Respect the `@cancellable` flag for `RestServlet`s and `BaseFederationServlet`s (#12699)

Both `RestServlet`s and `BaseFederationServlet`s register their handlers
with `HttpServer.register_paths` / `JsonResource.register_paths`. Update
`JsonResource` to respect the `@cancellable` flag on handlers registered
in this way.

Although `ReplicationEndpoint` also registers itself using
`register_paths`, it does not pass the handler method that would have the
`@cancellable` flag directly, and so needs separate handling.

Signed-off-by: Sean Quah <seanq@element.io>

1 files changed, 5 insertions, 0 deletions

diff --git a/synapse/http/server.py b/synapse/http/server.py
index f6d4d8db86..756c6e1aee 100644
--- a/synapse/http/server.py
+++ b/synapse/http/server.py
@@ -314,6 +314,9 @@ class HttpServer(Protocol):
         If the regex contains groups these gets passed to the callback via
         an unpacked tuple.
 
+        The callback may be marked with the `@cancellable` decorator, which will
+        cause request processing to be cancelled when clients disconnect early.
+
         Args:
             method: The HTTP method to listen to.
             path_patterns: The regex used to match requests.
@@ -544,6 +547,8 @@ class JsonResource(DirectServeJsonResource):
     async def _async_render(self, request: SynapseRequest) -> Tuple[int, Any]:
         callback, servlet_classname, group_dict = self._get_handler_for_request(request)
 
+        request.is_render_cancellable = is_method_cancellable(callback)
+
         # Make sure we have an appropriate name for this handler in prometheus
         # (rather than the default of JsonResource).
         request.request_metrics.name = servlet_classname