Jak stworzyć upload plików poprzez stronę?

Kod:
<?php



$site_name = $_SERVER['HTTP_HOST'];

$url_dir = "http://".$_SERVER['HTTP_HOST'].dirname($_SERVER['PHP_SELF']);

$url_this =  "http://".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF'];



$upload_dir = "upload_files/";

$upload_url = $url_dir."/upload_files/";

$message ="";



//create upload_files directory if not exist

//If it does not work, create on your own and change permission.

if (!is_dir("upload_files")) {

    die ("upload_files directory doesn't exist");

}



if ($_FILES['userfile']) {

    $message = do_upload($upload_dir, $upload_url);

}

else {

    $message = "Invalid File Specified.";

}



print $message;



function do_upload($upload_dir, $upload_url) {



    $temp_name = $_FILES['userfile']['tmp_name'];

    $file_name = $_FILES['userfile']['name']; 

    $file_type = $_FILES['userfile']['type']; 

    $file_size = $_FILES['userfile']['size']; 

    $result    = $_FILES['userfile']['error'];

    $file_url  = $upload_url.$file_name;

    $file_path = $upload_dir.$file_name;



    //File Name Check

    if ( $file_name =="") { 

        $message = "Invalid File Name Specified";

        return $message;

    }

    //File Size Check

    else if ( $file_size > 500000) {

        $message = "The file size is over 500K.";

        return $message;

    }

    //File Type Check

    else if ( $file_type == "text/plain" ) {

        $message = "Sorry, You cannot upload any script file" ;

        return $message;

    }



    $result  =  move_uploaded_file($temp_name, $file_path);

    $message = ($result)?"File url <a href=$file_url>$file_url</a>" :

              "Somthing is wrong with uploading a file.";



    return $message;

}

?>

<form name="upload" id="upload" ENCTYPE="multipart/form-data" method="post">

  Upload Image<input type="file" id="userfile" name="userfile">

  <input type="submit" name="upload" value="Upload">

</form>