How to use deku::input

[konradmoesch]

Hello, first of all thanks for the crate!
I have a file containing data blocks that start with a checksum and then some other fields, like this:

struct WriteBlock {
  checksum: u8,
  status: u8,
  installdate: Date,
  ...
}

I can successfully read the fields, but now I want to check whether the checksum is valid, maybe using

#[deku(assert_eq = "calculate_checksum(deku::input, 200, 32)")]

where 200 is the offset of the write block and 32 is the block size in bytes. WriteBlock is a member of another struct Dataset, that is read using Dataset::from_bytes()
However, I get the error cannot find value '__deku_input' in this scope. How can I use deku::input, and is this the way to go to get the raw bytes? Since the checksum field is at the beginning of the block, I also thought of using deku::rest, but this contains the data bit-wise I think.
Thanks for your help!

[wcampbell0x2a]

The following example might help you:

use deku::bitvec::{BitSlice, Msb0};
use deku::prelude::*;

#[derive(DekuRead, Debug, PartialEq, Eq)]
struct Block {
    other: u16,
    #[deku(assert_eq = "Self::calculate_checksum(deku::rest, 3)")]
    checksum: u8,
    field_a: u8,
    field_b: u8,
    field_c: u8,
}

impl Block {
    pub fn calculate_checksum(deku_rest: &BitSlice<u8, Msb0>, block_size: usize) -> u8 {
        let bytes: &[u8] = deku_rest.domain().region().unwrap().1;
        bytes.iter().take(block_size).sum::<u8>()
    }
}

fn main() {
    let block = Block {
        other: 0xffff,
        checksum: 0b0000_0111,
        field_a: 0b0000_0001,
        field_b: 0b0000_0010,
        field_c: 0b0000_0100,
    };

    let bytes = &[
        0xff,
        0xff,
        0b0000_0111,
        0b0000_0001,
        0b0000_0010,
        0b0000_0100,
    ];
    let test_block = Block::from_bytes((bytes, 0)).unwrap().1;
    assert_eq!(block, test_block);
}

[konradmoesch]

Thanks for your help, I will try that!