eip_712_utils 0.1.0

A Rust library providing utilities for EIP-712 message signing
Documentation 
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use hex::{self, encode};
use secp256k1::{Message, Secp256k1, SecretKey};

pub fn sign_message(message_hex: &str, private_key_uint: u32) -> String {
    let message = hex::decode(message_hex).expect("Decoding failed");

    // private key to [u8]
    let mut private_key_bytes = [0u8; 32];
    private_key_bytes[28..].copy_from_slice(&private_key_uint.to_be_bytes());

    let secret_key =
        SecretKey::from_slice(&private_key_bytes).expect("32 bytes, within curve order");
    let secp = Secp256k1::new();

    let message = Message::from_digest_slice(&message).expect("32 bytes");

    let sig = secp.sign_ecdsa_recoverable(&message, &secret_key);

    let (rec_id, signature_bytes) = sig.serialize_compact();

    // Convert to hex
    let signature_hex = encode(signature_bytes); // Use 'encode' from the 'hex' crate

    if rec_id.to_i32() == 0 {
        // append 27 in hex to the signature_hex
        let signature_hex = format!("{}{:x}", signature_hex, 27);
        return signature_hex;
    } else {
        let signature_hex = format!("{}{:x}", signature_hex, 29);
        return signature_hex;
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_signs_correctly() {
        let message = "77915d20c811f39572463a234db9b776d518d07d9682a825be0d79752745a4c7";
        let private_key = 659918_u32;
        let expected_signature = "b9c658f86d985ad0502584c70ea520cf68523e4013786f83f216de093ef9467e453d27fe627278ab0c8425906843a706f66a9c3120b37e88ac722aa217a04fcf1b";
        let signature = sign_message(message, private_key);
        assert_eq!(signature, expected_signature);
    }
}