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connection(_:willCacheResponse:)

Sent before the connection stores a cached response in the cache, to give the delegate an opportunity to alter it.

Declaration

optional func connection(_ connection: NSURLConnection, willCacheResponse cachedResponse: CachedURLResponse) -> CachedURLResponse?

Parameters

  • connection:

    The connection sending the message.

  • cachedResponse:

    The proposed cached response to store in the cache.

Return Value

The actual cached response to store in the cache. The delegate may return cachedResponse unmodified, return a modified cached response, or return nil if no cached response should be stored for the connection.

Discussion

This method is called only if the URLProtocol handling the request decides to cache the response. As a rule, responses are cached only when all of the following are true:

  • The request is for an HTTP or HTTPS URL (or your own custom networking protocol that supports caching).

  • The request was successful (with a status code in the 200–299 range).

  • The provided response came from the server, rather than out of the cache.

  • The NSURLRequest object’s cache policy allows caching.

  • The cache-related headers in the server’s response (if present) allow caching.

  • The response size is small enough to reasonably fit within the cache. (For example, if you provide a disk cache, the response must be no larger than about 5% of the disk cache size.)