How to track payments to contract

Question

Can I track received payments to smart contract on a block explorer or do I need to run a contract method for this? I need the amount and payment identification information (I need to identify the payer somehow - probably he will send some kind of tracking code as payload). Is the answer different for ETH and ERC20 tokens?

Answer 1

For ETH, you can check the amount the smart contract received without having to call any smart contract method, using any block explorer.

Programmatically, using an Ethereum node, you can call the eth.getBalance(<your address>) method to find the ETH balance of any address (including smart contracts).

For ERC20 tokens, you have to call the balanceOf(<your smart contract address>) method of the token's smart contract address.

As a proof, have a look at EtherDelta's smart contract on etherscan.io and see that the contract has ETH balance.

In order to receive payments reliably, it's best for you to generate 1 address/customer, so that your customers are able to send you funds from any wallet they might use.

Answer 2

Getting balance for a given Eth account, you can call below method

eth.getBalance('<ADDRESS>'); //Geth Console

web.eth.getBalance('<ADDRESS>'); //Web3js

Tracking ERC20 payments you no need to write any smart contract. Just need call contractObject.balanceOf().

ERC20 Balances:

contractObj.balanceOf('<ADDRESS>');

Check web3js for live/event driven transfers.

Event Driven:

contractObj.Transfer(function(error, result){
  if(error){
        console.log("Error", error);
        return;
    }
    //result.args.
});

Filter get all the transactions from address and to address for a ERC token:

methodID = web3.sha3('Transfer(address,address,uint256)');
const allEvents = eth.filter({
  fromBlock: 0,
  toBlock: 'latest',
  address: <CONTRACT_ADDRESS>,
  topics: [
    methodID, 
    '0x0000000000000000000000008fa31452a2bf4840ba358ce316defb9b20ad92d3',//FROM 32 Bytes padding
    '0x0000000000000000000000008fa31452a2bf4840ba358ce316defb9b20ad92d3', //TO 32 bytes padding
  ]
});
allEvents.get(function (err, events)) {
  console.log(events);
}

For more details web3js:

http://web3js.readthedocs.io/en/1.0/