Bridging Lucid Assets

Introduction

To bridge tokens from Chain A to Chain B, an Asset Controller contract must be deployed on both chains.

To successfully bridge tokens from a controller on a source chain, ensure that:

• The selected bridge adapter is whitelisted by an admin.

• The adapter has sufficient mint/burn limits (unless bridging without limits).

The following sections describe how to manually bridge tokens by interacting directly with the smart contracts. This is intended for advanced users. It is recommended to use the Lucid App to bridge tokens or to construct/export transactions for execution via Safe, Snapshot’s oSnap module, or a Governor proposal.

Bridging Tokens

To bridge Lucid assets, you interact directly with the Lucid Wrapper contract (address and deployed chains can be viewed here), which serves as the entry point to bridge Lucid assets across any chain. It also supports EIP-2612 (aka ERC20Permit) for compatible assets, so the erc20 approve transaction can be skipped. The following functions are available on the Lucid Wrapper contract:

23KB

lucidWrapper.abi.json

Open

Single Bridge

Using a single bridge is the default way to bridge tokens. You can initiate a transfer by calling transferTo on the Wrapper contract on the source chain:

transferTo

• Burns or locks tokens (depending on the configuration) on the source chain

• Sends a mint message to the destination chain via the selected bridge adapter

• msg.value must contain the bridge adapter fee

• The token allowance must be approved prior to calling this function

function transferTo(DepositInput calldata input, address adapter, bytes calldata bridgeOptions, bytes calldata data ) external payable

Name	Type	Description
input	DepositInput	A DepositInput struct
adapter	address	The address of the bridge adapter to use
bridgeOptions	bytes	Additional params to be used by the adapter. Refer to the documentation of the specific adapter you are using
data	bytes	Reserved for Multi-hop transfers. For regular transfers, pass 0x (default)

If the selected bridge adapter is not whitelisted, or if it does not have sufficient burn limits, the transaction will revert. Any account holding the token managed by the Asset Controller can initiate a transfer.

Events emitted

The following events are emitted after a transfer has been sent:

From the Lucid Wrapper contract:

event TransferSent( address indexed sender, address indexed controller, bool resent, bool multi, uint256 grossAmount, uint256 netAmount, bytes data );

The data bytes array is emitted unchanged from the input parameters.

From the Asset Controller contract:

event TransferCreated(bytes32 indexed transferId, uint256 indexed destChainId, uint256 threshold, address indexed sender, address recipient, uint256 amount, bool unwrap);

The transferId can be used to:

• Resend the transfer using another adapter

• Track delivery status on the destination chain or the Lucid App

transferToWPermit

This function works similar to transferTo() as outlined above, but it accepts an EIP-2612 signature to register the user's ERC20 approval, eliminating the need for a prior approve() transaction. If the signature is invalid, the transaction will revert.

Can only be used with tokens that implement EIP-2612. Check if the token you are bridging supports this functionality.

function transferToWPermit( DepositInput calldata input, PermitData calldata permit, address bridgeAdapter, bytes calldata bridgeOptions, bytes calldata data ) external payable

Name	Type	Description
input	DepositInput	A DepositInput struct
permit	PermitData	A PermitData struct
bridgeAdapter	address	The address of the bridge adapter to use
bridgeOptions	bytes	Additional params to be used by the adapter. Refer to the documentation of the specific adapter you are using
data	bytes	Reserved for Multi-hop transfers. For regular transfers, pass 0x (default)

resendTransfer

If a bridge fails to deliver a transfer to the destination chain, anyone can call resendTransfer, specifying the transferId and a different whitelisted adapter.

• No new tokens will be burned

• The original bridge message is resent using the new adapter

• The burn amount is deducted from the new adapter’s burn limit

• The function is payable, and msg.value must contain the new adapter’s fee

function resendTransfer( address controller, bytes32 transferId, address adapter, bytes calldata bridgeOptions, bytes calldata data ) external payable

Name	Type	Description
controller	address	The controller address of the asset to use
transferId	bytes32	The unique identifier of the message.
adapter	address	The address of the bridge adapter.
bridgeOptions	bytes	Additional abi-encoded options that are passed to the bridge adapter, specific for the bridge adapter.
data	bytes	Reserved for Multi-hop transfers. For regular transfers, pass 0x (default)

Events emitted

The following events are emitted after a transfer has been sent:

From the Lucid Wrapper contract:

event TransferSent( address indexed sender, address indexed controller, bool resent, bool multi, uint256 grossAmount, uint256 netAmount, bytes data );

From the Asset Controller contract:

event TransferResent(bytes32 indexed transferId);

Lucid will not automatically relay transactions bridged via Polymer when the destination chain is Ethereum Mainnet. In these cases, the recipient must manually execute the transaction and cover the required gas fees via the Lucid App.

Multiple Bridges (higher limits)

For transfers that exceed a single adapter’s limit, you can use multiple bridge adapters by calling the overloaded transferTo() function. This function:

• Burns tokens on the source chain

• Sends the mint message through multiple whitelisted adapters

• Requires the addresses of adapters that have been pre-approved for with higher limits

• msg.value must include any multi-bridge fees

• The token allowance must be set before calling this function.

To determine:

• The minimum number of adapters required for minting (if 0 is returned, then multiple bridges support is disabled):

function minBridges() public view returns (uint256);

To determine whether a specific adapter is approved for bridging with higher limits:

function multiBridgeAdapters(address adapter) public view returns (bool);

To get the current multi-bridge limits, call bridges(0x0).

transferTo (multiple bridges)

To send a transfer, call the following function:

function transferTo( DepositInput calldata input, address[] memory adapters, uint256[] memory fees, bytes[] calldata bridgeOptions, bytes calldata data ) external payable

Name	Type	Description
input	DepositInput	A DepositInput struct
adapters	address[]	The addresses of the bridge adapter to use.
fees	uint256[]	The fees to be paid to the bridge adapters (in the same order as adapters).
bridgeOptions	bytes[]	Additional params to be used by each adapter. Refer to the documentation of the specific adapter you are using
data	bytes	Reserved for Multi-hop transfers. For regular transfers, pass 0x (default)

A token allowance must be given before calling this function, which should include the multi-bridge fee, if any.

If the bridgeAdapter that was selected is not whitelisted, or the burn limits are not enough, then the transaction will revert.

Events emitted

The following events are emitted after a transfer has been sent:

From the Lucid Wrapper contract:

event TransferSent( address indexed sender, address indexed controller, bool resent, bool multi, uint256 grossAmount, uint256 netAmount, bytes data );

The data bytes array is emitted unchanged from the input parameters.

From the Asset Controller contract:

event TransferCreated(bytes32 indexed transferId, uint256 indexed destChainId, uint256 threshold, address indexed sender, address recipient, uint256 amount, bool unwrap);

The transferId can be used to:

• Resend the transfer using another adapter

• Track delivery status on the destination chain or the Lucid App

transferToWPermit (multiple bridges)

This function works similar to transferTo() as outlined above, but it accepts an EIP-2612 signature to register the user's ERC20 approval, eliminating the need for a prior approve() transaction. If the signature is invalid, the transaction will revert.

Can only be used with tokens that implement EIP-2612. Check if the token you are bridging supports this functionality.

function transferToWPermit( DepositInput calldata input, PermitData calldata permit, address[] memory adapters, uint256[] memory fees, bytes[] calldata bridgeOptions, bytes calldata data ) external payable

Name	Type	Description
input	DepositInput	A DepositInput struct
permit	PermitData	A PermitData struct
adapters	address[]	The addresses of the bridge adapter to use.
fees	uint256[]	The fees to be paid to the bridge adapters (in the same order as adapters).
bridgeOptions	bytes[]	Additional params to be used by each adapter. Refer to the documentation of the specific adapter you are using
data	bytes	Reserved for Multi-hop transfers. For regular transfers, pass 0x (default)

Events emitted

The following events are emitted after a transfer has been sent:

From the Lucid Wrapper contract:

event TransferSent( address indexed sender, address indexed controller, bool resent, bool multi, uint256 grossAmount, uint256 netAmount, bytes data );

The data bytes array is emitted unchanged from the input parameters.

From the Asset Controller contract:

event TransferCreated(bytes32 indexed transferId, uint256 indexed destChainId, uint256 threshold, address indexed sender, address recipient, uint256 amount, bool unwrap);

The transferId can be used to:

• Resend the transfer using another adapter

• Track delivery status on the destination chain or the Lucid App

resendTransfer (multiple bridges)

If delivery fails in a multi-bridge setup, the transfer can be resent using another whitelisted adapter by calling resendTransfer().

• Works similarly to the single-bridge resendTransfer transfer

• No additional tokens are burned

• The message is simply resent using the new adapter

function resendTransfer( address controller, bytes32 transferId, address[] calldata adapters, uint256[] calldata fees, bytes[] calldata bridgeOptions, bytes calldata data ) external payable

Name	Type	Description
controller	address	The controller address of the asset to use
transferId	bytes32	The unique identifier of the message.
adapters	address[]	The addresses of the bridge adapters.
fees	uint256[]	The fees to be paid to the bridge adapters (in the same order as adapters).
bridgeOptions	bytes[]	Additional params to be used by each adapter. Refer to the documentation of the specific adapter you are using
data	bytes	Reserved for Multi-hop transfers. For regular transfers, pass 0x (default)

Events emitted

The following events are emitted after a transfer has been sent:

From the Lucid Wrapper contract:

event TransferSent( address indexed sender, address indexed controller, bool resent, bool multi, uint256 grossAmount, uint256 netAmount, bytes data );

From the Asset Controller contract:

event TransferResent(bytes32 indexed transferId);

Structs

DepositInput

struct DepositInput {
    address controller; // address of the asset controller
    address recipient;
    uint256 amount;
    bool unwrap; // default to false
    uint256 destChainId;
}

For a list of the available asset controller addresses, check out this page.

PermitData

struct PermitData {
    uint256 deadline;
    uint8 v;
    bytes32 r;
    bytes32 s;
}

Fees

Before bridging assets, you should first estimate the fees. To do this, call the corresponding function on the Lucid Wrapper contract on the source chain, providing the controller address, the destination chain ID, and the amount to be bridged. The function will return both the estimated fee and the net amount you will receive on the destination chain.

Note that some transfers do not incur a fee, in which case you will receive the full amount.

function quote(address controller, uint256 destChainId, uint256 amount) external view returns (uint256 fee, uint256 net)

Multi-hop transfer

This is an advanced feature and it's recommended to use the quote endpoint of the API to create multi-hop transfers. For projects looking to integrate with Multi-hop, please reach out.

To create a multi-hop transfer, you construct and pass the multi-hop configuration in the data parameter of transferTo or transferToWPermit functions. If a transfer is not multi-hop, then the data parameter is an empty bytes array.

In multi-hop transfers, the recipient of the tokens in the mid-point chain is the 2-of-3 Safe multisig. The address of the multisig should be passed as the recipient in the DepositInput struct. As a result, the destChainId in the same struct is the chain id of the midpoint chain. For the addresses/chain ids, refer to this page.

Read more about how to construct the data parameter in this page.

Token Minting

Once the message is delivered to the destination Asset Controller by the bridge adapters, the transfer must be executed.

Lucid will automatically execute the transfer once it becomes eligible. However, anyone can manually execute it by calling the following function on the asset controller on the destination chain, passing the transfer ID:

function execute(bytes32 messageId) public;

This function can be called by any account.

Lucid will not automatically execute transactions bridged via Polymer when the destination chain is Ethereum Mainnet. In these cases, the recipient must manually execute the transaction and cover the required gas fees—either by calling the function directly or using the Lucid App.