fuse-native

Multithreaded FUSE bindings for Node JS.

Features

• N-API support means we ship prebuilds and in general works on new Node.js releases.
• Multithreading support means multiple calls to FUSE can run in parallel.
• Close to feature complete in terms of the the FUSE API.
• Embedded shared library support means users do not have to install FUSE from a 3rd party.
• API support for initial FUSE kernel extension configuration so you can control the user experience.

Installation

npm i fuse-native --save

Example

const ops = {
  readdir: function (path, cb) {
    if (path === '/') return cb(null, ['test'])
    return cb(Fuse.ENOENT)
  },
  getattr: function (path, cb) {
    if (path === '/') return cb(null, stat({ mode: 'dir', size: 4096 }))
    if (path === '/test') return cb(null, stat({ mode: 'file', size: 11 }))
    return cb(Fuse.ENOENT)
  },
  open: function (path, flags, cb) {
    return cb(0, 42)
  },
  release: function (path, fd, cb) {
    return cb(0)
  },
  read: function (path, fd, buf, len, pos, cb) {
    var str = 'hello world'.slice(pos, pos + len)
    if (!str) return cb(0)
    buf.write(str)
    return cb(str.length)
  }
}

const fuse = new Fuse(mnt, ops, { debug: true })
fuse.mount(function (err) {
  fs.readFile(path.join(mnt, 'test'), function (err, buf) {
    // buf should be 'hello world'
  })
})

API

In order to create a FUSE mountpoint, you first need to create a Fuse object that wraps a set of implemented FUSE syscall handlers:

const fuse = new Fuse(mnt, handlers, opts = {})

Create a new Fuse object.

mnt is the string path of your desired mountpoint.

handlers is an object mapping syscall names to implementations. The complete list of available syscalls is described below. As an example, if you wanted to implement a filesystem that only supports getattr, your handle object would look like:

{
  getattr: function (path, cb) {
    if (path === '/') return process.nextTick(cb, null, stat({ mode: 'dir', size: 4096 }))
    if (path === '/test') return process.nextTick(cb, null, stat({ mode: 'file', size: 11 }))
    return process.nextTick(cb, Fuse.ENOENT)
  }
}

opts can be include:

  displayFolder: 'Folder Name', // Add a name/icon to the mount volume on OSX,
  debug: false,  // Enable detailed tracing of operations.
  force: false,  // Attempt to unmount a the mountpoint before remounting.
  mkdir: false   // Create the mountpoint before mounting.

Additionally, all (FUSE-specific options)[http://man7.org/linux/man-pages/man8/mount.fuse.8.html] will be passed to the underlying FUSE module (though we use camel casing instead of snake casing).

Fuse.isConfigured(cb)

Returns true if FUSE has been configured on your machine and ready to be used, false otherwise.

Fuse.configure(cb)

Configures FUSE on your machine by enabling the FUSE kernel extension. You usually want to do this as part of an installation phase for your app. Might require sudo access.

Fuse.unconfigure(cb)

Unconfigures FUSE on your machine. Basically undos any change the above method does.

See the CLI section below on how to run these commands from the command line if you prefer doing that.

FUSE API

Most of the FUSE api is supported. In general the callback for each op should be called with cb(returnCode, [value]) where the return code is a number (0 for OK and < 0 for errors). See below for a list of POSIX error codes.

ops.init(cb)

Called on filesystem init.

ops.access(path, mode, cb)

Called before the filesystem accessed a file

ops.statfs(path, cb)

Called when the filesystem is being stat'ed. Accepts a fs stat object after the return code in the callback.

ops.statfs = function (path, cb) {
  cb(0, {
    bsize: 1000000,
    frsize: 1000000,
    blocks: 1000000,
    bfree: 1000000,
    bavail: 1000000,
    files: 1000000,
    ffree: 1000000,
    favail: 1000000,
    fsid: 1000000,
    flag: 1000000,
    namemax: 1000000
  })
}

ops.getattr(path, cb)

Called when a path is being stat'ed. Accepts a stat object (similar to the one returned in fs.stat(path, cb)) after the return code in the callback.

ops.getattr = function (path, cb) {
  cb(0, {
    mtime: new Date(),
    atime: new Date(),
    ctime: new Date(),
    size: 100,
    mode: 16877,
    uid: process.getuid(),
    gid: process.getgid()
  })
}

ops.fgetattr(path, fd, cb)

Same as above but is called when someone stats a file descriptor

ops.flush(path, fd, cb)

Called when a file descriptor is being flushed

ops.fsync(path, fd, datasync, cb)

Called when a file descriptor is being fsync'ed.

ops.fsyncdir(path, fd, datasync, cb)

Same as above but on a directory

ops.readdir(path, cb)

Called when a directory is being listed. Accepts an array of file/directory names after the return code in the callback

ops.readdir = function (path, cb) {
  cb(0, ['file-1.txt', 'dir'])
}

ops.truncate(path, size, cb)

Called when a path is being truncated to a specific size

ops.ftruncate(path, fd, size, cb)

Same as above but on a file descriptor

ops.readlink(path, cb)

Called when a symlink is being resolved. Accepts a pathname (that the link should resolve to) after the return code in the callback

ops.readlink = function (path, cb) {
  cb(null, 'file.txt') // make link point to file.txt
}

ops.chown(path, uid, gid, cb)

Called when ownership of a path is being changed

ops.chmod(path, mode, cb)

Called when the mode of a path is being changed

ops.mknod(path, mode, dev, cb)

Called when the a new device file is being made.

ops.setxattr(path, name, value, position, flags, cb)

Called when extended attributes is being set (see the extended docs for your platform).

Copy the value buffer somewhere to store it.

The position argument is mostly a legacy argument only used on MacOS but see the getxattr docs on Mac for more on that (you probably don't need to use that).

ops.getxattr(path, name, position, cb)

Called when extended attributes is being read.

Return the extended attribute as the second argument to the callback (needs to be a buffer). If no attribute is stored return null as the second argument.

The position argument is mostly a legacy argument only used on MacOS but see the getxattr docs on Mac for more on that (you probably don't need to use that).

ops.listxattr(path, cb)

Called when extended attributes of a path are being listed.

Return a list of strings of the names of the attributes you have stored as the second argument to the callback.

ops.removexattr(path, name, cb)

Called when an extended attribute is being removed.

ops.open(path, flags, cb)

Called when a path is being opened. flags in a number containing the permissions being requested. Accepts a file descriptor after the return code in the callback.

var toFlag = function(flags) {
  flags = flags & 3
  if (flags === 0) return 'r'
  if (flags === 1) return 'w'
  return 'r+'
}

ops.open = function (path, flags, cb) {
  var flag = toFlag(flags) // convert flags to a node style string
  ...
  cb(0, 42) // 42 is a file descriptor
}

ops.opendir(path, flags, cb)

Same as above but for directories

ops.read(path, fd, buffer, length, position, cb)

Called when contents of a file is being read. You should write the result of the read to the buffer and return the number of bytes written as the first argument in the callback. If no bytes were written (read is complete) return 0 in the callback.

var data = new Buffer('hello world')

ops.read = function (path, fd, buffer, length, position, cb) {
  if (position >= data.length) return cb(0) // done
  var part = data.slice(position, position + length)
  part.copy(buffer) // write the result of the read to the result buffer
  cb(part.length) // return the number of bytes read
}

ops.write(path, fd, buffer, length, position, cb)

Called when a file is being written to. You can get the data being written in buffer and you should return the number of bytes written in the callback as the first argument.

ops.write = function (path, fd, buffer, length, position, cb) {
  console.log('writing', buffer.slice(0, length))
  cb(length) // we handled all the data
}

ops.release(path, fd, cb)

Called when a file descriptor is being released. Happens when a read/write is done etc.

ops.releasedir(path, fd, cb)

Same as above but for directories

ops.create(path, mode, cb)

Called when a new file is being opened.

ops.utimens(path, atime, mtime, cb)

Called when the atime/mtime of a file is being changed.

ops.unlink(path, cb)

Called when a file is being unlinked.

ops.rename(src, dest, cb)

Called when a file is being renamed.

ops.link(src, dest, cb)

Called when a new link is created.

ops.symlink(src, dest, cb)

Called when a new symlink is created

ops.mkdir(path, mode, cb)

Called when a new directory is being created

ops.rmdir(path, cb)

Called when a directory is being removed

CLI

There is a CLI tool available to help you configure the FUSE kernel extension setup if you don't want to use the JavaScript API for that

npm install -g fuse-native
fuse-native is-configured # checks if the kernel extension is already configured
fuse-native configure # configures the kernel extension

License

MIT for these bindings.

See the OSXFUSE license for MacOS and the libfuse license for Linux/BSD for the FUSE shared library licence.