From 1e202a90f15a8f518e4350075d40d0423b64318d Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Mon, 11 Nov 2019 16:26:53 +0000
Subject: [PATCH] Implement v2 API for send_leave

---
 synapse/federation/federation_client.py | 41 ++++++++++++++++++++++---
 synapse/federation/transport/client.py  | 20 +++++++++++-
 2 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 4a8e65c292..289017b2ed 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -879,17 +879,50 @@ class FederationClient(FederationBase):
         @defer.inlineCallbacks
         def send_request(destination):
             time_now = self._clock.time_msec()
-            _, content = yield self.transport_layer.send_leave(
+            content = yield self._do_send_leave(destination, pdu)
+
+            logger.debug("Got content: %s", content)
+            return None
+
+        return self._try_destination_list("send_leave", destinations, send_request)
+
+    @defer.inlineCallbacks
+    def _do_send_leave(self, destination, pdu):
+        time_now = self._clock.time_msec()
+
+        try:
+            content = yield self.transport_layer.send_leave_v2(
                 destination=destination,
                 room_id=pdu.room_id,
                 event_id=pdu.event_id,
                 content=pdu.get_pdu_json(time_now),
             )
 
-            logger.debug("Got content: %s", content)
-            return None
+            return content
+        except HttpResponseException as e:
+            if e.code in [400, 404]:
+                err = e.to_synapse_error()
 
-        return self._try_destination_list("send_leave", destinations, send_request)
+                # If we receive an error response that isn't a generic error, or an
+                # unrecognised endpoint error, we  assume that the remote understands
+                # the v2 invite API and this is a legitimate error.
+                if not err.errcode in [Codes.UNKNOWN, Codes.UNRECOGNIZED]:
+                    raise err
+            else:
+                raise e.to_synapse_error()
+
+        logger.debug("Couldn't send_leave with the v2 API, falling back to the v1 API")
+
+        resp = yield self.transport_layer.send_leave_v1(
+            destination=destination,
+            room_id=pdu.room_id,
+            event_id=pdu.event_id,
+            content=pdu.get_pdu_json(time_now),
+        )
+
+        # We expect the v1 API to respond with [200, content], so we only return the
+        # content.
+        return resp[1]
 
     def get_public_rooms(
         self,
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index ba68f7c0b4..df2b5dc91b 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -289,7 +289,7 @@ class TransportLayerClient(object):
 
     @defer.inlineCallbacks
     @log_function
-    def send_leave(self, destination, room_id, event_id, content):
+    def send_leave_v1(self, destination, room_id, event_id, content):
         path = _create_v1_path("/send_leave/%s/%s", room_id, event_id)
 
         response = yield self.client.put_json(
@@ -305,6 +305,24 @@ class TransportLayerClient(object):
 
         return response
 
+    @defer.inlineCallbacks
+    @log_function
+    def send_leave_v2(self, destination, room_id, event_id, content):
+        path = _create_v2_path("/send_leave/%s/%s", room_id, event_id)
+
+        response = yield self.client.put_json(
+            destination=destination,
+            path=path,
+            data=content,
+            # we want to do our best to send this through. The problem is
+            # that if it fails, we won't retry it later, so if the remote
+            # server was just having a momentary blip, the room will be out of
+            # sync.
+            ignore_backoff=True,
+        )
+
+        return response
+
     @defer.inlineCallbacks
     @log_function
     def send_invite_v1(self, destination, room_id, event_id, content):