Update bind zones on public IP DHCP renew

gistfile1.txt

#!/home/doc/php/bin/php
<?php

$exit        = 0;
$exit_signal = 0;

function fork()
{
    $pid = pcntl_fork();
    if ($pid < 0) {
       exit(1);
    } else if ($pid) { // parent
        exit;
    } else { // child
        $pid = pcntl_fork();
        if ($pid < 0) { exit(1); }
        if ($pid) {
            exit;
        } else {
            $sid = posix_setsid();
           if ($sid < 0) {
               exit(1);
           }
            fclose(STDOUT);
            fclose(STDIN);
            fclose(STDERR);
        }
    }
}

function check_root()
{
    if (posix_getuid()) {
        echo "root needed\n";
        exit(1);
    }
}

function check_signals()
{
    global $exit, $exit_signal;

    if ($exit) {
        syslog(LOG_INFO, "exiting by signal $exit_signal");
        exit;
    }
}

function signal_handler($sig_no)
{
    global $exit, $exit_signal;

    $exit        = 1;
    $exit_signal = $sig_no;
}

function setup_signals(array $signals)
{
    pcntl_async_signals(true);

    foreach ($signals as $signal) {
        pcntl_signal($signal, 'signal_handler', false);
    }
}

function check_php()
{
    if (version_compare(PHP_VERSION, '7.1.0') <= 0) {
        echo "PHP >=7.1 needed\n";
        exit(1);
    }
}

function setup()
{
    openlog(__FILE__, LOG_NDELAY, LOG_LOCAL1);
    ini_set('default_socket_timeout', 2);
    setup_signals(SIGNALS);
}



/** ************ */


const BIND_FILES = [
    "/etc/bind/zones/db.jpauli.tech",
    "/etc/bind/zones/db.drarena.fr"
];
const SERVER_ADDR    = '127.0.0.1:6464';
const IP_URL         = 'http://ipv4.lafibre.info/ip.php';
const IP_REGEX       = '((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)';
const SIGNALS        = [SIGTERM, SIGINT, SIGHUP];
const NETWORK_SECRET = "ip\n";


check_php();
check_root();
fork();
setup();

$s = @stream_socket_server(SERVER_ADDR, $errno, $error);
if (!$s) {
    syslog(LOG_ERR, "Can't create server : '$error'\n");
    exit(1);
}

while(1) {
    check_signals();

while ($c = @stream_socket_accept($s, -1)) {
    check_signals();
    $content = stream_get_contents($c, 3);
    if ($content != NETWORK_SECRET) {
        syslog(LOG_CRIT, "Got wrong challenge\n");
        goto end;
    }
    $newip = @file_get_contents(IP_URL, null, null, null, 20);
    if (!$newip || !preg_match('/'.IP_REGEX.'/', $newip)) {
        syslog(LOG_ERR, "Could not retrieve ip from " .IP_URL. "\n"); 
        goto end;
    }
    $reload = 0;
    foreach (BIND_FILES as $zone) {
        $m = [];
        if (!preg_match('/\$IP\s('.IP_REGEX.')\n/', $content = file_get_contents($zone), $m)) {
            syslog(LOG_ERR, "Bind zone file '$zone' seems wrong, no \$IP pattern found\n");
            continue;
        }
        if ($newip == $m[1]) {
            syslog(LOG_INFO, "no update needed\n");
            goto end;
        }
        $content = str_replace($m[1], $newip, $content);
        file_put_contents($zone, $content);
        $reload = 1;
    }
    if ($reload) {
        exec('rndc reload');
        syslog(LOG_INFO, "Updated zones to public ip $newip\n");
        fwrite($c, "ok");
    }

end:
    fclose($c);
    check_signals();
}

}