From d88421ab03e72a6c7f69ca38a57b4b6212f1bc82 Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Tue, 9 Jul 2019 13:43:08 +0100
Subject: [PATCH] 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.
---
 changelog.d/5626.feature                     | 1 +
 synapse/rest/client/v2_alpha/relations.py    | 8 +++++---
 synapse/storage/relations.py                 | 2 +-
 tests/rest/client/v2_alpha/test_relations.py | 5 +++++
 4 files changed, 12 insertions(+), 4 deletions(-)
 create mode 100644 changelog.d/5626.feature

diff --git a/changelog.d/5626.feature b/changelog.d/5626.feature
new file mode 100644
index 000000000..5ef793b94
--- /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 8e362782c..458afd135 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 1b01934c1..9954bc094 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 6bb7d9263..58c695185 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(