sciss / asyncfile

A Scala library to read and write files asynchronously with a common API both for the JVM and for JavaScript (Scala.js).

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AsyncFile is a Scala library to read and write files asynchronously with a common API both for the JVM and for JavaScript (Scala.js). It is (C)opyright 2020–2021 by Hanns Holger Rutz. All rights reserved. This project is released under the GNU Affero General Public License v3+ and comes with absolutely no warranties. To contact the author, send an e-mail to contact at

This project is still in experimental state!

requirements / installation

This project builds with sbt against Scala 2.13, 2.12, Dotty (JVM) and Scala 2.13 (JS).

To use the library in your project:

"de.sciss" %% "asyncfile" % v

The current version v is "0.2.1"


Please see the file

getting started

A good way to understand the library is to look at AudioFile which is another library that uses AsyncFile.

The idea is to use as the common path representation, and to support the file scheme on the JVM, mapping to java.nio.channels.AsynchronousFileChannel, while introducing a new scheme idb for JS which is a virtual file system backed by IndexedDB, thus supporting client-side Scala.js in the browser. New file systems can be registered using AsyncFile.addFileSystem.

You obtain a file system for scheme by calling AsyncFile.getFileSystemProvider(scheme) where is "file" or "idb", for example. It is possible to register other file system providers. Once you have the file system, you can use—in a platform neutral way—fs.openRead(uri) and fs.openWrite(uri) to gain access to a file to be read or written.

You can also directly call DesktopFile.openRead(file) and DesktopFile.openWrite(file) on the desktop, and in the browser, you can directly use IndexedDBFile.openRead(uri) and IndexedDBFile.openWrite(uri).


  • IndexedDBFileSystem currently does not implement directory functionality, thus .listDir, .mkDirs etc. do not work and return failed futures.
  • IndexedDBFileSystem has a fixed block size and does not yet use caching. Performance improvements are to be expected in future versions with larger block sizes and in-memory caching in place.
  • IndexedDBFileSystem currently does not implement file watcher functionality (watchDir and watchFile throw exceptions).