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feat(baggage)!: add support for w3c baggage#200

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rachelyangdog merged 11 commits into
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rachel.yang/w3c-baggage
May 12, 2026
Merged

feat(baggage)!: add support for w3c baggage#200
rachelyangdog merged 11 commits into
mainfrom
rachel.yang/w3c-baggage

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@rachelyangdog

@rachelyangdog rachelyangdog commented Mar 27, 2026 •
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What does this PR do?

Adds W3C Baggage propagation support (baggage header) to the composite propagator. When baggage is included in the propagation style configuration, the global TextMapPropagator will read and write the baggage HTTP header using opentelemetry_sdk::propagation::BaggagePropagator.

Changes:

  • Adds TracePropagationStyle::Baggage variant, recognized case-insensitively from DD_TRACE_PROPAGATION_STYLE, DD_TRACE_PROPAGATION_STYLE_EXTRACT, and DD_TRACE_PROPAGATION_STYLE_INJECT

  • Adds baggage to the default propagation styles alongside datadog and tracecontext

  • Wires inject/extract separately at the DatadogPropagator layer, respecting the extract-vs-inject style override independently

  • Adds propagation::baggage module exposing the header key so fields() includes "baggage" when the style is configured

  • system-tests PR

Motivation

What inspired you to submit this pull request?

Additional Notes

  • No new dependencies: opentelemetry_sdk::propagation::BaggagePropagator was already a transitive dependency
  • Baggage propagation is orthogonal to trace context: it operates on OTel Context directly rather than through the internal Propagator trait (which is trace-ID-centric). The Baggage variant's extract/inject arms in that trait are intentional no-ops; the actual work happens one layer up in DatadogPropagator.
  • DD_TRACE_PROPAGATION_STYLE_EXTRACT and DD_TRACE_PROPAGATION_STYLE_INJECT can be used to enable baggage on only one direction independently of the other

@rachelyangdog rachelyangdog requested a review from a team as a code owner March 27, 2026 17:50
@rachelyangdog rachelyangdog marked this pull request as draft March 27, 2026 17:50
bantonsson
bantonsson reviewed Apr 1, 2026
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Looks good overall

Comment thread datadog-opentelemetry/src/text_map_propagator.rs Outdated
Comment thread datadog-opentelemetry/examples/propagator/src/server.rs Outdated
Comment thread datadog-opentelemetry/src/text_map_propagator.rs Outdated
Comment thread datadog-opentelemetry/src/text_map_propagator.rs Outdated
Comment thread datadog-opentelemetry/src/text_map_propagator.rs
@rachelyangdog rachelyangdog marked this pull request as ready for review April 3, 2026 15:28
iunanua
iunanua reviewed Apr 9, 2026
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Comment thread datadog-opentelemetry/src/text_map_propagator.rs Outdated
Comment thread datadog-opentelemetry/src/text_map_propagator.rs Outdated
Comment thread datadog-opentelemetry/src/text_map_propagator.rs Outdated
Comment thread datadog-opentelemetry/src/text_map_propagator.rs
iunanua
iunanua approved these changes Apr 28, 2026
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LGTM

bantonsson
bantonsson requested changes Apr 30, 2026
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Comment thread datadog-opentelemetry/src/text_map_propagator.rs Outdated
// propagator *writes*). inner.keys() is extractor-derived, so we strip the baggage key
// from it and re-add it solely based on baggage_inject.
let mut fields: Vec<String> = inner
.keys()

@bantonsson bantonsson Apr 30, 2026

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Why is this not using inner.fields()? If there is something wrong with the inner fields then that should be fixed.

@iunanua iunanua Apr 30, 2026

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By this comment, I have realized we are obtaining inner fields from extractors and as @rachelyangdog says they correspond with the injected headers

@iunanua iunanua Apr 30, 2026

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It's something we inherited from bottlecap 🤔

@iunanua iunanua Apr 30, 2026

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Because is the Otel Extrator trait which defines that keys() method
😕

@iunanua iunanua Apr 30, 2026

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Ok, I think get it. They are different things
We have to change the inner fields to fit the injectors.

@iunanua iunanua Apr 30, 2026

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Fix here
Thanks to both of you for bringing this issue to light!

Comment thread datadog-opentelemetry/src/core/configuration/configuration.rs
Some(vec![
TracePropagationStyle::Datadog,
TracePropagationStyle::TraceContext,
TracePropagationStyle::Baggage,

@bantonsson bantonsson Apr 30, 2026

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Since this is a change in behavior, it should be flagged as a breaking change feat(baggage)!:...

@paullegranddc paullegranddc May 5, 2026

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We should have made this enum #[non_exhaustive] 🫤

@rachelyangdog rachelyangdog changed the title feat(baggage): add support for w3c baggage feat(baggage)!: add support for w3c baggage Apr 30, 2026
@iunanua
feat(baggage): fix DatadogPropagator::fields (#217)
ff4221f 
# What does this PR do?

- change `DatadogCompositePropagator` to obtain keys from injectors
according to [Otel
spec](https://opentelemetry.io/docs/specs/otel/context/api-propagators/#fields-1).
- remove the not needed `DatadogPropagator::fields` property
@rachelyangdog rachelyangdog merged commit 45dbcc1 into main May 12, 2026
26 checks passed
@rachelyangdog rachelyangdog deleted the rachel.yang/w3c-baggage branch May 12, 2026 16:22
rachelyangdog added a commit that referenced this pull request May 12, 2026
@rachelyangdog @claude
chore: merge origin/main (feat(baggage)!: #200) into baggage-span-tags
1dd9466 
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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@iunanua iunanua iunanua approved these changes
@bantonsson bantonsson bantonsson approved these changes
@paullegranddc paullegranddc paullegranddc approved these changes

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@rachelyangdog @bantonsson @iunanua @paullegranddc