basic support for TCP fast open

src/libraries/Common/src/Interop/Unix/System.Native/Interop.Connect.cs

@@ -10,5 +10,8 @@ internal static partial class Sys
     {
         [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_Connect")]
         internal static unsafe partial Error Connect(SafeHandle socket, byte* socketAddress, int socketAddressLen);
+
+        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_Connectx")]
+        internal static unsafe partial Error Connectx(SafeHandle socket, byte* socketAddress, int socketAddressLen, Span<byte> buffer, int bufferLen, int enableTfo, int* sent);
     }
 }

src/libraries/System.Net.Sockets/ref/System.Net.Sockets.cs

@@ -568,6 +568,7 @@ public enum SocketOptionName
         DropMembership = 13,
         DontFragment = 14,
         AddSourceMembership = 15,
+        FastOpen = 15,
         DontRoute = 16,
         DropSourceMembership = 16,
         TcpKeepAliveRetryCount = 16,

src/libraries/System.Net.Sockets/src/System.Net.Sockets.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent)-windows;$(NetCoreAppCurrent)-unix;$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent)-windows;$(NetCoreAppCurrent)-unix;$(NetCoreAppCurrent)-osx;$(NetCoreAppCurrent)-ios;$(NetCoreAppCurrent)-tvos;$(NetCoreAppCurrent)</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <!-- SYSTEM_NET_SOCKETS_DLL is required to allow source-level code sharing for types defined within the
          System.Net.Internals namespace. -->
@@ -13,6 +13,8 @@
   <PropertyGroup>
     <TargetPlatformIdentifier>$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)'))</TargetPlatformIdentifier>
     <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetPlatformIdentifier)' == ''">SR.SystemNetSockets_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
+    <IsApplePlatform Condition="'$(TargetPlatformIdentifier)' == 'osx' or '$(TargetPlatformIdentifier)' == 'ios' or '$(TargetPlatformIdentifier)' == 'tvos'">true</IsApplePlatform>
+    <DefineConstants Condition="'$(IsApplePlatform)' == 'true'">$(DefineConstants);SYSTEM_NET_SOCKETS_APPLE_PLATFROM</DefineConstants>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' != ''">
@@ -181,7 +183,7 @@
              Link="Common\System\Net\CompletionPortHelper.Windows.cs" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'unix'">
+  <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'unix' or '$(TargetPlatformIdentifier)' == 'osx' or '$(TargetPlatformIdentifier)' == 'ios' or '$(TargetPlatformIdentifier)' == 'tvos'">
     <Compile Include="System\Net\Sockets\SafeSocketHandle.Unix.cs" />
     <Compile Include="System\Net\Sockets\Socket.Unix.cs" />
     <Compile Include="System\Net\Sockets\SocketAsyncContext.Unix.cs" />
@@ -301,7 +303,7 @@
     <Reference Include="System.Threading.ThreadPool" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'unix'">
+  <ItemGroup Condition="'$(TargetPlatformIdentifier)' != 'windows'">
     <Reference Include="System.Threading.Thread" />
   </ItemGroup>
 

src/libraries/System.Net.Sockets/src/System/Net/Sockets/SafeSocketHandle.Unix.cs

@@ -23,7 +23,9 @@ public partial class SafeSocketHandle
         internal bool ExposedHandleOrUntrackedConfiguration { get; private set; }
         internal bool PreferInlineCompletions { get; set; } = SocketAsyncEngine.InlineSocketCompletionsEnabled;
         internal bool IsSocket { get; set; } = true; // (ab)use Socket class for performing async I/O on non-socket fds.
-
+#if SYSTEM_NET_SOCKETS_APPLE_PLATFROM
+        internal bool TfoEnabled { get; set; }
+#endif
         internal void RegisterConnectResult(SocketError error)
         {
             switch (error)
@@ -44,6 +46,9 @@ internal void TransferTrackedState(SafeSocketHandle target)
             target.DualMode = DualMode;
             target.ExposedHandleOrUntrackedConfiguration = ExposedHandleOrUntrackedConfiguration;
             target.IsSocket = IsSocket;
+#if SYSTEM_NET_SOCKETS_APPLE_PLATFROM
+            target.TfoEnabled = TfoEnabled;
+#endif
         }
 
         internal void SetExposed() => ExposedHandleOrUntrackedConfiguration = true;

src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncContext.Unix.cs

@@ -362,7 +362,7 @@ public override unsafe void InvokeCallback(bool allowPooling) =>
                 Callback!(BytesTransferred, SocketAddress, SocketFlags.None, ErrorCode);
         }
 
-        private sealed class BufferMemorySendOperation : SendOperation
+        private class BufferMemorySendOperation : SendOperation
         {
             public Memory<byte> Buffer;
 
@@ -648,21 +648,47 @@ public override void InvokeCallback(bool allowPooling)
             }
         }
 
-        private sealed class ConnectOperation : WriteOperation
+        private sealed class ConnectOperation : BufferMemorySendOperation
         {
             public ConnectOperation(SocketAsyncContext context) : base(context) { }
 
-            public Action<SocketError>? Callback { get; set; }
-
             protected override bool DoTryComplete(SocketAsyncContext context)
             {
                 bool result = SocketPal.TryCompleteConnect(context._socket, out ErrorCode);
                 context._socket.RegisterConnectResult(ErrorCode);
+
+                if (result && ErrorCode == SocketError.Success &&  Buffer.Length > 0)
+                {
+                    SocketError error = context.SendToAsync(Buffer, 0, Buffer.Length, SocketFlags.None, Memory<byte>.Empty, ref BytesTransferred, Callback!, default);
+                    if (error != SocketError.Success && error != SocketError.IOPending)
+                    {
+                        context._socket.RegisterConnectResult(ErrorCode);
+                    }
+                }
                 return result;
             }
 
-            public override void InvokeCallback(bool allowPooling) =>
-                Callback!(ErrorCode);
+            public override unsafe void InvokeCallback(bool allowPooling)
+            {
+                var cb = Callback!;
+                int bt = BytesTransferred;
+                Memory<byte> sa = SocketAddress;
+                SocketError ec = ErrorCode;
+                Memory<byte> buffer = Buffer;
+
+                if (allowPooling)
+                {
+                    AssociatedContext.ReturnOperation(this);
+                }
+
+                if (buffer.Length == 0)
+                {
+                    // Invoke callback only when we are completely done.
+                    // In case data were provided for Connect we may or may not send them all.
+                    // If we did not we will need follow-up with Send operation
+                    cb(bt, sa, SocketFlags.None, ec);
+                }
+            }
         }
 
         private sealed class SendFileOperation : WriteOperation
@@ -1478,7 +1504,6 @@ public SocketError AcceptAsync(Memory<byte> socketAddress, out int socketAddress
         public SocketError Connect(Memory<byte> socketAddress)
         {
             Debug.Assert(socketAddress.Length > 0, $"Unexpected socketAddressLen: {socketAddress.Length}");
-
             // Connect is different than the usual "readiness" pattern of other operations.
             // We need to call TryStartConnect to initiate the connect with the OS,
             // before we try to complete it via epoll notification.
@@ -1503,7 +1528,7 @@ public SocketError Connect(Memory<byte> socketAddress)
             return operation.ErrorCode;
         }
 
-        public SocketError ConnectAsync(Memory<byte> socketAddress, Action<SocketError> callback)
+        public SocketError ConnectAsync(Memory<byte> socketAddress, Action<int, Memory<byte>, SocketFlags, SocketError> callback, Memory<byte> buffer, out int sentBytes)
         {
             Debug.Assert(socketAddress.Length > 0, $"Unexpected socketAddressLen: {socketAddress.Length}");
             Debug.Assert(callback != null, "Expected non-null callback");
@@ -1516,20 +1541,37 @@ public SocketError ConnectAsync(Memory<byte> socketAddress, Action<SocketError>
             SocketError errorCode;
             int observedSequenceNumber;
             _sendQueue.IsReady(this, out observedSequenceNumber);
-            if (SocketPal.TryStartConnect(_socket, socketAddress, out errorCode))
+#if SYSTEM_NET_SOCKETS_APPLE_PLATFROM
+            if (SocketPal.TryStartConnect(_socket, socketAddress, out errorCode, buffer.Span, _socket.TfoEnabled, out sentBytes))
+#else
+            if (SocketPal.TryStartConnect(_socket, socketAddress, out errorCode, buffer.Span, false, out sentBytes)) // In Linux, we can figure it out as needed inside PAL.
+#endif
             {
                 _socket.RegisterConnectResult(errorCode);
+
+                int remains = buffer.Length - sentBytes;
+
+                if (errorCode == SocketError.Success && remains > 0)
+                {
+                    errorCode = SendToAsync(buffer.Slice(sentBytes), 0, remains, SocketFlags.None, Memory<byte>.Empty, ref sentBytes, callback!, default);
+                }
                 return errorCode;
             }
 
             var operation = new ConnectOperation(this)
             {
                 Callback = callback,
                 SocketAddress = socketAddress,
+                Buffer = buffer.Slice(sentBytes),
+                BytesTransferred = sentBytes,
             };
 
             if (!_sendQueue.StartAsyncOperation(this, operation, observedSequenceNumber))
             {
+                if (operation.ErrorCode == SocketError.Success)
+                {
+                    sentBytes += operation.BytesTransferred;
+                }
                 return operation.ErrorCode;
             }
 
@@ -1880,7 +1922,8 @@ public SocketError Send(byte[] buffer, int offset, int count, SocketFlags flags,
 
         public SocketError SendAsync(Memory<byte> buffer, int offset, int count, SocketFlags flags, out int bytesSent, Action<int, Memory<byte>, SocketFlags, SocketError> callback, CancellationToken cancellationToken)
         {
-            return SendToAsync(buffer, offset, count, flags, Memory<byte>.Empty, out bytesSent, callback, cancellationToken);
+            bytesSent = 0;
+            return SendToAsync(buffer, offset, count, flags, Memory<byte>.Empty, ref bytesSent, callback, cancellationToken);
         }
 
         public SocketError SendTo(byte[] buffer, int offset, int count, SocketFlags flags, Memory<byte> socketAddress, int timeout, out int bytesSent)
@@ -1947,11 +1990,10 @@ public unsafe SocketError SendTo(ReadOnlySpan<byte> buffer, SocketFlags flags, M
             }
         }
 
-        public SocketError SendToAsync(Memory<byte> buffer, int offset, int count, SocketFlags flags, Memory<byte> socketAddress, out int bytesSent, Action<int, Memory<byte>, SocketFlags, SocketError> callback, CancellationToken cancellationToken = default)
+        public SocketError SendToAsync(Memory<byte> buffer, int offset, int count, SocketFlags flags, Memory<byte> socketAddress, ref int bytesSent, Action<int, Memory<byte>, SocketFlags, SocketError> callback, CancellationToken cancellationToken = default)
         {
             SetHandleNonBlocking();
 
-            bytesSent = 0;
             SocketError errorCode;
             int observedSequenceNumber;
             if (_sendQueue.IsReady(this, out observedSequenceNumber) &&

src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketAsyncEventArgs.Unix.cs

@@ -67,17 +67,24 @@ internal unsafe SocketError DoOperationAccept(Socket _ /*socket*/, SafeSocketHan
             return socketError;
         }
 
-        private void ConnectCompletionCallback(SocketError socketError)
+        private void ConnectCompletionCallback(int bytesTransferred, Memory<byte> socketAddress, SocketFlags receivedFlags, SocketError socketError)
         {
-            CompletionCallback(0, SocketFlags.None, socketError);
+            CompletionCallback(bytesTransferred, SocketFlags.None, socketError);
         }
 
         internal unsafe SocketError DoOperationConnectEx(Socket _ /*socket*/, SafeSocketHandle handle)
-            => DoOperationConnect(handle);
+        {
+            SocketError socketError = handle.AsyncContext.ConnectAsync(_socketAddress!.Buffer, ConnectCompletionCallback, _buffer.Slice(_offset, _count), out int sentBytes);
+            if (socketError != SocketError.IOPending)
+            {
+                FinishOperationSync(socketError, sentBytes, SocketFlags.None);
+            }
+            return socketError;
+        }
 
         internal unsafe SocketError DoOperationConnect(SafeSocketHandle handle)
         {
-            SocketError socketError = handle.AsyncContext.ConnectAsync(_socketAddress!.Buffer, ConnectCompletionCallback);
+            SocketError socketError = handle.AsyncContext.ConnectAsync(_socketAddress!.Buffer, ConnectCompletionCallback, Memory<byte>.Empty, out int _);
             if (socketError != SocketError.IOPending)
             {
                 FinishOperationSync(socketError, 0, SocketFlags.None);
@@ -299,11 +306,11 @@ internal SocketError DoOperationSendTo(SafeSocketHandle handle, CancellationToke
             _receivedFlags = System.Net.Sockets.SocketFlags.None;
             _socketAddressSize = 0;
 
-            int bytesSent;
+            int bytesSent = 0;
             SocketError errorCode;
             if (_bufferList == null)
             {
-                errorCode = handle.AsyncContext.SendToAsync(_buffer, _offset, _count, _socketFlags, _socketAddress!.Buffer, out bytesSent, TransferCompletionCallback, cancellationToken);
+                errorCode = handle.AsyncContext.SendToAsync(_buffer, _offset, _count, _socketFlags, _socketAddress!.Buffer, ref bytesSent, TransferCompletionCallback, cancellationToken);
             }
             else
             {

src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketOptionName.cs

@@ -132,12 +132,34 @@ public enum SocketOptionName
         #endregion
 
         #region SocketOptionLevel.Tcp
-        // Disables the Nagle algorithm for send coalescing.
+        /// <summary>
+        /// Disables the Nagle algorithm for send coalescing.
+        /// </summary>
         NoDelay = 1,
+        /// <summary>
+        /// Use urgent data as defined in RFC-1222. This option can be set only once; after it is set, it cannot be turned off.
+        /// </summary>
         BsdUrgent = 2,
+        /// <summary>
+        /// Use expedited data as defined in RFC-1222. This option can be set only once; after it is set, it cannot be turned off.
+        /// </summary>
         Expedited = 2,
+        /// <summary>
+        /// This enables TCP Fast Open as defined in RFC-7413. The actual observed behavior depend on OS configuration and state of kernel TCP cookie cache.
+        /// Enabling TFO can impact interoperability and casue connectivity issues.
+        /// </summary>
+        FastOpen = 15,
+        /// <summary>
+        /// The number of TCP keep alive probes that will be sent before the connection is terminated.
+        /// </summary>
         TcpKeepAliveRetryCount = 16,
+        /// <summary>
+        /// The number of seconds a TCP connection will remain alive/idle before keepalive probes are sent to the remote.
+        /// </summary>
         TcpKeepAliveTime = 3,
+        /// <summary>
+        /// The number of seconds a TCP connection will wait for a keepalive response before sending another keepalive probe.
+        /// </summary>
         TcpKeepAliveInterval = 17,
         #endregion
 

src/libraries/System.Net.Sockets/src/System/Net/Sockets/SocketPal.Unix.cs

@@ -647,9 +647,12 @@ public static unsafe bool TryCompleteAccept(SafeSocketHandle socket, Memory<byte
             return false;
         }
 
-        public static unsafe bool TryStartConnect(SafeSocketHandle socket, Memory<byte> socketAddress, out SocketError errorCode)
+        public static unsafe bool TryStartConnect(SafeSocketHandle socket, Memory<byte> socketAddress, out SocketError errorCode) => TryStartConnect(socket, socketAddress, out errorCode, Span<byte>.Empty, false, out int _ );
+
+        public static unsafe bool TryStartConnect(SafeSocketHandle socket, Memory<byte> socketAddress, out SocketError errorCode, Span<byte> data, bool tfo, out int sent)
         {
             Debug.Assert(socketAddress.Length > 0, $"Unexpected socketAddressLen: {socketAddress.Length}");
+            sent = 0;
 
             if (socket.IsDisconnected)
             {
@@ -660,7 +663,16 @@ public static unsafe bool TryStartConnect(SafeSocketHandle socket, Memory<byte>
             Interop.Error err;
             fixed (byte* rawSocketAddress = socketAddress.Span)
             {
-                err = Interop.Sys.Connect(socket, rawSocketAddress, socketAddress.Length);
+                if (data.Length > 0)
+                {
+                    int sentBytes = 0;
+                    err = Interop.Sys.Connectx(socket, rawSocketAddress, socketAddress.Length, data, data.Length, tfo ? 1 : 0, &sentBytes);
+                    sent = sentBytes;
+                }
+                else
+                {
+                    err = Interop.Sys.Connect(socket, rawSocketAddress, socketAddress.Length);
+                }
             }
 
             if (err == Interop.Error.SUCCESS)
@@ -1451,6 +1463,18 @@ public static unsafe SocketError SetSockOpt(SafeSocketHandle handle, SocketOptio
                 }
             }
 
+#if SYSTEM_NET_SOCKETS_APPLE_PLATFROM
+            // macOS fails to even query it if socket is not actively listening.
+            // To provide consistent platform experience we will track if
+            // it was ret and we will use it later as needed.
+            if (optionLevel == SocketOptionLevel.Tcp && optionName == SocketOptionName.FastOpen)
+            {
+                handle.TfoEnabled = optionValue != 0;
+                // Silently ignore errors - TFO is best effort and it may be disabled by configuration or not
+                // supported by OS.
+                err = Interop.Error.SUCCESS;
+            }
+#endif
             return GetErrorAndTrackSetting(handle, optionLevel, optionName, err);
         }
 
@@ -1580,6 +1604,17 @@ public static unsafe SocketError GetSockOpt(SafeSocketHandle handle, SocketOptio
             int optLen = sizeof(int);
             Interop.Error err = Interop.Sys.GetSockOpt(handle, optionLevel, optionName, (byte*)&value, &optLen);
 
+#if SYSTEM_NET_SOCKETS_APPLE_PLATFROM
+            // macOS fails to even query it if socket is not actively listening.
+            // To provide consistent platform experience we will track if
+            // it was set and we will use it later as needed.
+            if (optionLevel == SocketOptionLevel.Tcp && optionName == SocketOptionName.FastOpen && err != Interop.Error.SUCCESS)
+            {
+                value = handle.TfoEnabled ? 1 : 0;
+                err = Interop.Error.SUCCESS;
+            }
+#endif
+
             optionValue = value;
             return err == Interop.Error.SUCCESS ? SocketError.Success : GetSocketErrorForErrorCode(err);
         }

src/libraries/System.Net.Sockets/tests/FunctionalTests/Connect.cs

@@ -266,7 +266,6 @@ public sealed class ConnectEap : Connect<SocketHelperEap>
         public ConnectEap(ITestOutputHelper output) : base(output) {}
 
         [Theory]
-        [PlatformSpecific(TestPlatforms.Windows)]
         [InlineData(true)]
         [InlineData(false)]
         public async Task ConnectAsync_WithData_DataReceived(bool useArrayApi)