ob_start

(PHP 4, PHP 5, PHP 7, PHP 8)

ob_start — 打开输出控制缓冲

说明

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

此函数将打开输出缓冲。当输出缓冲激活后，脚本将不会输出内容，相反需要输出的内容被存储在内部缓冲区中。参阅缓冲什么输出？以了解哪些输出受到影响。

输出缓冲区是可堆叠的，也就是说，当一个缓冲区处于活动状态时也可以调用 ob_start()。如果有多重输出缓冲区是活跃的，输出内容会一直按嵌套的顺序依次过滤。参阅嵌套输出缓冲区获取更多详情。

有关输出缓冲区的详细信息，请参阅用户级别输出缓冲区

参数

callback

可以指定可选的 callback callable。也可以通过传递 null 来绕过它。

当冲刷（发送）、清理输出缓冲区或在脚本末尾冲刷输出缓冲区时，将调用 callback。

callback 的签名如下：

handler(string $buffer, int $phase = ?): string

buffer: 输出缓冲区中的内容。
phase: PHP_OUTPUT_HANDLER_* 常量。PHP_OUTPUT_HANDLER_* 常量的位掩码。有关更多详细信息，请参阅传递给输出处理程序的 flag。

如果 callback 返回 false，则返回缓冲区的内容。有关更多详细信息，请参阅输出处理程序的返回值。

警告

从输出处理程序中调用以下任何函数都将导致 fatal 错误 ob_clean()、ob_end_clean()、ob_end_flush()、ob_flush()、ob_get_clean()、ob_get_flush()、ob_start()。

有关 callback（输出处理程序）的更多详细信息，请参阅输出处理程序和使用输出处理程序。

chunk_size

如果传递了可选参数 chunk_size，则在任何导致缓冲区长度等于或大于 chunk_size 的代码块的输出之后，都会冲刷缓冲区。默认值 0 表示缓冲所有输出，直到缓冲区关闭。更多详细信息，请参阅缓冲区大小。

flags

flags 参数是位掩码，用于控制可以在输出缓冲区上执行的操作。默认是允许清理、冲刷和移除输出缓冲区，可以通过缓冲区控制 flag手动设置。参阅缓冲区中允许的操作获取更多详细信息。

每个标志都控制着对一组功能的访问，详细介绍如下：

常量	函数
`PHP_OUTPUT_HANDLER_CLEANABLE`	ob_clean()
`PHP_OUTPUT_HANDLER_FLUSHABLE`	ob_flush()
`PHP_OUTPUT_HANDLER_REMOVABLE`	ob_end_clean()、ob_end_flush()、ob_get_clean()、ob_get_flush()

返回值

成功时返回 true，或者在失败时返回 false。

示例

示例 #1 用户自定义回调函数的示例

<?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();

?>

以上示例会输出：

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

示例 #2 创建不可擦除的输出缓冲区

<?php

ob_start(null, 0, PHP_OUTPUT_HANDLER_STDFLAGS ^ PHP_OUTPUT_HANDLER_REMOVABLE);

?>

参见

ob_get_contents() - 返回输出缓冲区的内容
ob_end_clean() - 清空（擦除）活动缓冲区的内容并关闭它
ob_end_flush() - 冲刷（发送）活动输出处理程序的返回值，并关闭活动输出缓冲区
ob_implicit_flush() - 打开/关闭绝对刷送
ob_gzhandler() - ob_start 回调函数压缩输出缓冲区
ob_iconv_handler() - 以输出缓冲处理程序转换字符编码
mb_output_handler() - 在输出缓冲中转换字符编码的回调函数
ob_tidyhandler() - ob_start callback function to repair the buffer

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＋添加备注

用户贡献的备注 39 notes

down

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();
?>

down

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

down

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 =)

down

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')); ?>.

down

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 :)

down

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") ;
...
}

down

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();
}

down

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.

down

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.

down

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;
  }
}

?>

down

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.

down

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.

down

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!!

down

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;

down

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.

down

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).

down

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.

down

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;
}

down

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);
?>

down

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);
}

down

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();

down

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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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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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.

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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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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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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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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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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.

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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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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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cliff at NOSPAMtravelguides dot com ¶

22 years ago

good article on output buffering on devshed:



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

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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 !

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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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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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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

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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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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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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