Split Set-Cookie header correctly

packages/next/server/next-server.ts

@@ -108,6 +108,7 @@ import type { FetchEventResult } from './web/types'
 import type { MiddlewareManifest } from '../build/webpack/plugins/middleware-plugin'
 import type { ParsedNextUrl } from '../shared/lib/router/utils/parse-next-url'
 import type { ParsedUrl } from '../shared/lib/router/utils/parse-url'
+import { splitCookiesString } from './web/utils'
 
 const getCustomRouteMatcher = pathMatch(true)
 
@@ -1171,7 +1172,7 @@ export default class Server {
           for (const [key, value] of result.response.headers.entries()) {
             if (key !== 'content-encoding') {
               if (key.toLowerCase() === 'set-cookie') {
-                res.setHeader(key, value.split(', '))
+                res.setHeader(key, splitCookiesString(value))
               } else {
                 res.setHeader(key, value)
               }

packages/next/server/web/utils.ts

@@ -45,3 +45,79 @@ export function toNodeHeaders(headers?: Headers): NodeHeaders {
   }
   return result
 }
+
+/*
+  Set-Cookie header field-values are sometimes comma joined in one string. This splits them without choking on commas
+  that are within a single set-cookie field-value, such as in the Expires portion.
+  This is uncommon, but explicitly allowed - see https://tools.ietf.org/html/rfc2616#section-4.2
+  Node.js does this for every header *except* set-cookie - see https://github.com/nodejs/node/blob/d5e363b77ebaf1caf67cd7528224b651c86815c1/lib/_http_incoming.js#L128
+  React Native's fetch does this for *every* header, including set-cookie.
+  
+  Based on: https://github.com/google/j2objc/commit/16820fdbc8f76ca0c33472810ce0cb03d20efe25
+  Credits to: https://github.com/tomball for original and https://github.com/chrusart for JavaScript implementation
+*/
+export function splitCookiesString(cookiesString: string) {
+  var cookiesStrings = []
+  var pos = 0
+  var start
+  var ch
+  var lastComma
+  var nextStart
+  var cookiesSeparatorFound
+
+  function skipWhitespace() {
+    while (pos < cookiesString.length && /\s/.test(cookiesString.charAt(pos))) {
+      pos += 1
+    }
+    return pos < cookiesString.length
+  }
+
+  function notSpecialChar() {
+    ch = cookiesString.charAt(pos)
+
+    return ch !== '=' && ch !== ';' && ch !== ','
+  }
+
+  while (pos < cookiesString.length) {
+    start = pos
+    cookiesSeparatorFound = false
+
+    while (skipWhitespace()) {
+      ch = cookiesString.charAt(pos)
+      if (ch === ',') {
+        // ',' is a cookie separator if we have later first '=', not ';' or ','
+        lastComma = pos
+        pos += 1
+
+        skipWhitespace()
+        nextStart = pos
+
+        while (pos < cookiesString.length && notSpecialChar()) {
+          pos += 1
+        }
+
+        // currently special character
+        if (pos < cookiesString.length && cookiesString.charAt(pos) === '=') {
+          // we found cookies separator
+          cookiesSeparatorFound = true
+          // pos is inside the next cookie, so back up and return it.
+          pos = nextStart
+          cookiesStrings.push(cookiesString.substring(start, lastComma))
+          start = pos
+        } else {
+          // in param ',' or param separator ';',
+          // we continue from that comma
+          pos = lastComma + 1
+        }
+      } else {
+        pos += 1
+      }
+    }
+
+    if (!cookiesSeparatorFound || pos >= cookiesString.length) {
+      cookiesStrings.push(cookiesString.substring(start, cookiesString.length))
+    }
+  }
+
+  return cookiesStrings
+}

test/integration/middleware-core/pages/rewrites/_middleware.js

@@ -8,7 +8,7 @@ export async function middleware(request) {
     if (!bucket) {
       bucket = Math.random() >= 0.5 ? 'a' : 'b'
       const response = NextResponse.rewrite(`/rewrites/${bucket}`)
-      response.cookie('bucket', bucket)
+      response.cookie('bucket', bucket, { maxAge: 10000 })
       return response
     }
 

test/integration/middleware-core/test/index.test.js

@@ -115,6 +115,8 @@ function rewriteTests(locale = '') {
     )
     const html = await res.text()
     const $ = cheerio.load(html)
+    // Set-Cookie header with Expires should not be split into two
+    expect(res.headers.raw()['set-cookie']).toHaveLength(1)
     const bucket = getCookieFromResponse(res, 'bucket')
     const expectedText = bucket === 'a' ? 'Welcome Page A' : 'Welcome Page B'
     const browser = await webdriver(