🚀 New issue to ag2ai/faststream by @Lancetnik
📝 Bug: `StreamSub` warns that `no_ack` has no effect with a consumer group, but the flag is forwarded to XREADGROUP NOACK (#3126)


Describe the bug

StreamSub(..., group=..., consumer=..., no_ack=True) emits

RuntimeWarning: `no_ack` has no effect with consumer group

but the flag does have an effect: it reaches Redis as XREADGROUP ... NOACK, so entries never enter the PEL. The warning is a leftover from a time when the flag was not forwarded.

How to reproduce

from faststream.redis import RedisBroker, StreamSub

broker = RedisBroker()


@broker.subscriber(
    stream=StreamSub("my-stream", group="my-group", consumer="c1", no_ack=True),
)
async def handler(msg: str) -> None:
    ...

Constructing the StreamSub prints the warning. Running the app shows that the flag is honoured anyway: XPENDING my-stream my-group stays empty after messages are consumed.

Expected behavior

No warning. no_ack=True with a consumer group is a supported, documented mode ("equivalent to acknowledging the message when it is read", see docs/docs/en/redis/streams/groups.md).

Observed behavior

The warning is emitted in faststream/redis/schemas/stream_sub.py (the elif no_ack: branch under if group and consumer:), while the rest of the code base treats the flag as live:

• faststream/redis/subscriber/usecases/stream_subscriber.py passes noack=stream.no_ack to XREADGROUP;
• faststream/redis/subscriber/config.py switches the subscriber to AckPolicy.MANUAL when no_ack is set;
• faststream/redis/testing.py skips the PEL for no_ack subscribers;
• #3049 added a SetupError for claim_min_idle_time + no_ack, which only makes sense if no_ack works with groups.

History

• The warning was introduced in 0.3.5 (#1048), when no_ack was indeed not forwarded to XREADGROUP.
• #2309 kept the warning and reset no_ack = False right after it, so the flag really was ignored for a while.
• 0.6.0 (#1779) dropped that reset, and noack=stream.no_ack has been sent to Redis since, but the warning stayed.

The sibling warning, "no_ack is not supported by consumer group with last_id other than >", is a separate case and should be checked on its own: Redis documents NOACK for XREADGROUP regardless of the id, so it may be stale too.

Suggested fix

Remove the elif no_ack: warning branch in StreamSub.__init__ and add a test asserting that StreamSub("s", group="g", consumer="c", no_ack=True) raises no warning and that the subscriber calls xreadgroup with noack=True. Keep the claim_min_idle_time + no_ack SetupError as is.

Environment

Reproduced on main (commit 0307f09).


#bug #good_first_issue #redis #faststream #ag2ai
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