如何使用codeigniter正确启用浏览器缓存？

Question

Every time I do I search on this I get information about how to disable the browser cache. Never anything about enabling it.

How do I get the back button to use the cache and not regenerate the page?

Answer 1

As far as I know you can control to force a browser to reload the data by means of these meta tags:

<meta http-equiv="Pragma" content="no-cache">
<meta http-equiv="Cache-control" content="no-cache">
<meta http-equiv="Expires" content="0">

but you cannot force it to read from cache. The browser itself will do that for you if you don't explicitly specify to ignore the cache, and the page data are in fact cached and not expired.

This does not depend on CodeIgniter because it's client-side, but you might want to use the meta() function included in CI's html helper , which will simply output the corresponding meta tag. eg:

echo meta('Cache-control', 'no-cache', 'http-equiv');

would generate the second code line above.

Note:

1. The 1st meta tag is specified for http/1.0 while the 2nd one is for http/1.1 but both are used to allow backwards compatibility.

2. If you're using xhtml instead of html remember to close the meta tags with />

Answer 2

Browser caching has nothing to do with codeigniter. You can use html meta tags to instruct the browser specifically not to cache pages or you can set a cache expiry for an individual page like so:

<meta http-equiv="expires" content="Mon, 10 Dec 2001 00:00:00 GMT" />

You could use a bit of php to drop tomorrows date in there. The browser (depending on settings) will usually pull as much as it can from the cache automatically, including when clicking the back button - the cache for the back button will work the same as if you were coming in from any other link.

You could set expires headers through your htaccess using something like the following on an apache server (you would have to ask about how to do this on other server types) to tell the browser that is should cache certain types of content for a given periods of time:

ExpiresByType text/html "access plus 60 seconds"

This will tell the browser to store anything of mime type text/html for 60 seconds (this includes codeigniter output) BUT DONT DO THIS if your dealing with dynamic content It will stop any dynamic page content being loaded and will stop any changes to your content being loaded by returning visitors (Obviously this second part is not such an issue with a 60 second cache).

The key thing to realise is that Your page is not one thing, it's made up of lots of parts, some of these parts should be called from cache (js, css, images, etc.) some should not (often html will fall into this category). The browser will automatically call all the parts of your page from the cache where the cache has not expired.

Usually you would use .htaccess (or similar method) to cache your css, images, etc. (using versioning in filenames to force a reload when they change).

You should also take advantage of server side caching - codeigniter does this for whole pages but I dont tend to find this very helpful for any kind of dynamic site so I would take a look at for using phil sturgeons partial caching library for ci if you are interested in ss caching:

https://github.com/philsturgeon/codeigniter-cache

This wont stop a request being sent to the server but will mean that request requires less processing and can be served as one or several pieces of static content.