If-Modified-Since

If-Modified-Since

 

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The If-Modified-Since request header is used to make conditional requests. A client can use the GET method to request a resource from a server, having the response hinge on whether the resource has been modified since the client last requested it.

If the object has not been modified, the server will respond with a 304 Not Modified response, instead of with the resource. If the object has been modified, the server will respond as if it was a non-conditional GET request. Chapter 7discusses conditional requests in detail.

Type

Request header

Basic Syntax

If-Modified-Since: HTTP-date

Example

If-Modified-Since: Thu, 03 Oct 1997 17:15:00 GMT