|  support |  documentation |  report a bug |  advanced search |  search howto |  statistics |  random bug |  login
Bug #25701 Calling flush from within an output buffer prevents headers from being sent
Submitted: 2003-09-30 09:56 UTC Modified: 2004-04-21 20:28 UTC
Avg. Score:4.8 ± 0.4
Reproduced:5 of 5 (100.0%)
Same Version:5 (100.0%)
Same OS:4 (80.0%)
From: scottmacvicar at ntlworld dot com Assigned: iliaa
Status: Closed Package: Apache2 related
PHP Version: 4CVS OS: *
Private report: No CVE-ID:
 [2003-09-30 09:56 UTC] scottmacvicar at ntlworld dot com
Calling flush in Apache and Apache 2 produce different results.

Within Apache after calling flush you can still send headers as the output buffer prevents it from actually being flushed.

Within Apache 2 after calling flush you can no longer send headers even though headers_sent still returns false.

Reproduce code:


echo 'test';

$newtext = ob_get_clean();

if (strpos(' ' . $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') !== false AND !headers_sent())
	header('Content-Encoding: gzip');
	$newtext = gzencode($newtext, 1);

header('Content-Length: ' . strlen($newtext));
echo $newtext;


Expected result:

Actual result:
binary data


Add a Patch

Pull Requests

Add a Pull Request


AllCommentsChangesGit/SVN commitsRelated reports
 [2003-09-30 18:47 UTC]
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at and the instructions on how to report
a bug at

Unlike Apache 1, when Apache 2 recieves a directive to flush it does so right away sending any pending headers in the process. Since the headers & text were already sent it cannot send the header indicating the data that follows in gziped. Due to the missing header you get a whole bunch of binary data.
 [2003-09-30 19:22 UTC] scottmacvicar at ntlworld dot com
Shouldn't headers_sent() return true then?
 [2003-10-01 10:30 UTC] scottmacvicar at ntlworld dot com


echo 'test';

$newtext = ob_get_clean();

if (!headers_sent())
	echo 'in here<br />';

echo $newtext;


Based on what you've said above then you shouldn't see 'in here' within Apache 2.
 [2003-10-01 23:22 UTC]
This bug has been fixed in CVS.

In case this was a PHP problem, snapshots of the sources are packaged
every three hours; this change will be in the next snapshot. You can
grab the snapshot at
In case this was a documentation problem, the fix will show up soon at

In case this was a website problem, the change will show
up on the site and on the mirror sites in short time.
Thank you for the report, and for helping us make PHP better.

PHP Copyright © 2001-2015 The PHP Group
All rights reserved.
Last updated: Wed Nov 25 14:01:32 2015 UTC