4.1 KiB
Preamble
EIP: <to be assigned> (I Suggest 20)
Title: <EIP title>
Author: Fabian Vogelsteller <fabian@ethereum.org>, Vitalik Buterin <vitalik.buterin@ethereum.org>
Type: Informational
Status: Draft
Created: 2015-11-19
Simple Summary
A standard interface for tokens.
Abstract
The following standard allows for the implementation of a standard API for tokens within their smart contracts: it primarily provides basic functionality to transfer tokens and allow them to be approved to be spend by another on-chain third party.
Motivation
A standard interface allows any tokens on Ethereum to be re-used by other applications: from wallets to decentralized exchanges.
Specification
Token
Methods
NOTE: An important point is that callers should handle false from returns (bool success). Callers should not assume that false is never returned!
name
function name() constant returns (string name)
Returns the name of the token. E.g. "MyToken"
symbol
function symbol() constant returns (string symbol)
Returns the symbol of the token. E.g. "MYT"
decimals
function decimals() constant returns (uint8 decimals)
Returns the number of decimals the token uses. E.g. 8, which would mean to divide the token amount by 100000000 to get its user representation.
totalSupply
function totalSupply() constant returns (uint256 totalSupply)
Get the total token supply
balanceOf
function balanceOf(address _owner) constant returns (uint256 balance)
Get the account balance of another account with address _owner
transfer
function transfer(address _to, uint256 _value) returns (bool success)
Transfer _value amount of tokens to address _to
transferFrom
function transferFrom(address _from, address _to, uint256 _value) returns (bool success)
Send _value amount of tokens from address _from to address _to
The transferFrom method is used for a withdraw workflow, allowing contracts to send tokens on your behalf, for example to "deposit" to a contract address and/or to charge fees in sub-currencies; the command should fail unless the _from account has deliberately authorized the sender of the message via some mechanism; we propose these standardized APIs for approval:
approve
function approve(address _spender, uint256 _value) returns (bool success)
Allow _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. To prevent attack vectors like the one described here: https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/ make sure to set the allowance to 0 before setting it to another value for the same spender.
allowance
function allowance(address _owner, address _spender) constant returns (uint256 remaining)
Returns the amount which _spender is still allowed to withdraw from _owner
Events
Transfer
event Transfer(address indexed _from, address indexed _to, uint256 _value)
Triggered when tokens are transferred.
Approval
event Approval(address indexed _owner, address indexed _spender, uint256 _value)
Triggered whenever approve(address _spender, uint256 _value) is called.
Implementation
There are already plenty of ERC20-compliant tokens deployed on the Ethereum network and is the most widely used standard. Different implementations have been written by various teams that have different trade-offs: from gas saving to improved security.
Example implementations are available at
- https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/StandardToken.sol
- https://github.com/ConsenSys/Tokens/blob/master/Token_Contracts/contracts/StandardToken.sol
Implementation adding the force 0 before calling approve again:
Copyright
Copyright and related rights waived via CC0.