cpfp.js

const bitcore = require("bitcore-lib");
const axios = require("axios");

exports.childPaysForParent = async (req, res) => {
    try {
        // Load the Bitcoin private key
        const privateKey = new bitcore.PrivateKey.fromWIF(process.env.BITCOIN_PRIVATE_KEY, testnet);
        const address = privateKey.toAddress(testnet);

        // Fetch the unspent transaction outputs (UTXOs)
        const { data: utxos } = await axios.get(`https://blockstream.info/testnet/api/address/${address}/utxo`);

        // Identify the unconfirmed UTXO (the parent transaction we want to expedite)
        const unconfirmedUtxo = utxos.find(utxo => utxo.status.confirmed === false);

        if (!unconfirmedUtxo) {
            return res.status(400).send({ error: "No unconfirmed UTXOs found." });
        }

        const transaction = new bitcore.Transaction();

        const scriptPubKey = bitcore.Script.buildPublicKeyHashOut(privateKey.toPublicKey()).toString();

        // Use the unconfirmed UTXO in our new transaction
        transaction.from({
            txId: unconfirmedUtxo.txid,
            outputIndex: unconfirmedUtxo.vout,
            script: scriptPubKey,
            satoshis: unconfirmedUtxo.value
        });

        const fee = 100000; // Higher fee than the parent transaction
        const remaining = unconfirmedUtxo.value - fee;

        transaction.change(address);
        transaction.fee(fee);
        transaction.sign(privateKey);

        const serializedTransaction = transaction.serialize();

        const { data: result } = await axios.post(
            "https://api.blockcypher.com/v1/btc/test3/txs/push",
            { tx: serializedTransaction }
        );

        res.send({ txId: result.tx.hash });
    } catch (error) {
        console.error(error);
        res.status(500).send({ error: error.message });
    }
};