feat: handle circular structure serialization

lib/response.js

@@ -1021,11 +1021,7 @@ function sendfile(res, file, options, callback) {
  */
 
 function stringify (value, replacer, spaces, escape) {
-  // 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);
+  var json = stringifyWithFallback(value, replacer, spaces);
 
   if (escape && typeof json === 'string') {
     json = json.replace(/[<>&]/g, function (c) {
@@ -1045,3 +1041,77 @@ function stringify (value, replacer, spaces, escape) {
 
   return json
 }
+
+function stringifyWithFallback(value, replacer, spaces) {
+  try {
+    // v8 checks arguments.length for optimizing simple call
+    // https://bugs.chromium.org/p/v8/issues/detail?id=4730
+    return replacer || spaces
+      ? JSON.stringify(value, replacer, spaces)
+      : JSON.stringify(value);
+  } catch (err) {
+    if (!isCircularJsonError(err)) {
+      throw err;
+    }
+
+    return JSON.stringify(value, createCircularReplacer(replacer), spaces);
+  }
+}
+
+function createCircularReplacer(replacer) {
+  var stack = [];
+
+  return function (key, value) {
+    var replacement = value;
+
+    if (typeof replacer === "function") {
+      replacement = replacer.call(this, key, value);
+    } else if (
+      Array.isArray(replacer) &&
+      key !== "" &&
+      !Array.isArray(this) &&
+      !hasReplacerKey(replacer, key)
+    ) {
+      return undefined;
+    }
+
+    if (typeof replacement !== "object" || replacement === null) {
+      return replacement;
+    }
+
+    while (stack.length > 0 && stack[stack.length - 1] !== this) {
+      stack.pop();
+    }
+
+    if (stack.indexOf(replacement) !== -1) {
+      return "[Circular]";
+    }
+
+    stack.push(replacement);
+    return replacement;
+  };
+}
+
+function hasReplacerKey(replacer, key) {
+  for (var i = 0; i < replacer.length; i++) {
+    var value = replacer[i];
+
+    if (typeof value === "string" || typeof value === "number") {
+      if (String(value) === key) {
+        return true;
+      }
+    } else if (
+      typeof value === "object" &&
+      value !== null &&
+      String(value) === key
+    ) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+function isCircularJsonError(err) {
+  return err instanceof TypeError && /circular structure/i.test(err.message);
+}

test/res.json.js

@@ -101,6 +101,23 @@ describe('res', function(){
         .expect('Content-Type', 'application/json; charset=utf-8')
         .expect(200, '{"name":"tobi"}', done)
       })
+
+      it('should replace circular references', function (done) {
+        var app = express()
+
+        app.use(function (req, res) {
+          var error = { message: 'boom' }
+
+          error.self = error
+
+          res.json(error)
+        })
+
+        request(app)
+        .get('/')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '{"message":"boom","self":"[Circular]"}', done)
+      })
     })
 
     describe('"json escape" setting', function () {

test/res.jsonp.js

@@ -245,6 +245,23 @@ describe('res', function(){
           .expect('Content-Type', 'text/javascript; charset=utf-8')
           .expect(200, /cb\(\{"name":"tobi"\}\)/, done)
       })
+
+      it('should replace circular references', function (done) {
+        var app = express()
+
+        app.use(function (req, res) {
+          var error = { message: 'boom' }
+
+          error.self = error
+
+          res.jsonp(error)
+        })
+
+        request(app)
+          .get('/?callback=cb')
+          .expect('Content-Type', 'text/javascript; charset=utf-8')
+          .expect(200, /cb\(\{"message":"boom","self":"\[Circular\]"\}\)/, done)
+      })
     })
 
     describe('"json escape" setting', function () {