uwp-fs

📁 Node's fs module for Windows UWP apps. Wrapper of Windows.Storage APIs.

Windows 10 allows you to write native UWP (Windows store) apps with HTML and JavaScript but the Windows.Storage APIs for manipulating files is very difficult to use and the docs are confusing. To read a file you first have to get the right StorageFolder and/or StorageFile objects, that you have to storageFile.openAsync() to get an instance of (I)RandomAccessStream that needs to be passed into DataReader to then get an IBuffer that can be finally converted to something sensible like String or Uint8Array. And that is only when you've been granted access to directory(ies) after asking user with FilePicker. But wait there's also Windows.Storage.FileIO namespace and whole lot more... Easy right?

The Windows.Storage APIs are hostile and even a simple file-reading can turn into tens of lines of code. That's why this project tries to wrap that into a nice and simple Node.js style fs API where you can read the file with just a fs.readFile('path', (err, data) => console.log(data)) ;). Plus we've got Promises!

uwp-fs tries to be 1:1 drop in replacement for fs, with all the correct errors, like ENOENT, you've come to love :D. Except for synchronous methods. Those are unsupported in UWP.

Work in progress, contributions welcomed.

Installation & Usage

Installation

npm install uwp-fs

The uwp-fs module is bundled into single file (UMD) that will be located in ./node_modules/uwp-fs/index.js. Don't forget to include it to your Visual Studio Project.

Make sure you also include browser versions of buffer (and optionally stream). These do not come prebundled with uwp-fs but are necessary.

Usage

Just drop in the uwp-fs/index.js script along node modules (see Dependencies for more)

<script src="./path/to/events.js"></script>
<script src="./path/to/buffer.js"></script>
<script src="./path/to/util.js"></script>
<script src="./path/to/stream.js"></script>
<script src="./uwp-fs/index.js"></script>

uwp-fs is bundled as an UMD module and as such it's exported at window['uwp-fs'].

var fs = window['uwp-fs']

Dependencies

A few Node.js core modules are integral part of fs, and thus uwp-fs, and are imported/required as a dependency in the source code.

Required

• buffer. You can use buffer which is an exact port of Node's Buffer for use in browser, built on top of Uint8Array/ArrayBuffer. It is however not bundled with this module and has to be bundled and/or imported separately alongside this module.
• util: Needed as a peer dependency for buffer

Optional

Following modules are optional and are not need to be bundled or imported along with uwp-fs if you don't intend to methods and classes that require them.

• stream module is needed to enable fs.ReadStream/fs.WriteStream classes and fs.createWriteStream()/fs.createWriteStream() APIs.
• events's EventEmitter is needed for fs.watch (FSWatcher) and fs.watchFile (StatWatcher).

Note

uwp-fs comes prebundled as UMD module index.js. UMD format makes it get the buffer module from window.buffer (and its Buffer class is at window.buffer.Buffer), stream from window.steam (window.stream.ReadableStream, etc...)

Or you can give bundling it yourself a shot. Main file is at uwp-fs/index.mjs. It's written with ES Module import syntax and does not need to be tanspiled with babel unless you need to support older environments that do not support async/await.

Example

See example/demo.html, example/demo.js and try it yourself by building uwp-fs.sln in Visual Studio.

Supported APIs

Work in progress.

Most of the groundwork for reading is laid. open, read and close syscalls are emulated, enabling fs.readFile, fs.readdir. Streams and writing is on the way.

• fs.FSWatcher postponed. Initial implementation reveals unreliability of UWP's APIs

• fs.ReadStream Work in progress

• fs.WriteStream

• fs.access

• fs.appendFile

• fs.chmod

• fs.chown

• fs.close - Work in progress

• fs.constants

• fs.copyFile

• fs.createReadStream - Work in progress

• fs.createWriteStream

• fs.exists - deprecated

• fs.fchmod

• fs.fchown

• fs.fdatasync

• fs.fstat

• fs.fsync

• fs.ftruncate

• fs.futimes

• fs.lchmod

• fs.lchown

• fs.link

• fs.lstat

• fs.mkdir

• fs.mkdtemp

• fs.open - TODO: flags other than 'r'

• fs.read

• fs.readdir

• fs.readFile

• fs.readlink

• fs.realpath

• fs.rename

• fs.rmdir

• fs.stat - only contains size, file/folder type and times

• fs.symlink

• fs.truncate

• fs.unlink

• fs.unwatchFile

• fs.utimes

• fs.watch - postponed. Initial implementation reveals unreliability of UWP's APIs

• fs.watchFile

• fs.write - Work in progress

• fs.writeFile - Work in progress

Caveats

Windows UWP applications begin restricted and can only access installedLocation (read) and localFolder (read and write). To gain access to the whole filesystem, you have to first ask user to give you permissions to access C:\ or sub/directory that is sufficient for your app. This is done by opening a FilePicker and letting user select folder (or the whole drive). This only has to be done once. uwp-fs then stores these folders for you in AccessCache.StorageApplicationPermissions.futureAccessList for future access.

Encodings are not part of uwp-fs. Those are implemented in buffer module and their usage therefore relies on the version of buffer used. Utf8 is used in the background for most of the data manipulation.

Please try to use most recent versions of buffer and stream modules. uwp-fs is built on top of latest APIs (and breaking changes) introduced in Node versions 6 (Buffer.alloc(), Buffer.allocUnsafe()) and Node 8 (.destroy() method on streams).

None of the *Sync (readFileSync, writeFileSync, etc...) APIs are available because UWP does not suppor synchronous file system operations.

APIs that involve symlinks (fstat, lstat, stat, ...) were not properly explored and tested yet.

Testing

Testing is done comparatively by running the same tests in both UWP and Node. Log from Node results is saved and UWP is then tested against it. mouka module is used to that. mouka uses similar API to mocha but allows storing test results and then importing and using them for comparison.

Closing notes

node_bundles_modules folder contains couple of prebundled Node modules, that were not written by me, for a sake of the demo application and tests. Namely buffer by ferros; Node's stream, events, util bundled with rolup and rollup-plugin-node-builtins. All credit for these modules goes to their respective authors.