chore: add fields operation to TextMapPropagator

packages/opentelemetry-api/src/context/propagation/NoopTextMapPropagator.ts

@@ -27,6 +27,9 @@ export class NoopTextMapPropagator implements TextMapPropagator {
   extract(context: Context, carrier: unknown): Context {
     return context;
   }
+  fields(): string[] {
+    return [];
+  }
 }
 
 export const NOOP_TEXT_MAP_PROPAGATOR = new NoopTextMapPropagator();

packages/opentelemetry-api/src/context/propagation/TextMapPropagator.ts

@@ -64,6 +64,14 @@ export interface TextMapPropagator<Carrier = any> {
     carrier: Carrier,
     getter: TextMapGetter<Carrier>
   ): Context;
+
+  /**
+   * Return a list of all fields which may be used by the propagator.
+   *
+   * This list should be used to clear fields before calling inject if a carrier is
+   * used more than once.
+   */
+  fields(): string[];
 }
 
 /**

packages/opentelemetry-core/src/context/propagation/B3MultiPropagator.ts

@@ -138,4 +138,14 @@ export class B3MultiPropagator implements TextMapPropagator {
     }
     return context;
   }
+
+  fields(): string[] {
+    return [
+      X_B3_TRACE_ID,
+      X_B3_SPAN_ID,
+      X_B3_FLAGS,
+      X_B3_SAMPLED,
+      X_B3_PARENT_SPAN_ID,
+    ];
+  }
 }

packages/opentelemetry-core/src/context/propagation/B3Propagator.ts

@@ -49,12 +49,15 @@ export class B3Propagator implements TextMapPropagator {
     carrier: unknown,
     setter: TextMapSetter
   ) => void;
+  public readonly _fields: string[];
 
   constructor(config: B3PropagatorConfig = {}) {
     if (config.injectEncoding === B3InjectEncoding.MULTI_HEADER) {
       this._inject = this._b3MultiPropagator.inject;
+      this._fields = this._b3MultiPropagator.fields();
     } else {
       this._inject = this._b3SinglePropagator.inject;
+      this._fields = this._b3SinglePropagator.fields();
     }
   }
 
@@ -69,4 +72,8 @@ export class B3Propagator implements TextMapPropagator {
       return this._b3MultiPropagator.extract(context, carrier, getter);
     }
   }
+
+  fields(): string[] {
+    return this._fields;
+  }
 }

packages/opentelemetry-core/src/context/propagation/B3SinglePropagator.ts

@@ -88,4 +88,8 @@ export class B3SinglePropagator implements TextMapPropagator {
       traceFlags,
     });
   }
+
+  fields(): string[] {
+    return [B3_CONTEXT_HEADER];
+  }
 }

packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts

@@ -128,4 +128,8 @@ export class HttpTraceContext implements TextMapPropagator {
     }
     return setExtractedSpanContext(context, spanContext);
   }
+
+  fields(): string[] {
+    return [TRACE_PARENT_HEADER, TRACE_STATE_HEADER];
+  }
 }

packages/opentelemetry-core/src/context/propagation/composite.ts

@@ -28,6 +28,7 @@ import { CompositePropagatorConfig } from './types';
 export class CompositePropagator implements TextMapPropagator {
   private readonly _propagators: TextMapPropagator[];
   private readonly _logger: Logger;
+  private readonly _fields: string[];
 
   /**
    * Construct a composite propagator from a list of propagators.
@@ -37,6 +38,14 @@ export class CompositePropagator implements TextMapPropagator {
   constructor(config: CompositePropagatorConfig = {}) {
     this._propagators = config.propagators ?? [];
     this._logger = config.logger ?? new NoopLogger();
+    this._fields = Array.from(
+      new Set(
+        this._propagators
+          // older propagators may not have fields function, null check to be sure
+          .map(p => p?.fields() ?? [])
+          .reduce((x, y) => x.concat(y))
+      )
+    );
   }
 
   /**
@@ -81,4 +90,9 @@ export class CompositePropagator implements TextMapPropagator {
       return ctx;
     }, context);
   }
+
+  fields(): string[] {
+    // return a new array so our fields cannot be modified
+    return this._fields.slice();
+  }
 }

packages/opentelemetry-core/src/correlation-context/propagation/HttpCorrelationContext.ts

@@ -118,4 +118,8 @@ export class HttpCorrelationContext implements TextMapPropagator {
     }
     return { key, value };
   }
+
+  fields(): string[] {
+    return [CORRELATION_CONTEXT_HEADER];
+  }
 }

packages/opentelemetry-core/test/context/composite.test.ts

@@ -157,4 +157,8 @@ class ThrowingPropagator implements TextMapPropagator {
   extract(context: Context, carrier: unknown): Context {
     throw new Error('This propagator throws');
   }
+
+  fields(): string[] {
+    return [];
+  }
 }

packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts

@@ -43,4 +43,10 @@ export class DummyPropagation implements TextMapPropagator {
     headers[DummyPropagation.TRACE_CONTEXT_KEY] = spanContext.traceId;
     headers[DummyPropagation.SPAN_CONTEXT_KEY] = spanContext.spanId;
   }
+  fields(): string[] {
+    return [
+      DummyPropagation.TRACE_CONTEXT_KEY,
+      DummyPropagation.SPAN_CONTEXT_KEY,
+    ];
+  }
 }

packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts

@@ -43,4 +43,10 @@ export class DummyPropagation implements TextMapPropagator {
     headers[DummyPropagation.TRACE_CONTEXT_KEY] = spanContext.traceId;
     headers[DummyPropagation.SPAN_CONTEXT_KEY] = spanContext.spanId;
   }
+  fields(): string[] {
+    return [
+      DummyPropagation.TRACE_CONTEXT_KEY,
+      DummyPropagation.SPAN_CONTEXT_KEY,
+    ];
+  }
 }