Merge cookies

packages/astro/src/core/app/index.ts

@@ -347,10 +347,7 @@ export class App {
 			for (const setCookieHeaderValue of App.getSetCookieFromResponse(response)) {
 				response.headers.append('set-cookie', setCookieHeaderValue);
 			}
-		} else {
-			// It may have been set already in a rewrite
-			response.headers.delete('set-cookie');
-		}
+		} 
 
 		Reflect.set(response, responseSentSymbol, true);
 		return response;

packages/astro/src/core/cookies/cookies.ts

@@ -191,6 +191,19 @@ class AstroCookies implements AstroCookiesInterface {
 		}
 	}
 
+	/**
+	 * Merges a new AstroCookies instance into the current instance. Any new cookies
+	 * will be added to the current instance, overwriting any existing cookies with the same name.
+	 */
+	merge(cookies: AstroCookies) {
+		const outgoing = cookies.#outgoing;
+		if (outgoing) {
+			for (const [key, value] of outgoing) {
+				this.#ensureOutgoingMap().set(key, value);
+			}
+		}
+	}
+
 	/**
 	 * Astro.cookies.header() returns an iterator for the cookies that have previously
 	 * been set by either Astro.cookies.set() or Astro.cookies.delete().

packages/astro/src/core/cookies/response.ts

@@ -10,7 +10,7 @@ export function responseHasCookies(response: Response): boolean {
 	return Reflect.has(response, astroCookiesSymbol);
 }
 
-function getFromResponse(response: Response): AstroCookies | undefined {
+export function getFromResponse(response: Response): AstroCookies | undefined {
 	let cookies = Reflect.get(response, astroCookiesSymbol);
 	if (cookies != null) {
 		return cookies as AstroCookies;

packages/astro/src/core/render-context.ts

@@ -27,6 +27,7 @@ import {
 	responseSentSymbol,
 } from './constants.js';
 import { AstroCookies, attachCookiesToResponse } from './cookies/index.js';
+import { getFromResponse } from './cookies/response.js';
 import { AstroError, AstroErrorData } from './errors/index.js';
 import { callMiddleware } from './middleware/callMiddleware.js';
 import { sequence } from './middleware/index.js';
@@ -164,11 +165,11 @@ export class RenderContext {
 							this.routeData
 						);
 
-						if (result.cookies) {
-							for (const cookie of AstroCookies.consume(result.cookies)) {
-								response.headers.append('Set-Cookie', cookie);
-							}
+						const responseCookies = getFromResponse(response)
+						if (result.cookies && responseCookies) {
+								result.cookies?.merge(responseCookies);
 						}
+
 					} catch (e) {
 						// If there is an error in the page's frontmatter or instantiation of the RenderTemplate fails midway,
 						// we signal to the rest of the internals that we can ignore the results of existing renders and avoid kicking off more of them.