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Building a Transaction Manually

Manually creating a transaction using WalletConnect gives you precise control over UTXO selection, calldata crafting, and transaction parameters. This guide walks you through the process of building a transaction using WalletConnect, specifically for interactions with OP_NET smart contracts.

Steps to Build a Transaction​

1. Get Required Parameters​

Before deploying a contract, ensure you have the following parameters:

  • account: Wallet account for transaction signing.
  • signer: Wallet signer for transaction authorization.
import { useWallet } from "@btc-vision/walletconnect";

const { account, signer } = useWallet();

2. Obtaining Proper UTXOs​

Before building a transaction, you need to gather the required UTXOs for funding. Use the utxoManager from the JSONRpcProvider to fetch UTXOs associated with your address.

const utxos = await account.provider.utxoManager.getUTXOs({
  address: account.address.p2tr(account.network),
});
UTXO Management

Ensure you have enough UTXOs to cover the transaction inputs, gas fees, and any additional outputs.

Learn more about UTXO Manager.

3. Define the Contract Instance​

Use the getContract method to define the contract you want to interact with. This step ensures you have a properly typed contract instance that can encode calldata for the desired function.

const contractAddress = "bcrt1qexampleaddress"; // Replace with a valid contract address

const contractInstance = getContract<IOP_20Contract>(
  contractAddress, // Contract address
  OP_20_ABI, // Contract ABI
  provider: account.provider, // Provider instance
  network: account.network, // Target network
  address: account.address // Sender's address
);
Contract Interaction

Ensure the contract instance matches the contract you want to interact with, including the correct address and ABI.

Learn more about Interacting with Smart Contracts.

4. Encode Calldata​

Prepare the calldata for the contract interaction using the contract instance's methods, ensuring it matches the function you want to call.

const approveCall = await contractInstance.approve(account.address, 100n);
// Alternatively, you can manually encode the calldata
// const approveCall = contractInstance.encodeCalldata(
//   "approve", // Function name
//   [account.account, 100n] // Function arguments
// );

if (!approveCall || !approveCall.calldata)
  throw new Error("Approve call failed.");

5. Configure Interaction Parameters​

Set up the IInteractionParameters object, which includes details like the signer, sender, UTXOs, calldata, and gas settings.

const interactionParameters: IInteractionParameters = {
  signer: signer!, // OP_WALLET does not require a signer
  from: account.address.p2tr(account.network), // Sender's address (P2TR)
  to: contractAddress, // Contract address
  utxos, // UTXOs for funding
  network: account.network, // Target network
  feeRate: Number((await account.provider.gasParameters()).baseGas * 2n), // Gas fee rate (satoshis per byte)
  priorityFee: 5000n, // Priority fee for faster processing
  gasSatFee: 5000n, // Gas fee (satoshis)
  calldata: approveCall.calldata, // Call data from the approve function call
};

6. Signing the Deployment Transaction​

Use the signDeployment method from TransactionFactory to sign the interaction transaction.

const transactionFactory = new TransactionFactory();
const interactionResult = await transactionFactory.signInteraction(
  interactionParameters
);

console.log(interactionResult);

7. Broadcasting the Transaction​

Finally, broadcast the signed transaction to the network using the sendRawTransaction method.

const transactionReceipt = await account.provider.sendRawTransaction(
  interactionResult.interactionTransaction,
  false
);

const txId = transactionReceipt.result;

console.log(`Transaction ID: ${txId}`);

Full Example​

import {
  IInteractionParameters,
  TransactionFactory,
} from "@btc-vision/transaction";
import { SupportedWallets, useWallet } from "@btc-vision/walletconnect";
import { getContract, IOP_20Contract, OP_20_ABI } from "opnet";

function BuildAnApproveTransaction() {
  const { account, connect, disconnect, signer } = useWallet();

  async function approveRandomToken() {
    if (!account) throw new Error("Connect wallet first");

    const utxos = await account.provider.utxoManager.getUTXOs({
      address: account.address.p2tr(account.network),
    });

    const contractAddress = "bcrt1qexampleaddress"; // Replace with a valid contract address

    const contractInstance = getContract<IOP_20Contract>(
      contractAddress, // Contract address
      OP_20_ABI, // Contract ABI
      provider: account.provider, // Provider instance
      network: account.network, // Target network
      address: account.address // Sender's address
    );

    const approveCall = await contractInstance.approve(account.address, 100n);

    if (!approveCall || !approveCall.calldata)
      throw new Error("Approve call failed.");

    const interactionParameters: IInteractionParameters = {
      signer: signer!, // OP_WALLET does not require a signer
      from: account.address.p2tr(account.network), // Sender's address (P2TR)
      to: contractAddress, // Contract address
      utxos, // UTXOs for funding
      network: account.network, // Target network
      feeRate: Number((await account.provider.gasParameters()).baseGas * 2n), // Gas fee rate (satoshis per byte)
      priorityFee: 5000n, // Priority fee for faster processing
      gasSatFee: 5000n, // Gas fee (satoshis)
      calldata: approveCall.calldata, // Call data from the approve function call
    };

    const transactionFactory = new TransactionFactory();
    const interactionResult = await transactionFactory.signInteraction(
      interactionParameters
    );

    console.log(interactionResult); // This is not sent to the blockchain yet

    const transactionReceipt = await account.provider.sendRawTransaction(
      interactionResult.interactionTransaction,
      false
    );

    const txId = transactionReceipt.result;

    console.log(`Transaction ID: ${txId}`);
  }

  return (
    <div>
      {account ? (
        <div>
          <p>Connected Address: {account.address.p2tr(account.network)}</p>
          <button onClick={approveRandomToken}>Approve a random token</button>
          <button onClick={disconnect}>Disconnect</button>
        </div>
      ) : (
        <button onClick={() => connect(SupportedWallets.OP_WALLET)}>
          Connect Wallet
        </button>
      )}
    </div>
  );
}

export default BuildAnApproveTransaction;

Best Practices​

  • Always fetch UTXOs that meet the requirements of your transaction and validate their sufficiency.
  • Ensure your gas estimate includes a buffer to prevent transaction failures due to fluctuating network conditions.
  • Verify the calldata matches the intended contract interaction to avoid unexpected behavior.
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