Building a transaction for another wallet to sign and send

Question

Let's say I'm Wallet A, another user is Wallet B and I also have a smart contract.

With the smart contract I will build a transaction to send as Wallet B. So normally, for the transaction to be sent, Wallet B needs to manually sign it with his private key.

Is it possible to notify him on-chain for this transaction? Like, after I build and submit a transaction, if he is using his wallet at that time (for example he is connected to x dApp), is it possible that he gets notified through his wallet for that transaction?

If not, what are some possible ways to notify him on-chain?

Answer 1

You cannot notify another wallet as Ethereum does not have a built-in notification system like that. What smart contracts can do, is emit events, which are basically logs written to the blockchain. If connected to a dApp or any application that is listening for these events, you can use a websocket / JSON-RPC subscription. When the event is detected, the dApp can notify user.

basic example for the event

event EventFromWalletAToWalletB(address sender, address receiver, uint256 amount);
function requestTransaction(address receiver, uint256 amount) public {
    // ... some logic
    emit EventFromWalletAToWalletB(msg.sender, receiver, amount);
}

basic example in a dApp

const contract = new web3.eth.Contract(abi, contractAddress);

contract.events.EventFromWalletAToWalletB({})
    .on('data', (event) => {
        console.log('Custom event data:', event);
    })
    .on('error', console.error);

Obviously you need to adapt this concept to the contract and dApp your are building.

Answer 2

Thank you for the answers. Let me rephrase the question:

Metamask and other wallets have a "suggest transactions" permission that give to dApps whenever the wallet connects to them.

But is there another way to suggest a transaction to a wallet? As Wallet A or a smart contract owner, is it possible to suggest a transaction for Wallet B to approve or reject?

If no, how does this permission on the wallets work?