 6bb7d92638..58c6951852 100644
--- a/tests/rest/client/v2_alpha/test_relations.py
+++ b/tests/rest/client/v2_alpha/test_relations.py
@@ -126,6 +126,11 @@ class RelationsTestCase(unittest.HomeserverTestCase):
             channel.json_body["chunk"][0],
         )
 
+        # We also expect to get the original event (the id of which is self.parent_id)
+        self.assertEquals(
+            channel.json_body["original_event"]["event_id"], self.parent_id
+        )
+
         # Make sure next_batch has something in it that looks like it could be a
         # valid token.
         self.assertIsInstance(