A Delta algorithm ported to Rust

This algorithm is used in fossil where it has been implemented in C-99. This crate contains the same algorithm implemented in Rust.

It exports two functions: delta(a:&str, b:&str) -> String and deltainv(b:&str, d:&str) -> String.

// creating delta between a and its next version b
let d = delta(a, b);

// applying delta to b to get previous version a
let s = deltainv(b, d);

assert_eq!(s, a);

Suppose we have some text value a, and user has changed it to value b. Using delta function we can get a compressed delta value d that we can store and keep it along with the new text value b. If later user wants to see the previous version of text, we can use deltainv(b, d) to get the previous value a. If we keep all consequtive deltas we can use deltainv multiple times to get any of the earlier text versions.

The delta value calculated between two utf-8 encoded strings is itself utf-8 encoded string.

The algorithm is very well described here in the fossil wiki.

The code of this repository is best viewed in Leo editor. The outline containing the code is in a single outline file: fossil-delta-ref.leo.

This repository contains two more Rust crates, py-fossil-delta which exports fossil-delta functions to Python as an extension module.

The third crate is leo-ver-serv which is a binary (executable) web server which accepts snapshots from Leo, calculates the delta form the previous snapshot and stores all deltas in a database. On the other side, this server serves a small web application which allows user to browse history of known Leo files.