CrossChain Precompiled

Address: 0x0000000000000000000000000000000000001004

Interface: ICrossChain

ABI: ICrossChain

Overview: Use crossChain precompiled contract to call some functions of the crossChain module, such as: crossChain, cancelSendToExternal, etc.

Introduction

Before accessing the cross-chain precompiled contract, the cross-chain operations of the precompile can be called via the hook method.

Using a simple example, a specific event, say: CrossChain, is added to a token contract; and when the token contract is deployed and successfully executes a transaction that emits this specific event, the EVM module in f(x)Core will parse the event generated by the contract. If the emitted event is relevant to the cross-chain precompiled contract, the corresponding cross-chain logic will be executed based on the data in the CrossChain event.

Use-case Reference

Low-level Call (Sample contract)

function crossChain(
    address _token,
    string memory _receipt,
    uint256 _amount,
    uint256 _fee,
    bytes32 _target,
    string memory _memo
) internal returns (bool) {
    (bool result, bytes memory data) = CROSS_CHAIN_ADDRESS.call{
        value: msg.value
    }(Encode.crossChain(_token, _receipt, _amount, _fee, _target, _memo));
    Decode.ok(result, data, "cross-chain failed");
    return Decode.crossChain(data);
}

Encode.crossChain encodes the crossChain method and its parameters using abi.encodeWithSignature to create a bytes array that will be sent to the cross-chain precompiled contract to invoke the corresponding crossChain method along with the encoded parameters.

Contract Interface (Sample Contract)

interface ICrossChain {
    function crossChain(
        address _token,
        string memory _receipt,
        uint256 _amount,
        uint256 _fee,
        bytes32 _target,
        string memory _memo
    ) external payable returns (bool _result);
}

contract CrossChainTest {
    ICrossChain crossChain = 0x0000000000000000000000000000000000001004;

    function crossChain(
        address _token,
        string memory _receipt,
        uint256 _amount,
        uint256 _fee,
        bytes32 _target,
        string memory _memo
    ) external payable returns (bool) {
        bool success = _crossChain.crossChain(_token, _receipt, _amount, _fee, _target, _memo);
        require(success, "crossChain failed");
    }
}

The contract interface method is relatively simple. It only needs to define the contract interface with the appropriate method, and parameters are simply passed into it like a regular call to another contract’s function. It does not require encoding the method and its parameters since the contract interface takes care of that, however the reason cannot be obtained in the event of a failure.

The crossChain method has the payable keyword, so it can directly cross-chain f(x)Core’s native currency: FX. Note that there are some differences between executing a cross-chain transaction for FX and an ERC20 token:

• When using cross-chain for FX, _token needs to be the zero address (0x0000000000000000000000000000000000000000), and fill in: value = _amount + _fee.

• When using cross-chain for ERC20 token, an approval must first be granted to the address: 0x0000000000000000000000000000000000001004, and the authorized amount must be equals to: amount = _amount + _fee.

Method

crossChain

send token from f(x)Core to other chain, like ethereum, pundix, etc.

if token is erc20, must be approved before calling this method

function crossChain(
    address _token,
    string memory _receipt,
    uint256 _amount,
    uint256 _fee,
    bytes32 _target,
    string memory _memo
) external payable returns (result bool);

• _token: the token address on the f(x)Core(Tokens)

  • if token is origin token, _token address is 0x0000000000000000000000000000000000000000

• _receipt: the receipt address on the target chain

• _amount: the amount of the token to be cross chain

• _fee: the fee of the token to be cross chain

  • if cross chain to cosmos chain, _fee is 0

• _target: the target of the token on the target chain(more detail see Target

  • _target represents cross chain destination, such as chain ethereum, pundix

  • destination ethereum: _target is eth

  • destination other cosmos chain(example Pundix): _target is ibc/{id}/{prefix}.

    • id is the channel id of the target chain on f(x)Core(examples: Pundix: 0)

    • prefix is the address prefix of the target chain(examples: Pundix: px)

• _memo: the memo of cross chain

_target convert string to bytes, if less than 32, fill in 0 in behind, until 32 bytes

crossChain event

event CrossChain(
    address indexed sender,
    address indexed token,
    string denom,
    string receipt,
    uint256 amount,
    uint256 fee,
    bytes32 target,
    string memo
);

• sender: the sender address

• token: the erc20 token address on the f(x)Core

• denom: the cross chain token denom

• receipt: the receipt address on the target chain

• amount: the amount of the token to be cross chain

• fee: the fee of the token to be cross chain

• target: the target of cross chain

• memo: the memo of cross chain

cancelSendToExternal

cancel cross chain to external chain, like ethereum, bsc, etc.

only cancel send to external chain(ethereum,bsc, etc.) transaction, can't cancel send to cosmos chain(pundix, cosmoshub, etc.) transaction.

function cancelSendToExternal(
    string memory _chain,
    uint256 _txid
) external returns (result bool);

• _chain: the module name of the cross chain, like eth, bsc, etc.

• _txid: the txid of the cross chain transaction

cancelSendToExternal event

event CancelSendToExternal(
    address indexed sender,
    string chain,
    uint256 txID
);

• sender: the sender address

• chain: the module name of the cross chain, like eth, bsc, etc.

• txID: the txid of the cross chain transaction

increaseBridgeFee

increase fee for send to external chain transaction

only increase fee for send to external chain transaction, can't increase fee for send to cosmos chain transaction

not necessarily the initiator of the cross chain transaction, anyone can increase the fee for the cross chain transaction

if token is erc20, must be approved before calling this method

function increaseBridgeFee(
    string memory _chain,
    uint256 _txid,
    address _token,
    uint256 _fee
) external payable returns (result bool);

• _chain: the chain name of the cross chain, like eth, bsc, etc(not contain cosmos chain).

• _txid: the txid of the cross chain transaction

• _token: the address of cross chain fee token(Tokens)

  • if token is origin token, _token address is 0x0000000000000000000000000000000000000000

• _fee: increase fee amount

increaseBridgeFee event

event IncreaseBridgeFee(
    address indexed sender,
    address indexed token,
    string chain,
    uint256 txID,
    uint256 fee
);

• sender: the sender address

• token: the address of cross chain fee token

• chain: the module name of the cross chain, like eth, bsc, etc.

• txID: the txid of the cross chain transaction

• fee: increase fee amount