NSURLCache

NSURLCache provides a composite in-memory and on-disk caching mechanism for URL requests to your application. As part of Foundation’s URL Loading System, any request loaded through NSURLConnection will be handled by NSURLCache.

→ nshipster.com/nsurlcache/

NSURLCache is the built-in, automatic HTTP(S) cache used by NSURLConnection, NSURLSession (default/ephemeral configs), and WKWebView.

Key points:

• Default cache is tiny (almost no disk space). Always set a proper shared cache at launch (e.g. 20 MB memory + 100 MB disk).
• Caching is controlled by the request’s cachePolicy and the server’s HTTP headers (Cache-Control, ETag, Last-Modified, Expires).
• Server headers win: if none are sent, the response usually isn’t cached.
• HTTPS is cached on disk starting iOS 13 / macOS 10.15.
• You can override caching per response in the delegate methods.
• Do nothing else, the system handles the rest transparently.

Bottom line: two lines at startup give you free, fast, offline-capable networking. Don’t reinvent caching.