docs: update History.md to include bug fix for HTTP header conflict i…

…n res.send()
bjohansebas · Jun 16, 2026 · Apr 20, 2022 · Apr 21, 2022 · Apr 21, 2022 · Apr 21, 2022
commit dddae1894b8cca5f3b8f8f429def8ecf6bb98ab8
diff --git a/History.md b/History.md
@@ -1,5 +1,12 @@
 # Unreleased Changes
 
+## 🐞 Bug fixes
+
+- Fixed HTTP header conflict between Content-Length and Transfer-Encoding in res.send - by [@YuryShkoda](https://github.com/YuryShkoda) in [#4893](https://github.com/expressjs/express/pull/4893)
+
+
+    Fixed the behavior of `res.send()` to prevent conflicts between `Content-Length` and `Transfer-Encoding` HTTP headers in responses. The `Content-Length` header in `res.send()` is now only added when a `Transfer-Encoding` header is not present, complying with the HTTP specification that states both headers should not coexist in the same response
+
 ## 🚀 Improvements
 
 - Improve HTML structure in `res.redirect()` responses when HTML format is accepted by adding `<!DOCTYPE html>`, `<title>`, and `<body>` tags for better browser compatibility - by [@Bernice55231](https://github.com/Bernice55231) in [#5167](https://github.com/expressjs/express/pull/5167)

diff --git a/lib/response.js b/lib/response.js
@@ -168,7 +168,6 @@ res.send = function send(body) {
   var etagFn = app.get('etag fn')
   var generateETag = !this.get('ETag') && typeof etagFn === 'function'
 
-  // populate Content-Length
   // Because Content-Length and Transfer-Encoding can't be present in the response headers together,
   // Content-Length should be added only if there is no Transfer-Encoding header
   var len;