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Posted to commits@airflow.apache.org by "viiccwen (via GitHub)" <gi...@apache.org> on 2026/07/20 10:37:50 UTC
[PR] Reject zero step in mapped XCom slices [airflow]
viiccwen opened a new pull request, #70124:
URL: https://github.com/apache/airflow/pull/70124
A zero slice step is invalid sequence semantics, but the endpoint silently treated it as one and hid malformed client requests.
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closes #70123
The mapped XCom slice endpoint currently accepts `step=0` and silently treats it as `step=1`. This differs from sequence slice semantics, where a zero step is invalid, and can hide malformed requests from Task SDK clients.
Validate the query parameter before executing the XCom query so the current endpoint returns HTTP 422 for a zero step while preserving omitted, positive, and negative step behavior. Version the behavior through Cadwyn so clients using the previously released `2026-06-30` API retain the earlier interpretation of zero as the default step.
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Re: [PR] Reject zero step in mapped XCom slices [airflow]
Posted by "pierrejeambrun (via GitHub)" <gi...@apache.org>.
pierrejeambrun commented on code in PR #70124:
URL: https://github.com/apache/airflow/pull/70124#discussion_r4337745136
##########
airflow-core/src/airflow/api_fastapi/execution_api/routes/xcoms.py:
##########
@@ -190,6 +190,12 @@ def get_mapped_xcom_by_slice(
params: Annotated[GetXComSliceFilterParams, Query()],
session: SessionDep,
) -> XComSequenceSliceResponse:
+ if params.step == 0:
Review Comment:
Could we move this check into `GetXComSliceFilterParams` as a Pydantic validator instead? FastAPI then turns it into its standard 422 response for us. A plain `gt=0` constraint wouldn't work since negative steps are valid (`seq[::-1]`), so something like:
```python
class GetXComSliceFilterParams(BaseModel):
"""Class to house slice params."""
start: int | None = None
stop: int | None = None
step: int | None = None
include_prior_dates: bool = False
previous_iteration: bool = False
@field_validator("step")
@classmethod
def validate_step(cls, step: int | None) -> int | None:
if step == 0:
raise ValueError("slice step cannot be zero")
return step
```
With that in place, `params.step or 1` below can stay as it was, since 0 can no longer get there. The test would then check `response.json()["detail"][0]["loc"] == ["query", "step"]`.
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Re: [PR] Reject zero step in mapped XCom slices [airflow]
Posted by "viiccwen (via GitHub)" <gi...@apache.org>.
viiccwen commented on PR #70124:
URL: https://github.com/apache/airflow/pull/70124#issuecomment-5021320306
cc @jason810496, @henry3260. 🙌
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Re: [PR] Reject zero step in mapped XCom slices [airflow]
Posted by "viiccwen (via GitHub)" <gi...@apache.org>.
viiccwen commented on PR #70124:
URL: https://github.com/apache/airflow/pull/70124#issuecomment-5224882277
Hello @henry3260, politely tag for further review.
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Re: [PR] Reject zero step in mapped XCom slices [airflow]
Posted by "viiccwen (via GitHub)" <gi...@apache.org>.
viiccwen commented on PR #70124:
URL: https://github.com/apache/airflow/pull/70124#issuecomment-5029884626
> Thanks for the fix!
>
> IMO, I don't think this needs a new API version migration though. The old behavior (silently treating `step=0` as `step=1`) is exactly the bug being fixed — preserving it for clients declaring older API versions means their malformed requests keep being silently misinterpreted, which is what #70123 wants to surface.
Sure, that makes sense. I just updated.
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