feat: also allow Propagation objects in config

Author: kjin

src/config.ts

@@ -15,6 +15,7 @@
  */
 
 import * as path from 'path';
+import {Propagation} from './plugin-types';
 
 const pluginDirectory =
     path.join(path.resolve(__dirname, '..'), 'src', 'plugins');
@@ -110,13 +111,12 @@ export interface Config {
   plugins?: {[pluginName: string]: string;};
 
   /**
-   * A require-friendly path to an OpenCensus-compatible propagation module to
-   * support context propagation across services with HTTP headers, or a list of
-   * such paths. Any user-provided value will replace the default value. To
-   * disable propagation completely, pass an empty string or empty array for
-   * this field.
+   * Either a require-friendly path to an OpenCensus-compatible propagation
+   * module to support context propagation across services with HTTP headers or
+   * the module itself, or a list of such paths or modules. Any user-provided
+   * value will replace the default value.
    */
-  propagation?: string|string[];
+  propagation?: string|Propagation|Array<string|Propagation>;
 
   /**
    * The max number of frames to include on traces; pass a value of 0 to

src/index.ts

@@ -104,7 +104,7 @@ function initConfig(projectConfig: Forceable<Config>):
   // Canonicalize the user-specified propagation mechanism.
   if (!config.propagation) {
     config.propagation = [];
-  } else if (typeof config.propagation === 'string') {
+  } else if (!Array.isArray(config.propagation)) {
     config.propagation = [config.propagation];
   }
 

src/trace-api.ts

@@ -59,7 +59,7 @@ export enum TraceContextHeaderBehavior {
 export interface StackdriverTracerConfig extends TracePolicyConfig {
   enhancedDatabaseReporting: boolean;
   contextHeaderBehavior: TraceContextHeaderBehavior;
-  propagation: string[];
+  propagation: Array<string|Propagation>;
   rootSpanNameOverride: (path: string) => string;
   spansPerTraceSoftLimit: number;
   spansPerTraceHardLimit: number;
@@ -157,8 +157,13 @@ export class StackdriverTracer implements Tracer {
     this.config = config;
     this.policy = new TracePolicy(config);
     this.enabled = true;
-    this.propagationModules =
-        config.propagation.map(propModulePath => require(propModulePath));
+    this.propagationModules = config.propagation.map(propModule => {
+      if (typeof propModule === 'string') {
+        return require(propModule);
+      } else {
+        return propModule;
+      }
+    });
   }
 
   /**

test/test-config.ts

@@ -24,6 +24,7 @@ import * as testTraceModule from './trace';
 import { NormalizedConfig } from '../src/tracing';
 import { StackdriverTracer } from '../src/trace-api';
 import {Logger} from '../src/logger';
+import { Propagation } from '../src/plugin-types';
 
 describe('Behavior set by config for CLS', () => {
   const useAH = semver.satisfies(process.version, '>=8');
@@ -133,16 +134,21 @@ describe('Behavior set by config for Tracer', () => {
   });
 
   describe('Propagation behavior', () => {
+    const propagationString = `${__dirname}/fixtures/propagation-local`;
+    const fakePropagation = { extract: () => null, inject: () => {} };
     const testCases: Array<{
       // tslint:disable-next-line:no-any
       input: any;
-      expected: string[];
+      expected: Array<string|Propagation>;
     }> = [{
-      input: 'hi',
-      expected: ['hi']
+      input: propagationString,
+      expected: [propagationString]
     }, {
-      input: ['hi', 'bye'],
-      expected: ['hi', 'bye']
+      input: [propagationString, fakePropagation],
+      expected: [propagationString, fakePropagation]
+    }, {
+      input: fakePropagation,
+      expected: [fakePropagation]
     }, {
       input: '',
       expected: []

test/test-trace-api.ts

@@ -360,7 +360,7 @@ describe('Trace Interface', () => {
       it('should support multiple mechanisms if provided', () => {
         const tracer = createTraceAgent({
           propagation: [
-            `${__dirname}/fixtures/propagation-local`,
+            require(`${__dirname}/fixtures/propagation-local`),
             '@opencensus/propagation-stackdriver'
           ]
         });