In previous versions of PHP (before 4.2.2) when a form was submited containing an <input type="file"> field, if the browsed file size was 0 or if the file specified in the field didn't exist on the submitter's disk, the file name was reported "none" and no temporary file was created on the Server.  

I tried this with the following script in PHP 4.1.2 and PHP 4.2.2 both running in Solaris 7 Boxes with Apache 1.3  The file name of the script is "file_problem.php".

<?
if ($_REQUEST["answered"] == "ok") {
  echo "<pre>";
    echo $_SERVER["SERVER_SOFTWARE"] . "\n\n";
    echo "These are the contents of the \$_FILES array :: \n";
    print_r($_FILES);
  echo "</pre>";
  
} else {
?>

<form name="forma" action="file_problem.php" method="post"  ENCTYPE="multipart/form-data">
  <input type="file" name="userfile">
  <input type="hidden" name="answered" value="ok">
  <input type="submit">
</form>

<?}?>


***** When we click on the browse button and select a file from our localdisk this is returned in PHP 4.2.2 :

Apache/1.3.26 (Unix) PHP/4.2.2
These are the contents of the $_FILES array :: 
Array
(
    [userfile] => Array
        (
            [name] => fetuccinni.jpg
            [type] => image/pjpeg
            [tmp_name] => /var/tmp/phpHaaagK
            [error] => 0
            [size] => 12385
        )

)

***** Looks somewhat different to PHP 4.1.2 because of the "error" field but works fine.

Apache/1.3.24 (Unix) PHP/4.1.2
These are the contents of the $_FILES array :: 
Array
(
    [userfile] => Array
        (
            [name] => ellago.jpg
            [type] => image/pjpeg
            [tmp_name] => /var/tmp/phpenaW3e
            [size] => 10443
        )

)

****  When we browse a 0 byte file or type in a bogus file name in the field these are the different results:

Apache/1.3.26 (Unix) PHP/4.2.2
These are the contents of the $_FILES array :: 
Array
(
    [userfile] => Array
        (
            [name] => typedtext
            [type] => application/octet-stream
            [tmp_name] => /var/tmp/phpmxaqgK
            [error] => 0
            [size] => 0
        )

)

Apache/1.3.24 (Unix) PHP/4.1.2
These are the contents of the $_FILES array :: 
Array
(
    [userfile] => Array
        (
            [name] => typedtext
            [type] => application/octet-stream
            [tmp_name] => none
            [size] => 0
        )

)


This is incorrect because PHP assumes the file exists and creates a file in the server.  The only way we have to determine if we have to move the file or not is the "size" field, but there is no a way to determine if the user really uploaded a 0 byte file or simply if the file didn't existed in the user disk.