PHP Output Buffering

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


How often has this
happened to you?


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


What about this?


(Don’t worry, it’s fake. Yahoo!, please don’t sue.)


Content might not ﬂoat
correctly if it isn’t all there yet.
(This happened a lot more on dial-up)


Output buffering ﬁxes
both of these common issues.


ENABLE OUTPUT BUFFERING
(PHP.INI VERSION)

• output_buffering = On

• output_buffering = 4096 (bytes)


Buffers output.
Fixes both problems.


But there has to be more.

Or else this would be a lame
presentation.


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

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)


Call ob_start() at the top of your script
same as output_buffering = On in php.ini


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


MORE INFO ON CACHING
http://www.slideshare.net/csixty4/caching-data-for-performance


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


MODIFY THE BUFFER
(WHAT CAN YOU DO WITH IT?)

• Templating system

• Form building library

• Unicode character replacement (accents, fancy quotes)


(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.)


NESTING BUFFERS

• Call ob_start() as many times as you want

• Useful for capturing output from libraries as strings


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;


CAVEAT
You knew there had to be a catch


If output buffering is so good,
why isn’t it turned on by default?


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


Your script could run out of memory.


Your server could run out of RAM and have to swap
(sloooooooooooow)


(Fairly) easy to mitigate:
buy RAM
and increase memory_limit
in php.ini


Questions?


PHP Output Buffering

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