ob_start

add a note User Contributed Notes

butch at enterpol dot pl
02-Oct-2006 03:04


simple code to make phpsession $_GET nice for Valid XHTML 1.0 Transitional :)



function callback($buffer)

{

  $buffer = str_replace("&PHPSESSID", "&amp;PHPSESSID", $buffer);

  return $buffer;

}



ob_start("callback");



session_start();

net_navard at yahoo dot com
30-May-2006 10:09


Hello firends



ob_start() opens a buffer in which all output is stored. So every time you do an echo, the output of that is added to the buffer. When the script finishes running, or you call ob_flush(), that stored output is sent to the browser (and gzipped first if you use ob_gzhandler, which means it downloads faster). 



The most common reason to use ob_start is as a way to collect data that would otherwise be sent to the browser.



These are two usages of ob_start():



1-Well, you have more control over the output. Trivial example: say you want to show the user an error message, but the script has already sent some HTML to the browser. It'll look ugly, with a half-rendered page and then an error message. Using the output buffering functions, you can simply delete the buffer and sebuffer and send only the error message, which means it looks all nice and neat buffer and send 

2-The reason output buffering was invented was to create a seamless transfer, from: php engine -> apache -> operating system -> web user



If you make sure each of those use the same buffer size, the system will use less writes, use less system resources and be able to handle more traffic. 



With Regards, Hossein

(capitals) THE maYoR ANd thOSe@gmail
01-Feb-2006 06:14


One of the notes below mentions that ob_end_flush() is called automatically at the end of the script if you called ob_start without an ob_end. 



Because I couldn't find any other way to do it, I tried to use this fact to have some stuff run at the end of every script. It was a maintenance nightmare, so I'm putting a link here to the good way to do it, since it's nigh impossible to find with google.



http://php.net/register_shutdown_function

simon
25-Jan-2006 12:51


Found that variables in class instances we're not being set after the call to ob_start(). 

Call ob_start after the variables are set however and it works but that didn't seem to solve the goal of a self contained templating class.

The fix was to assign the class by reference with '&new'

Here is a simplified working example:

<?php

class Buffer {

var $template = ' - template set in class constructor';

function Buffer() { 

    $this->startBuffer(); 

}

function startBuffer() {

    ob_start(array(&$this, 'doFlush'));

}

function doFlush($buffer) {

    /* simple string concat to show use of a 

    template string and the buffer output */

    return $buffer . $this->template; 

}

}

/* template does not get set:

$buffer1 = new Buffer();

$buffer1->template = ' - template set in instance';

echo 'some buffer content';

*/

/* this works as expected */

$buffer2 = &new Buffer();

$buffer2->template = ' - template set in instance';

echo 'some buffer content';

ernest at vogelsinger dot at
09-Jan-2006 01:57


When you rely on URL rewriting to pass the PHP session ID you should be careful with ob_get_contents(), as this might disable URL rewriting completely.



Example:

ob_start();

session_start();

echo '<a href=".">self link</a>';

$data = ob_get_contents();

ob_end_clean();

echo $data;



In the example above, URL rewriting will never occur. In fact, rewriting would occur if you ended the buffering envelope using ob_end_flush(). It seems to me that rewriting occurs in the very same buffering envelope where the session gets started, not at the final output stage.



If you need a scenario like the one above, using an "inner envelope" will help:



ob_start();

ob_start();   // add the inner buffering envelope

session_start();

echo '<a href=".">self link</a>';

ob_end_flush(); // closing the inner envelope will activate URL rewriting

$data = ob_get_contents();

ob_end_clean();

echo $data;



In case you're interested or believe like me that this is rather a design flaw instead of a feature, please visit bug #35933 (http://bugs.php.net/bug.php?id=35933) and comment on it.

cyrille.berliat[no spam]free.fr
17-Oct-2005 06:07


If you're trying to use ob_start() in some PHP5 classes (probably works on PHP4 classes), this is the good way :



<?



class HTMLPage

{

//----------------------------------------------------------------- PUBLIC



//----------------------------------------------------- Mthodes publiques

    

    public static function ConvertIntoSGML( $source )

    // Mode d'emploi :

    //convertit une string en une SGML valide

    //

    // Renvoie :

    //la chaine traite

    //

    // Algorithme :

    //analyse char par char de la chaine. Si un caractre est de nombre ASCII > 127,

    //conversion en son code SGML.

    {

        $newString = '';

        

        for( $i = 0; $i < strlen( $source ) ; $i++ ) {

            $o = ord( $source{ $i } );

            

            $newString .= ( ( $o > 127 ) ? '&#'.$o.';': $source{ $i } );

        }

        

        return $newString;

    }

    

    public function FlushSite( $source )

    {

        return $this->ConvertIntoSGML ( $source );

    }

    

//-------------------------------------------- Constructeurs - destructeur

    function __construct()

    // Mode d'emploi (constructeur) :

    //initialise la buffurisation

    //

    // Contrat :

    //

    {

        ob_start( array (  & $this , 'FlushSite' ) );

    } //---- Fin du constructeur

    

//------------------------------------------------------ Mthodes Magiques



//------------------------------------------------------------------ PRIVE 



}



// Example :



$webdesign = new HTMLPage ( );



echo 'Hllo world'; // Will produce the source 'h&#233;llo world'



?>



Without the & before $this, you'll loose your content because ob_start() will call the flushsite() function from a clone of the object and not the caller object himself.



Note : call_back function must be public because ob_start() is in an extern scope from your class :)



I hope this will help you!

php at bucksvsbytes dot com
16-Sep-2005 01:29


The following should be added: "If outbut buffering is still active when the script ends, PHP outputs it automatically. In effect, every script ends with ob_end_flush()."

admin at bobfrank dot org
28-Aug-2005 11:50


If you want to run code in the middle of a string that you made, but you want to wait the printing...

(so if you want to allow php in bb-code style, and you want to execute it in order, and print everything in order...)



phpRun($code) {

    ob_start();

    exec($code);

    $output = ob_get_contents();

    ob_end_clean();

    return $output;

}



$str = str_replace("]\n", "]", $str);

$match = array('#\[php\](.*?)\[\/php\]#se');

$replace = array( phpRun( stripslashes('$1') ) );

$str= preg_replace($match, $replace, $str);



echo $str;

kasper at johansen dot tdcadsl dot dk
28-Aug-2005 10:29


Another way to make your code harder to copy, is to remove all line-breaks and tabs you have in it.



You can use this function to remove those.



You can choose to place "ob_start();" at the start of your main PHP-file, and "ob_end_clean();" at the end of it.



This is not the best solution though. If you are running Apache you might want to do something like this to a ".htaccess"-file:



php_value auto_prepend_file "/home/www/load_before.php"

php_value auto_append_file "/home/www/load_after.php"



(you should replace those files with files that actually exists).



In the "load_before.php" you can place the "ob_start();", and in the "load_after.php" you can do something like this:



<?

    $html = strtr(ob_get_contents(), array("\t" => "", "\n" => "", "\r" => ""));

    ob_end_clean();

    

    echo $html;

?>



This will clean your HTML of all kind of linebreaks (both \n and \r) and tabulators (\t). This will save your users some bandwidth, but it will also make your HTML, JavaScripts and more very difficult to read or copy. That way, making it harder for people to steal your code if you do not want them to.



This isnt in the spirit of OpenSource, but anyway you should be aware that this is possible.



Be aware that if you use PHP-files, to simulate pictures, all linebreaks will also be remove, making them corrupt. A solution to this, could be to check the headers (Content-Type), and if isnt set, or it is "text/html", you can go ahead and remove the linebreaks and tabs.



At my site, with more than 50.000 pictures and about 60 people online, I couldnt see any difference in the loadtime.



But still be aware, that your output will not be sent, before the script is finished, which will make your page slower to load that way also, since it cannot send any output while loading, but will have to wait until the load is finished.

geoffrey at nevra dot net
10-Aug-2005 03:05


When using a callback with ob_start(), functions like ob_get_contents() don't make use of it, use ob_end_flush() instead.



nb: not tested with every ob_* functions, just ob_get_contents() and ob_end_flush()

05-Aug-2005 10:54


I usually create my pages in four parts - variable initialisation, import header (using the variables just declared to configure), main body (mostly non-PHP), import footer.  I wondered about making the main body examinable by another PHP script if the main page was included into it.  I found I could control output of the main body by ending the header with an unclosed function which finishes at the start of the footer, thus enclosing the main body.  Output buffering can then be used to read this into a variable.  As a demonstration of how this can be used to control the order of output look at this example:



<?php

$output = "";



// Callback to process buffered output

function capture($buffer)

    {

    $GLOBALS['output'] .= $buffer;

    return "C ";

    }



// Calls the printE() function with output capture

function captureE()

    {

    ob_start("capture");

    printE();

    ob_end_flush();

    }

?>



A

<?php

// Output 'E' (the main body in the example scenario)

function printE()

    { // (End header after this line) ?>

E

    <?php // (Start footer with this line)

    }

?>

B

<?php captureE(); ?>

D

<?php print $output; ?>

F

<?php printE(); ?>

G



The output is A B C D E F E G.



For the application I mentioned above there are two points to note:

 - The page when executed alone must output its main body but the inspection script should suppress this, perhaps by means of a variable set before the page is included and then checked for in the footer output lines.

 - Because the main body is now inside a function it has a different namespace, thus changes may be required to prevent code breaking (e.g. use of globals, handling of functions defined within the main body).

oersoep at gmail dot com
08-Jul-2005 08:46


These are handy. First one has been mentioned before.



ob_start( array( 'lib_class', 'parse_output' ) );

ob_start( array( $this, 'parse_output' ) );



Note: $this is NOT a reference. Anything the callback saves or logs disappears in the clone ob_start works with. 

It does enable the callback to work with the attributes of $this, like $this->ar_tpl_value or whatever your style is.



The manual says:

"If the optional parameter chunk_size is passed, the callback function is called on every first newline after chunk_size bytes of output. The output_callback parameter may be bypassed by passing a NULL value."

This doesn't work with my 4.3.11. Might be the Zend optimizer though. Daren't turn it off to go see.

Aleksey
25-May-2005 03:08


This function dynamically changes title of HTML page:



  function change_title($new_title) {

    $output = ob_get_contents();

    ob_end_clean();



    $output = preg_replace("/<title>(.*?)<\/title>/", "<title>$new_title</title>", $output);

    echo $output;

  }



Example:

  ob_start();

  // ... some output

  change_title('NEW TITLE!');

jds1509 at NOSPAMrit dot edu
24-May-2005 10:06


This code demonstrates the affect of providing a value to the chunk_size parameter. A value of 1 or 0 will be ignored by php. Here's the Code:



<?



function callback($buffer)

{

    return "TRAPPED:".$buffer."<br/>";

}



ob_start("callback",2);



echo "long string, so callback";

echo "X";

echo " - no callback, less than 2 chars";



?>newlines,

but

no

callback

!<?



// PHP block



?>PHP block initiates callback.<?



echo "One more callback at EOF...";



?>



The code above outputs:



TRAPPED:long string, so callback

TRAPPED:X - no callback, less than 2 chars

TRAPPED:newlines, but no callback !

TRAPPED:PHP block initiates callback.

TRAPPED:One more callback at EOF...

TRAPPED:

rafa dot chacon at factorydea dot com
10-May-2005 05:10


If you're trying to include a php file inside a loop by require_once (in example, a dinamic email template) and change the value of some variables (in example, url to unsuscribe, different for each user), you should use



<?php



// ... some code



$usermail = array("email1", "email2", ...);



for($i = 0; $i < $MAX; $i++)

{

        $usermail_unsuscribe = $usermail[$i];

        ob_start();

        include("email_template.php");

        ob_clean();

}

?>



Otherwise $usermail_unsuscribe will get only "email1" value.

JM
09-May-2005 03:17


I don't claim to understand this--I would have expected the exact opposite--but it seems that 

  ob_start() ... ob_end_flush()

can massively improve perfomance, by at least a factor of 10 (admittedly a small number of samples).



I tried this after discovering that I could move a large (100ms) bottleneck in one of my scripts into

   echo "<!-- about 40 characters of junk -->";

which clearly shouldn't have taken long to run.



My unfounded theory is that without buffering, the interaction between PHP4.3.4 and Apache is not optimized, whereas with buffering, PHP delivers the entire page at once, which Apache handles better.



I should add that this is under https.

Ray Paseur (Paseur ... ImagineDB.com)
02-Mar-2005 05:50


You can use PHP to generate a static HTML page.  Useful if you have a complex script that, for performance reasons, you do not want site visitors to run repeatedly on demand.  A "cron" job can execute the PHP script to create the HTML page.  For example:



<?php // CREATE index.html

   ob_start();

/* PERFORM COMLEX QUERY, ECHO RESULTS, ETC. */

   $page = ob_get_contents();

   ob_end_clean();

   $cwd = getcwd();

   $file = "$cwd" .'/'. "index.html";

   @chmod($file,0755);

   $fw = fopen($file, "w");

   fputs($fw,$page, strlen($page));

   fclose($fw);

   die();

?>

eddie
14-Feb-2005 12:09


I use this function for deleting not needed characters within the html code before sending the whole stuff to the browser.



function callback($buffer){

    $buffer = str_replace("\n", "", $buffer);

    $buffer = str_replace("\t", "", $buffer);

    $buffer = str_replace(chr(13), "", $buffer);

    $buffer = ereg_replace("<!\-\- [\/\ a-zA-Z]* \-\->", "", $buffer);

    return $buffer;

}



First str_replace will delete any newlines, second any tabs and the third any carriage return. Finally the regular expression will delete any html-comment which consists of /, space, a-z or A-Z.

Using this saves about 1kb on every pageload.

FB
02-Feb-2005 10:59


I've noticed a bug with MSIE for non cached contents if your page is less than 4096 octets : you have to refresh the page each time to view its content !



Here is the solution to prevent this stupid behaviour of MSIE : just insert this code at the top of your scripts :



function ob_callback($buffer)

{

    return $buffer . str_repeat(' ', max(0, 4097 - strlen($buffer)));

}



ob_start('ob_callback');

d_spagnoli at yahoo dot it
28-Dec-2004 10:39


nl2br() is not a callable function, to make it work define a new one like this:



function mynl2br($str){

    return nl2br($str);

}



example:



ob_start("nl2br");

echo "under pressure\npushing down on me";

$str_error=ob_get_flush();



doesn't work, use ob_start("mynl2br") instead.



PHP 4.3.9

aaron at offtone.com
14-Nov-2004 09:19


My callback is stored in a function class, and using ob_start ('Class::callback') wasn't working. Not wanting to instantiate the class (no need, it's a function class) I tried this and it worked a charm:



ob_start (array (Class, 'callback'));



PHP 4.3.4

dev at kiwicore dot org
29-Oct-2004 04:49


I wanted to do things a very particular way with output buffering and shutdown functions; using register_shutdown_function instead of the built in callback feature of this function. However, one should note that this won't work, because the contents of the buffer are no longer in scope when PHP is calling the shutdown functions. This would have been easy to see EXCEPT that PHP graciously flushes any unsent buffers at the end of the script, or when calling exit. So:



<?php

    ob_start();

    echo 'hi';

    exit;

?>



Prints "hi". In a nutshell, if you want it to have a shutdown function that handles an output buffer, just specify it in ob_start() and let PHP automatically call it at the end of the script.

jkloss at hotmail dot com
17-Mar-2004 11:20


If ob_start does not seem to be working for you, note that with Apache 2 the flush() function causes PHP to send headers regardless of whether ob_start had been called before flush.



ob_start();

echo 'test';

flush();



will cause Apache 2 to send whatever headers may be stacked up - which means you can't use a header(location:xxx) after the flush.  To fix, remove the flush().  Spent several hours discovering this.  Apache 1.x didn't work this way.

mjr
11-Mar-2004 01:10


If you're using object-orientated code in PHP you may, like me, want to use a call-back function that is inside an object (i.e. a class function). In this case you send ob_start a two-element array as its single argument. The first element is the name of the object (without the $ at the start), and the second is the function to call. So to use a function 'indent' in an object called '$template' you would use <?php ob_start(array('template', 'indent')); ?>.

zeisss at web dot de
24-Nov-2003 01:03


Note that the current working directory changes in the callback procedure (Changed from htdocs\ to windows\system32\ on my system).



You have to use absolut paths if you want to open files on your local system.

ed.oohay (a) suamhcs_rodnan
22-Nov-2003 09:18


Output Buffering even works in nested scopes or might be applied in recursive structures... thought this might save someone a little time guessing and testing :)



<pre><?php

    

    ob_start();              // start output buffer 1

    echo "a";                // fill ob1

        

        ob_start();              // start output buffer 2

        echo "b";                // fill ob2

        $s1 = ob_get_contents(); // read ob2 ("b")

        ob_end_flush();          // flush ob2 to ob1

        

    echo "c";                // continue filling ob1

    $s2 = ob_get_contents(); // read ob1 ("a" . "b" . "c")

    ob_end_flush();          // flush ob1 to browser

    

    // echoes "b" followed by "abc", as supposed to:

    echo "<HR>$s1<HR>$s2<HR>";

    

?></pre>



... at least works on Apache 1.3.28



Nandor =)

venky_athome at yahoo dot com
18-Jan-2003 01:58


IE 55. sp2 and IE6 as on the date of adding this note have problems with content type gzip and caching http headers. The pages are never cached. I think this combination of http headers can also crash the browser. 



see http://support.microsoft.com/default.aspx?scid=kb;en-us;321722

06-Dec-2002 04:02


If you're using Apache (1.3x or 2.0), you might consider adding automatic compression capability to your delivered pages.



I assume you all know how to build compression classes and use them in your programs, but none has yet to offer the speed and robustness of a binary-compiled module. Furthermore, such modules also log the "compressable" hit in the web log file, thus allowing your favorite web anaysing program to show you reports of bandwidth saved.



Having said that, you might consider the following two modules for Apache:



1) Apache 1.3x: use mod_gzip, available from:

http://sourceforge.net/projects/mod-gzip/



2) Apache 2.x: use mod_gz, see here:

http://www.mail-archive.com/dev@httpd.apache.org/msg00734.html



3) Apache 1.3x: you may also want to use mod_defalte, from:

ftp://ftp.lexa.ru/pub/apache-rus/contrib/



Hope it helps.

cliff at NOSPAMtravelguides dot com
08-Aug-2002 06:36


good article on output buffering on devshed:





http://www.devshed.com/c/a/PHP/Output-Buffering-With-PHP

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ob_start

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