2.33 FeeProxy (EVM example)

	At a glance
What it is	Pay the gas for an ERC-20 transfer in a token other than XRP. Futureverse’s EVM example for The Root Network, with its README and source.
Where it sits	Part II — Building · Chapter 2.33
Covers	Examples · Source files
Source	github.com/futureversecom/trn-examples/tree/main/examples/evm/use-feeProxy

Pay the gas for an ERC-20 transfer in a token other than XRP. Reference: FeeProxy precompile.

Copied from Futureverse’s futureversecom/trn-examples, deleted with its GitHub organisation, at commit 44c9e16 of 2024-10-31. Apache-2.0: license. Before you run it, read Running the examples.

Offline destinations

Some places this page points to did not answer when last checked:

• docs-beta.therootnetwork.com — does not resolve (checked 2026-10-18)
• stackblitz.com/github/futureversecom — StackBlitz loads these projects from the deleted futureversecom organisation on GitHub (checked 2026-10-18)

Run in StackBlitz (repository deleted, checked 2026-10-18) · Precompile Documentation (offline, checked 2026-10-18)

IMPORTANT

Ensure the following ENV vars are available before running the examples

• CALLER_PRIVATE_KEY - Private key of an account that submits the transaction. Follow this guide to create and fund an account with some test tokens on Porcini (testnet) if you don't have one yet.

2.33.1 Examples

# change your working directory to this example first
cd examples/evm/use-feeProxy

# export all required environments
export CALLER_PRIVATE_KEY=

# `feeProxy.callWithFeePreferences` that wraps around `ERC20.transfer`
pnpm call:callERC20Transfer

2.33.2 Source files

src/callERC20Transfer.ts2.33.2.1

import { ERC20_ABI } from "@therootnetwork/evm";
import { ALICE } from "@trne/utils/accounts";
import { filterTransactionEvents } from "@trne/utils/filterTransactionEvents";
import { getERC20Contract } from "@trne/utils/getERC20Contract";
import { getFeeProxyContract } from "@trne/utils/getFeeProxyContract";
import { getFeeProxyPricePair } from "@trne/utils/getFeeProxyPricePair";
import { ASTO_ASSET_ID, SYLO_ASSET_ID } from "@trne/utils/porcini-assets";
import { withEthersProvider } from "@trne/utils/withEthersProvider";
import { ContractReceipt, utils } from "ethers";

/**
 * Use `feeProxy.callWithFeePreferences` to trigger a `transfer` call of SYLO token, and pay gas
 * in ASTO token.
 *
 * Assumes the caller has ASTO balance to pay for gas and SYLO balance to demonstrate
 * the transfer
 */
withEthersProvider("porcini", async (provider, wallet, logger) => {
	// contracts creation
	const feeProxy = getFeeProxyContract().connect(wallet);
	const sylo = getERC20Contract(SYLO_ASSET_ID).connect(wallet);
	const asto = getERC20Contract(ASTO_ASSET_ID).connect(wallet);

	// transfer call
	const transferAmount = utils.parseUnits("0.1", 18); // 1 SYLO
	const transferInput = new utils.Interface(ERC20_ABI).encodeFunctionData("transfer", [
		ALICE,
		transferAmount,
	]);
	const transferEstimate = await sylo.estimateGas.transfer(ALICE, transferAmount);

	logger.info(
		{
			parameters: {
				destination: ALICE,
				amount: transferAmount,
			},
		},
		`create a transfer call`
	);

	// retrieve the maxPayment and maxFeePerGas parameters with slippage to be 0.05 (5%)
	const { maxPayment, maxFeePerGas } = await getFeeProxyPricePair(
		provider,
		transferEstimate,
		ASTO_ASSET_ID,
		0.05
	);

	logger.info(`dispatch transaction from wallet=${wallet.address}`);
	const tx = await feeProxy.callWithFeePreferences(
		asto.address,
		maxPayment,
		sylo.address,
		transferInput,
		{
			gasLimit: transferEstimate,
			maxFeePerGas: maxFeePerGas,
			maxPriorityFeePerGas: 0,
		}
	);

	const receipt = (await tx.wait()) as unknown as ContractReceipt;

	const [transferEvent] = filterTransactionEvents(ERC20_ABI, receipt.logs, ["Transfer"]);

	logger.info(
		{
			result: {
				transactionHash: receipt.transactionHash,
				blockNumber: receipt.blockNumber,
				transferEvent: {
					name: transferEvent.name,
					args: transferEvent.args,
				},
			},
		},
		"receive result"
	);
});

package.json2.33.2.2

{
  "scripts": {
    "call": "tsx --tsconfig ../../../tsconfig.json",
    "call:callERC20Transfer": "pnpm call src/callERC20Transfer.ts"
  }
}

Source: futureversecom/trn-examples, examples/evm/use-feeProxy (deleted) · commit 44c9e16, 2024-10-31 · Apache-2.0, license · part of Code examples

Associated docs

Where else you might go from here. Following one is optional — this chapter stands without them.

Any-token Gas

See also — Users can pay gas fees using any approved token or have them covered by developers.

Back matter — read in order

See also — The whole of Back matter as one continuous page, reprinted from its chapters without change.

Code examples

See also — Futureverse’s code examples for The Root Network: scripts for the native API and the EVM, and two contract projects, each with its README and source.

Contents

See also — Every chapter in this book, each with the one line that tells you what you get by reading it.

FeeProxy (precompile)

See also — FeeProxy (precompile)

Front matter — read in order

See also — The whole of Front matter as one continuous page, reprinted from its chapters without change.

Guides for the code examples

See also — How Futureverse’s TRN code examples get a test account: create one in MetaMask and fund it from the Porcini faucet.

Index · A

See also — 609 index terms that start with A, each linked to the pages that define or use it.