the cache key will be also determined by the supported vary headers values, when present; this means easier lookups, and one level hash fetch, where the same url-verb request may have multiple entries depending on those headers
checking response vary header will therefore be something done at cache response lookup; writes may override when they shouldn't though, as a full match on supported vary headers will be performed, and one can't know in advance the combo of vary headers, which is why insterested parties will have to be judicious with the new option
response age wasn't being taken into account, and cache invalidation request was always being sent; fresh response will stay in the store until expired; when it expires, cache invalidation will be tried (if possible); if invalidated, the new response is put in the store; Bif validated, the body of the cached response is copied, and the cached response stays in the store
The reference for a request verb is now the string which is used
everywhere else, instead of the symbol corresponding to it. This was an
artifact from the import from httprb, and there is no advantage in it,
since these strings are frozen in most use cases, and the
transformations from symbol to strings being performed everywhere are
prooof that keeping the atom isn't really bringing any benefit.
