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The client doesn't need to know how the fingerprint is generated; it only needs to send it to the server on the next request.
If the fingerprint is still the same, then the resource hasn't changed and you can skip the download.
The good news is that every browser ships with an implementation of an HTTP cache.
If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins.
Once an URL is cached by a gateway cache, the cache will not ask the application for that content anymore.
For example, in the above exchange, the server returns a 1024-byte response, instructs the client to cache it for up to 120 seconds, and provides a validation token ("x234dff") that can be used after the response has expired to check if the resource has been modified.
Assume that 120 seconds have passed since the initial fetch and the browser has initiated a new request for the same resource.