refactor: improve cookie hash comparison logic and tests

- Add clearer comments explaining hash-based comparison flow
- Improve test coverage with more realistic scenarios
- Add test for multiple assignments in single request
- Update test names to be more descriptive

Author: YasserGomma

src/cookies.ts

@@ -181,7 +181,7 @@ export class Cookie<T> implements ElysiaCookie {
 		// Simple equality check
 		if (current === value) return
 
-		// For objects, do a deep equality check
+		// For objects, use hash-based comparison for performance
 		if (
 			typeof current === 'object' &&
 			current !== null &&
@@ -191,12 +191,15 @@ export class Cookie<T> implements ElysiaCookie {
 			try {
 				const newHash = hashObject(value)
 
+				// If hash differs from cached hash, value definitely changed
 				if (this.valueHash !== undefined && this.valueHash !== newHash) {
 					this.valueHash = newHash
-				} else {
+				}
+				// First set (valueHash undefined) OR hashes match: do deep comparison
+				else {
 					if (JSON.stringify(current) === JSON.stringify(value)) {
 						this.valueHash = newHash
-						return
+						return // Values are identical, skip update
 					}
 					this.valueHash = newHash
 				}

test/cookie/unchanged.test.ts

@@ -107,26 +107,82 @@ 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' }
+	it('should not send set-cookie header when setting same object value as incoming cookie', async () => {
+		const app = new Elysia().post('/update', ({ cookie: { data } }) => {
+			// Set to same value as incoming cookie
 			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)
+		// 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)
 	})
 
-	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 } }) => {
+	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
-			data.value = JSON.parse(JSON.stringify(large))
 			return 'ok'
 		})
 
-		const res = await app.handle(new Request('http://localhost/', { method: 'POST' }))
+		// 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)
+	})
+
+	it('should optimize multiple assignments of same object in single request', async () => {
+		const app = new Elysia().post('/multi', ({ cookie: { data } }) => {
+			// Multiple assignments of the same value
+			data.value = { id: 123, name: 'test' }
+			data.value = { id: 123, name: 'test' }
+			data.value = { id: 123, name: 'test' }
+			return 'ok'
+		})
+
+		const res = await app.handle(
+			new Request('http://localhost/multi', { method: 'POST' })
+		)
+
+		// Should only produce one Set-Cookie header
 		expect(res.headers.getAll('set-cookie').length).toBe(1)
 	})
 })