3 files changed, 52 insertions, 0 deletions
diff --git a/.changeset/thin-kangaroos-exist.md b/.changeset/thin-kangaroos-exist.md
new file mode 100644
index 000000000..5563e5638
--- /dev/null
+++ b/.changeset/thin-kangaroos-exist.md
@@ -0,0 +1,5 @@
+---
+"astro": patch
+---
+
+Fixes an issue where ReadableStream wasn't canceled in dev mode
diff --git a/packages/astro/src/vite-plugin-astro-server/response.ts b/packages/astro/src/vite-plugin-astro-server/response.ts
index 75649a714..54cf6ef3a 100644
--- a/packages/astro/src/vite-plugin-astro-server/response.ts
+++ b/packages/astro/src/vite-plugin-astro-server/response.ts
@@ -82,6 +82,12 @@ export async function writeWebResponse(res: http.ServerResponse, webResponse: Re
 			res.write(body);
 		} else {
 			const reader = body.getReader();
+			res.on('close', () => {
+				reader.cancel().catch((error: unknown) => {
+					// eslint-disable-next-line no-console
+					console.error('An unexpected error occurred in the middle of the stream.', error);
+				});
+			});
 			while (true) {
 				const { done, value } = await reader.read();
 				if (done) break;
diff --git a/packages/astro/test/units/vite-plugin-astro-server/response.test.js b/packages/astro/test/units/vite-plugin-astro-server/response.test.js
index a47769556..a9c06fd26 100644
--- a/packages/astro/test/units/vite-plugin-astro-server/response.test.js
+++ b/packages/astro/test/units/vite-plugin-astro-server/response.test.js
@@ -21,6 +21,28 @@ const fileSystem = {
 		headers.append('Set-Cookie', 'world');
 		return new Response(null, { headers });
 	}`,
+	'/src/pages/streaming.js': `export const GET = ({ locals }) => {
+		let sentChunks = 0;
+		
+		const readableStream = new ReadableStream({
+			async pull(controller) {
+				if (sentChunks === 3) return controller.close();
+				else sentChunks++;
+	
+				await new Promise(resolve => setTimeout(resolve, 1000));
+				controller.enqueue(new TextEncoder().encode('hello'));
+			},
+			cancel() {
+				locals.cancelledByTheServer = true;
+			}
+		});
+	
+		return new Response(readableStream, {
+			headers: {
+				"Content-Type": "text/event-stream"
+			}
+		})
+	}`,
 };
 
 describe('endpoints', () => {
@@ -60,4 +82,23 @@ describe('endpoints', () => {
 			'set-cookie': ['hello', 'world'],
 		});
 	});
+
+	it('Headers with multisple values (set-cookie special case)', async () => {
+		const { req, res, done } = createRequestAndResponse({
+			method: 'GET',
+			url: '/streaming',
+		});
+		
+		const locals = { cancelledByTheServer: false }
+		req[Symbol.for("astro.locals")] = locals
+
+		container.handle(req, res);
+
+		await new Promise(resolve => setTimeout(resolve, 500));
+		res.emit('close');
+		
+		await done;
+		
+		expect(locals).to.deep.equal({ cancelledByTheServer: true });
+	});
 });