browserfs

BrowserFS v0.4.2

BrowserFS is an in-browser file system that emulates the Node JS file system API and supports storing and retrieving files from various backends. BrowserFS also integrates nicely into the Emscripten file system.

Backends

BrowserFS is highly extensible, and ships with many filesystem backends:

• XmlHttpRequest: Downloads files on-demand from a webserver via XMLHttpRequest
• LocalStorage: Stores files in the browser's localStorage.
• HTML5FS: Stores files into the HTML5 FileSystem API
• IndexedDB: Stores files into the browser's IndexedDB object database.
• Dropbox: Stores files into the user's Dropbox account.
  • Note: You provide this filesystem with an authenticated DropboxJS client
• InMemory: Stores files in-memory. Thus, it is a temporary file store that clears when the user navigates away.
• ZipFS: Read-only zip file-backed FS. Lazily decompresses files as you access them.
• WorkerFS: Lets you mount the BrowserFS file system configured in the main thread in a WebWorker, or the other way around!
• MountableFileSystem: Lets you mount multiple file systems into a single directory hierarchy, as in *nix-based OSes.
• OverlayFS: Mount a read-only file system as read-write by overlaying a writable file system on top of it. Like Docker's overlayfs, it will only write changed files to the writable file system.
  • Note: Does not support asynchronous file systems at the moment. Wrap them in AsyncMirrorFS first.
• AsyncMirrorFS: Use an asynchronous backend synchronously. Invaluable for Emscripten; let your Emscripten applications write to larger file stores with no additional effort!
  • Note: Loads the entire contents of the file system into a synchronous backend during construction. Performs synchronous operations in-memory, and enqueues them to be mirrored onto the asynchronous backend.

More backends can be defined by separate libraries, so long as they extend the BaseFileSystem. Multiple backends can be active at once at different locations in the directory hierarchy.

For more information, see the wiki.

Building

Prerequisites:

• Node and NPM
• Grunt-cli globally installed: npm install -g grunt-cli
• Run npm install to install local dependencies

Release:

grunt

The minified release build can be found in build/browserfs.min.js.

Development:

grunt dev

The development build can be found as build/browserfs.js.

Custom builds:

If you want to build BrowserFS with a subset of the available backends, change the getBackends() function in Gruntfile.js to return an array of backends you wish to use. Then, perform a release build.

Using

Here's a simple example, using the LocalStorage-backed file system:

<script type="text/javascript" src="browserfs.min.js"></script>
<script type="text/javascript">
  // Installs globals onto window:
  // * Buffer
  // * require (monkey-patches if already defined)
  // * process
  // You can pass in an arbitrary object if you do not wish to pollute
  // the global namespace.
  BrowserFS.install(window);
  // Constructs an instance of the LocalStorage-backed file system.
  var lsfs = new BrowserFS.FileSystem.LocalStorage();
  // Initialize it as the root file system.
  BrowserFS.initialize(lsfs);
</script>

Now, you can write code like this:

var fs = require('fs');
fs.writeFile('/test.txt', 'Cool, I can do this in the browser!', function(err) {
  fs.readFile('/test.txt', function(err, contents) {
    console.log(contents.toString());
  });
});

Using with Browserify

As of BrowserFS 0.4.0, you can use BrowserFS with your Browserify projects! At the moment, you need to 'opt in' to the entire BrowserFS ecosystem -- e.g. you need to use BrowserFS's path, process, and Buffer in place of Browserify's builtins.

I have written an example project that illustrates how to do this.

In the future, we will support mixing and matching builtin modules.

Using with Emscripten

You can use any synchronous BrowserFS file systems with Emscripten! Persist particular folders in the Emscripten file system to localStorage, or enable Emscripten to synchronously download files from another folder as they are requested.

Include browserfs.min.js into the page, and add code similar to the following to your Module's preRun array:

/**
 * Mounts a localStorage-backed file system into the /data folder of Emscripten's file system.
 */
function setupBFS() {
  // Constructs an instance of the LocalStorage-backed file system.
  var lsfs = new BrowserFS.FileSystem.LocalStorage();
  // Initialize it as the root file system.
  BrowserFS.initialize(lsfs);
  // Grab the BrowserFS Emscripten FS plugin.
  var BFS = new BrowserFS.EmscriptenFS();
  // Create the folder that we'll turn into a mount point.
  FS.createFolder(FS.root, 'data', true, true);
  // Mount BFS's root folder into the '/data' folder.
  FS.mount(BFS, {root: '/'}, '/data');
}

Note: Do NOT use BrowserFS.install(window) on a page with an Emscripten application! Emscripten will be tricked into thinking that it is running in Node JS.

If you wish to use an asynchronous BrowserFS backend with Emscripten (e.g. Dropbox), you'll need to wrap it into an AsyncMirrorFS first:

/**
 * Run this prior to starting your Emscripten module.
 * @param dropboxClient An authenticated DropboxJS client.
 */
function asyncSetup(dropboxClient, cb) {
  var dbfs = new BrowserFS.FileSystem.Dropbox(dropboxClient);
  // Wrap in AsyncMirrorFS.
  var asyncMirror = new BrowserFS.FileSystem.AsyncMirrorFS(
    new BrowserFS.FileSystem.InMemory(), dbfs);

  // Downloads the entire contents of the Dropbox backend into memory.
  // You'll probably want to use an app folder, and check that you
  // aren't pulling in a huge amount of data here.
  asyncMirror.initialize((err?) => {
    // Initialize it as the root file system.
    BrowserFS.initialize(asyncMirror);
    // BFS is ready for Emscripten!
    cb();
  });
}
function setupBFS() {
  // Grab the BrowserFS Emscripten FS plugin.
  var BFS = new BrowserFS.EmscriptenFS();
  // Create the folder that we'll turn into a mount point.
  FS.createFolder(FS.root, 'data', true, true);
  // Mount BFS's root folder into the '/data' folder.
  FS.mount(BFS, {root: '/'}, '/data');
}

Testing

Prerequisites:

• Karma globally installed: npm install -g karma

To run unit tests, simply run grunt test (NOTE: This will launch multiple web browsers!). You may need to change build/karma.conf.js if you do not have Chrome, Safari, Opera, and Firefox installed.

License

BrowserFS is licensed under the MIT License. See LICENSE for details.