lz4

Implementation of LZ4 decompression for block and frame formats in Zig. Added reader type makes decoding streams easy.

Installation

build.zig.zon

.{
    .name = "yourProject",
    .version = "0.0.1",

    .dependencies = .{
        .lz4 = .{
            .url = "https://github.com/clickingbuttons/lz4/archive/refs/heads/master.tar.gz",
        },
    },
}

build.zig

const lz4 = b.dependency("lz4", .{
    .target = target,
    .optimize = optimize,
});
exe.addModule("lz4", lz4.module("lz4"));

Run zig build and then copy the expected hash into build.zig.zon.

Usage

Reader

You can wrap an existing reader using decompressStream.

const lz4 = @import("lz4");

const allocator = std.heap.page_allocator;
var file = try std.fs.cwd().openFile("file.lz4", .{});

var stream = lz4.decompressStream(allocator, file.reader(), true);
defer stream.deinit();
var reader = stream.reader();

// The LZ4 format does not require including the uncompressed size. You can guess a large size or
// iterate until EOS.
var buf: []u8 = try allocator.alloc(u8, 1_000_000);
defer allocator.free(buf);
const res = try reader.read(buf);
std.debug.print("{s}", .{ buf[0..res] });

Block

A LZ4 block contains its size, data, then a negative offset to the match.

const lz4 = @import("lz4");

const allocator = std.heap.page_allocator;
const compressed = "\xf7\x12this is longer than 15 characters\x0b\x00";

const decoded = try lz4.block.decode(allocator, compressed);
defer allocator.free(decoded);
std.log.debug("{s}\n", .{ decoded }); // this is longer than 15 characters characters

Frame

A LZ4 frame contains magic, a frame descriptor, data blocks (which may have checksums), and an optional content checksum. They can be created using the lz4 command.

const lz4 = @import("lz4");

const allocator = std.heap.page_allocator;
var file = try std.fs.cwd().openFile("frame.lz4", .{});

const decompressed = try lz4.frame.decode(allocator, reader, true);
defer allocator.free(decompressed);