Ethers.js: How to wait for certain number of confirmations ?

[subramanianv]

Sometimes geth node returns nonce too low when sending transactions in succession. so if we can wait for certain number of confirmations, this problem can be solved

[ricmoo]

This is something I've been thinking of adding for a while, so I will add it next week to the v4 branch.

I have a few ideas on how to add it to the API, but will experiment this weekend with a few options.

[ricmoo]

This weekend was spent entirely just refactoring and getting the TypeScript definitions all cozy, but I think things are starting to settle, so I will be able to get to this soon. :)

aside: There was also a crazy bug in nodejs that causes it to sort Japanese strings in a different order than browsers, but that is fixed now too. And not all BIP39 wordlists do a final sanity check after loading, and fail loud if the checksum doesn't match the derived wordlist.

[ricmoo]

This has been added in 4.0.3.

On the TransactionsResponse wait method, confirmations can be passed à la tx.wait(confirmations), which will return the TransactionReceipt, similarly provider.waitForTransaction(confirmations) will do the same.

Thanks! :)

[pstuermlinger]

Is there any chance this will be rewritten to return something like web3's promievent (https://www.npmjs.com/package/web3-core-promievent)? I'd need to be notified about each new confirmation as well as about chain re-organisations, which might lower the # of confirmations or even set it to 0.
Currently, I don't see a clear path how I could accomplish this. Should I just do a provider.getTransactionReceipt(hash) periodically and watch for the confirmations property - and if that returns null assume the tx being erased from the chain due to a reorg?

[ricmoo]

No, I those Prominevent things seem crazy to me. :p

You could exactly do as you describe:

Example:

let tx = contract.someFunction(params);

let lastConfirms = -1;
async function handler(blockNumber) {
    let receipt = await provider.getTransactionReceipt(tx.hash);
    if (receipt == null || receipt.confirmation < lastConfirms) {
        // A re-org; do what you need here
    }
}
provider.on("block", handler);

tx.wait(3).then((receipt) => {
    // This gets called once there are 3 confirmations
    provider.removeListener("block", handler);
});

In v5, this will be much easier, since you can just use provider.on("fork") or use a more complex event:

let forkEvent = new ForkEvent();

// Trigger if the block is orphaned
forkEvent.watchBlock(hash);

// Trigger if the confirmations ever lower
forkEvent.watchTransaction(hash);

// Trigger if the block hash (once set) changes
forkEvent.watchTransactionBlock(hash);

// Trigger if the transaction does not happen after other
formEvent.watchTransactionAfter(hash, otherHash);

provider.on(forkEvent, (event) => {
})

This API is still experimental, and I'm working on it now. :)

[pstuermlinger]

Hi Richard,
could receipt == null not also mean "hasn't been mined yet"? So probably the condition should be if (lastConfirms > 0 && (receipt == null || receipt.confirmations < lastConfirms)), shouldn't it?

The capabilities of the v5 API are looking promising. I'm very delighted at it :)

Thanks for your constant support and development on this project! :+1:

[EvilJordan]

Just found this closed issue and am thrilled there's already some thinking around it!

What would you recommend is the best way these days, given this is a year-and-a-half old, to wait to parse a transaction once a certain number of confirmations are hit, without blocking the rest of the program?

[EvilJordan]

Obviously, tx.wait(n) is the right way to do this, but how to combine with a contract listener with filter?

Does this make sense?:

contract.on(filter, (from, to, value, event) => {
    parseTransaction(event);
});

parseTransaction = async (transaction) => {
    const tx = await transaction.getTransaction();
    tx.wait(5);
    ...
}

[ricmoo]

@EvilJordan

Something like that would work fine, or you could use await provider.waitForTransaction(event.transactionHash, 5);

It probably makes sense for me to add confimarions to the event.getTransactionReceipt in v6... I’ll add it to my todo list. :)

[EvilJordan]

It works! Happy New Year! 🥳