Lib.rs

This crate provides a library for conversion between bytes/bits and heterogeneous lists (tuples).

Library features:

• implements compile time type checking
• neither declarative nor procedural macros exports
• mixed endianness from single bytes array

Examples

Parse complex data structure

use heterob::{P4, endianness::LeBytesInto, bit_numbering::LsbInto};

// Source is a [u8;6] bytes array
let data = [0x00u8,0x11,0x22,0x33,0x44,0x55,0b1010_1001];

// Target struct
#[derive(Debug, Clone, PartialEq, Eq)]
struct S {
    byte: u8,
    word: Option<u16>,
    bytes: [u8;3],
    is_byte6_bit0: bool,
    byte6_last_4_bits: u8,
}

// Parse bytes array as integers
let P4((byte, word, bytes, byte6)) = data.le_bytes_into();
// Parse last byte as bitfield. Unit type () used as placeholder
let (is_byte6_bit0, (), is_some_word, byte6_last_4_bits) =
    P4::<u8, 1, 2, 1, 4>(byte6).lsb_into();
// `is_some_word` coerce to bool via let statement
let _: bool = is_some_word;

// Final structure
let result = S {
    byte,
    word: is_some_word.then(|| word),
    bytes,
    is_byte6_bit0,
    byte6_last_4_bits,
};

let sample = S {
    byte: 0x00,
    word: Some(0x2211),
    bytes: [0x33,0x44,0x55],
    is_byte6_bit0: true,
    byte6_last_4_bits: 0b1010,
};

assert_eq!(sample, result);

Mixed endians

use heterob::{T3, endianness::{Be, Le}};
#[derive(Debug, Clone, PartialEq, Eq)]
struct S {
    le: u16,
    be: u16,
    bytes: [u8;2]
}

let data = [0x00,0x11,0x22,0x33,0x44,0x55];

let (Le(le),Be(be),bytes) = T3::from(data).into();
let s = S { le, be, bytes };

assert_eq!(S { le: 0x1100, be: 0x2233, bytes: [0x44,0x55] }, s, "{:x}", s.be);

Fallible bytes slice parsing

use heterob::{Seq, P3, endianness::Be};

// Source is a bytes slice
let data = [0x00u8,0x11,0x22,0x33,0x44,0x55,0b1010_1001].as_slice();

// Target struct
#[derive(Debug, Clone, PartialEq, Eq)]
struct S {
    byte: u8,
    word: u16,
    bytes: [u8;3],
}

// Parse bytes array as integers
let Seq { head: Be((byte, word, bytes)), .. } = P3(data).try_into().unwrap();

// Final structure
let result = S {
    byte,
    word,
    bytes,
};

let sample = S {
    byte: 0x00,
    word: 0x1122,
    bytes: [0x33,0x44,0x55],
};

assert_eq!(sample, result);

Compile time type checking

The idea of compile time checks taken from issue comment of static_assertions crate. Unfortunately it's hard to find the error source using this type of compile time checks. With stabilized constant generics arithmetics it should be much easy.

There are two things checking at compile time

1. Array spliting on multiple arrays

This check asserts that length of input array equal to sum of lengths of output arrays

# use heterob::T2;
let data = [0u8; 13];
let _ = T2::<[u8;4], [u8;3]>::from(data);

Trying to split 13 bytes length array to 2 arrays with lengths 4 + 3 = 7 will throw an error:

error[E0080]: evaluation of `<heterob::T2<[u8; 4], [u8; 3]> as heterob::ParamAndAssociatedConst<13_usize>>::LESS` failed
  --> src/lib.rs:21:25
   |
21 |     const LESS: usize = Self::VALUE - N;
   |                         ^^^^^^^^^^^^^^^ attempt to compute `7_usize - 13_usize`, which would overflow

note: the above error was encountered while instantiating `fn <heterob::T2<[u8; 4], [u8; 3]> as std::convert::From<[u8; 13]>>::from`
 --> src/lib.rs:86:9
  |
6 | let _ = T2::<[u8;4], [u8;3]>::from(data);
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

2. Bit index in arbitrary value

This check asserts that sum of bit indexes is less than value bits count

# use heterob::{P3, bit_numbering::LsbInto};
let data = 0u16;
let ((),(),()) = P3::<_, 2, 11, 5>(data).lsb_into();

Trying to extract bits 12-17 from 16 bits value will throw an error:

error[E0080]: evaluation of `<((), (), ()) as heterob::bit_numbering::FromLsb<heterob::P3<u16, 2_usize, 11_usize, 5_usize>>>::ASSERT_INDEX_IN_BOUNDS` failed
  --> src/bit_numbering.rs:81:43
   |
81 |     const ASSERT_INDEX_IN_BOUNDS: usize = Self::BITS - Self::MAX_BIT_INDEX;
   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attempt to compute `16_usize - 18_usize`, which would overflow

note: the above error was encountered while instantiating `fn <((), (), ()) as heterob::bit_numbering::FromLsb<heterob::P3<u16, 2_usize, 11_usize, 5_usize>>>::from_lsb`
  --> src/bit_numbering.rs:97:9
   |
97 |         U::from_lsb(self)
   |         ^^^^^^^^^^^^^^^^^