Report HTTP errors when flushing spans

src/reporters/http_sender.js

@@ -115,7 +115,14 @@ export default class HTTPSender {
     const req = requester(this._httpOptions, resp => {
       // consume response data to free up memory
       resp.resume();
-      SenderUtils.invokeCallback(callback, numSpans);
+
+      let error;
+      if (resp.statusCode >= 400) {
+        error = `error sending spans over HTTP: server responded with HTTP ${resp.statusCode}`;
+        this._logger.error(error);
+      }
+
+      SenderUtils.invokeCallback(callback, numSpans, error);
     });
 
     req.on('error', err => {

test/http_sender.js

@@ -257,6 +257,33 @@ describe('http sender', () => {
     });
   }).timeout(5000);
 
+  it('should log http errors when reporting', function(done) {
+    let loggedError = null;
+    const noop = () => {};
+    const logError = errMsg => {
+      loggedError = errMsg;
+    };
+
+    reporter = new InMemoryReporter();
+    tracer = new Tracer('test-service-name', reporter, new ConstSampler(true));
+    sender = new HTTPSender({
+      logger: { error: logError, info: noop },
+      endpoint: `http://localhost:${server.address().port}/404`,
+      maxSpanBatchSize: batchSize,
+    });
+    sender.setProcess(reporter._process);
+
+    let tracer = new Tracer('test-service-name', new RemoteReporter(sender), new ConstSampler(true));
+
+    tracer.startSpan('testSpan').finish();
+    sender.flush((numSpans, err) => {
+      assert.equal(numSpans, 1);
+      expect(err).to.have.string('error sending spans over HTTP: server responded with HTTP 404');
+      expect(loggedError).to.have.string('error sending spans over HTTP: server responded with HTTP 404');
+      tracer.close(done);
+    });
+  }).timeout(5000);
+
   it('should handle HTTPS collectors', done => {
     // Make it ignore the fact that our cert isn't valid.
     process.env.NODE_TLS_REJECT_UNAUTHORIZED = '0';