What is the purpose of signTransaction? How do you verify the signed tx on-chain?

[adriandelgg]

Hello, what is the purpose of using signTransaction()?
I'm confused as to what exactly it is that it's returning.

I'm trying to sign a transaction using Ethers.js, and then I want to be able to use that transaction in another transaction.
Is this possible?

Is it possible to batch transactions together?
For example: sign 2 transactions using signTransaction, then consolidate them together to only actually every call and spend Ether on 1 single transaction.

This is kind of what I was trying but wasn't working:

const tx = await contract.populateTransaction.approve(
  owner.address,
  contract.address
);

const signedTx = await wallet.signTransaction(tx);
const { v, r, s } = parseTransaction(signedTx);

await contract.verifyTxSplit(signedTx, v, r, s)
await contract.verifyTxHash(signedTx)

[ricmoo]

I don't quite understand what you are trying to do, but that isn't what .signTransaction is for. :)

There isn't really a way to verify a contract in a Contract, unless you write lots of complex Solidity code to parse RLP data, and understand the various transaction envelopes. This would be quite a bit of work. And it would be expensive.

You also cannot batch transactions together using an EOA (externally owned account), and this is something you would require a Smart Contract (SC) to achieve. The most popular SC wallet for executing multiple operations at once is Gnosis Safe if you are looking for a place to start.

If you are looking to verify the hash, as an opaque octet stream, your above example requires the transaction pre-image, which you can get using serializeTransaction(tx); that method accepts a second parameter which add a signature, but without the second parameter it provides the unserialized transaction, which is what you require as the digest for ecrecover.

The purpose of signTransaction is to prepare a transaction off-line, which can be provided to the network at a later time (using provider.sendTransaction) or handed to a counter-factual protocol, like Optimism. There are lots of cool things that can be done with signTransaction, but most of them are quite advanced usage, so it is not a common method to use. Also, keep in mind, platforms like MetaMask do not permit using .signMessage, since it affects nonce management and can lead to security concerns.

Does that make sense?

[adriandelgg]

This is the exact answer I was looking for!

Thank you for taking the time to answer this with so much detail!!star2