Implement the text format so that w3c trace context headers are propagated.

[jkwatson]

No description provided.

[codecov-io]

Codecov Report

Merging #601 into master will increase coverage by 0.41%.
The diff coverage is 95.23%.

@@             Coverage Diff             @@
##             master    #601      +/-   ##
===========================================
+ Coverage     78.28%   78.7%   +0.41%     
- Complexity      694     707      +13     
===========================================
  Files            86      87       +1     
  Lines          2459    2479      +20     
  Branches        233     236       +3     
===========================================
+ Hits           1925    1951      +26     
+ Misses          445     441       -4     
+ Partials         89      87       -2

Impacted Files	Coverage Δ	Complexity Δ
...stributedcontext/DistributedContextManagerSdk.java	66.66% <0%> (ø)	4 <0> (ø)	⬇️
...butedcontext/DistributedContextHttpTextFormat.java	100% <100%> (ø)	10 <10> (?)
...ntelemetry/sdk/trace/RecordEventsReadableSpan.java	95.93% <0%> (+1.16%)	55% <0%> (+1%)	⬆️
.../sdk/distributedcontext/DistributedContextSdk.java	91.83% <0%> (+2.04%)	15% <0%> (+1%)	⬆️
...elemetry/sdk/trace/export/BatchSpansProcessor.java	95.74% <0%> (+2.12%)	9% <0%> (ø)	⬇️
...ry/distributedcontext/EmptyDistributedContext.java	100% <0%> (+20%)	4% <0%> (+1%)	⬆️

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[bogdandrutu]

I think this is the correlation-context from the w3c.

[jkwatson]

Is there something you think should be renamed in here?

[arminru]

Hi John!

W3C Trace Context (text format) is already implemented here:
https://github.com/open-telemetry/opentelemetry-java/blob/master/api/src/main/java/io/opentelemetry/trace/propagation/HttpTraceContext.java

The DistributedContext you're trying to implement is a compound of the W3C Correlation Context (currently being drafted here) on the one hand and what is commonly referred to as "Baggage" on the other hand, but not the W3C Trace Context (unless I'm mixing things up myself here).
There's a proposal to properly split DistributedContext into Correlation Context and Baggage being discussed here: open-telemetry/oteps#42. It might be better to wait for this to be settled.

See also:

• https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/overview.md#distributedcontext
• https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/api-distributedcontext.md
• Proposal to separate context propagation from observability oteps#42
• Proposal to rename distributed context and add support for baggage. oteps#36

[jkwatson]

Sorry, the title of the PR is probably a little misleading. The purpose here was to at least propagate the trace context headers, so traces aren't broken. With the current implementation (that just throws UnsupportedOperationExceptions), traces are broken when requests flow through the tracers.

I'm happy to update any and all verbiage as appropriate, or simply have the methods return empty contexts and not inject anything (still resulting in broken traces, but at least not throwing exceptions).

[jkwatson]

I was confused about where the headers needed to be propagated. This is actually fixed for real in #608 . closing!