How to respect cache-control response headers?

[buscarini]

From what I'm seeing, it seems that Kingfisher just ignores the response cache-control headers, which is weird. How can I respect the max-age field so that some images refresh more often? It seems that Kingfisher is caching images forever, but some images need to be refreshed quite often.

[aronspringfield]

Kingfisher doesn't support any remote cache control. If you wanted to look at adding it, you can start by looking at this function in SessionDelegate.swift. This is where cache control would be accessible.

func urlSession(_ session: URLSession, 
    dataTask: URLSessionDataTask, 
    didReceive response: URLResponse
) async -> URLSession.ResponseDisposition

The only way to control age in Kingfisher is to use the cache config like so;

Kingfisher.ImageCache.default.memoryStorage.config.expiration = .seconds(180)
Kingfisher.ImageCache.default.diskStorage.config.expiration = .days(10)

[nenadvulic]

My approach, a new option, e.g. .respectCacheControl (off by default), so existing apps are unaffected.
When enabled, Kingfisher parses cache control from the HTTPURLResponse and translates it into the existing expiration model:

• max-age=N => StorageExpiration.seconds(N) for that item's disk store, overriding diskCacheExpiration for this response only.
• no-store => skip caching (memory-only / no persistence).

The mapping is clean because StorageExpiration already has exactly the .seconds(_) case we need.

The one design question I'd like your input on

The response headers are visible in SessionDelegate, but the cache store happens later in KingfisherManager via
options.diskCacheExpiration (ImageCache.swif, KingfisherManager.swift). So a parsed max-age needs to travel from the response to the store call.

Do you have a preferred place to thread it through — e.g. carrying it on the downloader's loading result, or resolving it inside KingfisherManager before the store?

I'd like to agree on the scope and approach with you @onevcat.