Unique, short filenames for pictures

What would be the best way to rename my user uploaded images to fairly short, yet unique names?

uniqid() ?
开发者_Go百科

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uniqid() would work.

But you could also use md5() or sha1() to make a hash value of the actual image. That would reduce redundant files if someone uploads an image twice.

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You will have to accept that your file names will probably not be short, but the best practice is RFC 4122, and one of the fastest PHP implementations is this:

// Execution (1000 IDs) took 7.509 milliseconds
// Example uuid: f40bc6a1-3bce-4472-add8-bbbe500b7f72
function mimec_uuid()
{
    return sprintf( '%04x%04x-%04x-%04x-%04x-%04x%04x%04x',
        mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ),
        mt_rand( 0, 0x0fff ) | 0x4000,
        mt_rand( 0, 0x3fff ) | 0x8000,
        mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ), mt_rand( 0, 0xffff ) );
}

Personally though, I have used the following (faster and shorter) algorithm successfully for projects that didn't need to scale like Flickr:

// Execution (1000 IDs) took 5.097 milliseconds
// Example uuid: 2c2e4067d1c92109660b8deecae1be08
function xuuid()
{
    return md5(microtime() . mt_rand( 0, 0xffff ));
}

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A very simple approach is to use some unique user identifier and a timestamp,

$imgName = md5($userEmail.microtime());

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I let images upload with the original image name, for SEO purposes. Google, et al, will find users' images of Batman or Eiffel Tower if I keep the original filename intact. So I simply add mktime to the front and then save it.

$imagename = str_replace(' ','-',$imagename);
$imagename = str_replace('_','-',$imagename);
$target_path = $_SERVER['DOCUMENT_ROOT']."/uploads/".mktime()."-".$imagename;

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What is wrong with a 32 digit MD5 generated image filename? Not too long really.

If like Bryan, you're going to let them use their own filenames, make sure you strip any bad characters like: '". etc for safety sake.