Add LocalForward API.

README.md

@@ -70,6 +70,7 @@ class SshClient : IDisposable
 
   Task<SshDataStream> OpenTcpConnectionAsync(string host, int port, CancellationToken cancellationToken = default);
   Task<SshDataStream> OpenUnixConnectionAsync(string path, CancellationToken cancellationToken = default);
+  Task<LocalForward> StartForwardTcpAsync(EndPoint bindEndpoint, string remoteHost, int remotePort, CancellationToken cancellationToken = default);
 
   Task<SftpClient> OpenSftpClientAsync(CancellationToken cancellationToken);
   Task<SftpClient> OpenSftpClientAsync(SftpClientOptions? options = null, CancellationToken cancellationToken = default)
@@ -112,8 +113,15 @@ class RemoteProcess : IDisposable
 }
 class SshDataStream : Stream
 {
+  void WriteEof();
   CancellationToken StreamAborted { get; }
 }
+class LocalForward : IDisposable
+{
+  EndPoint? EndPoint { get; }
+  CancellationToken ForwardStopped { get; }
+  void ThrowIfStopped();
+}
 class SftpClient : IDisposable
 {
   // Note: umask is applied on the server.

src/Tmds.Ssh/ISshChannel.cs

@@ -17,5 +17,7 @@ interface ISshChannel
             CancellationToken cancellationToken = default);
 
     ValueTask WriteAsync(ReadOnlyMemory<byte> data, CancellationToken cancellationToken = default);
+    void WriteEof();
+
     Exception CreateCloseException();
 }

src/Tmds.Ssh/LocalForward.cs

@@ -0,0 +1,273 @@
+// This file is part of Tmds.Ssh which is released under MIT.
+// See file LICENSE for full license details.
+
+using System.Net;
+using System.Net.Sockets;
+using System.Diagnostics;
+using Microsoft.Extensions.Logging;
+
+namespace Tmds.Ssh;
+
+public sealed class LocalForward : IDisposable
+{
+    // Sentinel stop reasons.
+    private static readonly Exception ConnectionClosed = new();
+    private static readonly Exception Disposed = new();
+
+    private readonly SshSession _session;
+    private readonly ILogger<LocalForward> _logger;
+    private readonly CancellationTokenSource _cancel;
+
+    private Func<CancellationToken, Task<SshDataStream>>? _connectToRemote;
+    private Socket? _serverSocket;
+    private EndPoint? _localEndPoint;
+    private CancellationTokenRegistration _ctr;
+    private Exception? _stopReason;
+    private string _remoteEndPoint;
+
+    private bool IsDisposed => ReferenceEquals(_stopReason, Disposed);
+
+    internal LocalForward(SshSession session, ILogger<LocalForward> logger)
+    {
+        _logger = logger;
+        _session = session;
+        _cancel = new();
+
+        _remoteEndPoint = "";
+    }
+
+    internal void StartTcpForward(EndPoint bindEndpoint, string remoteHost, int remotePort)
+    {
+        ArgumentNullException.ThrowIfNull(bindEndpoint);
+        ArgumentException.ThrowIfNullOrEmpty(remoteHost);
+        if (remotePort < 0 || remotePort > 0xffff)
+        {
+            throw new ArgumentException(nameof(remotePort));
+        }
+        if (bindEndpoint is not IPEndPoint)
+        {
+            throw new ArgumentException($"Unsupported EndPoint type: {bindEndpoint.GetType().FullName}.");
+        }
+
+        _remoteEndPoint = $"{remoteHost}:{remotePort}";
+        _connectToRemote = async ct => await _session.OpenTcpConnectionChannelAsync(remoteHost, remotePort, ct).ConfigureAwait(false);
+
+        Start(bindEndpoint);
+    }
+
+    private void Start(EndPoint bindEndpoint)
+    {
+        // Assign to bindEndPoint in case we fail to bind/listen so we have an address for logging.
+        _localEndPoint = bindEndpoint;
+
+        try
+        {
+            if (bindEndpoint is IPEndPoint ipEndPoint)
+            {
+                _serverSocket = new Socket(ipEndPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
+            }
+            else
+            {
+                // Type must be validated before calling this method.
+                throw new InvalidOperationException($"Unsupported EndPoint type: {bindEndpoint.GetType().FullName}.");
+            }
+
+            _serverSocket.Bind(bindEndpoint);
+            _serverSocket.Listen();
+
+            EndPoint localEndPoint = _serverSocket.LocalEndPoint!;
+            _localEndPoint = localEndPoint;
+
+            _ctr = _session.ConnectionClosed.UnsafeRegister(o => ((LocalForward)o!).Stop(ConnectionClosed), this);
+
+            _ = AcceptLoop(localEndPoint);
+        }
+        catch (Exception ex)
+        {
+            Stop(ex);
+
+            throw;
+        }
+    }
+
+    private async Task AcceptLoop(EndPoint localEndPoint)
+    {
+        try
+        {
+            _logger.ForwardStart(localEndPoint, _remoteEndPoint);
+            while (true)
+            {
+                Socket acceptedSocket = await _serverSocket!.AcceptAsync().ConfigureAwait(false);
+                _ = Accept(acceptedSocket, localEndPoint);
+            }
+        }
+        catch (Exception ex)
+        {
+            Stop(ex);
+        }
+    }
+
+    private async Task Accept(Socket acceptedSocket, EndPoint localEndpoint)
+    {
+        Debug.Assert(_connectToRemote is not null);
+        SshDataStream? forwardStream = null;
+        EndPoint? peerEndPoint = null;
+        try
+        {
+            peerEndPoint = acceptedSocket.RemoteEndPoint!;
+            _logger.AcceptConnection(localEndpoint, peerEndPoint, _remoteEndPoint);
+            acceptedSocket.NoDelay = true;
+
+            // We may want to add a timeout option, and the ability to stop the lister on some conditions like nr of successive fails to connect to the remote.
+            forwardStream = await _connectToRemote(_cancel!.Token).ConfigureAwait(false);
+            _ = ForwardConnectionAsync(new NetworkStream(acceptedSocket, ownsSocket: true), forwardStream, peerEndPoint);
+        }
+        catch (Exception ex)
+        {
+            _logger.ForwardConnectionFailed(peerEndPoint, _remoteEndPoint, ex);
+
+            acceptedSocket.Dispose();
+            forwardStream?.Dispose();
+        }
+    }
+
+    private async Task ForwardConnectionAsync(NetworkStream socketStream, SshDataStream sshStream, EndPoint peerEndPoint)
+    {
+        Exception? exception = null;
+        try
+        {
+            _logger.ForwardConnection(peerEndPoint, _remoteEndPoint);
+            Task first, second;
+            try
+            {
+                Task copy1 = CopyTillEofAsync(socketStream, sshStream, sshStream.WriteMaxPacketDataLength);
+                Task copy2 = CopyTillEofAsync(sshStream, socketStream, sshStream.ReadMaxPacketDataLength);
+
+                first = await Task.WhenAny(copy1, copy2).ConfigureAwait(false);
+                second = first == copy1 ? copy2 : copy1;
+            }
+            finally
+            {
+                // When the copy stops in one direction, stop it in the other direction too.
+                // Though TCP allows data still to be received when the writing is shutdown
+                // application protocols (usually) follow the pattern of only closing
+                // when they will no longer receive.
+                socketStream.Dispose();
+                sshStream.Dispose();
+            }
+            // The dispose will cause the second copy to stop.
+            await second.ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);
+
+            await first.ConfigureAwait(false); // Throws if faulted.
+        }
+        catch (Exception ex)
+        {
+            exception = ex;
+        }
+        finally
+        {
+            if (exception is null)
+            {
+                _logger.ForwardConnectionClosed(peerEndPoint, _remoteEndPoint);
+            }
+            else
+            {
+                _logger.ForwardConnectionAborted(peerEndPoint, _remoteEndPoint, exception);
+            }
+        }
+
+        static async Task CopyTillEofAsync(Stream from, Stream to, int bufferSize)
+        {
+            await from.CopyToAsync(to, bufferSize).ConfigureAwait(false);
+            if (to is NetworkStream ns)
+            {
+                ns.Socket.Shutdown(SocketShutdown.Send);
+            }
+            else if (to is SshDataStream ds)
+            {
+                ds.WriteEof();
+            }
+        }
+    }
+
+    public EndPoint? EndPoint
+    {
+        get
+        {
+            ObjectDisposedException.ThrowIf(IsDisposed, this);
+            return _localEndPoint;
+        }
+    }
+
+    public CancellationToken ForwardStopped
+    {
+        get
+        {
+            ObjectDisposedException.ThrowIf(IsDisposed, this);
+            return _cancel.Token;
+        }
+    }
+
+    public void ThrowIfStopped()
+    {
+        Exception? stopReason = _stopReason;
+        if (ReferenceEquals(stopReason, Disposed))
+        {
+            throw new ObjectDisposedException(typeof(LocalForward).FullName);
+        }
+        else if (ReferenceEquals(stopReason, ConnectionClosed))
+        {
+            throw _session.CreateCloseException();
+        }
+        else if (stopReason is not null)
+        {
+            throw new SshException($"{nameof(LocalForward)} stopped due to an unexpected error.", stopReason);
+        }
+    }
+
+    private void Stop(Exception stopReason)
+    {
+        bool disposing = ReferenceEquals(stopReason, Disposed);
+        if (disposing)
+        {
+            if (Interlocked.Exchange(ref _stopReason, Disposed) != null)
+            {
+                return;
+            }
+        }
+        else
+        {
+            if (Interlocked.CompareExchange(ref _stopReason, stopReason, null) != null)
+            {
+                return;
+            }
+        }
+
+        if (_localEndPoint is not null)
+        {
+            if (IsDisposed)
+            {
+                _logger.ForwardStopped(_localEndPoint, _remoteEndPoint);
+            }
+            else if (ReferenceEquals(stopReason, ConnectionClosed))
+            {
+                if (_logger.IsEnabled(LogLevel.Error))
+                {
+                    _logger.ForwardAborted(_localEndPoint, _remoteEndPoint, _session.CreateCloseException());
+                }
+            }
+            else
+            {
+                _logger.ForwardAborted(_localEndPoint, _remoteEndPoint, stopReason);
+            }
+            _ctr.Dispose();
+            _localEndPoint = null;
+            _serverSocket?.Dispose();
+        }
+
+        _cancel.Cancel();
+    }
+
+    public void Dispose()
+        => Stop(Disposed);
+}

src/Tmds.Ssh/SshChannel.cs

@@ -71,6 +71,7 @@ public CancellationToken ChannelAborted
     private int _disposed;
     private int _sendWindow;
     private Exception? _abortReason = null;
+    private bool _eofSent;
     private object _gate => _receiveQueue;
 
     public async ValueTask<(ChannelReadType ReadType, int BytesRead)> ReadAsync
@@ -173,16 +174,50 @@ string    data
         }
     }
 
+    public void WriteEof()
+    {
+        ThrowIfDisposed();
+        ThrowIfAborted();
+        ThrowIfEofSent();
+
+        _eofSent = true;
+        TrySendEofMessage();
+    }
+
+    private void ThrowIfEofSent()
+    {
+        if (_eofSent)
+        {
+            ThrowEofSent();
+        }
+
+        static void ThrowEofSent()
+        {
+            throw new InvalidOperationException("EOF already sent.");
+        }
+    }
+
+    private void ThrowIfAborted()
+    {
+        if (_abortState >= (int)AbortState.Closed)
+        {
+            ThrowCloseException();
+        }
+    }
+
+    private void ThrowCloseException()
+    {
+        throw CreateCloseException();
+    }
+
     public async ValueTask WriteAsync(ReadOnlyMemory<byte> memory, CancellationToken cancellationToken)
     {
         ThrowIfDisposed();
+        ThrowIfEofSent();
 
         while (memory.Length > 0)
         {
-            if (_abortState >= (int)AbortState.Closed)
-            {
-                throw CreateCloseException();
-            }
+            ThrowIfAborted();
 
             int sendWindow = Volatile.Read(ref _sendWindow);
             if (sendWindow > 0)
@@ -595,6 +630,9 @@ private Exception CreateObjectDisposedException()
     private void TrySendChannelFailureMessage()
         => TrySendPacket(_sequencePool.CreateChannelFailureMessage(RemoteChannel));
 
+    private void TrySendEofMessage()
+        => TrySendPacket(_sequencePool.CreateChannelEofMessage(RemoteChannel));
+
     private void TrySendChannelDataMessage(ReadOnlyMemory<byte> memory)
         => TrySendPacket(_sequencePool.CreateChannelDataMessage(RemoteChannel, memory));
 }