Correctly creating UnsignedTransaction

[pscott]

Hi,
I'm trying to create a serialized UnsignedTransaction (goal is to send it to ledgerjs' signTransaction). I need this unsignedTx to have a chainID (so either type 1 / 2 tx, or post EIP-155 tx).

I've searched on Google and found this answer. This will create a pre EIP-155 tx (without v).

I've found that I can add a transaction to populateTransaction. However, the only way I've found to specify the chainID is to specify it after I have generated the unsignedTx. Here's the code:

const abi  = // my ABI here
const contractAddr = '0x7f39c581f595b53c5cb19bd0b3f8da6c935e2ca0';

const contract = new ethers.Contract(contractAddr, abi)

let transaction = {
    nonce: Number(424242),
    gasLimit: Number(42),
    gasPrice: Number(4242),
//     chainId: 1, // Ideally chainId would be specified here but getting 'cannot override "chainId"'
}

let unsignedTx = await contract.populateTransaction.wrap(Number(10000000), transaction);
unsignedTx.chainId = 1; // Is this really how it should be done?
let ser = ethers.utils.serializeTransaction(unsignedTx);

So I guess I have two questions:

1. How can I make this cleaner, and put the chainId in the transaction object?
2. Is there a proper way to load the ABI from a file? Ideally I'd have something like const abi = ethers.abi.fromFile('abi.json'); or something similar.

[zemse]

How can I make this cleaner, and put the chainId in the transaction object?

First you can get a populated transaction and then add the other overrides to it.

const {data} = await contract.populateTransaction.wrap(Number(10000000));
let unsignedTx = {
    data,
    nonce: Number(424242),
    gasLimit: Number(42),
    gasPrice: Number(4242),
    chainId: 1
}

Ethers won't allow you to inject a chainId override because chainId is implicit from the provider you're using. In your use case, you have to set the chain id at the last (just before passing the unsignedTx to ledger signer)

Is there a proper way to load the ABI from a file? Ideally I'd have something like const abi = ethers.abi.fromFile('abi.json'); or something similar.

Ethers do not have file accessing as it is platform dependent thing. In node js you can simply do:

const abi = require('../path/to/abi.json'); // works if json

const content = fs.readFileSync('../path/to/abi.json', 'utf8')
const abi = JSON.parse(content);

[pscott]

Got it! Thanks a lot!