EVM To EVM Token Transfer

EVM-to-EVM token transfer example

In the following example, we will use the TESTNET environment to perform a cross-chain ERC-20 transfer with 5 ERC20LRTST tokens. The transfer will be initiated on the EVM-side via the Cronos testnet and received on the EVM-side via the Sepolia Ethereum testnet.

This is an example script that demonstrates the functionality of the Sygma SDK and the wider Sygma ecosystem of relayers and bridge and handler contracts. The complete example can be found in this repo.

Prerequisites

Before running the script, ensure that you have the following:

• Node.js v18
• Yarn (version 3.4.1 or higher)
• The exported private key of your development wallet
• Testnet CRO for gas
• An Ethereum provider (in case the hardcoded RPC within the script does not work)
• A development wallet funded with ERC20LRTest tokens from the Sygma faucet (you can use the UI below; please allow some time for minting as testnet may be congested)

Network Type

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Network Type *

Network

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Network *

Token

​

Token *

Destination address *

danger

We make use of the dotenv module to manage exported private keys with environment variables. Please note that accidentally committing a .env file containing private keys to a wallet with real funds, onto GitHub, could result in the complete loss of your funds. Never expose your private keys.

Getting started

1. Clone the repository

Clone the sygma-sdk repository into a directory of your choice, and then cd into the folder:

git clone git@github.com:sygmaprotocol/sygma-sdk.git
cd sygma-sdk/

2. Install dependencies

Install the project dependencies by running:

yarn install

3. Build the SDK

Build the SDK by running the following command:

yarn sdk:build

4. Usage

This example uses the dotenv module to manage private keys. To run the example, you will need to configure your environment variable to include your test development account's exported private key. A .env.sample is provided as a template.

DO NOT COMMIT PRIVATE KEYS WITH REAL FUNDS TO GITHUB. DOING SO COULD RESULT IN COMPLETE LOSS OF YOUR FUNDS.

Create a .env file in the evm-to-evm example folder:

cd examples/evm-to-evm-fungible-transfer
touch .env

Replace between the quotation marks your exported private key:

PRIVATE_KEY="YOUR_PRIVATE_KEY_HERE"

To send an ERC-20 example transfer from EVM to EVM, run:

cd examples/evm-to-evm-fungible-transfer
yarn run transfer

The example will use ethers in conjunction with the sygma-sdk to create a transfer from Cronos to Sepolia with the ERC20LRTST token. It will be received on Sepolia as the ERC20LRTST token.

Script functionality

This example script performs the following steps:

• Initializes the SDK by importing the required packages and defining the constants for the script.

import { EVMAssetTransfer, Environment, getTransferStatusData, TransferStatusResponse } from "@buildwithsygma/sygma-sdk-core";
import { Wallet, providers } from "ethers";

const SEPOLIA_CHAIN_ID = 11155111;
const RESOURCE_ID =
  "0x0000000000000000000000000000000000000000000000000000000000000300"; // This is the resource ID for the ERC20LRTEST token according to Sygma's testnet environment 
const CRONOS_RPC_URL = process.env.CRONOS_RPC_URL || "https://evm-t3.cronos.org" // use your own provider in case this RPC URL does not work
const getStatus = async (
  txHash: string
): Promise<TransferStatusResponse[]> => {
    const data = await getTransferStatusData(Environment.TESTNET, txHash);
    return data as TransferStatusResponse[];
};

• Configures the dotenv module and sets the privateKey as a value to be pulled from the .env file.

import dotenv from "dotenv";

dotenv.config()

const privateKey = process.env.PRIVATE_KEY;

if (!privateKey) {
  throw new Error("Missing environment variable: PRIVATE_KEY");
}

• Defines the ERC-20 transfer function.

export async function erc20Transfer(): Promise<void> {

• Set up the provider, wallet, and asset transfer objects using the TESTNET environment.

 const provider = new providers.JsonRpcProvider(CRONOS_RPC_URL); 
 const wallet = new Wallet(privateKey ?? "", provider);
  const assetTransfer = new EVMAssetTransfer();
  await assetTransfer.init(provider, Environment.TESTNET);

• Constructs a transfer object that defines the details of the ERC-20 token transfer using the previously declared constants, as well as the amount to be transferred. As we specify the getAddress method from the ethers.js wallet module for our recipient, the recipient will be the same address but on a different test network.

  const transfer = assetTransfer.createFungibleTransfer(
    await wallet.getAddress(),
    SEPOLIA_CHAIN_ID,
    await wallet.getAddress(), // Sending to the same address on a different chain
    RESOURCE_ID,
    "5000000000000000000" // 18 decimal places, so in this case, 5 tokens would be sent
  );

• Retrieves the fee required to complete the transfer from the SDK.
• Builds the necessary approval transactions for the transfer and sends them using the Ethereum wallet. The approval transactions are required to authorize the transfer of ERC-20 tokens.

const fee = await assetTransfer.getFee(transfer);
  const approvals = await assetTransfer.buildApprovals(transfer, fee);
  for (const approval of approvals) {
    const response = await wallet.sendTransaction(
      approval as providers.TransactionRequest
    );
    console.log("Sent approval with hash: ", response.hash);

• Invokes the getTransferStatusData and getStatus functions by taking the transaction hash as an input to periodically check the status of the cross-chain transaction.

const id = setInterval(() => {
    getStatus(response.hash)
      .then((data) => {
        if (data[0]) {
          console.log("Status of the transfer", data[0].status);
          if(data[0].status == "executed") {
            clearInterval(id);
            process.exit(0);
          }
        } else {
          console.log("Waiting for the TX to be indexed");
        }
      })
      .catch((e) => {
        console.log("error:", e);
      });
  }, 5000);
}

• Builds the final transfer transaction and sends it using the Ethereum wallet.

  const transferTx = await assetTransfer.buildTransferTransaction(
    transfer,
    fee
  );
  const response = await wallet.sendTransaction(
    transferTx as providers.TransactionRequest
  );
  console.log("Sent transfer with hash: ", response.hash);
}