w3c(phase 3): ensure tracecontext headers always take precedence

[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

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 77.79%. Comparing base (92560fa) to head (17dfb2c).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2667   +/-   ##
=========================================
  Coverage     77.78%   77.79%           
  Complexity     2223     2223           
=========================================
  Files           226      226           
  Lines         26347    26357   +10     
  Branches        988      988           
=========================================
+ Hits          20495    20505   +10     
  Misses         5326     5326           
  Partials        526      526           

Flag	Coverage Δ
appsec-extension	69.13% <ø> (ø)
tracer-extension	78.66% <80.00%> (+0.01%)	⬆️
tracer-php	80.33% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
ext/distributed_tracing_headers.c	84.63% <80.00%> (+0.17%)	⬆️

... and 1 file with indirect coverage changes

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[pr-commenter]

Benchmarks

Benchmark execution time: 2024-05-31 21:20:05

Comparing candidate commit 17dfb2c in PR branch munir-w3c-phase3 with baseline commit 92560fa in branch master.

Found 3 performance improvements and 1 performance regressions! Performance is the same for 174 metrics, 0 unstable metrics.

scenario:EmptyFileBench/benchEmptyFileBaseline-opcache

• 🟥 execution_time [+79.829µs; +203.211µs] or [+3.242%; +8.254%]

scenario:PDOBench/benchPDOBaseline

• 🟩 execution_time [-20.127µs; -16.833µs] or [-10.515%; -8.794%]

scenario:PDOBench/benchPDOOverhead

• 🟩 execution_time [-17.605µs; -13.760µs] or [-6.147%; -4.804%]

scenario:PDOBench/benchPDOOverheadWithDBM

• 🟩 execution_time [-18.892µs; -16.870µs] or [-6.057%; -5.409%]

[bwoebi]

Looks good now :-)