Cache and Conditional Request Headers

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Cache-Control: Cache Control
Pragma: Cache Control (Backward Compatibility)
Expires: Cache Expiration Period (Backward Compatibility)

Cache-Control #

Cache Directives

Cache-Control: max-age
- Cache validity period, in seconds
Cache-Control: no-cache
- Data can be cached, but always revalidate with the origin server before use
Cache-Control: no-store
- Contains sensitive data, so it must not be stored (use in memory and delete as quickly as possible)

Pragma #

Cache Control (Backward Compatibility)

Pragma: no-cache
HTTP/1.0 backward compatibility

Expires #

Specify Cache Expiration Date (Backward Compatibility)

expries: Mon, 01 Jan 1990 00:00:00 GMT
Specifies the cache expiration date as an exact date
Used since HTTP 1.0
Now, the more flexible Cache-Control: max-age is recommended
If used with Cache-Control: max-age, Expires is ignored