forward.php

<?php

/**
 * example script to receive webhook events for a wallet and forward the bitcoin to another address (by the mapping)
 */

use BitWasp\BitcoinLib\RawTransaction;
use Blocktrail\SDK\Blocktrail;
use Blocktrail\SDK\BlocktrailSDK;
use Blocktrail\SDK\Connection\Exceptions\ObjectNotFound;
use Blocktrail\SDK\TransactionBuilder;
use Blocktrail\SDK\Wallet;
use Blocktrail\SDK\WalletInterface;

require_once __DIR__ . "/../vendor/autoload.php";

/**
 * easy debugging helper, both var_dump and error_log for w/e you are
 * @param $m
 */
function debug($m) {
    var_dump($m);
    error_log(json_encode($m));
};

// address map of old -> new addresses
// you could read JSON file
// $addressMap = json_decode(file_get_contents(__DIR__ . "address_map.json"), true);
$addressMap = [
    // "old" => "new",
    "2NE51wGFR4dQYWAG6jUYTtnsAyDeBv3jUyV" => "2MvusSia19Yk19Rw8PjGVjj1TjvxcP1eT23", // example of my own wallet
];

// init SDK with API key + secret
$testnet = true;
$client = new BlocktrailSDK("MY_APIKEY", "MY_APISECRET", "BTC", $testnet);

// wallet identifier and password for a little down the line
$walletIdentifier = "testyrgridwallet";
$walletPassword = "testyrgridwallet";

// read POST JSON
$json = file_get_contents("php://input");
$data = json_decode($json, true);

// sanity check
if (!isset($data['network']) || !isset($data['event_type'])) {
    throw new \Exception("Invalid request");
}

// sanity check
if (($testnet && $data['network'] !== 'tBTC') || (!$testnet && $data['network'] !== 'BTC')) {
    throw new \Exception("Invalid network");
}

// sanity check
if ($data['event_type'] != "address-transactions") {
    debug("event we don't care about, ignore!");
    exit(0);
}

$transaction = $data['data'];
$confirmations = $transaction['confirmations'];
$walletInfo = $data['wallet'];
$addressInfo = $data['addresses'];

// we should always have a webhook call for either unconfirmed or fist confirmed, ignore others
//  it wouldn't hurt to replace this with something that keeps track if the transaction was already processed
//  because then we don't have to try and spend it (blindly), see also the trycatch around the sending of the TX
if ($confirmations > 1) {
    debug("> 1 confirmation, ignore!");
    exit(0);
}

// ignore outgoign txs
if ($walletInfo['balance'] <= 0) {
    debug("Outgoing transaction, ignore!");
    exit(0);
}

if (count($walletInfo['addresses']) > 0) {
    throw new \Exception("This is very weird, incoming transaction with multiple addresses owned by this wallet [{$transaction['hash']}]");
}

// uncommit for easy debugging info
// debug(json_encode($data));

// loop over all addresses that are part of the wallet
foreach ($walletInfo['addresses'] as $address) {
    // check if address received BTC (balance change is positive)
    $sum = $addressInfo[$address];

    if ($sum <= Blocktrail::BASE_FEE) {
        throw new \Exception("TX that isn't work forwarding because it's less than the fee [{$transaction['hash']}]");
    }

    if ($sum > 0) {
        // check if we know a mapping for this address
        if (!isset($addressMap[$address])) {
            throw new \Exception("Address not in mapping [{$address}] for TX [{$transaction['hash']}]");
        }

        // new address
        $newAddress = $addressMap[$address];

        // filter out the outputs that are relevant (we don't care about the change)
        $outputs = array_filter($transaction['outputs'], function($output) use($address) { return $output['address'] == $address; });

        // sanity check
        if (count($outputs) == 0) {
            throw new \Exception("Impossible");
        }

        // make a TxBuilder so we can construct a custom TX
        $txBuilder = new TransactionBuilder();

        // use the outputs of the TX as the inputs for the new TX
        foreach ($outputs as $output) {
            $txBuilder->spendOutput($transaction['hash'], $output['index'], $output['value'], $output['address']);
        }

        // use fixed BASE_FEE
        $fee = Blocktrail::BASE_FEE;

        // send total minus fee to new address
        //  alternatively you could hardcode an address of a completely seperate wallet for these funds
        //  when your webhook would support the old addresses still
        $txBuilder->addRecipient($newAddress, $sum - $fee);

        // fixed fee, so it won't do coinselection (which would probably cause change etc, to hard to deal with)
        $txBuilder->setFee($fee);

        // init wallet, need it now
        $wallet = $client->initWallet([
            "identifier" => $walletIdentifier,
            "passphrase" => $walletPassword
        ]);

        // send
        try {
            $txHash = $wallet->sendTx($txBuilder, false);

            debug($txHash);
            exit(0);
        } catch (\Exception $e) {
            if ($confirmations === 1) {
                // ignore, we probably failed to do the TX because we already did it when confirmations=0
            }
        }
    }
}