Fix log injection and applied sampling rule bug #6299

khanayan123 · 2025-08-19T00:47:47Z

What does this PR do?

Fix: Log injection no longer triggers sampling, preventing resource-based rules from being bypassed.

Changes:

Skip sampling for LOG format in inject() method
Add unit test confirming log injection doesn't trigger sampling
Integration test verifies resource-based rules work with log injection

Motivation

Since v5.57 a log injection bug was surfaced where default log injection caused sampling to run before web frameworks set resource names, bypassing resource-based rules. This issue has existed since v4.23.0 when we introduced resource based sampling

github-actions · 2025-08-19T00:48:51Z

Overall package size

Self size: 11.87 MB
Deduped: 111.49 MB
No deduping: 111.83 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | @datadog/libdatadog | 0.7.0 | 35.02 MB | 35.02 MB | | @datadog/native-appsec | 10.1.0 | 20.37 MB | 20.37 MB | | @datadog/native-iast-taint-tracking | 4.0.0 | 11.72 MB | 11.73 MB | | @datadog/pprof | 5.9.0 | 9.77 MB | 10.1 MB | | @opentelemetry/core | 1.30.1 | 908.66 kB | 7.16 MB | | protobufjs | 7.5.4 | 2.95 MB | 5.6 MB | | @datadog/wasm-js-rewriter | 4.0.1 | 2.85 MB | 3.58 MB | | @datadog/native-metrics | 3.1.1 | 1.02 MB | 1.43 MB | | @opentelemetry/api | 1.8.0 | 1.21 MB | 1.21 MB | | jsonpath-plus | 10.3.0 | 617.18 kB | 1.08 MB | | import-in-the-middle | 1.14.2 | 122.36 kB | 850.93 kB | | lru-cache | 10.4.3 | 804.3 kB | 804.3 kB | | opentracing | 0.14.7 | 194.81 kB | 194.81 kB | | source-map | 0.7.6 | 185.63 kB | 185.63 kB | | pprof-format | 2.1.0 | 111.69 kB | 111.69 kB | | @datadog/sketches-js | 2.1.1 | 109.9 kB | 109.9 kB | | lodash.sortby | 4.7.0 | 75.76 kB | 75.76 kB | | ignore | 7.0.5 | 63.38 kB | 63.38 kB | | istanbul-lib-coverage | 3.2.2 | 34.37 kB | 34.37 kB | | rfdc | 1.4.1 | 27.15 kB | 27.15 kB | | dc-polyfill | 0.1.10 | 26.73 kB | 26.73 kB | | @isaacs/ttlcache | 1.4.1 | 25.2 kB | 25.2 kB | | tlhunter-sorted-set | 0.1.0 | 24.94 kB | 24.94 kB | | shell-quote | 1.8.3 | 23.74 kB | 23.74 kB | | limiter | 1.1.5 | 23.17 kB | 23.17 kB | | retry | 0.13.1 | 18.85 kB | 18.85 kB | | semifies | 1.0.0 | 15.84 kB | 15.84 kB | | jest-docblock | 29.7.0 | 8.99 kB | 12.76 kB | | crypto-randomuuid | 1.0.0 | 11.18 kB | 11.18 kB | | ttl-set | 1.0.0 | 4.61 kB | 9.69 kB | | mutexify | 1.4.0 | 5.71 kB | 8.74 kB | | path-to-regexp | 0.1.12 | 6.6 kB | 6.6 kB | | koalas | 1.0.2 | 6.47 kB | 6.47 kB | | module-details-from-path | 1.0.4 | 3.96 kB | 3.96 kB |

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

codecov · 2025-08-19T00:49:11Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.72%. Comparing base (451946a) to head (8b53aea).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6299   +/-   ##
=======================================
  Coverage   83.72%   83.72%           
=======================================
  Files         476      476           
  Lines       20001    20001           
=======================================
  Hits        16745    16745           
  Misses       3256     3256

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pr-commenter · 2025-08-19T00:58:37Z

Benchmarks

Benchmark execution time: 2025-08-20 14:07:15

Comparing candidate commit 8b53aea in PR branch khanayan123/fix-log-injection-sampling-bug with baseline commit 451946a in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1271 metrics, 52 unstable metrics.

BridgeAR

Functionality wise this is LGTM, I believe the overall fix should be implemented somewhere else.

I think we could for example look into setting the resource.name earlier. If we manage that, the bug should also be fixed and it would likely also fix more situations (I could imagine this is also tricky in case other functionality relies on it as well).
This should for example not come with the performance overhead that this currently comes with.

…mpling

BridgeAR · 2025-08-20T13:19:37Z

integration-tests/log_injection.spec.js

+        assert.isArray(payload)
+        assert.strictEqual(payload.length, 1)
+        // Bug: previously got USER_REJECT instead of USER_KEEP when log injection is enabled,
+        // meaning resource rules are not applied & instead global sampling is applied
+        // Now gets USER_KEEP because resource rules are applied
+        assert.propertyVal(payload[0][0].metrics, '_sampling_priority_v1', USER_KEEP)


Nit: please change this to use our helper assertObjectContains for partial deep equal checks. That way there is additional debugging information in case of a failure and we don't add additional chai usage, which we want to prevent in the future (using Node.js assert instead).

The same applies to the other test.

…om:DataDog/dd-trace-js into khanayan123/fix-log-injection-sampling-bug

datadog-official · 2025-08-20T13:36:22Z

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 8b53aea | Docs | Was this helpful? Give us feedback!}

integration-tests/log_injection.spec.js

Co-authored-by: Ruben Bridgewater <ruben@bridgewater.de>

BridgeAR

LGTM

* fix log injection and sampling rule bug * instead of deferring sampling decision seperate log injection from sampling * revert * address feedback

khanayan123 added 2 commits August 18, 2025 20:47

fix log injection and sampling rule bug

3e7a7d1

Merge branch 'master' into khanayan123/fix-log-injection-sampling-bug

eebd4ad

khanayan123 added the semver-patch label Aug 19, 2025

khanayan123 marked this pull request as ready for review August 19, 2025 00:53

khanayan123 requested review from a team as code owners August 19, 2025 00:54

BridgeAR reviewed Aug 19, 2025

View reviewed changes

Merge branch 'master' into khanayan123/fix-log-injection-sampling-bug

a695f11

khanayan123 marked this pull request as draft August 19, 2025 16:28

khanayan123 added 2 commits August 19, 2025 14:40

instead of deferring sampling decision seperate log injection from sa…

6819325

…mpling

revert

bf726ab

khanayan123 requested a review from BridgeAR August 19, 2025 18:44

khanayan123 marked this pull request as ready for review August 19, 2025 18:45

Merge branch 'master' into khanayan123/fix-log-injection-sampling-bug

521e5e2

BridgeAR reviewed Aug 20, 2025

View reviewed changes

khanayan123 added 2 commits August 20, 2025 09:31

address feedback

dd958c4

Merge branch 'khanayan123/fix-log-injection-sampling-bug' of github.c…

fb1452e

…om:DataDog/dd-trace-js into khanayan123/fix-log-injection-sampling-bug

khanayan123 requested a review from BridgeAR August 20, 2025 13:31

Merge branch 'master' into khanayan123/fix-log-injection-sampling-bug

282bee8

khanayan123 enabled auto-merge (squash) August 20, 2025 13:33

BridgeAR reviewed Aug 20, 2025

View reviewed changes

integration-tests/log_injection.spec.js Outdated Show resolved Hide resolved

khanayan123 and others added 2 commits August 20, 2025 09:54

Update integration-tests/log_injection.spec.js

a61ffc8

Co-authored-by: Ruben Bridgewater <ruben@bridgewater.de>

clean up

8b53aea

khanayan123 requested a review from BridgeAR August 20, 2025 13:56

BridgeAR approved these changes Aug 20, 2025

View reviewed changes

khanayan123 merged commit f60b7f7 into master Aug 20, 2025
733 of 735 checks passed

khanayan123 deleted the khanayan123/fix-log-injection-sampling-bug branch August 20, 2025 14:26

dd-octo-sts bot pushed a commit that referenced this pull request Aug 21, 2025

Fix log injection and applied sampling rule bug (#6299)

8c9c09d

* fix log injection and sampling rule bug * instead of deferring sampling decision seperate log injection from sampling * revert * address feedback

dd-octo-sts bot mentioned this pull request Aug 21, 2025

v5.63.4 proposal #6323

Closed

tlhunter pushed a commit that referenced this pull request Aug 22, 2025

Fix log injection and applied sampling rule bug (#6299)

f22756b

* fix log injection and sampling rule bug * instead of deferring sampling decision seperate log injection from sampling * revert * address feedback

dd-octo-sts bot pushed a commit that referenced this pull request Aug 22, 2025

Fix log injection and applied sampling rule bug (#6299)

fb4b58d

* fix log injection and sampling rule bug * instead of deferring sampling decision seperate log injection from sampling * revert * address feedback

dd-octo-sts bot mentioned this pull request Aug 22, 2025

v5.64.0 proposal #6332

Merged

BridgeAR pushed a commit that referenced this pull request Aug 26, 2025

Fix log injection and applied sampling rule bug (#6299)

ab32c6d

* fix log injection and sampling rule bug * instead of deferring sampling decision seperate log injection from sampling * revert * address feedback

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What does this PR do?

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