Clarify B3 requirements and configuration (#1570)

open-telemetry · Mar 24, 2021 · 3f07b66 · 3f07b66
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -10,6 +10,7 @@ release.
 ### Context
 
 - Clarify composite `TextMapPropagator` method required and optional arguments. ([#1541](https://github.com/open-telemetry/opentelemetry-specification/pull/1541))
+- Clarify B3 requirements and configuration. ([#1570](https://github.com/open-telemetry/opentelemetry-specification/pull/1570))
 
 ### Traces
 

diff --git a/specification/context/api-propagators.md b/specification/context/api-propagators.md
@@ -376,3 +376,18 @@ When injecting B3, propagators:
   multi-header
 * MUST NOT propagate `X-B3-ParentSpanId` as OpenTelemetry does not support
   reusing the same id for both sides of a request.
+
+#### Fields
+
+Fields MUST return the header names that correspond to the configured format,
+i.e., the headers used for the inject operation.
+
+#### Configuration
+
+| Option    | Extract Order | Inject Format | Specification     |
+|-----------|---------------|---------------| ------------------|
+| B3 Single | Single, Multi | Single        | [Link][b3-single] |
+| B3 Multi  | Single, Multi | Multi         | [Link][b3-multi]  |
+
+[b3-single]: https://github.com/openzipkin/b3-propagation#single-header
+[b3-multi]: https://github.com/openzipkin/b3-propagation#multiple-headers
diff --git a/specification/sdk-environment-variables.md b/specification/sdk-environment-variables.md
@@ -41,8 +41,8 @@ Known values for OTEL_PROPAGATORS are:
 
 - `"tracecontext"`: [W3C Trace Context](https://www.w3.org/TR/trace-context/)
 - `"baggage"`: [W3C Baggage](https://www.w3.org/TR/baggage/)
-- `"b3"`: [B3 Single](https://github.com/openzipkin/b3-propagation#single-header)
-- `"b3multi"`: [B3 Multi](https://github.com/openzipkin/b3-propagation#multiple-headers)
+- `"b3"`: [B3 Single](./context/api-propagators.md#configuration)
+- `"b3multi"`: [B3 Multi](./context/api-propagators.md#configuration)
 - `"jaeger"`: [Jaeger](https://www.jaegertracing.io/docs/1.21/client-libraries/#propagation-format)
 - `"xray"`: [AWS X-Ray](https://docs.aws.amazon.com/xray/latest/devguide/xray-concepts.html#xray-concepts-tracingheader) (_third party_)
 - `"ottrace"`: [OT Trace](https://github.com/opentracing?q=basic&type=&language=) (_third party_)