Check if file exist before renaming file upon upload - php

Question

I need help with adding the feature to check whether a file exists when uploading.
This is how the upload.php code looks like for uploading:
$file_name = $HTTP_POST_FILES['ljudfil']['name'];
$random_digit=rand(0000,9999);
$mp3 ='.mp3';
$pdf ='.pdf';
$datum = date('Ymd');
$new_file_name=$random_digit.$file_name;
$target_path1 = $target_path . $orgnr . '_' . $gsm . $pdf;
$target_path3 = $target_path . 'AC' . $datum . $new_file_name . $mp3;
$target_path11 = $target_path4 . $orgnr . '_' . $gsm . $pdf;
$target_path33 = $target_path4 . 'AC' . $datum . $new_file_name . $mp3;
$targetljudfilftp = 'AC' . $datum . $new_file_name . $mp3;
move_uploaded_file($_FILES['avtalsfil1']['tmp_name'], $target_path1);
move_uploaded_file($_FILES["ljudfil"]["tmp_name"], $target_path3);
$sql = "INSERT INTO affarer (tid, cid, orgnr, ljudfilftp) VALUES
(CURDATE(),'$date','$cid','$orgnr', '$targetljudfilftp')";
As you can see, it renames the uploaded file including a random number.
Sometimes, it happens that it renames the file to a number that already exists.
When that happens, it overwrites the previous file on my server.
So, how can I add a function to check whether the target name exists before it is used for renaming?

Answer 1

You can use
if (file_exists($target_path1))
to verify whether a file exists.
You would do better, though, to change strategy and employ tempnam:
$target_path = tempnam ($target_path, 'AC' . $datum . $file_name . $mp3)
This will create a file such as "AC_2012_Anacreon.mp3_xTfKxy" but you have the guarantee of it being unique, while even using file_exists would expose you to the risk of a concurrency collision.
Of course the file no longer has a .mp3 extension, so you have to take it into account when you scan the directory and supply files for download.
A still not secure, but maybe easier way is this:
for(;;)
{
$newname = // some strategy to generate newname, including a random
if (!file_exists($newname))
touch($newname);
if (!filesize($newname))
break;
}
or you can use a lock file to guarantee no concurrency (and therefore, that file_exists will return the truth and it will stay the truth):
$fp = fopen('.flock', 'r+');
if (flock($fp, LOCK_EX))
{
for(;;)
{
$newname = // some strategy to generate newname, including a random
if (!file_exists($newname))
{
// this creates the file uniquely for us.
// all other writers will find the file already there
touch($newname);
}
}
flock($fp, LOCK_UN);
}
else
die("Locking error");
fclose($fp);
// $newname is now useable.

Answer 2

Use the file_exists builtin function.

Answer 3

You could change the way your random digists are created by using (for example) a time based method
$random_digit = microtime(TRUE);

Answer 4

You can use as below
$random_digit = time();

Answer 5

Instead off using 'rand' function which can generate a duplicated number, you can use 'uniqid'php function, it returns a unique id ( http://www.php.net/manual/en/function.uniqid.php ).
If you still want to use the 'rand' you can use 'file_exists' function with the generated file name as param ( http://www.php.net/manual/en/function.file-exists.php ), but if a file exists you must regenerate the file name, so you will iterate each time the file exists.
At last, think to use full time date('Ymdhis') format instead off date('Ymd'), it's also better to use timestamp by calling time() function ( http://www.php.net/manual/en/function.time.php )
Anas,

Answer 6

if (file_exists($random_digit)) {
$random_digit = rand(0000,9999);
}