fix: properly decode base64 strings inside read (#11682)

* fix: properly decode base64 strings inside `read`

* test

---------

Co-authored-by: Rich Harris <[email protected]>

Author: Rich-Harris

Diff for: .changeset/fluffy-schools-develop.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: properly decode base64 strings inside `read`

Diff for: packages/kit/src/runtime/app/server/index.js

@@ -1,6 +1,7 @@
 import { read_implementation, manifest } from '__sveltekit/server';
 import { base } from '__sveltekit/paths';
 import { DEV } from 'esm-env';
+import { b64_decode } from '../../utils.js';
 
 /**
  * Read the contents of an imported asset from the filesystem
@@ -30,7 +31,18 @@ export function read(asset) {
 		const [prelude, data] = asset.split(';');
 		const type = prelude.slice(5) || 'application/octet-stream';
 
-		const decoded = data.startsWith('base64,') ? atob(data.slice(7)) : decodeURIComponent(data);
+		if (data.startsWith('base64,')) {
+			const decoded = b64_decode(data.slice(7));
+
+			return new Response(decoded, {
+				headers: {
+					'Content-Length': decoded.byteLength.toString(),
+					'Content-Type': type
+				}
+			});
+		}
+
+		const decoded = decodeURIComponent(data);
 
 		return new Response(decoded, {
 			headers: {

Diff for: packages/kit/src/runtime/client/fetcher.js

@@ -1,5 +1,6 @@
 import { BROWSER, DEV } from 'esm-env';
 import { hash } from '../hash.js';
+import { b64_decode } from '../utils.js';
 
 let loading = 0;
 
@@ -77,22 +78,6 @@ if (DEV && BROWSER) {
 
 const cache = new Map();
 
-/**
- * @param {string} text
- * @returns {ArrayBufferLike}
- */
-function b64_decode(text) {
-	const d = atob(text);
-
-	const u8 = new Uint8Array(d.length);
-
-	for (let i = 0; i < d.length; i++) {
-		u8[i] = d.charCodeAt(i);
-	}
-
-	return u8.buffer;
-}
-
 /**
  * Should be called on the initial run of load functions that hydrate the page.
  * Saves any requests with cache-control max-age to the cache.

Diff for: packages/kit/src/runtime/server/page/load_data.js

@@ -1,6 +1,7 @@
 import { DEV } from 'esm-env';
 import { disable_search, make_trackable } from '../../../utils/url.js';
 import { validate_depends } from '../../shared.js';
+import { b64_encode } from '../../utils.js';
 
 /**
  * Calls the user's server `load` function.
@@ -207,25 +208,6 @@ export async function load_data({
 	return result ?? null;
 }
 
-/**
- * @param {ArrayBuffer} buffer
- * @returns {string}
- */
-function b64_encode(buffer) {
-	if (globalThis.Buffer) {
-		return Buffer.from(buffer).toString('base64');
-	}
-
-	const little_endian = new Uint8Array(new Uint16Array([1]).buffer)[0] > 0;
-
-	// The Uint16Array(Uint8Array(...)) ensures the code points are padded with 0's
-	return btoa(
-		new TextDecoder(little_endian ? 'utf-16le' : 'utf-16be').decode(
-			new Uint16Array(new Uint8Array(buffer))
-		)
-	);
-}
-
 /**
  * @param {Pick<import('@sveltejs/kit').RequestEvent, 'fetch' | 'url' | 'request' | 'route'>} event
  * @param {import('types').SSRState} state

Diff for: packages/kit/src/runtime/utils.js

@@ -0,0 +1,34 @@
+/**
+ * @param {string} text
+ * @returns {ArrayBufferLike}
+ */
+export function b64_decode(text) {
+	const d = atob(text);
+
+	const u8 = new Uint8Array(d.length);
+
+	for (let i = 0; i < d.length; i++) {
+		u8[i] = d.charCodeAt(i);
+	}
+
+	return u8.buffer;
+}
+
+/**
+ * @param {ArrayBuffer} buffer
+ * @returns {string}
+ */
+export function b64_encode(buffer) {
+	if (globalThis.Buffer) {
+		return Buffer.from(buffer).toString('base64');
+	}
+
+	const little_endian = new Uint8Array(new Uint16Array([1]).buffer)[0] > 0;
+
+	// The Uint16Array(Uint8Array(...)) ensures the code points are padded with 0's
+	return btoa(
+		new TextDecoder(little_endian ? 'utf-16le' : 'utf-16be').decode(
+			new Uint16Array(new Uint8Array(buffer))
+		)
+	);
+}

Diff for: packages/kit/test/apps/basics/src/routes/read-file/auto.txt

@@ -1 +1 @@
-Imported without ?url
+Imported without ?url 😎

Diff for: packages/kit/test/apps/basics/src/routes/read-file/url.txt

@@ -1 +1 @@
-Imported with ?url
+Imported with ?url 😎

Diff for: packages/kit/test/apps/basics/test/test.js

@@ -713,8 +713,9 @@ test.describe('$app/server', () => {
 		const auto = await page.textContent('[data-testid="auto"]');
 		const url = await page.textContent('[data-testid="url"]');
 
-		expect(auto.trim()).toBe('Imported without ?url');
-		expect(url.trim()).toBe('Imported with ?url');
+		// the emoji is there to check that base64 decoding works correctly
+		expect(auto.trim()).toBe('Imported without ?url 😎');
+		expect(url.trim()).toBe('Imported with ?url 😎');
 	});
 });