php flush not working

Question

<?php
for($i=0;$i<20;$i++)
{
    echo 'printing...<br />';
    ob_flush();
    flush();

    usleep(300000);
}

?>

Url that contains the code: http://domainsoutlook.com/sandbox/delayed.php

I have a dedicated server so I can make the changes. I am running apache and nginx as the proxy server.

Should `ob_flush()` come after `flush()`, and also you the loop. need to start an output buffer with `ob_start()` before the loop — RobertPitt, Jan 16 '11 at 16:36
@robertpitt, could you please edit the code and answer it, so i test it and also select your answers as the right one if the code works. thanks — Speedy Wap, Jan 16 '11 at 17:30
Duplicate of [PHP flush/ob_flush not working](http://stackoverflow.com/questions/4481235/php-flush-ob-flush-not-working) — netcoder, Jan 16 '11 at 17:55

Roger · Answer 1 · 2011-02-12T15:18:53.410

47

So that's what I found out:

Flush would not work under Apache's mod_gzip or Nginx's gzip because, logically, it is gzipping the content, and to do that it must buffer content to gzip it. Any sort of web server gzipping would affect this. In short, at the server side, we need to disable gzip and decrease the fastcgi buffer size. So:

In php.ini:

. output_buffering = Off

. zlib.output_compression = Off
In nginx.conf:

. gzip off;

. proxy_buffering off;

Also have this lines at hand, specially if you don't have acces to php.ini:

@ini_set('zlib.output_compression',0);
@ini_set('implicit_flush',1);
@ob_end_clean();
set_time_limit(0);

Last, if you have it, coment the code bellow:

ob_start('ob_gzhandler');
ob_flush();

PHP test code:

ob_implicit_flush(1);

for($i=0; $i<10; $i++){
    echo $i;

    //this is for the buffer achieve the minimum size in order to flush data
    echo str_repeat(' ',1024*64);

    sleep(1);
}

edited Feb 12 '11 at 15:18

answered Feb 12 '11 at 14:40

Roger

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14

The last thing "echoing 64k **senseless** whitespace" did the trick for me. Thank you Roger. – humanityANDpeace Mar 26 '13 at 21:01
. proxy_buffering off; was the problem in my config. Thanks! – Noam Apr 06 '15 at 15:50
I've done all these but not working on live centos7 apache with php 5.5. Working smooth locally even with output_buffering=4096 – Azghanvi Aug 31 '17 at 04:20
Using php7.2fpm the @ob_end_clean was what finally did it for me. – Jeff Beagley Oct 03 '18 at 17:19
1

I needed 5 hours to find the problem why the SSE FLUSH was not working... `this is for the buffer achieve the minimum size in order to flush data`. Oh what the Hack! ... And there is not yet a way around it, as it seems: https://stackoverflow.com/q/57207571/1066234 – Avatar Feb 18 '22 at 09:27
Note: `echo str_repeat(' ', 4096);` seems to be sufficient. https://www.php.net/manual/en/function.flush.php#51679 – Avatar Feb 18 '22 at 09:30
All methods seem to have a problem with Cloudflare - when you flush from server, it only flushes to Cloudflare. -- At least that's my theory. Any ideas? – Jomar Sevillejo Feb 19 '22 at 08:53

score 13 · Accepted Answer · edited Feb 26 '20 at 14:59

13

You're using ob_flush without ob_start, so there is nothing to flush for it.

It also depends on the webserver and proxy and its settings.

You should disable buffering for Nginx (add proxy_buffering off; to the config file and restart Nginx)

Also, check if your php.ini contains output_buffering = Off and zlib.output_compression = Off.

edited Feb 26 '20 at 14:59

Eje

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answered Jan 16 '11 at 16:30

schnaader

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where is the nginx config file usually where i can add these values – Speedy Wap Jan 16 '11 at 17:47
do i add this line for nginx in the http core module – Speedy Wap Jan 16 '11 at 18:06
4

I have got proxy_buffering = off, zlib.output_compression = off and proxy_buffering off as well. But it is still not working. Could you please point me to some code or anything else please. – Speedy Wap Jan 16 '11 at 18:37
In that case, you should see if you really need "dynamic" printing and try other ways to do so (AJAX etc.) – schnaader Jan 16 '11 at 18:39

score 12 · Answer 3 · answered Jan 08 '13 at 22:29

12

Main php file;

<?php
header('Content-Type: text/HTML; charset=utf-8');
header( 'Content-Encoding: none; ' );//disable apache compressed
session_start();
ob_end_flush();
ob_start();
set_time_limit(0);
error_reporting(0);

..... bla bla

for(each)........
{
   bla bla..
    echo "<br>>>>".$i."<<<br>";
    ob_flush();
    flush(); //ie working must

}
?>

it's working..

answered Jan 08 '13 at 22:29

Emin Kadıoğlu

121
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5

1

The Content-Encoding was what worked for me on nginx - without having to turn it off for the whole server. Thanks Emin! – Redzarf Jun 27 '13 at 10:13
2

Setting `Content-Encoding` finally made flushing work on Firefox, but somehow Chrome was still expecting a compressed response, so it threw an `ERR_CONTENT_DECODING_FAILED` error. – Jelle De Loecker Dec 13 '17 at 10:35

score 5 · Answer 4 · answered Apr 09 '14 at 10:14

5

You have to fill the buffer, so that it can be flushed to browser. Use this after echo

echo str_pad('',4096)."\n";

Complete code:

<?php
     if (ob_get_level() == 0) ob_start();

     for( $i=0 ; $i<20 ; $i++) {
        echo 'printing...<br />';
        echo str_pad('',4096)."\n";

        ob_flush();
        flush();

        usleep(300000);
     }
     ob_end_flush();
?>

answered Apr 09 '14 at 10:14

Ankit Sharma

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Awesome! Such a simple thing to solve my problem but I havent found this solution or requirement anywhere else. Thanks! – Cosworth66 Oct 17 '20 at 02:56

score 4 · Answer 5 · edited Feb 26 '20 at 14:15

4

In php.ini:

output_buffering = Off
zlib.output_compression = Off

In nginx.conf:

fastcgi_keep_conn on; # < solution
proxy_buffering off;
gzip off;

edited Feb 26 '20 at 14:15

Eje

354
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answered Jan 26 '13 at 18:51

Rodrigo Gregorio

91
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`fastcgi_keep_conn on` helped! Thanks! – artnikpro Jun 04 '20 at 18:00

score 3 · Answer 6 · edited Feb 19 '20 at 23:49

As I read, it seems a really hard problem to solve, and the only (dirty) way I found is writing something useless to output to fill the ≠ buffers.

Without SSL
- Without output_buffering, flush is needed.
  nginx buffers can be lowered until the PHP header size
- With output_buffering, ob_flush need to be added to have the same behavior as above
With SSL
- There is another buffer for SSL and NGX_SSL_BUFSIZE is fixed in nginx compilation

Here is my test.php file (call it with ?size=... to change space writing in the loop)

<!DOCTYPE html>
<html>
<head></head>
<body>
<?php
$vars = array('output_buffering', 'zlib.output_compression');
print('<p>');
foreach ($vars as $var) {
  print("$var : ");
  var_dump(ini_get($var));
  print('<br />');
}
print("ob_get_level() : " .ob_get_level());
print('</p>');
if (ob_get_level()) {
  $bytes = ob_get_length();
  ob_flush();
}

$nb_iterations = !empty($_GET['nb']) ? max(2, (int) $_GET['nb']) : 5;
$size = !empty($_GET['size']) ? $_GET['size'] : 0;

for ($i = 1; $i < $nb_iterations; $i++) {
  sleep(1);
  print(str_repeat(' ', 1024 * $size ));
  print("<p>wait $i s</p>");
  if (ob_get_level()) {
    $bytes += ob_get_length();
    print($bytes + strlen($bytes));
    ob_flush(); // this is working, results aren't depending on output_buffering value
  }
  flush(); // this is needed  
}
?>
</body>
</html>

And the lower conf I can set is

location ~ ^/test.php$ {
  gzip off;
  fastcgi_pass   unix:/var/run/php5-fpm/ssl.socket;
  fastcgi_param   QUERY_STRING            $query_string;  
  fastcgi_param   REQUEST_METHOD          $request_method;
  fastcgi_param   SCRIPT_FILENAME         $request_filename;   
  # if too low => upstream sent too big header while reading response header from upstream
  fastcgi_buffer_size 128; 
  fastcgi_buffers 2 128;  
  fastcgi_busy_buffers_size 128;
}

score 1 · Answer 7 · answered Jun 12 '13 at 18:18

1

Another possible cause is mod_security. It looks like it has it's own buffers. So if you are using it you will have to set :

SecResponseBodyAccess Off

Kind of a dirty workaround but so far that it the only way I got it to work.

answered Jun 12 '13 at 18:18

Chris Koston

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score 1 · Answer 8 · answered May 07 '14 at 14:54

Just wanted to add to the Roger's answer.

If you are using FastCGI php5-fpm module within Apache2 you must also make sure you are adding

-flush

argument in your Apache2 configuration, i.e.

<IfModule mod_fastcgi.c>
...
        FastCgiExternalServer /usr/lib/cgi-bin/php5-fcgi -flush -socket /tmp/php5-fpm.sock -idle-timeout 480 -pass-header Authorization
</IfModule>

score 1 · Answer 9 · edited Feb 11 '17 at 13:46

1

Check your server api with

echo phpinfo();

If you found your server api

Server API :  CGI/FastCGI

in CentOS then add this line in "/etc/httpd/conf.d/fcgid.conf"

OutputBufferSize 0

To test, restart your Apache server and try below code

ob_start();
for($i = 0; $i < 10; $i ++) {
    echo $i;
    echo '<br />';
    flush();
    ob_flush();
    sleep(1);
}

edited Feb 11 '17 at 13:46

mafu

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answered Dec 07 '16 at 08:36

gsm

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This is the one I'm looking for! Thanks @gsm ! I read all the answers/topic/blogs about this problem and all I needed is set the buffer size to zero in my Apache config file. Especially if you're running on Windows, and using `fcgid_module`, you should put `FcgidOutputBufferSize 0` to your httpd conf file where you set fcgid_module. – Zoltán Kurgya Jan 30 '20 at 12:53

score 0 · Answer 10 · answered May 07 '14 at 09:06

I have noticed that browsers react differently. Chrome, for example, holds on to the input forever, and doesn't seem to care about displaying it any earlier. Unsurprisingly, Firefox will display the input earlier, if the above tips (contributed by other stackoverflowers) are applied, so try with Firefox.

score 0 · Answer 11 · answered Oct 10 '16 at 07:43

I was able to flush only this way - adding session_write_close();

if (ob_get_level() == 0)
{
    if(!ob_start("ob_gzhandler"))ob_start();
}               
echo ('bla bla bla');

$ans=ob_get_contents();
ob_end_clean();

header('Connection: close');
header('Content-Length: '.strlen($ans));
header('Status: 200');

echo $ans;

session_write_close();
ob_flush();
flush();

score 0 · Answer 12 · answered Jul 18 '17 at 12:58

0

if(!ob_get_level()) ob_start();
echo json_encode(array('valid'=>true,'msg'=>'Flush occured.'));
$size = ob_get_length();
header("Content-Type: application/json");
// Set the content length of the response.
header("Content-Length: {$size}");
//Close the connection if you want to.
header("Connection: close");
// Flush all output.
ob_end_flush();
ob_flush();
flush();
// Close current session (if it exists).
if(session_id()) session_write_close();

answered Jul 18 '17 at 12:58

RahulD

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5
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Could you please elaborate on this code, and how does this answer the question? Thanks. – iehrlich Jul 18 '17 at 13:30

score 0 · Answer 13 · answered Aug 20 '19 at 09:18

I have tried many times when using php-fpm with nginx. Many answers just instruct:

In php.ini:

output_buffering = Off

zlib.output_compression = Off

In nginx.conf:

gzip off;

proxy_buffering off;

BUT they forgot the very important setting in nginx.conf:

fastcgi_keep_conn on;

php flush not working

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