Do not allow MSC3440 threads to fork threads (#11161)

Adds validation to the Client-Server API to ensure that
the potential thread head does not relate to another event
already. This results in not allowing a thread to "fork" into
other threads.

If the target event is unknown for some reason (maybe it isn't
visible to your homeserver), but is the target of other events
it is assumed that the thread can be created from it. Otherwise,
it is rejected as an unknown event.

1 files changed, 62 insertions, 0 deletions

diff --git a/tests/rest/client/test_relations.py b/tests/rest/client/test_relations.py
index 78c2fb86b9..b8a1b92a89 100644
--- a/tests/rest/client/test_relations.py
+++ b/tests/rest/client/test_relations.py
@@ -91,6 +91,49 @@ class RelationsTestCase(unittest.HomeserverTestCase):
         channel = self._send_relation(RelationTypes.ANNOTATION, EventTypes.Member)
         self.assertEquals(400, channel.code, channel.json_body)
 
+    def test_deny_invalid_event(self):
+        """Test that we deny relations on non-existant events"""
+        channel = self._send_relation(
+            RelationTypes.ANNOTATION,
+            EventTypes.Message,
+            parent_id="foo",
+            content={"body": "foo", "msgtype": "m.text"},
+        )
+        self.assertEquals(400, channel.code, channel.json_body)
+
+        # Unless that event is referenced from another event!
+        self.get_success(
+            self.hs.get_datastore().db_pool.simple_insert(
+                table="event_relations",
+                values={
+                    "event_id": "bar",
+                    "relates_to_id": "foo",
+                    "relation_type": RelationTypes.THREAD,
+                },
+                desc="test_deny_invalid_event",
+            )
+        )
+        channel = self._send_relation(
+            RelationTypes.THREAD,
+            EventTypes.Message,
+            parent_id="foo",
+            content={"body": "foo", "msgtype": "m.text"},
+        )
+        self.assertEquals(200, channel.code, channel.json_body)
+
+    def test_deny_invalid_room(self):
+        """Test that we deny relations on non-existant events"""
+        # Create another room and send a message in it.
+        room2 = self.helper.create_room_as(self.user_id, tok=self.user_token)
+        res = self.helper.send(room2, body="Hi!", tok=self.user_token)
+        parent_id = res["event_id"]
+
+        # Attempt to send an annotation to that event.
+        channel = self._send_relation(
+            RelationTypes.ANNOTATION, "m.reaction", parent_id=parent_id, key="A"
+        )
+        self.assertEquals(400, channel.code, channel.json_body)
+
     def test_deny_double_react(self):
         """Test that we deny relations on membership events"""
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", key="a")
@@ -99,6 +142,25 @@ class RelationsTestCase(unittest.HomeserverTestCase):
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")
         self.assertEquals(400, channel.code, channel.json_body)
 
+    def test_deny_forked_thread(self):
+        """It is invalid to start a thread off a thread."""
+        channel = self._send_relation(
+            RelationTypes.THREAD,
+            "m.room.message",
+            content={"msgtype": "m.text", "body": "foo"},
+            parent_id=self.parent_id,
+        )
+        self.assertEquals(200, channel.code, channel.json_body)
+        parent_id = channel.json_body["event_id"]
+
+        channel = self._send_relation(
+            RelationTypes.THREAD,
+            "m.room.message",
+            content={"msgtype": "m.text", "body": "foo"},
+            parent_id=parent_id,
+        )
+        self.assertEquals(400, channel.code, channel.json_body)
+
     def test_basic_paginate_relations(self):
         """Tests that calling pagination API correctly the latest relations."""
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")