Avoid issuing connection attempts for already cancelled requests (#66992)

* Avoid issuing connection attempts for already canceled requests

* Cancelled => Canceled

* Guard SocketsHttpHandler tests under SocketsHttpHandler.IsSupported

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPool.cs

@@ -472,7 +472,7 @@ private void CheckForHttp11ConnectionInjection()
         {
             Debug.Assert(HasSyncObjLock);
 
-            if (!_http11RequestQueue.TryPeekRequest(out HttpRequestMessage? request))
+            if (!_http11RequestQueue.TryPeekUncanceledRequest(this, out HttpRequestMessage? request))
             {
                 return;
             }
@@ -701,7 +701,7 @@ private void CheckForHttp2ConnectionInjection()
         {
             Debug.Assert(HasSyncObjLock);
 
-            if (!_http2RequestQueue.TryPeekRequest(out HttpRequestMessage? request))
+            if (!_http2RequestQueue.TryPeekUncanceledRequest(this, out HttpRequestMessage? request))
             {
                 return;
             }
@@ -2273,12 +2273,23 @@ public bool TryDequeueWaiter([MaybeNullWhen(false)] out TaskCompletionSourceWith
                 return false;
             }
 
-            public bool TryPeekRequest([MaybeNullWhen(false)] out HttpRequestMessage request)
+            public bool TryPeekUncanceledRequest(HttpConnectionPool pool, [MaybeNullWhen(false)] out HttpRequestMessage request)
             {
-                if (_queue is not null && _queue.TryPeek(out QueueItem item))
+                if (_queue is not null)
                 {
-                    request = item.Request;
-                    return true;
+                    while (_queue.TryPeek(out QueueItem item))
+                    {
+                        if (item.Waiter.Task.IsCanceled)
+                        {
+                            if (NetEventSource.Log.IsEnabled()) pool.Trace("Discarding canceled request from queue.");
+                            _queue.Dequeue();
+                        }
+                        else
+                        {
+                            request = item.Request;
+                            return true;
+                        }
+                    }
                 }
 
                 request = null;

src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.Cancellation.cs

@@ -12,6 +12,7 @@
 
 namespace System.Net.Http.Functional.Tests
 {
+    [ConditionalClass(typeof(SocketsHttpHandler), nameof(SocketsHttpHandler.IsSupported))]
     public abstract class SocketsHttpHandler_Cancellation_Test : HttpClientHandler_Cancellation_Test
     {
         protected SocketsHttpHandler_Cancellation_Test(ITestOutputHelper output) : base(output) { }
@@ -196,6 +197,70 @@ public async Task ConnectionFailure_AfterInitialRequestCancelled_SecondRequestSu
             options: new GenericLoopbackOptions() { UseSsl = useSsl });
         }
 
+        [Fact]
+        public async Task RequestsCanceled_NoConnectionAttemptForCanceledRequests()
+        {
+            if (UseVersion == HttpVersion.Version30)
+            {
+                // HTTP3 does not support ConnectCallback
+                return;
+            }
+
+            bool seenRequest1 = false;
+            bool seenRequest2 = false;
+            bool seenRequest3 = false;
+
+            var uri = new Uri("https://example.com");
+            HttpRequestMessage request1 = CreateRequest(HttpMethod.Get, uri, UseVersion, exactVersion: true);
+            HttpRequestMessage request2 = CreateRequest(HttpMethod.Get, uri, UseVersion, exactVersion: true);
+            HttpRequestMessage request3 = CreateRequest(HttpMethod.Get, uri, UseVersion, exactVersion: true);
+
+            TaskCompletionSource connectCallbackEntered = new(TaskCreationOptions.RunContinuationsAsynchronously);
+            TaskCompletionSource connectCallbackGate = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+            using HttpClientHandler handler = CreateHttpClientHandler();
+            handler.MaxConnectionsPerServer = 1;
+            GetUnderlyingSocketsHttpHandler(handler).ConnectCallback = async (context, cancellation) =>
+            {
+                if (context.InitialRequestMessage == request1) seenRequest1 = true;
+                if (context.InitialRequestMessage == request2) seenRequest2 = true;
+                if (context.InitialRequestMessage == request3) seenRequest3 = true;
+
+                connectCallbackEntered.TrySetResult();
+
+                await connectCallbackGate.Task.WaitAsync(TestHelper.PassingTestTimeout);
+
+                throw new Exception("No connection");
+            };
+            using HttpClient client = CreateHttpClient(handler);
+
+            Task request1Task = client.SendAsync(TestAsync, request1);
+            await connectCallbackEntered.Task.WaitAsync(TestHelper.PassingTestTimeout);
+            Assert.True(seenRequest1);
+
+            using var request2Cts = new CancellationTokenSource();
+            Task request2Task = client.SendAsync(TestAsync, request2, request2Cts.Token);
+            Assert.False(seenRequest2);
+
+            Task request3Task = client.SendAsync(TestAsync, request3);
+            Assert.False(seenRequest2);
+            Assert.False(seenRequest3);
+
+            request2Cts.Cancel();
+
+            await Assert.ThrowsAsync<TaskCanceledException>(() => request2Task).WaitAsync(TestHelper.PassingTestTimeout);
+            Assert.False(seenRequest2);
+            Assert.False(seenRequest3);
+
+            connectCallbackGate.SetResult();
+
+            await Assert.ThrowsAsync<HttpRequestException>(() => request1Task).WaitAsync(TestHelper.PassingTestTimeout);
+            await Assert.ThrowsAsync<HttpRequestException>(() => request3Task).WaitAsync(TestHelper.PassingTestTimeout);
+
+            Assert.False(seenRequest2);
+            Assert.True(seenRequest3);
+        }
+
         [OuterLoop("Incurs significant delay")]
         [Fact]
         public async Task Expect100Continue_WaitsExpectedPeriodOfTimeBeforeSendingContent()

src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs

@@ -1044,12 +1044,12 @@ public sealed class SocketsHttpHandlerTest_Cookies_Http11 : HttpClientHandlerTes
         public SocketsHttpHandlerTest_Cookies_Http11(ITestOutputHelper output) : base(output) { }
     }
 
+    [ConditionalClass(typeof(SocketsHttpHandler), nameof(SocketsHttpHandler.IsSupported))]
     public sealed class SocketsHttpHandler_HttpClientHandler_Http11_Cancellation_Test : SocketsHttpHandler_Cancellation_Test
     {
         public SocketsHttpHandler_HttpClientHandler_Http11_Cancellation_Test(ITestOutputHelper output) : base(output) { }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void ConnectTimeout_Default()
         {
             using (var handler = new SocketsHttpHandler())
@@ -1062,7 +1062,6 @@ public void ConnectTimeout_Default()
         [InlineData(0)]
         [InlineData(-2)]
         [InlineData(int.MaxValue + 1L)]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void ConnectTimeout_InvalidValues(long ms)
         {
             using (var handler = new SocketsHttpHandler())
@@ -1076,7 +1075,6 @@ public void ConnectTimeout_InvalidValues(long ms)
         [InlineData(1)]
         [InlineData(int.MaxValue - 1)]
         [InlineData(int.MaxValue)]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void ConnectTimeout_ValidValues_Roundtrip(long ms)
         {
             using (var handler = new SocketsHttpHandler())
@@ -1087,7 +1085,6 @@ public void ConnectTimeout_ValidValues_Roundtrip(long ms)
         }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void ConnectTimeout_SetAfterUse_Throws()
         {
             using (var handler = new SocketsHttpHandler())
@@ -1101,7 +1098,6 @@ public void ConnectTimeout_SetAfterUse_Throws()
         }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void Expect100ContinueTimeout_Default()
         {
             using (var handler = new SocketsHttpHandler())
@@ -1113,7 +1109,6 @@ public void Expect100ContinueTimeout_Default()
         [Theory]
         [InlineData(-2)]
         [InlineData(int.MaxValue + 1L)]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void Expect100ContinueTimeout_InvalidValues(long ms)
         {
             using (var handler = new SocketsHttpHandler())
@@ -1127,7 +1122,6 @@ public void Expect100ContinueTimeout_InvalidValues(long ms)
         [InlineData(1)]
         [InlineData(int.MaxValue - 1)]
         [InlineData(int.MaxValue)]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void Expect100ContinueTimeout_ValidValues_Roundtrip(long ms)
         {
             using (var handler = new SocketsHttpHandler())
@@ -1138,7 +1132,6 @@ public void Expect100ContinueTimeout_ValidValues_Roundtrip(long ms)
         }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Browser, "ConnectTimeout is not supported on Browser")]
         public void Expect100ContinueTimeout_SetAfterUse_Throws()
         {
             using (var handler = new SocketsHttpHandler())