Refundable Tokens

Abstract

This ERC adds refund functionality for initial token offerings to ERC-20, ERC-721, and ERC-1155. Funds are held in escrow until a predetermined time before they are claimable. Until that predetermined time passes, users can receive a refund for tokens they have purchased.

Motivation

The NFT and token spaces lack accountability. For the health of the ecosystem as a whole, better mechanisms to prevent rugpulls from happening are needed. Offering refunds provides greater protection for buyers and increases legitimacy for creators.

A standard interface for this particular use case allows for certain benefits:

• Greater Compliance with EU "Distance Selling Regulations," which require a 14-day refund period for goods (such as tokens) purchased online
• Interoperability with various NFT-related applications, such as portfolio browsers, and marketplaces
  • NFT marketplaces could place a badge indicating that the NFT is still refundable on listings, and offer to refund NFTs instead of listing them on the marketplace
  • DExes could offer to refund tokens if doing so would give a higher yield
• Better wallet confirmation dialogs
  • Wallets can better inform the user of the action that is being taken (tokens being refunded), similar to how transfers often have their own unique dialog
  • DAOs can better display the functionality of smart proposals that include refunding tokens

Specification

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

All implementations MUST use and follow the directions of ERC-165.

ERC-20 Refund Extension

// SPDX-License-Identifier: CC0-1.0

pragma solidity ^0.8.17;

import "ERC20.sol";
import "ERC165.sol";

/// @notice Refundable ERC-20 tokens
/// @dev    The ERC-165 identifier of this interface is `0xf0ca2917`
interface ERC20Refund is ERC20, ERC165 {
    /// @notice           Emitted when a token is refunded
    /// @dev              Emitted by `refund`
    /// @param  _from     The account whose assets are refunded
    /// @param  _amount   The amount of token (in terms of the indivisible unit) that was refunded
    event Refund(
        address indexed _from,
        uint256 indexed _amount
    );

    /// @notice           Emitted when a token is refunded
    /// @dev              Emitted by `refundFrom`
    /// @param  _sender   The account that sent the refund
    /// @param  _from     The account whose assets are refunded
    /// @param  _amount   The amount of token (in terms of the indivisible unit) that was refunded
    event RefundFrom(
        address indexed _sender,
        address indexed _from,
        uint256 indexed _amount
    );

    /// @notice         As long as the refund is active, refunds the user
    /// @dev            Make sure to check that the user has the token, and be aware of potential re-entrancy vectors
    /// @param  amount  The `amount` to refund
    function refund(uint256 amount) external;

    /// @notice         As long as the refund is active and the sender has sufficient approval, refund the tokens and send the ether to the sender
    /// @dev            Make sure to check that the user has the token, and be aware of potential re-entrancy vectors
    ///                 The ether goes to msg.sender.
    /// @param  from    The user from which to refund the assets
    /// @param  amount  The `amount` to refund
    function refundFrom(address from, uint256 amount) external;

    /// @notice         Gets the refund price
    /// @return _wei    The amount of ether (in wei) that would be refunded for a single token unit (10**decimals indivisible units)
    function refundOf() external view returns (uint256 _wei);
 
    /// @notice         Gets the first block for which the refund is not active
    /// @return block   The first block where the token cannot be refunded
    function refundDeadlineOf() external view returns (uint256 block);
}

ERC-721 Refund Extension

// SPDX-License-Identifier: CC0-1.0

pragma solidity ^0.8.17;

import "ERC721.sol";
import "ERC165.sol";

/// @notice Refundable ERC-721 tokens
/// @dev    The ERC-165 identifier of this interface is `0xe97f3c83`
interface ERC721Refund is ERC721 /* , ERC165 */ {
    /// @notice           Emitted when a token is refunded
    /// @dev              Emitted by `refund`
    /// @param  _from     The account whose assets are refunded
    /// @param  _tokenId  The `tokenId` that was refunded
    event Refund(
        address indexed _from,
        uint256 indexed _tokenId
    );

    /// @notice           Emitted when a token is refunded
    /// @dev              Emitted by `refundFrom`
    /// @param  _sender   The account that sent the refund
    /// @param  _from     The account whose assets are refunded
    /// @param  _tokenId  The `tokenId` that was refunded
    event RefundFrom(
        address indexed _sender,
        address indexed _from,
        uint256 indexed _tokenId
    );

    /// @notice         As long as the refund is active for the given `tokenId`, refunds the user
    /// @dev            Make sure to check that the user has the token, and be aware of potential re-entrancy vectors
    /// @param  tokenId The `tokenId` to refund
    function refund(uint256 tokenId) external;

    /// @notice         As long as the refund is active and the sender has sufficient approval, refund the token and send the ether to the sender
    /// @dev            Make sure to check that the user has the token, and be aware of potential re-entrancy vectors
    ///                 The ether goes to msg.sender.
    /// @param  from    The user from which to refund the token
    /// @param  tokenId The `tokenId` to refund
    function refundFrom(address from, uint256 tokenId) external;

    /// @notice         Gets the refund price of the specific `tokenId`
    /// @param  tokenId The `tokenId` to query
    /// @return _wei    The amount of ether (in wei) that would be refunded
    function refundOf(uint256 tokenId) external view returns (uint256 _wei);
 
    /// @notice         Gets the first block for which the refund is not active for a given `tokenId`
    /// @param  tokenId The `tokenId` to query
    /// @return block   The first block where token cannot be refunded
    function refundDeadlineOf(uint256 tokenId) external view returns (uint256 block);
}

Optional ERC-721 Batch Refund Extension

// SPDX-License-Identifier: CC0-1.0;

import "ERC721Refund.sol";

/// @notice Batch Refundable ERC-721 tokens
/// @dev    The ERC-165 identifier of this interface is ``
contract ERC721BatchRefund is ERC721Refund {
    /// @notice           Emitted when one or more tokens are batch refunded
    /// @dev              Emitted by `refundBatch`
    /// @param  _from     The account whose assets are refunded
    /// @param  _tokenId  The `tokenIds` that were refunded
    event RefundBatch(
        address indexed _from,
        uint256[] _tokenIds // This may or may not be indexed
    );

    /// @notice           Emitted when one or more tokens are batch refunded
    /// @dev              Emitted by `refundFromBatch`
    /// @param  _sender   The account that sent the refund
    /// @param  _from     The account whose assets are refunded
    /// @param  _tokenId  The `tokenId` that was refunded
    event RefundFromBatch(
        address indexed _sender,
        address indexed _from,
        uint256 indexed _tokenId
    );
    
    /// @notice           As long as the refund is active for the given `tokenIds`, refunds the user
    /// @dev              Make sure to check that the user has the tokens, and be aware of potential re-entrancy vectors
    ///                   These must either succeed or fail together; there are no partial refunds.
    /// @param  tokenIds  The `tokenId`s to refund
    function refundBatch(uint256[] tokenIds) external;

    /// @notice           As long as the refund is active for the given `tokenIds` and the sender has sufficient approval, refund the tokens and send the ether to the sender
    /// @dev              Make sure to check that the user has the tokens, and be aware of potential re-entrancy vectors
    ///                   The ether goes to msg.sender.
    ///                   These must either succeed or fail together; there are no partial refunds.
    /// @param  from      The user from which to refund the token
    /// @param  tokenIds  The `tokenId`s to refund
    function refundFromBatch(address from, uint256[] tokenIds) external;
}

ERC-1155 Refund Extension

// SPDX-License-Identifier: CC0-1.0

pragma solidity ^0.8.17;

import "ERC1155.sol";
import "ERC165.sol";

/// @notice Refundable ERC-1155 tokens
/// @dev    The ERC-165 identifier of this interface is `0x94029f5c`
interface ERC1155Refund is ERC1155 /* , ERC165 */ {
    /// @notice           Emitted when a token is refunded
    /// @dev              Emitted by `refund`
    /// @param  _from     The account that requested a refund
    /// @param  _tokenId  The `tokenId` that was refunded
    /// @param  _amount   The amount of `tokenId` that was refunded
    event Refund(
        address indexed _from,
        uint256 indexed _tokenId,
        uint256 _amount
    );

    /// @notice           Emitted when a token is refunded
    /// @dev              Emitted by `refundFrom`
    /// @param  _sender   The account that sent the refund
    /// @param  _from     The account whose assets are refunded
    /// @param  _tokenId  The `tokenId` that was refunded
    /// @param  _amount   The amount of `tokenId` that was refunded
    event RefundFrom(
        address indexed _sender,
        address indexed _from,
        uint256 indexed _tokenId
    );

    /// @notice         As long as the refund is active for the given `tokenId`, refunds the user
    /// @dev            Make sure to check that the user has enough tokens, and be aware of potential re-entrancy vectors
    /// @param  tokenId The `tokenId` to refund
    /// @param  amount  The amount of `tokenId` to refund
    function refund(uint256 tokenId, uint256 amount) external;

    /// @notice         As long as the refund is active and the sender has sufficient approval, refund the tokens and send the ether to the sender
    /// @dev            Make sure to check that the user has enough tokens, and be aware of potential re-entrancy vectors
    ///                 The ether goes to msg.sender.
    /// @param  from    The user from which to refund the token
    /// @param  tokenId The `tokenId` to refund
    /// @param  amount  The amount of `tokenId` to refund
    function refundFrom(address from, uint256 tokenId, uint256 amount) external;

    /// @notice         Gets the refund price of the specific `tokenId`
    /// @param  tokenId The `tokenId` to query
    /// @return _wei    The amount of ether (in wei) that would be refunded for a single token
    function refundOf(uint256 tokenId) external view returns (uint256 _wei);

    /// @notice         Gets the first block for which the refund is not active for a given `tokenId`
    /// @param  tokenId The `tokenId` to query
    /// @return block   The first block where the token cannot be refunded
    function refundDeadlineOf(uint256 tokenId) external view returns (uint256 block);
}

Optional ERC-1155 Batch Refund Extension

// SPDX-License-Identifier: CC0-1.0;

import "ERC1155Refund.sol";

/// @notice Batch Refundable ERC-1155 tokens
/// @dev    The ERC-165 identifier of this interface is ``
contract ERC1155BatchRefund is ERC1155Refund {
    /// @notice           Emitted when one or more tokens are batch refunded
    /// @dev              Emitted by `refundBatch`
    /// @param  _from     The account that requested a refund
    /// @param  _tokenIds The `tokenIds` that were refunded
    /// @param  _amounts  The amount of each `tokenId` that was refunded
    event RefundBatch(
        address indexed _from,
        uint256[] _tokenIds, // This may or may not be indexed
        uint256[] _amounts
    );

    /// @notice           Emitted when one or more tokens are batch refunded
    /// @dev              Emitted by `refundFromBatch`
    /// @param  _sender   The account that sent the refund
    /// @param  _from     The account whose assets are refunded
    /// @param  _tokenIds The `tokenIds` that was refunded
    /// @param  _amounts  The amount of each `tokenId` that was refunded
    event RefundFromBatch(
        address indexed _sender,
        address indexed _from,
        uint256[] _tokenId, // This may or may not be indexed
        uint256[] _amounts
    );
    
    /// @notice           As long as the refund is active for the given `tokenIds`, refunds the user
    /// @dev              Make sure to check that the user has enough tokens, and be aware of potential re-entrancy vectors
    ///                   These must either succeed or fail together; there are no partial refunds.
    /// @param  tokenIds  The `tokenId`s to refund
    /// @param  amounts   The amount of each `tokenId` to refund
    function refundBatch(uint256[] tokenIds, uint256[] amounts) external;

    /// @notice           As long as the refund is active for the given `tokenIds` and the sender has sufficient approval, refund the tokens and send the ether to the sender
    /// @dev              Make sure to check that the user has the tokens, and be aware of potential re-entrancy vectors
    ///                   The ether goes to msg.sender.
    ///                   These must either succeed or fail together; there are no partial refunds.
    /// @param  from      The user from which to refund the token
    /// @param  tokenIds  The `tokenId`s to refund
    /// @param  amounts   The amount of each `tokenId` to refund
    function refundFromBatch(address from, uint256[] tokenIds, uint256[] amounts external;
}

Rationale

refundDeadlineOf uses blocks instead of timestamps, as timestamps are less reliable than block numbers.

The function names of refund, refundOf, and refundDeadlineOf were chosen to fit the naming style of ERC-20, ERC-721, and ERC-1155.

ERC-165 is required as introspection by DApps would be made significantly harder if it were not.

Custom ERC-20 tokens are not supported, as it needlessly increases complexity, and the refundFrom function allows for this functionality when combined with a DEx.

Batch refunds are optional, as account abstraction would make atomic operations like these significantly easier. However, they might still reduce gas costs if properly implemented.

Backwards Compatibility

No backward compatibility issues were found.

Security Considerations

There is a potential re-entrancy risk with the refund function. Make sure to perform the ether transfer after the tokens are destroyed (i.e. obey the checks, effects, interactions pattern).

Copyright

Copyright and related rights waived via CC0.