feat(runtime): support better error formatting

__tests__/runtime/route.test.ts

@@ -5,6 +5,7 @@ import {
   Request as ExpressRequest,
   Response as ExpressResponse,
 } from 'express';
+import { Request as MockRequest } from 'jest-express/lib/request';
 import { Response as MockResponse } from 'jest-express/lib/response';
 import { twiml } from 'twilio';
 import { StartCliConfig } from '../../src/config/start';
@@ -25,12 +26,70 @@ const mockResponse = (new MockResponse() as unknown) as ExpressResponse;
 mockResponse.type = jest.fn(() => mockResponse);
 
 describe('handleError function', () => {
-  test('calls correct response methods', () => {
+  test('returns string error', () => {
+    const mockRequest = (new MockRequest() as unknown) as ExpressRequest;
+    mockRequest['useragent'] = {
+      isDesktop: true,
+      isMobile: false,
+    } as ExpressUseragent.UserAgent;
+
+    handleError('string error', mockRequest, mockResponse);
+
+    expect(mockResponse.status).toHaveBeenCalledWith(500);
+    expect(mockResponse.send).toHaveBeenCalledWith('string error');
+  });
+
+  test('handles objects as error argument', () => {
+    const mockRequest = (new MockRequest() as unknown) as ExpressRequest;
+    mockRequest['useragent'] = {
+      isDesktop: true,
+      isMobile: false,
+    } as ExpressUseragent.UserAgent;
+
+    handleError({ errorMessage: 'oh no' }, mockRequest, mockResponse);
+
+    expect(mockResponse.status).toHaveBeenCalledWith(500);
+    expect(mockResponse.send).toHaveBeenCalledWith({ errorMessage: 'oh no' });
+  });
+
+  test('wraps error object for desktop requests', () => {
+    const mockRequest = (new MockRequest() as unknown) as ExpressRequest;
+    mockRequest['useragent'] = {
+      isDesktop: true,
+      isMobile: false,
+    } as ExpressUseragent.UserAgent;
+
     const err = new Error('Failed to execute');
-    handleError(err, (mockResponse as unknown) as ExpressResponse);
+    handleError(err, mockRequest, mockResponse);
     expect(mockResponse.status).toHaveBeenCalledWith(500);
     expect(mockResponse.send).toHaveBeenCalledWith(wrapErrorInHtml(err));
   });
+
+  test('wraps error object for mobile requests', () => {
+    const mockRequest = (new MockRequest() as unknown) as ExpressRequest;
+    mockRequest['useragent'] = {
+      isDesktop: false,
+      isMobile: true,
+    } as ExpressUseragent.UserAgent;
+
+    const err = new Error('Failed to execute');
+    handleError(err, mockRequest, mockResponse);
+    expect(mockResponse.status).toHaveBeenCalledWith(500);
+    expect(mockResponse.send).toHaveBeenCalledWith(wrapErrorInHtml(err));
+  });
+
+  test('returns string version of error for other requests', () => {
+    const mockRequest = (new MockRequest() as unknown) as ExpressRequest;
+    mockRequest['useragent'] = {
+      isDesktop: false,
+      isMobile: false,
+    } as ExpressUseragent.UserAgent;
+
+    const err = new Error('Failed to execute');
+    handleError(err, mockRequest, mockResponse);
+    expect(mockResponse.status).toHaveBeenCalledWith(500);
+    expect(mockResponse.send).toHaveBeenCalledWith(err.toString());
+  });
 });
 
 describe('constructEvent function', () => {

package.json

@@ -54,6 +54,7 @@
     "debug": "^3.1.0",
     "dotenv": "^6.2.0",
     "express": "^4.16.3",
+    "express-useragent": "^1.0.13",
     "fast-redact": "^1.5.0",
     "got": "^9.6.0",
     "inquirer": "^6.5.0",
@@ -82,6 +83,7 @@
     "@types/common-tags": "^1.8.0",
     "@types/debug": "^4.1.4",
     "@types/dotenv": "^6.1.1",
+    "@types/express-useragent": "^0.2.21",
     "@types/got": "^9.6.0",
     "@types/jest": "^24.0.15",
     "@types/listr": "^0.14.0",

src/runtime/route.ts

@@ -65,13 +65,22 @@ export function constructGlobalScope(config: StartCliConfig): void {
 }
 
 export function handleError(
-  err: Error,
+  err: Error | string | object,
+  req: ExpressRequest,
   res: ExpressResponse,
   functionFilePath?: string
 ) {
   res.status(500);
-  res.type('text/html');
-  res.send(wrapErrorInHtml(err, functionFilePath));
+  if (!(err instanceof Error)) {
+    res.send(err);
+  } else {
+    if (req.useragent && (req.useragent.isDesktop || req.useragent.isMobile)) {
+      res.type('text/html');
+      res.send(wrapErrorInHtml(err, functionFilePath));
+    } else {
+      res.send(err.toString());
+    }
+  }
 }
 
 export function isTwiml(obj: object): boolean {
@@ -131,7 +140,7 @@ export function functionToRoute(
     ) {
       debug('Function execution %s finished', req.path);
       if (err) {
-        handleError(err, res, functionFilePath);
+        handleError(err, req, res, functionFilePath);
         return;
       }
       handleSuccess(responseObject, res);

src/runtime/server.ts

@@ -6,6 +6,7 @@ import express, {
   Request as ExpressRequest,
   Response as ExpressResponse,
 } from 'express';
+import userAgentMiddleware from 'express-useragent';
 import nocache from 'nocache';
 import { StartCliConfig } from '../config/start';
 import { wrapErrorInHtml } from '../utils/error-html';
@@ -48,6 +49,7 @@ export async function createServer(
   debug('Starting server with config: %p', config);
 
   const app = express();
+  app.use(userAgentMiddleware.express());
   app.use(bodyParser.urlencoded({ extended: false }));
   app.use(bodyParser.json());
   app.get('/favicon.ico', (req, res) => {