Add check for an array and falsey values

1. Remove unwanted check on getter.
2. Add check for an array or falsey value
3. Make sentence readable

Author: mayurkale22

packages/opencensus-propagation-b3/src/b3-format.ts

@@ -32,17 +32,13 @@ export class B3Format implements Propagation {
    * in the headers, null is returned.
    * @param getter
    */
-  extract(getter: HeaderGetter): SpanContext|null {
-    if (!getter) return null;
-    let opt = getter.getHeader(X_B3_SAMPLED);
-    if (opt instanceof Array) {
-      opt = opt[0];
-    }
+  extract(getter: HeaderGetter): SpanContext {
+    const opt = this.parseHeader(getter.getHeader(X_B3_SAMPLED));
     return {
-      traceId: getter.getHeader(X_B3_TRACE_ID),
-      spanId: getter.getHeader(X_B3_SPAN_ID),
+      traceId: this.parseHeader(getter.getHeader(X_B3_TRACE_ID)),
+      spanId: this.parseHeader(getter.getHeader(X_B3_SPAN_ID)),
       options: isNaN(Number(opt)) ? NOT_SAMPLED_VALUE : Number(opt)
-    } as SpanContext;
+    };
   }
 
   /**
@@ -54,7 +50,7 @@ export class B3Format implements Propagation {
     setter.setHeader(X_B3_TRACE_ID, spanContext.traceId || '');
     setter.setHeader(X_B3_SPAN_ID, spanContext.spanId || '');
     if (spanContext &&
-        (spanContext.options || NOT_SAMPLED_VALUE & SAMPLED_VALUE) !== 0) {
+        ((spanContext.options || NOT_SAMPLED_VALUE) & SAMPLED_VALUE) !== 0) {
       setter.setHeader(X_B3_SAMPLED, `${SAMPLED_VALUE}`);
     } else {
       setter.setHeader(X_B3_SAMPLED, `${NOT_SAMPLED_VALUE}`);
@@ -71,4 +67,12 @@ export class B3Format implements Propagation {
       options: SAMPLED_VALUE
     };
   }
+
+  /** Converts a headers type to a string. */
+  private parseHeader(str: string|string[]|undefined): string {
+    if (Array.isArray(str)) {
+      return str[0];
+    }
+    return str || '';
+  }
 }

packages/opencensus-propagation-b3/test/test-b3-format.ts

@@ -16,8 +16,9 @@
 
 import {HeaderGetter, HeaderSetter} from '@opencensus/core';
 import * as assert from 'assert';
+import * as uuid from 'uuid';
 
-import {B3Format, X_B3_SAMPLED, X_B3_SPAN_ID, X_B3_TRACE_ID} from '../src/';
+import {B3Format, NOT_SAMPLED_VALUE, SAMPLED_VALUE, X_B3_SAMPLED, X_B3_SPAN_ID, X_B3_TRACE_ID} from '../src/';
 
 const b3Format = new B3Format();
 
@@ -41,6 +42,43 @@ describe('B3Propagation', () => {
 
       assert.deepEqual(b3Format.extract(getter), spanContext);
     });
+
+    it('should return valid context when options and spanId are undefined',
+       () => {
+         const traceId = uuid.v4().split('-').join('');
+         // tslint:disable-next-line
+         const headers = {} as any;
+         headers[X_B3_TRACE_ID] = traceId;
+         headers[X_B3_SPAN_ID] = undefined;
+
+         const getter: HeaderGetter = {
+           getHeader(name: string) {
+             return headers[name];
+           }
+         };
+
+         assert.deepEqual(
+             b3Format.extract(getter),
+             {traceId, spanId: '', options: NOT_SAMPLED_VALUE});
+       });
+
+    it('should extract data from an array', () => {
+      const spanContext = b3Format.generate();
+      // tslint:disable-next-line
+      const headers = {} as any;
+      headers[X_B3_TRACE_ID] =
+          [spanContext.traceId, uuid.v4().split('-').join('')];
+      headers[X_B3_SPAN_ID] = [spanContext.spanId];
+      headers[X_B3_SAMPLED] = [SAMPLED_VALUE];
+
+      const getter: HeaderGetter = {
+        getHeader(name: string) {
+          return headers[name];
+        }
+      };
+
+      assert.deepEqual(b3Format.extract(getter), spanContext);
+    });
   });
 
   describe('inject', () => {