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Clarify b3 debug flag and parent span id handling #1045

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merged 4 commits into from
Oct 28, 2020
Merged

Clarify b3 debug flag and parent span id handling #1045

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10c99be
clarify handling b3 debug flag and parent span id propagation
mwear Oct 1, 2020
0606aa1
Apply suggestions from code review
mwear Oct 19, 2020
034e948
Update specification/context/api-propagators.md
mwear Oct 22, 2020
1ef93ec
Update specification/context/api-propagators.md
mwear Oct 27, 2020
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22 changes: 16 additions & 6 deletions specification/context/api-propagators.md
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Expand Up @@ -332,15 +332,23 @@ a community are:

### B3 Requirements

B3 has both single and multi-header encodings. To maximize compatibility between
implementations, the following guidelines have been established for B3
propagation in OpenTelemetry.
B3 has both single and multi-header encodings. It also has semantics that do not
map directly to OpenTelemetry such as a debug trace flag, and allowing spans
from both sides of request to share the same id. To maximize compatibility
between OpenTelemetry and Zipkin implementations, the following guidelines have
been established for B3 context propagation.

#### Extract

Propagators MUST attempt to extract B3 encoded using single and multi-header
formats. When extracting, the single-header variant takes precedence over
the multi-header version.
When extracting B3, propagators:

* MUST attempt to extract B3 encoded using single and multi-header
formats. The single-header variant takes precedence over
the multi-header version.
* MUST preserve a debug trace flag, if received, and propagate
it with subsequent requests. Additionally, an OpenTelemetry implementation
MUST set the sampled trace flag when the debug flag is set.
* MUST NOT reuse `X-B3-SpanId` as the id for the server-side span.

#### Inject

Expand All @@ -349,3 +357,5 @@ When injecting B3, propagators:
* MUST default to injecting B3 using the single-header format
* MUST provide configuration to change the default injection format to B3
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multi-header
* MUST NOT propagate `X-B3-ParentSpanId` as OpenTelemetry does not support
reusing the same id for both sides of a request.