[Foundation] Ensure NSUrlSessionHandler's session is cleaned up on dispose. Fixes #24376.

src/Foundation/NSUrlSessionHandler.cs

@@ -293,6 +293,7 @@ protected override void Dispose (bool disposing)
 
 				inflightRequests.Clear ();
 			}
+			session.InvalidateAndCancel ();
 			base.Dispose (disposing);
 		}
 

tests/monotouch-test/System.Net.Http/NSUrlSessionHandlerTest.cs

@@ -0,0 +1,63 @@
+//
+// NSUrlSessionHandlerTest.cs
+//
+
+using System;
+using System.Net.Http;
+using System.Threading.Tasks;
+using Foundation;
+using NUnit.Framework;
+using Xamarin.Utils;
+
+namespace MonoTests.System.Net.Http {
+	[TestFixture]
+	[Preserve (AllMembers = true)]
+	public class NSUrlSessionHandlerTest {
+
+		// https://github.com/dotnet/macios/issues/24376
+		[Test]
+		public void DisposeAndRecreateBackgroundSessionHandler ()
+		{
+			bool firstRequestSucceeded = false;
+
+			// First request - should succeed
+			var done = TestRuntime.TryRunAsync (TimeSpan.FromSeconds (30), async () => {
+				using (var handler = new NSUrlSessionHandler (NSUrlSessionConfiguration.CreateBackgroundSessionConfiguration ("test-id"))) {
+					using (var client = new HttpClient (handler)) {
+						var response = await client.GetByteArrayAsync (NetworkResources.MicrosoftUrl);
+						Assert.IsNotNull (response, "First request response");
+						Assert.IsTrue (response.Length > 0, "First request response length");
+						firstRequestSucceeded = true;
+					}
+				}
+			}, out var ex);
+
+			if (!done || !firstRequestSucceeded) {
+				TestRuntime.IgnoreInCI ("Transient network failure - ignore in CI");
+				Assert.Inconclusive ("First request failed or timed out - cannot verify the bug.");
+			}
+
+			TestRuntime.IgnoreInCIIfBadNetwork (ex);
+			Assert.IsNull (ex, "First request exception");
+
+			// Second request with new handler using same background session ID - should not timeout
+			done = TestRuntime.TryRunAsync (TimeSpan.FromSeconds (30), async () => {
+				using (var handler = new NSUrlSessionHandler (NSUrlSessionConfiguration.CreateBackgroundSessionConfiguration ("test-id"))) {
+					using (var client = new HttpClient (handler)) {
+						var response = await client.GetByteArrayAsync (NetworkResources.MicrosoftUrl);
+						Assert.IsNotNull (response, "Second request response");
+						Assert.IsTrue (response.Length > 0, "Second request response length");
+					}
+				}
+			}, out ex);
+
+			if (!done) {
+				TestRuntime.IgnoreInCI ("Transient network failure - ignore in CI");
+				Assert.Fail ("Second request timedout - this indicates the bug is present.");
+			}
+
+			TestRuntime.IgnoreInCIIfBadNetwork (ex);
+			Assert.IsNull (ex, "Second request exception");
+		}
+	}
+}