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perf: optimize splitCookiesString with charCode checks #91564

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perf: optimize splitCookiesString with charCode checks #91564

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d47456f
perf: optimize splitCookiesString with charCode checks instead of regex
benfavre Mar 18, 2026
a60fcc9
fix: add missing vertical tab to isWhitespace check
benfavre Mar 18, 2026
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34 changes: 27 additions & 7 deletions packages/next/src/server/web/utils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -37,10 +37,24 @@ export function fromNodeOutgoingHttpHeaders(
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
*/

// Inline charCode whitespace check — avoids regex allocation per character.
function isWhitespace(code: number): boolean {
// space, tab, newline, vertical tab, form feed, carriage return
return (
code === 32 ||
code === 9 ||
code === 10 ||
code === 11 ||
code === 12 ||
code === 13
)
}

export function splitCookiesString(cookiesString: string) {
var cookiesStrings = []
var pos = 0
Expand All @@ -51,25 +65,28 @@ export function splitCookiesString(cookiesString: string) {
var cookiesSeparatorFound

function skipWhitespace() {
while (pos < cookiesString.length && /\s/.test(cookiesString.charAt(pos))) {
while (
pos < cookiesString.length &&
isWhitespace(cookiesString.charCodeAt(pos))
) {
pos += 1
}
return pos < cookiesString.length
}

function notSpecialChar() {
ch = cookiesString.charAt(pos)
ch = cookiesString.charCodeAt(pos)

return ch !== '=' && ch !== ';' && ch !== ','
return ch !== 61 /* = */ && ch !== 59 /* ; */ && ch !== 44 /* , */
}

while (pos < cookiesString.length) {
start = pos
cookiesSeparatorFound = false

while (skipWhitespace()) {
ch = cookiesString.charAt(pos)
if (ch === ',') {
ch = cookiesString.charCodeAt(pos)
if (ch === 44 /* , */) {
// ',' is a cookie separator if we have later first '=', not ';' or ','
lastComma = pos
pos += 1
Expand All @@ -82,7 +99,10 @@ export function splitCookiesString(cookiesString: string) {
}

// currently special character
if (pos < cookiesString.length && cookiesString.charAt(pos) === '=') {
if (
pos < cookiesString.length &&
cookiesString.charCodeAt(pos) === 61 /* = */
) {
// we found cookies separator
cookiesSeparatorFound = true
// pos is inside the next cookie, so back up and return it.
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