vfs: address Aviv's review comments

- MockFSContext: use public properties instead of private + getters
- MockFSContext: use ctx.restore instead of restoreFS
- streams.js: use kEmptyObject for default options parameter
- streams.js: use getLazy for fd module import
- streams.js: remove unnecessary createVirtualReadStream wrapper
- file_system.js: use VirtualReadStream class directly

PR-URL: #61478

Author: mcollina

lib/internal/test_runner/mock/mock.js

@@ -413,28 +413,21 @@ const { restore: restoreProperty } = MockPropertyContext.prototype;
  * Context for mocking the file system using VFS.
  */
 class MockFSContext {
-  #vfs;
-  #prefix;
-
-  constructor(vfs, prefix) {
-    this.#vfs = vfs;
-    this.#prefix = prefix;
-  }
-
   /**
-   * Gets the underlying VirtualFileSystem instance.
-   * @returns {VirtualFileSystem}
+   * The underlying VirtualFileSystem instance.
+   * @type {VirtualFileSystem}
    */
-  get vfs() {
-    return this.#vfs;
-  }
+  vfs;
 
   /**
-   * Gets the mount prefix for the mock file system.
-   * @returns {string}
+   * The mount prefix for the mock file system.
+   * @type {string}
    */
-  get prefix() {
-    return this.#prefix;
+  prefix;
+
+  constructor(vfs, prefix) {
+    this.vfs = vfs;
+    this.prefix = prefix;
   }
 
   /**
@@ -443,15 +436,15 @@ class MockFSContext {
    * @param {string|Buffer} content - The file content.
    */
   addFile(filePath, content) {
-    this.#vfs.addFile(filePath, content);
+    this.vfs.addFile(filePath, content);
   }
 
   /**
    * Adds a directory to the mock file system.
    * @param {string} dirPath - The path of the directory.
    */
   addDirectory(dirPath) {
-    this.#vfs.addDirectory(dirPath);
+    this.vfs.addDirectory(dirPath);
   }
 
   /**
@@ -460,20 +453,18 @@ class MockFSContext {
    * @returns {boolean}
    */
   existsSync(path) {
-    const fullPath = join(this.#prefix, path);
-    return this.#vfs.existsSync(fullPath);
+    const fullPath = join(this.prefix, path);
+    return this.vfs.existsSync(fullPath);
   }
 
   /**
    * Restores the file system to its original state.
    */
   restore() {
-    this.#vfs.unmount();
+    this.vfs.unmount();
   }
 }
 
-const { restore: restoreFS } = MockFSContext.prototype;
-
 class MockTracker {
   #mocks = [];
   #timers;
@@ -832,7 +823,7 @@ class MockTracker {
     ArrayPrototypePush(this.#mocks, {
       __proto__: null,
       ctx,
-      restore: restoreFS,
+      restore: ctx.restore,
     });
 
     return ctx;

lib/internal/vfs/file_system.js

@@ -29,7 +29,7 @@ const {
   createENOTDIR,
   createEBADF,
 } = require('internal/vfs/errors');
-const { createVirtualReadStream } = require('internal/vfs/streams');
+const { VirtualReadStream } = require('internal/vfs/streams');
 const { emitExperimentalWarning } = require('internal/util');
 
 // Private symbols
@@ -882,7 +882,7 @@ class VirtualFileSystem {
    * @returns {ReadStream}
    */
   createReadStream(filePath, options) {
-    return createVirtualReadStream(this, filePath, options);
+    return new VirtualReadStream(this, filePath, options);
   }
 
   // ==================== Watch Operations ====================

lib/internal/vfs/streams.js

@@ -6,6 +6,12 @@ const {
 
 const { Readable } = require('stream');
 const { createEBADF } = require('internal/vfs/errors');
+const { getLazy, kEmptyObject } = require('internal/util');
+
+// Lazy-load fd module to avoid circular dependency
+const lazyGetVirtualFd = getLazy(
+  () => require('internal/vfs/fd').getVirtualFd,
+);
 
 /**
  * A readable stream for virtual files.
@@ -25,7 +31,7 @@ class VirtualReadStream extends Readable {
    * @param {string} filePath The path to the file
    * @param {object} [options] Stream options
    */
-  constructor(vfs, filePath, options = {}) {
+  constructor(vfs, filePath, options = kEmptyObject) {
     const {
       start = 0,
       end = Infinity,
@@ -81,7 +87,8 @@ class VirtualReadStream extends Readable {
     // Load content on first read (lazy loading)
     if (this.#content === null) {
       try {
-        const vfd = require('internal/vfs/fd').getVirtualFd(this.#fd);
+        const getVirtualFd = lazyGetVirtualFd();
+        const vfd = getVirtualFd(this.#fd);
         if (!vfd) {
           this.destroy(createEBADF('read'));
           return;
@@ -146,18 +153,6 @@ class VirtualReadStream extends Readable {
   }
 }
 
-/**
- * Creates a readable stream for a virtual file.
- * @param {VirtualFileSystem} vfs The VFS instance
- * @param {string} filePath The path to the file
- * @param {object} [options] Stream options
- * @returns {VirtualReadStream}
- */
-function createVirtualReadStream(vfs, filePath, options = {}) {
-  return new VirtualReadStream(vfs, filePath, options);
-}
-
 module.exports = {
-  createVirtualReadStream,
   VirtualReadStream,
 };