Add api::context::propagation::Carrier implementation for http::header::HeaderMap

[swilcox3]

Hey, I'm loving the direction this is going, I think it's really going to help me with my microservices backend written in tonic. I've already got my individual services reporting to Jaeger, now I'm trying to get context propagation working. tonic exposes a trace_fn that gives you a http::header::HeaderMap. I'm trying to use a B3Propagator to extract the context from the HeaderMap, but Carrier is only implemented for HashMap with &'static str as the key.
Could you make an implementation of Carrier for http::header::HeaderMap please? Because of Rust's rules around implementations, I can't make an implementation of a foreign trait on a foreign type.
Also in general, it seems like Carrier shouldn't be using &'static str, but should instead just be using &str. I can take a stab at a pull request if you like.

[jtescher]

Hey @swilcox3, moving to &str sounds like a good improvement. A PR there would be appreciated! Also you can see https://github.com/open-telemetry/opentelemetry-rust/tree/master/examples/grpc for a working example of the (currently sub-optimal) tonic usage.

I think adding an impl for http::header::HeaderMap would be good as well, maybe behind a http feature flag?

[swilcox3]

Oh I didn't see that example. You're right, it does the job, but there's definitely some boilerplate. I'll take a look at putting a PR together, it shouldn't be too complicated.

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On Mon, May 18, 2020, 12:00 PM Julian Tescher ***@***.***> wrote: Hey @swilcox3 <https://github.com/swilcox3>, moving to &str sounds like a good improvement. A PR there would be appreciated! Also you can see https://github.com/open-telemetry/opentelemetry-rust/tree/master/examples/grpc for a working example of the (currently sub-optimal) tonic usage. I think adding an impl for http::header::HeaderMap would be good as well, maybe behind a http feature flag? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#114 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFIDRMHGUVHAQHPGD25UALTRSFLRFANCNFSM4NEARDSA> .

[jtescher]

Resolved in #115