Bitcoin Transaction with MetaData

transaction.js

// Require the libraries we need to make this magic happen
var bitcoin = require(‘bitcoinjs-lib’);
var request = require(‘request’);
var blockchain = require(‘blockchain.info’);
var blockexplorer = require(‘blockchain.info/blockexplorer’);

// Export this module so you can easily call it from your main application
exports.opReturn = function (message, fromKey, toAddress) {
 // Create a new promise that can only resolve or reject
 return new Promise(function(resolve, reject) {

// Declare a few variables
 var network = bitcoin.networks.mainnet; // Specify we want to use the main net not the test net
 var keyPair = bitcoin.ECPair.fromWIF(fromKey); // Get the keypair from the WIF
 var address = keyPair.getAddress(); // Get the address from the WIF

// Lets get the unspent tranasctins for the address
var url = "https://blockchain.info/id/unspent?active="+address;
 request(url, function (error, response, body) {
 if (!error && response.statusCode == 200) {
  // Get the data back and parse it
 var body = JSON.parse(body);
 var tx = new bitcoin.TransactionBuilder(network); // Start to build the tranasction
 var data = new Buffer(message); // Message is inserted
 var dataScript = bitcoin.script.nullDataOutput(data);

// These must be atleast 9000 Satoshi to allow for 3000 for each recipient and 3000 for the miners fee
// You need to loop over and sum the value, here we just get the first two, I have a gist for this.
 var unspent = body.unspent_outputs[1].tx_hash_big_endian;
 var unspent = body.unspent_outputs[2].tx_hash_big_endian;
 tx.addInput(unspent, 0);
// End Loop

// Build and sign the transaction
 tx.addOutput(dataScript, 0);
 tx.addOutput(toAddress, 3000); // Specify we want to send 3000 satoshi to another address 
 tx.addOutput(address, 3000); // Specify we want to send 3000 satoshi back to ourselves
 tx.sign(0, keyPair); // Sign the transaction
 var txRaw = tx.build(); // Raw transaction
 var txId = txRaw.getId() // Transaction ID
 var hex = txRaw.toHex(); //Convert the transction to hex ready for transmitting 
 
 // and push the transaction to the blockchain (please wait)
 request.post("http://btc.blockr.io/api/v1/tx/push").form({hex:hex});
 resolve(hex); // Resolve the promise
 } else{
 reject(error); // Reject the poromise
 };
 })

}); // — END PROMISE
};// END FUNCTION