index.php

<?php
$sitemap    = "sitemap.xml";
$startUrl   = "http://php.net";
$extencions = [
    ".html",
    ".php",
    "/",
];
$scanned    = [];

function checkUrl($url)
{
    global $startUrl, $extencions, $scanned, $pf;

    if (in_array($url, $scanned) == true) {
        return;
    }

    array_push($scanned, $url);
    $html = getUrl($url);
    preg_match_all('/href="([^"]+)"/', $html, $links);

    foreach ($links[ 1 ] as $key => $link) {
        $baseUrl = preg_split('/[#|?]/', $link);
        $nextUrl = $baseUrl[ 0 ];

        if ((substr($nextUrl, 0, 7) == "mailto:") || (substr($nextUrl, 0, 6) == "ftp://")) {
            return;
        } elseif ((substr($nextUrl, 0, 7) != "http://") && (substr($nextUrl, 0, 8) != "https://")) {
            $nextUrl = @filterUrls($nextUrl, $startUrl);
        } else {
            $nextUrl = @checkHost($nextUrl, $startUrl);
        }

        if (substr($nextUrl, 0, strlen($startUrl)) == $startUrl) {
            $ignore = false;

            if (in_array($nextUrl, $scanned)) {
                $ignore = true;
            }

            if ( ! $ignore) {
                foreach ($extencions as $ext) {
                    if (strpos($nextUrl, $ext) != false) {
                        fwrite($pf, "  <url>\n" .
                                    "    <loc>" . $nextUrl . "</loc>\n" .
                                    "  </url>\n");
                        checkUrl($nextUrl);
                    }
                }
            }
        }
    }
}

function getUrl($url)
{
    $agent = 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36';
    $ch    = curl_init();
    curl_setopt($ch, CURLOPT_AUTOREFERER, true);
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_USERAGENT, $agent);
    curl_setopt($ch, CURLOPT_VERBOSE, 1);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5);
    $data = curl_exec($ch);
    curl_close($ch);

    return $data;
}

function checkHost($currentUrl, $startUrl)
{
    $parsedUrl = parse_url($startUrl);
    $host      = $parsedUrl[ 'host' ];

    if (parse_url($currentUrl, PHP_URL_HOST) != $host) {
        return;
    }
}

function filterUrls($currentUrl, $startUrl)
{
    $parsedUrl = parse_url($startUrl);
    $scheme    = $parsedUrl[ 'scheme' ];
    $host      = $parsedUrl[ 'host' ];

    if (strpos($currentUrl, "/") == 0) {
        return $scheme . '://' . $host . $currentUrl;
    }

    if ((parse_url($currentUrl, PHP_URL_SCHEME) == null) || ! strpos($currentUrl, "/")) {
        return $scheme . '://' . $host . '/' . $currentUrl;
    }


}

$pf = fopen($sitemap, "w");
fwrite($pf, "<urlset xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\"\n" .
            "xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"\n" .
            "xsi:schemaLocation=\"http://www.sitemaps.org/schemas/sitemap/0.9\n" .
            "http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd\">\n" .
            "   <url>\n" .
            "       <loc>" . $startUrl . "</loc>\n" .
            "   </url>\n");
checkUrl($startUrl);
fwrite($pf, "</urlset>\n");
fclose($pf);