How to sign a transaction in Rust

Question

Given a private key, I would like to sign a transaction offline, so it can be sent to a node or Infura without unlocking an account first. I can find many examples in javascript using ethereumjs-tx but I am using Rust and rust-web3 and can't find a single example that writes data. I need to be able to call functions, not just send value, so how to construct the function parameters is of particular interest. Also, how can I wait and process the return value if the function has a return value?

Answer 1

It is a function of wallet to store and use your private key. web3 API like rust-web3 usually leave transaction signing to wallet. Therefore your option is to reuse the code in Ethereum wallets that are written in Rust.

Answer 2

There is a package for this called ethereum-tx-sign on crates.io. It provides a RawTransaction structure with a sign method. It doesn't have any dependency on web3 and you can sign the transactions offline.

Answer 3

There's a trick using python's web3 package with cpython:

let gil = Python::acquire_gil();
let py = gil.python();
let web3 = py.import("web3").unwrap();

let transaction = {
    let transaction = PyDict::new(py);
    transaction.set_item(py, "gas", gas_limit).unwrap();
    transaction.set_item(py, "gasPrice", gas_price).unwrap();
    transaction.set_item(py, "nonce", nonce).unwrap();
    transaction.set_item(py, "data", data).unwrap();

    let web3 = web3.get(py, "Web3").unwrap();
    let to = web3.call_method(py, "toChecksumAddress", (to, ), None).unwrap();

    transaction.set_item(py, "to", to).unwrap();
    transaction.set_item(py, "value", value).unwrap();

    transaction
};

let account = web3.get(py, "Account").unwrap();
let signed_transaction = account.call_method(py, "signTransaction", (transaction, private_key), None).unwrap();

let raw_transaction: String = signed_transaction.getattr(py, "rawTransaction")
    .unwrap()
    .call_method(py, "hex", NoArgs, None)
    .unwrap()
    .extract(py)
    .unwrap();

Boom! Got it!

Btw, about ethereum-tx-sign. I've already try it, but it seems not work correctly. My target server doesn't recognize the signedRawTransaction. So I compare the its result with web3's result and I found they were different.