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feat: idempotent cookies #1641

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feat: idempotent cookies #1641

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97077a9
feat: idempotent cookie class
akim-bow Dec 29, 2025
9f9d4e7
self-review
akim-bow Dec 29, 2025
ecef0af
self-review: remove misleading readonly
akim-bow Dec 29, 2025
fcf4bdc
fix: tiny code improves
akim-bow Jan 6, 2026
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77 changes: 6 additions & 71 deletions src/cookies.ts
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Original file line number Diff line number Diff line change
@@ -1,29 +1,11 @@
import { parse, serialize } from 'cookie'

import decode from 'fast-decode-uri-component'

import { isNotEmpty, unsignCookie } from './utils'
import { InvalidCookieSignature } from './error'

import type { Context } from './context'
import type { Prettify } from './types'

// FNV-1a hash for fast string hashing
const hashString = (str: string): number => {
const FNV_OFFSET_BASIS = 2166136261
const FNV_PRIME = 16777619

let hash = FNV_OFFSET_BASIS
const len = str.length

for (let i = 0; i < len; i++) {
hash ^= str.charCodeAt(i)
hash = Math.imul(hash, FNV_PRIME)
}

return hash >>> 0
}

export interface CookieOptions {
/**
* Specifies the value for the {@link https://tools.ietf.org/html/rfc6265#section-5.2.3|Domain Set-Cookie attribute}. By default, no
Expand Down Expand Up @@ -141,10 +123,9 @@ export type ElysiaCookie = Prettify<
type Updater<T> = T | ((value: T) => T)

export class Cookie<T> implements ElysiaCookie {
private valueHash?: number

constructor(
private name: string,
// Modifications here lead to changes in the response headers. Empty at the start of a request.
private jar: Record<string, ElysiaCookie>,
private initial: Partial<ElysiaCookie> = {}
) {}
Expand All @@ -157,8 +138,6 @@ export class Cookie<T> implements ElysiaCookie {
if (!(this.name in this.jar)) this.jar[this.name] = this.initial

this.jar[this.name] = jar
// Invalidate hash cache when jar is modified directly
this.valueHash = undefined
}

protected get setCookie() {
Expand All @@ -176,42 +155,6 @@ export class Cookie<T> implements ElysiaCookie {
}

set value(value: T) {
// Check if value actually changed before creating entry in jar
const current = this.cookie.value

// Simple equality check
if (current === value) return

// For objects, use hash-based comparison for performance
// Note: Uses JSON.stringify for comparison, so key order matters
// { a: 1, b: 2 } and { b: 2, a: 1 } are treated as different values
if (
typeof current === 'object' &&
current !== null &&
typeof value === 'object' &&
value !== null
) {
try {
// Cache stringified value to avoid duplicate stringify calls
const valueStr = JSON.stringify(value)
const newHash = hashString(valueStr)

// If hash differs from cached hash, value definitely changed
if (this.valueHash !== undefined && this.valueHash !== newHash) {
this.valueHash = newHash
}
// First set (valueHash undefined) OR hashes match: do deep comparison
else {
if (JSON.stringify(current) === valueStr) {
this.valueHash = newHash
return // Values are identical, skip update
}
this.valueHash = newHash
}
} catch {}
}

// Only create entry in jar if value actually changed
if (!(this.name in this.jar)) this.jar[this.name] = { ...this.initial }
this.jar[this.name].value = value
}
Expand Down Expand Up @@ -347,18 +290,10 @@ export const createCookieJar = (

return new Proxy(store, {
get(_, key: string) {
if (key in store)
return new Cookie(
key,
set.cookie as Record<string, ElysiaCookie>,
Object.assign({}, initial ?? {}, store[key])
)

return new Cookie(
key,
set.cookie as Record<string, ElysiaCookie>,
Object.assign({}, initial)
)
return new Cookie(key, set.cookie as Record<string, ElysiaCookie>, {
...(initial ?? {}),
...(store[key] ?? {})
})
}
}) as Record<string, Cookie<unknown>>
}
Expand All @@ -385,7 +320,7 @@ export const parseCookie = async (
for (const [name, v] of Object.entries(cookies)) {
if (v === undefined) continue

let value = decode(v)
let value = v

if (value) {
const starts = value.charCodeAt(0)
Expand Down
39 changes: 2 additions & 37 deletions test/cookie/unchanged.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -108,7 +108,7 @@ describe('Cookie - Unchanged Values', () => {
expect(response.headers.getAll('set-cookie').length).toBeGreaterThan(0)
})

it('should not send set-cookie header when setting same object value as incoming cookie', async () => {
it('should idempotently create headers on cookie modifications', async () => {
const app = new Elysia().post('/update', ({ cookie: { data } }) => {
// Set to same value as incoming cookie
data.value = { id: 123, name: 'test' }
Expand All @@ -132,42 +132,7 @@ describe('Cookie - Unchanged Values', () => {
})
)

// Should not send Set-Cookie since value didn't change
expect(secondRes.headers.getAll('set-cookie').length).toBe(0)
})

it('should not send set-cookie header for large unchanged object values', async () => {
const large = {
users: Array.from({ length: 100 }, (_, i) => ({
id: i,
name: `User ${i}`
}))
}

const app = new Elysia().post('/update', ({ cookie: { data } }) => {
data.value = large
return 'ok'
})

// First request: set the cookie
const firstRes = await app.handle(
new Request('http://localhost/update', { method: 'POST' })
)
const setCookie = firstRes.headers.get('set-cookie')
expect(setCookie).toBeTruthy()

// Second request: send cookie back and set to same value
const secondRes = await app.handle(
new Request('http://localhost/update', {
method: 'POST',
headers: {
cookie: setCookie!.split(';')[0]
}
})
)

// Should not send Set-Cookie since value didn't change
expect(secondRes.headers.getAll('set-cookie').length).toBe(0)
expect(secondRes.headers.get('set-cookie')).toBeTruthy()
})

it('should optimize multiple assignments of same object in single request', async () => {
Expand Down
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