SftpClient: handle the SFTP session being closed by the server

src/Renci.SshNet/BaseClient.cs

@@ -72,7 +72,7 @@ private set
         /// <see langword="true"/> if this client is connected; otherwise, <see langword="false"/>.
         /// </value>
         /// <exception cref="ObjectDisposedException">The method was called after the client was disposed.</exception>
-        public bool IsConnected
+        public virtual bool IsConnected
         {
             get
             {
@@ -228,14 +228,19 @@ public void Connect()
             // forwarded port with a client instead of with a session
             //
             // To be discussed with Oleg (or whoever is interested)
-            if (IsSessionConnected())
+            if (IsConnected)
             {
                 throw new InvalidOperationException("The client is already connected.");
             }
 
             OnConnecting();
 
-            Session = CreateAndConnectSession();
+            // The session may already/still be connected here because e.g. in SftpClient, IsConnected also checks the internal SFTP session
+            var session = Session;
+            if (session is null || !session.IsConnected)
+            {
+                Session = CreateAndConnectSession();
+            }
 
             try
             {
@@ -287,14 +292,19 @@ public async Task ConnectAsync(CancellationToken cancellationToken)
             // forwarded port with a client instead of with a session
             //
             // To be discussed with Oleg (or whoever is interested)
-            if (IsSessionConnected())
+            if (IsConnected)
             {
                 throw new InvalidOperationException("The client is already connected.");
             }
 
             OnConnecting();
 
-            Session = await CreateAndConnectSessionAsync(cancellationToken).ConfigureAwait(false);
+            // The session may already/still be connected here because e.g. in SftpClient, IsConnected also checks the internal SFTP session
+            var session = Session;
+            if (session is null || !session.IsConnected)
+            {
+                Session = await CreateAndConnectSessionAsync(cancellationToken).ConfigureAwait(false);
+            }
 
             try
             {

src/Renci.SshNet/SftpClient.cs

@@ -108,6 +108,22 @@ public uint BufferSize
             }
         }
 
+        /// <summary>
+        /// Gets a value indicating whether this client is connected to the server and
+        /// the SFTP session is open.
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if this client is connected and the SFTP session is open; otherwise, <see langword="false"/>.
+        /// </value>
+        /// <exception cref="ObjectDisposedException">The method was called after the client was disposed.</exception>
+        public override bool IsConnected
+        {
+            get
+            {
+                return base.IsConnected && _sftpSession.IsOpen;
+            }
+        }
+
         /// <summary>
         /// Gets remote working directory.
         /// </summary>
@@ -2473,7 +2489,15 @@ protected override void OnConnected()
         {
             base.OnConnected();
 
-            _sftpSession = CreateAndConnectToSftpSession();
+            var sftpSession = _sftpSession;
+            if (sftpSession is null)
+            {
+                _sftpSession = CreateAndConnectToSftpSession();
+            }
+            else if (!sftpSession.IsOpen)
+            {
+                sftpSession.Connect();
+            }
         }
 
         /// <summary>

test/Renci.SshNet.IntegrationTests/ConnectivityTests.cs

@@ -287,6 +287,44 @@ public void Common_DetectLossOfNetworkConnectivityThroughSftpInvocation()
             }
         }
 
+        [TestMethod]
+        public void SftpClient_HandleSftpSessionClose()
+        {
+            using (var client = new SftpClient(_connectionInfoFactory.Create()))
+            {
+                client.Connect();
+                Assert.IsTrue(client.IsConnected);
+
+                client.SftpSession.Disconnect();
+                Assert.IsFalse(client.IsConnected);
+
+                client.Connect();
+                Assert.IsTrue(client.IsConnected);
+
+                client.Disconnect();
+                Assert.IsFalse(client.IsConnected);
+            }
+        }
+
+        [TestMethod]
+        public async Task SftpClient_HandleSftpSessionCloseAsync()
+        {
+            using (var client = new SftpClient(_connectionInfoFactory.Create()))
+            {
+                await client.ConnectAsync(CancellationToken.None);
+                Assert.IsTrue(client.IsConnected);
+
+                client.SftpSession.Disconnect();
+                Assert.IsFalse(client.IsConnected);
+
+                await client.ConnectAsync(CancellationToken.None);
+                Assert.IsTrue(client.IsConnected);
+
+                client.Disconnect();
+                Assert.IsFalse(client.IsConnected);
+            }
+        }
+
         [TestMethod]
         public void Common_DetectSessionKilledOnServer()
         {