ZenFS

ZenFS is a file system that emulates the NodeJS filesystem API. It works using a system of backends, which are used by ZenFS to store and retrieve data. ZenFS can also integrate with other tools.

Backends

ZenFS is modular and extensible. The core includes some built-in backends:

• InMemory: Stores files in-memory. This is cleared when the runtime ends (e.g. a user navigating away from a web page or a Node process exiting)
• Overlay: Use a read-only file system as read-write by overlaying a writable file system on top of it. (copy-on-write)
• Fetch: Downloads files over HTTP with the fetch API (readonly)
• Port: Interacts with a remote over a MessagePort-like interface (e.g. a worker)

ZenFS supports a number of other backends. Many are provided as separate packages under @zenfs. More backends can be defined by separate libraries by extending the FileSystem class and providing a Backend object.

You can find all of the packages available over on NPM.

As an added bonus, all ZenFS backends support synchronous operations. All of the backends included with the core are cross-platform.

For more information, see the docs.

Installing

npm install @zenfs/core

If you're using ZenFS, especially for big projects, please consider supporting the project. Thousands of hours have been dedicated to its development, and your acknowledgment or financial support would go a long way toward improving ZenFS and its community.

Usage

import { fs } from '@zenfs/core'; // You can also use the default export

fs.writeFileSync('/test.txt', 'You can do this anywhere, including browsers!');

const contents = fs.readFileSync('/test.txt', 'utf-8');
console.log(contents);

Using different and/or multiple backends

A single InMemory backend is created by default, mounted on /.

You can configure ZenFS to use a different backend and mount multiple backends. It is strongly recommended to do so using the configure function.

You can use multiple backends by passing an object to configure which maps paths to file systems.

The following example mounts a zip file to /zip, in-memory storage to /tmp, and IndexedDB to /home. Note that / has the default in-memory backend.

import { configure, InMemory } from '@zenfs/core';
import { IndexedDB } from '@zenfs/dom';
import { Zip } from '@zenfs/archives';

const res = await fetch('mydata.zip');

await configure({
	mounts: {
		'/mnt/zip': { backend: Zip, data: await res.arrayBuffer() },
		'/tmp': InMemory,
		'/home': IndexedDB,
	}
};

Note that while you aren't required to use absolute paths for the keys of mounts, it is a good practice to do so.

[!TIP] When configuring a mount point, you can pass in

1. A Backend object, if the backend has no required options
2. An object that has the options accepted by the backend and a backend property which is a Backend object
3. A FileSystem instance

Here is an example that mounts the WebStorage backend from @zenfs/dom on /:

import { configureSingle, fs } from '@zenfs/core';
import { WebStorage } from '@zenfs/dom';

await configureSingle({ backend: WebStorage });

if (!fs.existsSync('/test.txt')) {
	fs.writeFileSync('/test.txt', 'This will persist across reloads!');
}

const contents = fs.readFileSync('/test.txt', 'utf-8');
console.log(contents);

FS Promises

The FS promises API is exposed as promises.

import { configureSingle } from '@zenfs/core';
import { exists, writeFile } from '@zenfs/core/promises';
import { IndexedDB } from '@zenfs/dom';

await configureSingle({ backend: IndexedDB });

const exists = await exists('/myfile.txt');
if (!exists) {
	await writeFile('/myfile.txt', 'Lots of persistent data');
}

[!NOTE] You can import the promises API using:

1. Exports from @zenfs/core/promises
2. The promises export from @zenfs/core
3. fs.promises on the exported fs from @zenfs/core.

Mounting and unmounting, creating backends

If you would like to create backends without configure (e.g. to do something dynamic at runtime), you may do so by importing the backend and calling resolveMountConfig with it.

You can then mount and unmount the backend instance by using mount and umount.

import { configure, resolveMountConfig, InMemory } from '@zenfs/core';
import { IndexedDB } from '@zenfs/dom';
import { Zip } from '@zenfs/archives';

await configure({
	mounts: {
		'/tmp': InMemory,
		'/home': IndexedDB,
	},
});

fs.mkdirSync('/mnt');

const res = await fetch('mydata.zip');
const zipfs = await resolveMountConfig({ backend: Zip, data: await res.arrayBuffer() });
fs.mount('/mnt/zip', zipfs);

// do stuff with the mounted zip

fs.umount('/mnt/zip'); // finished using the zip

[!CAUTION] Instances of backends follow the internal API. You should never use a backend's methods unless you are extending a backend.

Devices and device files

ZenFS includes experimental support for device files. These are designed to follow Linux's device file behavior, for consistency and ease of use. You can automatically add some normal devices with the addDevices configuration option:

await configure({
	mounts: {
		/* ... */
	},
	addDevices: true,
});

fs.writeFileSync('/dev/null', 'Some data to be discarded');

const randomData = new Uint8Array(100);

const random = fs.openSync('/dev/random', 'r');
fs.readSync(random, randomData);
fs.closeSync(random);

You can create your own devices by implementing a DeviceDriver. For example, the null device looks similar to this:

const customNullDevice = {
	name: 'custom_null',
	// only 1 can exist per DeviceFS
	singleton: true,
	// optional if false
	isBuffered: false,
	read() {
		return 0;
	},
	write() {
		return 0;
	},
};

Note the actual implementation's write is slightly more complicated since it adds to the file position. You can find more information on the docs.

Finally, if you'd like to use your custom device with the file system:

import { addDevice, fs } from '@zenfs/core';

addDevice(customNullDevice);

fs.writeFileSync('/dev/custom', 'This gets discarded.');

Using with bundlers

ZenFS exports a drop-in for Node's fs module (up to the version of @types/node in package.json), so you can use it for your bundler of preference using the default export.

Sponsors

A huge thank you to Deco.cx for sponsoring ZenFS and helping to make this possible.

Building

• Make sure you have Node and NPM installed. You must have Node v18 or newer.
• Install dependencies with npm install
• Build using npm run build
• You can find the built code in dist.

Testing

Run unit tests with npm test.

BrowserFS Fork

ZenFS is a fork of BrowserFS. If you are using ZenFS in a research paper, you may want to cite BrowserFS.