feat(rest): Improve result serialization for http

Map number/boolean to json by default
Add support for buffer and stream.Readable

Author: raymondfeng

packages/rest/src/writer.ts

@@ -6,6 +6,8 @@
 import {ServerResponse as Response} from 'http';
 import {OperationRetval} from './internal-types';
 import {HttpError} from 'http-errors';
+import {Readable} from 'stream';
+
 /**
  * Writes the result from Application controller method
  * into the HTTP response
@@ -20,13 +22,26 @@ export function writeResultToResponse(
   result: OperationRetval,
 ): void {
   if (result) {
+    if (result instanceof Readable || typeof result.pipe === 'function') {
+      response.setHeader('Content-Type', 'application/octet-stream');
+      // Stream
+      result.pipe(response);
+      return;
+    }
     switch (typeof result) {
       case 'object':
-        // TODO(ritch) remove this, should be configurable
-        // See https://github.com/strongloop/loopback-next/issues/436
-        response.setHeader('Content-Type', 'application/json');
-        // TODO(bajtos) handle errors - JSON.stringify can throw
-        result = JSON.stringify(result);
+      case 'boolean':
+      case 'number':
+        if (Buffer.isBuffer(result)) {
+          // Buffer for binary data
+          response.setHeader('Content-Type', 'application/octet-stream');
+        } else {
+          // TODO(ritch) remove this, should be configurable
+          // See https://github.com/strongloop/loopback-next/issues/436
+          response.setHeader('Content-Type', 'application/json');
+          // TODO(bajtos) handle errors - JSON.stringify can throw
+          result = JSON.stringify(result);
+        }
         break;
       default:
         response.setHeader('Content-Type', 'text/plain');

packages/rest/test/unit/writer.test.ts

@@ -4,7 +4,7 @@
 // License text available at https://opensource.org/licenses/MIT
 
 import {ServerResponse, writeResultToResponse} from '../..';
-
+import {Duplex} from 'stream';
 import {expect, mockResponse, ShotObservedResponse} from '@loopback/testlab';
 
 describe('writer', () => {
@@ -31,22 +31,43 @@ describe('writer', () => {
     expect(result.payload).to.equal('{"name":"Joe"}');
   });
 
-  it('writes boolean result to response as text', async () => {
+  it('writes boolean result to response as json', async () => {
     writeResultToResponse(response, true);
     const result = await observedResponse;
 
-    expect(result.headers['content-type']).to.eql('text/plain');
+    expect(result.headers['content-type']).to.eql('application/json');
     expect(result.payload).to.equal('true');
   });
 
-  it('writes number result to response as text', async () => {
+  it('writes number result to response as json', async () => {
     writeResultToResponse(response, 2);
     const result = await observedResponse;
 
-    expect(result.headers['content-type']).to.eql('text/plain');
+    expect(result.headers['content-type']).to.eql('application/json');
     expect(result.payload).to.equal('2');
   });
 
+  it('writes buffer result to response as binary', async () => {
+    const buf = Buffer.from('ABC123');
+    writeResultToResponse(response, buf);
+    const result = await observedResponse;
+
+    expect(result.headers['content-type']).to.eql('application/octet-stream');
+    expect(result.payload).to.equal('ABC123');
+  });
+
+  it('writes stream result to response as binary', async () => {
+    const buf = Buffer.from('ABC123');
+    const stream = new Duplex();
+    stream.push(buf);
+    stream.push(null);
+    writeResultToResponse(response, stream);
+    const result = await observedResponse;
+
+    expect(result.headers['content-type']).to.eql('application/octet-stream');
+    expect(result.payload).to.equal('ABC123');
+  });
+
   function setupResponseMock() {
     const responseMock = mockResponse();
     response = responseMock.response;