Gin instrumentation: support reading Client IP from custom headers, and make sure proxy is trusted

[ItalyPaleAle]

With Gin, it's possible to configure the server to read the Client IP from custom headers; examples include X-Real-Ip or CF-Connecting-IP. This PR makes it possible to set as span attribute the same IP that Gin reads.

Additionally, it makes sure that headers such as "X-Forwarded-For" are used only if Gin is configured to trust the upstream server

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: ItalyPaleAle / name: Alessandro (Ale) Segala (5236a72, 31c7ea0, e1c00de, 33dd2c8, 8a45c9d, 689f2c9, b897983, 69d16d0, 91ecb8e, 5739da4)
• ✅ login: dmathieu / name: Damien Mathieu (b19ba59)

[dmathieu]

PS: Also fixed unit tests, where there were assertions inside handlers, which are executed in separate goroutines

Could you split that into another PR, to make things easier to review?

[ItalyPaleAle]

PS: Also fixed unit tests, where there were assertions inside handlers, which are executed in separate goroutines

Could you split that into another PR, to make things easier to review?

Done

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.8%. Comparing base (1883203) to head (b19ba59).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6095   +/-   ##
=====================================
  Coverage   75.7%   75.8%           
=====================================
  Files        207     207           
  Lines      19403   19469   +66     
=====================================
+ Hits       14695   14758   +63     
- Misses      4273    4275    +2     
- Partials     435     436    +1     

Files with missing lines	Coverage Δ
...lei/go-restful/otelrestful/internal/semconv/env.go	89.1% <100.0%> (ø)
...o-restful/otelrestful/internal/semconv/httpconv.go	86.9% <100.0%> (+0.1%)	⬆️
...go-restful/otelrestful/internal/semconv/v1.20.0.go	89.9% <100.0%> (ø)
...stful/otelrestful/internal/semconvutil/httpconv.go	95.7% <100.0%> (+<0.1%)	⬆️
...hub.com/emicklei/go-restful/otelrestful/restful.go	100.0% <100.0%> (ø)
...umentation/github.com/gin-gonic/gin/otelgin/gin.go	92.9% <100.0%> (+0.3%)	⬆️
....com/gin-gonic/gin/otelgin/internal/semconv/env.go	92.5% <100.0%> (ø)
...gin-gonic/gin/otelgin/internal/semconv/httpconv.go	86.9% <100.0%> (+0.1%)	⬆️
.../gin-gonic/gin/otelgin/internal/semconv/v1.20.0.go	89.9% <100.0%> (ø)
...gonic/gin/otelgin/internal/semconvutil/httpconv.go	95.7% <100.0%> (+<0.1%)	⬆️
... and 17 more

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[dmathieu]

This will need a changelog entry.

[ItalyPaleAle]

@dmathieu is this PR ready to be merged?

[dmathieu]

PRs need two approvals.

[ItalyPaleAle]

PRs need two approvals.

@dmathieu is there a way I get a review/approval from another person?

[dmathieu]

Ping @open-telemetry/go-approvers for review.

Note that this instrumentation has no owner, and is therefore in the process of being deprecated/removed unless someone steps up to own it (which also explains the lack of reviews).
#6190

[ItalyPaleAle]

Looks like this instrumentation may have an owner now. If I fix the merge conflicts, can this PR be merged now?
@open-telemetry/go-approvers @akats7

[akats7]

Hey @ItalyPaleAle, can you please resolve the conflicts

[ItalyPaleAle]

@akats7 sorry for the delay, as the amount of merge conflicts that had accumulated meant I had to recreate the PR from scratch.

Should be good for your review now!

[ItalyPaleAle]

Could I get a review on this please?

Also, is there a way to ensure PRs like this don't keep accumulating conflicts in the changelog?