In case you ever want to get a raw HTTP request for logging, analysis or filtering reasons, the code is simply:

function http_raw_request(){
  
  $http_request = ""; 

  foreach (getallheaders() as $key => $value){
    $http_request .= $key . ': ' . $value . "\n";
  }

  $http_request .= "\n";
  $http_request .= file_get_contents("php://input");

  return $http_request;

}

If, like me, you use php-fastcgi and lack the function getallheaders, it can be implemented as follows^link:

if (!function_exists('getallheaders')){ 
  function getallheaders(){ 
    $headers = ''; 
    foreach ($_SERVER as $name => $value){ 
      if (substr($name, 0, 5) == 'HTTP_'){ 
        $headers[str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($name, 5)))))] = $value; 
      } 
    } 
    return $headers; 
  } 
}

Example capture on a comment for this blog:

 Host: heapspray.net                                                               +
 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20100101 Firefox/15.0.1+
 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8           +
 Accept-Language: en-us,en;q=0.5                                                   +
 Accept-Encoding: gzip, deflate                                                    +
 Connection: keep-alive                                                            +
 Referer: http://heapspray.net/post/added-comments/                                +
 Content-Type: application/x-www-form-urlencoded                                   +
 Content-Length: 38                                                                +
                                                                                   +
 id=46&poster=test&email=test&text=test

Very useful for anything from site statistics to debugging and filtering spam (most spambots have very different request headers than most browsers).