fatfs

A standalone FAT16/FAT32 implementation that takes in a block-access interface and exposes something quite similar to require('fs') (i.e. the node.js built-in Filesystem API).

Installation

npm install fatfs

Example

var fatfs = require('fatfs'),
    fs = fatfs.createFileSystem(exampleDriver);      // see below
fs.stat("autoexec.bat", function (e,stats) {
    if (e) console.error(e);
    else console.log(stats);
});
// TODO: open a file and write to it or something…

API

• fs = fatfs.createFileSystem(vol, [opts], [cb]) — Simply pass in a block driver (see below) mapped to a FAT partition somewhere, and get back the API documented here. An options dictionary can be provided but is otherwise ignored right now. You may also optionally provide a callback cb(err) which will be automatically registered for the on 'ready' or 'error' event.
• 'ready' event — fired on fs when initial volume information has been determined and the API is ready to use. It is safe to call other fs methods before this fires only if you are sure the first sector will be readable and represents a valid FAT volume.
• 'error' event — fired if initialization fails for whatever reason.

That's it! The rest of the API (fs.readdir, fs.open, fs.createReadStream, fs.appendFile, etc.) is as documented by the node.js project.

Well, sort of…

Caveats

Temporary

• BETA BETA BETA. Seriously, this is a brand new, from scratch, completely unproven filesystem implementation. It does not have full automated test coverage, and it has not been manually tested very much either. Please please please make sure you have a backup of any important drive/image/card you unleash this upon.
• at the moment you would/should use this via the sdcard module; right now unless you pass in the first sector via an undocumented API you'll need to wait for an arbitrary amount of time before using any of the methods.
• mappings between FAT concepts (hidden/readonly/archive/etc.) and POSIX modes are not yet implemented
• date stamps are not quite hooked up
• need options like perms mapping mode, and readonly/noatime
• a few other methods are not quite implemented, either. If it's commented out in this part of the test suite, its implementation is Coming Soon™.

As-planned

Some of the differences between this module and the node.js fs module are "by design" for arhitectural simplicity and/or due to underlying FAT limitations.

• There are no fs.*Sync methods.
• This module does no read/write caching. This should be done in your volume driver, but see notes below.
• You'll need multiple createFileSystem instances for multiple volumes; paths are relative to each, and don't share a namespace.
• The FAT filesystem has no concept of symlinks, and hardlinks are not really an intentional feature. You will get an ENOSYS-like error when encountering this limitation.

"Volume driver" API

To use 'fatfs', you must provide a driver object with the following properties/methods:

• driver.sectorSize — number of bytes per sector on this device
• driver.numSectors — count of sectors available on this media
• driver.readSector(n, cb) — returns the requested block to cb(e, data)
• driver.writeSector(n, data, cb) — (optional) writes the data and notifies cb(e)

If you do not provide a writeSector method, then fatfs will work in readonly mode. Pretty simple, eh? And the 'fatfs' module makes a good effort to check the parameters passed to your driver methods!

TBD: to facilitate proper cache handling, this module might add an optional driver.flush(cb) method at some point in the future.

Here's an example taken from code used to run this module's own tests:

// NOTE: this assumes image at `path` has no partition table.
//       If it did, you'd need to translate positions, natch…
var fs = require('fs');

exports.createDriverSync = function (path, opts) {
    opts || (opts = {});
    
    var secSize = 512,
        ro = opts.readOnly || false,
        fd = fs.openSync(path, (ro) ? 'r' : 'r+'),
        s = fs.fstatSync(fd);
    
    return {
        sectorSize: secSize,
        numSectors: s.size / secSize,
        readSector: function (n, cb) {
            fs.read(fd, Buffer(secSize), 0, secSize, n*secSize, function (e,n,d) {
                cb(e,d);
            });
        },
        writeSector: (ro) ? null : function (n, data, cb) {
            fs.write(fd, data, 0, secSize, n*secSize, function (e) {
                cb(e);
            });
        }
    };
};

License

© 2014 Nathan Vander Wilt. Funding for this work was provided by Technical Machine, Inc.

Reuse under your choice of:

• BSD-2-Clause
• Apache 2.0