Request Cache-Control Directives
This section defines cache directives that can be used by a client in an HTTP request.
5.2.1.1. max-age
Argument: delta-seconds
The "max-age" request directive indicates that the client is unwilling to accept a response whose age is greater than the specified number of seconds. Unless the max-stale request directive is also present, the client is not willing to accept a stale response.
This directive uses the token form of the argument syntax: e.g., 'max-age=5' not 'max-age="5"'. A sender SHOULD NOT generate the quoted-string form.
5.2.1.2. max-stale
Argument: delta-seconds
The "max-stale" request directive indicates that the client is willing to accept a response that has exceeded its freshness lifetime. If max-stale is assigned a value, then the client is willing to accept a response that has exceeded its freshness lifetime by no more than the specified number of seconds. If no value is assigned to max-stale, then the client is willing to accept a stale response of any age.
This directive uses the token form of the argument syntax: e.g., 'max-stale=10' not 'max-stale="10"'. A sender SHOULD NOT generate the quoted-string form.
5.2.1.3. min-fresh
Argument: delta-seconds
The "min-fresh" request directive indicates that the client is willing to accept a response whose freshness lifetime is no less than its current age plus the specified time in seconds. That is, the client wants a response that will still be fresh for at least the specified number of seconds.
This directive uses the token form of the argument syntax: e.g., 'min-fresh=20' not 'min-fresh="20"'. A sender SHOULD NOT generate the quoted-string form.
5.2.1.4. no-cache
The "no-cache" request directive indicates that a cache MUST NOT use a stored response to satisfy the request without successful validation on the origin server.
5.2.1.5. no-store
The "no-store" request directive indicates that a cache MUST NOT store any part of either this request or any response to it. This directive applies to both private and shared caches. "MUST NOT store" in this context means that the cache MUST NOT intentionally store the information in non-volatile storage, and MUST make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it.
This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping.
Note that if a request containing this directive is satisfied from a cache, the no-store request directive does not apply to the already stored response.
5.2.1.6. no-transform
The "no-transform" request directive indicates that an intermediary (whether or not it implements a cache) MUST NOT transform the payload, as defined in Section 5.7.2 of [RFC7230].
5.2.1.7. only-if-cached
The "only-if-cached" request directive indicates that the client only wishes to obtain a stored response. If it receives this directive, a cache SHOULD either respond using a stored response that is consistent with the other constraints of the request, or respond with a 504 (Gateway Timeout) status code. If a group of caches is being operated as a unified system with good internal connectivity, a member cache MAY forward such a request within that group of caches.