Implement TCP Keep-Alive for WinHttpHandler

src/libraries/Common/src/Interop/Windows/WinHttp/Interop.winhttp_types.cs

@@ -164,6 +164,8 @@ internal partial class WinHttp
         public const uint WINHTTP_OPTION_WEB_SOCKET_RECEIVE_BUFFER_SIZE = 122;
         public const uint WINHTTP_OPTION_WEB_SOCKET_SEND_BUFFER_SIZE = 123;
 
+        public const uint WINHTTP_OPTION_TCP_KEEPALIVE = 152;
+
         public enum WINHTTP_WEB_SOCKET_BUFFER_TYPE
         {
             WINHTTP_WEB_SOCKET_BINARY_MESSAGE_BUFFER_TYPE = 0,
@@ -276,6 +278,15 @@ public struct WINHTTP_ASYNC_RESULT
             public uint dwError;
         }
 
+
+        [StructLayout(LayoutKind.Sequential)]
+        public struct tcp_keepalive
+        {
+            public uint onoff;
+            public uint keepalivetime;
+            public uint keepaliveinterval;
+        }
+
         public const uint API_RECEIVE_RESPONSE = 1;
         public const uint API_QUERY_DATA_AVAILABLE = 2;
         public const uint API_READ_DATA = 3;

src/libraries/System.Net.Http.WinHttpHandler/ref/System.Net.Http.WinHttpHandler.cs

@@ -44,6 +44,9 @@ public partial class WinHttpHandler : System.Net.Http.HttpMessageHandler
         public System.Func<System.Net.Http.HttpRequestMessage, System.Security.Cryptography.X509Certificates.X509Certificate2, System.Security.Cryptography.X509Certificates.X509Chain, System.Net.Security.SslPolicyErrors, bool>? ServerCertificateValidationCallback { get { throw null; } set { } }
         public System.Net.ICredentials? ServerCredentials { get { throw null; } set { } }
         public System.Security.Authentication.SslProtocols SslProtocols { get { throw null; } set { } }
+        public bool TcpKeepAliveEnabled { get { throw null; } set { } }
+        public System.TimeSpan TcpKeepAliveTime { get { throw null; } set { } }
+        public System.TimeSpan TcpKeepAliveInterval { get { throw null; } set { } }
         public System.Net.Http.WindowsProxyUsePolicy WindowsProxyUsePolicy { get { throw null; } set { } }
         protected override void Dispose(bool disposing) { }
         protected override System.Threading.Tasks.Task<System.Net.Http.HttpResponseMessage> SendAsync(System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) { throw null; }

src/libraries/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpHandler.cs

@@ -76,6 +76,13 @@ public class WinHttpHandler : HttpMessageHandler
         private TimeSpan _sendTimeout = TimeSpan.FromSeconds(30);
         private TimeSpan _receiveHeadersTimeout = TimeSpan.FromSeconds(30);
         private TimeSpan _receiveDataTimeout = TimeSpan.FromSeconds(30);
+
+        // Using OS defaults for "Keep-alive timeout" and "keep-alive interval"
+        // as documented in https://docs.microsoft.com/en-us/windows/win32/winsock/sio-keepalive-vals#remarks
+        private TimeSpan _tcpKeepAliveTime = TimeSpan.FromHours(2);
+        private TimeSpan _tcpKeepAliveInterval = TimeSpan.FromSeconds(1);
+        private bool _tcpKeepAliveEnabled;
+
         private int _maxResponseHeadersLength = HttpHandlerDefaults.DefaultMaxResponseHeadersLength;
         private int _maxResponseDrainSize = 64 * 1024;
         private IDictionary<string, object> _properties; // Only create dictionary when required.
@@ -188,6 +195,7 @@ public SslProtocols SslProtocols
             }
         }
 
+
         public Func<
             HttpRequestMessage,
             X509Certificate2,
@@ -369,16 +377,13 @@ public TimeSpan SendTimeout
 
             set
             {
-                if (value != Timeout.InfiniteTimeSpan && (value <= TimeSpan.Zero || value > s_maxTimeout))
-                {
-                    throw new ArgumentOutOfRangeException(nameof(value));
-                }
-
+                CheckTimeSpanPropertyValue(value);
                 CheckDisposedOrStarted();
                 _sendTimeout = value;
             }
         }
 
+
         public TimeSpan ReceiveHeadersTimeout
         {
             get
@@ -388,11 +393,7 @@ public TimeSpan ReceiveHeadersTimeout
 
             set
             {
-                if (value != Timeout.InfiniteTimeSpan && (value <= TimeSpan.Zero || value > s_maxTimeout))
-                {
-                    throw new ArgumentOutOfRangeException(nameof(value));
-                }
-
+                CheckTimeSpanPropertyValue(value);
                 CheckDisposedOrStarted();
                 _receiveHeadersTimeout = value;
             }
@@ -407,16 +408,74 @@ public TimeSpan ReceiveDataTimeout
 
             set
             {
-                if (value != Timeout.InfiniteTimeSpan && (value <= TimeSpan.Zero || value > s_maxTimeout))
-                {
-                    throw new ArgumentOutOfRangeException(nameof(value));
-                }
-
+                CheckTimeSpanPropertyValue(value);
                 CheckDisposedOrStarted();
                 _receiveDataTimeout = value;
             }
         }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether TCP keep-alive is enabled.
+        /// </summary>
+        /// <remarks>
+        /// If enabled, the values of <see cref="TcpKeepAliveInterval" /> and <see cref="TcpKeepAliveTime"/> will be forwarded
+        /// to set WINHTTP_OPTION_TCP_KEEPALIVE, enabling and configuring TCP keep-alive for the backing TCP socket.
+        /// </remarks>
+        public bool TcpKeepAliveEnabled
+        {
+            get
+            {
+                return _tcpKeepAliveEnabled;
+            }
+            set
+            {
+                CheckDisposedOrStarted();
+                _tcpKeepAliveEnabled = value;
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets the TCP keep-alive timeout.
+        /// </summary>
+        /// <remarks>
+        /// Has no effect if <see cref="TcpKeepAliveEnabled"/> is <see langword="false" />.
+        /// The default value of this property is 2 hours.
+        /// </remarks>
+        public TimeSpan TcpKeepAliveTime
+        {
+            get
+            {
+                return _tcpKeepAliveTime;
+            }
+            set
+            {
+                CheckTimeSpanPropertyValue(value);
+                CheckDisposedOrStarted();
+                _tcpKeepAliveTime = value;
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets the TCP keep-alive interval.
+        /// </summary>
+        /// <remarks>
+        /// Has no effect if <see cref="TcpKeepAliveEnabled"/> is <see langword="false" />.
+        /// The default value of this property is 1 second.
+        /// </remarks>
+        public TimeSpan TcpKeepAliveInterval
+        {
+            get
+            {
+                return _tcpKeepAliveInterval;
+            }
+            set
+            {
+                CheckTimeSpanPropertyValue(value);
+                CheckDisposedOrStarted();
+                _tcpKeepAliveInterval = value;
+            }
+        }
+
         public int MaxResponseHeadersLength
         {
             get
@@ -936,6 +995,28 @@ private void SetSessionHandleOptions(SafeWinHttpHandle sessionHandle)
             SetSessionHandleTlsOptions(sessionHandle);
             SetSessionHandleTimeoutOptions(sessionHandle);
             SetDisableHttp2StreamQueue(sessionHandle);
+            SetTcpKeepalive(sessionHandle);
+        }
+
+        private unsafe void SetTcpKeepalive(SafeWinHttpHandle sessionHandle)
+        {
+            if (_tcpKeepAliveEnabled)
+            {
+                var tcpKeepalive = new Interop.WinHttp.tcp_keepalive
+                {
+                    onoff = 1,
+
+                    // Timeout.InfiniteTimeSpan will be converted to uint.MaxValue milliseconds (~ 50 days)
+                    keepaliveinterval = (uint)_tcpKeepAliveInterval.TotalMilliseconds,
+                    keepalivetime = (uint)_tcpKeepAliveTime.TotalMilliseconds
+                };
+
+                SetWinHttpOption(
+                    sessionHandle,
+                    Interop.WinHttp.WINHTTP_OPTION_TCP_KEEPALIVE,
+                    (IntPtr)(&tcpKeepalive),
+                    (uint)sizeof(Interop.WinHttp.tcp_keepalive));
+            }
         }
 
         private void SetSessionHandleConnectionOptions(SafeWinHttpHandle sessionHandle)
@@ -1363,6 +1444,14 @@ private void CheckDisposedOrStarted()
             }
         }
 
+        private static void CheckTimeSpanPropertyValue(TimeSpan timeSpan)
+        {
+            if (timeSpan != Timeout.InfiniteTimeSpan && (timeSpan <= TimeSpan.Zero || timeSpan > s_maxTimeout))
+            {
+                throw new ArgumentOutOfRangeException("value");
+            }
+        }
+
         private void SetStatusCallback(
             SafeWinHttpHandle requestHandle,
             Interop.WinHttp.WINHTTP_STATUS_CALLBACK callback)

src/libraries/System.Net.Http.WinHttpHandler/tests/FunctionalTests/WinHttpHandlerTest.cs

@@ -168,7 +168,6 @@ public async Task GetAsync_SetCookieContainerMultipleCookies_CookiesSent()
                 Assert.Equal("POST", responseContent.Method);
                 Assert.Equal(payload, responseContent.BodyContent);
                 Assert.Equal(cookies.ToDictionary(c => c.Name, c => c.Value), responseContent.Cookies);
-
             };
         }
 
@@ -218,6 +217,28 @@ public async Task SendAsync_MultipleHttp2ConnectionsEnabled_CreateAdditionalConn
             }
         }
 
+        [OuterLoop("Uses external service")]
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsWindows10Version2004OrGreater))]
+        public async Task SendAsync_UseTcpKeepAliveOptions()
+        {
+            using var handler = new WinHttpHandler()
+            {
+                TcpKeepAliveEnabled = true,
+                TcpKeepAliveTime = TimeSpan.FromSeconds(1),
+                TcpKeepAliveInterval = TimeSpan.FromMilliseconds(500)
+            };
+
+            using var client = new HttpClient(handler);
+
+            var response = client.GetAsync(System.Net.Test.Common.Configuration.Http.RemoteEchoServer).Result;
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            string responseContent = await response.Content.ReadAsStringAsync();
+            _output.WriteLine(responseContent);
+
+            // Uncomment this to observe an exchange of "TCP Keep-Alive" and "TCP Keep-Alive ACK" packets:
+            // await Task.Delay(5000); 
+        }
+
         private async Task VerifyResponse(Task<HttpResponseMessage> task, string payloadText)
         {
             Assert.True(task.IsCompleted);

src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/APICallHistory.cs

@@ -70,6 +70,8 @@ public static ProxyInfo RequestProxySettings
 
         public static List<IntPtr> WinHttpOptionClientCertContext { get { return winHttpOptionClientCertContextList; } }
 
+        public static (uint OnOff, uint KeepAliveTime, uint KeepAliveInterval)? WinHttpOptionTcpKeepAlive { get; set; }
+
         public static void Reset()
         {
             sessionProxySettings.AccessType = null;
@@ -93,6 +95,7 @@ public static void Reset()
             WinHttpOptionRedirectPolicy = null;
             WinHttpOptionSendTimeout = null;
             WinHttpOptionReceiveTimeout = null;
+            WinHttpOptionTcpKeepAlive = null;
             winHttpOptionClientCertContextList.Clear();
         }
 

src/libraries/System.Net.Http.WinHttpHandler/tests/UnitTests/FakeInterop.cs

@@ -537,7 +537,7 @@ private static bool CopyToBufferOrFailIfInsufficientBufferLength(string value, I
             return true;
         }
 
-        public static bool WinHttpSetOption(
+        public unsafe static bool WinHttpSetOption(
             SafeWinHttpHandle handle,
             uint option,
             IntPtr optionData,
@@ -556,6 +556,11 @@ private static bool CopyToBufferOrFailIfInsufficientBufferLength(string value, I
             {
                 APICallHistory.WinHttpOptionClientCertContext.Add(optionData);
             }
+            else if (option == Interop.WinHttp.WINHTTP_OPTION_TCP_KEEPALIVE)
+            {
+                Interop.WinHttp.tcp_keepalive* ptr = (Interop.WinHttp.tcp_keepalive*)optionData;
+                APICallHistory.WinHttpOptionTcpKeepAlive = (ptr->onoff, ptr->keepalivetime, ptr->keepaliveinterval);
+            }
 
             return true;
         }