Smart Contract Interaction – How to Use Any ERC20

contract-developmenterc-20erc-223solidity

How can I interact with various tokens with my deployed smart contract? I want to be able to receive tokens, count them, and perform logic based on the aforementioned events.

I tried using the ERC20 standard function, Transfer, but cannot figure out how to specify which token is being delivered. I assume, at some point, the address of the ERC20 will need to be included in the function.

In looking at this answer, I get some insight.

Would using ERC223 be the answer here?

Best Answer

Firstly, I assume you mean a smart contract you will deploy, as you can't change the functionality of one already deployed.

With ERC20, there is no function triggered on your contract when it receives tokens, the token contract itself is all that gets called. To detect the change you would need some external program to monitor the blockchain for relevant transactions and fire some method on your contract when it finds one, but this solution isn't ideal.

Alternatively if you have full control over the software that might be sending tokens to your contract, you can have this 'approve' your contract address on the token contract, and then call a function on your smart contract which will perform the 'transferFrom' function, so you are in control of the transfer and can handle it as desired.

In either case you will need to feed your smart contract the token address in order to check balances or perform the 'transferFrom'

If you opt only for compatibility with ERC223 tokens instead, the situation is much simpler - any ERC223 token transfer to your smart contract will call the 'tokenFallback' method on your contract, so you can simply add your desired functionality there.

Related Solutions

Solidity Contract Development – How to Determine ERC20 Compliance

There wasn't a standard to determine if a contract support an interface at the time ERC20 was conceived (*).

Some block explorers and wallets can make verifications, for example for a ERC20 contracts they can verify if the public functions are available and return something useful, ie symbol, name, decimals, etc.

A block explorer that support contract verification can check the ABI for other methods to also be present, ie transfer, approve, etc.

That obviously is not enough, a contract that always throws, return false, or zero (depending on the function) can still comply with the EIP20 standard.

(*) There's now EIP 165 that allows to query a contract for supported interfaces.

[Ethereum] ERC20 tokens transactions’ history from Ethereum node

using ethersjs. This will return all transfer logs for all tokens on the network.

Under the hood it takes the signature from the event out of the ABI , which is the first element needed in the topics array (the remaining optional arguments are the indexed arguments from the event)

It then makes an RPC call for these events to the node you supplied when creating the provider.

On succesful response it parses the received hex-encoded data back to human readable data through reading the types from the ABI.

const provider = new providers.JsonRpcProvider('http...')
const event = (new Interface(StandardToken.abi)).events.Transfer
const topics = [event.topics[0]]
let logs = await provider.getLogs({
  fromBlock: 1,
  toBlock: 'latest',
  topics: topics
})

logs =  logs.map(log => event.parse(log.topics, log.data))

Best Answer

Related Solutions

Solidity Contract Development – How to Determine ERC20 Compliance

[Ethereum] ERC20 tokens transactions’ history from Ethereum node

Related Topic