[otelhttp] Data race warning causing test failures in Bitbucket pipelines

[BeautifuLie]

Description

During test execution in Bitbucket pipelines, a data race warning occurs when using otelhttp.NewTransport as the transport mechanism in the HTTP client and calling the Do() method from the standard Go "net/http" library. This warning leads to test failures in Bitbucket pipelines.This warning does not always appear, about 7 out of 10 times during test runs.

==================
WARNING: DATA RACE
Write at 0x00c00027e498 by goroutine 64:
  go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp.(*bodyWrapper).Read()
      /go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/[email protected]/wrap.go:40 +0x9c
  io.discard.ReadFrom()
      /usr/local/go/src/io/io.go:666 +0x91
  io.(*discard).ReadFrom()
      <autogenerated>:1 +0x4c
  io.copyBuffer()
      /usr/local/go/src/io/io.go:415 +0x22e
  io.CopyBuffer()
      /usr/local/go/src/io/io.go:402 +0x8f
  net/http.(*transferWriter).doBodyCopy()
      /usr/local/go/src/net/http/transfer.go:416 +0x144
  net/http.(*transferWriter).writeBody()
      /usr/local/go/src/net/http/transfer.go:376 +0x7ac
  net/http.(*Request).write()
      /usr/local/go/src/net/http/request.go:755 +0x1413
  net/http.(*persistConn).writeLoop()
      /usr/local/go/src/net/http/transport.go:2446 +0x379
  net/http.(*Transport).dialConn.gowrap3()
      /usr/local/go/src/net/http/transport.go:1799 +0x33
Previous read at 0x00c00027e498 by goroutine 58:
  go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp.(*Transport).RoundTrip()
      /go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/net/http/[email protected]/transport.go:185 +0xfa4
  net/http.send()
      /usr/local/go/src/net/http/client.go:259 +0x9a6
  net/http.(*Client).send()
      /usr/local/go/src/net/http/client.go:180 +0x14e
  net/http.(*Client).do()
      /usr/local/go/src/net/http/client.go:724 +0x11c8
  net/http.(*Client).Do()
      /usr/local/go/src/net/http/client.go:590 +0x464
....
  testing.tRunner()
      /usr/local/go/src/testing/testing.go:1689 +0x21e
  testing.(*T).Run.gowrap1()
      /usr/local/go/src/testing/testing.go:1742 +0x44
Goroutine 64 (running) created at:
  net/http.(*Transport).dialConn()
      /usr/local/go/src/net/http/transport.go:1799 +0x27fe
  net/http.(*Transport).dialConnFor()
      /usr/local/go/src/net/http/transport.go:1484 +0x124
  net/http.(*Transport).queueForDial.gowrap1()
      /usr/local/go/src/net/http/transport.go:1449 +0x44

Environment

• OS: [LINUX]
• Architecture: [amd64]
• Go Version: [1.21]
• otelhttp version: [v0.48.0]

Steps To Reproduce

1.Run the tests where otelhttp.NewTransport is used as the transport mechanism in the HTTP client.

httpClient := http.Client{
		Transport: otelhttp.NewTransport(http.DefaultTransport),
	}

2.Observe the data race warning that may occur when calling the Do() method of the HTTP client from the standard Go "net/http" library.
resp, err := httpClient.Do(req)

Note that this warning does not occur consistently but rather approximately 7 out of 10 times during test runs.

Expected behavior

The golang race detector shouldn't give a race report when using otelhttp.

[dmathieu]

Duplicate of #4895 that will be fixed with the next release.