Move integration code out of the main opentelemetry crate

[djc]

Into separate integration crates. This makes for more smaller crates, but makes sure we don't have dependencies in the core that we shouldn't have (which causes to have to upgrade in lockstep with their releases).

[djc]

Things that probably qualify:

• async-std
• bincode?
• regex?
• tokio
• tonic
• reqwest
• surf

[jtescher]

👍 could also consider http and the testing utils as candidates

[TommyCpp]

For proto definition. I'd suggest we move it to a separate it into separate crate(opentelemetry-proto maybe)? And support grpcio or tonic there.

[djc]

If we need to support grpcio and tonic, those should probably be two separate crates IMO.

[djc]

I spent the morning looking at this. The Injector and Extractor interfaces are tricky, because coherence requires that implementations for foreign types live in the same crate as the trait definitions. I did some experiments with using propagator types that implemented Extractor<T> (with T something like http::HeaderMap), but this clashes with the design of the global propagator, which cannot easily abstract over a particular type of propagator.

I did remove the regex dependency (#411, in favor of a small function that validates the trace state key) and moved bincode to dev-dependencies (#413, along with some other dependency management).

[djc]

#415 moves the dependencies on http, reqwest and surf into a separate opentelemetry-http crate. At this point I'm inclined to leave tokio and async-std in, as they're pretty stable anyway (especially now that tokio has gone 1.0).

[jtescher]

@djc is the work related to this issue complete? or should we keep this issue open

[TommyCpp]

I want to mention that we need to update the doc in opentelemetry/lib.rs. Especially the Crate Feature Flags part.

opentelemetry-rust/opentelemetry/src/lib.rs

Lines 36 to 54 in f79586b

	//! ## Crate Feature Flags
	//!
	//! The following core crate feature flags are available:
	//!
	//! * `trace`: Includes the trace API and SDK (enabled by default).
	//! * `metrics`: Includes the unstable metrics API and SDK.
	//! * `serialize`: Adds [serde] serializers for common types.
	//!
	//! Support for recording and exporting telemetry asynchronously can be added
	//! via the following flags:
	//!
	//! * `tokio-support`: Spawn telemetry tasks using [tokio]'s runtime.
	//! * `async-std`: Spawn telemetry tasks using [async-std]'s runtime.
	//!
	//! Finally the following flags can be used by exporter authors:
	//!
	//! * `reqwest`: Implementation of [`HttpClient`] for [reqwest].
	//! * `surf`: Implementation of [`HttpClient`] for [surf]`.
	//!

[djc]

@TommyCpp thanks for taking care of the documentation update.

I think this ticket is complete, closing.

[TommyCpp]

@jtescher @djc I don't think we published the opentelemetry-aws and opentelemetry-datadog. Should we do that?

[jtescher]

@TommyCpp yeah I think we could probably cut a new release, want to prepare the changelogs?