ETag is not implemented properly

[jsardev]

I think that this library has some wrong assumptions on the ETag header. As I see the code, the ETag is being set on the response, but it's never read afterwards (on the request).

The library should look at the If-None-Match header and compare it to the cached response ETag and return 304 Not Modified when they're the same. Now, the library always sends data after the response expired which is a waste.

[Kikobeats]

You're right, without If-None-Match validation then the process is not complete.

My concern right now is, is it worth to?

Why not remove it and just use cache-control?

[jsardev]

@Kikobeats By just using Cache-Control, your server will always send data on the next request after cache expiry. By implementing ETag + If-None-Match, the server will not send any data, just return 304, and the browser will understand that the cache is still valid. This is an improvement i.e. for mobile devices, which should save as much data on the network as possible.

If you don't mind I'd like to propose a PR with this 😄

[Kikobeats]

I'll be a pleasure to accept a PR about this 🙏