Add support for streaming async iterator responses to adapter-static

Author: jesseskinner

packages/adapter-static/test/apps/prerendered/src/routes/index.svelte

@@ -1 +1,3 @@
-<h1>This page was prerendered</h1>
+<h1>This page was prerendered</h1>
+
+<a href="/test.csv">csv</a>

packages/adapter-static/test/apps/prerendered/src/routes/test.csv.js

@@ -0,0 +1,12 @@
+/** @type {import('@sveltejs/kit').RequestHandler} */
+export function get() {
+	return {
+		headers: { 'Content-Type': 'text/csv' },
+		body: generateCSV()
+	};
+}
+
+async function* generateCSV() {
+	yield '1,one\n';
+	yield '2,two\n';
+}

packages/adapter-static/test/apps/spa/src/routes/__layout.svelte

@@ -1,6 +1,7 @@
 <nav>
 	<a href="/">home</a>
 	<a href="/about">about</a>
+	<a href="/test.txt">test.txt</a>
 </nav>
 
-<slot></slot>
+<slot></slot>

packages/adapter-static/test/apps/spa/src/routes/index.svelte

@@ -1 +1 @@
-<h1>This page was not prerendered</h1>
+<h1>This page was not prerendered</h1>

packages/adapter-static/test/apps/spa/src/routes/test.txt.js

@@ -0,0 +1,11 @@
+/** @type {import('@sveltejs/kit').RequestHandler} */
+export function get() {
+	return {
+		body: stream()
+	};
+}
+
+async function* stream() {
+	yield 'foo';
+	yield 'bar';
+}

packages/adapter-static/test/test.js

@@ -11,6 +11,10 @@ run('prerendered', (test) => {
 		await page.goto(base);
 		assert.equal(await page.textContent('h1'), 'This page was prerendered');
 	});
+
+	test('prerenders a streaming CSV file', async ({ cwd }) => {
+		assert.equal(String(fs.readFileSync(`${cwd}/build/test.csv`)), '1,one\n2,two\n');
+	});
 });
 
 run('spa', (test) => {
@@ -35,4 +39,13 @@ run('spa', (test) => {
 		await page.goto(`${base}/nosuchpage`);
 		assert.equal(await page.textContent('h1'), '404');
 	});
+
+	test('prerenders a streaming text file', async ({ cwd }) => {
+		assert.equal(String(fs.readFileSync(`${cwd}/build/test.txt`)), 'foobar');
+	});
+
+	test('renders a streaming text file', async ({ base, page }) => {
+		const response = await page.goto(`${base}/test.txt`);
+		assert.equal(String(await response.body()), 'foobar');
+	});
 });

packages/kit/src/core/adapt/prerender.js

@@ -206,8 +206,23 @@ export async function prerender({ cwd, out, log, config, build_data, fallback, a
 			}
 
 			if (rendered.status === 200) {
-				log.info(`${rendered.status} ${decoded_path}`);
-				writeFileSync(file, rendered.body || '');
+				log.info(`${rendered.status} ${path}`);
+
+				if (
+					rendered.body &&
+					typeof rendered.body === 'object' &&
+					typeof rendered.body[Symbol.asyncIterator] === 'function'
+				) {
+					let body = '';
+
+					for await (const chunk of rendered.body) {
+						body += chunk;
+					}
+
+					writeFileSync(file, body);
+				} else {
+					writeFileSync(file, rendered.body || '');
+				}
 				written_files.push(file);
 			} else if (response_type !== OK) {
 				error({ status: rendered.status, path, referrer, referenceType: 'linked' });

packages/kit/src/runtime/server/endpoint.js

@@ -15,6 +15,11 @@ function is_string(s) {
 	return typeof s === 'string' || s instanceof String;
 }
 
+/** @param {unknown} s */
+function is_async_iterator(s) {
+	return s && typeof s === 'object' && typeof s[Symbol.asyncIterator] === 'function';
+}
+
 /**
  * Decides how the body should be parsed based on its mime type. Should match what's in parse_body
  *
@@ -28,7 +33,8 @@ function is_content_type_textual(content_type) {
 		type === 'text/plain' ||
 		type === 'application/json' ||
 		type === 'application/x-www-form-urlencoded' ||
-		type === 'multipart/form-data'
+		type === 'multipart/form-data' ||
+		type === 'text/event-stream'
 	);
 }
 
@@ -67,17 +73,17 @@ export async function render_endpoint(request, route, match) {
 
 	const is_type_textual = is_content_type_textual(type);
 
-	if (!is_type_textual && !(body instanceof Uint8Array || is_string(body))) {
+	if (!is_type_textual && !(body instanceof Uint8Array || is_string(body) || is_async_iterator(body))) {
 		return error(
-			`${preface}: body must be an instance of string or Uint8Array if content-type is not a supported textual content-type`
+			`${preface}: body must be an instance of string or Uint8Array or an async iterator if content-type is not a supported textual content-type`
 		);
 	}
 
 	/** @type {import('types/hooks').StrictBody} */
 	let normalized_body;
 
 	// ensure the body is an object
-	if (body && typeof body === 'object' && typeof body[Symbol.asyncIterator] === 'function') {
+	if (is_async_iterator(body)) {
 		normalized_body = /** @type {object} */ (body);
 	} else if (
 		(typeof body === 'object' || typeof body === 'undefined') &&