Make FS proxying dependent on whether the FS is shared

Author: brandonpayton

packages/php-wasm/universal/src/lib/index.ts

@@ -79,7 +79,7 @@ export {
 } from './urls';
 
 export { isExitCode } from './is-exit-code';
-export { proxyFileSystem } from './proxy-file-system';
+export { proxyFileSystem, isPathToSharedFS } from './proxy-file-system';
 export { sandboxedSpawnHandlerFactory } from './sandboxed-spawn-handler-factory';
 
 export * from './api';

packages/php-wasm/universal/src/lib/proxy-file-system.ts

@@ -34,3 +34,23 @@ export function proxyFileSystem(
 		);
 	}
 }
+
+/**
+ * Answers whether the given path is to a shared filesystem.
+ *
+ * @param sourceOfTruth - The PHP instance that is the source of truth.
+ * @param path - The path to check.
+ * @returns True if the path is to a shared filesystem, false otherwise.
+ */
+export function isPathToSharedFS(sourceOfTruth: PHP, path: string) {
+	// We can't just import the symbol from the library because
+	// Playground CLI is built as ESM and php-wasm-node is built as
+	// CJS and the imported symbols will different in the production build.
+	const __private__symbol = Object.getOwnPropertySymbols(sourceOfTruth)[0];
+
+	// @ts-ignore
+	const FS = sourceOfTruth[__private__symbol].FS;
+
+	const fsResult = FS.lookupPath(path, { noent_okay: true });
+	return fsResult?.node?.isSharedFS ?? false;
+}

packages/playground/wordpress/src/boot.ts

@@ -10,6 +10,7 @@ import {
 	PHP,
 	PHPRequestHandler,
 	proxyFileSystem,
+	isPathToSharedFS,
 	rotatePHPRuntime,
 	sandboxedSpawnHandlerFactory,
 	setPhpIniEntries,
@@ -267,13 +268,23 @@ export async function bootRequestHandler(options: BootRequestHandlerOptions) {
 				joinPaths(new URL(options.siteUrl).pathname, 'phpinfo.php')
 			);
 		} else {
-			// Proxy the filesystem for all secondary PHP instances to
-			// the primary one.
-			proxyFileSystem(await requestHandler.getPrimaryPhp(), php, [
+			const pathsToShareBetweenPhpInstances = [
 				'/tmp',
 				requestHandler.documentRoot,
-				'/internal',
-			]);
+				'/internal/shared',
+				'/internal/symlinks',
+			];
+			const pathsToProxy = pathsToShareBetweenPhpInstances.filter(
+				(path) => !isPathToSharedFS(php, path)
+			);
+
+			// Proxy the filesystem for all secondary PHP instances to
+			// the primary one.
+			proxyFileSystem(
+				await requestHandler.getPrimaryPhp(),
+				php,
+				pathsToProxy
+			);
 		}
 
 		// Spawn handler is responsible for spawning processes for all the