I use the following to download a file with PHP:

  ob_start();

   $browser = id_browser();
   header('Content-Type: '.(($browser=='IE' || $browser=='OPERA')?
      'application/octetstream':'application/octet-stream'));
   header('Expires: '.gmdate('D, d M Y H:i:s').' GMT');
   header('Content-Transfer-Encoding: binary');
   header('Content-Length: '.filesize(realpath($fullpath)));
   //header("Content-Encoding: none");

   if($browser == 'IE')
   {
    header('Content-Disposition: attachment; filename="'.$file.'"');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Pragma: public');
   } else 
   {
    header('Content-Disposition: attachment; filename="'.$file.'"');
    header('Cache-Control: no-cache, must-revalidate');
    header('Pragma: no-cache');
   }


   //@set_time_limit( 0 );
   ReadFileChunked(utf8_decode($fullpath));   

   ob_end_flush();

The source code of ReadFileChunked is:

function ReadFileChunked($filename,$retbytes=true) 
{
 $chunksize = 1*(1024*1024); 
 $remainFileSize = filesize($filename);

 if($remainFileSize < $chunksize)
  $chunksize = $remainFileSize;

 $buffer = '';
 $cnt =0;
 // $handle = fopen($filename, 'rb');
 //echo $filename."<br>";
 $handle = fopen($filename, 'rb');
 if ($handle === false) {
  //echo 1;
  return false;
 }
 //echo 2;
 while (!feof($handle)) 
 {  
  //echo "current remain file size $remainFileSize<br>";
  //echo "current chunksize $chunksize<br>";
  $buffer = fread($handle, $chunksize);
  echo $buffer;
  sleep(1);
  ob_flush();
  flush();
  if ($retbytes) {
   $cnt += strlen($buffer);
  }

  $remainFileSize -= $chunksize;
  if($remainFileSize == 0)
   break;

  if($remainFileSize <  $chunksize)
  {
   $chunksize = $remainFileSize;   
  }
 }

 $status = fclose($handle);
 if ($retbytes && $status) {
  return $cnt; // return num. bytes delivered like readfile() does.
 }
 return $status;
}

The question is : The file downloaded will contiain some html tags which are the content of the html code generated by the php.

The error will happened when downloading the txt file with the file size smaller than 4096 bytes.

Please help me to slove this problem , thank you very much!

Chu