CacheControlHeader

CacheControlHeader refers to the HTTP Cache-Control header, a mechanism used to control how and for how long a response may be cached by clients and intermediate caches. It is part of HTTP/1.1 and can appear in both responses and requests, although its primary role is guidance for caches about stored content.

The header conveys caching policies through a list of directives, separated by commas. Common directives include public and private (controlling whether a response may be cached by shared caches or only by an end user’s browser), max-age and s-maxage (defining the freshness lifetime in seconds for private and shared caches respectively), no-cache and no-store (restricting caching or storage), and must-revalidate or proxy-revalidate (requiring revalidation with the origin server). Other directives such as immutable, min-fresh, max-stale, and stale-while-revalidate extend behavior for modern caches and specific scenarios.

Usage examples illustrate typical patterns: Cache-Control: public, max-age=31536000 allows long-lived caching by both browsers and shared caches; Cache-Control: no-store instructs caches not to store the response at all; Cache-Control: no-cache requires revalidation before reuse; Cache-Control: s-maxage=86400, public targets shared caches with a one-day freshness.

Security and performance considerations are important: sensitive data should not be cached, and overly aggressive caching can lead to stale or incorrect content. The header can interact with other mechanisms (ETag, Last-Modified, Vary) to optimize validation and content delivery. In implementation, Cache-Control is set by the server and respected by caches along the delivery path.