PHP readfile() and large downloads

While setting up an online file management system, and now I have hit a block.

I 开发者_C百科am trying to push the file to the client using this modified version of readfile:

function readfile_chunked($filename,$retbytes=true) { 
   $chunksize = 1*(1024*1024); // how many bytes per chunk 
   $buffer = ''; 
   $cnt =0; 
   // $handle = fopen($filename, 'rb'); 
   $handle = fopen($filename, 'rb'); 
   if ($handle === false) { 
       return false; 
   } 
   while (!feof($handle)) { 
       $buffer = fread($handle, $chunksize); 
       echo $buffer; 
       ob_flush(); 
       flush(); 
       if ($retbytes) { 
           $cnt += strlen($buffer); 
       } 
   } 
       $status = fclose($handle); 
   if ($retbytes && $status) { 
       return $cnt; // return num. bytes delivered like readfile() does. 
   } 
   return $status; 
}

But when I try to download a 13 MB file, it's just breaking at 4 MB. What would be the issue here? It's definitely not the time limit of any kind because I am working on a local network and speed is not an issue.

The memory limit in PHP is set to 300 MB.

Thank you for any help.

Most likely you are hitting the response buffer limit set by your webserver. IIS and FastCGI are known to have 4mb as the default buffer size. I would start your search with looking into the webserver<->PHP SAPI configuration.

do NOT flush your output but try to buffer it and then send it to teh client in one piece.

ob_clean(); // in case anything else was buffered
ob_start();

// do read/echo operations

ob_end_flush();