PHP OUTPUT BUFFERING
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

“The Output Control functions allow you to control when output
is sent from the script. This can be useful in several different
situations, especially if you need to send headers to the browser
after your script has began outputting data. The Output Control
functions do not affect headers sent using header() or setcookie(),
only functions such as echo() and data between blocks of PHP
code.”
Source: http://www.php.net/manual/en/intro.outcontrol.php
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

How often has this
happened to you?
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Warning: Cannot modify header information - headers already sent
by (output started at /path/to/script.php:123) in /path/to/
otherscript.php on line 321
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

What about this?
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

(Don’t worry, it’s fake. Yahoo!, please don’t sue.)
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Content might not float
correctly if it isn’t all there yet.
(This happened a lot more on dial-up)
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Output buffering fixes
both of these common issues.
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

ENABLE OUTPUT BUFFERING
(PHP.INI VERSION)
• output_buffering = On
• output_buffering = 4096 (bytes)
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Buffers output.
Fixes both problems.
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

But there has to be more.
Or else this would be a lame
presentation.
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

ENABLE OUTPUT BUFFERING
(CODE VERSION)
• ob_start(); // Start a new output buffer
• ob_flush(); // Send contents to browser
• ob_end_flush(); // Send contents to browser, destroy buffer
• ob_clean(); // Discard buffer contents
• ob_end_clean(); // Discard buffer contents & destroy buffer
• ob_get_contents(); // Contents of the current buffer
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

ob_start
• bool ob_start ([ callback $output_callback [, int $chunk_size [,
bool $erase ]]] )
• Optional $output_callback routine called before outputting or
discarding buffer. Gets copy of buffer (string) and must return
string.
• Optional $chunk_size (size of the buffer)
• Optional $erase (false == don’t destroy buffer until script ends)
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Call ob_start() at the top of your script
same as output_buffering = On in php.ini
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

CACHING
• At script’s start, see if there’s a cached copy of the output
• If not, continue with the script
• Use ob_get_contents() or $output_callback to get buffer
contents and cache it
• Next time script runs, it’ll find the cached copy
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

MORE INFO ON CACHING
http://www.slideshare.net/csixty4/caching-data-for-performance
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

MODIFY THE BUFFER
• ob_get_contents() or $output_callback again
• Get the buffer as a string
• Do str_replace, maybe parse it as XML
• Return a string version
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

MODIFY THE BUFFER
(WHAT CAN YOU DO WITH IT?)
• Templating system
• Form building library
• Unicode character replacement (accents, fancy quotes)
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

(At this point, Mike Creuzer spent a few
minutes talking about a script he wrote
that calls a Twitter library and uses
an output buffer to capture the results,
then pulls what he wants out of the output.)
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

NESTING BUFFERS
• Call ob_start() as many times as you want
• Useful for capturing output from libraries as strings
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

NESTING BUFFERS
ob_start();
echo “stuff”;
ob_start(); // create a new buffer
generateATonOfHTML();
$buff = ob_get_contents(); ob_end_clean();
$buff = str_replace(‘Dog’, ‘Cat’, $buff);
echo $buff;
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

CAVEAT
You knew there had to be a catch
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

If output buffering is so good,
why isn’t it turned on by default?
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

BUFFERS TAKE UP MEMORY
• If
set to “On” or ob_start() called w/o $chunk_size, uses as
much RAM as needed
• Ifset to a number or ob_start() called with $chunk_size, uses
that much memory
• Memory use multiplied by # of nested buffers
• Each simultaneous script needs RAM
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Your script could run out of memory.
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Your server could run out of RAM and have to swap
(sloooooooooooow)
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

(Fairly) easy to mitigate:
buy RAM
and increase memory_limit
in php.ini
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009

Questions?
PHP Output Buffering :: David Ross :: Suburban Chicago PHP & Web Development Meetup :: suburbanchicagophp.org :: August 6, 2009