Fix memory leak of URLSession in SocketEngine #1524
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`SocketEngine` retains an instance of `URLSession`, and this value is replaced in `resetEngine()`. But this instance of `URLSession` is leaked unless you call `invalidateAndCancel()`, which breaks the references between the session and its delegate and callbacks. Note in contrast to other types in Foundation and UIKit, `URLSession` _strongly_ retains its delegate. So the default configuration of `SocketEngine` still has a retain cycle since it sets itself as the delegate of the `URLSession` that it owns. Breaking this retain cycle requires user of the library to provide a custom `URLSessionDelegate` during configuration.
adysart
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SocketEngineretains an instance ofURLSession, and this value is replaced inresetEngine(). But this instance ofURLSessionis leaked unless you callinvalidateAndCancel(), which breaks the references between the session and its delegate and callbacks.Note in contrast to other types in Foundation and UIKit,
URLSessionstrongly retains its delegate. So the default configuration ofSocketEnginestill has a retain cycle since it sets itself as the delegate of theURLSessionthat it owns. Breaking this retain cycle requires user of the library to provide a customURLSessionDelegateduring configuration.