Fix `failures` property in `/keys/query` (#17499)

Fixes: https://github.com/element-hq/synapse/issues/17498
Fixes: https://github.com/element-hq/element-web/issues/27867

1 files changed, 18 insertions, 8 deletions

diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 668cec513b..f78e66ad0a 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -291,13 +291,20 @@ class E2eKeysHandler:
 
             # Only try and fetch keys for destinations that are not marked as
             # down.
-            filtered_destinations = await filter_destinations_by_retry_limiter(
-                remote_queries_not_in_cache.keys(),
-                self.clock,
-                self.store,
-                # Let's give an arbitrary grace period for those hosts that are
-                # only recently down
-                retry_due_within_ms=60 * 1000,
+            unfiltered_destinations = remote_queries_not_in_cache.keys()
+            filtered_destinations = set(
+                await filter_destinations_by_retry_limiter(
+                    unfiltered_destinations,
+                    self.clock,
+                    self.store,
+                    # Let's give an arbitrary grace period for those hosts that are
+                    # only recently down
+                    retry_due_within_ms=60 * 1000,
+                )
+            )
+            failures.update(
+                (dest, _NOT_READY_FOR_RETRY_FAILURE)
+                for dest in (unfiltered_destinations - filtered_destinations)
             )
 
             await concurrently_execute(
@@ -1641,6 +1648,9 @@ def _check_device_signature(
         raise SynapseError(400, "Invalid signature", Codes.INVALID_SIGNATURE)
 
 
+_NOT_READY_FOR_RETRY_FAILURE = {"status": 503, "message": "Not ready for retry"}
+
+
 def _exception_to_failure(e: Exception) -> JsonDict:
     if isinstance(e, SynapseError):
         return {"status": e.code, "errcode": e.errcode, "message": str(e)}
@@ -1649,7 +1659,7 @@ def _exception_to_failure(e: Exception) -> JsonDict:
         return {"status": e.code, "message": str(e)}
 
     if isinstance(e, NotRetryingDestination):
-        return {"status": 503, "message": "Not ready for retry"}
+        return _NOT_READY_FOR_RETRY_FAILURE
 
     # include ConnectionRefused and other errors
     #