Substrate To EVM Token Transfer

EVM-to-Substrate token transfer example

In the following example, we will use the TESTNET environment to perform a cross-chain ERC-20 transfer with 0.5 sygUSD sygUSD tokens. The transfer will be initiated on the Substrate-side via the Rococo-Phala 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/pallets. 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 12-word mnemonic for your Substrate development wallet
• An Ethereum wallet to receive tokens into (the example presets an existing wallet address already)
• A Substrate provider (in case the hardcoded WSS within the script does not work)
• A Substrate development wallet funded with sygUSD tokens; you will need to run the EVM-to-Substrate example first to preload sygUSD tokens into a Substrate wallet

danger

We make use of the dotenv module to manage Substrate's private mnemonics with environment variables. Please note that accidentally committing a .env file containing private mnemonics 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 import the Substrate 12-word private mnemonic. To run the example, you will need to configure your environment variable to include your Substrate test development account's 12-word seed. A .env.sample is provided as a template.

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

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

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

Replace between the quotation marks your 12-word mnemonic:

PRIVATE_MNEMONIC="YOUR TWELVE WORD MNEMONIC HERE WITH SPACES"

Replace the placeholder value in the script for recipient with your preferred destination EVM address.

To send a Substrate token transfer from Substrate to EVM, run:

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

The example will use @polkadot/keyring in conjunction with the sygma-sdk to create a transfer from Rococo-Phala to Sepolia with the sygUSD token. It will be received on Sepolia as a sygUSD 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 { Keyring } from "@polkadot/keyring";
import { ApiPromise, WsProvider } from "@polkadot/api";
import { cryptoWaitReady } from "@polkadot/util-crypto";
import { Environment, Substrate, getTransferStatusData } from "@buildwithsygma/sygma-sdk-core";

const { SubstrateAssetTransfer } = Substrate;
const SEPOLIA_CHAIN_ID = 11155111;
const RESOURCE_ID = "0x0000000000000000000000000000000000000000000000000000000000001100"; // This is the resource ID for the sygUSD token according to Sygma's testnet environment 
const recipient = "0xD31E89feccCf6f2DE10EaC92ADffF48D802b695C"; // replace this value for your preferred EVM address 

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

import dotenv from "dotenv";

dotenv.config();

const MNEMONIC = process.env.PRIVATE_MNEMONIC;

if (!MNEMONIC) {
  throw new Error("Missing environment variable: PRIVATE_MNEMONIC");
}

• Defines the main Substrate transfer function, including the connection to the blockchain using a WebSocket provider, initializing the asset transfer instance, and setting up the keyring and account from the mnemonic phrase.

const substrateTransfer = async (): Promise<void> => {
  const keyring = new Keyring({ type: "sr25519" });
  await cryptoWaitReady();
  const account = keyring.addFromUri(MNEMONIC as string);
  const wsProvider = new WsProvider("wss://subbridge-test.phala.network/rhala/ws");
  const api = await ApiPromise.create({ provider: wsProvider });
  const assetTransfer = new SubstrateAssetTransfer();
  await assetTransfer.init(api, Environment.TESTNET);
  ...
}

• 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 getStatus = async (
  txHash: string
): Promise<{ status: string; explorerUrl: string } | void> => {
  try {
    const data = await getTransferStatusData(Environment.TESTNET, txHash);

    return data as { status: string; explorerUrl: string };
  } catch (e) {
    console.log("error: ", e);
  }
};

  let dataResponse: undefined | { status: string; explorerUrl: string };

    const id = setInterval(() => {
      getStatus(status.asInBlock.toString())
        .then((data) => {
          if (data) {
            dataResponse = data;
            console.log(data);
          }
        })
        .catch(() => {
          console.log("Transfer still not indexed, retrying...");
        });
    }, 5000);

    if (dataResponse && dataResponse.status === "executed") {
      console.log("Transfer executed successfully");
      clearInterval(id);
      process.exit(0);
    }
  });
};

• Constructs a transfer object that calculates the fee, then builds, signs, and sends the transaction.

const transfer = assetTransfer.createFungibleTransfer(
  account.address,
  SEPOLIA_CHAIN_ID,
  recipient,
  RESOURCE_ID,
   "500000000000000000" // 18 decimal places, so in this case 0.5 sygUSD tokens
);
const fee = await assetTransfer.getFee(transfer);
const transferTx = assetTransfer.buildTransferTransaction(transfer, fee);
const unsub = await transferTx.signAndSend(account, ({ status }) => {
  ...
});

• Logs the current status of the transaction, and if it's included in a block or finalized, outputs the respective block hash.

const unsub = await transferTx.signAndSend(account, ({ status }) => {
  console.log(`Current status is ${status.toString()}`);
  if (status.isInBlock) {
    console.log(`Transaction included at blockHash ${status.asInBlock.toString()}`);
  } else if (status.isFinalized) {
    console.log(`Transaction finalized at blockHash ${status.asFinalized.toString()}`);
    unsub();
  }
});