[Website] Support data URLs in blueprint-url query parameter (#158)

## Motivation for the change, related issues

Ensures URLs with data URL-based Blueprints, such as 

```
https://playground.wordpress.net?blueprint-url=data%3Aapplication%2Fjson%3Bbase64%2CeyJsYW5kaW5nUGFnZSI...
```

continue to work. They stopped working in
Automattic/wordpress-playground-private#75 due
to FetchFilesystem class. It assumed a non-data URL and constructed a
`new URL('./', baseUrl)` object in its constructor – which failed when
`baseUrl` was a data URL.

See
Automattic/wordpress-playground-private#157
for more details


## Testing Instructions (or ideally a Blueprint)

Confirm E2E tests pass – this PR ships a new one

Try [this
data URL
Blueprint](http://127.0.0.1:5400/website-server/?blueprint-url=data%3Aapplication%2Fjson%3Bbase64%2CeyJsYW5kaW5nUGFnZSI6Ii9mcmllbmRzLz9yZWZyZXNoJndlbGNvbWUiLCJmZWF0dXJlcyI6eyJuZXR3b3JraW5nIjp0cnVlfSwic3RlcHMiOlt7InN0ZXAiOiJta2RpciIsInBhdGgiOiJ3b3JkcHJlc3Mvd3AtY29udGVudC9tdS1wbHVnaW5zIn0seyJzdGVwIjoid3JpdGVGaWxlIiwicGF0aCI6IndvcmRwcmVzcy93cC1jb250ZW50L211LXBsdWdpbnMvYWRkRmlsdGVyLTEucGhwIiwiZGF0YSI6Ijw%2FcGhwIGFkZF9hY3Rpb24oICdyZXF1ZXN0cy1yZXF1ZXN0cy5iZWZvcmVfcmVxdWVzdCcsIGZ1bmN0aW9uKCAmJHVybCApIHtcbiR1cmwgPSAnaHR0cHM6Ly9wbGF5Z3JvdW5kLndvcmRwcmVzcy5uZXQvY29ycy1wcm94eS5waHA%2FJyAuICR1cmw7XG59ICk7In0seyJzdGVwIjoic2V0U2l0ZU9wdGlvbnMiLCJvcHRpb25zIjp7InBlcm1hbGlua19zdHJ1Y3R1cmUiOiIvJXBvc3RuYW1lJS8ifX0seyJzdGVwIjoiaW5zdGFsbFBsdWdpbiIsInBsdWdpbkRhdGEiOnsicmVzb3VyY2UiOiJ3b3JkcHJlc3Mub3JnL3BsdWdpbnMiLCJzbHVnIjoiZnJpZW5kcyJ9LCJvcHRpb25zIjp7ImFjdGl2YXRlIjp0cnVlfX0seyJzdGVwIjoicnVuUEhQIiwiY29kZSI6Ijw%2FcGhwIHJlcXVpcmVfb25jZSAnd29yZHByZXNzL3dwLWxvYWQucGhwJztcbmlmICggY2xhc3NfZXhpc3RzKCdGcmllbmRzXFxJbXBvcnQnKSkge1xuRnJpZW5kc1xcSW1wb3J0OjpvcG1sKFwiPD94bWwgdmVyc2lvbj1cXFwiMS4wXFxcIiBlbmNvZGluZz1cXFwidXRmLThcXFwiPz48b3BtbCB2ZXJzaW9uPVxcXCIyLjBcXFwiPlxuPGhlYWQ%2BXG48dGl0bGU%2BU3Vic2NyaXB0aW9uczwvdGl0bGU%2BXG48L2hlYWQ%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)

Author: adamziel

packages/playground/storage/src/lib/filesystems.ts

@@ -170,11 +170,16 @@ export interface FetchFilesystemOptions {
  * It can optionally use a CORS proxy and resolve paths relative to a base URL.
  */
 export class FetchFilesystem implements Filesystem {
-	private baseUrl: string;
+	private baseUrl = '';
 	private options: FetchFilesystemOptions;
+	private isDataUrl: boolean;
 
 	constructor(options: FetchFilesystemOptions) {
 		this.options = options;
+		this.isDataUrl = options.baseUrl.startsWith('data:');
+		if (this.isDataUrl) {
+			return;
+		}
 		// Ensure the base URL ends with a slash
 		const url = new URL('./', options.baseUrl);
 		if (url.protocol !== 'http:' && url.protocol !== 'https:') {
@@ -188,6 +193,12 @@ export class FetchFilesystem implements Filesystem {
 	}
 
 	async read(path: string): Promise<StreamedFile> {
+		if (this.isDataUrl) {
+			throw new Error(
+				'FetchFilesystem cannot fetch files from data URLs'
+			);
+		}
+
 		// Make sure there's no .. segments in the path
 		path = normalizePath(path);
 		// Prevent escaping the base URL

packages/playground/website/playwright/e2e/blueprints.spec.ts

@@ -32,6 +32,21 @@ test('?blueprint-url=... should work with simple blueprints', async ({
 	);
 });
 
+test('?blueprint-url=... should accept data URLs', async ({
+	page,
+	website,
+	wordpress,
+}) => {
+	await website.goto('/');
+	const blueprintUrl = encodeURIComponent(
+		`data:application/json;base64,eyJsYW5kaW5nUGFnZSI6Ii9weWdtYWxpb24udHh0Iiwic3RlcHMiOlt7InN0ZXAiOiJ3cml0ZUZpbGUiLCJwYXRoIjoiL3dvcmRwcmVzcy9weWdtYWxpb24udHh0IiwiZGF0YSI6IlBSRUZBQ0UgVE8gUFlHTUFMSU9OIn1dfQ==`
+	);
+	await website.goto(`/?blueprint-url=${blueprintUrl}`);
+	await expect(wordpress.locator('body')).toContainText(
+		'PREFACE TO PYGMALION'
+	);
+});
+
 test('?blueprint-url=... should work with ZIP bundles', async ({
 	page,
 	website,