Adding net/http client instrumentor

[oxeye-gal]

Hi,

This PR attempts to add instrumentation for net/http client.

We do it by writing a fake tophash value (as calculating the correct one will be harder to achieve) to the first headers map bucket and writing the "traceparent" header key and value into memory.

This was tested with Go versions 1.12-1.19.

Our test environment consisted of instrumented Python application that sends a request to instrumented Go http server which in turn sends an http request to an additional instrumented Go http server.

The produced trace looks like the following:

We would love to get your feedback on this.
Thanks!

[edeNFed]

So sorry for the huge delay! I promise to finish looking on this by the end of this week

[vreynolds]

@oxeye-gal any interest in re-opening this in https://github.com/open-telemetry/opentelemetry-go-instrumentation ?

[oxeye-gal]

Hi @vreynolds, sure thing i'll do it later this week.

[MikeGoldsmith]

Hey @oxeye-gal - If you would like help porting this to the OTel repo, let me know -- I'm happy to help however I can.

[vreynolds]

fwiw, I was able to see this work writing traceparent headers in a test app, with a small change to how link.UprobeOptions are initialized. Looks like in the OTel repo the offsets should be passed as Address option rather than Offset