Ignore stale classic remoting reader ACKs#3173
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Motivation: Classic remoting ACKs forwarded by EndpointReader were not tied to the reader UID, so a delayed ACK from an old reader could affect the resend buffer after a new UID was confirmed. Modification: Tag decoded ACKs with the EndpointReader UID and have ReliableDeliverySupervisor only process ACKs from the currently confirmed UID. Add a supervisor-level regression test covering stale and current reader ACKs. Result: Stale reader ACKs are ignored while current-reader ACKs still acknowledge the active resend buffer. Tests: - sbt "remote / Test / testOnly org.apache.pekko.remote.ReliableDeliverySupervisorSpec" - sbt headerCreateAll - sbt +headerCheckAll - scalafmt --mode diff-ref=origin/main - scalafmt --list --mode diff-ref=origin/main - git diff --check - qodercli -p --output-format stream-json --attachment /tmp/pekko-3160-qoder-review.diff (No must-fix findings) - sbt sortImports (failed: scalafix/scala.meta NoSuchMethodError in stream-tests and multi-node-testkit) References: Fixes apache#3160
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Pull request overview
This PR fixes a classic remoting reliability gap where delayed ACKs decoded by an old EndpointReader instance (stale UID) could incorrectly affect the current resend buffer after a new UID is confirmed. It does so by tagging decoded ACKs with the reader UID and only processing ACKs that match the currently confirmed UID, with a focused regression test to prevent reintroductions.
Changes:
- Introduce
ReliableDeliverySupervisor.AckFromReader(readerUid, ack)and ignore untaggedAckmessages in the supervisor. - Update
EndpointReader(both normal andnotReadingmodes) to forwardAckFromReader(uid, ack)instead of a bareAck. - Add a deterministic regression spec verifying stale-reader ACKs are ignored while current-reader ACKs still advance the resend buffer.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| remote/src/main/scala/org/apache/pekko/remote/Endpoint.scala | Tags forwarded ACKs with EndpointReader UID and gates ACK processing in ReliableDeliverySupervisor to the confirmed UID. |
| remote/src/test/scala/org/apache/pekko/remote/ReliableDeliverySupervisorSpec.scala | Adds regression coverage for ignoring stale-reader ACKs and accepting current-reader ACKs. |
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Motivation
Classic remoting ACKs forwarded by EndpointReader were not tied to the reader UID, so a delayed ACK from an old reader could affect the resend buffer after a new UID was confirmed.
Modification
Tag decoded ACKs with the EndpointReader UID and have ReliableDeliverySupervisor only process ACKs from the currently confirmed UID.
Add a deterministic supervisor-level regression test covering stale and current reader ACKs. This keeps the regression focused on the actor/UID contract rather than relying on multi-node timing races.
Result
Stale reader ACKs are ignored while current-reader ACKs still acknowledge the active resend buffer.
Tests
References
Fixes #3160