fs-monkey

What is fs-monkey?

The fs-monkey package is a utility library for Node.js that allows you to patch or virtualize the Node.js file system (fs) module. This can be particularly useful for testing purposes, where you might want to avoid performing I/O operations on the actual file system. It provides functionalities to patch the global fs module, or to create a virtual file system that can be used independently.

What are fs-monkey's main functionalities?

Patching the global fs module

This feature allows you to patch the global fs module with a virtual file system. In the code sample, a virtual file system is created with a single file '/foo.txt' containing the text 'bar'. The global fs module is then patched, so any subsequent fs operations in the process will interact with this virtual file system instead of the real one.

const {patchFs} = require('fs-monkey');
const {Volume} = require('memfs');
const vol = Volume.fromJSON({'/foo.txt': 'bar'});
patchFs(vol);

Creating a union file system

This feature allows you to create a union file system, which combines multiple file systems into a single coherent file system interface. In the code sample, a virtual file system is created and then combined with the real fs module using the union file system. This allows for fallback to the real file system for files not found in the virtual file system.

const {ufs} = require('fs-monkey');
const {Volume} = require('memfs');
const vol = Volume.fromJSON({'/foo.txt': 'bar'});
ufs.use(vol);
ufs.use(require('fs'));

Other packages similar to fs-monkey

memfs

Similar to fs-monkey, memfs provides an in-memory file system that mimics the Node.js fs module. While fs-monkey offers utilities to patch or virtualize the fs module, memfs focuses more on creating an in-memory file system that can be used directly or with fs-monkey for patching the global fs.

unionfs

Unionfs is another package that is closely related to fs-monkey, specifically to its union file system functionality. It allows you to transparently overlay multiple file systems into one cohesive file system. While fs-monkey provides this functionality through its ufs feature, unionfs is dedicated solely to creating and managing union file systems.

README

fs-monkey

Monkey-patches for filesystem related things. Rewrite require function, load Node's modules from memory. Or rewrite the whole fs filesystem module.

Terms

An fs-like object is an object that implements methods of Node's filesystem API. It is denoted as vol:

let vol = {
    readFile: () => { /* ... */ },
    readFileSync: () => { /* ... */ },
    // etc...
}

fs-monkey API

• patchFs(vol[, fs]) - rewrites Node's filesystem module fs with fs-like object vol
• patchRequire(vol[, Module]) - rewrites require function, patches Node's module module to use a give fs-like object vol for module loading

patchFs(vol[, fs])

Rewrites Node's filesystem module fs with fs-like object.

• vol - fs-like object
• fs (optional) - a filesystem to patch, defaults to require('fs')

import {patchFs} from 'fs-monkey';

const myfs = {
    readFileSync: () => 'hello world',
};

patchFs(myfs);
console.log(require('fs').readFileSync('/foo/bar')); // hello world

You don't need to create fs-like objects yourself, use memfs to create a virtual filesystem for you:

import {vol} from 'memfs';
import {patchFs} from 'fs-monkey';

vol.fromJSON({'/dir/foo': 'bar'});
patchFs(vol);
console.log(require('fs').readdirSync('/')); // [ 'dir' ]

patchRequire(vol[, unixifyPaths[, Module]])

Patches Node's module module to use a given fs-like object vol for module loading.

• vol - fs-like object
• unixifyPaths (optional) - whether to convert Windows paths to unix style paths, defaults to false.
• Module (optional) - a module to patch, defaults to require('module')

Monkey-patches the require function in Node, this way you can make Node.js to require modules from your custom filesystem.

It expects an object with three filesystem methods implemented that are needed for the require function to work.

let vol = {
    readFileSync: () => {},
    realpathSync: () => {},
    statSync: () => {},
};

If you want to make Node.js to require your files from memory, you don't need to implement those functions yourself, just use the memfs package:

import {vol} from 'memfs';
import {patchRequire} from 'fs-monkey';

vol.fromJSON({'/foo/bar.js': 'console.log("obi trice");'});
patchRequire(vol);
require('/foo/bar'); // obi trice

Now the require function will only load the files from the vol file system, but not from the actual filesystem on the disk.

If you want the require function to load modules from both file systems, use the unionfs package to combine both filesystems into a union:

import {vol} from 'memfs';
import {patchRequire} from 'fs-monkey';
import {ufs} from 'unionfs';
import * as fs from 'fs';

vol.fromJSON({'/foo/bar.js': 'console.log("obi trice");'});
ufs
    .use(vol)
    .use(fs);
patchRequire(ufs);
require('/foo/bar.js'); // obi trice

License

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means.

In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to http://unlicense.org/