Gelato MetaBox SDK Hello World

Send Hello World transactions using Gelato MetaBox SDK

Prerequisite

• Check metabox-sdk npm package page to know more about how to use the Gelato's MetaBox relayer
  
  

How to use

1. Install project dependencies:

yarn install

2. Create a .env file to use on mumbai network:

CHAIN_ID=80001
PROVIDER_URL="https://rpc-mumbai.maticvigil.com/"
USER_PK=""
SPONSOR_PK=""

• USER_PK refers to private key of the Hello World application user. We only use it in this tutorial to produce a dApp's user signature, while in reality the signature would have been obtained in a safe way!

• SPONSOR_PK refers to the EOA that will pay transaction fee. Can be same as USER_PK. Note: On testnets like mumbai Gelato will pay transaction fees. But on production networks SPONSOR is expected to already hold a balance with Gelato.

Examples

1. Send a transaction using MetaBox SDK

• First, use MetaBoxSDK.isChainSupported to verify that your network is supported by Gelato MetaBox:

if (!process.env.CHAIN_ID) {
  throw new Error("chainId is missing");
}

const chainId = parseInt(process.env.CHAIN_ID);
const isChainSupported = await MetaBoxSDK.isChainSupported(chainId);
if (!isChainSupported) {
  console.log("ChainId not supported");
  return;
}

• Then, use MetaBoxSDK.metaBoxRequest to build the necessary data to be signed and submitted:

// address of HelloWorld's user (may be same EOA as sponsor)
const userAddress = await user.getAddress();

const { address, abi } = MetaBoxSDK.getMetaBoxAddressAndABI(chainId);
const gelatoMetaBox = new Contract(address, abi, provider);
// user's smart contract nonce (to prevent replay attacks)
const nonce: number = parseInt(await gelatoMetaBox.nonce(userAddress));
// HelloWorld uses EIP-2771 for compatability with meta transactions:
// msg.sender will safely be interpreted as userAddress
const isEIP2771 = true;

const request = MetaBoxSDK.metaBoxRequest(
  chainId,
  // target contract to call
  HELLO_WORLD,
  data,
  // feeToken
  ETH,
  userAddress,
  nonce,
  isEIP2771
);

• Compute digest by hashing request data, and then sign with each private key to produce userSignature and sponsorSignature:

// Distill request data into a hash
const digest = MetaBoxSDK.getDigestToSign(request);

// user signs digest
const userSignature = utils.joinSignature(
  await user._signingKey().signDigest(digest)
);

// sponsor signs digest
// Sponsor commits to paying transaction fee
// by having its balance deducted from Gelato Diamond SponsorFacet
let sponsorSignature: string | undefined = undefined;
if (sponsorPK && sponsorPK.length > 0) {
  const sponsor = new Wallet(sponsorPK);

  sponsorSignature = utils.joinSignature(
    await sponsor._signingKey().signDigest(digest)
  );
}

Note: This is NOT the recommended way of obtaining userSignature for UI users!

Only useful for illustration purposes.

If user is interacting with a UI using a wallet, consider using MetaBoxSDK.getWalletPayloadToSign(request), and then call rpc method eth_signTypedData_v4 to get userSignature.

• Finally, use MetaBoxSDK.sendMetaBoxTransaction to send transaction payload to Gelato MetaBox relayer:

const taskId = await MetaBoxSDK.sendMetaBoxTransaction(
  request,
  userSignature,
  sponsorSignature
);

Check this transaction for an example. Notice how the user address is not msg.sender but rather request.user, due to the fact that req.isEIP2771 was set as true.

By inheriting the ERC2771Context contract as we did in HelloWorld, and replacing all occurrences of msg.sender by _msgSender(), dApps can ensure that GelatoMetaBox safely passes on the original user's address whenever required. Alternatively, for dApps whose logic does not rely on who msg.sender or _msgSender() is, request.isEIP2771 should be set as false and no smart contract changes are required.

• Check the example source code send-tx.ts and try it yourself using:

yarn send-tx