Remove BinaryFormat and HttpTextFormat from Tracer

[songy23]

Fixes #112. Those formats are moved into Propagators.

[bogdandrutu]

I think we still need this. We need a Binary/Http formats for SpanContext and for DistributedContext. Do you take a dependency on trace/distributedCtxt there?

[bogdandrutu]

The propagators define a format that will be a template because they do not depend on SpanContext or DistributedContext. I am not sure how do I get an instance of the BinaryFormat that knows to serialize a SpanContext vs one that knows to serialize a DistributedContext.

[bogdandrutu]

The propagators define a format that will be a template because they do not depend on SpanContext or DistributedContext. I am not sure how do I get an instance of the BinaryFormat that knows to serialize a SpanContext vs one that knows to serialize a DistributedContext.

[songy23]

@bogdandrutu From my understanding the Propagators API will take a dependency on distributed context/span context. An example from https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/api-propagators.md:

ToBytes:
Required arguments:
the value to serialize, can be SpanContext or DistributedContext.

The point here is we should have a different entry that holds the formats rather than Tracer. So it will be something like

OpenTelemetry.getPropagator().getTracingBinaryFormat();

rather than

OpenTelemetry.getTracer().getBinaryFormat();

Which is closer to what we had in OpenCensus (PropagationComponent vs. Tracer).

[bogdandrutu]

Ok so you need to propose the entire change not just removing the once in the tracer, currently I don't see anywhere documented the API you suggested.

[songy23]

Added a note in 4aa2b6c. I think this matched what Go (open-telemetry/opentelemetry-go#85) and Python (open-telemetry/opentelemetry-python#78) did.

[carlosalberto]

you need to propose the entire change not just removing the once in the tracer

Agree with this (unless that other changes happens to be too big).

[rghetia]

@songy23 is it fair to say that we have an agreement on principle but requires additional changes in this PR before it can be merged?

[songy23]

Looks this is addressed in #209 (https://github.com/open-telemetry/opentelemetry-specification/pull/209/files#diff-ea4f4a46fe8755cf03f9fb3a6434cb0cR130):

The Tracer SHOULD allow end users to configure other tracing components that
control how Spans are passed across process boundaries, inclucding the binary
and text format Propagators used to serialize Spans created by the
Tracer.

Since it says "SHOULD" rather than "MUST" I would assume having Tracer.GetBinaryFormat and Tracer.GetHttpTextFormat is still recommended but not required.

[songy23]

Superseded by #209.

[rghetia]

The Tracer SHOULD allow end users to configure other tracing components that control how
Spans are passed across process boundaries, including the binary and text format Propagators
used to serialize Spans created by the Tracer.

And

The implementation MUST provide no-op binary and text Propagators, which the Tracer
SHOULD use by default if other propagators are not configured. SDKs SHOULD use the W3C
HTTP Trace Context as the default text format. For more details, see trace-context.

It is not clear. First paragraph says that Tracer SHOULD but DOESN'T HAVE TO allow end user..
In the second paragraph it says that Trace MUST provide no-op binary and text propagator.