Refactor splunkhttp config processing

[pellared]

Why

#30 (comment)

Make the functional options API more user-friendly.
Currently, sample usage looks like this:

handler = splunkhttp.NewHandler(handler, "server", splunkhttp.WithOTelOpts(otelhttp.WithTracerProvider(provider)), splunkhttp.WithTraceResponseHeader(false))

What

Refactor config processing in splunkhttp package.

The changes allows achieving the following usage:

handler = splunkhttp.NewHandler(handler, "server", otelhttp.WithTracerProvider(provider), splunkhttp.WithTraceResponseHeader(false))

splunkhttp.WithOTelOpts() is no longer needed.

Deeper analysis and comparison to other possible approaches can be found here: open-telemetry/opentelemetry-go-contrib#746

Moreover, some tests were moved to appropriate files (see comments in PR).

[pellared]

Moved to trace_response_header_test.go

[pellared]

Moved to handler_test.go

[owais]

Why is the one supposed to be more beautiful highlighted with nice colors and the old one b/w? I see what you did there. I'll remember this trick :D

[owais]

Really like the net effect it has on API. Implementation looks fine and can be improve/changed later. 👍

[pellared]

@owais @MrAlias
I think we can merge it if you like this PR. All other proposals in open-telemetry/opentelemetry-go-contrib#746 have the same exported API.

Moreover, we could publish the first release of https://github.com/signalfx/splunk-otel-go 😉

However, there are good remarks in open-telemetry/opentelemetry-go-contrib#746 (comment)

[pellared]

@owais @MrAlias

I feel convinced to refactor this proposal. I put rationale further down in the issue.

Or we can keep the current design which is already in main.

What do you think?

[owais]

That looks pretty good to me. Only concern is that this works with the HTTP handler. Will it work with other types of instrumentations as easily?

[pellared]

That looks pretty good to me. Only concern is that this works with the HTTP handler. Will it work with other types of instrumentations as easily?

This PR and current design on main branch will not.

But this proposal will. I will make a PR on Monday

[owais]

Yeah, I meant the proposal. 👍

[pellared]

@owais Here is the new PR #41