fix(kafka): stop mutating caller-owned message.headers#8388
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Both kafkajs's producer wrap and the `@confluentinc/kafka-javascript`
KafkaJS-compat producer wrap mutated the caller's `message.headers` in
place. The kafkajs boundary seeded `headers: {}` on every message before
the plugin injected trace context; the confluent KafkaJS-compat path
handed `payload.messages` straight to the underlying client, which then
wrote `headers: null` on messages without headers. Either path leaves
the caller holding the side effects of someone else's instrumentation.
The boundary now hands kafkajs and the underlying confluent client a
shallow clone of the messages array via a single `cloneMessages`
helper. With injection enabled the helper seeds `headers: {}` on the
clone for the plugin to inject into; with injection disabled (after the
broker reported `KafkaJSProtocolError UNKNOWN` /
`KafkaJSError ERR_UNKNOWN`) the helper preserves the absence of
`headers` so brokers that reject any header field can recover.
Refs: #5270
Refs: #8253
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Overall package sizeSelf size: 5.81 MB Dependency sizes| name | version | self size | total size | |------|---------|-----------|------------| | import-in-the-middle | 3.0.1 | 82.56 kB | 817.39 kB | | dc-polyfill | 0.1.11 | 25.74 kB | 25.74 kB |🤖 This report was automatically generated by heaviest-objects-in-the-universe |
🎉 All green!❄️ No new flaky tests detected 🎯 Code Coverage (details) 🔗 Commit SHA: 0e57fad | Docs | Datadog PR Page | Give us feedback! |
BenchmarksBenchmark execution time: 2026-05-09 19:08:31 Comparing candidate commit 0e57fad in PR branch Found 0 performance improvements and 0 performance regressions! Performance is the same for 1733 metrics, 111 unstable metrics. |
tlhunter
approved these changes
May 11, 2026
Merged
rochdev
pushed a commit
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this pull request
May 13, 2026
Both kafkajs's producer wrap and the `@confluentinc/kafka-javascript`
KafkaJS-compat producer wrap mutated the caller's `message.headers` in
place. The kafkajs boundary seeded `headers: {}` on every message before
the plugin injected trace context; the confluent KafkaJS-compat path
handed `payload.messages` straight to the underlying client, which then
wrote `headers: null` on messages without headers. Either path leaves
the caller holding the side effects of someone else's instrumentation.
The boundary now hands kafkajs and the underlying confluent client a
shallow clone of the messages array via a single `cloneMessages`
helper. With injection enabled the helper seeds `headers: {}` on the
clone for the plugin to inject into; with injection disabled (after the
broker reported `KafkaJSProtocolError UNKNOWN` /
`KafkaJSError ERR_UNKNOWN`) the helper preserves the absence of
`headers` so brokers that reject any header field can recover.
Refs: #5270
Refs: #8253
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Summary
Both kafkajs's producer wrap and the
@confluentinc/kafka-javascriptKafkaJS-compat producer wrap mutated the caller'smessage.headersin place. Either path leaves the caller holding the side effects of someone else's instrumentation.headers: {}on every message before the plugin injected trace context.payload.messagesstraight to the underlying client, which then wroteheaders: nullon messages without headers.The boundary now hands kafkajs and the underlying confluent client a shallow clone of the messages array via a single
cloneMessages(messages, ensureHeaders)helper. With injection enabled the helper seedsheaders: {}on the clone for the plugin to inject into; with injection disabled (after the broker reportedKafkaJSProtocolError UNKNOWN/KafkaJSError ERR_UNKNOWN) the helper preserves the absence ofheadersso brokers that reject any header field can recover.Test plan
./node_modules/.bin/mocha packages/datadog-instrumentations/test/helpers/kafka.spec.js— unit tests forcloneMessages.PLUGINS=kafkajs SPEC=index npm run test:plugins— exercises the deep-frozen-input regression test and theKafkaJSProtocolError UNKNOWNrecovery path that pins the no-headers: {}seeding invariant.PLUGINS=confluentinc-kafka-javascript SPEC=dsm npm run test:plugins— pins the same invariant for the KafkaJS-compat path.Refs: #5270
Refs: #8253