rsync client library
C++ Python C
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Acrosync is a new cross-platform rsync client for Windows/Max/iOS/Android that we built from scratch, without taking any code from the open source rsync project.

This is the library behind Acrosync, which implements a large portion of the client-side of the (undocumented) rsync protocol, including the famous delta sync algorithm.

PhotoBackup, our iOS app for uploading photos and videos to computers, uses a slightly modified version of this library.


  • Talks the rsync protocol version 29 (rsync 2.6.4+) and version 30 (rsync 3.x.x).
  • Written in C++ and builds on Win32, Mac OS X, Linux, iOS, and Android.
  • The only dependencies are libssh2 and openssl.
  • Can connect to the rsync server either via ssh, or via the rsync daemon protocol.
  • For ssh connections, supports both password login and public key authentication (with or without a passphrase).
  • Symbolic links are supported.

Build Instructions

First you'll need to install openssl and libssh2. Assume we're on a linux machine and these two packages are already installed in the default locations.

Run the following command to build the test programs:

$ python qi/ test

You will find a new executable build-linux/rsync/t_rsync_client which can download a remote directory using the rsync over ssh protocol:

$ build-linux/rsync/t_rsync_client <server> <username> <password> <remote dir> <local dir>

The same build command works for Mac and Windows, but you will need to install openssl and libssh2 to a subdirectory named install-mac or install-win under the top level directory.

Here the build system is written with Qi-Make, a tool that we developed by extending the basic syntax of make. The file qi/qi_build.h contains actual rules for building intermediate objects and final test programs. It should be fairly easy to make changes for your own build environments.


This library is licensed under the Reciprocal Public License. If this license does not work for you, a commercial license is available for a one-time fee or on a subscription basis. Contact for licensing details.