ABI Encoding for offline method calls

Hi ! I’m using ethers in combination with web3 in order to achieve the following:

• have the user import his json wallet/restore from mnemonic
• connect to the smart contract
• create a transaction that calls a non-constant method of the SC (ethers)
• sign the transaction offline or client side
• send the transaction to any node I need this so that the user can be the only one with access to the wallet

It seems fine with simple methods, like those that pass integers. But I got issues with more complex data. The code I use is this:

                    w1 =  new ethers.Wallet(priv, provider);
                    iface = new ethers.utils.Interface(contract_abi);
                    txdata = iface.functions[method].encode(args);
                    signonce = await w1.getTransactionCount();
                    tx = {
                        "from" : addr,
                        "to" : contract_address,
                        "gasLimit" : 1500000,
                        "gasPrice" : 2,
                        "nonce" : signonce,
                        "data" : txdata,
                        "value" : 0,
                    };
                    web3 = new Web3( new Web3.providers.HttpProvider(rpcEndpoint));
                    account = await  web3.eth.accounts.privateKeyToAccount(priv);
                    stx1 = await web3.eth.accounts.signTransaction(tx, priv);
                    web3.eth.sendSignedTransaction(stx1.rawTransaction)

This part works well. The problem is creating agrs to be encoded. If a prameter is an int or a string, no problem.

var args = {"i":32};

But how do I encode bytes? arrays? addresses? I get errors about the format/type/length of the parameter

Any help/advice/feedback would be greatly appreciated.

TIA

[ricmoo]

Heya!

I also recommend you try out v5, which has a. simpler API for dealing with Interface and Contracts for offline signing.

w1 =  new ethers.Wallet(priv, provider);
contract = new ethers.Contract(contract_address, contract_abi, w1);
overrides = {
  nonce: w1.getTransactionCount(),
  gasLimit: 1500000,
  gasPrice: utils.parseUnits("2.0", "gwei"),
  value: 0
};
unsignedTx = await contract.populateTransaction[method](...args, overrides);

signedTx = w1.signTransaction(unsignedTx);

provider.sendTransaction(signedTx);

This is all doable in v4 too, but v5 specifically added some API to make offline-signing easier. 😃

[zemse]

@xzbnm

// This line returns the transaction object, which is already signed and sent
let unsignedTx = await contract.functions.populateTransaction(toAddress,numberOfTokens,transaction)

// Just replace that line with bellow one, it should probably work in your code
let unsignedTx = await contract.populateTransaction.populateTransaction(toAddress,numberOfTokens,transaction)

Edit: Hey, I got a feeling that you probably don’t have a populateTransaction in a smart contract and you actually meant to create a populated tx for transfer method? If that’s the case:

let unsignedTx = await contract.populateTransaction.transfer(toAddress,numberOfTokens,transaction)