Cache

The response can be cached at the client side. In response header, Cache-Control controls the cache.

• max-age: the available duration
• no-store: the reponse can't be cached
• no-cache: before using cache, ask server to check if it can be used.
• must-revalidate: After expiring, ask server to check if it can be used in the future.

When the cache is used

When we click backward.

If we refresh the web, the browser will send the request with Cache-Control: max-age=0. (Ctrl + F5 will add Cache-Control: no-cache.)

Use the cache

1. if-Modified-Since and Last-modified

   The previous response will set Last-modified, a timestamp. The current request will put it in if-Modified-Since. If there is no update, the server will return a 304 Not Modified response.

2. If-None-Match and ETag

   The previous response will set ETag, a unique resource identifier. The current request will put it in If-None-Match. If there is matched, the server will return a 304 Not Modified response.