feat(baggage): add support for baggage span tags by rachelyangdog · Pull Request #223 · DataDog/dd-trace-rs

rachelyangdog · 2026-05-08T18:22:31Z

What does this PR do?

Implements the DD_TRACE_BAGGAGE_TAG_KEYS feature, which automatically promotes W3C Baggage entries to span tags at extraction time.

When a span is created with a remote parent, baggage entries matching the configured filter are attached as span attributes prefixed with baggage.:

baggage: user.id=alice,session.id=xyz123
→ span tag baggage.user.id = "alice"
→ span tag baggage.session.id = "xyz123"

Tags are only applied at extraction time, not to locally-created root spans.

Baggage Tagging Behavior

"" (empty): Disabled — no baggage keys become span tags
"*": All baggage keys are tagged
"user.id,session.id": Only the listed keys are tagged
(unset): Default is user.id, session.id, account.id

W3C spec compliance fix
Per the W3C Baggage spec, a malformed member (empty key, empty value, or missing =) must cause all subsequent members to be dropped — not just the malformed one. This PR fixes the extraction to use stop-at-first-error semantics instead of skip-and-continue.

Before: user.id=,session.id=abc → {session.id: "abc"} (partial extraction)
After: user.id=,session.id=abc → {} (entire header dropped after malformed entry)

Configuration

Env var: DD_TRACE_BAGGAGE_TAG_KEYS
Default: "user.id,session.id,account.id"

Motivation

What inspired you to submit this pull request?

Additional Notes

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chatgpt-codex-connector · 2026-05-08T18:26:10Z

+            for kv in baggage_span_tags(parent_ctx.baggage(), self.config.trace_baggage_tag_keys())
+            {
+                span.set_attribute(kv);


Promote baggage tags on baggage-only root spans

When an incoming request carries only a baggage header (or a local root span is started with baggage) and no valid remote trace context, extract_with_context still attaches the baggage to parent_ctx, but this loop only runs inside the is_remote() branch. That makes DD_TRACE_BAGGAGE_TAG_KEYS silently ineffective for baggage-only propagation, even though this change adds baggage as a supported propagation style; the local-root path should also apply these baggage span tags.

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datadog-datadog-prod-us1-2 · 2026-05-08T18:29:12Z

✨ Fix all issues with BitsAI or with Cursor

⚠️ Warnings

🧪 1 Test failed

tests.parametric.test_headers_baggage.Test_Headers_Baggage_Span_Tags.test_baggage_span_tags_malformed_header[parametric-rust]

from system_tests_suite

(Fix with Cursor)

AssertionError: assert '' is None
 +  where '' = <built-in method get of dict object at 0x7fd064859880>('baggage.user.id')
 +    where <built-in method get of dict object at 0x7fd064859880> = {'_dd.p.dm': '-0', 'baggage.account.id': 'abcd', 'baggage.session.id': 'mysession', 'baggage.user.id': '', ...}.get

self = <tests.parametric.test_headers_baggage.Test_Headers_Baggage_Span_Tags object at 0x7fd096592180>
test_agent = <utils.docker_fixtures._test_agent.TestAgentAPI object at 0x7fd06411d550>
test_library = <utils.docker_fixtures._test_clients._test_client_parametric.ParametricTestClientApi object at 0x7fd06411f4a0>

    def test_baggage_span_tags_malformed_header(self, test_agent: TestAgentAPI, test_library: APMLibrary) -> None:
        with test_library:
...

ℹ️ Info

No other issues found (see more)

❄️ No new flaky tests detected

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

🔗 Commit SHA: 23d9998 | Docs | Datadog PR Page | Give us feedback!}

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Per W3C Baggage spec, a malformed member invalidates the rest of the header. Change extraction to stop on the first unparseable entry (including entries with empty keys or values) rather than skipping and continuing. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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W3C Baggage spec defines value = *baggage-octet (zero or more), so empty values are valid. Only empty keys are truly malformed (key = 1*tchar requires at least one character). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

An input like "," or ", ," produces an empty key list after filtering, which behaves identically to Disabled. Normalize it explicitly so Keys always contains at least one entry. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Empty values are valid per W3C spec (value = *baggage-octet), so this test case that was removed when we incorrectly rejected empty values should be present. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

…ced default Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iunanua · 2026-05-14T07:52:26Z

A ST is failing because it expects all items get dropped if a value is missing 🙃

Points to the updated test_baggage_span_tags_malformed_header which uses an empty key (=doggo,...) as the malformed case, per W3C spec (empty values are valid, only empty keys are not). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rachelyangdog and others added 10 commits March 27, 2026 13:47

feat(baggage): add support for w3c baggage

3888ccb

feedback

b224bf1

lint

30e42c6

trying lint again

338ea53

update with changes

b4e2ce8

lint

49d43e5

lint again

b8acd2e

update

e182215

feat(baggage): add extraction limits on the baggage code

09d0f8a

WIP: feat(baggage): add support for baggage span tags

d604f8e

rachelyangdog requested a review from a team as a code owner May 8, 2026 18:22

rachelyangdog marked this pull request as draft May 8, 2026 18:22

chore: apply cargo fmt

05f787b

chatgpt-codex-connector Bot reviewed May 8, 2026

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rachelyangdog and others added 3 commits May 12, 2026 13:00

chore: merge origin/main into rachel.yang/baggage-span-tags

0fe6bd0

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

chore: merge origin/main (feat(baggage)!: #200) into baggage-span-tags

1dd9466

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rachelyangdog changed the title ~~WIP: feat(baggage): add support for baggage span tags~~ feat(baggage): add support for baggage span tags May 12, 2026

rachelyangdog marked this pull request as ready for review May 12, 2026 20:13

chore: apply cargo fmt

6bce926

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

chatgpt-codex-connector Bot reviewed May 12, 2026

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Comment thread datadog-opentelemetry/src/propagation/baggage.rs Outdated

iunanua reviewed May 13, 2026

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Comment thread datadog-opentelemetry/src/propagation/baggage.rs

Comment thread datadog-opentelemetry/src/core/configuration/configuration.rs Outdated

Comment thread datadog-opentelemetry/src/propagation/baggage.rs

rachelyangdog and others added 3 commits May 13, 2026 10:58

test(baggage): restore valid-header-with-no-value test case

4c2e7b4

Empty values are valid per W3C spec (value = *baggage-octet), so this test case that was removed when we incorrectly rejected empty values should be present. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fix(config): correct DD_TRACE_BAGGAGE_TAG_KEYS type to array with spa…

71121f7

…ced default Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rachelyangdog and others added 2 commits May 14, 2026 10:43

ci: revert system-tests pin back to main SHA

23d9998

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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feat(baggage): add support for baggage span tags#223

feat(baggage): add support for baggage span tags#223
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