ERC777: token recipient contract has no implementer for ERC777TokensRecipient

Question

In my Hardhat test, I can deploy the following:

• ERC1820 contract via a Hardhat plugin
• ERC777 contract
• Staking contract to hold ERC777 tokens

Then I can mint some ERC777 tokens to an user:

await lpToken777.connect(owner).mint(user1Addr, userInitBalance);

But when I tried to mint some ERC777 tokens to my Staking contract

await rwToken777.connect(owner).mint(erc777StakingAddr, rwTokenTotalSupply);

That failed with the error message: "ERC777: token recipient contract has no implementer for ERC777TokensRecipient"

I found some explanation about that error:

https://docs.openzeppelin.com/contracts/4.x/erc777 : recipient contract has not registered itself as aware of the ERC777 protocol, so transfers to it are disabled to prevent tokens from being locked forever

https://docs.openzeppelin.com/contracts/4.x/api/utils#ERC1820Implementer IERC1820Registry.setInterfaceImplementer should then be called for the registration to be complete.

I traced that error back to OpenZeppelin's ERC777Upgradeable.sol, which the parent contract of my ERC777 contract:

    function _callTokensReceived(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData,
        bool requireReceptionAck
    ) private {
        address implementer = _ERC1820_REGISTRY.getInterfaceImplementer(to, _TOKENS_RECIPIENT_INTERFACE_HASH);
        if (implementer != address(0)) {
            IERC777RecipientUpgradeable(implementer).tokensReceived(operator, from, to, amount, userData, operatorData);
        } else if (requireReceptionAck) {
            require(!to.isContract(), "ERC777: token recipient contract has no implementer for ERC777TokensRecipient");
        }
    }

I see I need to deploy this _ERC1820_REGISTRY contract somehow, then register my Staking contract onto it... That sounds like a lot of extra work... Is there a much better way for me to do it? how can I deploy erc1820 with OpenZeppelin and register my staking contract?

Answer 1

To deploy an erc1820 or _ERC1820_REGISTRY contract, use this Hardhat plugin from https://www.npmjs.com/package/hardhat-erc1820:

Install it: yarn add hardhat-erc1820

Add this line in hardhat.config.ts: import "hardhat-erc1820";

Then that plugin will somehow deploy an _ERC1820_REGISTRY contract for you at the default address: 0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24

Then we need to implement tokensReceived() function in our staking contract:

Copy code from ERC777SenderRecipientMock.sol https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/mocks/ERC777SenderRecipientMock.sol

    IERC1820RegistryUpgradeable internal constant _ERC1820_REGISTRY = IERC1820RegistryUpgradeable(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
    bytes32 private constant _TOKENS_SENDER_INTERFACE_HASH = keccak256("ERC777TokensSender");
    bytes32 private constant _TOKENS_RECIPIENT_INTERFACE_HASH = keccak256("ERC777TokensRecipient");

    function tokensReceived(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData
    ) external {
        ...
    }

    function tokensToSend(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes calldata userData,
        bytes calldata operatorData
    ) external {
        ...
    }

    function initialize() external initializer {
        __Ownable_init();
        __Pausable_init();

        // register interfaces
        // register our staking contract at _ERC1820_REGISTRY contract
        _ERC1820_REGISTRY.setInterfaceImplementer(address(this), _TOKENS_RECIPIENT_INTERFACE_HASH, address(this));
        _ERC1820_REGISTRY.setInterfaceImplementer(address(this), _TOKENS_SENDER_INTERFACE_HASH, address(this));
    }