Return a binary tuple from a Rust NIF

Hello,

I’m trying to make a NIF that splits binary once using a delimiter (like :binary.split(bin, separator, parts: 2)) but in Rust I don’t quite understand how to use rustler::Binary, rustler::OwnedBinary and rustler::NewBinary.

Here’s the code I currently have, it’s working but it could be improved (I think):

#[rustler::nif]
fn next<'a>(env: Env<'a>, raw: Binary<'a>) -> (Option<Binary<'a>>, Binary<'a>) {
    match do_next(raw.as_slice()) {
        Some((packet, remaining)) => {
            let mut pb = NewBinary::new(env, packet.len());
            pb.as_mut_slice().copy_from_slice(packet);
            let mut rb = NewBinary::new(env, remaining.len());
            rb.as_mut_slice().copy_from_slice(remaining);

            (Some(pb.into()), rb.into())
        }
        None => (None, raw)
    }
}

fn do_next(raw: &[u8]) -> Option<(&[u8], &[u8])> {
    let index = raw.iter().position(|&r| r == SEPARATOR);

    match index {
        Some(i) => Some((&raw[0..i], &raw[i + 1..])),
        _ => None,
    }
}

I’ve few questions:

• Why is it possible to return an OwnedBinary but not if it’s in a tuple ?

Example:

// This works
#[rustler::nif]
fn encrypt(raw: String) -> OwnedBinary {
    let enc: Vec<u8> = do_encrypt(raw.as_bytes());
    let mut binary: OwnedBinary = OwnedBinary::new(enc.len()).unwrap();
    binary.as_mut_slice().copy_from_slice(&enc);

    binary
}

// But this don't
// The error is: the trait bound `OwnedBinary: Encoder` is not satisfied
#[rustler::nif]
fn encrypt(raw: String) -> (OwnedBinary , OwnedBinary) {
    let enc: Vec<u8> = do_encrypt(raw.as_bytes());
    let mut binary: OwnedBinary = OwnedBinary::new(enc.len()).unwrap();
    binary.as_mut_slice().copy_from_slice(&enc);

    (binary, binary)
}

• It is possible to return a binary inside a tuple but without to manually allocate it using the env ?

Thanks in advance