fix(grpc.aio): resolve distributed tracing concurrency bug

[mabdinur]

Previously the tracer accessed the grpc metadata (which contained distributing tracing headers) directly from the Server’s HandlerCallDetails (here). This was not a safe operation, since the server’s handlerdetails is modified/set by every request. When multiple requests were handled concurrently the grpcaio integration would overwrite distributing tracing headers and clobber multiple unrelated trace chunks into one trace.

This PR ensures distributed tracing headers are extracted from the call handler details that's unique to the request: ServicerContext.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, 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

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/contrib/internal/grpc/aio_server_interceptor.py                 @DataDog/apm-core-python @DataDog/apm-idm-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: munir/grpc-use-ServicerContext-context-to-get-metadata
Commit report: c3042e2
Test service: dd-trace-py

✅ 0 Failed, 610 Passed, 586 Skipped, 20m 2.89s Total duration (16m 7.22s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-11-15 16:19:57

Comparing candidate commit c3042e2 in PR branch munir/grpc-use-ServicerContext-context-to-get-metadata with baseline commit 19f6a8c in branch main.

Found 1 performance improvements and 3 performance regressions! Performance is the same for 384 metrics, 2 unstable metrics.

scenario:iast_aspects-ospathdirname_aspect

• 🟥 execution_time [+385.270ns; +463.568ns] or [+10.343%; +12.445%]

scenario:iast_aspects-ospathjoin_aspect

• 🟥 execution_time [+470.899ns; +541.946ns] or [+9.046%; +10.411%]

scenario:iast_aspects-ospathnormcase_aspect

• 🟩 execution_time [-253.877ns; -218.525ns] or [-9.242%; -7.955%]

scenario:iast_aspects-ospathsplit_aspect

• 🟥 execution_time [+592.409ns; +671.214ns] or [+15.048%; +17.050%]