driodev driodev - 3 months ago 9
HTTP Question

What is difference between max-age and max-stale in cache control mechanism

I know this is a simple question, and I am sure that no body will mark this as duplicate question, because I have searched all over the SO. so my question is what is the difference between max-age and max-stale in Cache control mechanism of Http, I've read it in here, but I felt its little complex, so if anybody can explain about this ? it would be great help

Joe Joe
Answer

From RFC 7234:

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.

...

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.

That is, max-age is the oldest that a response can be, as long as the Cache-Control from the origin server indicates that it is still fresh. max-stale indicates that, even if the response is known to be stale, you will also accept it as long as it's only stale by that number of seconds.

As per Serving Stale Responses:

A cache SHOULD generate a Warning header field with the 110 warn-code (see Section 5.5.1) in stale responses.

So, if you specified max-stale and received a no-longer-fresh response, the Warning header would let you know.