feat(#362): adds flush method to http reporter. (#417)

packages/zipkin/index.d.ts

@@ -274,6 +274,7 @@ declare namespace zipkin {
   class BatchRecorder implements Recorder {
     constructor(args: { logger: Logger, timeout?: number });
     record: (rec: Record) => void;
+    flush: () => void;
   }
 
   class ConsoleRecorder implements Recorder {

packages/zipkin/src/batch-recorder.js

@@ -135,6 +135,17 @@ class BatchRecorder {
     }
   }
 
+  /**
+   * Calling this will flush any pending spans to the transport.
+   *
+   * Note: the transport itself may be batching, in such case you may need to flush that also.
+   */
+  flush() {
+    this.partialSpans.forEach((span, id) => {
+      this._writeSpan(id, span);
+    });
+  }
+
   record(rec) {
     const id = rec.traceId;
 

packages/zipkin/test/batch-recorder.test.js

@@ -302,8 +302,29 @@ describe('Batch Recorder - integration test', () => {
         'http.status_code': '200'
       }
     });
+  });
+
+  it('should only flush spans when calling flush method', () => {
+    recorder = new BatchRecorder({
+      logger: {
+        logSpan: (span) => {
+          spans.push(JSON.parse(JSON_V2.encode(span)));
+        }
+      }
+    });
+
+    recorder.record(record(rootId, 1, new Annotation.ServerRecv()));
 
     expect(spans).to.be.empty; // eslint-disable-line no-unused-expressions
+
+    recorder.flush();
+
+    expect(popSpan()).to.deep.equal({
+      traceId: rootId.traceId,
+      id: rootId.spanId,
+      kind: 'SERVER',
+      timestamp: 1
+    });
   });
 
   it('should handle overlapping server and client', () => {