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Hello World

Create your Farcaster account programatically and publish your first "Hello World" message.

The example shows you how to:

  • Make onchain transactions to create an account
  • Rent a storage unit so you can publish messages
  • Add an account key to sign messages
  • Acquire an fname for your account
  • Create, sign and publish messages

This example can be checked out as a fully functional repository here.

Requirements

  • Write access to a hub (either your own, or a 3rd party hub)
  • An ETH wallet with about ~10$ USD of ETH bridged to Optimism
  • An ETH RPC URL for OP Mainnet (e.g. via Alchemy,Infura or QuickNode).

1. Set up constants

typescript
import {
  ID_GATEWAY_ADDRESS,
  idGatewayABI,
  KEY_GATEWAY_ADDRESS,
  keyGatewayABI,
  ID_REGISTRY_ADDRESS,
  idRegistryABI,
  FarcasterNetwork,
} from '@farcaster/hub-web';
import { zeroAddress } from 'viem';
import { optimism } from 'viem/chains';

/**
 * Populate the following constants with your own values
 */
const MNEMONIC = '<REQUIRED>';
const OP_PROVIDER_URL = '<REQUIRED>'; // Alchemy or Infura url
const RECOVERY_ADDRESS = zeroAddress; // Optional, using the default value means the account will not be recoverable later if the mnemonic is lost
const ACCOUNT_KEY_PRIVATE_KEY: Hex = zeroAddress; // Optional, using the default means a new account key will be created each time

// Note: nemes is the Farcaster team's mainnet hub, which is password protected to prevent abuse. Use a 3rd party hub
// provider like https://neynar.com/ Or, run your own mainnet hub and broadcast to it permissionlessly.
const HUB_URL = 'nemes.farcaster.xyz:2283'; // URL + Port of the Hub
const HUB_USERNAME = ''; // Username for auth, leave blank if not using TLS
const HUB_PASS = ''; // Password for auth, leave blank if not using TLS
const USE_SSL = false; // set to true if talking to a hub that uses SSL (3rd party hosted hubs or hubs that require auth)
const FC_NETWORK = FarcasterNetwork.MAINNET; // Network of the Hub

const CHAIN = optimism;

const IdGateway = {
  abi: idGatewayABI,
  address: ID_GATEWAY_ADDRESS,
  chain: CHAIN,
};
const IdContract = {
  abi: idRegistryABI,
  address: ID_REGISTRY_ADDRESS,
  chain: CHAIN,
};
const KeyContract = {
  abi: keyGatewayABI,
  address: KEY_GATEWAY_ADDRESS,
  chain: CHAIN,
};

2. Register and pay for storage

Create a function to register an FID and pay for storage. This function will check if the account already has an FID and return early if so.

typescript
const getOrRegisterFid = async (): Promise<number> => {
  const balance = await walletClient.getBalance({ address: account.address });
  // Check if we already have an fid
  const existingFid = (await walletClient.readContract({
    ...IdContract,
    functionName: 'idOf',
    args: [account.address],
  })) as bigint;

  if (existingFid > 0n) {
    return parseInt(existingFid.toString());
  }

  const price = await walletClient.readContract({
    ...IdGateway,
    functionName: 'price',
  });
  if (balance < price) {
    throw new Error(
      `Insufficient balance to rent storage, required: ${price}, balance: ${balance}`
    );
  }
  const { request: registerRequest } = await walletClient.simulateContract({
    ...IdGateway,
    functionName: 'register',
    args: [RECOVERY_ADDRESS],
    value: price,
  });
  const registerTxHash = await walletClient.writeContract(registerRequest);
  const registerTxReceipt = await walletClient.waitForTransactionReceipt({
    hash: registerTxHash,
  });
  // Now extract the FID from the logs
  const registerLog = decodeEventLog({
    abi: idRegistryABI,
    data: registerTxReceipt.logs[0].data,
    topics: registerTxReceipt.logs[0].topics,
  });
  const fid = parseInt(registerLog.args['id']);
  return fid;
};

const fid = await getOrRegisterFid();

3. Add an account key

Now, we will add an account key to the key registry. Every account key must have a signed metadata field from the fid of the app requesting it. In our case, we will use our own fid. Note, this requires you to sign a message with the private key of the address holding the fid. If this is not possible, register a separate fid for the app first and use that.

typescript
const getOrRegisterAccountKey = async (fid: number) => {
  if (ACCOUNT_KEY_PRIVATE_KEY !== zeroAddress) {
    // If a private key is provided, we assume the account key is already in the key registry
    const privateKeyBytes = fromHex(ACCOUNT_KEY_PRIVATE_KEY, 'bytes');
    const publicKeyBytes = ed25519.getPublicKey(privateKeyBytes);
    return privateKeyBytes;
  }

  const privateKey = ed25519.utils.randomPrivateKey();
  const publicKey = toHex(ed25519.getPublicKey(privateKey));

  const eip712signer = new ViemLocalEip712Signer(appAccount);
  // To add a key, we need to sign the metadata with the fid of the app we're adding the key on behalf of
  // Use your personal fid, or register a separate fid for the app
  const metadata = await eip712signer.getSignedKeyRequestMetadata({
    requestFid: APP_FID,
    key: APP_PRIVATE_KEY,
    deadline: Math.floor(Date.now() / 1000) + 60 * 60, // 1 hour from now
  });

  const { request: signerAddRequest } = await walletClient.simulateContract({
    ...KeyContract,
    functionName: 'add',
    args: [1, publicKey, 1, metadata], // keyType, publicKey, metadataType, metadata
  });

  const accountKeyAddTxHash = await walletClient.writeContract(
    signerAddRequest
  );
  await walletClient.waitForTransactionReceipt({ hash: accountKeyAddTxHash });
  // Sleeping 30 seconds to allow hubs to pick up the accountKey tx
  await new Promise((resolve) => setTimeout(resolve, 30000));
  return privateKey;
};

const accountPrivateKey = await getOrRegisterAccountKey(fid);

4. Register an fname

Now that the on-chain actions are complete, let's register an fname using the farcaster off-chain fname registry. Registering an fname requires a signature from the custody address of the fid.

typescript
const registerFname = async (fid: number) => {
  try {
    // First check if this fid already has an fname
    const response = await axios.get(
      `https://fnames.farcaster.xyz/transfers/current?fid=${fid}`
    );
    const fname = response.data.transfer.username;
    return fname;
  } catch (e) {
    // No username, ignore and continue with registering
  }

  const fname = `fid-${fid}`;
  const timestamp = Math.floor(Date.now() / 1000);
  const userNameProofSignature = await walletClient.signTypedData({
    domain: USERNAME_PROOF_DOMAIN,
    types: USERNAME_PROOF_TYPE,
    primaryType: 'UserNameProof',
    message: {
      name: fname,
      timestamp: BigInt(timestamp),
      owner: account.address,
    },
  });

  const response = await axios.post('https://fnames.farcaster.xyz/transfers', {
    name: fname, // Name to register
    from: 0, // Fid to transfer from (0 for a new registration)
    to: fid, // Fid to transfer to (0 to unregister)
    fid: fid, // Fid making the request (must match from or to)
    owner: account.address, // Custody address of fid making the request
    timestamp: timestamp, // Current timestamp in seconds
    signature: userNameProofSignature, // EIP-712 signature signed by the current custody address of the fid
  });
  return fname;
};

const fname = await registerFname(fid);

Note that this only associated the name to our fid, we still need to set it as our username.

5. Write to the hub

Finally, we're now ready to submit messages to the hub. First, we shall set the fname as our username. And then post a cast.

typescript
const submitMessage = async (resultPromise: HubAsyncResult<Message>) => {
  const result = await resultPromise;
  if (result.isErr()) {
    throw new Error(`Error creating message: ${result.error}`);
  }
  await hubClient.submitMessage(result.value);
};

const accountKey = new NobleEd25519Signer(accountPrivateKey);
const dataOptions = {
  fid: fid,
  network: FC_NETWORK,
};
const userDataUsernameBody = {
  type: UserDataType.USERNAME,
  value: fname,
};
// Set the username
await submitMessage(
  makeUserDataAdd(userDataUsernameBody, dataOptions, accountKey)
);

// Post a cast
await submitMessage(
  makeCastAdd(
    {
      text: 'Hello World!',
    },
    dataOptions,
    accountKey
  )
);

Now, you can view your profile on any farcaster client. To see it on Warpcast, visit https://warpcast.com/@<fname>