Listening for account and extracting output from transaction, how to get block resulting from slot?

Question

I just got started with Solana so please be gentle :)

I'm trying to extract information from a transaction in order to perform subsequent processing. I'm using @solana/web3.js with connection.getBlock to query a block and I can extract the information I need.

However the problem is that I want to extract this information as soon as the transaction has been finalized. I was under the impression that I could just listen for changes to a certain account using connection.onAccountChange and then using information from the callback to query the transaction. However the event provides me with a slot which seems to be 1 or 2 integer values lower than the block in which the transaction is finalized.

I thought that changing the commitment level to finalized on the connection and in the getBlock call would do the job, but this just gives me a wrong block.

The code I just is:

const connection = new web3.Connection(web3.clusterApiUrl('mainnet-beta'), 'finalized');
const sub = createSubscription = connection.onAccountChange(
    pubkey,
    async (accountInfo, context) => {
        const blockConfig = {
            maxSupportedTransactionVersion: 1, 
            transactionDetails: 'full', 
            rewards: false,
            commitment: 'finalized'
        };
        const block = await connection.getBlock(context.slot, blockConfig);
        // block is not null, it just doesn't contain my transaction. If I look on-chain
        // the transaction is actually in block# -> context.slot+1 or context.slot+2 
    }, 
    {
        'commitment': 'finalized'
    }
);

Is there some built-in way to do what I'm trying to achieve? Basically get the block that contains the finalized transaction that triggered onAccountChange?

Answer 1

You can try this. I just modified your code

const connection = new web3.Connection(web3.clusterApiUrl('mainnet-beta'), 'finalized');

const sub = connection.onAccountChange( pubkey, async (accountInfo, context) => { let block = null; const blockConfig = { maxSupportedTransactionVersion: 1, transactionDetails: 'full', rewards: false, commitment: 'finalized' };

    // Try getting the block in the current slot, and if not found, check the next two slots
    for (let i = 0; i < 3; i++) {
        block = await connection.getBlock(context.slot + i, blockConfig);
        if (block && block.transactions && block.transactions.length > 0) {
            // Check if the block contains your transaction
            const transactionFound = block.transactions.find(tx => {
                // Add your logic to find the specific transaction
                // For example, by checking tx.transaction.signatures or other criteria
                return tx.transaction.signatures.includes("your-transaction-signature");
            });

            if (transactionFound) {
                console.log("Transaction found in block:", context.slot + i);
                break;
            }
        }
    }

    if (!block) {
        console.error("Transaction not found in expected slots");
    }
}, 
{ commitment: 'finalized' }

);

Using getConfirmedSignaturesForAddress2 allows you to get the signatures of confirmed transactions affecting a specific account and then retrieve the transaction details using those signatures.

You can read more about this here => https://solana-labs.github.io/solana-web3.js/