[Ethereum] token sell and buy prices

contract-designcontract-development

Hi for a while now i have been testing ethereum capabilities and there is something i wanted to test and i cant figure how to do. When creating a contract of a custom token (using the code given in the ethereum official site) there is a sell price to set and a buy price for a token, in what way can i use this to give a token sell price of another token?

What I mean is, is there a way to give token A price in token B? essentialy making it possible to a user who have Token B to buy token A? and could a contract hold more than 1 kind of a token? like a contract that holds both token A and B? and maybe even more?

Best Answer

The Token contract has a function that allows the token owner to approve an address for a certain amount. This other address will be able to send up to this amount of the approver's tokens:

function approve(address _spender, uint256 _value) {}

So let's say you have 2 people Alice and Bob. Alice has 3 TokenA and Bob has 4 TokenB. They agree to exchange them. You create the re-usable Trade contract to make that happen.

contract Trade {
    function exchange(address alice, 
                    address tokenA,
                    uint qtyTokenA,
                    address bob,
                    address tokenB,
                    uint qtyTokenB) 
        returns (bool success) {
        success = Token(tokenA).transferFrom(alice, bob, qtyTokenA)
            && Token(tokenB).transferFrom(bob, alice, qtyTokenB);
        if (!success) throw;
    }
}

In TokenA, Alice approves the trade contract for 3. In TokenB, Bob approves the trade contract for 4. Then someone calls the exchange function with the proper values.

I understand that, as it stands, there is a security risk whereby Carol calls the method before others, to steal from Alice. IRL, you would have Alice and Bob to both approve the exchange function call.

To get the price

First you'll have to get the price. You can get price easily by using Chainlink Price Feeds.

// note, this is using node.js syntax. see the docs for remix syntax
pragma solidity ^0.6.7;

import "@chainlink/contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";

contract PriceConsumerV3 {

    AggregatorV3Interface internal priceFeed;

    /**
     * Network: Kovan
     * Aggregator: ETH/USD
     * Address: 0x9326BFA02ADD2366b30bacB125260Af641031331
     */
    constructor() public {
        priceFeed = AggregatorV3Interface(0x9326BFA02ADD2366b30bacB125260Af641031331);
    }

    /**
     * Returns the latest price
     */
    function getLatestPrice() public view returns (int) {
        (
            uint80 roundID, 
            int price,
            uint startedAt,
            uint timeStamp,
            uint80 answeredInRound
        ) = priceFeed.latestRoundData();
        // If the round is not complete yet, timestamp is 0
        require(timeStamp > 0, "Round not complete");
        return price;
    }
}

Otherwise you can use an oracle to make an API call to an API with the price.

To make it dynamic

You'll need some off-chain service making a call to update periodically. You could use something like the Chainlink alarm clock, or Chainlink cron initiator for it to be automatic. You'd set one of these up to call your price updating contract (deployed from above) at the intervals you'd please.

Hope it helps.

[Ethereum] ERC223 Token Fallback Function Usage

After the "Trade" Smart Contract received the token, Token Fallback Function in "Trade" Smart Contract is called and executed the "Sell" function in that Contract.

Yes.

As you can see, in the transfer function, if the receiver is a contract, then it must have the a fallback function for the token, otherwise it won't work.

You need to implement this function in your contract.

if(isContract(_to)) {
        ERC223ReceivingContract receiver = ERC223ReceivingContract(_to);
        receiver.tokenFallback(msg.sender, _value, _data);
    }

As you can see, based on the abstract contract ERC223ReceivingContract, the signature of the function must be :

function tokenFallback(address _from, uint _value, bytes _data) public

Best Answer

Related Solutions

[Ethereum] How to set dynamic buy and sell price for the token

To get the price

To make it dynamic

[Ethereum] ERC223 Token Fallback Function Usage

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