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zchunk

zchunk

A pure-Go, cross-platform toolkit for the zchunk file format — content-defined chunking with per-chunk checksums, enabling HTTP-Range delta updates (as used by Fedora/DNF). Interoperable with the reference zck / unzck tools.

Repository: github.com/go-deltasync/zchunk

go install github.com/go-deltasync/zchunk/cmd/zchunk@latest

Quick start 

# create a .zck from a file (fixed-size chunks, zstd)
zchunk create disk.img disk.img.zck

# train + embed a zstd dictionary, then create with it
zchunk gen-zdict disk.img disk.dict
zchunk create --dict disk.dict disk.img disk.img.zck

# delta-download an update: fetch only the chunks missing locally,
# reusing an older local copy
zchunk download --local old.img.zck https://example.com/disk.img.zck new.img.zck

Library 

import "github.com/go-deltasync/zchunk"

comp, _ := zchunk.CompressChunk(zchunk.CompressionZstd, nil, data)
// Builder writes .zck files; ReadLead/ReadPreface/ReadIndex parse them;
// PlanDelta + DownloadDelta over a RangeReader perform delta downloads.