From fadebf353c63427120ef1a4741d74f1027bb903c Mon Sep 17 00:00:00 2001
From: Amir Blum <amirgiraffe@gmail.com>
Date: Thu, 14 Jan 2021 00:07:46 +0200
Subject: [PATCH] fix(api): add public 'fields' function to api.propagator
 (#1813)

* fix(api): add public 'fields' function to api.propagator

* chore: remove redundant comment

Co-authored-by: Daniel Dyla <dyladan@users.noreply.github.com>
---
 packages/opentelemetry-api/src/api/propagation.ts          | 7 +++++++
 .../src/context/propagation/TextMapPropagator.ts           | 3 ---
 packages/opentelemetry-api/test/api/api.test.ts            | 7 +++++++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/packages/opentelemetry-api/src/api/propagation.ts b/packages/opentelemetry-api/src/api/propagation.ts
index a07b88b94d..b99dada22a 100644
--- a/packages/opentelemetry-api/src/api/propagation.ts
+++ b/packages/opentelemetry-api/src/api/propagation.ts
@@ -96,6 +96,13 @@ export class PropagationAPI {
     return this._getGlobalPropagator().extract(context, carrier, getter);
   }
 
+  /**
+   * Return a list of all fields which may be used by the propagator.
+   */
+  public fields(): string[] {
+    return this._getGlobalPropagator().fields();
+  }
+
   /** Remove the global propagator */
   public disable() {
     delete _global[GLOBAL_PROPAGATION_API_KEY];
diff --git a/packages/opentelemetry-api/src/context/propagation/TextMapPropagator.ts b/packages/opentelemetry-api/src/context/propagation/TextMapPropagator.ts
index 59f2d39f8a..b659a9704d 100644
--- a/packages/opentelemetry-api/src/context/propagation/TextMapPropagator.ts
+++ b/packages/opentelemetry-api/src/context/propagation/TextMapPropagator.ts
@@ -67,9 +67,6 @@ export interface TextMapPropagator<Carrier = any> {
 
   /**
    * 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[];
 }
diff --git a/packages/opentelemetry-api/test/api/api.test.ts b/packages/opentelemetry-api/test/api/api.test.ts
index 01aaf32df6..cc02a460f8 100644
--- a/packages/opentelemetry-api/test/api/api.test.ts
+++ b/packages/opentelemetry-api/test/api/api.test.ts
@@ -150,6 +150,13 @@ describe('API', () => {
         assert.strictEqual(data.carrier, carrier);
         assert.strictEqual(data.getter, getter);
       });
+
+      it('fields', () => {
+        api.propagation.setGlobalPropagator(new TestTextMapPropagation());
+
+        const fields = api.propagation.fields();
+        assert.deepStrictEqual(fields, ['TestField']);
+      });
     });
   });
 });