NSURLSession and cfsocket/cfstream

Question

Hi, QuinnFrom figure 1-1 and 1-2 of the below link:https://developer.apple.com/library/content/documentation/Networking/Conceptual/CFNetwork/Concepts/Concepts.html#//apple_ref/doc/uid/TP30001132-CH4-DontLinkElementID_17Does it mean that the implementation of NSURLSession/NSURLConnection is based on the APIs from CFNetwork and CFNetwork APIs is based on those of CFStream/CFSocket? For example, for code below, CFSocketConnectToAddress or CFSocketCreateConnectedToSocketSignature or some similar function will eventually be called underneath??   NSURLSessionDataTask *imageTask = [session dataTaskWithRequest:request completionHandler:                                  ^(NSData *data, NSURLResponse *response, NSError *error) {                                     ..                                                                    }];    [imageTask resume];Or is it using raw socket and bypassing CFStream/CFSocket?Just want to find out the concrete/exact relations between APIs from differenct network layers but could not google it out..Thanks,Rao

eskimo · Answer

Or is it using raw socket and bypassing CFStream/CFSocket?The answer here is “It depends.”  Way back when NSURLConnection was first introduced the relationship was NSURLConnection &amp;gt; NSStream &amp;gt; CFSocketStream &amp;gt; CFSocket &amp;gt; BSD Sockets.  However, that was just an implementation detail and not something we guaranteed would persist forever.  Over the years there’s been a bunch of changes in this space:We introduced CFURLConnection (a private CFNetwork-style API), that’s NSURLConnection’s entry to CFNetwork.We introduced NSURLSession, with a corresponding CFURLSession.We’ve reshuffled those four subsystems around multiple times, with the goal to unify stuff and implement the legacy mechanisms in terms of the new mechanisms.The user space TCP abstraction — TLS, proxies, and so on — used to be implemented by CFSocketStream but much of that work has been pushed down into libnetwork, a private framework that’s now the primary point of responsibility for that job.  CFNetwork calls that API through its own internal abstraction layer.This stuff is not documented because, as a user of these APIs, you should not care how they work under the covers.  OTOH, understanding these relationships can come in handy when debugging.Share and Enjoy — Quinn “The Eskimo!” Apple Developer Relations, Developer Technical Support, Core OS/Hardware let myEmail &#x3D; "eskimo" + "1" + "@apple.com"

vzrao · Answer

Thank you, Quinn.This is definitely very helpful, especially in debugging as you said.Best regards,Rao

boch · Answer

Hi Quinn,I have a vpn framework that use socket low level network api andI wish to use nsurlsession that use this socket, is there a way to do that ? Thank for you reply

NSURLSession and cfsocket/cfstream

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