Function payload_hash 

pub fn payload_hash(payload: &str) -> String

The hash of a payload, in hex. Two copies of one message have the same hash.

use riff_core::signed::payload_hash;

assert_eq!(payload_hash("abc"), payload_hash("abc"));
assert_ne!(payload_hash("abc"), payload_hash("abd"));
assert_eq!(payload_hash("abc").len(), 64);