Stabilize support for MSC3970: updated transaction semantics (scope to `device_id`) (#15629)

For now this maintains compatible with old Synapses by falling back
to using transaction semantics on a per-access token. A future version
of Synapse will drop support for this.

1 files changed, 6 insertions, 6 deletions

diff --git a/synapse/rest/client/transactions.py b/synapse/rest/client/transactions.py
index 0d8a63d8be..3d814c404d 100644
--- a/synapse/rest/client/transactions.py
+++ b/synapse/rest/client/transactions.py
@@ -50,8 +50,6 @@ class HttpTransactionCache:
         # for at *LEAST* 30 mins, and at *MOST* 60 mins.
         self.cleaner = self.clock.looping_call(self._cleanup, CLEANUP_PERIOD_MS)
 
-        self._msc3970_enabled = hs.config.experimental.msc3970_enabled
-
     def _get_transaction_key(self, request: IRequest, requester: Requester) -> Hashable:
         """A helper function which returns a transaction key that can be used
         with TransactionCache for idempotent requests.
@@ -78,18 +76,20 @@ class HttpTransactionCache:
         elif requester.app_service is not None:
             return (path, "appservice", requester.app_service.id)
 
-        # With MSC3970, we use the user ID and device ID as the transaction key
-        elif self._msc3970_enabled:
+        # Use the user ID and device ID as the transaction key.
+        elif requester.device_id:
             assert requester.user, "Requester must have a user"
             assert requester.device_id, "Requester must have a device_id"
             return (path, "user", requester.user, requester.device_id)
 
-        # Otherwise, the pre-MSC3970 behaviour is to use the access token ID
+        # Some requsters don't have device IDs, these are mostly handled above
+        # (appservice and guest users), but does not cover access tokens minted
+        # by the admin API. Use the access token ID instead.
         else:
             assert (
                 requester.access_token_id is not None
             ), "Requester must have an access_token_id"
-            return (path, "user", requester.access_token_id)
+            return (path, "user_admin", requester.access_token_id)
 
     def fetch_or_execute_request(
         self,