Added possibility to pass options such as validate function and transform function

Author: shmuga

README.md

@@ -30,6 +30,15 @@ module.exports.lambda = R((data) => {
 });
 ```
 
+Also it's possible to pass `handler` as second param and `settings` object as first.
+
+Default `settings` fields:
+```
+const defaultSettings = {
+    transform: data => data, // called first 
+    validate: data => data,  // than validate and after validation handler is called
+}
+```
 
 ## Responses
 

lib/index.js

@@ -16,24 +16,44 @@ const isEmpty = v => v === null || v === undefined;
 /**
  * Wrapper for function that handled aws event, context, callback
  * and returns unified response for errors and success statuses
+ * @param {object} settings - Optional settings for function
  * @param {handlerFunction} handler - Handles the response
  */
-function R(handler) {
+function R(...params) {
+  const defaultSettings = {
+    validate: data => Promise.resolve(data),
+    transform: data => Promise.resolve(data),
+  };
+
+  let settings;
+  let handler;
+
+  if (params.length === 2) {
+    [settings, handler] = params;
+  }
+
+  if (params.length === 1) {
+    [handler] = params;
+    settings = {};
+  }
+
+  const usedSettings = Object.assign({}, defaultSettings, settings);
+
   return (event, context, callback) => {
     const startTime = process.hrtime();
     const data = event && event.body
       ? JSON.parse(event.body)
       : event.queryStringParameters || {};
 
     // calling handler for function
-    let result;
-    try {
-      result = handler(data);
-    } catch (e) {
-      result = Promise.reject(e);
-    }
+    let transformed;
 
-    Promise.resolve(result)
+    Promise.resolve(usedSettings.transform(data))
+      .then(usedSettings.validate)
+      .then((transformedData) => {
+        transformed = transformedData;
+        return handler(transformedData);
+      })
       .then((response) => {
         callback(null, {
           statusCode: 200,
@@ -45,7 +65,7 @@ function R(handler) {
             requestId: context.requestId,
             dataAvailable: !isEmpty(response),
             executionTimeInMs: calculateExecution(process.hrtime(startTime)),
-            originalRequest: data,
+            originalRequest: transformed,
             data: response,
           }),
         });
@@ -61,7 +81,7 @@ function R(handler) {
             requestId: context.requestId,
             dataAvailable: false,
             executionTimeInMs: calculateExecution(process.hrtime(startTime)),
-            originalRequest: data,
+            originalRequest: transformed,
             errorMessage: err.message || 'Unknown error. No error message',
             errorName: err.name || 'UnknownError',
             errorData: err.data ? err.data : null,

test/index.test.js

@@ -2,6 +2,46 @@ const { expect } = require('chai');
 const R = require('../lib/index');
 
 describe('Test handling request', () => {
+  it('should check if transform works correctly', (cb) => {
+    const event = require('./sample-requests/GET-request-aws.json');
+
+    const handler = R({
+      transform: (data) => {
+        expect(data).to.be.deep.equal(event.queryStringParameters);
+        return Object.assign({}, data, { newField: 12134 });
+      }
+    },(data) => {
+      expect(data.newField).to.be.equal(12134);
+      return { ok: 1 };
+    });
+
+    handler(event, { requestId: 12345 }, (err, result) => {
+
+      cb();
+    });
+  });
+
+
+  it('should check if validation works correctly', (cb) => {
+    const event = require('./sample-requests/GET-request-aws.json');
+
+    const handler = R({
+      validate: (data) => {
+        expect(data).to.be.deep.equal(event.queryStringParameters);
+        throw new Error('VALIDATION');
+      }
+    },(data) => {
+      return { ok: 1 };
+    });
+
+    handler(event, { requestId: 12345 }, (err, result) => {
+      expect(result.body).to.be.a('string');
+      const body = JSON.parse(result.body);
+      expect(body.errorMessage).to.be.equal('VALIDATION');
+      cb();
+    });
+  });
+
   it('should check if get params parsed correctly', (cb) => {
     const event = require('./sample-requests/GET-request-aws.json');