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Fee Handling

Omni fees are charged synchronously on xcall call to a portal contract. This function is therefore payable. It allows specification of a custom gas limit, enforced at the destination chain.

interface IOmniPortal {

  /**
   * @notice Call a contract on another chain
   * @dev Uses OmniPortal.XMSG_DEFAULT_GAS_LIMIT as execution gas limit
   *      on destination chain
   * @dev Fees are denomninated in wei, and paid via msg.value. Call reverts
   * 	   if fees are insufficient. Calculate fees with feeFor(...)
   * @param destChainId Destination chain ID
   * @param to Address of contract to call on destination chain
   * @param data Encoded function calldata (use abi.encodeWithSignature
   * 	or abi.encodeWithSelector)
   */
  function xcall(uint64 destChainId, address to, bytes calldata data)
external
payable;

 /**
   * @notice Call a contract on another chain
   * @dev Uses provide gasLimit as execution gas limit on destination chain.
   *      Reverts if gasLimit < XMSG_MAX_GAS_LIMIT or gasLimit > XMSG_MAX_GAS_LIMIT
   * @dev Fees are denomninated in wei, and paid via msg.value. Call reverts
   * 	   if fees are insufficient. Calculate fees with feeFor(...)
   * @param destChainId Destination chain ID
   * @param to Address of contract to call on destination chain
   * @param data Encoded function calldata (use abi.encodeWithSignature
   * 	or abi.encodeWithSelector)
   */
  function xcall(uint64 destChainId, address to, bytes calldata data, uint64 gasLimit)
external
payable;

}

Native fees must be provided explicitly in the call. An interface must therefore be exposed to allow synchronous fee calculation. This interface is exposed via the portal.

interface IOmniPortal {
  // ...

  /**
   * @notice Calculate the fee for calling a contract on another chain
   * @dev Uses OmniPortal.XMSG_DEFAULT_GAS_LIMIT
   * @dev Fees denominated in wei
   * @param destChainId Destination chain ID
   * @param data Encoded function calldata (use abi.encodeWithSignature
   * 	or abi.encodeWithSelector)
   */
  function feeFor(uint64 destChainId, bytes calldata data)
external
view
returns (uint256);

  /**
   * @notice Calculate the fee for calling a contract on another chain
   * @dev Fees denominated in wei
   * @param destChainId Destination chain ID
   * @param data Encoded function calldata (use abi.encodeWithSignature
   * 	or abi.encodeWithSelector)
   * @param gasLimit Custom gas limit, enforced on destination chain
   */
  function feeFor(uint64 destChainId, bytes calldata data, uint64 gasLimit)
external
 view
returns (uint256);

    // ...
}

Collection​

Each portal will be configured with a feeTo address. All collected fees will be sent to this address. This address is set to the relayer address.

Pricing​

Portal contracts need to know how much to charge for each transaction, implemented in the feeFor method. The parameters to fee calculation are:

  • Destination chain id
  • Calldata
  • Gas limit