Xdelta

Xdelta is a command-line tool and C library for differential compression: it computes and applies binary deltas between files using the VCDIFF/RFC 3284 format. It is well suited to distributing updates, since a delta between two similar files is typically far smaller than the files themselves.

This is the documentation for Xdelta version 3 (the maintained 3.2.x series). The sources live at https://github.com/jmacd/xdelta.

Quick start

Create a patch from old_file to new_file:

xdelta3 -e -s old_file new_file delta_file

Apply the patch to reconstruct new_file:

xdelta3 -d -s old_file delta_file decoded_new_file

Run xdelta3 -h for brief help and xdelta3 test for the built-in self test.

Highlights

• VCDIFF (RFC 3284) encoding and decoding, with 64-bit file support on Linux, macOS, Windows, and other platforms.
• Optional secondary compression: lzma (when built with liblzma), plus the built-in djw and fgk coders. See Better compression.
• Armor mode: whole-file BLAKE3 verification embedded in the delta, on by default, so applying a patch with the wrong source fails fast with a clear message.
• A stable streaming C API for embedding. See the Programming guide.

Where to go next

• Command-line syntax — the full option reference.
• Armor mode — how whole-file verification works.
• Tuning the memory budget — -B, -W, -I, -P.
• Programming guide — the encode/decode API.
• Licensing — the maintained branches are Apache 2.0.

History

Xdelta 1.x (first released in 1999) and the original GPL-licensed Xdelta 3 are no longer maintained here. The GPL line lives at https://github.com/jmacd/xdelta-gpl.