output buffering

devinemke

i recently started employing output buffering on some of the sites i run and it's working out very well. one site is a commerce site that securely collects credit card numbers and sends all of the data off to Verisign for payment processing. basically what i'm doing is running ob_start() at the top of my index page and if the users chooses to pay by credit card then the form data is collected and i am using the header() function to send all the data off by appending to the url.

ob_start ();

...collect user data via form...

if ($payment_option == 'credit card')
{
...build $url from the form input data...
ob_end_clean ();
header ("location: $url");
exit ();
}

else
{
...tell user that they will receive a bill by mail...
}

ob_end_flush ();

my question is this: is it necessary to call ob_end_clean() right before the header() function and exit() right after? the script works either way but is it considered good housecleaning practice to blow out the buffer after it is no longer needed? are they any potential pitfalls doing it this way?

thanks

kriek

Originally posted by devinemke
Is it necessary to call ob_end_clean() right before the header() function and exit() right after?

Nope, fortunately it is not necessary.

ob_end_flush() isn't needed in MOST cases because it is called automatically at the end of script execution by PHP itself when output buffering is turned on either in the php.ini or by calling ob_start()

I should also mention that 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.

devinemke

i guess then it is not necessary to call exit() after calling header()?

kriek

Personally I would leave exit() in place, because the exit() function terminates execution of the script, but it also prints status just before exiting.

Norman_Graham

At the web hoster I'm planning to use, output buffering is on and given as 4096 (in the php_info() print out). What does this mean? Is the buffer limit 4096 bytes, kilobytes, megabytes even? I know I could ask them, but I thought I'd get my answer quicker here.

I assume the buffer is fairly large, but thought I'd check.

Thanks

Norman

kriek

If you have access to your php.ini you should find a line similar to

output_buffering=4096

Your host has limited the size of the buffer to 4096 bytes.

Norman_Graham

Thanks for that reply, Kriek. That is not a lot of room to play with: 4096 bytes or characters. That's less than one A4 page of continuous text - an A4 page at 12pt font size is about 4800 characters and spaces, i.e. bytes. So pictures are out of the question and more than about 8 text paragraphs would also go over the limit.

Hmmm ... i'll need to think what to do about this. Is 4096 a standard setting, as you seem to suggest?

Any tips as to how to deal with this?

Thanks

Norman

kriek

If I am not mistaken 4096 is the default size of the buffer; alter this via php.ini

Norman_Graham

Thanks, Kriek, but I wouldn't be able to alter the php.ini at my webhoster, where the setting is also 4096. I've since discovered that ob_start() ain't gonna help me anyway - I thought I could use it as a simple trick for evaluating PHP code that is contained within text in a MySQL table. Seems that this isn't the case. I have to use eval(), so I'll just have to knuckle down and get on with it. I was trying to avoid eval() because I don't even begin to understand the explanation in the manual at PHP.net, but I'll work it out eventually.

Thanx

Norm