Prevent duplicate DLQ messages when afterDlq throws after successful publish#76
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Pull request overview
Fixes a duplication bug in BaseQueueHandler.addToDLQ where a thrown afterDlq hook could cause the catch-path fallback publish to send a second (duplicate) DLQ message even after the initial DLQ publish succeeded.
Changes:
- Track whether the primary DLQ publish succeeded (
dlqPublished) and skip fallback republish when it did. - Update/extend tests to assert the “no duplicate DLQ entry” invariant and validate raw-buffer fallback behavior.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| ts/base-queue-handler.ts | Adds a dlqPublished flag to prevent fallback republish when the first DLQ publish already succeeded. |
| test/base-queue-handler.test.ts | Reworks DLQ tests to assert single DLQ delivery and raw-buffer fallback on publish failure. |
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Dimitris-Ilias
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May 8, 2026
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| it('should add raw buffer to dlq when afterDlq throws to prevent double-encoding', async function () { | ||
| it('should not duplicate dlq message when afterDlq throws after successful publish', async function () { |
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ℹ️ This is the new test but diff is a little out of whack because these two tests have very similar setup
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Summary
As found on #75, on
BaseQueueHandler.addToDLQwhen anafterDlqhook throws after a successful DLQ publish a duplicate message is published on the DLQ.This PR tackles this issue
Before this PR
BaseQueueHandler.addToDLQwraps the decode → publish →afterDlqsequence in a single try/catch. The catch-path republishes the message as a raw-buffer fallback so that messages still reach the DLQ when something goes wrong.decode(msg)throws or when the firstrabbit.publishis rejected by the broker — the DLQ entry is missing and the catch-path provides it.afterDlqthrows after a successful first publish, the catch-path runs anyway and publishes a second copy of the same message. The DLQ ends up with two entries for one input.afterDlqfailure under load.After this PR
addToDLQtracks whether the first publish resolved by setting a localdlqPublishedflag. The catch-path republishes only when!dlqPublished, so a successful publish + failingafterDlqproduces exactly one DLQ entry.decodethrows → fallback republish runs → 1 entry.rabbit.publishrejects → fallback republish runs → 1 entry.afterDlqthrows after success → fallback skipped → 1 entry (new behavior).