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    ob_start

    (PHP 4, PHP 5, PHP 7)

    ob_start — Turn on output buffering

    Descrierea

    ob_start ( callable $callback = null , int $chunk_size = 0 , int $flags = PHP_OUTPUT_HANDLER_STDFLAGS ) : bool

    This function will turn output buffering on. While output buffering is active no output is sent from the script (other than headers), instead the output is stored in an internal buffer.

    The contents of this internal buffer may be copied into a string variable using ob_get_contents(). To output what is stored in the internal buffer, use ob_end_flush(). Alternatively, ob_end_clean() will silently discard the buffer contents.

    Avertizare

    Some web servers (e.g. Apache) change the working directory of a script when calling the callback function. You can change it back by e.g. chdir(dirname($_SERVER['SCRIPT_FILENAME'])) in the callback function.

    Output buffers are stackable, that is, you may call ob_start() while another ob_start() is active. Just make sure that you call ob_end_flush() the appropriate number of times. If multiple output callback functions are active, output is being filtered sequentially through each of them in nesting order.

    Parametri

    callback

    An optional callback function may be specified. This function takes a string as a parameter and should return a string. The function will be called when the output buffer is flushed (sent) or cleaned (with ob_flush(), ob_clean() or similar function) or when the output buffer is flushed to the browser at the end of the request. When callback is called, it will receive the contents of the output buffer as its parameter and is expected to return a new output buffer as a result, which will be sent to the browser. If the callback is not a callable function, this function will return false. This is the callback signature:

    handler ( string $buffer , int $phase = ? ) : string
    buffer
    Contents of the output buffer.
    phase
    Bitmask of PHP_OUTPUT_HANDLER_* constants.

    If callback returns false original input is sent to the browser.

    The callback parameter may be bypassed by passing a null value.

    ob_end_clean(), ob_end_flush(), ob_clean(), ob_flush() and ob_start() may not be called from a callback function. If you call them from callback function, the behavior is undefined. If you would like to delete the contents of a buffer, return "" (a null string) from callback function. You can't even call functions using the output buffering functions like print_r($expression, true) or highlight_file($filename, true) from a callback function.

    Notă:

    ob_gzhandler() function exists to facilitate sending gz-encoded data to web browsers that support compressed web pages. ob_gzhandler() determines what type of content encoding the browser will accept and will return its output accordingly.

    chunk_size

    If the optional parameter chunk_size is passed, the buffer will be flushed after any output call which causes the buffer's length to equal or exceed chunk_size. The default value 0 means that the output function will only be called when the output buffer is closed.

    Prior to PHP 5.4.0, the value 1 was a special case value that set the chunk size to 4096 bytes.

    flags

    The flags parameter is a bitmask that controls the operations that can be performed on the output buffer. The default is to allow output buffers to be cleaned, flushed and removed, which can be set explicitly via PHP_OUTPUT_HANDLER_CLEANABLE | PHP_OUTPUT_HANDLER_FLUSHABLE | PHP_OUTPUT_HANDLER_REMOVABLE, or PHP_OUTPUT_HANDLER_STDFLAGS as shorthand.

    Each flag controls access to a set of functions, as described below:

    Constant Functions
    PHP_OUTPUT_HANDLER_CLEANABLE ob_clean(), ob_end_clean(), and ob_get_clean().
    PHP_OUTPUT_HANDLER_FLUSHABLE ob_end_flush(), ob_flush(), and ob_get_flush().
    PHP_OUTPUT_HANDLER_REMOVABLE ob_end_clean(), ob_end_flush(), and ob_get_flush().

    Valorile întoarse

    Întoarce valoarea true în cazul succesului sau false în cazul eșecului.

    Exemple

    Example #1 User defined callback function example

    <?php

    function callback($buffer)
    {
          // replace all the apples with oranges
          return (str_replace("apples", "oranges", $buffer));
    }

    ob_start("callback");

    ?>
    <html>
    <body>
    <p>It's like comparing apples to oranges.</p>
    </body>
    </html>
    <?php

    ob_end_flush    ();

    ?>

    Exemplul de mai sus va afișa:

    <html>
<body>
<p>It's like comparing oranges to oranges.</p>
</body>
</html>

    Example #2 Creating an uneraseable output buffer in a way compatible with both PHP 5.3 and 5.4

    <?php

    if (version_compare(PHP_VERSION, '5.4.0', '>=')) {
          ob_start(null, 0, PHP_OUTPUT_HANDLER_STDFLAGS ^
            PHP_OUTPUT_HANDLER_REMOVABLE);
    } else {
          ob_start(null, 0, false);
    }

    ?>

    A se vedea și

    add a note add a note

    User Contributed Notes 39 notes

    up
    52
    Ray Paseur (Paseur ... ImagineDB.com)
    19 years ago
    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();
    ?>
    up
    25
    ed.oohay (a) suamhcs_rodnan
    21 years ago
    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 =)
    up
    10
    net_navard at yahoo dot com
    18 years ago
    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
    up
    19
    mjr
    20 years ago
    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')); ?>.
    up
    4
    jhlavon
    11 years ago
    When used in constructor part of class it have to be prefixed by "self::" or by classname, else PHP fails to create buffer.

    function __construct ()
    {

    $bo = ob_start ("self::callback_ob") ;
    ...
    }
    up
    2
    mbutscher at gmx dot de
    8 years ago
    In case of an error the contents of the output buffer are shown along with the error message. If it is really important that this does never happen, you can do the following (but this also eats up the error message):

    <?php
    $outputbufferOutput     = FALSE;

    function     switchableOutputHandler($buffer) {
        global     $outputbufferOutput;

        if (    $outputbufferOutput)
            return     $buffer;
        else
            return     "";
    }

    function     internob_start() {
        global     $outputbufferOutput;

            $outputbufferOutput = FALSE;
        return     ob_start("switchableOutputHandler");
    }

    function     internob_get_clean() {
        global     $outputbufferOutput;
       
            $outputbufferOutput = TRUE;
            $result = ob_get_clean();
            $outputbufferOutput = FALSE;
        return     $result;
    }

    ?>

    You can then use internob_start() and internob_get_clean() instead of ob_start() and ob_get_clean(). Other functions can be replaced accordingly.
    up
    11
    mchojrin at gmail dot com
    12 years ago
    Just a word of warning to those like myself who are upgrading from 5.3. I have a piece of code that used to work:

    <?php
    if ( !ob_start( !DEBUGMODE ? 'ob_gzhandler' : '' ) ) {
            ob_start();
    }
    ?>

    Which is not working anymore (I get an error like: Warning: ob_start(): function '' not found or invalid function name).

    It's easily fixed though, just changed the '' to a null, like this:

    <?php
    if ( !ob_start( !DEBUGMODE ? 'ob_gzhandler' : null ) ) {
            ob_start();
    }       
    ?>

    Which preserves the code intention but works :)
    up
    7
    Asher Haig (ahaig at ridiculouspower dot com)
    17 years ago
    When a script ends, all buffered output is flushed (this is not a bug: http://bugs.php.net/bug.php?id=42334&thanks=4). What happens when the script throws an error (and thus ends) in the middle of an output buffer? The script spits out everything in the buffer before printing the error!

    Here is the simplest solution I have been able to find. Put it at the beginning of the error handling function to clear all buffered data and print only the error:

    $handlers = ob_list_handlers();
    while ( ! empty($handlers) )    {
        ob_end_clean();
        $handlers = ob_list_handlers();
    }
    up
    1
    aaron at offtone.com
    20 years ago
    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
    up
    7
    Chris
    14 years ago
    Careful with while using functions that change headers of a page; that change will not be undone when ending output buffering.

    If you for instance have a class that generates an image and sets the appropriate headers, they will still be in place after the end of ob.

    For instance:
    <?php
      ob_start    ();
          myClass::renderPng(); //header("Content-Type: image/png"); in here
          $pngString = ob_get_contents();
          ob_end_clean();
    ?>

    will put the image bytes into $pngString, and set the content type to image/png. Though the image will not be sent to the client, the png header is still in place; if you do html output here, the browser will most likely display "image error, cannot be viewed", at least firefox does.

    You need to set the correct image type (text/html) manually in this case.
    up
    3
    ernest at vogelsinger dot at
    18 years ago
    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.
    up
    2
    jkloss at hotmail dot com
    20 years ago
    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.
    up
    2
    tracey AT archive DOT org
    17 years ago
    Way to make all stdout and stderr write to a log
    from *inside* a php script.
    You simply need to make sure to call elog() every
    once in awhile to get output.
    It's a nice way to "daemonize" a script w.r.t. its logging.

    // This allows us to capture all stdout and stderr (and error_log() calls)
    // to this logfile...
    // The "collected output" will be flushed anytime "elog()" is used...
    ini_set("error_log", "/var/log/script.log");
    ob_start();

    function elog($str)
    {
      // get anything written to stdout or stderr that did *NOT* use elog()
      // and write it now...
      $writeme = ob_get_contents();
      if ($writeme)
      {
        error_log($writeme);
        ob_end_clean();
        ob_start();
      }
      // now write message this method was called with
      error_log($str);
    }
    up
    3
    dan at roteloftet dot com
    16 years ago
    Some web hosting servers (mine do, at least) have in their php.ini the following setting:
    output_handler = ob_gzhandler

    This proved problematic for php-scripts which returns an image or a binary file in general, since there is no way to determine the content length of the compressed file.

    Since I spent a lot of time scouring the net searching for a work-around (.htaccess-modifications were out of the picture for various reasons), I found this to work nicely to cancel out the ob_gzhandler specified in the php.ini:

    <?php
    while (ob_get_level())
                ob_end_clean();
    header("Content-Encoding: None", true);
    ?>

    Put this at the top of the script before anything else is written to the page, and the script result will not be compressed.
    up
    3
    lucky760 at yahoo dot com
    18 years ago
    In extension to the compress() function posted below, here's a nifty little class that improves the idea a bit. Basically, running that compress() function for all your CSS for every single page load is clearly far less than optimal, especially since the styles will change only infrequently at the very worst.

    With this class you can simply specify an array of your CSS file names and call dump_style(). The contents of each file are saved in compress()'d form in a cache file that is only recreated when the corresponding source CSS changes.

    It's intended for PHP5, but will work identically if you just un-OOP everything and possibly define file_put_contents.

    Enjoy!

    <?php

    $CSS_FILES     = array(
          '_general.css'
    );

    $css_cache = new CSSCache($CSS_FILES);
    $css_cache->dump_style();

    //
    // class CSSCache
    //

    class CSSCache {
      private     $filenames = array();
      private     $cwd;
       
      public function     __construct($i_filename_arr) {
        if (!    is_array($i_filename_arr))
              $i_filename_arr = array($i_filename_arr);
       
            $this->filenames = $i_filename_arr;
            $this->cwd = getcwd() . DIRECTORY_SEPARATOR;
       
        if (    $this->style_changed())
              $expire = -72000;
        else
              $expire = 3200;
       
            header('Content-Type: text/css; charset: UTF-8');
            header('Cache-Control: must-revalidate');
            header('Expires: ' . gmdate('D, d M Y H:i:s', time() + $expire) . ' GMT');
      }
     
      public function     dump_style() {
            ob_start('ob_gzhandler');
       
        foreach (    $this->filenames as $filename)
              $this->dump_cache_contents($filename);
       
            ob_end_flush();
      }
     
        private function     get_cache_name($filename, $wildcard = FALSE) {
            $stat = stat($filename);
        return     $this->cwd . '.' . $filename . '.' .
          (    $wildcard ? '*' : ($stat['size'] . '-' . $stat['mtime'])) . '.cache';
      }
     
      private function     style_changed() {
        foreach (    $this->filenames as $filename)
          if (!    is_file($this->get_cache_name($filename)))
            return     TRUE;
        return     FALSE;
      }

      private function     compress($buffer) {
            $buffer = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $buffer);
            $buffer = str_replace(array("\r\n", "\r", "\n", "\t", '  '), '', $buffer);
            $buffer = str_replace('{ ', '{', $buffer);
            $buffer = str_replace(' }', '}', $buffer);
            $buffer = str_replace('; ', ';', $buffer);
            $buffer = str_replace(', ', ',', $buffer);
            $buffer = str_replace(' {', '{', $buffer);
            $buffer = str_replace('} ', '}', $buffer);
            $buffer = str_replace(': ', ':', $buffer);
            $buffer = str_replace(' ,', ',', $buffer);
            $buffer = str_replace(' ;', ';', $buffer);
        return     $buffer;
      }
     
      private function     dump_cache_contents($filename) {
            $current_cache = $this->get_cache_name($filename);
       
            // the cache exists - just dump it
            if (is_file($current_cache)) {
          include(    $current_cache);
          return;
        }
       
            // remove any old, lingering caches for this file
            if ($dead_files = glob($this->get_cache_name($filename, TRUE), GLOB_NOESCAPE))
          foreach (    $dead_files as $dead_file)
                unlink($dead_file);
       
            $compressed = $this->compress(file_get_contents($filename));
            file_put_contents($current_cache, $compressed);
       
        echo     $compressed;
      }
    }

    ?>
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    1
    Filip Dalge
    12 years ago
    When a fatal error is thrown, PHP will output the current buffer of Output-Control without postprocessing before printing the error message. If you are working with several output control levels, this might not result in the desired behavior.

    You can use an output callback handler to handle this and discard the output.

    Therefore, use ob_start("ob_error_handler") in connection with the following:

    function ob_error_handler($str) {
        $error = error_get_last();
        if ($error && $error["type"] == E_USER_ERROR || $error["type"] == E_ERROR) {
            return ini_get("error_prepend_string").
              "\nFatal error: $error[message] in $error[file] on line $error[line]\n".
              ini_get("error_append_string");
        }
        return $str;
    }
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    1
    clancy hood at gmail dot com
    15 years ago
    With ob callback: note that the second parameter sent to your method won't help you differentiate between flush calls and calls to ob_clean, but the buffer contents is sent in both cases, so you end up parsing data that isn't going to be used. Also, note that the constant PHP_OUTPUT_HANDLER_START is never actually sent, rather the integer "3" turns up on first flush:
    <?php

            function ob_handler($string, $flag){
            static     $input = array();
                $done = false;
            switch(    $flag){
                case     PHP_OUTPUT_HANDLER_START:   
                        $flag_sent = "PHP_OUTPUT_HANDLER_START ($flag)";
                    break; 
                case     PHP_OUTPUT_HANDLER_CONT:
                        $flag_sent = "PHP_OUTPUT_HANDLER_CONT ($flag)";
                    break;
                case     PHP_OUTPUT_HANDLER_END:
                        $done = true;
                        $flag_sent = "PHP_OUTPUT_HANDLER_END ($flag)";
                    break;
                default:
                        $flag_sent = "Flag is not a constant ($flag)";
            }
                $input[] = "$flag_sent: $string<br />";
                $output = "$string<br />";
            if(!    $done) return $output;
                // print_r($input, 1) causes an error and var_export just doesn't work
                $output .= '<br />';
            foreach(    $input as $k=>$v) $output .= "$k: $v";
            return     $output;
        }

            ob_start('ob_handler');

        echo     'flush';
            ob_flush();

        echo     'flush 2';
            ob_flush();

        echo     'clean';
            ob_clean();

        echo     'flush 3';
            ob_flush();

        echo     'end flush';
            ob_end_flush();
    ?>
     
    flush
    flush 2
    flush 3
    end flush

    0: Flag is not a constant (3): flush
    1: PHP_OUTPUT_HANDLER_CONT (2): flush 2
    2: PHP_OUTPUT_HANDLER_CONT (2): clean
    3: PHP_OUTPUT_HANDLER_CONT (2): flush 3
    4: PHP_OUTPUT_HANDLER_END (4): end flush

    I suppose the START flag problem *may* be a bug but I'm not able to upgrade before reporting since I must have the same version as my server (I'm on PHP 5.2.6). If anyone has 5.2.11 or other stable version feel free to test/report as you see fit.
    up
    1
    Francois Hill
    17 years ago
    Following clement dot ayme at st dot com 's remark :

    In my experience it seems that the output IS buffered, but ALSO sent to the standard output !
    up
    1
    Charlie Farrow
    17 years ago
    Under certain freak conditions, when an error ocours perfoming an action on an object that cannot be done (either because the object does not exist or the method does not exist) inside of an ob_start() the script will exit and print everything the current function generates before the error, but nothing else, including no error message.

    I am at a loss to why no error message appears and am trying to get a working example for the developers that is simpler than my whole program!

    So if you are using ob_start() and you get no output, check your objects.... you have made a mistake on them somewhere. The only trouble is you will not know where as there is no error!!
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    1
    Bitwise
    15 years ago
    There is no start flag problem. One just has to notice that the second parameter is not a mode but consists of bitwise-OR'ed flags.

    <?php
    function ob_handler($string, $flags) {
            static     $input = array();
            if (     $flags & PHP_OUTPUT_HANDLER_START )
                        $flags_sent[] = "PHP_OUTPUT_HANDLER_START";
            if (     $flags & PHP_OUTPUT_HANDLER_CONT )
                        $flags_sent[] = "PHP_OUTPUT_HANDLER_CONT";
            if (     $flags & PHP_OUTPUT_HANDLER_END )
                        $flags_sent[] = "PHP_OUTPUT_HANDLER_END";
                $input[] = implode(' | ', $flags_sent) . " ($flags): $string<br />";
                $output  = "$string<br />";
            if (     $flags & PHP_OUTPUT_HANDLER_END ) {
                        $output .= '<br />';
                    foreach(    $input as $k => $v) $output .= "$k: $v";
            }
            return     $output;
    }

    ob_start('ob_handler');

    echo     'flush';
    ob_flush();

    echo     'flush 2';
    ob_flush();

    echo     'clean';
    ob_clean();

    echo     'flush 3';
    ob_flush();

    echo     'end flush';
    ob_end_flush();
    ?>

    flush
    flush 2
    flush 3
    end flush

    0: PHP_OUTPUT_HANDLER_START | PHP_OUTPUT_HANDLER_CONT (3): flush
    1: PHP_OUTPUT_HANDLER_CONT (2): flush 2
    2: PHP_OUTPUT_HANDLER_CONT (2): clean
    3: PHP_OUTPUT_HANDLER_CONT (2): flush 3
    4: PHP_OUTPUT_HANDLER_END (4): end flush
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    1
    admin at bobfrank dot org
    19 years ago
    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;
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    0
    bty-adminf2 at trebly dot net
    9 years ago
    This concerns the default values used for ob_start().

    Note that I could verify that ob_start() and ob_start(null,0) are not always equivalent.

    It seems that with ob_start() the output buffer is open with current default parameters of your configuration if they have been explicitly defined.

    So, if you have set $chunk_size to any value previously and send data larger than $chunk_size the data will be automatically flushed by blocks of $chunk_size.

    If you explicitely define $chunk_size=0, later, when you will use any function as $my_ob_dataoutput=ob_get_clean(); you  will get back the whole content of your output (quite unlimited with $chunk_size=0).

    I discover this because my var $my_ob_dataoutput was truncated. Using "ob_get_status (true)" function, I could verify that an error (in a lower level or by default out of my control) was setting previously the $chunk_size of ob at 4096.
    I changed "ob_start()" for "ob_start(null,0)" and everything became OK.
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    me at haravikk dot com
    12 years ago
    I think it's worth noting that while you can't call any output functions such as echo or print from within a callback function, you can still send headers (presumably including cookies, haven't checked). Of course this only works in the first callback, like so:

    <?php

    function myCallback($buffer, $flags) {
        if (    $flags & PHP_OUTPUT_HANDLER_START) {
                header('Server: LastMinuteHeaderServer');
        }
    }

    ob_start('myCallback');
    echo     "Hello World!";
    ob_end_flush();

    ?>

    Not the most inspiring example, but in this case the code is able to sneak a last-minute header in before the headers part of the response is sent. This can be handy if you want to avoid replacing header values that are uncertain.

    For example if your code may return an image, but you don't want to set content type until you're sure that the image can be sent successfully, you can use the callback to leave the decision right until the very last moment, by which point you're hopefully sure of what's being sent in the HTTP body.
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    -2
    php REMOVETHIS at kennel17 dot co dot uk
    3 years ago
    Be very careful when returning false from your callback function!

    Despite what the documentation says, this is *not* the same as returning the supplied $buffer value, unmodified.  In the context of a 'clean' operation (e.g. ob_clean()) this will result in your callback function being disabled and skipped for any subsequent output.

    The answer is to ensure you always return a string value from your callback.  This is likely a bug, and it may get fixed at some point, but it applies to all versions since PHP 5.4 up to the current version (8.1 at time of writing).  Note that it was not an issue on PHP 5.3 and below.

    Some more detail can be seen on this Stack Overflow question: https://stackoverflow.com/questions/69845122/

    A demonstration of the issue has been set up in this fiddle: https://3v4l.org/66cai
    up
    1
    Anonymous
    19 years ago
    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).
    up
    1
    oersoep at gmail dot com
    19 years ago
    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.
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    1
    rafa dot chacon at factorydea dot com
    19 years ago
    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.
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    0
    mariusads at helpedia dot com
    15 years ago
    Make sure the editor you use does not add the UTF8/UTF16 BOM at the start of the scripts if you want to use ob_start("ob_gzhandler");

    If those three characters are present, browsers like Firefox won't be able to decode the pages and will report:

    Content Encoding Error

    The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.

    The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.

    Google Chrome will simply report "Error 2 (net::ERR_FAILED): Unknown error."

    With the ob_start command commented out, the page is successfully load and the browser will usually detect the BOM and not show it on the page, so everything's hard to debug.
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    cj at ceejayoz dot com
    15 years ago
    Note that since PHP 5.1.x, all objects have their destructors called before the output buffer callback function executes. Thus, globalised objects will not be available as expected in the function.

    This is stated to be intended behaviour, per http://bugs.php.net/bug.php?id=40104
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    fordiman at gmail dot com
    16 years ago
    Here's a nifty function I use daily.  Essentially: include a PHP file - but render its output to a variable, rather than to the buffer.  It's also set up to load the script with a variable set, and automagically loads globals into the script's namespace, making it an effective templating scheme.  It also has error handling, so that you're not flying blind when using output buffering.

    <?php
    $GLOBALS    ['BufferedErrors']=Array();
    function     errorParse($errno, $errstr, $errfile, $errline, $errcontext) {
            $errorTypes = Array(
                E_ERROR => 'Fatal Error',
                E_WARNING => 'Warning',
                E_PARSE => 'Parse Error',
                E_NOTICE => 'Notice',
                E_CORE_ERROR => 'Fatal Core Error',
                E_CORE_WARNING => 'Core Warning',
                E_COMPILE_ERROR => 'Compilation Error',
                E_COMPILE_WARNING => 'Compilation Warning',
                E_USER_ERROR => 'Triggered Error',
                E_USER_WARNING => 'Triggered Warning',
                E_USER_NOTICE => 'Triggered Notice',
                E_STRICT => 'Deprecation Notice',
                E_RECOVERABLE_ERROR => 'Catchable Fatal Error'
            );
            $ret=(object)Array(
                'number'=>$errno,
                'message'=>$errstr,
                'file'=>$errfile,
                'line'=>$errline,
                'context'=>$errcontext,
                'type'=>$errorTypes[$errno]
        );
            $GLOBALS['BufferedErrors'][]=$ret;
        return     false;
    }
    function     parse($fileToInclude, $argumentsToFile=false) {
            $bufferedErrorStack = $GLOBALS['BufferedErrors'];
            set_error_handler('errorParse', error_reporting());
            $GLOBALS['BufferedErrors']=Array();
       
        if (!    file_exists($fileToInclude))
            return     '';
        if (    $argumentsToFile === false)
                $argumentsToFile = Array();
            $argumentsToFile = array_merge($GLOBALS, $argumentsToFile);
        foreach (    $argumentsToFile as $variableName => $variableValue)
            $    $variableName = $variableValue;
            ob_start();
        include(    $fileToInclude);
            $ret = ob_get_contents();
            ob_end_clean();
       
            restore_error_handler();
            $errors = $GLOBALS['BufferedErrors'];
            $GLOBALS['BufferedErrors'] = $bufferedErrorStack;
        if (    count($errors)>0) {
                $ret.='<ul class="error">';
            foreach (    $errors as $error)
                    $ret.=
                        '<li>'.
                            '<b>'.$error->type.'</b>: '.
                            $error->message.
                            '<blockquote>'.
                                '<i>file</i>: '.$error->file.'<br />'.
                                '<i>line</i>: '.$error->line.
                            '</blockquote>'.
                        '</li>';
                $ret.='</ul>';
        }
        return     $ret;
    }
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    0
    coldshine at gmail dot com
    16 years ago
    Referring to dan at roteloftet dot com's comment:

    RFC 2616 (HTTP) specifies a "transparent" Content-Encoding, "identity" (§ 3.5), that nicely suits what you tried to do with the (invalid) "None". So this equally working, and it's also RFC-compliant:

    <?php
    header    ('Content-Encoding: identity', true);
    ?>
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    0
    butch at enterpol dot pl
    18 years ago
    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();
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    0
    simon
    18 years ago
    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';
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    geoffrey at nevra dot net
    19 years ago
    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()
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    0
    Aleksey
    19 years ago
    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!');
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    0
    Anonymous
    22 years ago
    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.
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    -1
    Anonymous
    13 years ago
    In case you're in for some readable representation for flags, this is a variant as a private class member:

    <?php
    class foo {
        private function     getFlagsReadable($flags) {
                $flagNames = array('PHP_OUTPUT_HANDLER_START', 'PHP_OUTPUT_HANDLER_CONT', 'PHP_OUTPUT_HANDLER_END');
                $readable = '';
            foreach(    $flagNames as $flagName)
                if (    $flags & constant($flagName) )
                        $readable .= (strlen($readable) ? ' | ' : '') . $flagName
                    ;       
            return     $readable;
        }
    }
    ?>
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    -2
    codextasy at gmail dot com
    16 years ago
    There is a difference between the documentation and real callback functions invocation.
    Manual says: "The function will be called when ob_end_flush() is called, or when the output buffer is flushed to the browser at the end of the request."

    Actually, the callback function, once set by ob_start(), will be called regardless.
    Here are the functions that invoke callback function immediately:
    ob_clean
    ob_end_clean
    ob_end_flush
    ob_flush
    ob_get_clean

    BUT only two of them return the result returned by the callback (ob_end_flush, ob_flush), other functions discard it.

    At the end of the request, even if none of the functions listed above is called, the callback will be called anyway, and its result will be returned to the browser (well, at least this is corresponding to the manual).

    There is one more trick:
    If you set callback function with chunk_size > 1, callback function will be called each time output buffer is equal or exceeds chunk_size and its result will be output to the browser, even if you call any of ob_clean(), ob_end_clean(), ob_get_clean() later, so be aware of this fact.
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