Add 'json stringifier' option

lib/response.js

@@ -257,7 +257,8 @@ res.json = function json(obj) {
   var escape = app.get('json escape')
   var replacer = app.get('json replacer');
   var spaces = app.get('json spaces');
-  var body = stringify(val, replacer, spaces, escape)
+  var stringifier = app.get('json stringifier');
+  var body = stringify(val, replacer, spaces, escape, stringifier)
 
   // content-type
   if (!this.get('Content-Type')) {
@@ -300,7 +301,8 @@ res.jsonp = function jsonp(obj) {
   var escape = app.get('json escape')
   var replacer = app.get('json replacer');
   var spaces = app.get('json spaces');
-  var body = stringify(val, replacer, spaces, escape)
+  var stringifier = app.get('json stringifier');
+  var body = stringify(val, replacer, spaces, escape, stringifier)
   var callback = this.req.query[app.get('jsonp callback name')];
 
   // content-type
@@ -837,8 +839,10 @@ res.cookie = function (name, value, options) {
     throw new Error('cookieParser("secret") required for signed cookies');
   }
 
+  var app = this.app;
+  var stringifier = app.get('json stringifier');
   var val = typeof value === 'object'
-    ? 'j:' + JSON.stringify(value)
+    ? 'j:' + stringify(value, undefined, undefined, undefined, stringifier)
     : String(value);
 
   if (signed) {
@@ -1111,16 +1115,19 @@ function sendfile(res, file, options, callback) {
  * @param {function} replaces
  * @param {number} spaces
  * @param {boolean} escape
+ * @param {function} stringifier
  * @returns {string}
  * @private
  */
 
-function stringify (value, replacer, spaces, escape) {
+function stringify (value, replacer, spaces, escape, stringifier) {
+  var jsonStringify = stringifier || JSON.stringify
+
   // v8 checks arguments.length for optimizing simple call
   // https://bugs.chromium.org/p/v8/issues/detail?id=4730
   var json = replacer || spaces
-    ? JSON.stringify(value, replacer, spaces)
-    : JSON.stringify(value);
+    ? jsonStringify(value, replacer, spaces)
+    : jsonStringify(value);
 
   if (escape) {
     json = json.replace(/[<>&]/g, function (c) {

test/res.cookie.js

@@ -19,6 +19,24 @@ describe('res', function(){
       .expect('Set-Cookie', 'user=j%3A%7B%22name%22%3A%22tobi%22%7D; Path=/')
       .expect(200, done)
     })
+
+    it('should generate a JSON cookie with a custom JSON stringifier', function(done){
+      var app = express();
+
+      app.set('json stringifier', function(value) {
+        value.name = 'asdf'
+        return JSON.stringify(value)
+      });
+
+      app.use(function(req, res){
+        res.cookie('user', { name: 'tobi' }).end();
+      });
+
+      request(app)
+      .get('/')
+      .expect('Set-Cookie', 'user=j%3A%7B%22name%22%3A%22asdf%22%7D; Path=/')
+      .expect(200, done)
+    })
   })
 
   describe('.cookie(name, string)', function(){

test/res.json.js

@@ -166,6 +166,37 @@ describe('res', function(){
         .expect(200, '{\n  "name": "tobi",\n  "age": 2\n}', done)
       })
     })
+
+    describe('"json stringifier" setting', function(){
+      it('should be undefined by default', function(){
+        var app = express();
+        assert(undefined === app.get('json stringifier'));
+      })
+
+      it('should be used instead of JSON.stringify', function(done){
+        var app = express();
+
+        app.set('json replacer', function(key, val){
+          return key[0] === '_'
+            ? undefined
+            : val;
+        });
+        app.set('json spaces', 2);
+        app.set('json stringifier', function(value, replacer, space) {
+          value.name = 'asdf'
+          return JSON.stringify(value, replacer, space);
+        });
+
+        app.use(function(req, res){
+          res.json({ name: 'tobi', age: 2, _id: 1234 });
+        });
+
+        request(app)
+        .get('/')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '{\n  "name": "asdf",\n  "age": 2\n}', done)
+      })
+    })
   })
 
   describe('.json(status, object)', function(){

test/res.jsonp.js

@@ -306,6 +306,37 @@ describe('res', function(){
         .expect(200, '{\n  "name": "tobi",\n  "age": 2\n}', done)
       })
     })
+
+    describe('"json stringifier" setting', function(){
+      it('should be undefined by default', function(){
+        var app = express();
+        assert(undefined === app.get('json stringifier'));
+      })
+
+      it('should be used instead of JSON.stringify', function(done){
+        var app = express();
+
+        app.set('json replacer', function(key, val){
+          return key[0] === '_'
+            ? undefined
+            : val;
+        });
+        app.set('json spaces', 2);
+        app.set('json stringifier', function(value, replacer, space) {
+          value.name = 'asdf'
+          return JSON.stringify(value, replacer, space);
+        });
+
+        app.use(function(req, res){
+          res.jsonp({ name: 'tobi', age: 2, _id: 1234 });
+        });
+
+        request(app)
+        .get('/')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '{\n  "name": "asdf",\n  "age": 2\n}', done)
+      })
+    })
   })
 
   describe('.jsonp(status, object)', function(){