HTTP Caching (RFC 9111)

1. Overview of cache operation

   Shared vs private caches and how stored responses are reused.

2. Storing responses

   What a cache may store and the rules for storing responses.

3. Constructing responses from caches

   Selecting a stored response using the Vary header and cache key.

4. Freshness

   Freshness lifetime, heuristic freshness and age calculation.

5. Validation

   Revalidating stale responses with If-None-Match and If-Modified-Since.

6. Invalidation

   Unsafe methods invalidating cached entries.

7. Cache-Control directives

   max-age, no-cache, no-store, private, public, must-revalidate and more.

8. stale-while-revalidate and stale-if-error

   Extension directives for serving stale content.

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