How to generate the hash of a transaction?

Question

How can I generate an ID of a transaction before submitting it to an RPC node? I know I can get a transaction signature as a result of web3.sendAndConfirmTransaction call but is it possible to generate the signature deterministically?

Answer 1

You can manually sign the transaction before sending it, and then retrieve signature:

const bs58 = require('bs58');

// build a transaction
const transaction = new Transaction(...);

// sign it explicitly
transaction.sign(...signers);

// retrieve the signature as base58
const signature = bs58.encode(transaction.signature())

You will need to already have a blockhash defined and set against the transaction for this to work.

This will not work with sendTransaction, which re-signs everything. So serialize the message directly to send:

const message = transaction.serialize();
connection.sendRawTransaction(message)