fix "client not connected" after SFTP reconnect

src/Renci.SshNet/BaseClient.cs

@@ -240,6 +240,11 @@ public void Connect()
             var session = Session;
             if (session is null || !session.IsConnected)
             {
+                if (session is not null)
+                {
+                    DisposeSession(session);
+                }
+
                 Session = CreateAndConnectSession();
             }
 
@@ -304,6 +309,11 @@ public async Task ConnectAsync(CancellationToken cancellationToken)
             var session = Session;
             if (session is null || !session.IsConnected)
             {
+                if (session is not null)
+                {
+                    DisposeSession(session);
+                }
+
                 Session = await CreateAndConnectSessionAsync(cancellationToken).ConfigureAwait(false);
             }
 

src/Renci.SshNet/SftpClient.cs

@@ -2496,15 +2496,8 @@ protected override void OnConnected()
         {
             base.OnConnected();
 
-            var sftpSession = _sftpSession;
-            if (sftpSession is null)
-            {
-                _sftpSession = CreateAndConnectToSftpSession();
-            }
-            else if (!sftpSession.IsOpen)
-            {
-                sftpSession.Connect();
-            }
+            _sftpSession?.Dispose();
+            _sftpSession = CreateAndConnectToSftpSession();
         }
 
         /// <summary>

test/Renci.SshNet.IntegrationTests/ConnectivityTests.cs

@@ -326,6 +326,54 @@ public async Task SftpClient_HandleSftpSessionCloseAsync()
             }
         }
 
+        [TestMethod]
+        public void SftpClient_HandleSftpSessionAbortByServer()
+        {
+            using (var client = new SftpClient(_connectionInfoFactory.Create()))
+            {
+                client.Connect();
+                Assert.IsTrue(client.IsConnected);
+
+                _sshConnectionDisruptor.BreakConnections();
+                WaitForConnectionInterruption(client);
+                Assert.IsFalse(client.IsConnected);
+
+                client.Connect();
+                Assert.IsTrue(client.IsConnected);
+
+                foreach (var file in client.ListDirectory("."))
+                {
+                }
+
+                client.Disconnect();
+                Assert.IsFalse(client.IsConnected);
+            }
+        }
+
+        [TestMethod]
+        public async Task SftpClient_HandleSftpSessionAbortByServerAsync()
+        {
+            using (var client = new SftpClient(_connectionInfoFactory.Create()))
+            {
+                await client.ConnectAsync(CancellationToken.None);
+                Assert.IsTrue(client.IsConnected);
+
+                _sshConnectionDisruptor.BreakConnections();
+                WaitForConnectionInterruption(client);
+                Assert.IsFalse(client.IsConnected);
+
+                await client.ConnectAsync(CancellationToken.None);
+                Assert.IsTrue(client.IsConnected);
+
+                await foreach (var file in client.ListDirectoryAsync(".", CancellationToken.None))
+                {
+                }
+
+                client.Disconnect();
+                Assert.IsFalse(client.IsConnected);
+            }
+        }
+
         [TestMethod]
         public void Common_DetectSessionKilledOnServer()
         {