monkey-patch formData to enable multipart parsing (#5292)

* monkey-patch formData to enable multipart parsing

* convert ReadableStream to stream.Readable without buffering

* remove obsolete code

* bypass turbo cache

* oops, wrong one

* belt and braces

* well that wasnt it

* trying something

* install polyfills unconditionally

* remove debugging code

* add test

* changeset

Author: Rich-Harris

.changeset/empty-roses-obey.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Enable multipart formdata parsing with node-fetch

packages/kit/package.json

@@ -33,6 +33,7 @@
 		"locate-character": "^2.0.5",
 		"marked": "^4.0.16",
 		"mime": "^3.0.0",
+		"node-fetch": "^3.2.4",
 		"port-authority": "^1.2.0",
 		"rollup": "^2.75.3",
 		"selfsigned": "^2.0.1",

packages/kit/src/node/index.js

@@ -1,4 +1,6 @@
 import * as set_cookie_parser from 'set-cookie-parser';
+import { Request as NodeFetchRequest } from 'node-fetch';
+import { Readable } from 'stream';
 
 /** @param {import('http').IncomingMessage} req */
 function get_raw_body(req) {
@@ -55,11 +57,22 @@ export async function getRequest(base, req) {
 		delete headers[':scheme'];
 	}
 
-	return new Request(base + req.url, {
+	const request = new Request(base + req.url, {
 		method: req.method,
 		headers,
 		body: get_raw_body(req)
 	});
+
+	request.formData = async () => {
+		return new NodeFetchRequest(request.url, {
+			method: request.method,
+			headers: request.headers,
+			// @ts-expect-error TypeScript doesn't understand that ReadableStream implements Symbol.asyncIterator
+			body: request.body && Readable.from(request.body)
+		}).formData();
+	};
+
+	return request;
 }
 
 /** @type {import('@sveltejs/kit/node').setResponse} */

packages/kit/src/node/polyfills.js

@@ -17,8 +17,6 @@ const globals = {
 // exported for dev/preview and node environments
 export function installPolyfills() {
 	for (const name in globals) {
-		if (name in globalThis) continue;
-
 		Object.defineProperty(globalThis, name, {
 			enumerable: true,
 			configurable: true,

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

@@ -38,17 +38,13 @@ export function is_pojo(body) {
 
 	if (body) {
 		if (body instanceof Uint8Array) return false;
+		if (body instanceof ReadableStream) return false;
 
 		// if body is a node Readable, throw an error
 		// TODO remove this for 1.0
 		if (body._readableState && typeof body.pipe === 'function') {
 			throw new Error('Node streams are no longer supported — use a ReadableStream instead');
 		}
-
-		if (body instanceof ReadableStream) return false;
-
-		// similarly, it could be a web ReadableStream
-		if (typeof ReadableStream !== 'undefined' && body instanceof ReadableStream) return false;
 	}
 
 	return true;

packages/kit/test/apps/basics/src/routes/shadowed/error-post.js

@@ -6,11 +6,13 @@ export function get() {
 	};
 }
 
-export function post() {
+export async function post({ request }) {
+	const data = await request.formData();
+
 	return {
 		status: 400,
 		body: {
-			post_message: 'hello from post'
+			post_message: `echo: ${data.get('message')}`
 		}
 	};
 }

packages/kit/test/apps/basics/src/routes/shadowed/index.svelte

@@ -14,6 +14,7 @@
 	<button type="submit" id="redirect-post-with-cookie">redirect</button>
 </form>
 
-<form action="/shadowed/error-post" method="post">
+<form action="/shadowed/error-post" method="post" enctype="multipart/form-data">
+	<input name="message" value="posted data" />
 	<button type="submit" id="error-post">error</button>
 </form>

packages/kit/test/apps/basics/test/test.js

@@ -543,7 +543,7 @@ test.describe.parallel('Shadowed pages', () => {
 	test('Merges bodies for 4xx and 5xx responses from non-GET', async ({ page }) => {
 		await page.goto('/shadowed');
 		await Promise.all([page.waitForNavigation(), page.click('#error-post')]);
-		expect(await page.textContent('h1')).toBe('hello from get / hello from post');
+		expect(await page.textContent('h1')).toBe('hello from get / echo: posted data');
 	});
 
 	test('Responds from endpoint if Accept includes application/json but not text/html', async ({