Ethereum BSC blockchain transaction data

Question

I'm trying to play with web3js over the Binance Smart Chain blockchain and I hit a wall understanding the transaction data. I don't understand what determines the number of transfers for a single transaction. And how to retrieve that data using web3js.

I would like to know the amount of BNB paid and the amount of the Tokens received in that transaction and vice versa if the transaction was about selling the tokens instead of buying.

I managed to get the Price paid and token amount but only for transactions where there are 2 Token transfers. But if there are 3 or more I can't manage to get this information.

web3.eth.getTransaction('0x899e7f3c2138d051eb5246850ded99d519ab65eba58e5f806245cf346ab40e83').then((result) => { console.log(result) console.log(web3.utils.fromWei(result.value)) let tx_data = result.input; let input_data = '0x' + tx_data.slice(10); // get only data without function selector let params = web3.eth.abi.decodeParameters([ { indexed: false, internalType: 'uint256', name: 'value', type: 'uint256' }, { indexed: false, internalType: 'uint256', name: 'ethReceived', type: 'uint256' }, ] , input_data); console.log(params) })

This portion of the code gives me data only for 2 token transfers. How to make it return the amount of paid/received cash/tokens no matter how many transfers there are in the transactions?? Is it possible?? From what I can see, always the 1st transfer and the last transfer in the transaction would be the values that I'm interested in. IS there an easy way to get those? I'm struggling with understanding this and getting work with the ABIs for decoding. Can they be somewhat generic?

Answer 1

The "Tokens Transferred" information comes from event logs. Most token standards define an event Transfer(address indexed from, address indexed to, uint256 value), so you can look for logs of this event in the transaction.

Event logs are available in getTransactionReceipt(), not the regular getTransaction().

The indexed modifier in the event definition means that the value is going to be available in the topics property (topics[0] is the keccak256 hash of the event signature, following the indexed values).

const transferEventSignature = web3.utils.keccak256('Transfer(address,address,uint256)'); // 0xddf252... const jsonAbi = [{ "constant" :true, "inputs": [], "name": "decimals", "outputs": [{"name":"","type":"uint8"}], "type": "function" }]; // simplified JSON abi that is only able to read decimals web3.eth.getTransactionReceipt('0x899e7f3c2138d051eb5246850ded99d519ab65eba58e5f806245cf346ab40e83').then(async (result) => { for (const log of result.logs) { if (log.topics[0] !== transferEventSignature) { continue; // only interested in Transfer events } const from = web3.eth.abi.decodeParameter('address', log.topics[1]); const to = web3.eth.abi.decodeParameter('address', log.topics[2]); const value = web3.eth.abi.decodeParameter('uint256', log.data); const tokenContractAddress = log.address; const contractInstance = new web3.eth.Contract(jsonAbi, tokenContractAddress); const decimals = await contractInstance.methods.decimals().call(); console.log('From: ', from); console.log('To: ', to); console.log('Value: ', value); console.log('Token contract: ', tokenContractAddress); console.log('Token decimals: ', decimals); console.log('---'); } });

Output:

From: 0xC6A93610eCa5509E66f9B2a95A5ed1d576cC9b7d To: 0xE437fFf464c6FF2AA5aD5c15B4CCAD98DF38cF52 Value: 31596864050517135 Token contract: 0x78F1A99238109C4B834Ac100d1dfCf14e3fC321C Token decimals: 9 --- From: 0xE437fFf464c6FF2AA5aD5c15B4CCAD98DF38cF52 To: 0x58F876857a02D6762E0101bb5C46A8c1ED44Dc16 Value: 4064578781674512 Token contract: 0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c Token decimals: 18 --- From: 0x58F876857a02D6762E0101bb5C46A8c1ED44Dc16 To: 0xC6A93610eCa5509E66f9B2a95A5ed1d576cC9b7d Value: 2552379452401563824 Token contract: 0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56 Token decimals: 18