Added init to allow usage of pre-made URLSession instance

NetworkOperation.swift

@@ -10,28 +10,62 @@ import Foundation
 
 /// Subclass of [AsyncOperation](https://github.com/radianttap/Swift-Essentials/blob/master/Operation/AsyncOperation.swift)
 ///	that handles all aspects of direct data download over network.
-///	It uses QoS.utility by default.
 ///
 ///	It will automatically handle Auth challenges, using URLSession.serverTrustPolicy. Returns `userCancelledAuthentication` error if that fails.
 ///
 ///	In the simplest case, you can supply just URLRequest and a `Callback` which accepts `NetworkPayload` instance.
 ///
-///	Or you can also supply custom URLSessionConfiguration just for this request.
+///	Or you can also supply custom URLSessionConfiguration just for this request. Or URLSession instance if you have it somewhere else.
 final class NetworkOperation: AsyncOperation {
 	typealias Callback = (NetworkPayload) -> Void
 
 	/// Set network start timestamp, creates URLSessionDataTask and starts it (resume)
 	override func workItem() {
 		payload.start()
 
-		task = localURLSession.dataTask(with: payload.urlRequest)
+		if localURLSession == nil {
+			if self.isUsingURLSessionDelegate {
+				localURLSession = URLSession(configuration: self.urlSessionConfiguration,
+				                  delegate: self,
+				                  delegateQueue: nil)
+			} else {
+				localURLSession = URLSession(configuration: self.urlSessionConfiguration)
+			}
+		}
+
+		if isUsingURLSessionDelegate {
+			task = localURLSession.dataTask(with: payload.urlRequest)
+
+		} else {
+			task = localURLSession.dataTask(with: payload.urlRequest, completionHandler: {
+				[weak self] data, response, error in
+				guard let `self` = self else { return }
+
+				self.payload.response = response as? HTTPURLResponse
+				if let e = error {
+					self.payload.error = .urlError(e as? URLError)
+				} else {
+					self.payload.data = data
+				}
+
+				self.finish()
+			})
+		}
+
+		taskMetrics[.tsStart] = Date()
 		task?.resume()
 	}
 
 	fileprivate func finish() {
+		if isUsingURLSessionDelegate {
+			localURLSession.invalidateAndCancel()
+		}
+		taskMetrics[.tsEnd] = Date()
+
 		payload.end()
 		markFinished()
 
+//		log(level: .debug, "Metrics:\n\( NetworkTaskMetric.printout(taskMetrics) )")
 		callback(payload)
 	}
 
@@ -49,43 +83,52 @@ final class NetworkOperation: AsyncOperation {
 	}
 
 
-	/// Designated initializer
+	/// Designated initializer, allows to create one URLSession per Operation. Can be used with URLSessionDelegate or with completion handler.
 	///
 	/// - Parameters:
-	///   - request: `URLRequest` value to execute
+	///   - urlRequest: `URLRequest` value to execute
 	///   - urlSessionConfiguration: `URLSessionConfiguration` for this particular network call. Fallbacks to `default` if not specified
 	///   - callback: A closure to pass the result back
-	init(urlRequest: URLRequest,
-	     urlSessionConfiguration: URLSessionConfiguration = URLSessionConfiguration.default,
-	     callback: @escaping (NetworkPayload) -> Void)
-	{
+	init(urlRequest: URLRequest, urlSessionConfiguration: URLSessionConfiguration = URLSessionConfiguration.default, usesDelegate: Bool = false, callback: @escaping (NetworkPayload) -> Void) {
 		self.payload = NetworkPayload(urlRequest: urlRequest)
 		self.callback = callback
 		self.urlSessionConfiguration = urlSessionConfiguration
+		self.isUsingURLSessionDelegate = usesDelegate
 		super.init()
+	}
 
-		self.qualityOfService = .utility
+	/// Designated initializer, uses supplied URLSession instance. Always uses completionHandler form of URLSessionDataTask
+	///
+	/// - Parameters:
+	///   - urlRequest: `URLRequest` value to execute
+	///   - urlSession: URLSession instance to use for this Operation
+	///   - callback: A closure to pass the result back
+	init(urlRequest: URLRequest, urlSession: URLSession, callback: @escaping (NetworkPayload) -> Void) {
+		self.payload = NetworkPayload(urlRequest: urlRequest)
+		self.callback = callback
+		self.urlSessionConfiguration = urlSession.configuration
+		self.localURLSession = urlSession
+		self.isUsingURLSessionDelegate = false
+		super.init()
 	}
 
 	fileprivate(set) var payload: NetworkPayload
 	private(set) var callback: Callback
+	private(set) var isUsingURLSessionDelegate = false
 
 	fileprivate var incomingData = Data()
 
 	///	Configuration to use for the URLSession that will handle `urlRequest`
 	private(set) var urlSessionConfiguration : URLSessionConfiguration
 
 	///	URLSession is built for each request. Delegate calls are handled internally
-	fileprivate var localURLSession: URLSession {
-		return URLSession(configuration: urlSessionConfiguration,
-		                  delegate: self,
-		                  delegateQueue: nil)
-	}
+	fileprivate var localURLSession: URLSession!
 
 	///	Actual network task, generated by `localURLSession`
 	fileprivate var task: URLSessionDataTask?
 
 	var allowEmptyData: Bool = true
+	fileprivate var taskMetrics: [NetworkTaskMetric: Any] = [:]
 }
 
 
@@ -152,7 +195,9 @@ extension NetworkOperation: URLSessionDataDelegate {
 			payload.error = .urlError(e as? URLError)
 		} else {
 			if incomingData.isEmpty {
-				payload.error = .noData
+				if !allowEmptyData {
+					payload.error = .noData
+				}
 			} else {
 				payload.data = incomingData
 			}