From b22da5734dace60693da2245001fb2311c6604ff Mon Sep 17 00:00:00 2001
From: tsctx <91457664+tsctx@users.noreply.github.com>
Date: Sat, 2 Mar 2024 16:33:53 +0900
Subject: [PATCH 1/2] perf(headers): a single set-cookie

---
 benchmarks/fetch/headers-length32.mjs | 2 +-
 lib/web/fetch/headers.js              | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/benchmarks/fetch/headers-length32.mjs b/benchmarks/fetch/headers-length32.mjs
index 744263f2569..a9b7a52a40e 100644
--- a/benchmarks/fetch/headers-length32.mjs
+++ b/benchmarks/fetch/headers-length32.mjs
@@ -19,7 +19,7 @@ const headers = new Headers(
     'Width',
     'Accept-CH',
     'Via',
-    'Refresh',
+    'Set-Cookie',
     'Server',
     'Sec-Fetch-Dest',
     'Sec-CH-UA-Model',
diff --git a/lib/web/fetch/headers.js b/lib/web/fetch/headers.js
index f21c33b438d..b3ec5a70711 100644
--- a/lib/web/fetch/headers.js
+++ b/lib/web/fetch/headers.js
@@ -536,7 +536,7 @@ class Headers {
     const cookies = this[kHeadersList].cookies
 
     // fast-path
-    if (cookies === null) {
+    if (cookies === null || cookies.length === 1) {
       // Note: The non-null assertion of value has already been done by `HeadersList#toSortedArray`
       return (this[kHeadersList][kHeadersSortedMap] = names)
     }

From a98a09a771edb18a91ba822e0ae9d9bdd0f94bf5 Mon Sep 17 00:00:00 2001
From: Aras Abbasi <aras.abbasi@googlemail.com>
Date: Sun, 3 Mar 2024 09:35:38 +0100
Subject: [PATCH 2/2] add unit test

---
 test/fetch/headers.js | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/test/fetch/headers.js b/test/fetch/headers.js
index acdf5ab611e..00798559e90 100644
--- a/test/fetch/headers.js
+++ b/test/fetch/headers.js
@@ -694,7 +694,7 @@ test('Headers.prototype.getSetCookie', async (t) => {
   })
 
   // https://github.com/nodejs/undici/issues/1935
-  await t.test('When Headers are cloned, so are the cookies', async (t) => {
+  await t.test('When Headers are cloned, so are the cookies (single entry)', async (t) => {
     const server = createServer((req, res) => {
       res.setHeader('Set-Cookie', 'test=onetwo')
       res.end('Hello World!')
@@ -709,6 +709,22 @@ test('Headers.prototype.getSetCookie', async (t) => {
     assert.deepStrictEqual(res.headers.getSetCookie(), ['test=onetwo'])
     assert.ok('set-cookie' in entries)
   })
+
+  await t.test('When Headers are cloned, so are the cookies (multiple entries)', async (t) => {
+    const server = createServer((req, res) => {
+      res.setHeader('Set-Cookie', ['test=onetwo', 'test=onetwothree'])
+      res.end('Hello World!')
+    }).listen(0)
+
+    await once(server, 'listening')
+    t.after(closeServerAsPromise(server))
+
+    const res = await fetch(`http://localhost:${server.address().port}`)
+    const entries = Object.fromEntries(res.headers.entries())
+
+    assert.deepStrictEqual(res.headers.getSetCookie(), ['test=onetwo', 'test=onetwothree'])
+    assert.ok('set-cookie' in entries)
+  })
 })
 
 test('When the value is updated, update the cache', (t) => {