Show HN: Zeekstd – Rust Implementation of the ZSTD Seekable Format

Hello,

I would like to share a Rust implementation of the Zstandard seekable format I've been working on.

Regular zstd compressed files consist of a single frame, meaning you have to start decompression at the beginning. The seekable format splits compressed data into a series of independent frames, each compressed individually, so that decompression of a section in the middle of an archive only requires zstd to decompress at most a frame's worth of extra data, instead of the entire archive.

I started working with the seekable format because I wanted to resume downloads of big zstd compressed files that are decompressed and written to disk on the fly. At first I created and used bindings to the C functions that are available upstream[1], however, I stumbled over the first segfault rather quickly (it's now fixed) and found out that the functions only allow basic things. After looking closer at the upstream implementation, I noticed that is uses functions of the core API that are now deprecated and it doesn't allow access to low-level (de)compression contexts. To me it looks like a PoC/demo implementation that isn't maintained the same way as the zstd core API, probably that's also the reason it's in the contrib directory.

My use-case seemed to require a complete rewrite of the seekable format, so I decided to implement it from scratch in Rust using bindings to the advanced zstd compression API, available from zstd 1.4.0.

The result is a single dependency library crate[2], and a CLI crate[3] for the seekable format that feels similar to the regular zstd tool.

Any feedback is highly appreciated!