Can PHP's ob_start be called more then once?

Question

Can PHP's ob_start be called more then once?

Sorry if this is a dumb question but I really don't know.

My site is really large (file quantity), its a social network and one of the included files uses ob_start PHP's output buffer for something, i'm not ure someone else started my site a long time ago and now it is mine I need to look into it more to see what it's doing exactly.

Anyways I am wanting to use ob_start ("ob_gzhandler"); to compress CSS files and all files on my site get loaded (included) through the index file so I am wanting to know if I am able to use that even though it is already in use somewhere else in the code?

Answer 1

Yes, you can call it more than once. It creates a new buffer each time however, so be careful.

From the manual: "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."

Answer 2

You say this :

I am wanting to use ob_start ("ob_gzhandler"); to compress CSS files

I would rather serving and compressing JS/CSS (well, static) files is the job of the Web server (ie, Apache), and not PHP.

About that, you can take a look at mod_deflate -- at least, if you are using Apache 2.

all files on my site get loaded (included) through the index file

Is that really necessary ? You're having PHP work with no apparent (?) reason, that way.
(Note that even if CSS/JS files are served through PHP, Apache should be able to compress them with mod_deflate ; same is also true for HTML, JSON, ... btw)

Another advantage of not going through PHP to server those files is that it would be easier to get them served by another server, as your site will grow (if it grows enough, actually) :

• you could have a bunch of "PHP servers", to process PHP pages
• and one or two "static-files servers", to server only CSS/JS/images, and lighten the load or your "application servers" ; no need for PHP on these ones ; you could also use something like lighttpd instead of Apache

That being said, ob_start says this :

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.

So, I think the answer to your question is "yes" :-)