host-detection.php

<?php

// Plugin name: Host Detection

/*

CREATE TABLE `shared_host_landing` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `host` varchar(128) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL DEFAULT '' COMMENT 'The hosting company',
  `hash` char(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL DEFAULT '' COMMENT 'The md5 hash of the html landing page',
  `html` text CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT 'The html landing page served up when no domain is specified to the shared host',
  PRIMARY KEY (`id`),
  UNIQUE KEY `hash` (`hash`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

*/

function get_host_details_by_url( $url ) {
	$domain = wp_parse_url( $url, PHP_URL_HOST );
	$ips = gethostbynamel( $domain ); // Domains can have multiple A records, let's grab them all.

	if ( ! $ips ) {
		return null;
	}

	// Return details on the first one we find.
	foreach ( $ips as $ip ) {
		$details = get_host_details_by_ip( $ip );
		if ( $details ) {
			return $details;
		}
	}

	return null;
}

function get_host_details_by_ip( $ip ) {
	$url = "http://{$ip}";
	$response = wp_remote_get( esc_url_raw( $url ) );
	$html = wp_remote_retrieve_body( $response );

	return check_landing_page_details( $html );
}

function check_landing_page_details( $html ) {
	global $wpdb;

	// If we want to apply some regex check or something before checking the db, let's give it a shot.
	$host = apply_filters( 'pre_guess_host_from_landing_page', null, $html );
	if ( $host ) {
		return $host;
	}

	$html = trim( $html );
	$hash = md5( $html );

	$host = $wpdb->get_var( $wpdb->prepare( "SELECT `host` FROM `shared_host_landing` WHERE `hash` = '%s'", $hash ) );

	// If it comes back as null, we don't have a record of it, insert.
	if ( is_null( $host ) ) {
		// Possibly easier way for other bits of code to recognize the landing page.
		$host = apply_filters( 'guess_host_from_landing_page', $host, $html );
		$wpdb->insert(
			'shared_host_landing',
			array(
				'host' => $host,
				'hash' => $hash,
				'html' => $html,
			)
		);
	}

	return $host;
}