Fixes adding set-cookie headers multiple times

.changeset/calm-dolphins-remain.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix for adding set-cookie multiple times

packages/astro/src/vite-plugin-astro-server/index.ts

@@ -47,7 +47,24 @@ function writeHtmlResponse(res: http.ServerResponse, statusCode: number, html: s
 
 async function writeWebResponse(res: http.ServerResponse, webResponse: Response) {
 	const { status, headers, body } = webResponse;
-	res.writeHead(status, Object.fromEntries(headers.entries()));
+
+	let _headers = {};
+	if('raw' in headers) {
+		// Node fetch allows you to get the raw headers, which includes multiples of the same type.
+		// This is needed because Set-Cookie *must* be called for each cookie, and can't be
+		// concatenated together.
+		type HeadersWithRaw = Headers & {
+			raw: () => Record<string, string[]>
+		};
+
+		for(const [key, value] of Object.entries((headers as HeadersWithRaw).raw())) {
+			res.setHeader(key, value);
+		}
+	} else {
+		_headers = Object.fromEntries(headers.entries());
+	}
+
+	res.writeHead(status, _headers);
 	if (body) {
 		if (body instanceof Readable) {
 			body.pipe(res);

packages/astro/test/fixtures/ssr-api-route/src/pages/login.js

@@ -0,0 +1,11 @@
+
+export function post() {
+  const headers = new Headers();
+  headers.append('Set-Cookie', `foo=foo; HttpOnly`);
+  headers.append('Set-Cookie', `bar=bar; HttpOnly`);
+
+  return new Response('', {
+    status: 201,
+    headers,
+  });
+}

packages/astro/test/ssr-api-route.test.js

@@ -56,5 +56,13 @@ describe('API routes in SSR', () => {
 			const text = await response.text();
 			expect(text).to.equal(`ok`);
 		});
+
+		it('Can set multiple headers of the same type', async () => {
+			const response = await fixture.fetch('/login', {
+				method: 'POST',
+			});
+			const setCookie = response.headers.get('set-cookie');
+			expect(setCookie).to.equal('foo=foo; HttpOnly, bar=bar; HttpOnly');
+		});
 	});
 });