fix(yang-push): defer subscription updates while a schema fetch is in-flight - #35
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process_cache_response correlates responses by subscription id only. A SubscriptionModified arriving while the prior SubscriptionStarted's fetch was still in-flight caused check_subscription_new to remove the old entry (dropping buffered packets) and start a second fetch; the stale first response then clobbered the newer entry and cleared schema_fetch_pending prematurely. Defer SubscriptionStarted/SubscriptionModified like ordinary push-updates whenever a fetch is already pending, so at most one fetch is ever in-flight per subscription id. Adds subscription_update_deferred counter and a regression test.
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Pull request overview
This PR addresses a correctness bug in the YANG-Push validation actor where SubscriptionModified (or duplicate SubscriptionStarted) arriving while a prior schema fetch is still in-flight could clobber cache state, drop buffered packets, and potentially validate packets against the wrong schema. The fix enforces “at most one schema fetch in-flight per (peer, subscription id)” by buffering started/modified notifications while a fetch is pending, and replaying them once the pending fetch resolves.
Changes:
- Defer (
buffer)SubscriptionStarted/SubscriptionModifiednotifications whenschema_fetch_pendingis already true for the same subscription id, preventing stale cache responses from overwriting newer subscription generations. - Add a new OpenTelemetry counter
netcalyx.yang_push.validation.subscription_update.deferredto measure deferred subscription updates. - Add a regression test intended to validate correct ordering/behavior when a
SubscriptionModifiedarrives during an in-flight fetch.
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| // Enqueue all four messages before the actor has any chance to run, so | ||
| // fetch #1 (triggered by message 1) is guaranteed to still be pending | ||
| // when messages 2-4 are handled. | ||
| udp_notif_tx | ||
| .send(make_packet(1, &started_payload)) |
ustorbeck
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Aug 19, 2026
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This PR depends on #29. Issue spotted by @ustorbeck during review or #23.
Problem
A
SubscriptionModifiedarriving while the priorSubscriptionStarted's fetchwas still in-flight caused
check_subscription_newto remove the old entry(silently dropping any buffered packets) and start a second, independent fetch.
The stale first response then clobbered the newer entry and cleared
schema_fetch_pendingprematurely — packets could validate against thewrong schema or slip through unvalidated.
Fix
Defer
SubscriptionStarted/SubscriptionModifiednotifications likeordinary push-updates whenever a fetch is already pending for that
subscription id, guaranteeing at most one fetch in-flight per id. The
deferred update replays after the buffer drains, correctly triggering a
fresh fetch. Adds a
subscription_update_deferredcounter.