Set Expires header when caching responses

[RealOrangeOne]

Browsers are rather smart, but also dumb. This uses the Expires header
alongside cache-control to better prompt the browser to actually
cache.

Unfortunately, firefox still tries to "race" its own cache, in an
attempt to respond to requests faster, so still ends up making a bunch
of requests which could have been cached. Doesn't appear there's any way
around this.

See also #1453 (comment)

[BlackDex]

Looks good indeed. But do we really need an extra crate for this??
Can't this also be done with Chrono maybe?

[RealOrangeOne]

do we really need an extra crate for this

It's already depended on by hyper to do the same thing, but I couldn't see an interface to get to the implementation we need which is exposed through rocket. I agree it's not ideal. I'll take another look and see what I can find.

[RealOrangeOne]

@BlackDex I've written my own implementation, which seems to work as expected. I'm not entirely convinced it's better, as httpdate is already a dependency of hyper, do it doesn't bloat the binary. Unfortunately hyper doesn't expose any of httpdate's functionality, so the only option is to either depend on it ourselves, or write a custom implementation.

[williamdes]

Very nice to not have one more dependency

[dani-garcia]

Thanks, we can keep it this way, if it causes issues we can consider adding that dependency back.