HttpCache

HTTP caching is the process of storing copies of HTTP responses so that subsequent requests for the same resource can be served more quickly, reducing latency and network traffic. Caches can be located at the client (for example, a web browser), at intermediary points such as proxies and gateways, or at the origin server itself via server-side caching.

Caches operate by determining whether a stored response is fresh and can be reused. Freshness is controlled by headers in the response, most notably Cache-Control directives (such as max-age, s-maxage, public, private, no-cache, and no-store) and Expires. Shared caches (like proxies) often use s-maxage, while private caches (like a browser) use max-age or no-store. Validators such as ETag with If-None-Match, or Last-Modified with If-Modified-Since, allow a cache to revalidate a stale response and receive a 304 Not Modified if the resource has not changed. The Vary header indicates that the response depends on certain request headers and should not be served for different request variants without revalidation.

Not all responses are cachable; methods like GET are typically cacheable, while POST responses are rarely cached unless explicitly indicated. Invalidation and cache busting may occur through explicit expiration, revalidation, or changing the request URL (for example, by query parameters or versioning). Security considerations include avoiding caching of sensitive data in shared caches and respecting privacy requirements.

HTTP caching interacts with modern protocols (HTTP/1.1 and beyond) and content delivery networks, enabling scalable performance while requiring careful configuration to maintain freshness and correctness.