Inbound Bitcoin Transaction

Before going any further, make sure you have a testnet Wanchain node and a testnet Bitcoin node running, and that you have a funded Wanchain account and a funded Bitcoin address. With those in place, we are ready to set up a Bitcoin cross-chain transaction.

Getting started

To get started, let’s create a new directory and initialize npm in it, and then add the dependencies we will be using in our example scripts.

$ mkdir wanchain-bitcoin-crosschain
$ cd !$
$ npm init
$ npm install --save wanx web3 keythereum wanchainjs-tx node-bitcoin-rpc moment bignumber.js

Before setting up our transaction script, let’s add a file (./utils.js) that includes the Wanchain helper function introduced before with the Ethereum integration, but now also with another utility function for sending bitcoin to a given address. We’ll use this sendBtc function to add funds to the P2SH lock address that we create.

utils.js

const WanTx = require('wanchainjs-tx');

module.exports = {
  sendBtc,
  sendRawWanTx,
};

function callRpc(bitcoinRpc, method, args) {
  return new Promise((resolve, reject) => {
    bitcoinRpc.call(method, args, (err, res) => {
      if (err) {
        return reject(err);
      } else if (res.error) {
        return reject(res.error);
      }

      resolve(res.result);
    });
  });
}

async function sendBtc(bitcoinRpc, toAddress, toAmount, changeAddress) {

  const rawTx = await callRpc(bitcoinRpc, 'createrawtransaction', [[], { [toAddress]: toAmount }]);

  const fundArgs = { changePosition: 1 };

  if (changeAddress) {
    fundArgs.changeAddress = changeAddress;
  }

  const fundedTx = await callRpc(bitcoinRpc, 'fundrawtransaction', [rawTx, fundArgs]);

  const signedTx = await callRpc(bitcoinRpc, 'signrawtransactionwithwallet', [fundedTx.hex]);

  const txid = await callRpc(bitcoinRpc, 'sendrawtransaction', [signedTx.hex]);

  return txid;
}

async function sendRawWanTx(web3, rawTx, fromAccount, privateKey) {

  // Get the tx count to determine next nonce
  const txCount = await web3.eth.getTransactionCount(fromAccount);

  // Add the nonce to tx
  rawTx.nonce = web3.utils.toHex(txCount);

  // Sign and serialize the tx
  const transaction = new WanTx(rawTx);
  transaction.sign(privateKey);
  const serializedTx = transaction.serialize().toString('hex');

  // Send the lock transaction on Ethereum
  const receipt = await web3.eth.sendSignedTransaction('0x' + serializedTx);

  return receipt;
}

The sendBtc function creates a funded raw transaction with the change address in the second output.

Note: a Bitcoin lock transaction is considered valid by Storeman group nodes only if the output that funds the P2SH address is the first output (0) in the transaction. Any change address outputs should come after the initial funding output.

The sendRawWanTx function adds the account’s next nonce to the transaction object, signs the transaction with the provided private key, and then sends the transaction to the network.

Make the transaction

Now let’s start on our script that will make the inbound Bitcoin cross-chain transaction, btc2wbtc.js. To remind you, this script will convert bitcoin (BTC) to the bitcoin token on Wanchain (wBTC), and it will do so by following the steps previously mentioned.

To start, add the necessary dependencies to the top of the script.

btc2wbtc.js

const WanX = require('wanx');
const Web3 = require('web3');
const keythereum = require('keythereum');
const bitcoinRpc = require('node-bitcoin-rpc');
const BigNumber = require('bignumber.js');
const moment = require('moment');

const utils = require('./utils');

Next, set up an RPC connection with the bitcoin node, making sure to fill in the correct address, port, and RPC username and password. Also, since the default timeout for the bitcoin RPC package is quite low and can cause problems, go ahead and increase that to 2 seconds.

const btcNode = [ 'localhost', 18332, '<btcuser>', '<btcpassword>' ];

bitcoinRpc.init(...btcNode);
bitcoinRpc.setTimeout(2000);

Then set up WanX, as well as Web3, which like before we’ll use for communicating with the Wanchain node.

const config = {
  wanchain: { url: 'http://localhost:18545' },
};

const wanx = new WanX('testnet', config);

const web3wan = new Web3(new Web3.providers.HttpProvider(config.wanchain.url));

For the final piece of the setup, let’s use keythereum and unlock the Wanchain account keystore. Make sure to put in the correct Wanchain address, the correct path to the keystore file, as well as the correct keystore passphrase.

const wanAddress = '<myWanchainAddress>';

const wanDatadir = '/home/<myuser>/.wanchain/testnet/';
const wanKeyObject = keythereum.importFromFile(wanAddress, wanDatadir);
const wanPrivateKey = keythereum.recover('mypassword', wanKeyObject);

Now we are ready to initialize a new wanx chain and start our cross-chain transaction. First, let’s set up the new chain with wanx, using the newChain method. The 1st argument specifies the chain we want to connect with, in this case “btc”, and the 2nd argument indicates that this will be an inbound transaction (true for inbound, and false for outbound).

// bitcoin, inbound
const cctx = wanx.newChain('btc', true);

Our final setup action will be to define the transaction options. Each chain type requires certain parameters to be passed within the options, which can be deduced from the WanX Documentation.

In the options we need to define the Bitcoin address that will be the revoker address. The revoker address must be a legacy address, and it does not need to be funded. Thus, we will create a new legacy bitcoin address for the sole purpose of revoking.

$ bitcoin-cli -testnet getnewaddress '' legacy

Now add the revoker address to our btc2wbtc.js script.

const revokerAddress = 'mvTfNujpcQwHaefMxfJRix4vhfNBxSFbBe';

At last, let’s define the transaction options.

const opts = {
  // Revoker bitcoin address
  from: revokerAddress,

  // Recipient wanchain address
  to: wanAddress,

  // Value in satshis
  value: '210000',

  // Storeman group addresses
  storeman: {
    wan: '0x9ebf2acd509e0d5f9653e755f26d9a3ddce3977c',
    btc: '0x83e5ca256c9ffd0ae019f98e4371e67ef5026d2d',
  },

  // Generate a new redeemKey
  redeemKey: wanx.newRedeemKey('sha256'),
};

The options include the revoker address, the Wanchain address, the amount to be sent (210000 satoshis), the addresses of the Storeman group, and a new redeemKey. The redeemKey includes two parts, a random string (x, which is the key needed to redeem the token) and the hash of the random string (xHash, which is the transaction identifier). For the case of Bitcoin, we need the redeemKey hash to be a SHA256 hash.

Before the transaction gets kicked off, let’s also log out the transaction opts. In the crude example the redeemKey is not stored anywhere, so we need to make sure to print it to stdOut so that we can capture the redeemKey, in case we need to redeem or revoke later.

console.log('Tx opts:', opts)

If the script runs perfectly you will not need to know or keep the redeemKey. But if the scripts has an error and the transaction does not complete, you will not be able to recover any lost funds without the redeemKey.

Next, let’s go ahead and add in the basic logic of the transaction. We’ll fill in the missing functions in a bit.

Promise.resolve([])
  .then(lockBitcoin)
  .then(sendLock)
  .then(confirmLock)
  .then(sendRedeem)
  .then(confirmRedeem)
  .catch(err => {
    console.log('Error:', err);
  });

Let’s go ahead and define the functions for these five steps.

async function lockBitcoin() {

  // Step 1: generate a new P2SH lock address and send bitcoin to it

  // Create new P2SH lock address
  const contract = cctx.buildHashTimeLockContract(opts);

  // Log the P2SH address details
  console.log('Created new BTC contract', contract);

  // Add the lockTime to opts
  opts.lockTime = contract.lockTime;

  // Convert BTC amount from satoshis to bitcoin
  const sendAmount = (new BigNumber(opts.value)).div(100000000).toString();

  console.log('Send amount', sendAmount);

  // Send BTC to P2SH lock address
  const txid = await btcUtils.sendBtc(bitcoinRpc, contract.address, sendAmount);

  // Add txid to opts
  opts.txid = txid;

  console.log('BTC tx sent', txid);
}

async function sendLock() {

  // Get the raw lock tx
  const lockTx = cctx.buildLockTx(opts);

  // Send the lock tx on Ethereum
  const receipt = await utils.sendRawWanTx(web3eth, lockTx, opts.to, wanPrivateKey);

  console.log('Lock sent:', receipt);
}

async function confirmLock() {

  // Get the current block number on Wanchain
  const blockNumber = await web3wan.eth.getBlockNumber();

  // Scan for the lock confirmation from the storeman
  const log = await cctx.listenLock(opts, blockNumber);

  console.log('Lock confirmed:', log);
}

async function sendRedeem() {

  // Get the raw redeem tx
  const redeemTx = cctx.buildRedeemTx(opts);

  // Send the redeem transaction on Wanchain
  const receipt = await utils.sendRawWanTx(web3wan, redeemTx, opts.to, wanPrivateKey);

  console.log('Redeem sent:', receipt);
}

async function confirmRedeem(receipt) {

  // Scan for the lock confirmation from the storeman
  const log = await cctx.listenRedeem(opts, receipt.blockNumber);

  console.log('Redeem confirmed:', log);
  console.log('COMPLETE!!!');
}

As you can see, the sendLock function generates a new P2SH lock address (buildHashTimeLockContract) and sends bitcoin to it (sendBtc). The lockTime and txid are saved to opts, as they are needed parameters in the next step where we send a lock notice contract call on Wanchain (buildLockTx). Once the lock notice is sent, it waits for a response from the storeman (listenLock). After the Storeman group confirms the lock, it sends a redeem call on Wanchain. And then finally, it waits for the Storeman group to confirm the redeem.

Note: the confirmRedeem function call is technically not needed, since the Wanchain token are sent to the recipient's account once the sendRedeem succeeds. The example adds the final step only for completeness.

If everything went well, the Wanchain account used in the opts should now have 0.0021 Bitcoin token. The token is a WRC-20 token, so you can make the usual token contract calls, such as balanceOf, transfer, transferFrom, etc. Alternatively, you can check the explorer site to that the transaction completed and that the Wanchain account has Bitcoin token.