Caching and headers

[eluser]Aquillyne[/eluser]
[quote author="Randy Casburn" date="1216705596"]First, the short term fix:[/quote]

A good fix for the meantime, although far from desirable.


[quote author="Randy Casburn" date="1216705596"]If "you want the CSS cached" you MUST load the remainder of the style information into an appropriate storage location for the CSS to be cached along with the header.[/quote]

I'm not sure what you're getting at. Let's say I have a controller "styles/css", containing:

Code:

$data["body"] = array("background" => "white");

$this->load->view("styles/css_file", $data)

The view simply converts that $data into a CSS document, e.g.:

Code:

body {
background: white
}

The view also - as it must - has a first line:

Code:

$this->output->set_header("Content-Type: text/css");

This completes the use scenario. My XHTML links to the styles controller like so:

Code:

<link rel="stylesheet" href="styles/css" type="text/css" media="all" />

So when the page loads, the browser loads the CSS via the CSS controller, which outputs CSS specified in the controller and tidied into a document by the view. And crucially, either the CSS controller or view outputs the CSS header - or the browser will interpret the link as plain text and not render the CSS.

So now I've got controller-delivered CSS, which has a host of uses I needn't go into. However, as that CSS might go through long period where it isn't changed, I'd like to cache it. So in the CSS controller I insert the line:

Code:

$this->output->cache(1440)

This now means that everything output by the controller and the view, i.e.

Code:

body {
background: white
}

is cached and that cache is served directly next time, rather than the controller running at all.

But there's the problem - because the cache skips the controller, that CSS file is delivered on subsequent loads without the "text/css" header, meaning on subsequent loads there is no CSS rendering.

There are of course more solutions to this than caching headers, but actually if you think about it it's the best one. Here are three basic reasons:

1. Headers are attached to documents. That's what they're for. They're meta-data, but they aren't separate. If a user has elected to use $this->output->set_header() then he's clearly wanted a header to be sent with his document. And he clearly wants it every time that document is delivered, too. (But if he doesn't, using header() will bypass header-caching under my proposed changes).

2. The CI code comments actually say "Darn, we need to figure out how to cache headers."

3. It's the most intuitive behaviour. I found it stunning that using the integrated function from the Output class didn't include my headers sent with the same class. It seemed all too obvious. Why not? As an original respondant wrote:

[quote author="Seppo" date="1215792983"]I believe that if you send the header trhough the output class ($this->output->set_header) it will also be cached and delivered the next time... but I hadn't use it, so I'm not sre[/quote]

I hope that explains a usage scenario for you. But obviously there are a host more than just for dynamically generated CSS.

And I will point out again that I'm not trying to do anything extra-funky here, I'm not changing the way the cache works and nor am I trying to cache things in a strange way. Nor am I creating any new errors (e.g. the suffix error is nothing to do with this; that's already a problem in CI addressed separately by the Suffix cache extension).

I'm just caching a file that needs its headers, but loses them in the cache. I'm trying to put them together again.