Go std net HTTP/1 clients: avoid injecting the traceparent twice

[mariomac]

Summary

This is the first PR of a series that would fix issue #2732 (duplicate traceparent in SDK instrumented workloads) at different levels/protocol.

This PR fixes the issue for Go standard net package (HTTP/1) clients. It adds a uprobe to the return address of header_writeSubset: when headers are written in the request, we check for a header containing Traceparent:. If it already exists, we abort the context propagation. Otherwise we inject the Traceparent: header.

Validation

• I have read and followed the contributing guidelines
• If this enhances / fixes / changes a core feature, I have updated the features documentation and support matrix as needed.

[mmat11]

I see 5.10 is failing with

bpf_verifier_test.go:109: BPF verifier rejected program(s):
    load program: invalid argument:
        number of funcs in func_info doesn't match number of subprogs

Probably the new programs need to be added to FixupSpec() because of the non-inlined subprog passed to bpf_loop

[Copilot]

Pull request overview

Note

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This PR addresses duplicate traceparent injection for Go net/http (HTTP/1.x) clients by adding a return uprobe that detects whether the application already serialized a Traceparent header, and skips eBPF injection when present.

Changes:

• Add an entry/return uprobe pair around net/http.Header.writeSubset to detect an existing Traceparent and avoid double-injection.
• Introduce a privileged integration test plus a small helper binary to validate both “header already present” and “header absent” scenarios.
• Wire the new return probe into the gotracer probe descriptor list.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 11 comments.

File	Description
pkg/internal/ebpf/gotracer/tphttp_privileged_test.go	Adds privileged end-to-end test that attaches the tracer to a live Go process and asserts Traceparent is not duplicated.
pkg/internal/ebpf/gotracer/testdata/tphttpclient/main.go	Adds helper program that runs an HTTP/1 server/client loop and reports how many Traceparent values were received.
pkg/internal/ebpf/gotracer/gotracer.go	Registers a return (“End”) probe for net/http.Header.writeSubset to support conditional injection.
bpf/gotracer/go_nethttp.c	Implements the new return uprobe logic: stash writer state on entry, scan serialized headers on return, and inject only if missing.

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@7204eac). Learn more about missing BASE report.
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/ebpf/common/common.go	85.71%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2752   +/-   ##
=======================================
  Coverage        ?   69.76%           
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  Files           ?      359           
  Lines           ?    51142           
  Branches        ?        0           
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  Hits            ?    35678           
  Misses          ?    13236           
  Partials        ?     2228           

Flag	Coverage Δ
integration-test	50.21% <62.50%> (?)
integration-test-arm	25.31% <55.55%> (?)
integration-test-vm-5.15-lts	26.69% <100.00%> (?)
integration-test-vm-6.18-lts	26.15% <62.50%> (?)
k8s-integration-test	33.97% <62.50%> (?)
oats-test	34.77% <62.50%> (?)
unittests	67.85% <62.50%> (?)

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[grcevski]

LGTM! Nice this is the right approach. I'll let you deal with the copilot comments.