How to split a slice into a header array reference and a tail slice?

July 17, 2023

I’m looking for a function with a signature similar to:

split_header_and_tail(buf: &[u8]) -> Option<(&[u8; HEADER_LENGTH], &[u8])>

If the supplied slice is too short, the result is None, but if it’s long enough a reference to the first HEADER_LENGTH bytes and the tail slice are returned.

The first part must be a reference to a fixed-length array, as I need to subdivide it into various fixed-length fields.

>Solution :

On nightly, there is split_array_ref():

#![feature(split_array)]

fn split_header_and_tail(buf: &[u8]) -> Option<(&[u8; HEADER_LENGTH], &[u8])> {
    if buf.len() < HEADER_LENGTH {
        None
    } else {
        Some(buf.split_array_ref())
    }
}

On stable, you can use TryInto:

fn split_header_and_tail(buf: &[u8]) -> Option<(&[u8; HEADER_LENGTH], &[u8])> {
    if buf.len() < HEADER_LENGTH {
        None
    } else {
        let (head, tail) = buf.split_at(HEADER_LENGTH);
        Some((head.try_into().unwrap(), tail))
    }
}