Payable Token

Simple Summary

Defines a token interface for ERC-20 tokens that supports executing recipient code after transfer or transferFrom, or spender code after approve.

Abstract

Standard functions a token contract and contracts working with tokens can implement to make a token Payable.

transferAndCall and transferFromAndCall will call an onTransferReceived on a ERC1363Receiver contract.

approveAndCall will call an onApprovalReceived on a ERC1363Spender contract.

Motivation

There is no way to execute code after a ERC-20 transfer or approval (i.e. making a payment), so to make an action it is required to send another transaction and pay GAS twice.

This proposal wants to make token payments easier and working without the use of any other listener. It allows to make a callback after a transfer or approval in a single transaction.

There are many proposed uses of Ethereum smart contracts that can accept ERC-20 payments.

Examples could be

• to create a token payable crowdsale
• selling services for tokens
• paying invoices
• making subscriptions

For these reasons it was named as "Payable Token".

Anyway you can use it for specific utilities or for any other purposes who require the execution of a callback after a transfer or approval received.

This proposal has been inspired by the ERC-721 onERC721Received and ERC721TokenReceiver behaviours.

Specification

Implementing contracts MUST implement the ERC-1363 interface as well as the ERC-20 and ERC-165 interfaces.

pragma solidity ^0.8.0;

interface ERC1363 /* is ERC20, ERC165 */ {
  /*
   * Note: the ERC-165 identifier for this interface is 0xb0202a11.
   * 0xb0202a11 ===
   *   bytes4(keccak256('transferAndCall(address,uint256)')) ^
   *   bytes4(keccak256('transferAndCall(address,uint256,bytes)')) ^
   *   bytes4(keccak256('transferFromAndCall(address,address,uint256)')) ^
   *   bytes4(keccak256('transferFromAndCall(address,address,uint256,bytes)')) ^
   *   bytes4(keccak256('approveAndCall(address,uint256)')) ^
   *   bytes4(keccak256('approveAndCall(address,uint256,bytes)'))
   */

  /**
   * @notice Transfer tokens from `msg.sender` to another address and then call `onTransferReceived` on receiver
   * @param to address The address which you want to transfer to
   * @param value uint256 The amount of tokens to be transferred
   * @return true unless throwing
   */
  function transferAndCall(address to, uint256 value) external returns (bool);

  /**
   * @notice Transfer tokens from `msg.sender` to another address and then call `onTransferReceived` on receiver
   * @param to address The address which you want to transfer to
   * @param value uint256 The amount of tokens to be transferred
   * @param data bytes Additional data with no specified format, sent in call to `to`
   * @return true unless throwing
   */
  function transferAndCall(address to, uint256 value, bytes memory data) external returns (bool);

  /**
   * @notice Transfer tokens from one address to another and then call `onTransferReceived` on receiver
   * @param from address The address which you want to send tokens from
   * @param to address The address which you want to transfer to
   * @param value uint256 The amount of tokens to be transferred
   * @return true unless throwing
   */
  function transferFromAndCall(address from, address to, uint256 value) external returns (bool);


  /**
   * @notice Transfer tokens from one address to another and then call `onTransferReceived` on receiver
   * @param from address The address which you want to send tokens from
   * @param to address The address which you want to transfer to
   * @param value uint256 The amount of tokens to be transferred
   * @param data bytes Additional data with no specified format, sent in call to `to`
   * @return true unless throwing
   */
  function transferFromAndCall(address from, address to, uint256 value, bytes memory data) external returns (bool);

  /**
   * @notice Approve the passed address to spend the specified amount of tokens on behalf of msg.sender
   * and then call `onApprovalReceived` on spender.
   * @param spender address The address which will spend the funds
   * @param value uint256 The amount of tokens to be spent
   * @return true unless throwing
   */
  function approveAndCall(address spender, uint256 value) external returns (bool);

  /**
   * @notice Approve the passed address to spend the specified amount of tokens on behalf of msg.sender
   * and then call `onApprovalReceived` on spender.
   * @param spender address The address which will spend the funds
   * @param value uint256 The amount of tokens to be spent
   * @param data bytes Additional data with no specified format, sent in call to `spender`
   * @return true unless throwing
   */
  function approveAndCall(address spender, uint256 value, bytes memory data) external returns (bool);
}

interface ERC20 {
  function totalSupply() external view returns (uint256);
  function balanceOf(address account) external view returns (uint256);
  function transfer(address recipient, uint256 amount) external returns (bool);
  function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
  function allowance(address owner, address spender) external view returns (uint256);
  function approve(address spender, uint256 amount) external returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
  event Approval(address indexed owner, address indexed spender, uint256 value);
}

interface ERC165 {
  function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

A contract that wants to accept token payments via transferAndCall or transferFromAndCall MUST implement the following interface:

/**
 * @title ERC1363Receiver interface
 * @dev Interface for any contract that wants to support `transferAndCall` or `transferFromAndCall`
 *  from ERC1363 token contracts.
 */
interface ERC1363Receiver {
  /*
   * Note: the ERC-165 identifier for this interface is 0x88a7ca5c.
   * 0x88a7ca5c === bytes4(keccak256("onTransferReceived(address,address,uint256,bytes)"))
   */

  /**
   * @notice Handle the receipt of ERC1363 tokens
   * @dev Any ERC1363 smart contract calls this function on the recipient
   * after a `transfer` or a `transferFrom`. This function MAY throw to revert and reject the
   * transfer. Return of other than the magic value MUST result in the
   * transaction being reverted.
   * Note: the token contract address is always the message sender.
   * @param operator address The address which called `transferAndCall` or `transferFromAndCall` function
   * @param from address The address which are token transferred from
   * @param value uint256 The amount of tokens transferred
   * @param data bytes Additional data with no specified format
   * @return `bytes4(keccak256("onTransferReceived(address,address,uint256,bytes)"))`
   *  unless throwing
   */
  function onTransferReceived(address operator, address from, uint256 value, bytes memory data) external returns (bytes4);
}

A contract that wants to accept token payments via approveAndCall MUST implement the following interface:

/**
 * @title ERC1363Spender interface
 * @dev Interface for any contract that wants to support `approveAndCall`
 *  from ERC1363 token contracts.
 */
interface ERC1363Spender {
  /*
   * Note: the ERC-165 identifier for this interface is 0x7b04a2d0.
   * 0x7b04a2d0 === bytes4(keccak256("onApprovalReceived(address,uint256,bytes)"))
   */

  /**
   * @notice Handle the approval of ERC1363 tokens
   * @dev Any ERC1363 smart contract calls this function on the recipient
   * after an `approve`. This function MAY throw to revert and reject the
   * approval. Return of other than the magic value MUST result in the
   * transaction being reverted.
   * Note: the token contract address is always the message sender.
   * @param owner address The address which called `approveAndCall` function
   * @param value uint256 The amount of tokens to be spent
   * @param data bytes Additional data with no specified format
   * @return `bytes4(keccak256("onApprovalReceived(address,uint256,bytes)"))`
   *  unless throwing
   */
  function onApprovalReceived(address owner, uint256 value, bytes memory data) external returns (bytes4);
}

Rationale

The choice to use transferAndCall, transferFromAndCall and approveAndCall derives from the ERC-20 naming. They want to highlight that they have the same behaviours of transfer, transferFrom and approve with the addition of a callback on receiver or spender.

Backwards Compatibility

This proposal has been inspired also by ERC-223 and ERC-677 but it uses the ERC-721 approach, so it doesn't override the ERC-20 transfer and transferFrom methods and defines the interfaces IDs to be implemented maintaining the ERC-20 backwards compatibility.

Security Considerations

The approveAndCall and transferFromAndCall methods can be affected by the same issue of the standard ERC-20 approve and transferFrom method.

Changing an allowance with the approveAndCall methods brings the risk that someone may use both the old and the new allowance by unfortunate transaction ordering.

One possible solution to mitigate this race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards (EIP-20#issuecomment-263524729).

Copyright

Copyright and related rights waived via CC0.