Polkadot tx-wrapper offline signing

Question

What does ExtrinsicPayload exactly do? I want to replicate the logic but something is missing.

import {
    getRegistry
} from '@substrate/txwrapper-polkadot';

const registry = getRegistry({
        chainName: 'Polkadot',
        specName,
        specVersion,
        metadataRpc,
    });

const extrinsicPayload = registry.createType('ExtrinsicPayload', unsigned, {version: unsigned.version});
const extrinsicPayloadU8a = extrinsicPayload.toU8a({method: true})
const actualPayload = extrinsicPayloadU8a.length > 256 ? registry.hash(extrinsicPayloadU8a) : extrinsicPayloadU8a;

const s1 = u8aToHex(alice.sign(actualPayload));
console.log("s1", s1, s1.length);
const s2 = extrinsicPayload.sign(alice).signature;
console.log("s2", s2, s2.length);

s1 and s2 should have the same length but they don't. What's the reason?

Answer 1

You should pass {"withType": true} to the sign method too.

const s1 = u8aToHex(alice.sign(actualPayload, {"withType": true}));

sr25519 uses randomness for signing, so the results won't be the same, but they should have the same length.