Virtual File System for Node.js

doc/api/index.md

@@ -66,6 +66,7 @@
 * [URL](url.md)
 * [Utilities](util.md)
 * [V8](v8.md)
+* [Virtual File System](vfs.md)
 * [VM](vm.md)
 * [WASI](wasi.md)
 * [Web Crypto API](webcrypto.md)

doc/api/single-executable-applications.md

@@ -174,6 +174,57 @@ const raw = getRawAsset('a.jpg');
 See documentation of the [`sea.getAsset()`][], [`sea.getAssetAsBlob()`][],
 [`sea.getRawAsset()`][] and [`sea.getAssetKeys()`][] APIs for more information.
 
+### Virtual File System (VFS) for assets
+
+> Stability: 1 - Experimental
+
+Instead of using the `node:sea` API to access individual assets, you can use
+the Virtual File System (VFS) to access bundled assets through standard `fs`
+APIs. When running as a Single Executable Application, the VFS is automatically
+initialized and mounted at `/sea`. All assets defined in the SEA configuration
+are accessible through this virtual path.
+
+```cjs
+const fs = require('node:fs');
+
+// Assets are automatically available at /sea when running as SEA
+const config = JSON.parse(fs.readFileSync('/sea/config.json', 'utf8'));
+const data = fs.readFileSync('/sea/data/file.txt');
+
+// Directory operations work too
+const files = fs.readdirSync('/sea/assets');
+
+// Check if a bundled file exists
+if (fs.existsSync('/sea/optional.json')) {
+  // ...
+}
+```
+
+The VFS supports the following `fs` operations on bundled assets:
+
+* `readFileSync()` / `readFile()` / `promises.readFile()`
+* `statSync()` / `stat()` / `promises.stat()`
+* `lstatSync()` / `lstat()` / `promises.lstat()`
+* `readdirSync()` / `readdir()` / `promises.readdir()`
+* `existsSync()`
+* `realpathSync()` / `realpath()` / `promises.realpath()`
+* `accessSync()` / `access()` / `promises.access()`
+* `openSync()` / `open()` - for reading
+* `createReadStream()`
+
+#### Loading modules from VFS in SEA
+
+You can use `require()` directly with absolute VFS paths:
+
+```cjs
+// Require bundled modules directly
+const myModule = require('/sea/lib/mymodule.js');
+const utils = require('/sea/utils/helpers.js');
+```
+
+The SEA's `require()` function automatically detects VFS paths (paths starting
+with `/sea/`) and loads modules from the virtual file system.
+
 ### Startup snapshot support
 
 The `useSnapshot` field can be used to enable startup snapshot support. In this

doc/api/test.md

@@ -2340,6 +2340,94 @@ test('mocks a counting function', (t) => {
 });
 ```
 
+### `mock.fs([options])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.0 - Early development
+
+* `options` {Object} Optional configuration options for the mock file system.
+  The following properties are supported:
+  * `prefix` {string} The mount point prefix for the virtual file system.
+    **Default:** `'/mock'`.
+  * `files` {Object} An optional object where keys are file paths (relative to
+    the VFS root) and values are the file contents. Contents can be strings,
+    Buffers, or functions that return strings/Buffers.
+* Returns: {MockFSContext} An object that can be used to manage the mock file
+  system.
+
+This function creates a mock file system using the Virtual File System (VFS).
+The mock file system is automatically cleaned up when the test completes.
+
+## Class: `MockFSContext`
+
+The `MockFSContext` object is returned by `mock.fs()` and provides the
+following methods and properties:
+
+* `vfs` {VirtualFileSystem} The underlying VFS instance.
+* `prefix` {string} The mount prefix.
+* `addFile(path, content)` Adds a file to the mock file system.
+* `addDirectory(path[, populate])` Adds a directory to the mock file system.
+* `existsSync(path)` Checks if a path exists (path is relative to prefix).
+* `restore()` Manually restores the file system to its original state.
+
+The following example demonstrates how to create a mock file system for testing:
+
+```js
+const { test } = require('node:test');
+const assert = require('node:assert');
+const fs = require('node:fs');
+
+test('reads configuration from mock file', (t) => {
+  const mockFs = t.mock.fs({
+    prefix: '/app',
+    files: {
+      '/config.json': JSON.stringify({ debug: true }),
+      '/data/users.txt': 'user1\nuser2\nuser3',
+    },
+  });
+
+  // Files are accessible via standard fs APIs
+  const config = JSON.parse(fs.readFileSync('/app/config.json', 'utf8'));
+  assert.strictEqual(config.debug, true);
+
+  // Check file existence
+  assert.strictEqual(fs.existsSync('/app/config.json'), true);
+  assert.strictEqual(fs.existsSync('/app/missing.txt'), false);
+
+  // Use mockFs.existsSync for paths relative to prefix
+  assert.strictEqual(mockFs.existsSync('/config.json'), true);
+});
+
+test('supports dynamic file content', (t) => {
+  let counter = 0;
+  const mockFs = t.mock.fs({ prefix: '/dynamic' });
+
+  mockFs.addFile('/counter.txt', () => {
+    counter++;
+    return String(counter);
+  });
+
+  // Each read calls the function
+  assert.strictEqual(fs.readFileSync('/dynamic/counter.txt', 'utf8'), '1');
+  assert.strictEqual(fs.readFileSync('/dynamic/counter.txt', 'utf8'), '2');
+});
+
+test('supports require from mock files', (t) => {
+  t.mock.fs({
+    prefix: '/modules',
+    files: {
+      '/math.js': 'module.exports = { add: (a, b) => a + b };',
+    },
+  });
+
+  const math = require('/modules/math.js');
+  assert.strictEqual(math.add(2, 3), 5);
+});
+```
+
 ### `mock.getter(object, methodName[, implementation][, options])`
 
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