Respect cache_until when retrieving embeds

The oEmbed spec defines cache_age as

The suggested cache lifetime for this resource, in seconds. Consumers may choose to use this value or not.

My initial search hasn’t pulled up any details about this being used. It would be helpful if this was stored on the embed model. This could be used in conjunction with last_modified for automatically refreshing stale content.

Since last_modified doesn’t necessarily translate to when the data was fetched, there could ideally be an additional field that captures the fetch time.

This could also be combined into one DateTime field cache_until which would simplify queries and simply be set to the fetch time plus the cache age.

[gasman]

Thanks @thenewguy! I’d be inclined to treat stale embeds in the same way as an embed that has never been fetched at all - if the re-fetch fails then I think it’s reasonable enough to propagate that failure back to the end-user. From a quick look I think that can be done as a two-line change to get_embed - exclude embeds with a cache_until in the past when fetching, and change the get_or_create to an update_or_create so that the stale embed is overwritten on successful fetch.

In the meantime, I’ll go ahead and merge your PR as that all looks good to me.

[gasman]

Fixed in #7279