Simple PHP code act as a dig tool to find dns records (using specific given nameservers)

dns.php

<?php
$result = array();
$result_html = '';

function getDnsRecords($domain) {
    $result = array();
    $servers = array("8.8.8.8", "8.8.8.8", "8.8.8.8", "8.8.8.8", "8.8.8.8", "8.8.8.8", "8.8.8.8", "8.8.8.8");    

    foreach ($servers as $server) {
        $dnsResult = dns_get_record_from($server, "A", $domain);
        foreach ($dnsResult as $record) {
            reset($record);
            $host = $domain;
            $type = "A";
            $value = $record;
            $result[] = array(
                'server' => $server,
                'host' => $host,
                'type' => $type,
                'value' => $value
            );
        }
    }

    return $result;
}

if (isset($_POST['domain']) && !empty($_POST['domain'])) {
    $domain = $_POST['domain'];
    $domain_regex = '/[a-z\d][a-z\-\d\.]+[a-z\d]/i';
    if (preg_match($domain_regex, $domain)) {
        if ($url = parse_url($domain)) {
            if (isset($url['host'])) {
                $result = getDnsRecords($url['host']);
            } else if (isset($url['path'])) {
                $result = getDnsRecords($domain);
            }
        }
    }

    if (empty($result)) {
        $result_html = '<hr>Nothing found or Domain Invalid';
    } else {
        $result_html .= "<hr>\n<table>\n";
        foreach ($result as $record) {
            $result_html .= sprintf("<tr><td>%s</td><td>%s</td><td>%s</td><td>%s</td></tr>\n", $record['server'], $record['host'], $record['type'], $record['value']);
        }
        $result_html .= "</table>\n";
    }
}

function dns_get_record_from(string $server, string $type, string $record): array
{
	// Source: https://github.com/metaregistrar/php-dns-client/blob/master/DNS/dnsData/dnsTypes.php
	static $types = [
		1   => 'A',
		2   => 'NS',
		5   => 'CNAME',
		6   => 'SOA',
		12  => 'PTR',
		15  => 'MX',
		16  => 'TXT',
		28  => 'AAAA',
		255 => 'ANY',
	];

	$typeid = array_search($type, $types, true);

	if (!$typeid) {
		throw new \InvalidArgumentException('Invalid type');
	}

	$host = 'udp://' . $server;

	if (!$socket = @fsockopen($host, 53, $errno, $errstr, 10)) {
		throw new \RuntimeException('Failed to open socket to ' . $host);
	}

	$labels = explode('.', $record);
	$question_binary = '';

	foreach ($labels as $label) {
		$question_binary .= pack("C", strlen($label)); // size byte first
		$question_binary .= $label; // then the label
	}

	$question_binary .= pack("C", 0); // end it off

	$id = rand(1,255)|(rand(0,255)<<8);	// generate the ID

	// Set standard codes and flags
	$flags = (0x0100 & 0x0300) | 0x0020; // recursion & queryspecmask | authenticated data

	$opcode = 0x0000; // opcode

	// Build the header
	$header = "";
	$header .= pack("n", $id);
	$header .= pack("n", $opcode | $flags);
	$header .= pack("nnnn", 1, 0, 0, 0);
	$header .= $question_binary;
	$header .= pack("n", $typeid);
	$header .= pack("n", 0x0001); // internet class
	$headersize = strlen($header);
	$headersizebin = pack("n", $headersize);

	$request_size = fwrite($socket, $header, $headersize);
	$rawbuffer = fread($socket, 4096);
	fclose($socket);

	if (strlen($rawbuffer) < 12) {
		throw new \RuntimeException("DNS query return buffer too small");
	}

	$pos = 0;

	$read = function ($len) use (&$pos, $rawbuffer) {
		$out = substr($rawbuffer, $pos, $len);
		$pos += $len;
		return $out;
	};

	$read_name_pos = function ($offset) use ($rawbuffer) {
		$out = [];

		while (($len = ord(substr($rawbuffer, $offset, 1))) && $len > 0) {
			$out[] = substr($rawbuffer, $offset + 1, $len);
			$offset += $len + 1;
		}

		return $out;
	};

	$read_name = function() use (&$read, $read_name_pos) {
		$out = [];

		while (($len = ord($read(1))) && $len > 0) {
			if ($len >= 64) {
				$offset = (($len & 0x3f) << 8) + ord($read(1));
				$out = array_merge($out, $read_name_pos($offset));
				break;
			}
			else {
				$out[] = $read($len);
			}
		}

		return implode('.', $out);
	};

	$header = unpack("nid/nflags/nqdcount/nancount/nnscount/narcount", $read(12));
	$flags = sprintf("%016b\n", $header['flags']);

	// No answers
	if (!$header['ancount']) {
		return [];
	}

	$is_authorative = $flags[5] == 1;

	// Question section
	if ($header['qdcount']) {
		// Skip name
		$read_name();

		// skip question part
		$pos += 4; // 4 => QTYPE + QCLASS
	}

	$responses = [];

	for ($a = 0; $a < $header['ancount']; $a++) {
		$read_name(); // Skip name
		$ans_header = unpack("ntype/nclass/Nttl/nlength", $read(10));

		$t = $types[$ans_header['type']] ?? null;

		if ($type != 'ANY' && $t != $type) {
			// Skip type that was not requested
			$t = null;
		}

		switch ($t) {
			case 'A':
				$responses[] = implode(".", unpack("Ca/Cb/Cc/Cd", $read(4)));
				break;
			case 'AAAA':
				$responses[] = implode(':', unpack("H4a/H4b/H4c/H4d/H4e/H4f/H4g/H4h", $read(16)));
				break;
			case 'MX':
				$prio = unpack('nprio', $read(2)); // priority
				$responses[$prio['prio']] = $read_name();
				break;
			case 'NS':
			case 'CNAME':
			case 'PTR':
				$responses[] = $read_name();
				break;
			case 'TXT':
				$responses[] = $read($ans_header['length']);
				break;
			default:
				// Skip
				$read($ans_header['length']);
				break;
		}
	}

	return $responses;
}
?>


<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>DNS Lookup</title>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">
    <style>
        body {
            padding: 20px;
        }
        .form-inline {
            margin-bottom: 10px;
        }
        table {
            margin: auto;
            width: 100%;
        }
    </style>
</head>
<body>
    <div class="container">
        <h1 class="text-center">DNS Lookup</h1>
        <form method="post">
            <div class="form-inline justify-content-center">
                <label for="domain">Domain:</label>
                <input id="domain" type="text" name="domain" class="form-control mx-2" value="<?= empty($_POST['domain']) ? '' : $_POST['domain'] ?>">
                <button type="submit" class="btn btn-primary">Lookup</button>
            </div>
        </form>
        <div class="mt-4">
            <?= $result_html ? $result_html : '' ?>
        </div>
        <hr>
    </div>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>
</body>
</html>