Add Propagator interface (#55)

* Add Propagation interface

* minor doc fix

* Rename interface Propagation to Propagator

packages/opentelemetry-types/src/context/propagation/Propagator.ts

@@ -0,0 +1,43 @@
+/**
+ * Copyright 2019, 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.
+ */
+
+import { SpanContext } from '../../trace/span_context';
+
+/** Defines a Propagator interface. */
+export interface Propagator {
+  /**
+   * Injects the given {@link SpanContext} instance to transmit over the wire.
+   *
+   * OpenTelemetry defines a common set of format values (BinaryFormat and
+   * HTTPTextFormat), and each has an expected `carrier` type.
+   *
+   * @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.
+   */
+  inject(spanContext: SpanContext, format: string, carrier: unknown): 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.
+   * @returns SpanContext The extracted SpanContext, or null if no such
+   *     SpanContext could be found in carrier.
+   */
+  extract(format: string, carrier: unknown): SpanContext | null;
+}

packages/opentelemetry-types/src/index.ts

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+export * from './context/propagation/Propagator';
 export * from './resources/Resource';
 export * from './trace/attributes';
 export * from './trace/link';