ob_gzhandler

add a note User Contributed Notes

fpiat at bigfoot dot com
27-Aug-2006 08:55


DON'T compress/gzip your Error pages :



i can think of two good reasons not to compress your error pages:

1. You want to make sure that people can read you error pages, don't you ?

2. Compressing pages have a "side effect" : it's smaller !! if you return "HTTP/1.x 404 Document Not fount" (or any other HTTP error), MSIE will display it's built in error message, not yours if it's small than 513bytes. (see "HOW TO: Turn Off the Internet Explorer 5.x and 6.x 'Show Friendly HTTP Error Messages' Feature on the Server Side" http://support.microsoft.com/default.aspx?scid=kb;en-us;Q294807 )

spam_this at zleelz dot com
27-Aug-2006 02:49


When writing scripts for distribution, I would usually "null" out the following deprecated superglobals so that users who uses the script will not be able to use them.

<?php

$HTTP_GET_VARS = null;

$HTTP_POST_VARS = null;

$HTTP_COOKIE_VARS = null;

$HTTP_POST_FILES = null;

$HTTP_SERVER_VARS = null;

?>



However, when using ob_start('ob_gzhandler'), one of those superglobals somehow disable this function.



Found out that it was $HTTP_SERVER_VARS that's causing the problems.



<?php

ob_start('ob_gzhandler');



$HTTP_GET_VARS = null;

$HTTP_POST_VARS = null;

$HTTP_COOKIE_VARS = null;

$HTTP_POST_FILES = null;

/**

 * Causing the trouble

 */

//$HTTP_SERVER_VARS = null;

?>



I don't know why it does that, but I just want to point that out.

richard at mf2fm dot com
11-Jul-2006 05:50


According to the manual, if ob_gzhander detects that the browser is unable to support deflate or gzip it returns FALSE.  Does this mean that if you use ob_start("ob_gzhandler"), any browsers that do not support gzip/deflate will receive a blank page?



I've been having problems with IE6 displaying gzipped pages and adding a test:



<?php



if (substr_count($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip')) ob_start("ob_gzhandler");



else ob_start();



?>



solved the problem.  Surely if ob_gzhandler detects a lack of support for deflation it should return the input unchanged and not FALSE?

michael at michaelphipps dot com
30-Apr-2006 06:34


It is also possible to use ob_gzhandler to compress css and javascript files, however some browsers such as firefox expect content type text/css on css files.



To get around this send a content type header:



<?php

ob_start('ob_gzhandler');

?>



.... your css content ...



<?php

header("Content-Type: text/css");

header("Content-Length: ".ob_get_length());

ob_end_flush();

?>

mariusads[at]helpedia[dot]com
05-Feb-2006 01:56


Please be aware that, as other users have already mentioned, the compression will fail if there are characters before the php start tag "< ?". 



This is also the case when saving files in UTF-8 format with editors such as Ultraedit. Make sure you save the file using the defined option UTF-8 NO BOM or delete the BOM otherwise the two UTF BOM characters will be written at the start of the file.

lapoint2 at msu dot edu
07-Sep-2005 09:40


So why doesn't the web server just do this by default?  

This works for me if I do:

ini_set('zlib.output_compression_level', 3);  ob_start("ob_gzhandler"); 

or even just:

ob_start("ob_gzhandler"); 



I did the level 3 compression, I think the default was 6 and I didn't want to put too much load on the server.  For a 895k file (my largest) the compression levels were:

1 = 189k

3 = 178k

4 = 163k

6 = 156k    (I believe 6 is the default if you leave out the ini_set)

9 = 155k

I use http://www.whatsmyip.org/mod_gzip_test/ to check the sizes.



FYI: This works with dynamic files in Movable Type 3.x (I'm testing it in 3.2) I've got the above command in the first line of my mtview.php file.



More info here: http://www.whatsmyip.org/forum/viewtopic.php?t=43



On several sites I've read the some browsers don't like compressed CSS.

Tony Piper
14-Jun-2005 10:11


I just spent 30 minutes wondering why my browser wasn't getting the gzipped version :-O



If you're using Google Web Access your pages will  be delivered to the browser uncompressed unless you tell GWA to ignore the specific site. 



Obvious, really.

25-May-2005 06:27


No matter the circumstances, you MUST NOT check the user agent string to find out if gzip compression is enabled. HTTP defines the Accept-Encoding header for exactly this purpose and you MUST check it before enabling compression.

m at rtij dot nl
16-Apr-2005 08:29


All versions of MSIE have a bug where they don't cache gzipd contents. If your application depends on caching, this is something to keep in mind. In the end, I did:



<?php



// These are so benificial, they default to true.

if (!isset($use_page_cache))

    $use_page_cache = 1;

if (!isset($use_compression))

    $use_compression = 1;



// Add browsers here as we must detect them. Opera is an oddball, if we don't detect

// it specifically, it will turn up as MSIE



$browser="other";

if (isset($_SERVER['HTTP_USER_AGENT'])) {

    $agent = $_SERVER['HTTP_USER_AGENT'];

    if (eregi("opera",$agent)){

    $browser="opera";

    }elseif(eregi("msie",$agent)){

    $browser="msie";

    }

}



if ($use_compression && !( $use_page_cache && $browser == "msie")) {

    // Turn on compression, makes quite a difference in bandwith usage.

    // However, MSIE (all versions) have a bug with compression and caching. So for MSIE

    // it's either compression or caching. We choose caching.

    ob_start('ob_gzhandler');

}



session_cache_limiter("must-revalidate");



session_start();



// ... put stuff in $content ...



if ($use_page_cache) {

    // MD5 is slow, however with a fast server (PIII or better) we should be OK

    $hash = md5($content);

    $headers = getallheaders();

    if (isset($headers['If-None-Match']) && ereg($hash, $headers['If-None-Match']))

    {

    header('HTTP/1.1 304 Not Modified');

    exit;

    }

    header("ETag: \"$hash\"");

}



print $content;



?>

John
17-Mar-2005 11:30


I found a site you can use to verify if your gzipping is working:

http://www.whatsmyip.org/mod_gzip_test/

It tests the gzip'ness of your page.

grange (at) club-internet (dot) fr
07-Mar-2005 11:17


It may seem obvious but if you use ob_start("ob_gzhandler"),  make sure no content is unintentionally echo'ed before : this could be blank lines before '<?php' or after '?>' tags in included files or even errors.



Otherwise, only a part of the content (the content sent after ob_start()) will be compressed, which will confuse the client.



Setting compression using zlib.output_compression either in php.ini or in Apache configuration file (with directive php_flag) is safer in this regard.

wallacebw at some-domain dot com
22-Feb-2005 01:50


IE 6+ appears to validate the CRC and disgard invalid gzip content FYI...

Brian

andy dot rem dot ove dot this at occ dot be
01-Apr-2004 06:21


From what I can understand, quite some people seem to have problems with this functionality.  If you want to do this quick, like i did, you can use the outstanding class gzip_encode made by Leknor at http://leknor.com/code/php/view/class.gzip_encode.php.txt

mazsolt at yahoo dot com
18-Mar-2004 11:20


if you want to send an output to the browser (which accepts gzip), and you haven't set the buffering callback ob_start("ob_gzhandler"), you may use the gzencode() function.



header("Content-Encoding: gzip");

echo gzencode("some output", 9, FORCE_GZIP);

daijoubuNOSP at Mvideotron dot ca
27-Oct-2003 06:05


So much code...here's a lighter/faster one:


<?php





if ( $do_gzip_compress )


{


    $gzip_size        = ob_get_length();


    $gzip_contents    = ob_get_clean(); // PHP < 4.3 use ob_get_contents() + ob_end_clean() 


    


    echo "\x1f\x8b\x08\x00\x00\x00\x00\x00",


         substr(gzcompress($gzip_contents, 9), 0, - 4), // substr -4 isn't needed


         pack('V', crc32($gzip_contents)),    // crc32 and


         pack('V', $gzip_size);               // size are ignored by all the browsers i have tested


}





exit;


?>


I wouldn't recommande using level 9, waste of CPU, something between 1 and 6 would be more resonable


I have tested without the substr/crc/size and it worked flawlessly in IE5/5.5/6, Opera7.11/7.21, IE5.5 MAC

brewthatistrue at plzYnoAspamHorOevilO dot com
21-Sep-2003 05:04


i had a LOT of trouble trying to get gzipping working correctly

i kept getting a blank page on the first load, although subsequent pages loaded fine.

i tried stuff with ob_flush and ob_end_clean and all kinds of stuff i didn't understand. i'm totally confused about different versions of php and different methods of gzipping.



in the end, i got it working (maybe i'll understand it later).

i ended up using phpBB's code (stripped of non-gz stuff, and ever-so-slightly modified)

http://phpbb.com/



index.php:

------------

<?php

require_once('top.php');



echo "<html>\n<head>\n<title>Gzip Test</title>\n<body>\n<h1>testing</h1>\n</body>\n</html>";



require_once('bottom.php');

?>



gz_header.php - taken form phpBB's page_header.php

--------------

<?php

    $phpver = phpversion();



    $useragent = (isset($_SERVER["HTTP_USER_AGENT"]) ) ? $_SERVER["HTTP_USER_AGENT"] : $HTTP_USER_AGENT;



    if ( $phpver >= '4.0.4pl1' && ( strstr($useragent,'compatible') || strstr($useragent,'Gecko') ) )

    {

        if ( extension_loaded('zlib') )

        {

            ob_start('ob_gzhandler');

        }

    }

    else if ( $phpver > '4.0' )

    {

        if ( strstr($HTTP_SERVER_VARS['HTTP_ACCEPT_ENCODING'], 'gzip') )

        {

            if ( extension_loaded('zlib') )

            {

                $do_gzip_compress = TRUE;

                ob_start();

                ob_implicit_flush(0);



                header('Content-Encoding: gzip');

            }

        }

    }

?>

gz_footer.php - taken form phpBB's page_tail.php

------------

<?php

// Compress buffered output if required and send to browser

if ( $do_gzip_compress )

{

    //

    // Borrowed from php.net!

    //

    $gzip_contents = ob_get_contents();

    ob_end_clean();



    $gzip_size = strlen($gzip_contents);

    $gzip_crc = crc32($gzip_contents);



    $gzip_contents = gzcompress($gzip_contents, 9);

    $gzip_contents = substr($gzip_contents, 0, strlen($gzip_contents) - 4);



    echo "\x1f\x8b\x08\x00\x00\x00\x00\x00";

    echo $gzip_contents;

    echo pack('V', $gzip_crc);

    echo pack('V', $gzip_size);

}



exit;

?>



i must admit to not seeing this working in opera 7.11. perhaps i will figure that one out.

if there is anything i should change email me and i can edit my post

jazfresh at SPAM-JAVELIN dot hotmail dot com
18-Sep-2003 10:54


In the set_error_handler notes, there is a technique described for capturing all errors (even parse errors) before they are displayed the user, using a special error handler and output handler. If this output handler detects a fatal error in the output buffer, it's captured and dealt with before it can be displayed to the user. If no error was detected, then output buffer is displayed verbatim (i.e. without being compressed).



If you are using this method, you can still take advantage of ob_gzhandler's compression. However, you MUST specify a mode argument (I'm using 4.2.2 on RedHat9). The mode value affects which headers are automatically added (Content-Encoding, etc). A value of '5' worked for me. '0' or discarding the argument produces a blank screen under Mozilla. 



<?php



function my_output_handler(&$buffer) {

  // Detect errors in the output

  if(ereg("(error</b>:)(.+) in <b>(.+)</b> on line <b>(.+)</b>", $buffer, $regs)) {

    my_error_handler(E_ERROR, $regs[2], $regs[3], $regs[4]);

    // ...

    // ... Insert your error handling here ...

    // ...

    return 'An internal error occurred.';

  } else {

    // The page rendered without any errors, so compress

    // and output.

    return ob_gzhandler($buffer, 5);

  }

}

?>

daijoubu at videotron dot ca
07-Sep-2003 07:35


About the previous note from Davey:



ob_start(array('ob_gzhandler',9));



Does not work. The output size isnt affected at all, stays the same.



ob_gzhandler compression level use zlib.output_compression_level, which is -1 per default, level 6.



To change the compression level on the fly, simply use ini_set:

<?php

ini_set('zlib.output_compression_level', 1);

ob_start('ob_gzhandler');

echo 'This is compressed at level 1';

?>

nospam at 1111-internet dot com
15-Apr-2003 04:47


Following up on my previous post - it appears that while:



<?php

ini_set("zlib.output_compression", "Off"); // with no headers yet sent

// followed by the rest of your code...

?>



did not work in php 4.2.3, it did begin to work as of php 4.3.0 as an override to the php.ini "zlib.output_compression=on" setting. I did not see this in the change log.



In light of this, I'd say using zlib.output_compression is definitely the way to go over ob_gzhandler() in most cases.

10-Apr-2003 01:47


When using ob_start("ob_gzhandler"), be aware that the output buffer has to be flushed in order to invoke the ob_gzhandler callback function. 



This may not always happen. For example, if you use ob_get_contents() to copy the output buffer to a string for further manipulation and then silently discard the buffer with ob_end_clean(), the output buffer is never "flushed" and as a result, the ob_gzhandler callback function is never invoked. And your pages won't be compressed.



This will be the case, for example, if you use the PHP Fusebox architecture/framework.

davey at its-explosive dot net
04-Apr-2003 10:41


To pass the second argument to ob_gzhandler() which specifies what level of compression should be used (which I assume is 1-9 as with the gzip binary, with 9 using the most processor and time to do, 4 is the standard IIRC) you must call ob_start() like so:



ob_start(array('ob_gzhandler',9));



- Davey

nospam at 1111-internet dot com
09-Mar-2003 07:23


Differences between zlib.output_compression and ob_gzhandler:



zlib.output_compression runs in parallel with script execution - it begins compressing as soon as it receives any output from your script, and sends data to the client each time its buffer (4K by default) gets full. ob_gzhandler (actually 'ob_start("ob_gzhandler");') will not start compressing until the script flushes (or, usually, exits), and will in turn send the entire compressed document at once - which makes it more susceptible to causing a perception of latency.



Advantage: zlib.output_compression



On the other hand, ob_gzhandler gives you script-level control allowing you to use it selectively or to unset it after setting it in certain cases. Despite some documentation to the contrary, zlib.output_compression does not appear to be able to be set or unset on a script level; you must instead set it globally (in php.ini) or in your webserver configs or .htaccess files, possibly using FilesMatch-type mechanisms to control which scripts it will or won't apply to - which could get unwieldy for large projects - particularly those which employ PHP to produce images and other non-text output in addition to normal text output.



Advantage: ob_gzhandler



Net advantage: depends on your particular needs. I'm trying zlib.output_compression for now, but I miss the flexibility that ob_gzhandler would provide.



p.s. here's an Apache 1.3.* httpd.conf/.htaccess file snippet that demonstrates the syntax for conditionally setting zlib.output_compression:



<FilesMatch "\.(php|html?)$">

# turn it on with the buffer set to 2K using php_value

php_value zlib.output_compression 2048

# or just turn it on using php_flag

# php_flag zlib.output_compression On

</FilesMatch>

aki at robotnik dot net
05-Mar-2003 03:13


if you get errors like:

"output handler 'ob_gzhandler' cannot be used twice"

if you are using 

"ob_start("ob_gzhandler");"



check for your php.ini file, it should look like this:



output_buffering = Off  ; delete the 4096k value

output_handler = 

zlib.output_compression = Off

dsugar100 at dolphinsoft dot com
07-Nov-2002 07:33


I have noticed that if you have the php setting for zlib.output_compression set to 'On' AND you attempt to use hte ob_gzhandler handler to ob_start () the output you get in the browser WILL be garbled in PHP 4.2.3.  I'm guessing that the output buffering is compressing the output to be sent, and then zlib is doing it a second time, but the browser is only uncompressing it once.



But using either one will give you the same results (compressed output from the script)

nid at home dot se
30-Sep-2002 07:10


If you are trying to use the ob_gzhandler in a MSHTA (Microsoft HTML Application) you will find that your pages does not show up. the MSHTA-browser probably says it can handle gzip, but it just won't work (IE:6, PHP:4.1.2)

psychones at ifrance dot com
08-Aug-2002 08:18


Problem revelate by xn@bnw.com



cause real problem when you have a global call

to ob_gzhandler , for example in an include configuration

file , and you want send a non gzip content , for any reason ...



To resolve it ,



put this after your global call to ob_gzhandler 



include("conf_that_call_ob_gzhandler.php");

-->ob_end_clean();

-->header("Content-Encoding: none");



If you try to overload the header before the the ob_gzhandler call

or during the buffering output , it will not work .

( probably erase at the call of ob_gzhandler  and not allow during

buffering ).



Hope this help

isoma at altavista dot net
24-Jun-2002 10:44


RFC 2616 suggests that a more correct way to compress documents on the fly is to use gzip transfer encoding rather than gzip content encoding.    However, it's perhaps not advisable to use this since client support for it is extremely limited.



The difference is most evident when you come to save a file from your browser.  If it's gzip content encoded then the browser should (and may well) save it gzipped.  If it's gzip transfer encoded then the browser should uncompress it first.

Sven dot Dickert at planb dot de
29-May-2002 07:54


Following Browsers send

Accept-Encoding: gzip

but have Problems with

Content-Encoding: gzip



* netscape < 5 have problems with CSS/Javascript parts sendet in gzip

* opera 5.x,6 store downloads compressed

* lynx 2.8.4 store downloads compressed but tells this with attaching ".gz" to the filename



You should know about:

* Internet Explorer 5.x,6 should turned to HTTP 1.1 to get "Accept-Encoding: gzip"

* In Mozilla 1.0 RC2 you can write the "Accept-Encoding:" in Preferences/Advanced/HTTP Networking

xn at bnw dot com
13-Apr-2002 11:40


if you call ob_end_clean() after ob_start("ob_gzhandler"), the "Content-Encoding: gzip" header will still get sent (assuming the browser supports the encoding).  if you don't call ob_start() again with the ob_gzhandler callback function, the output will not be compressed, but the header will say it is.  this causes mozilla (as of build 2002032808) to display a blank page.

junior at jaj dot com
05-Mar-2002 02:12


To get this to work properly, you have to compile PHP with "--with-zlib". If you don't, you won't get any errors, it just won't actually compress anything. This is a phenomenal thing. For just a small bit of processor time, you can DRASTICALLY reduce the bandwidth requirement of your scripts. There are very few circumstances in which this should not be used.

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ob_gzhandler

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