Download file question

[LLLLLLL]

On PHP 5.2.14.

 

I want to make files downloadable from my website. This seems easy enough:

<?php
$file = "downloads/someFile.txt";
// Set headers
header( "Content-Description: File Transfer" );
header( "Content-Type: application/force-download");
header( "Content-Length: " . filesize( $filename ) );
header( "Content-Disposition: attachment; filename=$file");
//	header( "Content-Transfer-Encoding: binary");
readfile( $file );
unlink( $file );
?>

You'll notice, however, that I have "unlink" at the end of this file. That's exactly what I want: to remove the file from the server once it has been downloaded, to prevent anyone else from downloading it.

 

Here's the conundrum: When the user navigates to this URL, browsers offer the choice of Open/Save/Cancel. I don't want users to "open", and if the user presses "cancel", well then I probably don't really want the file deleted.

 

In short: I want the file SAVED, only. And I want to delete the file immediately after it has been downloaded.

 

Thoughts?

[premiso]

You cannot control how the browsers asks the users what they want to do. You cannot tell if the user "truly" downloaded the file either. So yea, you are stuck between a hardspot and a rock. Sorry mate. 

 

EDIT:

However, using a Java or Flash application, this may be possible, but I am not 100% on that (or at least a bandwidth monitor for the current connections should be possible). I would suggest looking into that route.

[LLLLLLL]

I kinda figured. Argh.

 

Related question: I've read that readfile() may not be the best option, especially for large files. Some of the files I'm providing are around 10MB. How would you change the code to handle that?

[jayarsee]

I know how you can do it.

 

You could write some simple CLI PHP that hooks into the Apache logs (assuming you're using that) to see what the per-file / per-IP activity was and make a decision about what to do with the file that way. Just setup your logs with %B:

 

http://httpd.apache.org/docs/2.0/mod/mod_log_config.html#formats

 

You can compare how many bytes were transferred with the actual bytes to see if the file was downloaded or not. Just use exec() (or its cousins) with cat and grep to find the lines of the log you need.

 

I bet you could do it in less than 50-100 lines. Let me know if I can clarify further.

[jayarsee]

This comment from the PHP Manual seems to address your second question:

 

To anyone that's had problems with Readfile() reading large  files  into memory the problem is not Readfile() itself, it's because you have output buffering on. Just turn off output buffering immediately before the call to Readfile(). Use something like ob_end_flush().

[premiso]

Addressing the readfile question, aside from jayarsee's information on the output buffering, another option is a custom user function: here http://us.php.net/manual/en/function.readfile.php#88549

 

Which is:

 

    function readfile_chunked ($filename,$type='array') { 
      $chunk_array=array(); 
      $chunksize = 1*(1024*1024); // how many bytes per chunk 
      $buffer = ''; 
      $handle = fopen($filename, 'rb'); 
      if ($handle === false) { 
       return false; 
      } 
      while (!feof($handle)) { 
          switch($type) 
          { 
              case'array': 
              // Returns Lines Array like file() 
              $lines[] = fgets($handle, $chunksize); 
              break; 
              case'string': 
              // Returns Lines String like file_get_contents() 
              $lines = fread($handle, $chunksize); 
              break; 
          } 
      } 
       fclose($handle); 
       return $lines; 
    } 

 

I have used this and it has worked for me. It may be able to be optimized a bit, but yea.