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CRC20 Tokens Cross Space

This tutorial guides developers on transferring any CRC20 token from Core Space to eSpace, using FansCoin (FC) as an example. The goal is to transfer a CRC20 token (A) issued on coreSpace to become an ERC20 token (eA) in eSpace. Currently, if there is no corresponding token in eSpace, it's not possible to use the official cross-space bridge directly.

Can not cross space

Before initiating cross-space operations, let's review several key contracts associated with the cross-space bridge:

On CoreSpace:

  • BeaconProxy Proxy Contract: cfx:acfcrckktgx99scxwr6jtjx81yhm4ggsfatprwzb3x
  • BeaconProxy Logic Contract - ConfluxSide: cfx:acc7gpd3380pv6v112s5c2y3g3g6jvm32egm5mhnk7

On eSpace:

  • BeaconProxy Proxy Contract: 0x4f9e3186513224cf152016ccd86019e7b9a3c809
  • BeaconProxy Logic Contract - EvmSide: 0x4fa28072bd5b551dde70213aa02cb05bd022e34b

Cross-Space Methods​

Step 1: Registering a Core Space ERC20 Token to eSpace​

First, call the registerMetadata method (Write as Proxy) in the BeaconProxy proxy contract on coreSpace, passing the token address Address_A. This function invokes the crossSpaceCall contract for cross-space operations, registering the A contract in the EVM space. The code is as follows:

// Register token metadata to EVM space
function registerMetadata(IERC20 _token) public override {
    require(
        sourceTokens[address(_token)] == address(0),
        "ConfluxSide: token is mapped from EVM space"
    );
    // Cross-space call to EVM contract EvmSide, which is the BeaconProxy proxy contract in eSpace
    crossSpaceCall.callEVM(
        bytes20(evmSide),
        abi.encodeWithSelector(
            // Calls eSpace's BeaconProxy contract's registerCRC20 to register the current token address in eSpace contract
            IEvmSide.registerCRC20.selector,
            address(_token),
            _token.name(),
            _token.symbol(),
            _token.decimals()
        )
    );
}

call the registerMetadata method

After registration, the crc20Metadata function in eSpace's BeaconProxy contract can retrieve the CRC20 token's metadata in eSpace as name (string), symbol (string), decimals (uint8), registered (bool).

metadata

Step 2: Creating Token Mapping​

In eSpace's BeaconProxy contract, call the createMappedToken method, passing the CRC20 token address.

create map token

The internal implementation is as follows:

function createMappedToken(address _crc20) public override {
    require(crc20Metadata[_crc20].registered, "EvmSide: not registered");
    TokenMetadata memory d = crc20Metadata[_crc20];
    _deploy(_crc20, d.name, d.symbol, d.decimals);
}
...

function _deploy(
        address _token,
        string memory _name,
        string memory _symbol,
        uint8 _decimals
    ) internal returns (address mappedToken) {
        if (mappedTokens[_token] == address(0)) {
            mappedToken = address(
                new BeaconProxy{salt: keccak256(abi.encodePacked(_token))}(
                    beacon,
                    ""
                )
            );
            UpgradeableERC20(mappedToken).initialize(
                _name,
                _symbol,
                _decimals,
                owner()
            );
            mappedTokens[_token] = mappedToken;
            sourceTokens[mappedToken] = _token;
            mappedTokenList.push(_token);
        } else {
            mappedToken = mappedTokens[_token];
        }
    }

This operation creates a new BeaconProxy contract and deploys an UpgradeableERC20 contract, setting the new BeaconProxy contract address as the corresponding mappedToken for the CRC20 token.

At this point, the CRC20 and ERC20 tokens on both Core Space and eSpace are fully paired.

Step 3: Using the Official Cross-Space Bridge​

Now you can perform cross-space operations through the official cross-space bridge, which involves calling the crossToEVM function in coreSpace's BeaconProxy contract (after first approving the CRC20 token to the BeaconProxy contract).

use cross space

Step 4: Updating Logo and Token Tag Information​

The remaining issue is that after crossing to eSpace, the token lacks logo and tag information. This might require official action through the Announcement contract.

add logo

Step 5: Displaying on Cross-Space Bridge​

To be displayed on the official cross-chain bridge, modify the native_token_list_mainnet.json file and submit a pull request to the conflux-evm-bridge repository, requesting to add your token to the default display.

default display

You can also visit the community-deployed version at community cross-space bridge, or submit a PR at this repository to directly display your token on the community cross-space bridge.

community default display