SEP20: Tokens on smartBCH

1. Summary

This SEP proposes an interface standard to create token contracts on smartBCH.

2. Abstract

The following standard defines the implementation of APIs for token smart contracts. It is proposed by deriving the ERC20 protocol of Ethereum and provides the basic functionality to transfer tokens, allow tokens to be approved so they can be spent by another on-chain third party.

3. Motivation

A standard interface allows any tokens on smartBCH to be used by other applications: from wallets to decentralized exchanges in a consistent way. Besides, this standard interface also extends ERC20 to facilitate cross chain transfer.

4. Status

This SEP is under draft.

5. Specification

5.1 Token

NOTES:

  • The following specifications use syntax from Solidity 0.5.16 (or above)

  • Callers MUST handle false from returns (bool success). Callers MUST NOT assume that false is never returned!

5.1.1 Methods

5.1.1.1 name

function name() external view returns (string)
  • 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.

5.1.1.2 symbol

function symbol() external view returns (string)
  • Returns the symbol of the token. E.g. β€œHIX”.

  • This method can be used to improve usability

  • NOTE - This method is optional in EIP20. In SEP20, this is a required method.

5.1.1.3 decimals

function decimals() external view returns (uint8)
  • Returns the number of decimals the token uses - e.g. 8, means to divide the token amount by 100000000 to get its user representation.

  • This method can be used to improve usability

  • NOTE - This method is optional in EIP20. In SEP20, this is a required method.

5.1.1.4 totalSupply

function totalSupply() external view returns (uint256)
  • Returns the total token supply.

5.1.1.5 balanceOf

function balanceOf(address _owner) external view returns (uint256 balance)
  • Returns the account balance of another account with address _owner.

5.1.1.6 owner

function owner() external view returns (address);
  • Returns the sep20 token owner which is necessary for binding with sep20 token.

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

5.1.1.7 transfer

function transfer(address _to, uint256 _value) external returns (bool success)
  • Transfers _value amount of tokens to address _to, and MUST fire the Transfer event. The function SHOULD throw if the message caller’s account balance does not have enough tokens to spend.

  • NOTE - Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.

  • NOTE - If there are some permission-control mechanism in the smart contract (such as blacklist), transfers of 0 values MUST be treated as normal transfers and undergo the same permission checks.

5.1.1.8 transferFrom

function transferFrom(address _from, address _to, uint256 _value) external returns (bool success)
  • Transfers _value amount of tokens from address _from to address _to, and MUST fire the Transfer event.

  • 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 unless the _from account has deliberately authorized the sender of the message via some mechanism.

  • NOTE - Transfers of 0 values MUST be treated as normal transfers and fire the Transfer event.

5.1.1.9 approve

function approve(address _spender, uint256 _value) external returns (bool success)
  • 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.

  • NOTE - To prevent attack vectors like the one described here and discussed here, clients SHOULD make sure to create user interfaces in such a way that they set the allowance first to 0 before setting it to another value for the same spender. THOUGH The contract itself shouldn’t enforce it, to allow backwards compatibility with contracts deployed before

5.1.1.10 allowance

function allowance(address _owner, address _spender) external view returns (uint256 remaining)
  • Returns the amount which _spender is still allowed to withdraw from _owner.

5.1.1.11 increaseAllowance

function increaseAllowance(address _spender, uint256 _delta) external returns (bool success)
  • Increases the amount which _spender is still allowed to withdraw from you.

  • OPTIONAL - This method can be used to prevent attack vectors, but interfaces and other contracts MUST NOT expect these values to be present.

5.1.1.12 decreaseAllowance

function decreaseAllowance(address _spender, uint256 _delta) external returns (bool success)
  • Decreases the amount which _spender is still allowed to withdraw from you.

  • OPTIONAL - This method can be used to prevent attack vectors, but interfaces and other contracts MUST NOT expect these values to be present.

5.1.2 Events

5.1.2.1 Transfer

event Transfer(address indexed _from, address indexed _to, uint256 _value)
  • MUST trigger when tokens are transferred, including zero value transfers.

  • A token contract which creates new tokens SHOULD trigger a Transfer event with the _from address set to 0x0 when tokens are created.

5.1.2.2 Approval

event Approval(address indexed _owner, address indexed _spender, uint256 _value)

MUST trigger on any successful call to approve(address _spender, uint256 _value), increaseAllowance(address _spender, uint256 _delta) or decreaseAllowance(address _spender, uint256 _delta). OPTIONAL may trigger on any successful call to transferFrom(address _from, address _to, uint256 _value) which changes allowance, but it is not required.

6. License

The content is licensed under CC0.