chore: add typing to propagator carrier (open-telemetry#772)

api/src/context/propagation/HttpTextFormat.ts

@@ -15,6 +15,7 @@
  */
 
 import { SpanContext } from '../../trace/span_context';
+import { Carrier } from './carrier';
 
 /**
  * Injects and extracts a value as text into carriers that travel in-band
@@ -35,18 +36,18 @@ export interface HttpTextFormat {
    *
    * @param spanContext the SpanContext to transmit over the wire.
    * @param format the format of the carrier.
-   * @param carrier the carrier of propagation fields, such as an http request.
+   * @param carrier the carrier of propagation fields, such as http request headers.
    */
-  inject(spanContext: SpanContext, format: string, carrier: unknown): void;
+  inject(spanContext: SpanContext, format: string, carrier: Carrier): void;
 
   /**
    * Returns a {@link SpanContext} instance extracted from `carrier` in the
    * given format from upstream.
    *
    * @param format the format of the carrier.
-   * @param carrier the carrier of propagation fields, such as an http request.
+   * @param carrier the carrier of propagation fields, such as http request headers.
    * @returns SpanContext The extracted SpanContext, or null if no such
    *     SpanContext could be found in carrier.
    */
-  extract(format: string, carrier: unknown): SpanContext | null;
+  extract(format: string, carrier: Carrier): SpanContext | null;
 }

api/src/context/propagation/NoopHttpTextFormat.ts

@@ -15,16 +15,17 @@
  */
 
 import { SpanContext } from '../../trace/span_context';
+import { Carrier } from './carrier';
 import { HttpTextFormat } from './HttpTextFormat';
 
 /**
  * No-op implementations of {@link HttpTextFormat}.
  */
 export class NoopHttpTextFormat implements HttpTextFormat {
   // By default does nothing
-  inject(spanContext: SpanContext, format: string, carrier: unknown): void {}
+  inject(spanContext: SpanContext, format: string, carrier: Carrier): void {}
   // By default does nothing
-  extract(format: string, carrier: unknown): SpanContext | null {
+  extract(format: string, carrier: Carrier): SpanContext | null {
     return null;
   }
 }

api/src/context/propagation/carrier.ts

@@ -0,0 +1,19 @@
+/*!
+ * Copyright 2020, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export type Carrier = {
+  [key: string]: unknown;
+};

api/src/index.ts

@@ -17,6 +17,7 @@
 export * from './common/Logger';
 export * from './common/Time';
 export * from './context/propagation/BinaryFormat';
+export * from './context/propagation/carrier';
 export * from './context/propagation/HttpTextFormat';
 export * from './distributed_context/DistributedContext';
 export * from './distributed_context/EntryValue';