Throw Error on malformed responses

Author: nuxy

package-lock.json

@@ -33,6 +33,7 @@
   "devDependencies": {
     "@types/aws-lambda": "^8.10.111",
     "chai": "^4.3.7",
+    "chai-as-promised": "^7.1.1",
     "chai-http": "^4.3.0",
     "eslint": "^7.32.0",
     "mocha": "^9.2.2",

package.json

@@ -108,23 +108,30 @@ function initServer(handler, port) {
           body = Buffer.from(body, 'base64');
         }
 
-        res.statusCode = status;
+        if (status) {
+          res.statusCode = status;
+        }
 
         res.end(body);
       };
 
-      // Run lambda-lambda-lambda
-      if (isAsyncFunc(handler) || isPromise(handler)) {
+      try {
 
-        // Asynchronous handling.
-        handler(event)
-          .then(function(response) {
-            callback(null, response);
-          });
-      } else {
+        // Run lambda-lambda-lambda
+        if (isAsyncFunc(handler) || isPromise(handler)) {
 
-        // Synchronous handling.
-        handler(event, null, callback);
+          // Asynchronous handling.
+          handler(event)
+            .then(function(response) {
+              callback(null, response);
+            });
+        } else {
+
+          // Synchronous handling.
+          handler(event, null, callback);
+        }
+      } catch (err) {
+        this.emit('error', Error('Malformed handler method. Exiting..'));
       }
     });
   }).listen(port, () => {

server.js

@@ -0,0 +1,6 @@
+/**
+ * @see AWS::Serverless::Function
+ */
+exports.handler = function(event, context, callback) {
+  callback(null, {});
+};

test/error/handler.js

@@ -1,9 +1,11 @@
 'use strict';
 
-const chai       = require('chai');
-const chaiHttp   = require('chai-http');
-const resetCache = require('resnap')();
+const chai           = require('chai');
+const chaiAsPromised = require('chai-as-promised');
+const chaiHttp       = require('chai-http');
+const resetCache     = require('resnap')();
 
+chai.use(chaiAsPromised);
 chai.use(chaiHttp);
 
 const {expect, request} = chai;
@@ -76,4 +78,29 @@ describe('Handler method', function() {
       expect(result.text).to.equal('Success');
     });
   });
+
+  describe('error', function() {
+    let agent, result;
+
+    before(function() {
+      resetCache();
+
+      process.env.TEST_HANDLER = './test/error/handler.js';
+
+      const server = require('../server');
+      agent = request.agent(server);
+
+      result = async function() {
+        await agent.get('/');
+      };
+    });
+
+    after(function() {
+      agent.close();
+    });
+
+    it('should throw error', function() {
+      expect(result()).to.eventually.be.rejectedWith(Error, /Malformed handler method/);
+    });
+  });
 });