SR-13028: URLSession does not call willPerformHTTPRedirection

- Check if the session delegate conforms to URLSessionTaskDelegate
  instead of using the task behaviour, as dataTask()s created with
  a completion handler dont have a .callDelegate behaviour. This was
  preventing the delegate method from being called.

Author: spevans

Sources/FoundationNetworking/URLSession/HTTP/HTTPURLProtocol.swift

@@ -460,8 +460,8 @@ internal class _HTTPURLProtocol: _NativeProtocol {
         }
 
         guard let session = task?.session as? URLSession else { fatalError() }
-        switch session.behaviour(for: task!) {
-        case .taskDelegate(let delegate):
+
+        if let delegate = session.delegate as? URLSessionTaskDelegate {
             // At this point we need to change the internal state to note
             // that we're waiting for the delegate to call the completion
             // handler. Then we'll call the delegate callback
@@ -471,7 +471,6 @@ internal class _HTTPURLProtocol: _NativeProtocol {
 
             //TODO: Should the `public response: URLResponse` property be updated
             // before we call delegate API
-
             self.internalState = .waitingForRedirectCompletionHandler(response: response, bodyDataDrain: bodyDataDrain)
             // We need this ugly cast in order to be able to support `URLSessionTask.init()`
             session.delegateQueue.addOperation {
@@ -482,7 +481,7 @@ internal class _HTTPURLProtocol: _NativeProtocol {
                     }
                 }
             }
-        case .noDelegate, .dataCompletionHandler, .downloadCompletionHandler:
+        } else {
             // Follow the redirect. Need to configure new request with cookies, etc.
             let configuredRequest = session._configuration.configure(request: request)
             task?.knownBody = URLSessionTask._Body.none

Tests/Foundation/Tests/TestURLSession.swift

@@ -870,6 +870,32 @@ class TestURLSession: LoopbackServerTest {
         }
     }
 
+    func test_willPerformRedirect() throws {
+        let urlString = "http://127.0.0.1:\(TestURLSession.serverPort)/redirect/1"
+        let url = try XCTUnwrap(URL(string: urlString))
+        let redirectURL = try XCTUnwrap(URL(string: "http://127.0.0.1:\(TestURLSession.serverPort)/jsonBody"))
+        let delegate = SessionDelegate()
+        let session = URLSession(configuration: .default, delegate: delegate, delegateQueue: nil)
+        let expect = expectation(description: "GET \(urlString)")
+
+        let task = session.dataTask(with: url) { (data, response, error) in
+            defer { expect.fulfill() }
+            XCTAssertNil(error)
+            XCTAssertNotNil(data)
+            XCTAssertNotNil(response)
+            XCTAssertEqual(delegate.redirectionRequest?.url, redirectURL)
+
+            let callBacks = [
+                "urlSession(_:task:willPerformHTTPRedirection:newRequest:completionHandler:)",
+            ]
+            XCTAssertEqual(delegate.callbacks.count, callBacks.count)
+            XCTAssertEqual(delegate.callbacks, callBacks)
+        }
+
+        task.resume()
+        waitForExpectations(timeout: 5)
+    }
+
     func test_httpNotFound() throws {
         let urlString = "http://127.0.0.1:\(TestURLSession.serverPort)/404"
         let url = try XCTUnwrap(URL(string: urlString))
@@ -1812,6 +1838,7 @@ class TestURLSession: LoopbackServerTest {
             ("test_httpRedirectionTimeout", test_httpRedirectionTimeout),
             ("test_httpRedirectionChainInheritsTimeoutInterval", test_httpRedirectionChainInheritsTimeoutInterval),
             ("test_httpRedirectionExceededMaxRedirects", test_httpRedirectionExceededMaxRedirects),
+            ("test_willPerformRedirect", test_willPerformRedirect),
             ("test_httpNotFound", test_httpNotFound),
             /* ⚠️ */ ("test_http0_9SimpleResponses", testExpectedToFail(test_http0_9SimpleResponses, "Breaks on Ubunut20.04")),
             ("test_outOfRangeButCorrectlyFormattedHTTPCode", test_outOfRangeButCorrectlyFormattedHTTPCode),