librsync

librsync implements the rolling-checksum algorithm of remote file synchronization that was popularized by the rsync utility.

This algorithm transfers the differences between 2 files without needing both files on the same system.

librsync does not implement the rsync wire protocol. If you want to talk to an rsync server to transfer files you'll need to shell out to rsync. You cannot make use of librsync to talk to an rsync server.

librsync also does not include any network functions for talking to SSH or any other server. To access a remote filesystem, you need to provide your own code or make use of some other virtual filesystem layer.

librsync is for building other programs that transfer files as efficiently as rsync. You can use librsync in a program you write to do backups, distribute binary patches to programs, or sync directories to a server or between peers.

This tree also produces the rdiff command-line tool that exposes the key operations of librsync: generating file signatures, generating the delta from a signature to a new file, and applying the delta to regenerate the new file given the old file.

Copyright

librsync is Copyright 1999-2015 Martin Pool and others.

librsync is distributed under the GNU LGPL v2.1 (see COPYING), which basically means that you can dynamically link librsync into non-GPL programs, but you must redistribute the librsync source, with any modifications you have made.

librsync contains the BLAKE2 hash algorithm, written by Samuel Neves and released under the CC0 public domain dedication, http://creativecommons.org/publicdomain/zero/1.0/.

Contact

librsync's home is

There are two mailing lists:

There are some questions and answers about librsync on stackoverflow.com tagged librsync. That is a good place to start if you have questions.

Requirements

To build librsync you will need:

A C compiler and appropriate headers and libraries
Make
popt command line parsing library

Available from http://rpm5.org/files/popt/

A cut-down version of popt1.5 is included and will be used automatically if there is no popt library on your build host.
automake, libtool, and autoconf

Compiling

$ ./autogen.sh

To build and test librsync then do

$ ./configure
$ make all check

You can also do what's called a VPATH build, where the build products are kept separate from the source tree:

$ mkdir _build   # for example
$ cd _build
$ ../configure && make check

After building you can install rdiff and librsync for system-wide use. The destination is controlled by --prefix and related options to ./configure.

$ sudo make install

Note for Windows

With cygwin you can build using gcc as under a normal unix system. It is also possible to compile under cygwin using MSVC++. You must have environment variables needed by MSCV set using the Vcvars32.bat script. With these variables set, you just do;

$ ./configure.msc
$ make all check

The PCbuild directory contains a project and pre-generated config files for use with the MSVC++ IDE. This should be enought to compile rdiff.exe without requiring cygwin.

Library Versions

librsync uses the GNU libtool library versioning system, so the filename does not correspond to the librsync release. To show the library release and version, use the librsyncinfo tool. See libversions.txt for more information.

Platforms

librsync should be widely portable. Patches to fix portability bugs are welcome.

Documentation

Documentation for the rdiff command-line tool:

and for the library:

These are all produced from the source tree.

Debugging

If you are using GNU libc, you might like to use

MALLOC_CHECK_=2 ./rdiff

to detect some allocation bugs.

librsync has annotations for the SPLINT static checking tool.

Testing

You can run the tests with make check.

Tests are automatically run at https://travis-ci.org/librsync/librsync.

License

Rasuka/librsync

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