From 2151c6452d00e5b17f8e8a6cd86f72549e85f66c Mon Sep 17 00:00:00 2001
From: vaibhavmashal <vaibhavmashal098@gmail.com>
Date: Tue, 25 Aug 2026 22:19:16 +0530
Subject: [PATCH 1/2] fix(res): remove magic from res.set() Content-Type

---
 lib/response.js  | 11 +++--------
 test/res.send.js |  4 ++--
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/lib/response.js b/lib/response.js
index bc672434890..dc2fef6ca69 100644
--- a/lib/response.js
+++ b/lib/response.js
@@ -241,7 +241,7 @@ res.json = function json(obj) {
 
   // content-type
   if (!this.get('Content-Type')) {
-    this.set('Content-Type', 'application/json');
+    this.type('json');
   }
 
   return this.send(body);
@@ -271,7 +271,7 @@ res.jsonp = function jsonp(obj) {
   // content-type
   if (!this.get('Content-Type')) {
     this.set('X-Content-Type-Options', 'nosniff');
-    this.set('Content-Type', 'application/json');
+    this.type('json');
   }
 
   // fixup callback
@@ -282,7 +282,7 @@ res.jsonp = function jsonp(obj) {
   // jsonp
   if (typeof callback === 'string' && callback.length !== 0) {
     this.set('X-Content-Type-Options', 'nosniff');
-    this.set('Content-Type', 'text/javascript');
+    this.type('text/javascript');
 
     // restrict callback charset
     callback = callback.replace(/[^\[\]\w$.]/g, '');
@@ -655,9 +655,6 @@ res.append = function append(field, val) {
  *
  * Aliased as `res.header()`.
  *
- * When the set header is "Content-Type", the type is expanded to include
- * the charset if not present using `mime.contentType()`.
- *
  * @param {String|Object} field
  * @param {String|Array} val
  * @return {ServerResponse} for chaining
@@ -671,12 +668,10 @@ res.header = function header(field, val) {
       ? val.map(String)
       : String(val);
 
-    // add charset to content-type
     if (field.toLowerCase() === 'content-type') {
       if (Array.isArray(value)) {
         throw new TypeError('Content-Type cannot be set to an Array');
       }
-      value = mime.contentType(value)
     }
 
     this.setHeader(field, value);
diff --git a/test/res.send.js b/test/res.send.js
index f38ffde9776..f6930f326d6 100644
--- a/test/res.send.js
+++ b/test/res.send.js
@@ -200,7 +200,7 @@ describe('res', function(){
 
       request(app)
       .get('/')
-      .expect('Content-Type', 'text/plain; charset=utf-8')
+      .expect('Content-Type', 'text/plain')
       .expect(200, 'hey', done);
     })
 
@@ -213,7 +213,7 @@ describe('res', function(){
 
       request(app)
         .get("/")
-        .expect("Content-Type", "text/plain; charset=utf-8")
+        .expect("Content-Type", "text/plain")
         .expect(200, "hey", done);
     })
 

From 5ab54bc5ea8921f9706bcd8df2924dec40e9bfc5 Mon Sep 17 00:00:00 2001
From: vaibhavmashal <vaibhavmashal098@gmail.com>
Date: Mon, 31 Aug 2026 21:05:10 +0530
Subject: [PATCH 2/2] fix(format): migrate res.format to res.type for
 Content-Type expansion

---
 lib/response.js    | 20 ++++++++------------
 test/res.format.js | 17 +++++++++++++++++
 2 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/lib/response.js b/lib/response.js
index dc2fef6ca69..9b2b4fd359c 100644
--- a/lib/response.js
+++ b/lib/response.js
@@ -506,7 +506,7 @@ res.contentType =
 res.type = function contentType(type) {
   var ct = type.indexOf('/') === -1
     ? (mime.contentType(type) || 'application/octet-stream')
-    : type;
+    : (mime.contentType(type) || type);
 
   return this.set('Content-Type', ct);
 };
@@ -535,25 +535,21 @@ res.type = function contentType(type) {
  *        res.send('<p>hey</p>');
  *      },
  *
- *      'application/json': function () {
+ *      'application/json': function(){
  *        res.send({ message: 'hey' });
  *      }
  *    });
  *
- * In addition to canonicalized MIME types you may
- * also use extnames mapped to these types:
+ * In addition to an object of callbacks you may also provide a function
+ * which will be invoked when no match is made and the "Accept" header is
+ * present, otherwise 406 "Not Acceptable" is sent.
  *
  *    res.format({
  *      text: function(){
  *        res.send('hey');
  *      },
- *
- *      html: function(){
- *        res.send('<p>hey</p>');
- *      },
- *
- *      json: function(){
- *        res.send({ message: 'hey' });
+ *      default: function(){
+ *        res.send('hey');
  *      }
  *    });
  *
@@ -582,7 +578,7 @@ res.format = function(obj){
   this.vary("Accept");
 
   if (key) {
-    this.set('Content-Type', normalizeType(key).value);
+    this.type(normalizeType(key).value);
     obj[key](req, this, next);
   } else if (obj.default) {
     obj.default(req, this, next)
diff --git a/test/res.format.js b/test/res.format.js
index 0d770d57651..13ba0ff84ba 100644
--- a/test/res.format.js
+++ b/test/res.format.js
@@ -176,6 +176,23 @@ describe('res', function(){
 
       test(app)
     })
+
+    it('should set Content-Type with charset when formatter uses res.end()', function (done) {
+      var app = express();
+
+      app.use(function (req, res) {
+        res.format({
+          'text/plain': function () {
+            res.end('ok');
+          }
+        });
+      });
+
+      request(app)
+        .get('/')
+        .expect('Content-Type', 'text/plain; charset=utf-8')
+        .expect(200, 'ok', done);
+    })
   })
 })