Fee Abstraction on Celo L2

Fee Abstraction Addresses

Celo allows paying gas fees in currencies other than the native currency. The tokens that can be used to pay gas fees are controlled via governance and the list of tokens allowed is maintained in FeeCurrencyDirectory.sol.

Fee abstraction on Celo works with EOAs. No paymaster required!

Get a list of whitelisted Fee Currencies

# Alfajores testnet
celocli network:whitelist --node https://alfajores-forno.celo-testnet.org
# Celo mainnet
celocli network:whitelist --node https://forno.celo.org

Using Fee Abstraction with Celo CLI

Transfer 1 USDC using USDC as fee currency, with the celocli using the --gasCurrency flag

celocli transfer:erc20 --erc20Address 0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B --from 0x22ae7Cf4cD59773f058B685a7e6B7E0984C54966 --to 0xDF7d8B197EB130cF68809730b0D41999A830c4d7 --value 1000000 --gasCurrency 0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B --privateKey [PRIVATE_KEY]

Symbol	Token Address (Mainnet)	Adapter Address (Mainnet)
cAUD	0x7175504C455076F15c04A2F90a8e352281F492F9
cCAD	0xff4Ab19391af240c311c54200a492233052B6325
cCHF	0xb55a79F398E759E43C95b979163f30eC87Ee131D
cCOP	0x8A567e2aE79CA692Bd748aB832081C45de4041eA
cEUR	0xD8763CBa276a3738E6DE85b4b3bF5FDed6D6cA73
cGBP	0xCCF663b1fF11028f0b19058d0f7B674004a40746
cGHS	0xfAeA5F3404bbA20D3cc2f8C4B0A888F55a3c7313
cJPY	0xc45eCF20f3CD864B32D9794d6f76814aE8892e20
cKES	0x456a3D042C0DbD3db53D5489e98dFb038553B0d0
cNGN	0xE2702Bd97ee33c88c8f6f92DA3B733608aa76F71
cREAL	0xe8537a3d056DA446677B9E9d6c5dB704EaAb4787
cUSD	0x765DE816845861e75A25fCA122bb6898B8B1282a
cZAR	0x4c35853A3B4e647fD266f4de678dCc8fEC410BF6
eXOF	0x73F93dcc49cB8A239e2032663e9475dd5ef29A08
PUSO	0x105d4A9306D2E55a71d2Eb95B81553AE1dC20d7B
USD₮	0x0E2A3e05bc9A16F5292A6170456A710cb89C6f72	0x0E2A3e05bc9A16F5292A6170456A710cb89C6f72
USDC	0xcebA9300f2b948710d2653dD7B07f33A8B32118C	0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B

When using USDC or USDC for fee abstraction, you have to use the adapter address instead of the token address. This is necessary to avoid inaccuracies due to their low number of decimals (6 compared to 18 for the other tokens).

Using Fee Abstraction Programmatically

You can use Fee Abstraction by specifying a token/adapter address as a value for the feeCurrency property in the transaction object. The feeCurrency property in the transaction object is exclusive to Celo and allows paying gas fees using assets other than the native currency of the network.

info

Wallets will overwrite the feeCurrency, which is why this is recommended for wallet developers or backend developers.

When using Fee Abstraction for a wallet or inside your dApp we recommend using viem or wagmi.

info

While we recommend viem, web3.js has added as of 4.13.1 support for feeCurrency via the usage of plugins. There is a celo-specific plugin for web3@4 available on github.

warning

Currently, ethers.js doesn't support the feeCurrency property

Sending transaction using Fee Abstraction

Sending transactions with fee currency other than the native currency of the network is pretty straightforward. All you need to do is set the feeCurrency property in the transaction object with the address of the token/adapter you want to use to pay for gas fees.

The below code snippet demonstrates transferring 1 USDC using USDC as gas currency.

import { createWalletClient, http } from "viem";
import { celo } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";
import { stableTokenAbi } from "@celo/abis";

// Creating account from private key, you can choose to do it any other way.
const account = privateKeyToAccount("0x432c...");

// WalletClient can perform transactions.
const client = createWalletClient({
  account,

  // Passing chain is how viem knows to try serializing tx as cip42.
  chain: celo,
  transport: http(),
});

const USDC_ADAPTER_MAINNET = "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B";
const USDC_MAINNET = "0xcebA9300f2b948710d2653dD7B07f33A8B32118C";

/*
  The UI of the wallet should calculate the transaction fees, show it and consider the amount to not be part of the asset that the user i.e the amount corresponding to transaction fees should not be transferrable.
*/
async function calculateTransactionFeesInUSDC(transaction) {
  // Implementation of getGasPriceInUSDC is in the above code snippet
  const gasPriceInUSDC = await getGasPriceInUSDC();

  // Implementation of estimateGasInUSDC is in the above code snippet
  const estimatedGasPrice = await estimateGasInUSDC(transaction);

  return gasPriceInUSDC * estimatedGasPrice;
}

async function send(amountInWei) {
  const to = USDC_MAINNET;

  // Data to perform an ERC20 transfer
  const data = encodeFunctionData({
    abi: stableTokenAbi,
    functionName: "transfer",
    args: [
      "0xccc9576F841de93Cd32bEe7B98fE8B9BD3070e3D",
      // Different tokens can have different decimals, cUSD (18), USDC (6)
      amountInWei,
    ],
  });

  const transactionFee = await calculateTransactionFeesInUSDC({ to, data });

  const tokenReceivedbyReceiver = parseEther("1") - transactionFee;

  /* 
    Now the data has to be encode again but with different transfer value because the receiver receives the amount minus the transaction fee.
  */
  const dataAfterFeeCalculation = encodeFunctionData({
    abi: stableTokenAbi,
    functionName: "transfer",
    args: [
      "0xccc9576F841de93Cd32bEe7B98fE8B9BD3070e3D",
      // Different tokens can have different decimals, cUSD (18), USDC (6)
      tokenReceivedbyReceiver,
    ],
  });

  // Transaction hash
  const hash = await client.sendTransaction({
    ...{ to, data: dataAfterFeeCalculation },

    /*
      In case the transaction request does not include the feeCurrency property, the wallet can add it or change it to a different currency based on the user balance.

      Notice that we use the USDC_ADAPTER_MAINNET address not the token address this is because at the protocol level only 18 decimals tokens are supported, but USDC is 6 decimals, the adapter acts a unit converter.
    */
    feeCurrency: USDC_ADAPTER_MAINNET,
  });

  return hash;
}