librsyncr
librsyncr is a Rust library to calculate differences between two files without having access to both files on the same system. It is a rewrite of the librsync C library (without looking at the librsync source code), and the signature and delta files are compatible with that library. The C library is 3562 lines of C (not including comments or vendored Blake2 and MD4 code), but this library is only 753.
strong_hash Feature
The default hash used for looking up blocks from a signature file is not resistant to hash DoS attacks. If you are using this library in a web service to process untrusted signature files, you will likely want to enable the strong_hash feature.
Performance
Testing with Wikiquote dump files (about 38 MB) on a Intel Core-i7-6700K 4.0 GHz processor:
# this library
./target/release/examples/rdiff signature ./enwikiquote-20170501-abstract.xml ./enwikiquote-20170501-abstract-sig.xml
85ms (447 MB/s)
# librsync
./rdiff signature ./enwikiquote-20170501-abstract.xml ./enwikiquote-20170501-abstract-sig.xml
77ms (494 MB/s)
# this library
./target/release/examples/rdiff delta ./enwikiquote-20170501-abstract-sig.xml ./enwikiquote-20170701-abstract.xml ./enwikiquote-delta.xml
115ms (330 MB/s)
# librsync
./rdiff delta ./enwikiquote-20170501-abstract-sig.xml ./enwikiquote-20170701-abstract.xml ./enwikiquote-delta.xml
118ms (322 MB/s)
# this library
./target/release/examples/rdiff patch ./enwikiquote-20170501-abstract.xml ./enwikiquote-delta.xml ./enwikiquote-new.xml
67ms (567 MB/s)
# librsync
./rdiff patch ./enwikiquote-20170501-abstract.xml ./enwikiquote-delta.xml ./enwikiquote-new.xml
24ms (1583 MB/s)
File formats
The C librsync library has documentation on the signature file format, and the .NET librsync library has documentation on the delta file format.
License
Licensed under the Mozilla Public License Version 2.0.