Create Unique Image Names

Question

What\'s a good way to create a unique name for an image that my user is uploading?

I don\'t want to have any duplicates so something like MD5($filename) isn\'t suita

Answer 1

For good performance and uniqueness you can use approach like this:

• files will be stored on a server with names like md5_file($file).jpg

• the directory to store file in define from md5 file name, by stripping first two chars (first level), and second two (second level) like that:

  uploaded_files\ 30 \ c5 \ 30 c5 67139b64ee14c80cc5f5006d8081.pdf

• create record in database with file_id, original file name, uploaded user id, and path to file on server

• on server side create script that'll get role of download providing - it'll get file by id from db, and output its content with original filename provided by user (see php example of codeigniter download_helper ). So url to file will look like that:

  http://site.com/download.php?file=id

---

Pros:

• minified collisions threat

• good performance at file lookup (not much files in 1 directory, not much directories at the same level)

• original file names are saved

• you can adjust access to files by server side script (check session or cookies)

Cons:

• Good for small filesizes, because before user can download file, server have to read this file in memory

Answer 2

Grab the file extension from uploaded file:

$ext = pathinfo($uploaded_filename, PATHINFO_EXTENSION);

Grab the time to the second: time()

Grab some randomness: md5(microtime())

Convert time to base 36: base_convert (time(), 10, 36) - base 36 compresses a 10 byte string down to about 6 bytes to allow for more of the random string to be used

Send the whole lot out as a 16 char string:

$unique_id = substr( base_convert( time(), 10, 36 ) . md5( microtime() ), 0, 16 ) . $ext;

I doubt that will ever collide - you could even not truncate it if you don't mind very long file names.

Answer 3

Something like this could work for you:

while (file_exists('/uploads/' . $filename . '.jpeg')) {
   $filename .= rand(10, 99);
}

Answer 4

as it was mentioned, i think that best way to create unique file name is to simply add time(). that would be like

$image_name = time()."_".$image_name;

Answer 5

How big is the probablity of two users uploading image with same name on same microsecond ?

try

    $currTime = microtime(true);
    $finalFileName = cleanTheInput($fileName)."_".$currTime;

// you can also append a _.rand(0,1000) in the end to have more foolproof name collision

    function cleanTheInput($input)
    {
     // do some formatting here ...
    }

This would also help you in tracking the upload time of the file for analysis. or may be sort the files,manage the files.

Answer 6

http://php.net/manual/en/function.uniqid.php maybe?

• You can prefix it with the user id to avoid collisions between 2 users (in less than one millisecond).