applesauce-core 0.3.3

A low level library interface for compressing and decompressing files using macos transparent compression
Documentation 
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use crate::compressor::lz;
use libc::c_int;
use std::ffi::c_void;
use std::mem::MaybeUninit;
use std::{cmp, mem};

pub type Lzvn = lz::Lz<Impl>;

pub enum Impl {}

impl lz::Impl for Impl {
    const UNCOMPRESSED_PREFIX: Option<u8> = Some(0x06);

    fn scratch_size() -> usize {
        cmp::max(
            mem::size_of::<DecoderState>() + mem::align_of::<DecoderState>(),
            // Safety: this function is always safe to call
            unsafe { lzvn_encode_scratch_size() },
        )
    }

    unsafe fn encode(dst: &mut [u8], src: &[u8], scratch: &mut [u8]) -> usize {
        // SAFETY: function is always safe to call
        debug_assert!(scratch.len() >= unsafe { lzvn_encode_scratch_size() });

        // SAFETY: Buffers are valid for the specified lengths, and caller must ensure scratch is large enough
        let res = unsafe {
            lzvn_encode_buffer(
                dst.as_mut_ptr(),
                dst.len(),
                src.as_ptr(),
                src.len(),
                scratch.as_mut_ptr().cast(),
            )
        };
        debug_assert!(res <= dst.len());
        res
    }

    unsafe fn decode(dst: &mut [u8], src: &[u8], _scratch: &mut [u8]) -> usize {
        // SAFETY: decoder state is all numeric and safe to zero init
        let mut state: DecoderState = unsafe { MaybeUninit::zeroed().assume_init() };

        let src_range = src.as_ptr_range();
        state.src = src_range.start;
        state.src_end = src_range.end;

        let dst_range = dst.as_mut_ptr_range();
        state.dst = dst_range.start;
        state.dst_begin = dst_range.start;
        state.dst_end = dst_range.end;

        // SAFETY: state is fully initialized
        unsafe {
            lzvn_decode(&mut state);
        }

        assert!(dst_range.contains(&state.dst));
        // SAFETY: lvzn_decode will have updated the dst ptr on state,
        //         but kept within range dst..dst_end
        unsafe { state.dst.offset_from(dst.as_mut_ptr()) }
            .try_into()
            .unwrap()
    }
}

// Forcing linking even if lzfse isn't included
const _: () = {
    let _ = lzfse_sys::lzfse_encode_buffer;
};

#[repr(C)]
struct DecoderState {
    src: *const u8,
    src_end: *const u8,

    dst: *mut u8,
    dst_begin: *mut u8,
    dst_end: *mut u8,
    dst_current: *mut u8,

    l: usize,
    m: usize,
    d: usize,

    d_prev: isize,

    end_of_stream: c_int,
}

// These symbols are actually provided by lzfse, as long as we're linking to lzfse,
// these will be available
extern "C" {
    fn lzvn_encode_scratch_size() -> usize;

    fn lzvn_encode_buffer(
        dst: *mut u8,
        dst_size: usize,
        src: *const u8,
        src_size: usize,
        work: *mut c_void,
    ) -> usize;

    fn lzvn_decode(state: *mut DecoderState);
}

#[test]
fn round_trip() {
    let mut compressor = Lzvn::new();
    super::tests::compressor_round_trip(&mut compressor);
}