prova.php
codice:
<?php
print_r($_SERVER);
$file = fopen ("http://localhost/prova2.php", "r");
?>
prova2.php
codice:
<?php
print_r($_SERVER);
$buffer = ob_get_flush();
file_put_contents('buffer.txt', $buffer);
?>
http://localhost/prova.php


output sul browser:

Array ( [HTTP_HOST] => localhost [HTTP_USER_AGENT] => Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8) Gecko/20051111 Firefox/1.5 [HTTP_ACCEPT] => text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 [HTTP_ACCEPT_LANGUAGE] => it-it,it;q=0.8,en-us;q=0.5,en;q=0.3 [HTTP_ACCEPT_ENCODING] => gzip,deflate [HTTP_ACCEPT_CHARSET] => ISO-8859-1,utf-8;q=0.7,*;q=0.7 [HTTP_KEEP_ALIVE] => 300 [HTTP_CONNECTION] => keep-alive [HTTP_CACHE_CONTROL] => max-age=0 [PATH] => C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32 \Wbem;C:\Programmi\MySQL\MySQL Server 5.0\bin [SystemRoot] => C:\WINDOWS [COMSPEC] => C:\WINDOWS\system32\cmd.exe [PATHEXT] => .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH [WINDIR] => C:\WINDOWS [SERVER_SIGNATURE] =>
Apache/2.0.55 (Win32) PHP/5.1.1 Server at localhost Port 80
[SERVER_SOFTWARE] => Apache/2.0.55 (Win32) PHP/5.1.1 [SERVER_NAME] => localhost [SERVER_ADDR] => 127.0.0.1 [SERVER_PORT] => 80 [REMOTE_ADDR] => 127.0.0.1 [DOCUMENT_ROOT] => D:/works/PHP [SERVER_ADMIN] => guidoz@email.it [SCRIPT_FILENAME] => D:/works/PHP/prova.php [REMOTE_PORT] => 2363 [GATEWAY_INTERFACE] => CGI/1.1 [SERVER_PROTOCOL] => HTTP/1.1 [REQUEST_METHOD] => GET [QUERY_STRING] => [REQUEST_URI] => /prova.php [SCRIPT_NAME] => /prova.php [PHP_SELF] => /prova.php [REQUEST_TIME] => 1136749986 )
cioè:
[HTTP_USER_AGENT] => Mozilla/5.0 (Windows; U; Windows NT 5.1; it; rv:1.8) Gecko/20051111 Firefox/1.5


outpput su file (quindi i dati registrati al momento della richiesta come la tua)
Array
(
[HTTP_HOST] => localhost
[PATH] => C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32 \Wbem;C:\Programmi\MySQL\MySQL Server 5.0\bin
[SystemRoot] => C:\WINDOWS
[COMSPEC] => C:\WINDOWS\system32\cmd.exe
[PATHEXT] => .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
[WINDIR] => C:\WINDOWS
[SERVER_SIGNATURE] => <address>Apache/2.0.55 (Win32) PHP/5.1.1 Server at localhost Port 80</address>

[SERVER_SOFTWARE] => Apache/2.0.55 (Win32) PHP/5.1.1
[SERVER_NAME] => localhost
[SERVER_ADDR] => 127.0.0.1
[SERVER_PORT] => 80
[REMOTE_ADDR] => 127.0.0.1
[DOCUMENT_ROOT] => D:/works/PHP
[SERVER_ADMIN] => guidoz@email.it
[SCRIPT_FILENAME] => D:/works/PHP/prova2.php
[REMOTE_PORT] => 2364
[GATEWAY_INTERFACE] => CGI/1.1
[SERVER_PROTOCOL] => HTTP/1.0
[REQUEST_METHOD] => GET
[QUERY_STRING] =>
[REQUEST_URI] => /prova2.php
[SCRIPT_NAME] => /prova2.php
[PHP_SELF] => /prova2.php
[REQUEST_TIME] => 1136749986
)
user agent non è nemneno presente

Prova con la tua versione di php ma suppongo sia lo stesso.

Tieni conto che invece di usare fopen puoi usare le socket (è + complicato però) e a quel punto puoi spacciarti per qualsiasi browser ^_^