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SOLUTIONS.md

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Solutions for Beginners (React Native)

If you're new to developing with Bitcoin and React Native, this guide will help you get started with coding your own Bitcoin wallet. Below, you'll find solutions for important functions such as creating wallets, generating addresses, syncing with the blockchain, and handling transactions. Try implementing these functions on your own before checking the solutions. Remember, coding is a flexible process, and there may be multiple ways to achieve the same result.

1. Generate a New Wallet

This function creates a new wallet using a mnemonic:

const createWallet = async () => {
  try {
    _loading(true); // Set loading state to true to show loading UI
    const mnemonic = await new Mnemonic().fromString(mnemonicString); // Create wallet mnemonic from string
    const wallet = await Wallet.new({
      mnemonic, // Use mnemonic to generate wallet
      network: networkString, // Network type (e.g., mainnet or testnet)
      databaseConfig: DatabaseConfig.memory(), // Use in-memory storage for testing
    });
    console.log('Wallet created successfully:', wallet); // Log success
    _loading(false); // Stop loading once the wallet is created
  } catch (err) {
    console.log('Wallet creation error:', err); // Handle errors during wallet creation
    _loading(false); // Stop loading if an error occurs
  }
};

2. Get Wallet Balance

This function retrieves the current balance of the wallet:

const getWalletBalance = async () => {
  try {
    _loading(true); // Show loading UI
    const balance = await wallet.getBalance(); // Retrieve the balance of the wallet
    console.log('Wallet balance:', balance); // Log the balance for reference

    _loading(false); // Hide loading UI
  } catch (err) {
    console.log('Error fetching wallet balance:', err); // Handle errors in fetching balance
    _loading(false); // Hide loading UI on error
  }
};

3. Generate a New Bitcoin Address

This function generates a new Bitcoin receiving address from the wallet:

const getNewAddress = async () => {
  try {
    _loading(true); // Show loading UI
    const address = await wallet.getAddress(AddressIndex.NEW); // Generate a new unused address
    console.log('New Address:', address); // Log the new address for receiving funds

    _loading(false); // Hide loading UI
  } catch (err) {
    console.log('Error generating new address:', err); // Handle errors in address generation
    _loading(false); // Hide loading UI on error
  }
};

4. Sync the Wallet

This function synchronizes the wallet with the blockchain:

const syncWallet = async () => {
  try {
    _loading(true); // Show loading UI
    let blockchain = new BlockchainElectrumConfig({url: 'electrum_url'}); // Create Electrum blockchain config
    await blockchain.sync(); // Sync the wallet with the blockchain
    console.log('Wallet synchronized with the blockchain'); // Log successful sync

    _loading(false); // Hide loading UI
  } catch (err) {
    console.log(err); // Handle sync errors
    _loading(false); // Hide loading UI on error
  }
};

5. Pay to an Address

This function handles sending Bitcoin to a specified address:

const pay = async (
  invoice,
  amountSat,
  satPerVbyte = null,
  absoluteFeeSat = null,
) => {
  try {
    _loading(true); // Show loading UI
    const address = await Address.create(invoice); // Convert the address string to a Bitcoin Address object
    const script = await address.scriptPubKey(); // Get the scriptPubKey for locking funds to the address

    const txBuilder = new TxBuilder(); // Initialize a new transaction builder
    txBuilder.addRecipient(script, amountSat); // Add recipient and amount

    // Set the transaction fee
    if (satPerVbyte) {
      txBuilder.feeRate(satPerVbyte); // Set fee rate per vbyte
    } else if (absoluteFeeSat) {
      txBuilder.feeAbsolute(absoluteFeeSat); // Set absolute fee
    }

    txBuilder.enableRbf(); // Enable Replace-By-Fee (RBF)
    const txBuilderResult = await txBuilder.finish(wallet); // Finalize transaction

    const signedTx = await wallet.sign(txBuilderResult.psbt); // Sign the transaction
    const tx = await signedTx.extractTx(); // Extract finalized transaction

    await blockchain.broadcast(tx); // Broadcast transaction to the blockchain
    console.log('Transaction successful:', tx.txid()); // Log transaction ID

    _loading(false); // Hide loading UI
  } catch (err) {
    console.log('Error sending payment:', err); // Handle errors during transaction
    _loading(false); // Hide loading UI on error
  }
};

6. Generate Mnemonic

This function generates a new mnemonic for the wallet:

const genMnemonic = async () => {
  try {
    _loading(true); // Show loading indicator
    let seed = await Mnemonic.create(); // Generate a new Bitcoin mnemonic (seed phrase)
    _responseText(seed.value); // Store or display the generated seed
    _loading(false); // Hide loading indicator
  } catch (err) {
    _loading(false); // Hide loading indicator in case of error
  }
};

7. Get Extended Private Key

This function retrieves the extended private key (XPRV):

const getXprv = async () => {
  try {
    _seedModal(false); // Close seed modal
    _loading(true); // Show loading indicator
    let res = await BdkRn.createExtendedKey({
      network: 'testnet',
      mnemonic,
      password: '',
    });
    _responseText(JSON.stringify(res.value)); // Display the extended private key (XPRV)
    _loading(false); // Hide loading indicator
  } catch (err) {
    _loading(false); // Hide loading indicator in case of error
  }
};

8. Initialize Blockchain

This function initializes the blockchain instance:

const initBlockChain = async () => {
  try {
    _loading(true); // Show loading indicator
    let config: BlockchainRpcConfig = {
      url: 'http://127.0.0.1:18443',
      network: networkString,
      walletName: 'w1',
      authUserPass: {username: 'polaruser', password: 'polarpass'},
      syncParams: {
        startScriptCount: 15,
        startTime: 15,
        forceStartTime: true,
        pollRateSec: 120,
      },
    };

    setBlockchain(await blockchainInstance.create(config, BlockChainNames.Rpc)); // Initialize blockchain instance
    const height = await blockchain.getHeight(); // Retrieve the current block height
    const hash = await blockchain.getBlockHash(height); // Retrieve the block hash for the current height
    _response(`Height: ${height},
 Hash: ${hash}`); // Display the blockchain height and hash
    _loading(false); // Hide loading indicator
  } catch (e) {
    console.log('RPC error', e); // Log any RPC error
    _loading(false); // Hide loading indicator in case of error
  }
};

9. Sign Transaction

This function signs a Bitcoin transaction using the private key:

const signTransaction = async () => {
  try {
    _loading(true); // Show loading indicator
    let psbt = PartiallySignedTransaction.fromBase64(psbtString); // Create PSBT from base64 string

    // Create the secret key from the mnemonic
    let mnemonic = await new Mnemonic().fromString(mnemonicString);
    const descSecretKeyObj = new DescriptorSecretKey();
    let xprv = await descSecretKeyObj.create(networkString, mnemonic);

    // Sign the transaction with the private key
    let signedTx = await psbt.sign(xprv, signOptions);
    console.log('Signed Transaction:', await signedTx.toBase64()); // Log the signed transaction

    _loading(false); // Hide loading indicator
  } catch (err) {
    console.log(err); // Log any error that occurs during signing
    _loading(false); // Hide loading indicator in case of error
  }
};

10. Broadcast Transaction

This function broadcasts a signed Bitcoin transaction to the network:

const broadcastTransaction = async () => {
  try {
    _loading(true); // Show loading indicator
    let tx = Transaction.fromBase64(psbtString); // Convert PSBT from base64 to Transaction object
    await blockchain.broadcast(tx); // Broadcast transaction to the Bitcoin network
    console.log('Transaction broadcasted successfully'); // Log success message
    _loading(false); // Hide loading indicator
  } catch (err) {
    console.log(err); // Log any error that occurs during broadcast
    _loading(false); // Hide loading indicator in case of error
  }
};