fix(runtime-handler): fall back to assets/index.html for root path

In production the Functions environment will fall back to serving the contents of /assets/index.html
if / is not registered as its own content.

fix #371

Author: dkundel

packages/runtime-handler/src/dev-runtime/server.ts

@@ -141,12 +141,15 @@ export class LocalDevelopmentServer extends EventEmitter {
     app.all(
       '/*',
       (req: ExpressRequest, res: ExpressResponse, next: NextFunction) => {
-        if (!this.routeMap.has(req.path)) {
-          res.status(404).send('Could not find request resource');
-          return;
+        let routeInfo = this.routeMap.get(req.path);
+
+        if (!routeInfo && req.path === '/') {
+          log('Falling back to /assets/index.html');
+          // In production we automatically fall back to the contents of /assets/index.html
+          routeInfo = this.routeMap.get('/assets/index.html');
         }
 
-        if (req.method === 'OPTIONS') {
+        if (req.method === 'OPTIONS' && routeInfo) {
           res.set({
             'access-control-allow-origin': '*',
             'access-control-allow-headers':
@@ -163,8 +166,6 @@ export class LocalDevelopmentServer extends EventEmitter {
           return;
         }
 
-        const routeInfo = this.routeMap.get(req.path);
-
         if (routeInfo && routeInfo.type === 'function') {
           const functionPath = routeInfo.filePath;
           try {