Find an ethereum address with a given balance of an ERC-20 token

Question

I know it is easy to lookup the token balance of a particular Ethereum address (e.g. etherscan or via code such as this stackexchange question).

If I want to find a wallet with a particular ERC-20 token balance at a particular point in time is there a way to do this? In other words, is it possible to find a wallet that either currently has (a more simple case perhaps) or at a point in time that can be specified had a certain ERC-20 balance.

For example can I identify an address (or list of addresses) that has/have had:

KNC 100.01

Either currently or at a particular point in time?

And just to be clear, the unknown would be the address. The balance would be known for a particular token.

Answer 1

You can construct a snapshot of all addresses holding a specific token at a specific point in time, using the Transfer events emitted on that token's contract, starting from the moment it was deployed and up until the desired point in time.

For example, in order to construct a snapshot of the KNC token at block #4270000, you can do:

const Web3 = require("web3");
const Decimal = require("decimal.js");
Decimal.set({precision: 80, rounding: Decimal.ROUND_DOWN});

const NODE_ADDRESS  = "YourNodeAddress";
const TOKEN_ADDRESS = "0xdd974d5c2e2928dea5f71b9825b8b646686bd200";
const GENESIS_BLOCK = 4264898;
const DESIRED_BLOCK = 4270000;
const TOKEN_ABI = [
    {"constant":true,"inputs":[],"name":"decimals","outputs":[{"name":"","type":"uint256"}],"payable":false,"type":"function"},
    {"anonymous":false,"inputs":[{"indexed":true,"name":"_from","type":"address"},{"indexed":true,"name":"_to","type":"address"},{"indexed":false,"name":"_value","type":"uint256"}],"name":"Transfer","type":"event"}
];

async function getPastEvents(contract, eventName, fromBlock, toBlock) {
    if (fromBlock <= toBlock) {
        try {
            return await contract.getPastEvents(eventName, {fromBlock: fromBlock, toBlock: toBlock});
        }
        catch (error) {
            const midBlock = (fromBlock + toBlock) >> 1;
            const arr1 = await getPastEvents(contract, eventName, fromBlock, midBlock);
            const arr2 = await getPastEvents(contract, eventName, midBlock + 1, toBlock);
            return [...arr1, ...arr2];
        }
    }
    return [];
}

async function run() {
    const web3 = new Web3(NODE_ADDRESS);
    const contract = new web3.eth.Contract(TOKEN_ABI, TOKEN_ADDRESS);
    const events = await getPastEvents(contract, "Transfer", GENESIS_BLOCK, DESIRED_BLOCK);
    const decimals = await contract.methods.decimals().call();

    const balances = {};

    for (const event of events) {
        const src = Web3.utils.toChecksumAddress(event.returnValues._from);
        const dst = Web3.utils.toChecksumAddress(event.returnValues._to);
        const val = Web3.utils.toBN(event.returnValues._value);
        balances[src] = src in balances ? balances[src].sub(val) : val.neg();
        balances[dst] = dst in balances ? balances[dst].add(val) : val;
    }

    for (const [address, balance] of Object.entries(balances)) {
        if (balance.gtn(0)) {
            console.log(address + " owns " + Decimal(balance.toString()).div(`1e${decimals}`).toFixed() + " tokens");
        }
    }
}

run();