fix(w3c): ensure tracecontext headers take precedence over datadog

[mabdinur]

Description

Ensures when trace headers with the same trace_id but different span_ids are received by an application the tracecontext headers are treated as the source of truth.

• The traceparent header will be used to set the parent_id
• If the conflicting trace information was extracted from datadog headers, the span_id from the datadog headers will be stored in the _dd.parent_id parent_id tag.
• All other propagation styles are third class citizens. If they conflict with tracecontext headers their span_ids will be overwritten.

This behavior will be validated by the following system-tests: DataDog/system-tests#2385

Checklist

• Change(s) are motivated and described in the PR description
• Testing strategy is described if automated tests are not included in the PR
• Risks are described (performance impact, potential for breakage, maintainability)
• Change is maintainable (easy to change, telemetry, documentation)
• Library release note guidelines are followed or label changelog/no-changelog is set
• Documentation is included (in-code, generated user docs, public corp docs)
• Backport labels are set (if applicable)
• If this PR changes the public interface, I've notified @DataDog/apm-tees.

Reviewer Checklist

• Title is accurate
• All changes are related to the pull request's stated goal
• Description motivates each change
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Change is maintainable (easy to change, telemetry, documentation)
• Release note makes sense to a user of the library
• Author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: munir/w3c-phase-3-take2
Commit report: 40c47e0
Test service: dd-trace-py

✅ 0 Failed, 141918 Passed, 29870 Skipped, 7h 44m 31.7s Total duration (1h 51m 29.09s time saved)
⌛ 1 Performance Regression

⌛ Performance Regressions vs Default Branch (1)

• test_app_service_name - test_grpc.py 10.88s (+10.01s, +1148%) - Details

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-05-20 20:22:46

Comparing candidate commit 8f7eea9 in PR branch munir/w3c-phase-3-take2 with baseline commit c045d04 in branch main.

Found 0 performance improvements and 1 performance regressions! Performance is the same for 208 metrics, 9 unstable metrics.

scenario:httppropagationextract-datadog_tracecontext_tracestate_propagated_on_trace_id_match

• 🟥 execution_time [+6.276µs; +6.483µs] or [+14.670%; +15.155%]

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 9.09091% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 10.28%. Comparing base (66b96e9) to head (40c47e0).
Report is 6 commits behind head on main.

Files	Patch %	Lines
ddtrace/propagation/http.py	10.00%	9 Missing ⚠️
ddtrace/internal/constants.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #9254       +/-   ##
===========================================
- Coverage   76.02%   10.28%   -65.75%     
===========================================
  Files        1294     1264       -30     
  Lines      122816   120999     -1817     
===========================================
- Hits        93370    12439    -80931     
- Misses      29446   108560    +79114     

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[brettlangdon]

isn't the point of the configuration value for the inject/extract styles to denote precedence order of headers to look at?

[brettlangdon]

isn't the point of the configuration value for the inject/extract styles to denote precedence order of headers to look at?

we talked about this off GitHub. "yes", but there is an edge case where that behavior is not desired. this change is really a bug fix for a known edge case when things break.

[brettlangdon]

Even those this is a fix we are not going to backport it right now. There are other changes needed on intake to make this fix work properly. Waiting until 2.10.0 release will be acceptable for this. We can choose to backport this in the future once the intake pieces are ready.