OpenTelemetry Propagator B3

The OpenTelemetry b3 propagator package provides multiple propagator implementations for systems using the b3 context format. See the b3 specification for complete details.

B3 Formats

Single-Header Format:

b3: {TraceId}-{SpanId}-{SamplingState}-{ParentSpanId}

Multi-Header Format:

X-B3-TraceId: {TraceId}
X-B3-SpanId: {SpanId}
X-B3-ParentSpanId: {ParentSpanId}
X-B3-Sampled: {SamplingState}

{TraceId}
- Required
- Encoded as 32 or 16 lower-hex characters
- 16 character traceIds will be converted to 32 characters by left-padding with 0s to conform with the OpenTelemetry specification
{SpanId}
- Required
- Encoded as 16 lower-hex characters
{ParentSpanId}
- Optional
- Used to support the Zipkin functionality where the client and server spans that make up an HTTP request share the same id
- Not propagated by this library
{SamplingState} - Single-header
- Optional
- Valid values
  - 1 - Accept
  - 0 - Deny
  - d - Debug
  - Absent - Defer sampling decision
{SamplingState} - Multi-header
- Optional
- Valid values
  - 1 - Accept
  - 0 - Deny
{Flags} - Multi-header
- Optional
- Debug is encoded as X-B3-Flags: 1. Absent or any other value can be ignored. Debug implies an accept decision, so don't also send the X-B3-Sampled header.

B3 Propagation

The default B3Propagator implements b3 propagation according to the OpenTelemetry specification. It extracts b3 context from multi and single header encodings and injects context using the single-header b3 encoding by default. The inject encoding can be changed to multi-header via configuration. See the examples below.

B3 Single-Header Configuration

const api = require('@opentelemetry/api');
const { B3Propagator } = require('@opentelemetry/propagator-b3');

api.propagation.setGlobalPropagator(new B3Propagator());

B3 Multi-Header Configuration

const api = require('@opentelemetry/api');
const { B3Propagator, B3InjectEncoding } = require('@opentelemetry/propagator-b3');

api.propagation.setGlobalPropagator(
  new B3Propagator({ injectEncoding: B3InjectEncoding.MULTI_HEADER })
);

B3 Single and Multi-Header Configuration

The B3Propagator always extracts both the single and multi-header b3 encodings. If you need to inject both encodings this can accomplished using a composite propagator.

const api = require('@opentelemetry/api');
const { CompositePropagator } = require('@opentelemetry/core');
const { B3Propagator, B3InjectEncoding } = require('@opentelemetry/propagator-b3');
api.propagation.setGlobalPropagator(
  new CompositePropagator({
    propagators: [
      new B3Propagator(),
      new B3Propagator({ injectEncoding: B3InjectEncoding.MULTI_HEADER }),
    ],
  })
);

Useful links

For more information on OpenTelemetry, visit: https://opentelemetry.io/
For more about OpenTelemetry JavaScript: https://github.com/open-telemetry/opentelemetry-js
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