Add "escape json" setting for res.json and res.jsonp

closes #3268
closes #3269

Author: Greg Guthe

History.md

@@ -1,6 +1,7 @@
 unreleased
 ==========
 
+  * Add `"json escape"` setting for `res.json` and `res.jsonp`
   * Improve error message when autoloading invalid view engine
   * Improve error messages when non-function provided as middleware
   * Skip `Buffer` encoding when not generating ETag for small response

lib/response.js

@@ -254,9 +254,10 @@ res.json = function json(obj) {
 
   // settings
   var app = this.app;
+  var escape = app.get('json escape')
   var replacer = app.get('json replacer');
   var spaces = app.get('json spaces');
-  var body = stringify(val, replacer, spaces);
+  var body = stringify(val, replacer, spaces, escape)
 
   // content-type
   if (!this.get('Content-Type')) {
@@ -296,9 +297,10 @@ res.jsonp = function jsonp(obj) {
 
   // settings
   var app = this.app;
+  var escape = app.get('json escape')
   var replacer = app.get('json replacer');
   var spaces = app.get('json spaces');
-  var body = stringify(val, replacer, spaces);
+  var body = stringify(val, replacer, spaces, escape)
   var callback = this.req.query[app.get('jsonp callback name')];
 
   // content-type
@@ -1098,14 +1100,38 @@ function sendfile(res, file, options, callback) {
 }
 
 /**
- * Stringify JSON, like JSON.stringify, but v8 optimized.
+ * Stringify JSON, like JSON.stringify, but v8 optimized, with the
+ * ability to escape characters that can trigger HTML sniffing.
+ *
+ * @param {*} value
+ * @param {function} replaces
+ * @param {number} spaces
+ * @param {boolean} escape
+ * @returns {string}
  * @private
  */
 
-function stringify(value, replacer, spaces) {
+function stringify (value, replacer, spaces, escape) {
   // v8 checks arguments.length for optimizing simple call
   // https://bugs.chromium.org/p/v8/issues/detail?id=4730
-  return replacer || spaces
+  var json = replacer || spaces
     ? JSON.stringify(value, replacer, spaces)
     : JSON.stringify(value);
+
+  if (escape) {
+    json = json.replace(/[<>&]/g, function (c) {
+      switch (c.charCodeAt(0)) {
+        case 0x3c:
+          return '\\u003c'
+        case 0x3e:
+          return '\\u003e'
+        case 0x26:
+          return '\\u0026'
+        default:
+          return c
+      }
+    })
+  }
+
+  return json
 }

test/res.json.js

@@ -102,6 +102,28 @@ describe('res', function(){
       })
     })
 
+    describe('"json escape" setting', function () {
+      it('should be undefined by default', function () {
+        var app = express()
+        assert.strictEqual(app.get('json escape'), undefined)
+      })
+
+      it('should unicode escape HTML-sniffing characters', function (done) {
+        var app = express()
+
+        app.enable('json escape')
+
+        app.use(function (req, res) {
+          res.json({ '&': '<script>' })
+        })
+
+        request(app)
+        .get('/')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '{"\\u0026":"\\u003cscript\\u003e"}', done)
+      })
+    })
+
     describe('"json replacer" setting', function(){
       it('should be passed to JSON.stringify()', function(done){
         var app = express();

test/res.jsonp.js

@@ -242,6 +242,28 @@ describe('res', function(){
       })
     })
 
+    describe('"json escape" setting', function () {
+      it('should be undefined by default', function () {
+        var app = express()
+        assert.strictEqual(app.get('json escape'), undefined)
+      })
+
+      it('should unicode escape HTML-sniffing characters', function (done) {
+        var app = express()
+
+        app.enable('json escape')
+
+        app.use(function (req, res) {
+          res.jsonp({ '&': '\u2028<script>\u2029' })
+        })
+
+        request(app)
+        .get('/?callback=foo')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect(200, /foo\({"\\u0026":"\\u2028\\u003cscript\\u003e\\u2029"}\)/, done)
+      })
+    })
+
     describe('"json replacer" setting', function(){
       it('should be passed to JSON.stringify()', function(done){
         var app = express();