Helper to bypass mock FS & expose real files/directories

lib/bypass.js

@@ -0,0 +1,55 @@
+const realBinding = process.binding('fs');
+let storedBinding;
+
+/**
+ * Perform action, bypassing mock FS
+ * @example
+ * // This file exists on the real FS, not on the mocked FS
+ * const filePath = '/path/file.json';
+ * const data = mock.bypass(() => fs.readFileSync(filePath, 'utf-8'));
+ */
+exports = module.exports = function bypass(fn) {
+  if (typeof fn !== 'function') {
+    throw new Error(`Must provide a function to perform for mock.bypass()`);
+  }
+
+  exports.disable();
+
+  try {
+    // Perform action
+    const res = fn();
+
+    // Handle promise return
+    if (typeof res.then === 'function') {
+      res.then(exports.enable);
+      res.catch(exports.enable);
+    } else {
+      exports.enable();
+    }
+
+    return res;
+  } catch (e) {
+    exports.enable();
+    throw e;
+  }
+};
+
+/**
+ * Temporarily disable Mocked FS
+ */
+exports.disable = () => {
+  if (realBinding._mockedBinding) {
+    storedBinding = realBinding._mockedBinding;
+    delete realBinding._mockedBinding;
+  }
+};
+
+/**
+ * Enables Mocked FS after being disabled by mock.disable()
+ */
+exports.enable = () => {
+  if (storedBinding) {
+    realBinding._mockedBinding = storedBinding;
+    storedBinding = undefined;
+  }
+};

lib/filesystem.js

@@ -112,6 +112,8 @@ FileSystem.prototype.getItem = function(filepath) {
     if (item) {
       if (item instanceof Directory && name !== currentParts[i]) {
         // make sure traversal is allowed
+        // This fails for Windows directories which do not have execute permission, by default. It may be a good idea
+        // to change this logic to windows-friendly. See notes in mock.createDirectoryInfoFromPaths()
         if (!item.canExecute()) {
           throw new FSError('EACCES', filepath);
         }

lib/index.js

@@ -5,6 +5,8 @@ const FSError = require('./error');
 const FileSystem = require('./filesystem');
 const realBinding = process.binding('fs');
 const path = require('path');
+const loader = require('./loader');
+const bypass = require('./bypass');
 const fs = require('fs');
 
 const toNamespacedPath = FileSystem.toNamespacedPath;
@@ -183,3 +185,17 @@ exports.directory = FileSystem.directory;
  * Create a symbolic link factory.
  */
 exports.symlink = FileSystem.symlink;
+
+/**
+ * Automatically maps specified paths (for use with `mock()`)
+ */
+exports.load = loader.load;
+
+/**
+ * Perform action, bypassing mock FS
+ * @example
+ * // This file exists on the real FS, not on the mocked FS
+ * const filePath = '/path/file.json';
+ * const data = mock.bypass(() => fs.readFileSync(filePath, 'utf-8'));
+ */
+exports.bypass = bypass;

lib/item.js

@@ -88,6 +88,19 @@ function Item() {
   this.links = 0;
 }
 
+/**
+ * Add execute if read allowed
+ * See notes in index.js -> mapping#addDir
+ */
+// prettier-ignore
+Item.fixWin32Permissions = mode =>
+  (process.platform !== 'win32')
+  ? mode
+  : mode |
+      ((mode & permissions.USER_READ) && permissions.USER_EXEC) |
+      ((mode & permissions.GROUP_READ) && permissions.GROUP_EXEC) |
+      ((mode & permissions.OTHER_READ) && permissions.OTHER_EXEC);
+
 /**
  * Determine if the current user has read permission.
  * @return {boolean} The current user can read.
@@ -140,8 +153,8 @@ Item.prototype.canExecute = function() {
   let can = false;
   if (uid === 0) {
     can = true;
-  } else if (uid === this._uid || uid !== uid) {
-    // (uid !== uid) means uid is NaN, only for windows
+  } else if (uid === this._uid || isNaN(uid)) {
+    // NaN occurs on windows
     can = (permissions.USER_EXEC & this._mode) === permissions.USER_EXEC;
   } else if (gid === this._gid) {
     can = (permissions.GROUP_EXEC & this._mode) === permissions.GROUP_EXEC;

lib/loader.js

@@ -0,0 +1,118 @@
+const {fixWin32Permissions} = require('./item');
+const path = require('path');
+const FileSystem = require('./filesystem');
+const fs = require('fs');
+const bypass = require('./bypass');
+
+const createContext = ({output, options = {}, target}, newContext) =>
+  Object.assign(
+    {
+      // Assign options and set defaults if needed
+      options: {
+        recursive: options.recursive !== false,
+        lazyLoad: options.lazyLoad !== false
+      },
+      output,
+      target
+    },
+    newContext
+  );
+
+function addFile(context, stats, isRoot) {
+  const {output, target} = context;
+  const {lazyLoad} = context.options;
+
+  if (!stats.isFile()) {
+    throw new Error(`${target} is not a valid file!`);
+  }
+
+  const outputPropKey = isRoot ? target : path.basename(target);
+
+  output[outputPropKey] = () => {
+    const content = !lazyLoad ? fs.readFileSync(target) : '';
+    const file = FileSystem.file(Object.assign({}, stats, {content}))();
+
+    if (lazyLoad) {
+      Object.defineProperty(file, '_content', {
+        get() {
+          const res = bypass(() => fs.readFileSync(target));
+          Object.defineProperty(file, '_content', {
+            value: res,
+            writable: true
+          });
+          return res;
+        },
+        set(data) {
+          Object.defineProperty(file, '_content', {
+            value: data,
+            writable: true
+          });
+        },
+        configurable: true
+      });
+    }
+
+    return file;
+  };
+
+  return output[outputPropKey];
+}
+
+function addDir(context, stats, isRoot) {
+  const {target, output} = context;
+  const {recursive} = context.options;
+
+  if (!stats.isDirectory()) {
+    throw new Error(`${target} is not a valid directory!`);
+  }
+
+  stats = Object.assign({}, stats);
+  const outputPropKey = isRoot ? target : path.basename(target);
+
+  // On windows platforms, directories do not have the executable flag, which causes FileSystem.prototype.getItem
+  // to think that the directory cannot be traversed. This is a workaround, however, a better solution may be to
+  // re-think the logic in FileSystem.prototype.getItem
+  // This workaround adds executable privileges if read privileges are found
+  stats.mode = fixWin32Permissions(stats.mode);
+
+  // Create directory factory
+  const directoryItems = {};
+  output[outputPropKey] = FileSystem.directory(
+    Object.assign(stats, {items: directoryItems})
+  );
+
+  fs.readdirSync(target).forEach(p => {
+    const absPath = path.join(target, p);
+    const stats = fs.statSync(absPath);
+    const newContext = createContext(context, {
+      target: absPath,
+      output: directoryItems
+    });
+
+    if (recursive && stats.isDirectory()) {
+      addDir(newContext, stats);
+    } else if (stats.isFile()) {
+      addFile(newContext, stats);
+    }
+  });
+
+  return output[outputPropKey];
+}
+
+/**
+ * Load directory or file from real FS
+ */
+exports.load = function(p, options) {
+  return bypass(() => {
+    p = path.resolve(p);
+
+    const stats = fs.statSync(p);
+    const context = createContext({output: {}, options, target: p});
+
+    if (stats.isDirectory()) {
+      return addDir(context, stats, true);
+    } else if (stats.isFile()) {
+      return addFile(context, stats, true);
+    }
+  });
+};

readme.md

@@ -1,3 +1,5 @@
+[![Build Status](https://github.com/tschaub/mock-fs/workflows/Test/badge.svg)](https://github.com/tschaub/mock-fs/actions?workflow=Test)
+
 # `mock-fs`
 
 The `mock-fs` module allows Node's built-in [`fs` module](http://nodejs.org/api/fs.html) to be backed temporarily by an in-memory, mock file system.  This lets you run tests against a set of mock files and directories instead of lugging around a bunch of test fixtures.
@@ -58,6 +60,42 @@ The second (optional) argument may include the properties below.
  * `createCwd` - `boolean` Create a directory for `process.cwd()`.  This is `true` by default.
  * `createTmp` - `boolean` Create a directory for `os.tmpdir()`.  This is `true` by default.
 
+### Loading real files & directories
+
+You can load real files and directories into the mock system using `mock.load()`
+
+#### Notes
+
+- All stat information is duplicated (dates, permissions, etc) 
+- By default, all files are lazy-loaded, unless you specify the `{ lazyLoad: false }` option
+
+#### <a id='mappingoptions'>options</a>
+
+| Option    | Type    | Default | Description |
+| --------- | ------- | ------- | ------------
+| lazyLoad  | boolean | true    | File content isn't loaded until explicitly read
+| recursive | boolean | true    | Load all files and directories recursively
+
+#### `mock.load(path, options)`
+
+```js
+mock({
+  // Lazy-load file
+  'my-file.txt': mock.load(path.resolve(__dirname, 'assets/special-file.txt')),
+
+  // Pre-load js file
+  'ready.js': mock.load(path.resolve(__dirname, 'scripts/ready.js'), { lazyLoad: false }),
+
+  // Recursively loads all node_modules
+  'node_modules': mock.load(path.resolve(__dirname, '../node_modules')),
+
+  // Creates a directory named /tmp with only the files in /tmp/special_tmp_files (no subdirectories), pre-loading all content
+  '/tmp': mock.load('/tmp/special_tmp_files', { recursive: false, lazyLoad:false }),
+
+  'fakefile.txt': 'content here'
+});
+```
+
 ### Creating files
 
 When `config` property values are a `string` or `Buffer`, a file is created with the provided content.  For example, the following configuration creates a single file with string content (in addition to the two default directories).
@@ -187,6 +225,33 @@ beforeEach(function() {
 afterEach(mock.restore);
 ```
 
+### Bypassing the mock file system
+
+#### <a id='mockbypass'>`mock.bypass(fn)`</a>
+
+Execute calls to the real filesystem with mock.bypass()
+
+```js
+// This file exists only on the real FS, not on the mocked FS
+const realFilePath = '/path/to/real/file.txt';
+const myData = mock.bypass(() => fs.readFileSync(realFilePath, 'utf-8'));
+```
+
+#### <a id='bypassasync'>Async Warning</a>
+
+Asynchronous calls are supported, however, they are not recommended as they could produce unintended consequences if 
+anything else tries to access the mocked filesystem before they've completed.
+
+```js
+async function getFileInfo(fileName) {
+  return await mock.bypass(async () => {
+    const stats = await fs.promises.stat(fileName);
+    const data = await fs.promises.readFile(fileName);
+    return { stats, data };
+  });
+}
+```
+
 ## Install
 
 Using `npm`:
@@ -222,6 +287,4 @@ expect(actual).toMatchSnapshot()
 ```
 
 Note: it's safe to call `mock.restore` multiple times, so it can still be called in `afterEach` and then manually
-in test cases which use snapshot testing.
-
-[![Build Status](https://github.com/tschaub/mock-fs/workflows/Test/badge.svg)](https://github.com/tschaub/mock-fs/actions?workflow=Test)
+in test cases which use snapshot testing.

test/assets/dir/file2.txt

@@ -0,0 +1 @@
+data2

test/assets/dir/subdir/file3.txt

@@ -0,0 +1 @@
+data3

test/assets/file1.txt

@@ -0,0 +1 @@
+data1