create_signed_tx.rs

use parity_scale_codec::{ Encode, Decode};
use sp_core::{H256, H512, Pair};

type Salt = u8;

const SALT: Salt = 5u8;

#[derive(Encode, Decode, Debug, PartialEq, Eq, Clone)]
pub struct BasicExtrinsic {
	operation: Operation,
	salt: Salt,
	signature: H512,
	signer: H256
}

#[derive(Encode, Decode, Debug, PartialEq, Eq, Clone)]
pub enum Operation {
	Add(u32),
	Subtract(u32),
	Multiply(u32),
	Divide(u32),
}
fn main() {
	let operation = Operation::Add(11u32);
	let pair: sp_core::sr25519::Pair = Pair::generate_with_phrase(Some("key")).0;
	let payload = (&operation, SALT).encode();
	println!("{:02x?}", payload);
	let payload: [u8; 6] = payload.try_into().unwrap();
	println!("{:02x?}", payload);
	let signature = pair.sign(&payload);
	let tx = BasicExtrinsic { operation, salt: SALT, signature: sp_core::H512(signature.0), signer: sp_core::H256(pair.public().0) };
	let print_string = format!("{:02x?}", tx.encode());
	let print_string = print_string.replace(", ", "");
	let print_string = print_string.replace('[', "");
	let print_string = print_string.replace(']', "");
    println!("{}", print_string);
}