consume.rs

#![feature(split_array)]

// https://rust.godbolt.org/z/6o5T55K9v

/// Consume a value which implements `from_le_bytes` from a buffer, advancing
/// the buffer beyond the bytes that were consumed
#[macro_export]
macro_rules! consume {
    ($buf:expr, $ty:ty) => {{
        const SIZE: usize = std::mem::size_of::<$ty>();

        // check that we have enough bytes to extract a $ty
        // + 1 instead of >= because >= confuses llvm/rustc so it 
        // refuses to fuse multiple checks with multiple consume! calls
        if $buf.len() + 1 > SIZE {
            // split into &[u8; SIZE] and &[u8]
            let (x, rest) = $buf.split_array_ref::<SIZE>();

            // get the val
            let val = <$ty>::from_le_bytes(*x);

            // advance the buffer
            $buf = rest;
            Some(val)
        } else {
            None
        }
    }}
}

pub fn parse(mut ptr: &[u8]) -> Option<(u32, u64, u32, u32)> {
    Some((
        consume!(ptr, u32)?,
        consume!(ptr, u64)?,
        consume!(ptr, u32)?,
        consume!(ptr, u32)?,
    ))
}