RFC7234#section-7.1.4 conformance

[aodhol]

The implementation returns nil upon seeing the Vary header but is that what the standard implies? Shouldn't the cache keys be expanded instead?

swift-corelibs-foundation/Sources/FoundationNetworking/URLSession/HTTP/HTTPURLProtocol.swift

Lines 215 to 226 in 36a411b

	// Vary: https://tools.ietf.org/html/rfc7231#section-7.1.4
	/* "1. To inform cache recipients that they MUST NOT use this response
	to satisfy a later request unless the later request has the same
	values for the listed fields as the original request (Section 4.1
	of [RFC7234]). In other words, Vary expands the cache key
	required to match a new request to the stored cache entry."
	If we do not store this response, we will never use it to satisfy a later request, including a later request for which it would be incorrect.
	*/
	if httpResponse.allHeaderFields["Vary"] != nil {
	return false
	}

A use case here might be Vary: Accept-Language to allow responses for different languages to be cached separately so if a user changes languages in a mobile-App for example, a response in the wrong language wouldn't be returned to them / the right response would be returned to them if it had been cached for the cache keys derived from the header...