Merge pull request swiftlang#2255 from finestructure/swift-5.0-branch

Don't fail a URLSessionTask on a 401 response

Author: millenomi

Foundation/URLSession/URLSessionTask.swift

@@ -574,11 +574,8 @@ extension _ProtocolClient : URLProtocolClient {
                                                                      sender: `protocol` as! _HTTPURLProtocol)
                 task.previousFailureCount += 1
                 urlProtocol(`protocol`, didReceive: authenticationChallenge)
-            } else {
-                let urlError = URLError(_nsError: NSError(domain: NSURLErrorDomain, code: NSURLErrorUserAuthenticationRequired, userInfo: nil))
-                urlProtocol(`protocol`, didFailWithError: urlError)
+                return
             }
-            return
         }
         switch session.behaviour(for: task) {
         case .taskDelegate(let delegate):

TestFoundation/TestURLSession.swift

@@ -766,9 +766,10 @@ class TestURLSession : LoopbackServerTest {
         let expect = expectation(description: "GET \(urlString): with a completion handler")
         var expectedResult = "unknown"
         let session = URLSession(configuration: URLSessionConfiguration.default)
-        let task = session.dataTask(with: url) { _, _, error in
+        let task = session.dataTask(with: url) { _, response, error in
             defer { expect.fulfill() }
-            XCTAssertNotNil(error)
+            XCTAssertNotNil(response)
+            XCTAssertNil(error)
         }
         task.resume()
         waitForExpectations(timeout: 12, handler: nil)