Adding baggage limits for OT Baggage by mhlidd · Pull Request #12303 · DataDog/dd-trace-java

mhlidd · 2026-08-26T13:50:51Z

What Does This Do

This PR adds limits to the size and number of objects allowed to be extracted for the legacy OT Baggage. However, Haystack has no size limit for traceID/spanID, and uses baggage to store the full header that can't be stored with DDTraceID. Enforcing limits may drop these keys, so reserved baggage items are necessary to ensure that context propagation is not broken.

This PR also fixes an old bug where comma-concatenated Haystack traceID/spanID/parentID headers were parsed using the entire header value, causing context extraction to fail. We now parse and preserve only the first traceID/spanID/parentID from the headers.

Finally, max baggage items and size config values are forced to 0 if a negative value is set.

Motivation

Additional Notes

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Format the title according to the contribution guidelines
Assign the type: and (comp: or inst:) labels in addition to any other useful labels
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Use solves instead, and assign the PR milestone to the issue
Update the CODEOWNERS file on source file addition, migration, or deletion
Update public documentation with any new configuration flags or behaviors
Once approved, use merge queue to merge the PR

Jira ticket: [PROJ-IDENT]

dd-octo-sts · 2026-08-26T13:51:05Z

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datadog-datadog-prod-us1

More details

The shared limit accounting covers all changed extraction paths and preserves reserved Haystack trace identifiers.

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dd-octo-sts · 2026-08-26T14:17:55Z

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	14.84 s	14.68 s	[+0.2%; +2.0%] (maybe worse)
startup:insecure-bank:tracing:Agent	13.53 s	13.72 s	[-2.5%; -0.4%] (maybe better)
startup:petclinic:appsec:Agent	16.87 s	17.12 s	[-5.9%; +3.0%] (no difference)
startup:petclinic:iast:Agent	17.36 s	17.41 s	[-1.3%; +0.7%] (no difference)
startup:petclinic:profiling:Agent	16.60 s	17.31 s	[-8.4%; +0.2%] (no difference)
startup:petclinic:sca:Agent	17.27 s	17.26 s	[-0.9%; +1.0%] (no difference)
startup:petclinic:tracing:Agent	16.61 s	16.21 s	[-1.8%; +6.8%] (no difference)

Commit: f2941d69 · CI Pipeline · Benchmarking Platform UI

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

Copilot

Pull request overview

This PR adds configurable limits for legacy OpenTracing-style baggage extraction (including ot-baggage-* headers and equivalent baggage segments in other propagators) by centralizing baggage acceptance, byte-budgeting, and “reserved” key protection in ContextInterpreter, then updating codec implementations and tests accordingly.

Changes:

Enforce trace.baggage.max.items and trace.baggage.max.bytes during extraction across Datadog, W3C, X-Ray, and Haystack propagators.
Prevent caller-controlled baggage (including mapped baggage) from overwriting reserved propagation bookkeeping keys (e.g., Haystack lossless IDs).
Add/extend extractor tests to validate item/byte truncation, replacement semantics, and reserved-key behavior.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
dd-trace-core/src/main/java/datadog/trace/core/propagation/ContextInterpreter.java	Centralizes baggage limiting (items/bytes), replacement accounting, and reserved-key protection for extraction.
dd-trace-core/src/main/java/datadog/trace/core/propagation/DatadogHttpCodec.java	Routes OT baggage extraction through the new `ContextInterpreter` baggage limiter.
dd-trace-core/src/main/java/datadog/trace/core/propagation/W3CHttpCodec.java	Routes OT baggage extraction through the new `ContextInterpreter` baggage limiter.
dd-trace-core/src/main/java/datadog/trace/core/propagation/XRayHttpCodec.java	Routes X-Ray “key=value” segment baggage extraction through the new limiter and preserves parsing after truncation.
dd-trace-core/src/main/java/datadog/trace/core/propagation/HaystackHttpCodec.java	Treats Haystack trace/span IDs as reserved baggage (non-evictable by caller baggage) while keeping Parent-ID subject to limits.
dd-trace-core/src/test/java/datadog/trace/core/propagation/DatadogHttpExtractorTest.java	Adds tests for OT baggage item/byte limits, replacement semantics, and UTF-8 byte counting.
dd-trace-core/src/test/java/datadog/trace/core/propagation/W3CHttpExtractorTest.java	Adds tests for OT baggage item/byte truncation under W3C extraction.
dd-trace-core/src/test/java/datadog/trace/core/propagation/XRayHttpExtractorTest.java	Adds tests for X-Ray header baggage truncation and for continued parsing of trace context after truncation.
dd-trace-core/src/test/java/datadog/trace/core/propagation/HaystackHttpExtractorTest.java	Adds tests ensuring reserved Haystack IDs survive baggage limits and mapped baggage cannot overwrite them.

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Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.

PerfectSlayer

💭 thought: ‏I think the PR is confusing in multiple parts.
First the introduction of "reversed" baggage.
Then the tree map for the size. If it's only to keep track of the size, why don't we only compute the size of the evicted element to apply the difference? That would save the tree at the cost of duplicated key (which should only happen on rare occasion and never from the dd-trace-* SDK as defined by spec).
Then the variables are now confusing: baggage should be baggageItems, and baggageItems should be baggageItemCount, etc... But getting rid of the baggageItemBytes would help.

PerfectSlayer · 2026-08-28T11:35:04Z

+    final String decodedValue = HttpCodec.decode(value);
+    if (baggage.isEmpty()) {
+      baggage = new TreeMap<>();
+      baggageItemBytes = new TreeMap<>();


❔ question: ‏Why do we need ordering here? (TreeMap)

TreeMap was used in the old diff when OT Baggage was introduced, so I kept it here. Unsure of reasons it was used then (commit message says "use TreeMap everywhere for now"), but if unnecessary I can replace it w/ a HashMap.

PerfectSlayer · 2026-08-28T11:42:44Z

+  // that caller-supplied headers cannot evict it. Exempt from the configured limits, but not
+  // unbounded: the value is capped here rather than left to each caller to validate, so the total
+  // retained stays within trace.baggage.max.bytes plus a fixed amount per reserved key.
+  protected final void addReservedBaggageItem(String key, String value) {


💭 thought: ‏I don't get the whole reserved baggage… If it's only for XRay and in case of conflict, I don't see the point having it.

Moving to HaystackHttpCodec.java.

It's needed because Haystack has no limit to what size the traceID/spanID headers are. We can only hold 64 bits, so the rest of the header was historically stored in OT baggage.

Now that we introduce limits for OT baggage, we risk dropping the traceID/spanID items, which would break context propagation downstream. However, I made a change to no longer remove an already parsed baggage item, and instead allow going over the limits for reserved items (e.g. traceID/spanID).

Note: I still enforce a max length of 64 characters for reserved items so we don't store extremely large values.

Replace okio Utf8.size with String.length() for baggage size accounting, and normalize negative trace.baggage.max.* values to 0 in Config with a warning. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

… mappedBaggage

datadog-datadog-prod-us1

More details

The item and byte limits reset for each extraction. Haystack now uses the first trace ID and span ID in a comma-separated header.

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Disambiguates the running item counter from the baggage map itself, and from DDSpanContext.baggageItems which holds a map rather than a count. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

adding baggage limits for OT Baggage

1b4215c

mhlidd requested a review from a team as a code owner August 26, 2026 13:50

mhlidd requested review from mcculls and removed request for a team August 26, 2026 13:50

mhlidd added type: bug fix Bug fix comp: context propagation Trace context propagation labels Aug 26, 2026

mhlidd requested a review from PerfectSlayer August 26, 2026 13:51

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Comment thread dd-trace-core/src/main/java/datadog/trace/core/propagation/ContextInterpreter.java Outdated

Comment thread dd-trace-core/src/main/java/datadog/trace/core/propagation/ContextInterpreter.java Outdated

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adding accurate utf length checking

e8c5cb5

mhlidd requested a lite review from Copilot August 26, 2026 16:33

Copilot started reviewing on behalf of mhlidd August 26, 2026 16:33 View session

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Comment thread dd-trace-core/src/main/java/datadog/trace/core/propagation/ContextInterpreter.java

Comment thread dd-trace-core/src/test/java/datadog/trace/core/propagation/DatadogHttpExtractorTest.java

updating test fix and early exit when ot-baggage extraction is disabled

740ce66

mhlidd requested a lite review from Copilot August 26, 2026 17:00

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Comment thread dd-trace-core/src/main/java/datadog/trace/core/propagation/HaystackHttpCodec.java

mhlidd added 2 commits August 26, 2026 13:31

fixing haystack traceid spanid concatenation bug

0048d3b

Merge branch 'master' into mhlidd/ot_baggage_fix

3424e8d

mhlidd requested a lite review from Copilot August 26, 2026 17:35

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PerfectSlayer added type: bug fix Bug fix and removed type: bug fix Bug fix labels Aug 27, 2026

PerfectSlayer reviewed Aug 28, 2026

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mhlidd added the tag: ai generated Largely based on code generated by an AI or LLM label Aug 28, 2026

mhlidd added 2 commits August 28, 2026 14:12

move addReservedBaggageItem to HaystackHttpCodec and revert logic for…

091a531

… mappedBaggage

add back decode and parentID first value storage

f1e2f2b

mhlidd requested a review from a team as a code owner August 28, 2026 21:12

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mhlidd and others added 2 commits August 28, 2026 14:31

Rename baggageItems to baggageItemCount

ebc1ed2

Disambiguates the running item counter from the baggage map itself, and from DDSpanContext.baggageItems which holds a map rather than a count. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

cleanup

f2941d6

mhlidd requested a review from PerfectSlayer August 28, 2026 21:37

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