Implementation of URLSessionTask.cancel()

Author: Pushkar Kulkarni

Foundation/NSURLSession/NSURLSessionTask.swift

@@ -202,8 +202,21 @@ open class URLSessionTask : NSObject, NSCopying {
      * cases, the task may signal other work before it acknowledges the
      * cancelation.  -cancel may be sent to a task that has been suspended.
      */
-    open func cancel() { NSUnimplemented() }
-    
+    open func cancel() {
+        workQueue.sync {
+            guard self.state == .running || self.state == .suspended else { return }
+            self.state = .canceling
+            self.workQueue.async {
+                guard let s = self.session as? URLSession else { fatalError() }
+                guard let delegate  = s.delegate as? URLSessionTaskDelegate else { fatalError() }
+                s.delegateQueue.addOperation {
+                    delegate.urlSession(s, task: self, didCompleteWithError: NSError(domain: NSURLErrorDomain, code: NSURLErrorCancelled, userInfo: nil))
+                    self.internalState = .taskCompleted
+                }
+            }
+        }
+    }
+
     /*
      * The current state of the task within the session.
      */

TestFoundation/TestNSURLSession.swift

@@ -29,7 +29,8 @@ class TestURLSession : XCTestCase {
             ("test_downloadTaskWithURLRequest", test_downloadTaskWithURLRequest),
             ("test_downloadTaskWithRequestAndHandler", test_downloadTaskWithRequestAndHandler),
             ("test_downloadTaskWithURLAndHandler", test_downloadTaskWithURLAndHandler),
-            ("test_finishTaskAndInvalidate", test_finishTasksAndInvalidate)
+            ("test_finishTaskAndInvalidate", test_finishTasksAndInvalidate),
+            ("test_cancelTask", test_cancelTask),
         ]
     }
 
@@ -262,6 +263,27 @@ class TestURLSession : XCTestCase {
         session.finishTasksAndInvalidate()
         waitForExpectations(timeout: 12)
     }
+
+    func test_cancelTask() {
+        let serverReady = ServerSemaphore()
+        globalDispatchQueue.async {
+            do {
+                try self.runServer(with: serverReady)
+            } catch {
+                XCTAssertTrue(true)
+                return
+            }
+        }
+        serverReady.wait()
+        let url = URL(string: "http://127.0.0.1:\(serverPort)/Peru")!
+        let d = DataTask(with: expectation(description: "Task to be canceled"))
+        d.dataTaskExpectation.fulfill() //we aren't interested in this expectation
+        d.cancelExpectation = expectation(description: "URLSessionTask wasn't canceled")
+        d.run(with: url)
+        d.cancel()
+        waitForExpectations(timeout: 12)
+    }
+
 }
 
 class SessionDelegate: NSObject, URLSessionDelegate {
@@ -279,6 +301,8 @@ class DataTask : NSObject {
     var capital = "unknown"
     var session: URLSession! = nil
     var task: URLSessionDataTask! = nil
+    var cancelExpectation: XCTestExpectation?
+
     public var error = false
 
     init(with expectation: XCTestExpectation) {
@@ -300,20 +324,24 @@ class DataTask : NSObject {
         task = session.dataTask(with: url)
         task.resume()
     }
+
+    func cancel() {
+        task.cancel()
+    }
 }
 
 extension DataTask : URLSessionDataDelegate {
-     public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
-         capital = String(data: data, encoding: String.Encoding.utf8)!
-         dataTaskExpectation.fulfill()
-     }
+    public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
+        capital = String(data: data, encoding: String.Encoding.utf8)!
+        dataTaskExpectation.fulfill()
+    }
 }
 
 extension DataTask : URLSessionTaskDelegate {
-    public func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: NSError?) {
-         guard let e = error else { return }
-         XCTAssertEqual(e.code, NSURLErrorTimedOut, "Unexpected error code")
-         dataTaskExpectation.fulfill()
+    public func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
+         if let cancellation = cancelExpectation {
+             cancellation.fulfill()
+         }
          self.error = true
      }
 }