feat(cache): use vary headers to compare cached response with request headers

[IsakT]

In this first commit, the cache handler handles multiple cached entries from the same cache key. It then tries to find which of the entries match the request, if any.

What I can't get my head around is how we are supposed to set the cache. We need both the response and the request at the same time. We need the vary headers and data from the response - the vary headers so that we can compare, the data to cache the response, and the request headers to have something to compare against.

My interpretation of the current functionality is that after we fetch an existing entry from the cache, the onComplete method caches that object again. What is the purpose of caching the same entry again?

[IsakT]

I implemented a CacheStore, with a simple interface so that it could be exchanged for a different cache if needed. Can we move the current implementation of CacheStore out of the cache.js file - maybe to util.js or to its own file? The reason would be so that we can export it and so that it can be tested and/or used elsewhere.

[IsakT]

I tried to make the CacheStore class accessible from the outside using Symbol(), but couldn't get it to work. I exported it explicitly with export which works for now.

[ronag]

What about range queries? Are those implicit vary?

[ronag]

Is like to have max entry size and max entry ttl options

[ronag]

Also more tests wouldn't hurt

[IsakT]

Is like to have max entry size and max entry ttl options

What should happen when the cache gets full? Simply ignore more entries to be stored, or delete an old one when there is a new entry?

Also, what do you mean with 'max entry ttl options'? The maximum amount of ttl a single entry can have?

[IsakT]

What about range queries? Are those implicit vary?

No, technically Range headers are not implicit Vary, because a server could choose to ignore Range headers and send the same response no matter what the Range header is. But if the server deems them as valid of course, you could say they are practically implicit Vary. But then the server also needs to respond with 206 Partial Content and include a Content-Range header.

I will implement the case where the server responds with a 307 Redirect where it's also dependent on the Range header.

[ronag]

Continued in nodejs/undici#3562