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Pay for your onchain transactions

Setting up fees is essential for your app to interact with both the EVMx and supported blockchains. There is only one type of fees you need to manage: onchain transaction sponsorship

Onchain Transaction Sponsorship​

Configure fee data​

Set up the Fees structure for your app:

struct Fees {
    uint32 feePoolChain;
    address feePoolToken;
    uint256 maxFees;
}

Fees fees = Fees({
    feePoolChain: <CHAINSLUG>,
    feePoolToken: <TOKEN_ADDRESS>,
    maxFees: <MAX_FEE_PER_TRANSACTION>
});

The maxFees parameter serves a dual purpose:

  • It represents the minimum amount of fees that must be available in the contract to process the transaction
  • It also represents the maximum amount the user is willing to pay for this transaction to be included in a batch

User must have deposited at least this amount to the contract before initiating the transaction, which ensures the transmitter (entity processing batches) is guaranteed compensation for including this transaction.

Apply fee configuration​

Set the fee configuration in your contracts:

AppGateway(appGatewayAddress).setFees(fees);

or set them in the constructor of the AppGateway.

The Fees structure is designed to manage fee-related parameters for transactions in a dual-execution environment (EVMx and onchain). Here's how it's implemented:

Fees memory fees = Fees({
    feePoolChain: 421614,      // Chain ID where fees are collected
    feePoolToken: ETH_ADDRESS, // Token used for fee payments (ETH in this case)
    maxFees: 0.001 ether       // Maximum fee amount allowed and minimum required deposit
});

Fees key components​

  1. feePoolChain Specifies the blockchain network ID where fees are collected and managed. In this case, it's set to 421614, which is Arbitrum Sepolia's chain ID.

  2. feePoolToken Defines which token is used for fee payments. Here it's set to ETH_ADDRESS, meaning Ethereum is used as the payment token.

  3. maxFees Sets an upper limit for transaction fees, preventing excessive charges. In this example, it's set to 0.001 ETH. The user must have deposited at least this amount, ensuring the transmitter gets compensated for including this transaction in a batch. If the actual cost is less than this amount, the user only pays what's needed.

Dual purpose usage​

EVMx Transactions

  • Acts as a fee configuration for processing offchain computations
  • Ensures users have enough balance to cover computational costs
  • Provides a predictable fee structure for offchain operations

Onchain Transactions

  • Sets parameters for standard blockchain transaction fees
  • Manages gas costs for contract interactions
  • Provides fee limits for user protection

Implementation context​

The Fees structure is passed to the SomeAppGateway contract ensuring consistent fee handling across the entire system, whether transactions are processed offchain or onchain:

SomeAppGateway gateway = new SomeAppGateway(
    addressResolver,
    fees,
    owner
);

Deposit sponsorship tokens to pay for transactions​

First, deposit testnet ETH to the FeesPlug contract on your chosen chain:

cast send <CHOSEN_CHAIN_FEES_PLUG> "deposit(address,address,uint256)" \
    0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE \
    $APP_GATEWAY \
    <AMOUNT> \
    --value <AMOUNT> \
    --rpc-url $SEPOLIA_RPC \
    --private-key $PRIVATE_KEY

You may also call or adapt the existing PayFeesInArbitrumETH script in SOCKET Protocol repository. You may also check your AppGateway total fee balance with AppGatewayFeeBalance script.

info

Currently only testnet ETH is supported. Support for additional tokens is coming soon.