mirror of https://github.com/status-im/EIPs.git
154 lines
4.1 KiB
Markdown
154 lines
4.1 KiB
Markdown
## Preamble
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EIP: <to be assigned> (I Suggest 20)
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Title: <EIP title>
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Author: Fabian Vogelsteller <fabian@ethereum.org>, Vitalik Buterin <vitalik.buterin@ethereum.org>
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Type: Informational
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Status: Draft
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Created: 2015-11-19
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## Simple Summary
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A standard interface for tokens.
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## Abstract
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The following standard allows for the implementation of a standard API for tokens within their smart contracts:
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it primarily provides basic functionality to transfer tokens and allow them to be approved to be spend by another on-chain third party.
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## Motivation
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A standard interface allows any tokens on Ethereum to be re-used by other applications: from wallets to decentralized exchanges.
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## Specification
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## Token
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### Methods
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**NOTE**: An important point is that callers should handle `false` from `returns (bool success)`. Callers should not assume that `false` is never returned!
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#### name
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``` js
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function name() constant returns (string name)
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```
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Returns the name of the token. E.g. "MyToken"
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#### symbol
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``` js
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function symbol() constant returns (string symbol)
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```
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Returns the symbol of the token. E.g. "MYT"
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#### decimals
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``` js
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function decimals() constant returns (uint8 decimals)
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```
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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.
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#### totalSupply
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``` js
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function totalSupply() constant returns (uint256 totalSupply)
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```
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Get the total token supply
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#### balanceOf
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``` js
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function balanceOf(address _owner) constant returns (uint256 balance)
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```
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Get the account balance of another account with address `_owner`
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#### transfer
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``` js
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function transfer(address _to, uint256 _value) returns (bool success)
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```
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Transfer `_value` amount of tokens to address `_to`
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#### transferFrom
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``` js
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function transferFrom(address _from, address _to, uint256 _value) returns (bool success)
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```
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Send `_value` amount of tokens from address `_from` to address `_to`
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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:
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#### approve
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``` js
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function approve(address _spender, uint256 _value) returns (bool success)
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```
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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.
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To prevent attack vectors like the one described here: https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/
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make sure to set the allowance to 0 before setting it to another value for the same spender.
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#### allowance
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``` js
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function allowance(address _owner, address _spender) constant returns (uint256 remaining)
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```
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Returns the amount which `_spender` is still allowed to withdraw from `_owner`
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### Events
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#### Transfer
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``` js
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event Transfer(address indexed _from, address indexed _to, uint256 _value)
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```
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Triggered when tokens are transferred.
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#### Approval
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``` js
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event Approval(address indexed _owner, address indexed _spender, uint256 _value)
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```
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Triggered whenever `approve(address _spender, uint256 _value)` is called.
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## Implementation
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There are already plenty of ERC20-compliant tokens deployed on the Ethereum network and is the most widely used standard.
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Different implementations have been written by various teams that have different trade-offs: from gas saving to improved security.
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#### Example implementations are available at
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- https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/StandardToken.sol
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- https://github.com/ConsenSys/Tokens/blob/master/Token_Contracts/contracts/StandardToken.sol
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#### Implementation adding the force 0 before calling approve again:
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- https://github.com/Giveth/minime/blob/master/MiniMeToken.sol
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## Copyright
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Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
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