PHP output buffering (ob_start, ob_flush) - php

Question

I used php output buffering earlier in order to create csv file from database, because i didn't want to create an existing file, just wanted to make content downloadable.
CSV is text-based file, so its easy to create this way, you set the header and flush the text content. But! What if, I want to create an exe from hex data? (The project is: I have an existing exe file and I want that users can write something inside a HTML textbox and I convert that to hex and exchange the old text to the new one)
Thanks.

Answer 1

Use following code to download exe file by reading from hard disk.
<?php
$file = 'test.exe';
if (file_exists($file)) {
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($file));
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($file));
ob_clean();
flush();
readfile($file);
exit;
}

Answer 2

If you want to replace part of binary file, for example from 100th byte to 200th byte you could use substr() and str_pad():
$binFile = file_get_contents('/pathto/exec/file.exec');
$replacedBinFile = substr($binFile, 0, 100) . str_pad(substr($_POST['text'], 0, 100), 100, "\x00") . substr($binFile, 200);
file_put_contents('/pathto/exec/file_replaced.exec', $replacedBinFile);