Make StreamToken and RoomStreamToken methods propagate cancellations

changelog.d/12366.misc

@@ -0,0 +1 @@
+Make `StreamToken.from_string` and `RoomStreamToken.parse` propagate cancellations instead of replacing them with `SynapseError`s.

synapse/types.py

@@ -39,6 +39,7 @@
 from unpaddedbase64 import decode_base64
 from zope.interface import Interface
 
+from twisted.internet.defer import CancelledError
 from twisted.internet.interfaces import (
     IReactorCore,
     IReactorPluggableNameResolver,
@@ -516,6 +517,8 @@ async def parse(cls, store: "PurgeEventsStore", string: str) -> "RoomStreamToken
                     stream=stream,
                     instance_map=frozendict(instance_map),
                 )
+        except CancelledError:
+            raise
         except Exception:
             pass
         raise SynapseError(400, "Invalid room stream token %r" % (string,))
@@ -631,6 +634,8 @@ async def from_string(cls, store: "DataStore", string: str) -> "StreamToken":
             return cls(
                 await RoomStreamToken.parse(store, keys[0]), *(int(k) for k in keys[1:])
             )
+        except CancelledError:
+            raise
         except Exception:
             raise SynapseError(400, "Invalid stream token")