feat: add progress events (#540)

src/util.ts

@@ -23,7 +23,7 @@ import {GoogleAuth, GoogleAuthOptions} from 'google-auth-library';
 import {CredentialBody} from 'google-auth-library';
 import * as r from 'teeny-request';
 import * as retryRequest from 'retry-request';
-import {Duplex, DuplexOptions, PassThrough, Readable, Writable} from 'stream';
+import {Duplex, DuplexOptions, Readable, Transform, Writable} from 'stream';
 import {teenyRequest} from 'teeny-request';
 
 import {Interceptor} from './service-object';
@@ -453,7 +453,8 @@ export class Util {
   ) {
     onComplete = onComplete || util.noop;
 
-    const writeStream = new PassThrough();
+    const writeStream = new ProgressStream();
+    writeStream.on('progress', evt => dup.emit('progress', evt));
     dup.setWritable(writeStream);
 
     const defaultReqOpts = {
@@ -864,5 +865,20 @@ export class Util {
   }
 }
 
+/**
+ * Basic Passthrough Stream that records the number of bytes read
+ * every time the cursor is moved.
+ */
+class ProgressStream extends Transform {
+  bytesRead = 0;
+  // tslint:disable-next-line: no-any
+  _transform(chunk: any, encoding: string, callback: Function) {
+    this.bytesRead += chunk.length;
+    this.emit('progress', {bytesWritten: this.bytesRead, contentLength: '*'});
+    this.push(chunk);
+    callback();
+  }
+}
+
 const util = new Util();
 export {util};

test/util.ts

@@ -574,6 +574,21 @@ describe('common/util', () => {
       util.makeWritableStream(dup, {makeAuthenticatedRequest() {}});
     });
 
+    it('dup should emit a progress event with the bytes written', done => {
+      let happened = false;
+
+      const dup = duplexify();
+      dup.on('progress', (progress: {}) => {
+        happened = true;
+      });
+
+      util.makeWritableStream(dup, {makeAuthenticatedRequest() {}}, util.noop);
+      dup.write(Buffer.from('abcdefghijklmnopqrstuvwxyz'), 'utf-8', util.noop);
+
+      assert.strictEqual(happened, true);
+      done();
+    });
+
     it('should emit an error if the request fails', done => {
       const dup = duplexify();
       const fakeStream = new stream.Writable();