Fees

When you're making a cross-chain call using xCall, there's a fee that covers the costs of sending the message between different blockchains. sendCallMessage is payable, so the fee should be included in the transaction. You can get the fee by calling getFee.

getFee(String _net, boolean _rollback) returns the total fee (relay + protocol) for sending a message to the specified network. If a rollback data is provided, the _rollback param should be set as true because there is an additional backward direction fee (from destination back to source) if rollback is used.

This fee is split into two parts:

Relay Fee: This fee is for the service that actually sends your message from one blockchain to another.

Protocol Fee: This is the fee for using the cross-chain communication protocol underlying xCall.

Relay Fee

• If a relay successfully delivers a cross-chain message, it can claim a reward. The first relay to successfully deliver a cross-chain message gets the reward.
• The reward claim can be made using the claimReward function, which requires the network address of the reward (_network) and the address of the receiver (_receiver).
• The accrued reward for each relay can be checked using the getReward function.

Protocol Fee

• The protocol fee is set on the xCall contract by an admin wallet.

Burning Fees and Impact to ICX Tokenomics

Native fees generated by protocol fees and relays managed by the ICON Foundation are swapped to native ICX and burned.

Example

The process of fetching the cross chain transaction fee is done by making a readonly call to the getFee(String _net, Boolean _rollback) method of the xCall contract in the origin chain.

The following code sample showcase how to get the fee of a crosschain message originating on the Berlin testnet on ICON and the destination chain being the Sepolia testnet on Ethereum.

const IconService = require("icon-sdk-js");
 
const { IconBuilder, HttpProvider } = IconService.default;
 
const { CallBuilder } = IconBuilder;
const ICON_RPC_URL = "https://berlin.net.solidwallet.io/api/v3/icon_dex";
const XCALL_PRIMARY = "cxf4958b242a264fc11d7d8d95f79035e35b21c1bb";
const NETWORK_LABEL_SECONDARY = "0xaa36a7.eth2";
 
const HTTP_PROVIDER = new HttpProvider(ICON_RPC_URL);
const ICON_SERVICE = new IconService.default(HTTP_PROVIDER);
 
/*
 * getFee - calls the getFee method of the xcall contract
 * @param {boolean} useRollback - whether to use rollback
 * @returns {String} - the fee as a hex value
 * @throws {Error} - if there is an error getting the fee
 */
async function getFee(useRollback = false) {
  try {
    const params = {
      _net: NETWORK_LABEL_SECONDARY,
      _rollback: useRollback ? "0x1" : "0x0"
    };
 
    const txObj = new CallBuilder()
      .to(XCALL_PRIMARY)
      .method("getFee")
      .params(params)
      .build();
 
    return await ICON_SERVICE.call(txObj).execute();
  } catch (e) {
    console.log("error getting fee", e);
    throw new Error("Error getting fee");
  }
}
 
async function main() {
  const fee = await getFee();
  console.log("fee", fee);
}
 
main();