oss_16_baggage_metadata_and_percent_encoding

[ocelotl]

W3C Baggage: stop dropping entry metadata, and percent-encode spaces as %20 not + (Linear OSS-16, findings P2/P3).

Branch / worktree: oss_16_baggage_metadata_and_percent_encoding

Linear issue: https://linear.app/dash0/issue/OSS-16/p2-p3-w3c-baggage-metadata-dropped-wrong-percent-encoding-vs-percent20

[ocelotl]

🔒 Internal (dash0) — not for upstream.

Tracking for the W3C Baggage fix (metadata + %20 encoding).

• Linear: https://linear.app/dash0/issue/OSS-16/p2-p3-w3c-baggage-metadata-dropped-wrong-percent-encoding-vs-percent20 (findings P2/P3)
• Slug/branch/worktree: oss_16_baggage_metadata_and_percent_encoding
• Commit: c35142d9e · PR: oss_16_baggage_metadata_and_percent_encoding #24
• Validation: api suite 45 passed (baggage + w3c propagator); scope api + changelog.
• Reviewer note: 3 pre-existing tests asserted the OLD buggy behavior (+ space encoding; metadata inlined into value) and were updated to assert the corrected behavior. Metadata is stored in a separate context entry so get_baggage/get_all still return plain strings (backward compatible).

[ocelotl]

📣 Public-facing draft — to be opened upstream in open-telemetry/opentelemetry-python. No internal references; copy verbatim.

Title: W3C Baggage propagator drops entry metadata and mis-encodes spaces as +

Summary

The W3CBaggagePropagator in opentelemetry-api has two conformance gaps against the W3C Baggage spec and the OpenTelemetry Baggage API spec.

P1 — Entry metadata is dropped on extract and never re-injected

opentelemetry-api/src/opentelemetry/baggage/propagation/__init__.py (extract loop, ~L124-135): an entry's ;-delimited metadata is passed through validation only, then discarded. The API cannot store it: set_baggage(name, value, context=None) (opentelemetry-api/src/opentelemetry/baggage/__init__.py, ~L54) has no metadata parameter. On inject, _encode_baggage_pairs percent-encodes the whole value, so even stuffing metadata into the value corrupts it. The Baggage API spec (specification/baggage/api.md) says entries carry optional metadata that implementations SHOULD retain and propagate unmodified (Go baggage.Property; Java BaggageEntryMetadata).

P2 — Spaces are encoded as + instead of %20

Same file: inject uses quote_plus, extract uses unquote_plus, so a space becomes +. The W3C Baggage format (https://www.w3.org/TR/baggage/) requires RFC 3986 percent-encoding where a space is %20; + is read literally by compliant receivers, so "a b" becomes "a+b" for other SDKs/collectors.

Proposed fix

1. Add an optional metadata parameter to set_baggage, add a get_baggage_metadata accessor, store metadata so it survives extract → store → inject, and re-append it after ; on inject.
2. Replace quote_plus/unquote_plus with quote(..., safe="")/unquote so a space is %20.