How to load data BOTH from cache and from network using Alamofire?

Question

I'm trying to use caching to make my iOS app more snappy. What I would like to do for every request is to:

1. return data from cache if present
2. if connected to the internet, load data from API in the background
3. if data from API is different from what was already in the cache, update the cache and return that data again so that the UI can be refreshed

I'm aware that if there is already some data in the cache and I'm connected to the Internet, there could be 2 successive calls to my response code, but that's what I want: the first set of data, potentially out-of-date returned from the cache gives me something right away, and the second set of data makes sure everything is up-to-date.

All the caching approaches I have used so far only let me implement an EITHER/OR approach solely based on cache age. Right now, I'm using AlamofireURLCache5. Is it possible to implement such a cache with Alamofire 5 or do I have to implement it manually?

EDIT: I've been told what I am trying to do is called a Stale-While-Revalidate sort of cache.

Answer 1

Alamofire only supports URLCache and the functionality provided by URLSession. You can implement equivalent patterns above Alamofire, perhaps in a type that keeps the last successful value while updating from the network.

As an aside, you probably don't want your "if connected to internet" condition. Instead you should just request the resource and update if it succeeds.