otelhttp.NewHandler adds backpropagation

[pellared]

This code makes a "backpropagation" by adding the propagation headers to the HTTP response.

opentelemetry-go-contrib/instrumentation/net/http/otelhttp/wrap.go

Line 94 in 8cf7954

w.props.Inject(w.ctx, propagation.HeaderCarrier(w.Header()))

I feel that it is not right as it is a leakage of the internals.

I am not aware of any other OTel instrumentation (in whatever language/ecosystem) that adds "backpropagation".

I think that it should not work that way by default. Additionally, such an option should first be described in the spec. I understand that such a feature may be useful for implementing "Real User Monitoring".

[MrAlias]

It looks like this was introduced quite a while ago: open-telemetry/opentelemetry-go#218. There isn't an explicit reason it was added there.

Let's remove this as it is unspecified behavior.

[TylerHelmuth]

I can take a look at this.