erlang-rsync is an Erlang wrapper of librsync library. It provides basic functions for direct file manipulations (sig/1, delta/2, etc) as well as low-level functions for fine-grained control (sig_init/0, delta_update/2, etc). The low-level interface is somewhat similar to the hashing functions from crypto module.

• GNU Make.
• GCC.
• rebar.
• librsync (runtime library and header files).
• Erlang/OTP 17.1 or higher.

$ git clone git://github.com/zinid/erlang-rsync.git
$ cd erlang-rsync
$ ./configure
$ make

The whole API documentation is located in the doc directory and can be built using edoc

$ make doc

Let's say we have two files: local_file and remote_file, and we want local_file to have the content of remote_file. We first generate the signature of local_file. The signature is written in sig_file:

> rsync:sig("local_file", "sig_file").
ok.

We then generate the delta from remote_file and sig_file. The delta is written in delta_file:

> rsync:delta("sig_file", "remote_file", "delta_file").
ok.

Finally, using delta_file and local_file we reconstruct remote_file. The result is written in new_local_file.

> rsync:patch("local_file", "delta_file", "new_local_file").
ok.

Now new_local_file is "equal" to remote_file.

> file:read_file("new_local_file") == file:read_file("remote_file").
true.

For patch/2, patch/3 and patch_init/1 functions to work the whole content of the original file should be read into the memory. This is due to a limitation of librsync API and Erlang's NIF API. So don't use these functions for extremely large files.