Context Propagation

/**
 * Propagates SpanContext through W3C Trace Context format
 * Based on https://www.w3.org/TR/trace-context/
 */
class W3CTraceContextPropagator implements TextMapPropagator {
  /**
   * Inject trace context into carrier using traceparent and tracestate headers
   * @param context - OpenTelemetry context containing span information
   * @param carrier - Object to inject headers into (typically HTTP headers)
   * @param setter - Function to set header values in the carrier
   */
  inject(context: Context, carrier: unknown, setter: TextMapSetter): void;

  /**
   * Extract trace context from carrier headers
   * @param context - OpenTelemetry context to enhance with extracted span context
   * @param carrier - Object containing headers (typically HTTP request headers) 
   * @param getter - Function to retrieve header values from the carrier
   * @returns Context with extracted span context
   */
  extract(context: Context, carrier: unknown, getter: TextMapGetter): Context;

  /**
   * Get list of header fields used by this propagator
   * @returns Array of header field names
   */
  fields(): string[];
}

const TRACE_PARENT_HEADER: string;
const TRACE_STATE_HEADER: string;

/**
 * Parse traceparent header value into SpanContext
 * @param traceParent - Traceparent header value in format: version-traceId-spanId-flags
 * @returns SpanContext object or null if parsing fails
 */
function parseTraceParent(traceParent: string): SpanContext | null;

import { W3CTraceContextPropagator, TRACE_PARENT_HEADER } from "@opentelemetry/core";
import { trace } from "@opentelemetry/api";

const propagator = new W3CTraceContextPropagator();
const headers: Record<string, string> = {};

// Inject current trace context into HTTP headers
const span = trace.getActiveSpan();
if (span) {
  const context = trace.setSpan(trace.context.active(), span);
  propagator.inject(context, headers, {
    set: (carrier, key, value) => carrier[key] = value
  });
  
  console.log(headers[TRACE_PARENT_HEADER]); // e.g., "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01"
}

// Extract trace context from incoming HTTP headers
const incomingHeaders = {
  "traceparent": "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01",
  "tracestate": "congo=t61rcWkgMzE"
};

const extractedContext = propagator.extract(trace.context.active(), incomingHeaders, {
  get: (carrier, key) => carrier[key]
});

const spanContext = trace.getSpanContext(extractedContext);
console.log(spanContext?.traceId); // "4bf92f3577b34da6a3ce929d0e0e4736"

/**
 * Propagates Baggage through W3C Baggage format
 * Based on https://w3c.github.io/baggage/
 */
class W3CBaggagePropagator implements TextMapPropagator {
  /**
   * Inject baggage into carrier using baggage header
   * @param context - OpenTelemetry context containing baggage
   * @param carrier - Object to inject headers into
   * @param setter - Function to set header values in the carrier
   */
  inject(context: Context, carrier: unknown, setter: TextMapSetter): void;

  /**
   * Extract baggage from carrier headers
   * @param context - OpenTelemetry context to enhance with extracted baggage
   * @param carrier - Object containing headers
   * @param getter - Function to retrieve header values from the carrier
   * @returns Context with extracted baggage
   */
  extract(context: Context, carrier: unknown, getter: TextMapGetter): Context;

  /**
   * Get list of header fields used by this propagator
   * @returns Array of header field names
   */
  fields(): string[];
}

/**
 * Parse baggage header string into key-value pairs
 * @param value - Baggage header value
 * @returns Record of key-value pairs
 */
function parseKeyPairsIntoRecord(value?: string): Record<string, string>;

import { W3CBaggagePropagator } from "@opentelemetry/core";
import { propagation } from "@opentelemetry/api";

const baggagePropagator = new W3CBaggagePropagator();
const headers: Record<string, string> = {};

// Create baggage and inject into headers
const baggage = propagation.createBaggage({
  "user.id": { value: "12345" },
  "session.id": { value: "abcdef" }
});

const contextWithBaggage = propagation.setBaggage(propagation.active(), baggage);
baggagePropagator.inject(contextWithBaggage, headers, {
  set: (carrier, key, value) => carrier[key] = value
});

console.log(headers.baggage); // "user.id=12345,session.id=abcdef"

// Extract baggage from incoming headers
const incomingHeaders = {
  "baggage": "user.id=12345,session.id=abcdef,theme=dark"
};

const extractedContext = baggagePropagator.extract(propagation.active(), incomingHeaders, {
  get: (carrier, key) => carrier[key]
});

const extractedBaggage = propagation.getBaggage(extractedContext);
console.log(extractedBaggage?.getEntry("user.id")?.value); // "12345"

/**
 * Configuration object for composite propagator
 */
interface CompositePropagatorConfig {
  /**
   * List of propagators to run. Propagators run in list order.
   * If a propagator later in the list writes the same context key
   * as a propagator earlier in the list, the later one will "win".
   */
  propagators?: TextMapPropagator[];
}

/**
 * Combines multiple propagators into a single propagator
 */
class CompositePropagator implements TextMapPropagator {
  /**
   * Construct a composite propagator from a list of propagators
   * @param config - Configuration object for composite propagator
   */
  constructor(config?: CompositePropagatorConfig);

  /**
   * Run each of the configured propagators with the given context and carrier.
   * Propagators are run in the order they are configured.
   * @param context - Context to inject
   * @param carrier - Carrier into which context will be injected
   * @param setter - Function to set values in carrier
   */
  inject(context: Context, carrier: unknown, setter: TextMapSetter): void;

  /**
   * Run each of the configured propagators with the given context and carrier.
   * Propagators are run in the order they are configured.
   * @param context - Context to add values to
   * @param carrier - Carrier from which to extract context
   * @param getter - Function to get values from carrier
   * @returns Enhanced context with extracted values
   */
  extract(context: Context, carrier: unknown, getter: TextMapGetter): Context;

  /**
   * Get combined list of header fields from all configured propagators
   * @returns Array of header field names
   */
  fields(): string[];
}

import {
  CompositePropagator,
  W3CTraceContextPropagator,
  W3CBaggagePropagator
} from "@opentelemetry/core";

// Create composite propagator with multiple propagators
const compositePropagator = new CompositePropagator({
  propagators: [
    new W3CTraceContextPropagator(),
    new W3CBaggagePropagator(),
  ],
});

// Use composite propagator for both trace context and baggage
const headers: Record<string, string> = {};

compositePropagator.inject(currentContext, headers, {
  set: (carrier, key, value) => carrier[key] = value
});

// Headers now contain both traceparent and baggage
console.log(headers.traceparent); // "00-..."
console.log(headers.baggage);     // "key1=value1,key2=value2"

// Extract from headers containing multiple propagation formats
const incomingHeaders = {
  "traceparent": "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01",
  "baggage": "user.id=12345,session.id=abcdef"
};

const extractedContext = compositePropagator.extract(
  propagation.active(), 
  incomingHeaders, 
  { get: (carrier, key) => carrier[key] }
);

// Context now contains both span context and baggage
const spanContext = trace.getSpanContext(extractedContext);
const baggage = propagation.getBaggage(extractedContext);