parse transaction logs to get NFT Transfer information

Question

Is there any easy way to parse transaction logs in order to get information about: who sent the token who received the token what token has been transferred what was the price for that

?

Answer 1

Yes. Use web3 getPastEvents filtering the Transfer event.

https://web3js.readthedocs.io/en/v1.7.3/web3-eth-contract.html#getpastevents

Answer 2

Dev Advocate at Chainstack.

You can use a simple script to fetch and decode logs using ethers.js.

Here is an example to fetch the Transfer event from the BAYC collection:

const ethers = require('ethers');

// Initialize connection to the node. 
const nodeUrl = "CHAINSTACK_NODE_URL";
const provider = new ethers.JsonRpcProvider(nodeUrl);

// Import and parse ABI for ERC-721 standard.
const abi = [
  // Importing the 'Transfer' event part of the ABI for ERC-721.
  "event Transfer(address indexed from, address indexed to, uint256 indexed tokenId)"
];

// Create contract instance using an ERC-721 contract address and ABI.
// Replace this address with your desired ERC-721 token contract address.
const address = '0xBC4CA0EdA7647A8aB7C2061c2E118A18a936f13D';
const contract = new ethers.Contract(address, abi, provider)

async function getLogs() {
  const range = 500; // Define the range of blocks you're interested in.
  const latestBlock = await provider.getBlockNumber();
  const from = latestBlock - range;

  // queryFilter to get 'Transfer' event logs.
  const transferEvents = await contract.queryFilter('Transfer', from, latestBlock);
  return transferEvents;
}

async function main() {
  const logs = await getLogs();

  // Parse and log the details of each transfer.
  for (let object of logs) {
      console.log(`Transaction hash: ${object.transactionHash}`);
      console.log(`From: ${object.args.from}`);
      console.log(`To: ${object.args.to}`);
      console.log(`Token ID transferred: ${object.args.tokenId.toString()} \n`);
  }
}

main();

This will parse and decode the following fields:

• Transaction hash
• From
• To
• Token ID

And will give you a similar log:

Transaction hash: 0xdb662be3d9916db892036e37b5e02ed137261034e8db182271682ac1992c3220
From: 0x4Ec2F9588B7BD0f4976651d2B6c7315d6B866f15
To: 0xde02FFFb824720E25674a604BaF2277f21c66a0F
Token ID transferred: 4500 

To fetch the price is a bit more complex. You could use the debug_traceTransaction method on the transaction hash to see all the internal steps and find out how much ETH was exchanged for the NFT.