Fix baggage header escaping of non-ASCII values

[RoseannaM]

What Does This Do

Fixes PercentEscaper.nextEscapeIndex() skipping non-ASCII characters, so baggage keys and values are now fully percent-escaped.

Motivation

See Jira APMS-20590

nextEscapeIndex() duplicated part of needsEncoding() but tested only the unsafe-octet table, dropping the c > '~' and c <= ' ' conditions. Those tables are 93 entries (values) / 126 (keys), so every non-ASCII character sits outside them and the scan skipped straight past it.

The first character was still escaped via the escape(String, boolean[]) fast path, so the bug only showed from the second escape onward — raw UTF-8 bytes went into the header value and were mangled in transit.

Testing

• New PercentEscaperTest — 12 tests covering the 2-byte, 3-byte and 4-byte (surrogate pair) UTF-8 branches, non-ASCII at the start vs. after an escape, repeated interleaving, and both the key and value octet tables. All pass; 10 fail with the fix reverted.
• Verified end to end in a Spring Boot app: released 1.66.0 emits the mangled header above, a local build of this branch emits the fully escaped one.

Additional Notes

Contributor Checklist

• Format code with ./gradlew spotlessApply
• Tests added

🤖 Generated with Claude Code

Jira ticket: [PROJ-IDENT]

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-18T12:09:26.470152Z	173a447	PR opened
🔒 Security Review	✅ Completed 2026-09-18T12:12:18.225692Z	173a447	PR opened

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[datadog-prod-us1-6]

🎯 Code Coverage (details)
• Patch Coverage: 50.00%
• Overall Coverage: 59.12% (+0.02%)

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🔗 Commit SHA: 6eb3ad9 | Docs | Give us feedback!}

[datadog-prod-us1-6]

More details

The shared encoding check now stops the scan at each unsafe ASCII or non-ASCII character. All later characters stay in the percent-encoding path.

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[dd-octo-sts]

🟢 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	14.01 s	13.89 s	[-0.0%; +1.7%] (no difference)
startup:insecure-bank:tracing:Agent	12.90 s	13.00 s	[-1.5%; +0.1%] (no difference)
startup:petclinic:appsec:Agent	17.01 s	17.01 s	[-0.9%; +1.0%] (no difference)
startup:petclinic:iast:Agent	17.02 s	17.07 s	[-1.0%; +0.4%] (no difference)
startup:petclinic:profiling:Agent	16.98 s	16.43 s	[+2.3%; +4.3%] (significantly worse)
startup:petclinic:sca:Agent	16.92 s	16.70 s	[+0.3%; +2.3%] (maybe worse)
startup:petclinic:tracing:Agent	16.24 s	16.22 s	[-0.8%; +1.0%] (no difference)

Commit: 6eb3ad9b · CI Pipeline · Benchmarking Platform UI

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[jordan-wong]

Approved from IDM perspective but we do not really touch this area of the codebase - would like to see some review from Capabilities, tagging @mhlidd as the current sole file contributor

[mhlidd]

Some additional fixes that are relevant to the issue.

[Copilot]

Copilot review overview

🔵 Needs a closer look

URL-decoded values and keys can still round-trip incorrectly for + and %.

Review effort: Lite
Findings: None

What changed in this PR

Fixes baggage header percent escaping for non-ASCII characters.

Changes:

• Corrects escape scanning logic.
• Adds Unicode, control-character, and key/value regression tests.

File	Summary
dd-trace-core/​src/​main/​java/​datadog/​trace/​core/​util/​PercentEscaper.java	Updates escaping logic; moderate issues remain for + in values and % in keys.
dd-trace-core/​src/​test/​java/​datadog/​trace/​core/​util/​PercentEscaperTest.java	Adds comprehensive escaping regression coverage; round-trip tests for the remaining issues are requested.

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[dd-octo-sts]

/merge

[gh-worker-devflow-routing-ef8351]

View all feedbacks in Devflow UI.

2026-09-25 09:43:30 UTC ℹ️ Start processing command /merge

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2026-09-25 09:43:34 UTC ℹ️ MergeQueue: pull request added to the queue

The expected merge time in master is approximately 1h (p90).

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2026-09-25 10:59:33 UTC ℹ️ MergeQueue: This merge request was merged