time out problem with gethostbyaddr() function in php - php

Question

recently i noticed that on my new server the gethostbyaddr() function which is used on my site to get the referes' hosts, it makes the page load 5 times slower.
and when I removed it the time out problem is gone
what is wrong with this function and my new Centos linux server config.
and what else i can use instead of this php function to get the host name of my referers.

Answer 1

It may be a temporary slowness in DNS resolution and it may clear itself up later. There really isn't any alternative to gethostbyaddr() other than to make a system call like the following from PHP. (gethostbyaddr() does essentially this anyway)
`nslookup $ip_address`
// Or
`host $ip_address`
You can test to see if resolutions are slow from the command line with :
# choose an IP address you know the resolution of...
$ host 123.123.123.123
If this doesn't return quickly you may have a DNS problem.
Check the contents of /etc/resolv.conf and if you have an alternate DNS server you can point it to, try that one instead.

Answer 2

I wrote this useful replacement for gethostbyaddr():
//faster alternative to gethostbyaddr()
private function gethost( $ip )
{
//Make sure the input is not going to do anything unexpected
//IPs must be in the form x.x.x.x with each x as a number
if( preg_match( '/^(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)(?:[.](?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)){3}$/', $ip ) )
{
$host = `host -s -W 1 $ip`;
$host = ( $host ? end( explode( ' ', trim( trim( $host ), '.' ) ) ) : $ip );
if( in_array( $host, Array( 'reached', 'record', '2(SERVFAIL)', '3(NXDOMAIN)' ) ) )
{
return sprintf( '(error fetching domain name for %s)', $ip );
}
else
{
return $host;
}
}
else
{
return '(invalid IP address)';
}
}
The trick is to use the host function, but you have to check if the $ip is a real IP to avoid exploits.
I set the timout to 1 second.
It's much faster than using gethostbyaddr, although it is still slow when used in a loop.

Answer 3

What kind of web hosting do you have? Shared, VPS or dedicated. gethostbyaddr() performance is dependent on how effective your web server DNS resolution is. There are some scenarios which might decrease its performance but you would still need to say at least what type of hosting you are using.

Answer 4

I think you should just implement some type of caching system for gethostbyaddr() results (Well, most of DNS servers have built-in caching system, but your can malfunction for some reason) or try to use alternative DNS servers(with system call or better with PHP's sockets).

Answer 5

Unfortunately some isp's don't maintain reverse dns records for some ip addresses, and therefore a dns lookup will always fail. The problem is how long to wait before giving it up.
Some hosting services set the gethostbyaddr function timeout real short, and if a lookup isn't successful, the ip address will be substituted for the host name. This speeds things up, preventing long delays in displaying pages that call this function.
You should always scrutinize log entries that don't show host names, as they rather frequently indicate that the visitor is from an ip address with a reputation for nefarious Internet activity.

Answer 6

As gethostbyaddr() does not support timeouts and my hosting setup does not allow shell commands I decided to use a local API:
<?php
$ip = isset($_GET['ip']) ? filter_var($_GET['ip'], FILTER_VALIDATE_IP) : false;
if ($ip) {
echo json_encode(gethostbyaddr($ip));
}
?>
And now I send a request to this hostAPI.php through file_get_contents() as follows:
<?php
// prepare host url
function isSecure() {
return ((isset($_SERVER['HTTPS']) && !empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off') || $_SERVER['SERVER_PORT'] == 443) ? 's' : '';
}
$protocol_host = 'http' . isSecure() . '://' . filter_input(INPUT_SERVER, 'HTTP_HOST', FILTER_SANITIZE_URL);
// dns request
$context = stream_context_create(array(
'http' => array(
'timeout' => 0.4,// 400 ms
)
));
$ip = long2ip(mt_rand(0, "4294967295"));
// note: the host url needs public access!
$host = json_decode(#file_get_contents($protocol_host . '/hostAPI.php?ip=' . $ip, false, $context), true);
// output
echo 'IP: ' . $ip . "<br>\n";
echo 'HOST: ' . ($host ? $host : 'Timeout!') . "<br>\n";
echo 'Execution Time: ' . round((microtime(true) - $_SERVER["REQUEST_TIME_FLOAT"]) * 1000) . ' ms';
?>
As you can see I set the timeout through stream_context_create().
Sample output:
IP: 56.152.200.204
HOST: Timeout!
Execution Time: 801 ms
IP: 81.139.131.130
HOST: host81-139-131-130.range81-139.btcentralplus.com
Execution Time: 52 ms
I do not know why, but on my setup the 0.4 timeout kicks in after > 800 ms so I needed to double the value to get the final timeout. Maybe someone else can comment that.
Warning
This creates one additional http request on your server for every request on your main script!

Answer 7

After upgrading from XP to 7 it effected PHP's handling of IPv4 versus IPv6 (e.g. 127.0.0.1 is returned as ::1) I had adapted some code to temporarily address this issue. It turns out that I was using gethostbyaddr on the IPv6 patch and thus it was getting stuck timing out for PHP.
Before...
$ip = ip2long6($ip);
$host = gethostbyaddr($ip);
After...
$host = gethostbyaddr($_SERVER['REMOTE_ADDR']);
You can use Xdebug and WinCacheGrind (I use XAMPP for local testing) to find what is timing out, here is a video tutorial for a quick run-through...
http://www.warpconduit.net/2012/09/01/quick-tip-profiling-php-applications-with-xdebug-wincachegrind-xampp-for-windows/
Hope this saves someone some sanity. :-)