ZTP-20

Simple Summary

A standard interface for tokens.

Abstract

The following standard allows for the implementation of a standard API for tokens within smart contracts. This standard provides basic functionality to transfer tokens, as well as allow tokens to be approved so they can be spent by another on-chain third party.

Motivation

A standard interface allows any tokens on Zetrix to be re-used by other applications: from wallets to decentralized exchanges.

Specification Token Methods

Matadata

name

Returns the name of the token - e.g. "MyToken"

OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.

self.name = function () {
    let info = BasicOperationUtil.loadObj(CONTRACT_INFO);
    return info.name;
};

symbol

Returns the symbol of the token. E.g. “MYTKN”

OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present.

self.symbol = function () {
    let info = BasicOperationUtil.loadObj(CONTRACT_INFO);
    return info.symbol;
};

decimals

Returns the number of decimals the token uses - e.g. 6, means to divide the token amount by 1000000 to get its user representation.

self.decimals = function () {
        let info = BasicOperationUtil.loadObj(CONTRACT_INFO);
        return info.decimals;
};

Core

totalSupply

Returns the total token supply.

self.totalSupply = function () {
    let info = BasicOperationUtil.loadObj(CONTRACT_INFO);
    let supply = info.supply;
    if (supply === false) {
        supply = "0";
    }
    return supply;
};

balanceOf

Returns the account balance of another account with address account.

self.balanceOf = function (paramObj) {
    let balance = BasicOperationUtil.loadObj(BasicOperationUtil.getKey(BALANCES_PRE, paramObj.account));
    if (balance === false) {
        balance = "0";
    }
    return balance;
};

transfer

Transfers value amount of tokens to address to. The function SHOULD throw an exception if the message caller’s account balance does not have enough tokens to spend.

self.transfer = function (paramObj) {
    _transfer(Chain.msg.sender, paramObj.to, paramObj.value);
    return true;
};

transferFrom

Transfers value amount of tokens from address from to address to.

The transferFrom method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf. This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies. The function SHOULD throw an exception unless the from account has deliberately authorized the sender of the message.

self.transferFrom = function (paramObj) {
    let spender = Chain.msg.sender;
    self.p.spendAllowance(paramObj.from, spender, paramObj.value);
    _transfer(paramObj.from, paramObj.to, paramObj.value);
    return true;
};

approve

Allows spender to withdraw from your account multiple times, up to the value amount. If this function is called again it overwrites the current allowance with value.

self.approve = function (paramObj) {
    self.p.approve(Chain.msg.sender, paramObj.spender, paramObj.value);
    return true;
};

allowance

Returns the amount which spender is still allowed to withdraw from owner.

self.allowance = function (paramObj) {
    let allowance = BasicOperationUtil.loadObj(BasicOperationUtil.getKey(ALLOWANCES_PRE, paramObj.owner, paramObj.spender));
    if (allowance === false) {
        allowance = "0";
    }
    return allowance;
};

Extension

Permit

The permit function enables gasless approvals for ZTP20 tokens by allowing an owner to approve a spender via an off-chain signature, instead of an on-chain approve transaction. This design is inspired by EIP-2612, adapted for the Zetrix / ZTP20 execution environment and cryptographic primitives.

The permit mechanism allows a token holder to approve an allowance via an off-chain signature, which may subsequently be submitted on-chain by any relayer that pays the associated transaction fee.

Function Signature

function permit(owner, spender, value, deadline, p, s){
  let nonce = useNonce(owner);
  let hash = Utils.sha256(PERMIT_TYPEHASH + owner + spender + value + nonce.toString() + deadline, 1);
  let validateSign = Utils.ecVerify(s, p, hash);
  let validatePubKey = Utils.toAddress(p) === owner;
  let allowKey = makeAllowanceKey(owner, spender);
  Chain.store(allowKey, value);
  Chain.tlog('Approval', owner, spender, value);
  Chain.tlog('Permit', owner, spender, value, deadline);
  return true;
}

Parameters

Parameter	Type	Description
owner	address	Token holder granting the allowance
spender	address	Address receiving spending rights
value	int64 (string)	Allowance amount to approve
deadline	int64 (string)	Expiration timestamp for the permit
p	bytes	Public key of the signer
s	bytes	Signature generated by the owner

Zetrix Ecosystem Proposals

Sample ZTP20 contract can be found here.