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Asked: 2026-05-13T15:24:28+00:00

Ok, I’m confused. I’m trying to send back the magic headers from my server

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Ok, I’m confused. I’m trying to send back the magic headers from my server that will prevent a client from hitting the server again until a resource is stale.

I understand how ETag or Last-Modified works (Validation) – the client will ALWAYS still hit the server, and the server needs to validate the date or etag against the current value to know whether to bother serving up a new one.

Cache-Control and Expires, however, I don’t think I understand. I’ve set the following: 

Cache-Control: max-age=86400, must-revalidate

No matter what I do, my client (my browser, curl, NSURLConnection) always hits the server again on the second request. Is this a client thing? What headers should I send back to get the client to use it’s private cache for a certain length of time?

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1 Answer

  1. Editorial Team

    As Nathan hints at in his answer, clients can issue a subsequent request with an If-Modified-Since header to determine whether or not their cache is stale. If the client receives a 304 Not Modified response, it will serve the content out of the local cache.

    According to RFC 2616 (the HTTP 1.1 specification), the presence of must-revalidate within the Cache-control header forces clients to re-check their cache’s status with the originating server prior to serving out of the cache.

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