Introduction
Web page caching can significantly improve user experience by reducing load times and conserving bandwidth. However, it poses challenges when dealing with sensitive information that should not be cached for security reasons. This tutorial covers how to prevent web pages from being cached across various browsers including Internet Explorer 6+, Firefox 1.5+, Safari 3+, Opera 9+, and Chrome.
Understanding HTTP Headers
To control caching effectively, you need to understand the role of certain HTTP headers:
- Cache-Control: Directs caches on what they can store.
- Pragma: Serves as a fallback for older HTTP/1.0 clients that may not support Cache-Control.
- Expires: Specifies an expiration date/time for cached entries.
The Correct Combination
To ensure no caching occurs, the following headers should be set:
Cache-Control: no-cache, no-store, must-revalidate
Pragma: no-cache
Expires: 0
Explanation of Headers:
no-cache: Forces caches to submit the request to the origin server for validation before releasing a cached copy.no-store: Prevents any storage of the response in caches or browsers.must-revalidate: Ensures that once a resource is stale, it must not be used without revalidation.
Implementing Cache Control
Below are examples of how to set these headers across different programming languages and frameworks:
PHP
header("Cache-Control: no-cache, no-store, must-revalidate"); // HTTP 1.1.
header("Pragma: no-cache"); // HTTP 1.0.
header("Expires: 0"); // Proxies.
Java Servlet or Node.js
response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
response.setHeader("Pragma", "no-cache");
response.setHeader("Expires", "0");
ASP.NET MVC
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Cache.AppendCacheExtension("no-store, must-revalidate");
Response.AppendHeader("Pragma", "no-cache");
Response.AppendHeader("Expires", "0");
Ruby on Rails
headers["Cache-Control"] = "no-cache, no-store, must-revalidate"
headers["Pragma"] = "no-cache"
headers["Expires"] = "0"
Python/Flask and Django
response = make_response(render_template(...))
response.headers["Cache-Control"] = "no-cache, no-store, must-revalidate"
response.headers["Pragma"] = "no-cache"
response.headers["Expires"] = "0"
HTML Meta Tags
Although HTTP headers take precedence, HTML meta tags can be used for non-networked views:
<meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate">
<meta http-equiv="Pragma" content="no-cache">
<meta http-equiv="Expires" content="0">
Verifying Headers
Use your browser’s developer tools to inspect HTTP response headers. In Chrome and Firefox, press F12 and navigate to the "Network" tab to view the details of HTTP requests and responses.
Special Considerations for File Downloads
For file downloads, it’s typically better to allow caching unless security concerns dictate otherwise. If you must prevent caching, be aware of browser-specific quirks such as issues with IE7/8 when downloading files over HTTPS.
By setting these headers correctly, you can ensure that your web pages are not cached unintentionally, maintaining both performance and security standards across different browsers.