fix: optimize cookie value comparison using FNV-1a hash

- Add FNV-1a hash function for fast object comparison
- Use hash-based comparison to avoid unnecessary cookie updates
- Add tests for repeated identical object values and large objects

Author: YasserGomma

src/cookies.ts

@@ -8,6 +8,23 @@ import { InvalidCookieSignature } from './error'
 import type { Context } from './context'
 import type { Prettify } from './types'
 
+// FNV-1a hash for fast object comparison
+const hashObject = (obj: unknown): number => {
+	const FNV_OFFSET_BASIS = 2166136261
+	const FNV_PRIME = 16777619
+
+	let hash = FNV_OFFSET_BASIS
+	const str = JSON.stringify(obj)
+	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
@@ -125,6 +142,8 @@ export type ElysiaCookie = Prettify<
 type Updater<T> = T | ((value: T) => T)
 
 export class Cookie<T> implements ElysiaCookie {
+	private valueHash?: number
+
 	constructor(
 		private name: string,
 		private jar: Record<string, ElysiaCookie>,
@@ -170,10 +189,18 @@ export class Cookie<T> implements ElysiaCookie {
 			value !== null
 		) {
 			try {
-				if (JSON.stringify(current) === JSON.stringify(value)) return
-			} catch {
-				// If stringify fails, proceed with setting the value
-			}
+				const newHash = hashObject(value)
+
+				if (this.valueHash !== undefined && this.valueHash !== newHash) {
+					this.valueHash = newHash
+				} else {
+					if (JSON.stringify(current) === JSON.stringify(value)) {
+						this.valueHash = newHash
+						return
+					}
+					this.valueHash = newHash
+				}
+			} catch {}
 		}
 
 		// Only create entry in jar if value actually changed

test/cookie/unchanged.test.ts

@@ -106,4 +106,27 @@ describe('Cookie - Unchanged Values', () => {
 
 		expect(response.headers.getAll('set-cookie').length).toBeGreaterThan(0)
 	})
+
+	it('should handle repeated identical object values', async () => {
+		const app = new Elysia().post('/', ({ cookie: { data } }) => {
+			data.value = { id: 123, name: 'test' }
+			data.value = { id: 123, name: 'test' }
+			return 'ok'
+		})
+
+		const res = await app.handle(new Request('http://localhost/', { method: 'POST' }))
+		expect(res.headers.getAll('set-cookie').length).toBe(1)
+	})
+
+	it('should handle large object values efficiently', async () => {
+		const large = { users: Array.from({ length: 100 }, (_, i) => ({ id: i, name: `User ${i}` })) }
+		const app = new Elysia().post('/', ({ cookie: { data } }) => {
+			data.value = large
+			data.value = JSON.parse(JSON.stringify(large))
+			return 'ok'
+		})
+
+		const res = await app.handle(new Request('http://localhost/', { method: 'POST' }))
+		expect(res.headers.getAll('set-cookie').length).toBe(1)
+	})
 })