Function parse_nar_str 

pub fn parse_nar_str<S>(s: &S) -> Option<([u8; 32], &[u8])>
where
    S: AsRef<[u8]> + ?Sized,

Parses a 14cx20k6z4hq508kqi2lm79qfld5f9mf7kiafpqsjs3zlmycza0k.nar.xz string and returns the nixbase32-decoded digest, as well as the compression suffix (which might be empty).