Add final handler

Author: tomas-polach

src/lambda-wrapper.js

@@ -5,36 +5,40 @@ const { Request } = require('./request');
  * API Gateway handler generator for Lambda
  *
  * @param {object} router Express compatible router instance
+ * @param {function} finalHandler Process response before sending it. Function params: err, out, req, res
  * @return {function} Lambda handler for API gateway events
  * @public
  */
 
-exports.ApiGatewayHandler = (router) => {
-  // TODO: check router param
+exports.ApiGatewayHandler = (router, finalHandler) => {
   /**
    * Lambda Handler for API Gateway invocations
    *
    * @param {object} event API Gateway event object
    * @param {object} context API Gateway context object
    * @return {promise} Returns undefined if callback param is set. Return a promise if callback param is undefined.
    */
-  return function handleApiGatewayEvent(event, context) {
+  return handleApiGatewayEvent = (event, context) => {
     return new Promise((resolve, reject) => {
+
       const req = new Request(event);
-      const res = new Response(req, resolve);
-      req.res = res;
+      const res = req.res = new Response(req, out => {
+        resolve(finalHandler(null, out, req, res))
+      });
+
       // run middleware managed by router
-      router(req, res, err => {
+      router(req, res, async err => {
         if (err) {
-          // unexpected errors
-          reject(err);
+          // unexpected errors should be handled by final handler
+          resolve(finalHandler(err, null, req, res))
         } else if (res.writableEnded) {
-          console.error('ERROR: next() should not be used after res.send() within routing middleware')
+          console.error('ERROR: next() should not be used after res.send() within routing middleware');
         } else {
           // expected error
           res.status(404).send('Not found');
         }
       })
+
     })    
   }
-}
+}

src/lambda-wrapper.spec.js

@@ -2,6 +2,10 @@ const { ApiGatewayHandler } = require('./lambda-wrapper');
 const Router = require('router');
 const bodyParser = require('body-parser');
 
+function finalHandlerPassTrough (err, out, req, res) {
+  return out
+}
+
 describe('Lambda Wrapper', () => {
   const proxyRequest = {
     body: null,
@@ -24,7 +28,7 @@ describe('Lambda Wrapper', () => {
     router.use((req, res) => {
       res.json({a: 1});
     })
-    const lambdaHandler = ApiGatewayHandler(router);
+    const lambdaHandler = ApiGatewayHandler(router, finalHandlerPassTrough);
     const proxyRequest = {
       body: '',
       headers: {},
@@ -59,7 +63,7 @@ describe('Lambda Wrapper', () => {
     router.use((req, res) => {
       res.json(req.body);
     })
-    const lambdaHandler = ApiGatewayHandler(router);
+    const lambdaHandler = ApiGatewayHandler(router, finalHandlerPassTrough);
 
     const requestObject = JSON.stringify({a: 1});
     const proxyRequest = {
@@ -104,7 +108,7 @@ describe('Lambda Wrapper', () => {
     router.use((req, res) => {
       res.json({b: req.fromFirstEndpoint});
     })
-    const lambdaHandler = ApiGatewayHandler(router);
+    const lambdaHandler = ApiGatewayHandler(router, finalHandlerPassTrough);
 
     const result = await lambdaHandler(proxyRequest, {});
 
@@ -118,43 +122,32 @@ describe('Lambda Wrapper', () => {
   });
 
   it('should handle errors', async () => {
-    expect.assertions(2);
+    expect.assertions(1);
 
     const router = Router()
     router.use((req, res, next) => {
       throw Error('test');
     })
-    const lambdaHandler = ApiGatewayHandler(router);
-
-    try{
-      await lambdaHandler(proxyRequest, {})
-    } catch (err) {
-      expect(err).toEqual(Error('test'));
-    }
 
-    await lambdaHandler(proxyRequest, {}).catch(err => {
+    const lambdaHandler2 = ApiGatewayHandler(router, err => {
+      console.log('OK2')
       expect(err).toEqual(Error('test'));
     })
+    await lambdaHandler2(proxyRequest, {})
   })
 
   it('should handle next(error)', async () => {
-    expect.assertions(2);
+    expect.assertions(1);
 
     const router = Router()
     router.use((req, res, next) => {
       next('test');
     })
-    const lambdaHandler = ApiGatewayHandler(router);
-
-    try{
-      await lambdaHandler(proxyRequest, {})
-    } catch (err) {
+    const lambdaHandler = ApiGatewayHandler(router, err => {
       expect(err).toEqual('test');
-    }
+    });
+    await lambdaHandler(proxyRequest, {})
 
-    await lambdaHandler(proxyRequest, {}).catch(err => {
-      expect(err).toEqual('test');
-    })
   })
 
   it('GET with path', async () => {
@@ -168,7 +161,7 @@ describe('Lambda Wrapper', () => {
       res.json({a: req.fromFirstEndpoint, b: 2});
     });
 
-    const lambdaHandler = ApiGatewayHandler(router);
+    const lambdaHandler = ApiGatewayHandler(router, finalHandlerPassTrough);
     const proxyRequest = {
       body: '',
       headers: {},
@@ -207,7 +200,7 @@ describe('Lambda Wrapper', () => {
       res.json({a: req.foo, b: 2});
     });
 
-    const lambdaHandler = ApiGatewayHandler(router);
+    const lambdaHandler = ApiGatewayHandler(router, finalHandlerPassTrough);
 
     const result = await lambdaHandler(proxyRequest, {});
     expect(result).toEqual({
@@ -231,7 +224,7 @@ describe('Lambda Wrapper', () => {
     const router = Router()
     router.use('/testing', subRouter)
 
-    const lambdaHandler = ApiGatewayHandler(router);
+    const lambdaHandler = ApiGatewayHandler(router, finalHandlerPassTrough);
 
     let request = {}
     Object.assign(request, proxyRequest)