Merging file chunks in PHP

Question

For the educational purposes, I wanted to create file chunks upload. How do you guys know when all of the chunks are uploaded?

I tried to move chunks from temp

Answer 1

Sorry for my previous comments, I misunderstood a question. This quiestion is interesting and fun to play with.

The expression you are looking for is this:

$target_path = ROOT.'/upload/';

$tmp_name = $_FILES['upload']['tmp_name'];
$filename = $_FILES['upload']['name'];
$target_file = $target_path.$filename;
$num = $_POST['num'];
$num_chunks = $_POST['num_chunks'];

move_uploaded_file($tmp_name, $target_file.$num);

// count ammount of uploaded chunks
$chunksUploaded = 0;
for ( $i = 1, i <= $num; $i++ ) {
    if ( file_exists( $target_file.$i ) ) {
         ++$chunksUploaded;
    }
}

// and THAT's what you were asking for
// when this triggers - that means your chunks are uploaded
if ($chunksUploaded === $num_chunks) {

    /* here you can reassemble chunks together */
    for ($i = 1; $i <= $num_chunks; $i++) {

      $file = fopen($target_file.$i, 'rb');
      $buff = fread($file, 2097152);
      fclose($file);

      $final = fopen($target_file, 'ab');
      $write = fwrite($final, $buff);
      fclose($final);

      unlink($target_file.$i);
    }
}

And this must be mentioned:

Point of fragility of my version - is when you expect files

• 'tmp-1',

• 'tmp-2',

• 'tmp-3'

but, let's assume that after sending 'tmp-2' we were interrupted - that tmp-2 pollutes tmp folder, and it will interfere with future uploads with the same filename - that would be a sleeping bomb.

To counter that - you must find a way to change tmp to something more original.

• 'tmp-ABCew-1',

• 'tmp-ABCew-2',

• 'tmp-ABCew-3'

is a bit better - where 'ABCew' could be called 'chunksSessionId' - you provide it when sending your POST, you make it randomly. Still, collisions are possible - as space of random names depletes. You could add time to equation - for example - you can see that

• 'tmp-ABCew-2016-03-17-00-11-22--1',

• 'tmp-ABCew-2016-03-17-00-11-22--2',

• 'tmp-ABCew-2016-03-17-00-11-22--3'

Is much more collision-resistant but it is difficult to implement - a whole can of worms here - client date and time is controlled by client and could be spoofed - this data is unreliable.

So making tmp-name unique is a complex task. Designing a system that makes it reliable - is an interesting problem ^ ^ You can play with that.