LP-3363: LRC-1363 Payable Token

Abstract

LRC-1363 extends LRC-20 with transferAndCall and approveAndCall functions, enabling tokens to notify receiving contracts in a single transaction. Compatible with ERC-1363.

Motivation

Standard LRC-20 requires two transactions for token payments:

User approves contract
Contract pulls tokens

LRC-1363 enables single-transaction payments:

User calls transferAndCall
Contract receives tokens + callback

Specification

Interface

interface ILRC1363 is ILRC20 {
    function transferAndCall(address to, uint256 value) external returns (bool);
    
    function transferAndCall(
        address to, 
        uint256 value, 
        bytes calldata data
    ) external returns (bool);
    
    function transferFromAndCall(
        address from, 
        address to, 
        uint256 value
    ) external returns (bool);
    
    function transferFromAndCall(
        address from, 
        address to, 
        uint256 value, 
        bytes calldata data
    ) external returns (bool);
    
    function approveAndCall(
        address spender, 
        uint256 value
    ) external returns (bool);
    
    function approveAndCall(
        address spender, 
        uint256 value, 
        bytes calldata data
    ) external returns (bool);
}

Receiver Interface

interface ILRC1363Receiver {
    function onTransferReceived(
        address operator,
        address from,
        uint256 value,
        bytes calldata data
    ) external returns (bytes4);
}

interface ILRC1363Spender {
    function onApprovalReceived(
        address owner,
        uint256 value,
        bytes calldata data
    ) external returns (bytes4);
}

Implementation

contract LRC1363Token is LRC20, ILRC1363 {
    function transferAndCall(
        address to, 
        uint256 value, 
        bytes calldata data
    ) public returns (bool) {
        require(transfer(to, value), "Transfer failed");
        require(
            _checkOnTransferReceived(msg.sender, msg.sender, to, value, data),
            "Receiver rejected"
        );
        return true;
    }
    
    function _checkOnTransferReceived(
        address operator,
        address from,
        address to,
        uint256 value,
        bytes memory data
    ) private returns (bool) {
        if (to.code.length == 0) return true;
        
        try ILRC1363Receiver(to).onTransferReceived(
            operator, from, value, data
        ) returns (bytes4 retval) {
            return retval == ILRC1363Receiver.onTransferReceived.selector;
        } catch {
            return false;
        }
    }
}

Magic Values

bytes4 constant RECEIVER_MAGIC = 0x88a7ca5c; // onTransferReceived selector
bytes4 constant SPENDER_MAGIC = 0x7b04a2d0;  // onApprovalReceived selector

Use Cases

Token Payments

contract Merchant is ILRC1363Receiver {
    function onTransferReceived(
        address, address from, uint256 value, bytes calldata data
    ) external returns (bytes4) {
        bytes32 orderId = abi.decode(data, (bytes32));
        processOrder(orderId, from, value);
        return this.onTransferReceived.selector;
    }
}

Staking

contract StakingPool is ILRC1363Receiver {
    function onTransferReceived(
        address, address from, uint256 value, bytes calldata
    ) external returns (bytes4) {
        stakes[from] += value;
        return this.onTransferReceived.selector;
    }
}

Rationale

Single transaction improves UX
Callback pattern proven (ERC-721)
Backwards compatible with LRC-20

Backwards Compatibility

This standard is fully backwards compatible with existing contracts and infrastructure. The standard is additive and does not modify existing functionality.

Reference Implementation

Repository: https://github.com/luxfi/standard Local Path: /Users/z/work/lux/standard/

Contracts

Contract	Description
`lib/openzeppelin-contracts/contracts/token/ERC20/extensions/ERC1363.sol`	ERC20 with transfer callbacks

Interfaces

Build and Test

cd /Users/z/work/lux/standard/

# Build all contracts
forge build

# Run tests
forge test -vvv

# Gas report
forge test --gas-report

LRC-1363 Payable Token