function get_remote_file not working behind a proxy

The board I administrate is running on a computer that is behind a proxy. It would very useful if I could define some variables to tell php open connections using proxy itself, otherwise I can't do things like version check.
It just needs a few lines to modify in functions_admin.php:

function get_remote_file($host, $directory, $filename, &$errstr, &$errno, $port = 80, $timeout = 10)
{
global $user;

// these line are just for example, variables shoult be placed in config!
$proxy_host = 'dummyproxy.example.com';
$proxy_port = '8080';
$proxy_user = 'dummyuser';
$proxy_pass = 'myDummyPassWord';

// some more code is needed here, just some control to check if proxy is required or not...
if ($fsock = @fsockopen($proxy_host, $proxy_port, $errno, $errstr, $timeout))

{ @fputs($fsock, 'Proxy-Authorization: Basic ' . base64_encode("$proxy_user:$proxy_pass") . "\r\n\r\n"); @fputs($fsock, "GET [http://$host$directory/$filename] HTTP/1.1\r\n"); @fputs($fsock, "HOST: $host\r\n"); @fputs($fsock, "Connection: close\r\n\r\n"); // [rest of code unchanged....] }