Merge remote-tracking branch 'upstream/develop' into net10

.github/workflows/build.yml

@@ -15,7 +15,7 @@ jobs:
         fetch-depth: 0 # needed for Nerdbank.GitVersioning
 
     - name: Setup .NET
-      uses: actions/setup-dotnet@v4
+      uses: actions/setup-dotnet@v5
 
     - name: Build Unit Tests .NET
       run: dotnet build -f net10.0 test/Renci.SshNet.Tests/
@@ -62,7 +62,7 @@ jobs:
         fetch-depth: 0 # needed for Nerdbank.GitVersioning
 
     - name: Setup .NET
-      uses: actions/setup-dotnet@v4
+      uses: actions/setup-dotnet@v5
 
     - name: Build Solution
       run: dotnet build Renci.SshNet.sln
@@ -103,8 +103,8 @@ jobs:
           -p:CoverletOutput=../../coverlet/windows_unit_test_net_4_6_2_coverage.xml `
           test/Renci.SshNet.Tests/
 
-  Windows-Integration-Tests:
-    name: Windows Integration Tests
+  Windows-Integration-Tests-NetFramework:
+    name: Windows Integration Tests .NET Framework
     runs-on: windows-2025
     steps:
     - name: Checkout
@@ -113,7 +113,7 @@ jobs:
         fetch-depth: 0 # needed for Nerdbank.GitVersioning
 
     - name: Setup .NET
-      uses: actions/setup-dotnet@v4
+      uses: actions/setup-dotnet@v5
 
     - name: Setup WSL2
       uses: Vampire/setup-wsl@6a8db447be7ed35f2f499c02c6e60ff77ef11278 # v6.0.0
@@ -142,7 +142,49 @@ jobs:
     - name: Archive Coverlet Results
       uses: actions/upload-artifact@v4
       with:
-        name: Coverlet Results Windows
+        name: Coverlet Results Windows .NET Framework
+        path: coverlet
+
+  Windows-Integration-Tests-Net:
+    name: Windows Integration Tests .NET
+    runs-on: windows-2025
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v5
+      with:
+        fetch-depth: 0 # needed for Nerdbank.GitVersioning
+
+    - name: Setup .NET
+      uses: actions/setup-dotnet@v5
+
+    - name: Setup WSL2
+      uses: Vampire/setup-wsl@6a8db447be7ed35f2f499c02c6e60ff77ef11278 # v6.0.0
+      with:
+        distribution: Ubuntu-24.04
+
+    - name: Setup SSH Server
+      shell: wsl-bash {0}
+      run: |
+        apt-get update && apt-get upgrade -y
+        apt-get install -y podman
+        podman build -t renci-ssh-tests-server-image -f test/Renci.SshNet.IntegrationTests/Dockerfile test/Renci.SshNet.IntegrationTests/
+        podman run --rm -h renci-ssh-tests-server -d -p 2222:22 renci-ssh-tests-server-image
+
+    - name: Run Integration Tests .NET
+      run:
+        dotnet test `
+          -f net10.0 `
+          --logger "console;verbosity=normal" `
+          --logger GitHubActions `
+          -p:CollectCoverage=true `
+          -p:CoverletOutputFormat=cobertura `
+          -p:CoverletOutput=..\..\coverlet\windows_integration_test_net_9_coverage.xml `
+          test\Renci.SshNet.IntegrationTests\
+
+    - name: Archive Coverlet Results
+      uses: actions/upload-artifact@v4
+      with:
+        name: Coverlet Results Windows .NET
         path: coverlet
 
   Publish:
@@ -153,6 +195,8 @@ jobs:
     needs:
       - Windows
       - Linux
+      - Windows-Integration-Tests-NetFramework
+      - Windows-Integration-Tests-Net
     steps:
       - name: Download NuGet Package
         uses: actions/download-artifact@v5

.github/workflows/docs.yml

@@ -28,7 +28,7 @@ jobs:
         uses: actions/configure-pages@v5
 
       - name: Setup .NET
-        uses: actions/setup-dotnet@v4
+        uses: actions/setup-dotnet@v5
 
       - name: Setup docfx
         run: dotnet tool update -g docfx

src/Renci.SshNet/Abstractions/SocketAbstraction.cs

@@ -12,34 +12,6 @@ namespace Renci.SshNet.Abstractions
 {
     internal static partial class SocketAbstraction
     {
-        public static bool CanRead(Socket socket)
-        {
-            if (socket.Connected)
-            {
-                return socket.Poll(-1, SelectMode.SelectRead) && socket.Available > 0;
-            }
-
-            return false;
-        }
-
-        /// <summary>
-        /// Returns a value indicating whether the specified <see cref="Socket"/> can be used
-        /// to send data.
-        /// </summary>
-        /// <param name="socket">The <see cref="Socket"/> to check.</param>
-        /// <returns>
-        /// <see langword="true"/> if <paramref name="socket"/> can be written to; otherwise, <see langword="false"/>.
-        /// </returns>
-        public static bool CanWrite(Socket socket)
-        {
-            if (socket != null && socket.Connected)
-            {
-                return socket.Poll(-1, SelectMode.SelectWrite);
-            }
-
-            return false;
-        }
-
         public static Socket Connect(IPEndPoint remoteEndpoint, TimeSpan connectTimeout)
         {
             var socket = new Socket(remoteEndpoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp) { NoDelay = true };

src/Renci.SshNet/Common/Extensions.cs

@@ -12,7 +12,6 @@ using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Threading;
 
-using Renci.SshNet.Abstractions;
 using Renci.SshNet.Messages;
 
 namespace Renci.SshNet.Common
@@ -321,16 +320,6 @@ namespace Renci.SshNet.Common
             return concat;
         }
 
-        internal static bool CanRead(this Socket socket)
-        {
-            return SocketAbstraction.CanRead(socket);
-        }
-
-        internal static bool CanWrite(this Socket socket)
-        {
-            return SocketAbstraction.CanWrite(socket);
-        }
-
         internal static bool IsConnected(this Socket socket)
         {
             if (socket is null)

src/Renci.SshNet/Security/KeyExchangeEC.cs

@@ -1,4 +1,6 @@
-using Renci.SshNet.Messages.Transport;
+using System;
+
+using Renci.SshNet.Messages.Transport;
 
 namespace Renci.SshNet.Security
 {
@@ -76,5 +78,23 @@ namespace Renci.SshNet.Security
             _serverPayload = message.GetBytes();
             _clientPayload = Session.ClientInitMessage.GetBytes();
         }
+
+        protected abstract class Impl : IDisposable
+        {
+            public abstract byte[] GenerateClientPublicKey();
+
+            public abstract byte[] CalculateAgreement(byte[] serverPublicKey);
+
+            protected virtual void Dispose(bool disposing)
+            {
+            }
+
+            public void Dispose()
+            {
+                // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
+                Dispose(disposing: true);
+                GC.SuppressFinalize(this);
+            }
+        }
     }
 }

src/Renci.SshNet/Security/KeyExchangeECCurve25519.BclImpl.cs

@@ -0,0 +1,57 @@
+#if NET
+using System.Security.Cryptography;
+
+namespace Renci.SshNet.Security
+{
+    internal partial class KeyExchangeECCurve25519
+    {
+        protected sealed class BclImpl : Impl
+        {
+            private readonly ECCurve _curve;
+            private readonly ECDiffieHellman _clientECDH;
+
+            public BclImpl()
+            {
+                _curve = ECCurve.CreateFromFriendlyName("Curve25519");
+                _clientECDH = ECDiffieHellman.Create();
+            }
+
+            public override byte[] GenerateClientPublicKey()
+            {
+                _clientECDH.GenerateKey(_curve);
+
+                var q = _clientECDH.PublicKey.ExportParameters().Q;
+
+                return q.X;
+            }
+
+            public override byte[] CalculateAgreement(byte[] serverPublicKey)
+            {
+                var parameters = new ECParameters
+                {
+                    Curve = _curve,
+                    Q = new ECPoint
+                    {
+                        X = serverPublicKey,
+                        Y = new byte[serverPublicKey.Length]
+                    },
+                };
+
+                using var serverECDH = ECDiffieHellman.Create(parameters);
+
+                return _clientECDH.DeriveRawSecretAgreement(serverECDH.PublicKey);
+            }
+
+            protected override void Dispose(bool disposing)
+            {
+                base.Dispose(disposing);
+
+                if (disposing)
+                {
+                    _clientECDH.Dispose();
+                }
+            }
+        }
+    }
+}
+#endif

src/Renci.SshNet/Security/KeyExchangeECCurve25519.BouncyCastleImpl.cs

@@ -0,0 +1,38 @@
+using Org.BouncyCastle.Crypto.Agreement;
+using Org.BouncyCastle.Crypto.Generators;
+using Org.BouncyCastle.Crypto.Parameters;
+
+using Renci.SshNet.Abstractions;
+
+namespace Renci.SshNet.Security
+{
+    internal partial class KeyExchangeECCurve25519
+    {
+        protected sealed class BouncyCastleImpl : Impl
+        {
+            private X25519Agreement _keyAgreement;
+
+            public override byte[] GenerateClientPublicKey()
+            {
+                var g = new X25519KeyPairGenerator();
+                g.Init(new X25519KeyGenerationParameters(CryptoAbstraction.SecureRandom));
+
+                var aKeyPair = g.GenerateKeyPair();
+                _keyAgreement = new X25519Agreement();
+                _keyAgreement.Init(aKeyPair.Private);
+
+                return ((X25519PublicKeyParameters)aKeyPair.Public).GetEncoded();
+            }
+
+            public override byte[] CalculateAgreement(byte[] serverPublicKey)
+            {
+                var publicKey = new X25519PublicKeyParameters(serverPublicKey);
+
+                var k1 = new byte[_keyAgreement.AgreementSize];
+                _keyAgreement.CalculateAgreement(publicKey, k1, 0);
+
+                return k1;
+            }
+        }
+    }
+}

src/Renci.SshNet/Security/KeyExchangeECCurve25519.cs

@@ -1,18 +1,19 @@
-using System.Security.Cryptography;
+using System.Security.Cryptography;
 
-using Org.BouncyCastle.Crypto.Agreement;
-using Org.BouncyCastle.Crypto.Generators;
-using Org.BouncyCastle.Crypto.Parameters;
-
-using Renci.SshNet.Abstractions;
 using Renci.SshNet.Common;
 using Renci.SshNet.Messages.Transport;
 
 namespace Renci.SshNet.Security
 {
-    internal sealed class KeyExchangeECCurve25519 : KeyExchangeEC
+    internal partial class KeyExchangeECCurve25519 : KeyExchangeEC
     {
-        private X25519Agreement _keyAgreement;
+#pragma warning disable SA1401 // Fields should be private
+#if NET
+        protected Impl _impl;
+#else
+        protected BouncyCastleImpl _impl;
+#endif
+#pragma warning restore SA1401 // Fields should be private
 
         /// <summary>
         /// Gets algorithm name.
@@ -37,29 +38,46 @@ namespace Renci.SshNet.Security
         public override void Start(Session session, KeyExchangeInitMessage message, bool sendClientInitMessage)
         {
             base.Start(session, message, sendClientInitMessage);
+#if NET
+            if (System.OperatingSystem.IsWindowsVersionAtLeast(10))
+            {
+                _impl = new BclImpl();
+            }
+            else
+#endif
+            {
+                _impl = new BouncyCastleImpl();
+            }
 
+            StartImpl();
+        }
+
+        /// <summary>
+        /// The implementation of start key exchange algorithm.
+        /// </summary>
+        protected virtual void StartImpl()
+        {
             Session.RegisterMessage("SSH_MSG_KEX_ECDH_REPLY");
 
             Session.KeyExchangeEcdhReplyMessageReceived += Session_KeyExchangeEcdhReplyMessageReceived;
 
-            var g = new X25519KeyPairGenerator();
-            g.Init(new X25519KeyGenerationParameters(CryptoAbstraction.SecureRandom));
-
-            var aKeyPair = g.GenerateKeyPair();
-            _keyAgreement = new X25519Agreement();
-            _keyAgreement.Init(aKeyPair.Private);
-            _clientExchangeValue = ((X25519PublicKeyParameters)aKeyPair.Public).GetEncoded();
+            _clientExchangeValue = _impl.GenerateClientPublicKey();
 
             SendMessage(new KeyExchangeEcdhInitMessage(_clientExchangeValue));
         }
 
-        /// <summary>
-        /// Finishes key exchange algorithm.
-        /// </summary>
+        /// <inheritdoc/>
         public override void Finish()
         {
             base.Finish();
+            FinishImpl();
+        }
 
+        /// <summary>
+        /// The implementation of finish key exchange algorithm.
+        /// </summary>
+        protected virtual void FinishImpl()
+        {
             Session.KeyExchangeEcdhReplyMessageReceived -= Session_KeyExchangeEcdhReplyMessageReceived;
         }
 
@@ -100,11 +118,19 @@ namespace Renci.SshNet.Security
             _hostKey = hostKey;
             _signature = signature;
 
-            var publicKey = new X25519PublicKeyParameters(serverExchangeValue);
-
-            var k1 = new byte[_keyAgreement.AgreementSize];
-            _keyAgreement.CalculateAgreement(publicKey, k1, 0);
+            var k1 = _impl.CalculateAgreement(serverExchangeValue);
             SharedKey = k1.ToBigInteger2().ToByteArray(isBigEndian: true);
         }
+
+        /// <inheritdoc/>
+        protected override void Dispose(bool disposing)
+        {
+            base.Dispose(disposing);
+
+            if (disposing)
+            {
+                _impl?.Dispose();
+            }
+        }
     }
 }

src/Renci.SshNet/Security/KeyExchangeECDH.BclImpl.cs

@@ -17,7 +17,7 @@ namespace Renci.SshNet.Security
                 _clientECDH = ECDiffieHellman.Create();
             }
 
-            public override byte[] GenerateClientECPoint()
+            public override byte[] GenerateClientPublicKey()
             {
                 _clientECDH.GenerateKey(_curve);
 
@@ -26,9 +26,9 @@ namespace Renci.SshNet.Security
                 return EncodeECPoint(q);
             }
 
-            public override byte[] CalculateAgreement(byte[] serverECPoint)
+            public override byte[] CalculateAgreement(byte[] serverPublicKey)
             {
-                var q = DecodeECPoint(serverECPoint);
+                var q = DecodeECPoint(serverPublicKey);
 
                 var parameters = new ECParameters
                 {

src/Renci.SshNet/Security/KeyExchangeECDH.BouncyCastleImpl.cs

@@ -20,7 +20,7 @@ namespace Renci.SshNet.Security
                 _keyAgreement = new ECDHCBasicAgreement();
             }
 
-            public override byte[] GenerateClientECPoint()
+            public override byte[] GenerateClientPublicKey()
             {
                 var g = new ECKeyPairGenerator();
                 g.Init(new ECKeyGenerationParameters(_domainParameters, CryptoAbstraction.SecureRandom));
@@ -31,10 +31,10 @@ namespace Renci.SshNet.Security
                 return ((ECPublicKeyParameters)aKeyPair.Public).Q.GetEncoded();
             }
 
-            public override byte[] CalculateAgreement(byte[] serverECPoint)
+            public override byte[] CalculateAgreement(byte[] serverPublicKey)
             {
                 var c = _domainParameters.Curve;
-                var q = c.DecodePoint(serverECPoint);
+                var q = c.DecodePoint(serverPublicKey);
                 var publicKey = new ECPublicKeyParameters("ECDH", q, _domainParameters);
 
                 return _keyAgreement.CalculateAgreement(publicKey).ToByteArray();

src/Renci.SshNet/Security/KeyExchangeECDH.cs

@@ -1,6 +1,4 @@
-using System;
-
-using Org.BouncyCastle.Asn1.X9;
+using Org.BouncyCastle.Asn1.X9;
 
 using Renci.SshNet.Common;
 using Renci.SshNet.Messages.Transport;
@@ -41,7 +39,7 @@ namespace Renci.SshNet.Security
             Session.KeyExchangeEcdhReplyMessageReceived += Session_KeyExchangeEcdhReplyMessageReceived;
 
 #if NET
-            if (!OperatingSystem.IsWindows() || OperatingSystem.IsWindowsVersionAtLeast(10))
+            if (!System.OperatingSystem.IsWindows() || System.OperatingSystem.IsWindowsVersionAtLeast(10))
             {
                 _impl = new BclImpl(Curve);
             }
@@ -51,7 +49,7 @@ namespace Renci.SshNet.Security
                 _impl = new BouncyCastleImpl(CurveParameter);
             }
 
-            _clientExchangeValue = _impl.GenerateClientECPoint();
+            _clientExchangeValue = _impl.GenerateClientPublicKey();
 
             SendMessage(new KeyExchangeEcdhInitMessage(_clientExchangeValue));
         }
@@ -106,23 +104,5 @@ namespace Renci.SshNet.Security
                 _impl?.Dispose();
             }
         }
-
-        private abstract class Impl : IDisposable
-        {
-            public abstract byte[] GenerateClientECPoint();
-
-            public abstract byte[] CalculateAgreement(byte[] serverECPoint);
-
-            protected virtual void Dispose(bool disposing)
-            {
-            }
-
-            public void Dispose()
-            {
-                // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-                Dispose(disposing: true);
-                GC.SuppressFinalize(this);
-            }
-        }
     }
 }

src/Renci.SshNet/Security/KeyExchangeMLKem768X25519Sha256.cs

@@ -2,7 +2,6 @@
 using System.Linq;
 using System.Security.Cryptography;
 
-using Org.BouncyCastle.Crypto.Agreement;
 using Org.BouncyCastle.Crypto.Generators;
 using Org.BouncyCastle.Crypto.Kems;
 using Org.BouncyCastle.Crypto.Parameters;
@@ -13,10 +12,9 @@ using Renci.SshNet.Messages.Transport;
 
 namespace Renci.SshNet.Security
 {
-    internal sealed class KeyExchangeMLKem768X25519Sha256 : KeyExchangeEC
+    internal sealed class KeyExchangeMLKem768X25519Sha256 : KeyExchangeECCurve25519
     {
         private MLKemDecapsulator _mlkemDecapsulator;
-        private X25519Agreement _x25519Agreement;
 
         /// <summary>
         /// Gets algorithm name.
@@ -38,10 +36,8 @@ namespace Renci.SshNet.Security
         }
 
         /// <inheritdoc/>
-        public override void Start(Session session, KeyExchangeInitMessage message, bool sendClientInitMessage)
+        protected override void StartImpl()
         {
-            base.Start(session, message, sendClientInitMessage);
-
             Session.RegisterMessage("SSH_MSG_KEX_HYBRID_REPLY");
 
             Session.KeyExchangeHybridReplyMessageReceived += Session_KeyExchangeHybridReplyMessageReceived;
@@ -53,28 +49,18 @@ namespace Renci.SshNet.Security
             _mlkemDecapsulator = new MLKemDecapsulator(MLKemParameters.ml_kem_768);
             _mlkemDecapsulator.Init(mlkem768KeyPair.Private);
 
-            var x25519KeyPairGenerator = new X25519KeyPairGenerator();
-            x25519KeyPairGenerator.Init(new X25519KeyGenerationParameters(CryptoAbstraction.SecureRandom));
-            var x25519KeyPair = x25519KeyPairGenerator.GenerateKeyPair();
-
-            _x25519Agreement = new X25519Agreement();
-            _x25519Agreement.Init(x25519KeyPair.Private);
-
             var mlkem768PublicKey = ((MLKemPublicKeyParameters)mlkem768KeyPair.Public).GetEncoded();
-            var x25519PublicKey = ((X25519PublicKeyParameters)x25519KeyPair.Public).GetEncoded();
+
+            var x25519PublicKey = _impl.GenerateClientPublicKey();
 
             _clientExchangeValue = mlkem768PublicKey.Concat(x25519PublicKey);
 
             SendMessage(new KeyExchangeHybridInitMessage(_clientExchangeValue));
         }
 
-        /// <summary>
-        /// Finishes key exchange algorithm.
-        /// </summary>
-        public override void Finish()
+        /// <inheritdoc/>
+        protected override void FinishImpl()
         {
-            base.Finish();
-
             Session.KeyExchangeHybridReplyMessageReceived -= Session_KeyExchangeHybridReplyMessageReceived;
         }
 
@@ -115,21 +101,20 @@ namespace Renci.SshNet.Security
             _hostKey = hostKey;
             _signature = signature;
 
-            if (serverExchangeValue.Length != _mlkemDecapsulator.EncapsulationLength + _x25519Agreement.AgreementSize)
+            if (serverExchangeValue.Length != _mlkemDecapsulator.EncapsulationLength + X25519PublicKeyParameters.KeySize)
             {
                 throw new SshConnectionException(
                     string.Format(CultureInfo.CurrentCulture, "Bad S_Reply length: {0}.", serverExchangeValue.Length),
                     DisconnectReason.KeyExchangeFailed);
             }
 
-            var secret = new byte[_mlkemDecapsulator.SecretLength + _x25519Agreement.AgreementSize];
+            var mlkemSecret = new byte[_mlkemDecapsulator.SecretLength];
 
-            _mlkemDecapsulator.Decapsulate(serverExchangeValue, 0, _mlkemDecapsulator.EncapsulationLength, secret, 0, _mlkemDecapsulator.SecretLength);
+            _mlkemDecapsulator.Decapsulate(serverExchangeValue, 0, _mlkemDecapsulator.EncapsulationLength, mlkemSecret, 0, _mlkemDecapsulator.SecretLength);
 
-            var x25519PublicKey = new X25519PublicKeyParameters(serverExchangeValue, _mlkemDecapsulator.EncapsulationLength);
-            _x25519Agreement.CalculateAgreement(x25519PublicKey, secret, _mlkemDecapsulator.SecretLength);
+            var x25519Agreement = _impl.CalculateAgreement(serverExchangeValue.Take(_mlkemDecapsulator.EncapsulationLength, X25519PublicKeyParameters.KeySize));
 
-            SharedKey = SHA256.HashData(secret);
+            SharedKey = SHA256.HashData(mlkemSecret.Concat(x25519Agreement));
         }
     }
 }

src/Renci.SshNet/Security/KeyExchangeSNtruP761X25519Sha512.cs

@@ -1,10 +1,7 @@
-using System;
-using System.Globalization;
+using System.Globalization;
 using System.Linq;
 using System.Security.Cryptography;
 
-using Org.BouncyCastle.Crypto.Agreement;
-using Org.BouncyCastle.Crypto.Generators;
 using Org.BouncyCastle.Crypto.Parameters;
 using Org.BouncyCastle.Pqc.Crypto.NtruPrime;
 
@@ -14,10 +11,9 @@ using Renci.SshNet.Messages.Transport;
 
 namespace Renci.SshNet.Security
 {
-    internal sealed class KeyExchangeSNtruP761X25519Sha512 : KeyExchangeEC
+    internal sealed class KeyExchangeSNtruP761X25519Sha512 : KeyExchangeECCurve25519
     {
         private SNtruPrimeKemExtractor _sntrup761Extractor;
-        private X25519Agreement _x25519Agreement;
 
         /// <summary>
         /// Gets algorithm name.
@@ -39,10 +35,8 @@ namespace Renci.SshNet.Security
         }
 
         /// <inheritdoc/>
-        public override void Start(Session session, KeyExchangeInitMessage message, bool sendClientInitMessage)
+        protected override void StartImpl()
         {
-            base.Start(session, message, sendClientInitMessage);
-
             Session.RegisterMessage("SSH_MSG_KEX_ECDH_REPLY");
 
             Session.KeyExchangeEcdhReplyMessageReceived += Session_KeyExchangeEcdhReplyMessageReceived;
@@ -53,28 +47,18 @@ namespace Renci.SshNet.Security
 
             _sntrup761Extractor = new SNtruPrimeKemExtractor((SNtruPrimePrivateKeyParameters)sntrup761KeyPair.Private);
 
-            var x25519KeyPairGenerator = new X25519KeyPairGenerator();
-            x25519KeyPairGenerator.Init(new X25519KeyGenerationParameters(CryptoAbstraction.SecureRandom));
-            var x25519KeyPair = x25519KeyPairGenerator.GenerateKeyPair();
-
-            _x25519Agreement = new X25519Agreement();
-            _x25519Agreement.Init(x25519KeyPair.Private);
-
             var sntrup761PublicKey = ((SNtruPrimePublicKeyParameters)sntrup761KeyPair.Public).GetEncoded();
-            var x25519PublicKey = ((X25519PublicKeyParameters)x25519KeyPair.Public).GetEncoded();
+
+            var x25519PublicKey = _impl.GenerateClientPublicKey();
 
             _clientExchangeValue = sntrup761PublicKey.Concat(x25519PublicKey);
 
             SendMessage(new KeyExchangeEcdhInitMessage(_clientExchangeValue));
         }
 
-        /// <summary>
-        /// Finishes key exchange algorithm.
-        /// </summary>
-        public override void Finish()
+        /// <inheritdoc/>
+        protected override void FinishImpl()
         {
-            base.Finish();
-
             Session.KeyExchangeEcdhReplyMessageReceived -= Session_KeyExchangeEcdhReplyMessageReceived;
         }
 
@@ -123,14 +107,12 @@ namespace Renci.SshNet.Security
             }
 
             var sntrup761CipherText = serverExchangeValue.Take(_sntrup761Extractor.EncapsulationLength);
-            var secret = _sntrup761Extractor.ExtractSecret(sntrup761CipherText);
-            var sntrup761SecretLength = secret.Length;
 
-            var x25519PublicKey = new X25519PublicKeyParameters(serverExchangeValue, _sntrup761Extractor.EncapsulationLength);
-            Array.Resize(ref secret, sntrup761SecretLength + _x25519Agreement.AgreementSize);
-            _x25519Agreement.CalculateAgreement(x25519PublicKey, secret, sntrup761SecretLength);
+            var sntrup761Secret = _sntrup761Extractor.ExtractSecret(sntrup761CipherText);
 
-            SharedKey = SHA512.HashData(secret);
+            var x25519Agreement = _impl.CalculateAgreement(serverExchangeValue.Take(_sntrup761Extractor.EncapsulationLength, X25519PublicKeyParameters.KeySize));
+
+            SharedKey = SHA512.HashData(sntrup761Secret.Concat(x25519Agreement));
         }
     }
 }

src/Renci.SshNet/Session.cs

@@ -78,12 +78,6 @@ namespace Renci.SshNet
         private readonly ISocketFactory _socketFactory;
         private readonly ILogger _logger;
 
-        /// <summary>
-        /// Holds an object that is used to ensure only a single thread can read from
-        /// <see cref="_socket"/> at any given time.
-        /// </summary>
-        private readonly Lock _socketReadLock = new Lock();
-
         /// <summary>
         /// Holds an object that is used to ensure only a single thread can write to
         /// <see cref="_socket"/> at any given time.
@@ -102,7 +96,7 @@ namespace Renci.SshNet
         /// This is also used to ensure that <see cref="_socket"/> will not be disposed
         /// while performing a given operation or set of operations on <see cref="_socket"/>.
         /// </remarks>
-        private readonly SemaphoreSlim _socketDisposeLock = new SemaphoreSlim(1, 1);
+        private readonly Lock _socketDisposeLock = new Lock();
 
         /// <summary>
         /// Holds an object that is used to ensure only a single thread can connect
@@ -276,17 +270,11 @@ namespace Renci.SshNet
         {
             get
             {
-                if (_disposed || _isDisconnectMessageSent || !_isAuthenticated)
-                {
-                    return false;
-                }
-
-                if (_messageListenerCompleted is null || _messageListenerCompleted.WaitOne(0))
-                {
-                    return false;
-                }
-
-                return IsSocketConnected();
+                return !_disposed &&
+                    !_isDisconnectMessageSent &&
+                    _isAuthenticated &&
+                    _messageListenerCompleted?.WaitOne(0) == false &&
+                    _socket.IsConnected();
             }
         }
 
@@ -1043,7 +1031,7 @@ namespace Renci.SshNet
         /// <exception cref="InvalidOperationException">The size of the packet exceeds the maximum size defined by the protocol.</exception>
         internal void SendMessage(Message message)
         {
-            if (!_socket.CanWrite())
+            if (!_socket.IsConnected())
             {
                 throw new SshConnectionException("Client not connected.");
             }
@@ -1158,9 +1146,7 @@ namespace Renci.SshNet
         /// </remarks>
         private void SendPacket(byte[] packet, int offset, int length)
         {
-            _socketDisposeLock.Wait();
-
-            try
+            lock (_socketDisposeLock)
             {
                 if (!_socket.IsConnected())
                 {
@@ -1169,10 +1155,6 @@ namespace Renci.SshNet
 
                 SocketAbstraction.Send(_socket, packet, offset, length);
             }
-            finally
-            {
-                _ = _socketDisposeLock.Release();
-            }
         }
 
         /// <summary>
@@ -1256,77 +1238,71 @@ namespace Renci.SshNet
             byte[] data;
             uint packetLength;
 
-            // avoid reading from socket while IsSocketConnected is attempting to determine whether the
-            // socket is still connected by invoking Socket.Poll(...) and subsequently verifying value of
-            // Socket.Available
-            lock (_socketReadLock)
+            // Read first block - which starts with the packet length
+            var firstBlock = new byte[blockSize];
+            if (TrySocketRead(socket, firstBlock, 0, blockSize) == 0)
             {
-                // Read first block - which starts with the packet length
-                var firstBlock = new byte[blockSize];
-                if (TrySocketRead(socket, firstBlock, 0, blockSize) == 0)
+                // connection with SSH server was closed
+                return null;
+            }
+
+            var plainFirstBlock = firstBlock;
+
+            // First block is not encrypted in AES GCM mode.
+            if (_serverCipher is not null and not Security.Cryptography.Ciphers.AesGcmCipher)
+            {
+                _serverCipher.SetSequenceNumber(_inboundPacketSequence);
+
+                // First block is not encrypted in ETM mode.
+                if (_serverMac == null || !_serverEtm)
+                {
+                    plainFirstBlock = _serverCipher.Decrypt(firstBlock);
+                }
+            }
+
+            packetLength = BinaryPrimitives.ReadUInt32BigEndian(plainFirstBlock);
+
+            // Test packet minimum and maximum boundaries
+            if (packetLength < Math.Max((byte)8, blockSize) - 4 || packetLength > MaximumSshPacketSize - 4)
+            {
+                throw new SshConnectionException(string.Format(CultureInfo.CurrentCulture, "Bad packet length: {0}.", packetLength),
+                                                 DisconnectReason.ProtocolError);
+            }
+
+            // Determine the number of bytes left to read; We've already read "blockSize" bytes, but the
+            // "packet length" field itself - which is 4 bytes - is not included in the length of the packet
+            var bytesToRead = (int)(packetLength - (blockSize - packetLengthFieldLength)) + serverMacLength;
+
+            // Construct buffer for holding the payload and the inbound packet sequence as we need both in order
+            // to generate the hash.
+            //
+            // The total length of the "data" buffer is an addition of:
+            // - inboundPacketSequenceLength (4 bytes)
+            // - packetLength
+            // - serverMacLength
+            //
+            // We include the inbound packet sequence to allow us to have the the full SSH packet in a single
+            // byte[] for the purpose of calculating the client hash. Room for the server MAC is foreseen
+            // to read the packet including server MAC in a single pass (except for the initial block).
+            data = new byte[bytesToRead + blockSize + inboundPacketSequenceLength];
+            BinaryPrimitives.WriteUInt32BigEndian(data, _inboundPacketSequence);
+
+            // Use raw packet length field to calculate the mac in AEAD mode.
+            if (_serverAead)
+            {
+                Buffer.BlockCopy(firstBlock, 0, data, inboundPacketSequenceLength, blockSize);
+            }
+            else
+            {
+                Buffer.BlockCopy(plainFirstBlock, 0, data, inboundPacketSequenceLength, blockSize);
+            }
+
+            if (bytesToRead > 0)
+            {
+                if (TrySocketRead(socket, data, blockSize + inboundPacketSequenceLength, bytesToRead) == 0)
                 {
-                    // connection with SSH server was closed
                     return null;
                 }
-
-                var plainFirstBlock = firstBlock;
-
-                // First block is not encrypted in AES GCM mode.
-                if (_serverCipher is not null and not Security.Cryptography.Ciphers.AesGcmCipher)
-                {
-                    _serverCipher.SetSequenceNumber(_inboundPacketSequence);
-
-                    // First block is not encrypted in ETM mode.
-                    if (_serverMac == null || !_serverEtm)
-                    {
-                        plainFirstBlock = _serverCipher.Decrypt(firstBlock);
-                    }
-                }
-
-                packetLength = BinaryPrimitives.ReadUInt32BigEndian(plainFirstBlock);
-
-                // Test packet minimum and maximum boundaries
-                if (packetLength < Math.Max((byte)8, blockSize) - 4 || packetLength > MaximumSshPacketSize - 4)
-                {
-                    throw new SshConnectionException(string.Format(CultureInfo.CurrentCulture, "Bad packet length: {0}.", packetLength),
-                                                     DisconnectReason.ProtocolError);
-                }
-
-                // Determine the number of bytes left to read; We've already read "blockSize" bytes, but the
-                // "packet length" field itself - which is 4 bytes - is not included in the length of the packet
-                var bytesToRead = (int)(packetLength - (blockSize - packetLengthFieldLength)) + serverMacLength;
-
-                // Construct buffer for holding the payload and the inbound packet sequence as we need both in order
-                // to generate the hash.
-                //
-                // The total length of the "data" buffer is an addition of:
-                // - inboundPacketSequenceLength (4 bytes)
-                // - packetLength
-                // - serverMacLength
-                //
-                // We include the inbound packet sequence to allow us to have the the full SSH packet in a single
-                // byte[] for the purpose of calculating the client hash. Room for the server MAC is foreseen
-                // to read the packet including server MAC in a single pass (except for the initial block).
-                data = new byte[bytesToRead + blockSize + inboundPacketSequenceLength];
-                BinaryPrimitives.WriteUInt32BigEndian(data, _inboundPacketSequence);
-
-                // Use raw packet length field to calculate the mac in AEAD mode.
-                if (_serverAead)
-                {
-                    Buffer.BlockCopy(firstBlock, 0, data, inboundPacketSequenceLength, blockSize);
-                }
-                else
-                {
-                    Buffer.BlockCopy(plainFirstBlock, 0, data, inboundPacketSequenceLength, blockSize);
-                }
-
-                if (bytesToRead > 0)
-                {
-                    if (TrySocketRead(socket, data, blockSize + inboundPacketSequenceLength, bytesToRead) == 0)
-                    {
-                        return null;
-                    }
-                }
             }
 
             // validate encrypted message against MAC
@@ -1858,84 +1834,6 @@ namespace Renci.SshNet
             return message;
         }
 
-        /// <summary>
-        /// Gets a value indicating whether the socket is connected.
-        /// </summary>
-        /// <returns>
-        /// <see langword="true"/> if the socket is connected; otherwise, <see langword="false"/>.
-        /// </returns>
-        /// <remarks>
-        /// <para>
-        /// As a first check we verify whether <see cref="Socket.Connected"/> is
-        /// <see langword="true"/>. However, this only returns the state of the socket as of
-        /// the last I/O operation.
-        /// </para>
-        /// <para>
-        /// Therefore we use the combination of <see cref="Socket.Poll(int, SelectMode)"/> with mode <see cref="SelectMode.SelectRead"/>
-        /// and <see cref="Socket.Available"/> to verify if the socket is still connected.
-        /// </para>
-        /// <para>
-        /// The MSDN doc mention the following on the return value of <see cref="Socket.Poll(int, SelectMode)"/>
-        /// with mode <see cref="SelectMode.SelectRead"/>:
-        /// <list type="bullet">
-        ///     <item>
-        ///         <description><see langword="true"/> if data is available for reading;</description>
-        ///     </item>
-        ///     <item>
-        ///         <description><see langword="true"/> if the connection has been closed, reset, or terminated; otherwise, returns <see langword="false"/>.</description>
-        ///     </item>
-        /// </list>
-        /// </para>
-        /// <para>
-        /// <c>Conclusion:</c> when the return value is <see langword="true"/> - but no data is available for reading - then
-        /// the socket is no longer connected.
-        /// </para>
-        /// <para>
-        /// When a <see cref="Socket"/> is used from multiple threads, there's a race condition
-        /// between the invocation of <see cref="Socket.Poll(int, SelectMode)"/> and the moment
-        /// when the value of <see cref="Socket.Available"/> is obtained. To workaround this issue
-        /// we synchronize reads from the <see cref="Socket"/>.
-        /// </para>
-        /// <para>
-        /// We assume the socket is still connected if the read lock cannot be acquired immediately.
-        /// In this case, we just return <see langword="true"/> without actually waiting to acquire
-        /// the lock. We don't want to wait for the read lock if another thread already has it because
-        /// there are cases where the other thread holding the lock can be waiting indefinitely for
-        /// a socket read operation to complete.
-        /// </para>
-        /// </remarks>
-        private bool IsSocketConnected()
-        {
-            _socketDisposeLock.Wait();
-
-            try
-            {
-                if (!_socket.IsConnected())
-                {
-                    return false;
-                }
-
-                if (!_socketReadLock.TryEnter())
-                {
-                    return true;
-                }
-
-                try
-                {
-                    var connectionClosedOrDataAvailable = _socket.Poll(0, SelectMode.SelectRead);
-                    return !(connectionClosedOrDataAvailable && _socket.Available == 0);
-                }
-                finally
-                {
-                    _socketReadLock.Exit();
-                }
-            }
-            finally
-            {
-                _ = _socketDisposeLock.Release();
-            }
-        }
-
         /// <summary>
         /// Performs a blocking read on the socket until <paramref name="length"/> bytes are received.
         /// </summary>
@@ -1958,44 +1856,37 @@ namespace Renci.SshNet
         /// </summary>
         private void SocketDisconnectAndDispose()
         {
-            if (_socket != null)
+            lock (_socketDisposeLock)
             {
-                _socketDisposeLock.Wait();
-
-                try
+                if (_socket is null)
                 {
-                    if (_socket != null)
+                    return;
+                }
+
+                if (_socket.Connected)
+                {
+                    try
                     {
-                        if (_socket.Connected)
-                        {
-                            try
-                            {
-                                _logger.LogDebug("[{SessionId}] Shutting down socket.", SessionIdHex);
+                        _logger.LogDebug("[{SessionId}] Shutting down socket.", SessionIdHex);
 
-                                // Interrupt any pending reads; should be done outside of socket read lock as we
-                                // actually want shutdown the socket to make sure blocking reads are interrupted.
-                                //
-                                // This may result in a SocketException (eg. An existing connection was forcibly
-                                // closed by the remote host) which we'll log and ignore as it means the socket
-                                // was already shut down.
-                                _socket.Shutdown(SocketShutdown.Send);
-                            }
-                            catch (SocketException ex)
-                            {
-                                _logger.LogInformation(ex, "Failure shutting down socket");
-                            }
-                        }
-
-                        _logger.LogDebug("[{SessionId}] Disposing socket.", SessionIdHex);
-                        _socket.Dispose();
-                        _logger.LogDebug("[{SessionId}] Disposed socket.", SessionIdHex);
-                        _socket = null;
+                        // Interrupt any pending reads; should be done outside of socket read lock as we
+                        // actually want shutdown the socket to make sure blocking reads are interrupted.
+                        //
+                        // This may result in a SocketException (eg. An existing connection was forcibly
+                        // closed by the remote host) which we'll log and ignore as it means the socket
+                        // was already shut down.
+                        _socket.Shutdown(SocketShutdown.Both);
+                    }
+                    catch (SocketException ex)
+                    {
+                        _logger.LogInformation(ex, "Failure shutting down socket");
                     }
                 }
-                finally
-                {
-                    _ = _socketDisposeLock.Release();
-                }
+
+                _logger.LogDebug("[{SessionId}] Disposing socket.", SessionIdHex);
+                _socket.Dispose();
+                _logger.LogDebug("[{SessionId}] Disposed socket.", SessionIdHex);
+                _socket = null;
             }
         }
 
@@ -2016,25 +1907,6 @@ namespace Renci.SshNet
                         break;
                     }
 
-                    try
-                    {
-                        // Block until either data is available or the socket is closed
-                        var connectionClosedOrDataAvailable = socket.Poll(-1, SelectMode.SelectRead);
-                        if (connectionClosedOrDataAvailable && socket.Available == 0)
-                        {
-                            // connection with SSH server was closed or connection was reset
-                            break;
-                        }
-                    }
-                    catch (ObjectDisposedException)
-                    {
-                        // The socket was disposed by either:
-                        // * a call to Disconnect()
-                        // * a call to Dispose()
-                        // * a SSH_MSG_DISCONNECT received from server
-                        break;
-                    }
-
                     var message = ReceiveMessage(socket);
                     if (message is null)
                     {
@@ -2070,25 +1942,12 @@ namespace Renci.SshNet
         /// <param name="exp">The <see cref="Exception"/>.</param>
         private void RaiseError(Exception exp)
         {
-            var connectionException = exp as SshConnectionException;
-
             _logger.LogInformation(exp, "[{SessionId}] Raised exception", SessionIdHex);
 
-            if (_isDisconnecting)
+            if (_isDisconnecting && exp is SshConnectionException or ObjectDisposedException)
             {
-                // a connection exception which is raised while isDisconnecting is normal and
-                // should be ignored
-                if (connectionException != null)
-                {
-                    return;
-                }
-
-                // any timeout while disconnecting can be caused by loss of connectivity
-                // altogether and should be ignored
-                if (exp is SocketException socketException && socketException.SocketErrorCode == SocketError.TimedOut)
-                {
-                    return;
-                }
+                // Such an exception raised while isDisconnecting is expected and can be ignored.
+                return;
             }
 
             // "save" exception and set exception wait handle to ensure any waits are interrupted
@@ -2097,10 +1956,10 @@ namespace Renci.SshNet
 
             ErrorOccured?.Invoke(this, new ExceptionEventArgs(exp));
 
-            if (connectionException != null)
+            if (exp is SshConnectionException connectionException)
             {
                 _logger.LogInformation(exp, "[{SessionId}] Disconnecting after exception", SessionIdHex);
-                Disconnect(connectionException.DisconnectReason, exp.ToString());
+                Disconnect(connectionException.DisconnectReason, exp.Message);
             }
         }
 

src/Renci.SshNet/Sftp/Requests/SftpMkDirRequest.cs

@@ -8,7 +8,6 @@ namespace Renci.SshNet.Sftp.Requests
     internal sealed class SftpMkDirRequest : SftpRequest
     {
         private byte[] _path;
-        private byte[] _attributesBytes;
 
         public override SftpMessageTypes SftpMessageType
         {
@@ -23,18 +22,6 @@ namespace Renci.SshNet.Sftp.Requests
 
         public Encoding Encoding { get; private set; }
 
-        private SftpFileAttributes Attributes { get; set; }
-
-        private byte[] AttributesBytes
-        {
-            get
-            {
-                _attributesBytes ??= Attributes.GetBytes();
-
-                return _attributesBytes;
-            }
-        }
-
         /// <summary>
         /// Gets the size of the message in bytes.
         /// </summary>
@@ -48,36 +35,30 @@ namespace Renci.SshNet.Sftp.Requests
                 var capacity = base.BufferCapacity;
                 capacity += 4; // Path length
                 capacity += _path.Length; // Path
-                capacity += AttributesBytes.Length; // Attributes
+                capacity += 4; // Attributes
                 return capacity;
             }
         }
 
         public SftpMkDirRequest(uint protocolVersion, uint requestId, string path, Encoding encoding, Action<SftpStatusResponse> statusAction)
-            : this(protocolVersion, requestId, path, encoding, SftpFileAttributes.Empty, statusAction)
-        {
-        }
-
-        private SftpMkDirRequest(uint protocolVersion, uint requestId, string path, Encoding encoding, SftpFileAttributes attributes, Action<SftpStatusResponse> statusAction)
             : base(protocolVersion, requestId, statusAction)
         {
             Encoding = encoding;
             Path = path;
-            Attributes = attributes;
         }
 
         protected override void LoadData()
         {
             base.LoadData();
             _path = ReadBinary();
-            Attributes = ReadAttributes();
+            _ = ReadAttributes();
         }
 
         protected override void SaveData()
         {
             base.SaveData();
             WriteBinaryString(_path);
-            Write(AttributesBytes);
+            Write(0u); // empty attributes
         }
     }
 }

src/Renci.SshNet/Sftp/Requests/SftpOpenRequest.cs

@@ -9,7 +9,6 @@ namespace Renci.SshNet.Sftp.Requests
     {
         private readonly Action<SftpHandleResponse> _handleAction;
         private byte[] _fileName;
-        private byte[] _attributes;
 
         public override SftpMessageTypes SftpMessageType
         {
@@ -24,12 +23,6 @@ namespace Renci.SshNet.Sftp.Requests
 
         public Flags Flags { get; }
 
-        public SftpFileAttributes Attributes
-        {
-            get { return SftpFileAttributes.FromBytes(_attributes); }
-            private set { _attributes = value.GetBytes(); }
-        }
-
         public Encoding Encoding { get; }
 
         /// <summary>
@@ -46,23 +39,17 @@ namespace Renci.SshNet.Sftp.Requests
                 capacity += 4; // FileName length
                 capacity += _fileName.Length; // FileName
                 capacity += 4; // Flags
-                capacity += _attributes.Length; // Attributes
+                capacity += 4; // Attributes
                 return capacity;
             }
         }
 
         public SftpOpenRequest(uint protocolVersion, uint requestId, string fileName, Encoding encoding, Flags flags, Action<SftpHandleResponse> handleAction, Action<SftpStatusResponse> statusAction)
-            : this(protocolVersion, requestId, fileName, encoding, flags, SftpFileAttributes.Empty, handleAction, statusAction)
-        {
-        }
-
-        private SftpOpenRequest(uint protocolVersion, uint requestId, string fileName, Encoding encoding, Flags flags, SftpFileAttributes attributes, Action<SftpHandleResponse> handleAction, Action<SftpStatusResponse> statusAction)
             : base(protocolVersion, requestId, statusAction)
         {
             Encoding = encoding;
             Filename = fileName;
             Flags = flags;
-            Attributes = attributes;
 
             _handleAction = handleAction;
         }
@@ -79,7 +66,7 @@ namespace Renci.SshNet.Sftp.Requests
 
             WriteBinaryString(_fileName);
             Write((uint)Flags);
-            Write(_attributes);
+            Write(0u); // empty attributes
         }
 
         public override void Complete(SftpResponse response)

src/Renci.SshNet/Sftp/Responses/SftpVersionResponse.cs

@@ -11,14 +11,14 @@ namespace Renci.SshNet.Sftp.Responses
 
         public uint Version { get; set; }
 
-        public IDictionary<string, string> Extentions { get; set; }
+        public IDictionary<string, string> Extensions { get; set; }
 
         protected override void LoadData()
         {
             base.LoadData();
 
             Version = ReadUInt32();
-            Extentions = ReadExtensionPair();
+            Extensions = ReadExtensionPair();
         }
 
         protected override void SaveData()
@@ -27,9 +27,9 @@ namespace Renci.SshNet.Sftp.Responses
 
             Write(Version);
 
-            if (Extentions != null)
+            if (Extensions != null)
             {
-                Write(Extentions);
+                Write(Extensions);
             }
         }
     }

src/Renci.SshNet/Sftp/SftpFileAttributes.cs

@@ -1,7 +1,10 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
-using System.Globalization;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
+using System.Text;
 
 using Renci.SshNet.Common;
 
@@ -23,8 +26,8 @@ namespace Renci.SshNet.Sftp
         private const uint S_IFCHR = 0x2000; // character device
         private const uint S_IFIFO = 0x1000; // FIFO
         private const uint S_ISUID = 0x0800; // set UID bit
-        private const uint S_ISGID = 0x0400; // set-group-ID bit (see below)
-        private const uint S_ISVTX = 0x0200; // sticky bit (see below)
+        private const uint S_ISGID = 0x0400; // set-group-ID bit
+        private const uint S_ISVTX = 0x0200; // sticky bit
         private const uint S_IRUSR = 0x0100; // owner has read permission
         private const uint S_IWUSR = 0x0080; // owner has write permission
         private const uint S_IXUSR = 0x0040; // owner has execute permission
@@ -43,12 +46,7 @@ namespace Renci.SshNet.Sftp
         private readonly int _originalUserId;
         private readonly int _originalGroupId;
         private readonly uint _originalPermissions;
-        private readonly IDictionary<string, string> _originalExtensions;
-
-        private bool _isBitFiledsBitSet;
-        private bool _isUIDBitSet;
-        private bool _isGroupIDBitSet;
-        private bool _isStickyBitSet;
+        private readonly Dictionary<string, string>? _originalExtensions;
 
         internal bool IsLastAccessTimeChanged
         {
@@ -82,6 +80,7 @@ namespace Renci.SshNet.Sftp
 
         internal bool IsExtensionsChanged
         {
+            [MemberNotNullWhen(true, nameof(Extensions))]
             get { return _originalExtensions != null && Extensions != null && !_originalExtensions.SequenceEqual(Extensions); }
         }
 
@@ -169,7 +168,13 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if file represents a socket; otherwise, <see langword="false"/>.
         /// </value>
-        public bool IsSocket { get; private set; }
+        public bool IsSocket
+        {
+            get
+            {
+                return (Permissions & S_IFMT) == S_IFSOCK;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether file represents a symbolic link.
@@ -177,7 +182,13 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if file represents a symbolic link; otherwise, <see langword="false"/>.
         /// </value>
-        public bool IsSymbolicLink { get; private set; }
+        public bool IsSymbolicLink
+        {
+            get
+            {
+                return (Permissions & S_IFMT) == S_IFLNK;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether file represents a regular file.
@@ -185,7 +196,13 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if file represents a regular file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool IsRegularFile { get; private set; }
+        public bool IsRegularFile
+        {
+            get
+            {
+                return (Permissions & S_IFMT) == S_IFREG;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether file represents a block device.
@@ -193,7 +210,13 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if file represents a block device; otherwise, <see langword="false"/>.
         /// </value>
-        public bool IsBlockDevice { get; private set; }
+        public bool IsBlockDevice
+        {
+            get
+            {
+                return (Permissions & S_IFMT) == S_IFBLK;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether file represents a directory.
@@ -201,7 +224,13 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if file represents a directory; otherwise, <see langword="false"/>.
         /// </value>
-        public bool IsDirectory { get; private set; }
+        public bool IsDirectory
+        {
+            get
+            {
+                return (Permissions & S_IFMT) == S_IFDIR;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether file represents a character device.
@@ -209,7 +238,13 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if file represents a character device; otherwise, <see langword="false"/>.
         /// </value>
-        public bool IsCharacterDevice { get; private set; }
+        public bool IsCharacterDevice
+        {
+            get
+            {
+                return (Permissions & S_IFMT) == S_IFCHR;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether file represents a named pipe.
@@ -217,7 +252,88 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if file represents a named pipe; otherwise, <see langword="false"/>.
         /// </value>
-        public bool IsNamedPipe { get; private set; }
+        public bool IsNamedPipe
+        {
+            get
+            {
+                return (Permissions & S_IFMT) == S_IFIFO;
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether the setuid bit is set.
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if the setuid bit is set; otherwise, <see langword="false"/>.
+        /// </value>
+        public bool IsUIDBitSet
+        {
+            get
+            {
+                return (Permissions & S_ISUID) == S_ISUID;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_ISUID;
+                }
+                else
+                {
+                    Permissions &= ~S_ISUID;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether the setgid bit is set.
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if the setgid bit is set; otherwise, <see langword="false"/>.
+        /// </value>
+        public bool IsGroupIDBitSet
+        {
+            get
+            {
+                return (Permissions & S_ISGID) == S_ISGID;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_ISGID;
+                }
+                else
+                {
+                    Permissions &= ~S_ISGID;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether the sticky bit is set.
+        /// </summary>
+        /// <value>
+        /// <see langword="true"/> if the sticky bit is set; otherwise, <see langword="false"/>.
+        /// </value>
+        public bool IsStickyBitSet
+        {
+            get
+            {
+                return (Permissions & S_ISVTX) == S_ISVTX;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_ISVTX;
+                }
+                else
+                {
+                    Permissions &= ~S_ISVTX;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the owner can read from this file.
@@ -225,7 +341,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if owner can read from this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool OwnerCanRead { get; set; }
+        public bool OwnerCanRead
+        {
+            get
+            {
+                return (Permissions & S_IRUSR) == S_IRUSR;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IRUSR;
+                }
+                else
+                {
+                    Permissions &= ~S_IRUSR;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the owner can write into this file.
@@ -233,7 +366,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if owner can write into this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool OwnerCanWrite { get; set; }
+        public bool OwnerCanWrite
+        {
+            get
+            {
+                return (Permissions & S_IWUSR) == S_IWUSR;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IWUSR;
+                }
+                else
+                {
+                    Permissions &= ~S_IWUSR;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the owner can execute this file.
@@ -241,7 +391,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if owner can execute this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool OwnerCanExecute { get; set; }
+        public bool OwnerCanExecute
+        {
+            get
+            {
+                return (Permissions & S_IXUSR) == S_IXUSR;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IXUSR;
+                }
+                else
+                {
+                    Permissions &= ~S_IXUSR;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the group members can read from this file.
@@ -249,7 +416,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if group members can read from this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool GroupCanRead { get; set; }
+        public bool GroupCanRead
+        {
+            get
+            {
+                return (Permissions & S_IRGRP) == S_IRGRP;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IRGRP;
+                }
+                else
+                {
+                    Permissions &= ~S_IRGRP;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the group members can write into this file.
@@ -257,7 +441,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if group members can write into this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool GroupCanWrite { get; set; }
+        public bool GroupCanWrite
+        {
+            get
+            {
+                return (Permissions & S_IWGRP) == S_IWGRP;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IWGRP;
+                }
+                else
+                {
+                    Permissions &= ~S_IWGRP;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the group members can execute this file.
@@ -265,7 +466,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if group members can execute this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool GroupCanExecute { get; set; }
+        public bool GroupCanExecute
+        {
+            get
+            {
+                return (Permissions & S_IXGRP) == S_IXGRP;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IXGRP;
+                }
+                else
+                {
+                    Permissions &= ~S_IXGRP;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the others can read from this file.
@@ -273,7 +491,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if others can read from this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool OthersCanRead { get; set; }
+        public bool OthersCanRead
+        {
+            get
+            {
+                return (Permissions & S_IROTH) == S_IROTH;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IROTH;
+                }
+                else
+                {
+                    Permissions &= ~S_IROTH;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the others can write into this file.
@@ -281,7 +516,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if others can write into this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool OthersCanWrite { get; set; }
+        public bool OthersCanWrite
+        {
+            get
+            {
+                return (Permissions & S_IWOTH) == S_IWOTH;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IWOTH;
+                }
+                else
+                {
+                    Permissions &= ~S_IWOTH;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets or sets a value indicating whether the others can execute this file.
@@ -289,7 +541,24 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// <see langword="true"/> if others can execute this file; otherwise, <see langword="false"/>.
         /// </value>
-        public bool OthersCanExecute { get; set; }
+        public bool OthersCanExecute
+        {
+            get
+            {
+                return (Permissions & S_IXOTH) == S_IXOTH;
+            }
+            set
+            {
+                if (value)
+                {
+                    Permissions |= S_IXOTH;
+                }
+                else
+                {
+                    Permissions &= ~S_IXOTH;
+                }
+            }
+        }
 
         /// <summary>
         /// Gets the extensions.
@@ -297,165 +566,11 @@ namespace Renci.SshNet.Sftp
         /// <value>
         /// The extensions.
         /// </value>
-        public IDictionary<string, string> Extensions { get; private set; }
+        public IDictionary<string, string>? Extensions { get; }
 
-        internal uint Permissions
-        {
-            get
-            {
-                uint permission = 0;
+        internal uint Permissions { get; private set; }
 
-                if (_isBitFiledsBitSet)
-                {
-                    permission |= S_IFMT;
-                }
-
-                if (IsSocket)
-                {
-                    permission |= S_IFSOCK;
-                }
-
-                if (IsSymbolicLink)
-                {
-                    permission |= S_IFLNK;
-                }
-
-                if (IsRegularFile)
-                {
-                    permission |= S_IFREG;
-                }
-
-                if (IsBlockDevice)
-                {
-                    permission |= S_IFBLK;
-                }
-
-                if (IsDirectory)
-                {
-                    permission |= S_IFDIR;
-                }
-
-                if (IsCharacterDevice)
-                {
-                    permission |= S_IFCHR;
-                }
-
-                if (IsNamedPipe)
-                {
-                    permission |= S_IFIFO;
-                }
-
-                if (_isUIDBitSet)
-                {
-                    permission |= S_ISUID;
-                }
-
-                if (_isGroupIDBitSet)
-                {
-                    permission |= S_ISGID;
-                }
-
-                if (_isStickyBitSet)
-                {
-                    permission |= S_ISVTX;
-                }
-
-                if (OwnerCanRead)
-                {
-                    permission |= S_IRUSR;
-                }
-
-                if (OwnerCanWrite)
-                {
-                    permission |= S_IWUSR;
-                }
-
-                if (OwnerCanExecute)
-                {
-                    permission |= S_IXUSR;
-                }
-
-                if (GroupCanRead)
-                {
-                    permission |= S_IRGRP;
-                }
-
-                if (GroupCanWrite)
-                {
-                    permission |= S_IWGRP;
-                }
-
-                if (GroupCanExecute)
-                {
-                    permission |= S_IXGRP;
-                }
-
-                if (OthersCanRead)
-                {
-                    permission |= S_IROTH;
-                }
-
-                if (OthersCanWrite)
-                {
-                    permission |= S_IWOTH;
-                }
-
-                if (OthersCanExecute)
-                {
-                    permission |= S_IXOTH;
-                }
-
-                return permission;
-            }
-            private set
-            {
-                _isBitFiledsBitSet = (value & S_IFMT) == S_IFMT;
-
-                IsSocket = (value & S_IFSOCK) == S_IFSOCK;
-
-                IsSymbolicLink = (value & S_IFLNK) == S_IFLNK;
-
-                IsRegularFile = (value & S_IFREG) == S_IFREG;
-
-                IsBlockDevice = (value & S_IFBLK) == S_IFBLK;
-
-                IsDirectory = (value & S_IFDIR) == S_IFDIR;
-
-                IsCharacterDevice = (value & S_IFCHR) == S_IFCHR;
-
-                IsNamedPipe = (value & S_IFIFO) == S_IFIFO;
-
-                _isUIDBitSet = (value & S_ISUID) == S_ISUID;
-
-                _isGroupIDBitSet = (value & S_ISGID) == S_ISGID;
-
-                _isStickyBitSet = (value & S_ISVTX) == S_ISVTX;
-
-                OwnerCanRead = (value & S_IRUSR) == S_IRUSR;
-
-                OwnerCanWrite = (value & S_IWUSR) == S_IWUSR;
-
-                OwnerCanExecute = (value & S_IXUSR) == S_IXUSR;
-
-                GroupCanRead = (value & S_IRGRP) == S_IRGRP;
-
-                GroupCanWrite = (value & S_IWGRP) == S_IWGRP;
-
-                GroupCanExecute = (value & S_IXGRP) == S_IXGRP;
-
-                OthersCanRead = (value & S_IROTH) == S_IROTH;
-
-                OthersCanWrite = (value & S_IWOTH) == S_IWOTH;
-
-                OthersCanExecute = (value & S_IXOTH) == S_IXOTH;
-            }
-        }
-
-        private SftpFileAttributes()
-        {
-        }
-
-        internal SftpFileAttributes(DateTime lastAccessTimeUtc, DateTime lastWriteTimeUtc, long size, int userId, int groupId, uint permissions, IDictionary<string, string> extensions)
+        internal SftpFileAttributes(DateTime lastAccessTimeUtc, DateTime lastWriteTimeUtc, long size, int userId, int groupId, uint permissions, Dictionary<string, string>? extensions)
         {
             LastAccessTimeUtc = _originalLastAccessTimeUtc = lastAccessTimeUtc;
             LastWriteTimeUtc = _originalLastWriteTimeUtc = lastWriteTimeUtc;
@@ -467,31 +582,118 @@ namespace Renci.SshNet.Sftp
         }
 
         /// <summary>
-        /// Sets the permissions.
+        /// Sets the POSIX permissions for this file.
         /// </summary>
-        /// <param name="mode">The mode.</param>
+        /// <param name="mode">
+        /// The permission mode as an octal number (e.g., <c>755</c>, <c>644</c>, <c>1777</c>).
+        /// </param>
+        /// <exception cref="ArgumentOutOfRangeException">
+        /// <paramref name="mode"/> has more than 4 digits or cannot be interpreted as an octal number.
+        /// </exception>
         public void SetPermissions(short mode)
         {
-            if (mode is < 0 or > 999)
+            var special = (uint)Math.DivRem(mode, 1000, out var userGroupOther);
+
+            var user = (uint)Math.DivRem(userGroupOther, 100, out var groupOther);
+
+            var group = (uint)Math.DivRem(groupOther, 10, out var iOther);
+
+            var other = (uint)iOther;
+
+            if ((special & ~7u) != 0 || (user & ~7u) != 0 || (group & ~7u) != 0 || (other & ~7u) != 0)
             {
                 throw new ArgumentOutOfRangeException(nameof(mode));
             }
 
-            var modeBytes = mode.ToString(CultureInfo.InvariantCulture).PadLeft(3, '0').ToCharArray();
+            Permissions = (Permissions & ~0xFFFu) | (special << 9) | (user << 6) | (group << 3) | other;
+        }
 
-            var permission = ((modeBytes[0] & 0x0F) * 8 * 8) + ((modeBytes[1] & 0x0F) * 8) + (modeBytes[2] & 0x0F);
+        /// <inheritdoc/>
+        public override string? ToString()
+        {
+            var sb = new StringBuilder();
 
-            OwnerCanRead = (permission & S_IRUSR) == S_IRUSR;
-            OwnerCanWrite = (permission & S_IWUSR) == S_IWUSR;
-            OwnerCanExecute = (permission & S_IXUSR) == S_IXUSR;
+            if (Permissions != default)
+            {
+                AppendPermissionsString(sb);
+                sb.Append(' ');
+            }
 
-            GroupCanRead = (permission & S_IRGRP) == S_IRGRP;
-            GroupCanWrite = (permission & S_IWGRP) == S_IWGRP;
-            GroupCanExecute = (permission & S_IXGRP) == S_IXGRP;
+            if (Size != -1)
+            {
+                sb.AppendFormat("Size: {0} ", Size);
+            }
 
-            OthersCanRead = (permission & S_IROTH) == S_IROTH;
-            OthersCanWrite = (permission & S_IWOTH) == S_IWOTH;
-            OthersCanExecute = (permission & S_IXOTH) == S_IXOTH;
+            if (LastWriteTime != default)
+            {
+                sb.AppendFormat("LastWriteTime: {0:s} ", LastWriteTime);
+            }
+
+            if (sb.Length > 0)
+            {
+                if (sb[sb.Length - 1] == ' ')
+                {
+                    sb.Length--;
+                }
+
+                Debug.Assert(sb.Length > 0);
+                Debug.Assert(sb[^1] != ' ');
+
+                return sb.ToString();
+            }
+
+            return base.ToString();
+        }
+
+        private void AppendPermissionsString(StringBuilder sb)
+        {
+            // https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ls.html
+
+            sb.Append(
+                IsRegularFile ? '-' :
+                IsDirectory ? 'd' :
+                IsSymbolicLink ? 'l' :
+                IsNamedPipe ? 'p' :
+                IsSocket ? 's' :
+                IsCharacterDevice ? 'c' :
+                IsBlockDevice ? 'b' :
+                '-');
+
+            sb.Append(OwnerCanRead ? 'r' : '-');
+            sb.Append(OwnerCanWrite ? 'w' : '-');
+
+            if (OwnerCanExecute)
+            {
+                sb.Append(IsUIDBitSet ? 's' : 'x');
+            }
+            else
+            {
+                sb.Append(IsUIDBitSet ? 'S' : '-');
+            }
+
+            sb.Append(GroupCanRead ? 'r' : '-');
+            sb.Append(GroupCanWrite ? 'w' : '-');
+
+            if (GroupCanExecute)
+            {
+                sb.Append(IsGroupIDBitSet ? 's' : 'x');
+            }
+            else
+            {
+                sb.Append(IsGroupIDBitSet ? 'S' : '-');
+            }
+
+            sb.Append(OthersCanRead ? 'r' : '-');
+            sb.Append(OthersCanWrite ? 'w' : '-');
+
+            if (OthersCanExecute)
+            {
+                sb.Append(IsStickyBitSet ? 't' : 'x');
+            }
+            else
+            {
+                sb.Append(IsStickyBitSet ? 'T' : '-');
+            }
         }
 
         /// <summary>
@@ -506,7 +708,7 @@ namespace Renci.SshNet.Sftp
             {
                 uint flag = 0;
 
-                if (IsSizeChanged && IsRegularFile)
+                if (IsSizeChanged)
                 {
                     flag |= 0x00000001;
                 }
@@ -533,7 +735,7 @@ namespace Renci.SshNet.Sftp
 
                 stream.Write(flag);
 
-                if (IsSizeChanged && IsRegularFile)
+                if (IsSizeChanged)
                 {
                     stream.Write((ulong)Size);
                 }
@@ -551,9 +753,9 @@ namespace Renci.SshNet.Sftp
 
                 if (IsLastAccessTimeChanged || IsLastWriteTimeChanged)
                 {
-                    var time = (uint)((LastAccessTimeUtc.ToFileTimeUtc() / 10000000) - 11644473600);
+                    var time = (uint)((DateTimeOffset)DateTime.SpecifyKind(LastAccessTimeUtc, DateTimeKind.Utc)).ToUnixTimeSeconds();
                     stream.Write(time);
-                    time = (uint)((LastWriteTimeUtc.ToFileTimeUtc() / 10000000) - 11644473600);
+                    time = (uint)((DateTimeOffset)DateTime.SpecifyKind(LastWriteTimeUtc, DateTimeKind.Utc)).ToUnixTimeSeconds();
                     stream.Write(time);
                 }
 
@@ -561,12 +763,8 @@ namespace Renci.SshNet.Sftp
                 {
                     foreach (var item in Extensions)
                     {
-                        /*
-                         * TODO: we write as ASCII but read as UTF8 !!!
-                         */
-
-                        stream.Write(item.Key, SshData.Ascii);
-                        stream.Write(item.Value, SshData.Ascii);
+                        stream.Write(item.Key, Encoding.UTF8);
+                        stream.Write(item.Value, Encoding.UTF8);
                     }
                 }
 
@@ -574,8 +772,6 @@ namespace Renci.SshNet.Sftp
             }
         }
 
-        internal static readonly SftpFileAttributes Empty = new SftpFileAttributes();
-
         internal static SftpFileAttributes FromBytes(SshDataStream stream)
         {
             const uint SSH_FILEXFER_ATTR_SIZE = 0x00000001;
@@ -592,7 +788,7 @@ namespace Renci.SshNet.Sftp
             uint permissions = 0;
             DateTime accessTime;
             DateTime modifyTime;
-            Dictionary<string, string> extensions = null;
+            Dictionary<string, string>? extensions = null;
 
             if ((flag & SSH_FILEXFER_ATTR_SIZE) == SSH_FILEXFER_ATTR_SIZE)
             {
@@ -613,12 +809,8 @@ namespace Renci.SshNet.Sftp
 
             if ((flag & SSH_FILEXFER_ATTR_ACMODTIME) == SSH_FILEXFER_ATTR_ACMODTIME)
             {
-                // The incoming times are "Unix times", so they're already in UTC.  We need to preserve that
-                // to avoid losing information in a local time conversion during the "fall back" hour in DST.
-                var time = stream.ReadUInt32();
-                accessTime = DateTime.FromFileTimeUtc((time + 11644473600) * 10000000);
-                time = stream.ReadUInt32();
-                modifyTime = DateTime.FromFileTimeUtc((time + 11644473600) * 10000000);
+                accessTime = DateTimeOffset.FromUnixTimeSeconds(stream.ReadUInt32()).UtcDateTime;
+                modifyTime = DateTimeOffset.FromUnixTimeSeconds(stream.ReadUInt32()).UtcDateTime;
             }
             else
             {
@@ -632,8 +824,8 @@ namespace Renci.SshNet.Sftp
                 extensions = new Dictionary<string, string>(extendedCount);
                 for (var i = 0; i < extendedCount; i++)
                 {
-                    var extensionName = stream.ReadString(SshData.Utf8);
-                    var extensionData = stream.ReadString(SshData.Utf8);
+                    var extensionName = stream.ReadString(Encoding.UTF8);
+                    var extensionData = stream.ReadString(Encoding.UTF8);
                     extensions.Add(extensionName, extensionData);
                 }
             }

src/Renci.SshNet/Sftp/SftpSession.cs

@@ -371,7 +371,7 @@ namespace Renci.SshNet.Sftp
                 if (response is SftpVersionResponse versionResponse)
                 {
                     ProtocolVersion = versionResponse.Version;
-                    _supportedExtensions = versionResponse.Extentions;
+                    _supportedExtensions = versionResponse.Extensions;
 
                     _ = _sftpVersionConfirmed.Set();
                 }

test/Renci.SshNet.IntegrationTests/Common/RemoteSshdConfigExtensions.cs

@@ -23,6 +23,7 @@ namespace Renci.SshNet.IntegrationTests.Common
                             .ClearHostKeyAlgorithms()
                             .ClearPublicKeyAcceptedAlgorithms()
                             .ClearMessageAuthenticationCodeAlgorithms()
+                            .PermitTTY(true)
                             .WithUsePAM(true)
                             .Update()
                             .Restart();

test/Renci.SshNet.IntegrationTests/TestsFixtures/InfrastructureFixture.cs

@@ -1,4 +1,6 @@
-using DotNet.Testcontainers.Builders;
+using System.Runtime.InteropServices;
+
+using DotNet.Testcontainers.Builders;
 using DotNet.Testcontainers.Containers;
 using DotNet.Testcontainers.Images;
 
@@ -28,26 +30,27 @@ namespace Renci.SshNet.IntegrationTests.TestsFixtures
 
         private IFutureDockerImage _sshServerImage;
 
-        public string SshServerHostName { get; set; }
+        public string SshServerHostName { get; private set; }
 
-        public ushort SshServerPort { get; set; }
+        public ushort SshServerPort { get; private set; }
 
-        public SshUser AdminUser = new SshUser("sshnetadm", "ssh4ever");
+        public SshUser AdminUser { get; } = new SshUser("sshnetadm", "ssh4ever");
 
-        public SshUser User = new SshUser("sshnet", "ssh4ever");
+        public SshUser User { get; } = new SshUser("sshnet", "ssh4ever");
 
         public async Task InitializeAsync()
         {
-            // for the .NET Framework Tests in CI, the Container is set up in WSL2 with Podman
-#if NETFRAMEWORK
-            if (Environment.GetEnvironmentVariable("CI") == "true")
+#pragma warning disable MA0144 // use System.OperatingSystem to check the current OS
+            // for the Windows Tests in CI, the Container is set up in WSL2 with Podman
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
+                Environment.GetEnvironmentVariable("CI") == "true")
+#pragma warning restore MA0144 // use System.OperatingSystem to check the current OS
             {
                 SshServerPort = 2222;
-                SshServerHostName = "localhost";
+                SshServerHostName = "127.0.0.1";
                 await Task.Delay(1_000);
                 return;
             }
-#endif
 
             var containerLogger = _loggerFactory.CreateLogger("testcontainers");
 

test/Renci.SshNet.Tests/Classes/AbstractionsTest.cs

@@ -9,12 +9,6 @@ namespace Renci.SshNet.Tests.Classes
     [TestClass]
     public class AbstractionsTest
     {
-        [TestMethod]
-        public void SocketAbstraction_CanWrite_ShouldReturnFalseWhenSocketIsNull()
-        {
-            Assert.IsFalse(SocketAbstraction.CanWrite(null));
-        }
-
         [TestMethod]
         public void CryptoAbstraction_GenerateRandom_ShouldPerformNoOpWhenDataIsZeroLength()
         {

test/Renci.SshNet.Tests/Classes/SessionTest_Connected_ConnectionReset.cs

@@ -64,8 +64,6 @@ namespace Renci.SshNet.Tests.Classes
 
             var connectionException = (SshConnectionException)exception;
             Assert.AreEqual(DisconnectReason.ConnectionLost, connectionException.DisconnectReason);
-            Assert.IsNull(connectionException.InnerException);
-            Assert.AreEqual("An established connection was aborted by the server.", connectionException.Message);
         }
 
         [TestMethod]
@@ -137,45 +135,29 @@ namespace Renci.SshNet.Tests.Classes
         public void ISession_WaitOnHandle_WaitHandle_ShouldThrowSshConnectionException()
         {
             var session = (ISession)Session;
-            var waitHandle = new ManualResetEvent(false);
+            using var waitHandle = new ManualResetEvent(false);
 
-            try
-            {
-                session.WaitOnHandle(waitHandle);
-                Assert.Fail();
-            }
-            catch (SshConnectionException ex)
-            {
-                Assert.AreEqual("An established connection was aborted by the server.", ex.Message);
-                Assert.IsNull(ex.InnerException);
-                Assert.AreEqual(DisconnectReason.ConnectionLost, ex.DisconnectReason);
-            }
+            var ex = Assert.ThrowsExactly<SshConnectionException>(() => session.WaitOnHandle(waitHandle));
+
+            Assert.AreEqual(DisconnectReason.ConnectionLost, ex.DisconnectReason);
         }
 
         [TestMethod]
         public void ISession_WaitOnHandle_WaitHandleAndTimeout_ShouldThrowSshConnectionException()
         {
             var session = (ISession)Session;
-            var waitHandle = new ManualResetEvent(false);
+            using var waitHandle = new ManualResetEvent(false);
 
-            try
-            {
-                session.WaitOnHandle(waitHandle, Timeout.InfiniteTimeSpan);
-                Assert.Fail();
-            }
-            catch (SshConnectionException ex)
-            {
-                Assert.AreEqual(DisconnectReason.ConnectionLost, ex.DisconnectReason);
-                Assert.IsNull(ex.InnerException);
-                Assert.AreEqual("An established connection was aborted by the server.", ex.Message);
-            }
+            var ex = Assert.ThrowsExactly<SshConnectionException>(() => session.WaitOnHandle(waitHandle));
+
+            Assert.AreEqual(DisconnectReason.ConnectionLost, ex.DisconnectReason);
         }
 
         [TestMethod]
         public void ISession_TryWait_WaitHandleAndTimeout_ShouldReturnDisconnected()
         {
             var session = (ISession)Session;
-            var waitHandle = new ManualResetEvent(false);
+            using var waitHandle = new ManualResetEvent(false);
 
             var result = session.TryWait(waitHandle, Timeout.InfiniteTimeSpan);
 
@@ -186,7 +168,7 @@ namespace Renci.SshNet.Tests.Classes
         public void ISession_TryWait_WaitHandleAndTimeoutAndException_ShouldReturnDisconnected()
         {
             var session = (ISession)Session;
-            var waitHandle = new ManualResetEvent(false);
+            using var waitHandle = new ManualResetEvent(false);
 
             var result = session.TryWait(waitHandle, Timeout.InfiniteTimeSpan, out var exception);
 

test/Renci.SshNet.Tests/Classes/SessionTest_Connected_ServerSendsBadPacket.cs

@@ -91,13 +91,20 @@ namespace Renci.SshNet.Tests.Classes
         }
 
         [TestMethod]
-        public void ReceiveOnServerSocketShouldReturnZero()
+        public void ServerShouldBeDisconnected()
         {
-            var buffer = new byte[1];
+            try
+            {
+                var buffer = new byte[1];
 
-            var actual = ServerSocket.Receive(buffer, 0, buffer.Length, SocketFlags.None);
+                var actual = ServerSocket.Receive(buffer, 0, buffer.Length, SocketFlags.None);
 
-            Assert.AreEqual(0, actual);
+                Assert.AreEqual(0, actual); // FIN
+            }
+            catch (SocketException sx)
+            {
+                Assert.AreEqual(SocketError.ConnectionReset, sx.SocketErrorCode); // RST
+            }
         }
 
         [TestMethod]

test/Renci.SshNet.Tests/Classes/Sftp/Requests/SftpFSetStatRequestTest.cs

@@ -8,6 +8,7 @@ using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Requests;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp.Requests
 {
@@ -29,7 +30,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp.Requests
             _requestId = (uint)random.Next(0, int.MaxValue);
             _handle = new byte[random.Next(1, 10)];
             random.NextBytes(_handle);
-            _attributes = SftpFileAttributes.Empty;
+            _attributes = SftpFileAttributesBuilder.Empty;
             _attributesBytes = _attributes.GetBytes();
         }
 

test/Renci.SshNet.Tests/Classes/Sftp/Requests/SftpMkDirRequestTest.cs

@@ -10,6 +10,7 @@ using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Requests;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp.Requests
 {
@@ -34,7 +35,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp.Requests
             _encoding = Encoding.Unicode;
             _path = random.Next().ToString(CultureInfo.InvariantCulture);
             _pathBytes = _encoding.GetBytes(_path);
-            _attributes = SftpFileAttributes.Empty;
+            _attributes = SftpFileAttributesBuilder.Empty;
             _attributesBytes = _attributes.GetBytes();
         }
 

test/Renci.SshNet.Tests/Classes/Sftp/Requests/SftpOpenRequestTest.cs

@@ -10,6 +10,7 @@ using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Requests;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp.Requests
 {
@@ -36,7 +37,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp.Requests
             _filename = random.Next().ToString(CultureInfo.InvariantCulture);
             _filenameBytes = _encoding.GetBytes(_filename);
             _flags = Flags.Read;
-            _attributes = SftpFileAttributes.Empty;
+            _attributes = SftpFileAttributesBuilder.Empty;
             _attributesBytes = _attributes.GetBytes();
         }
 

test/Renci.SshNet.Tests/Classes/Sftp/Requests/SftpSetStatRequestTest.cs

@@ -10,6 +10,7 @@ using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Requests;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp.Requests
 {
@@ -34,7 +35,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp.Requests
             _encoding = Encoding.Unicode;
             _path = random.Next().ToString(CultureInfo.InvariantCulture);
             _pathBytes = _encoding.GetBytes(_path);
-            _attributes = SftpFileAttributes.Empty;
+            _attributes = SftpFileAttributesBuilder.Empty;
             _attributesBytes = _attributes.GetBytes();
         }
 

test/Renci.SshNet.Tests/Classes/Sftp/Responses/SftpAttrsResponseTest.cs

@@ -5,6 +5,7 @@ using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp.Responses
 {
@@ -61,7 +62,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp.Responses
 
         private SftpFileAttributes CreateSftpFileAttributes()
         {
-            var attributes = SftpFileAttributes.Empty;
+            var attributes = SftpFileAttributesBuilder.Empty;
             attributes.GroupId = _random.Next();
             attributes.LastAccessTime = new DateTime(2014, 8, 23, 17, 43, 50, DateTimeKind.Local);
             attributes.LastWriteTime = new DateTime(2013, 7, 22, 16, 40, 42, DateTimeKind.Local);

test/Renci.SshNet.Tests/Classes/Sftp/SftpFileAttributesTest.cs

@@ -0,0 +1,223 @@
+using System;
+using System.Buffers.Binary;
+
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+using Renci.SshNet.Common;
+using Renci.SshNet.Sftp;
+
+namespace Renci.SshNet.Tests.Classes.Sftp
+{
+    [TestClass]
+    public class SftpFileAttributesTest
+    {
+        [TestMethod]
+        [DataRow(0xC000u, true, false, false, false, false, false, false)] // Socket
+        [DataRow(0xA000u, false, true, false, false, false, false, false)] // Symbolic link
+        [DataRow(0x8000u, false, false, true, false, false, false, false)] // Regular file
+        [DataRow(0x6000u, false, false, false, true, false, false, false)] // Block device
+        [DataRow(0x4000u, false, false, false, false, true, false, false)] // Directory
+        [DataRow(0x2000u, false, false, false, false, false, true, false)] // Character device
+        [DataRow(0x1000u, false, false, false, false, false, false, true)] // Named pipe
+        public void FileTypePropertiesAreMutuallyExclusive(
+            uint permissions,
+            bool isSocket,
+            bool isSymbolicLink,
+            bool isRegularFile,
+            bool isBlockDevice,
+            bool isDirectory,
+            bool isCharacterDevice,
+            bool isNamedPipe)
+        {
+            var attributeBytes = new byte[8];
+            attributeBytes[3] = 0x4; // SSH_FILEXFER_ATTR_PERMISSIONS
+            BinaryPrimitives.WriteUInt32BigEndian(attributeBytes.AsSpan(4), permissions);
+
+            var attributes = SftpFileAttributes.FromBytes(attributeBytes);
+
+            Assert.AreEqual(isSocket, attributes.IsSocket);
+            Assert.AreEqual(isSymbolicLink, attributes.IsSymbolicLink);
+            Assert.AreEqual(isRegularFile, attributes.IsRegularFile);
+            Assert.AreEqual(isBlockDevice, attributes.IsBlockDevice);
+            Assert.AreEqual(isDirectory, attributes.IsDirectory);
+            Assert.AreEqual(isCharacterDevice, attributes.IsCharacterDevice);
+            Assert.AreEqual(isNamedPipe, attributes.IsNamedPipe);
+        }
+
+        [TestMethod]
+        public void FromBytesGetBytes()
+        {
+            // 81a4 in hex = 100644 in octal
+            var attributes = SftpFileAttributes.FromBytes([0, 0, 0, 0x4, 0, 0, 0x81, 0xa4]);
+
+            Assert.IsTrue(attributes.IsRegularFile);
+
+            Assert.IsFalse(attributes.IsUIDBitSet);
+            Assert.IsFalse(attributes.IsGroupIDBitSet);
+            Assert.IsFalse(attributes.IsStickyBitSet);
+            Assert.IsTrue(attributes.OwnerCanRead);
+            Assert.IsTrue(attributes.OwnerCanWrite);
+            Assert.IsFalse(attributes.OwnerCanExecute);
+            Assert.IsTrue(attributes.GroupCanRead);
+            Assert.IsFalse(attributes.GroupCanWrite);
+            Assert.IsFalse(attributes.GroupCanExecute);
+            Assert.IsTrue(attributes.OthersCanRead);
+            Assert.IsFalse(attributes.OthersCanWrite);
+            Assert.IsFalse(attributes.OthersCanExecute);
+
+            Assert.AreEqual(-1, attributes.Size); // Erm, OK?
+            Assert.AreEqual(-1, attributes.UserId);
+            Assert.AreEqual(-1, attributes.GroupId);
+
+            Assert.AreEqual(default, attributes.LastAccessTimeUtc);
+            Assert.AreEqual(DateTimeKind.Utc, attributes.LastAccessTimeUtc.Kind);
+
+            Assert.AreEqual(default, attributes.LastWriteTimeUtc);
+            Assert.AreEqual(DateTimeKind.Utc, attributes.LastWriteTimeUtc.Kind);
+
+            Assert.AreEqual("-rw-r--r--", attributes.ToString());
+
+            // No changes
+            CollectionAssert.AreEqual(
+                new byte[] { 0, 0, 0, 0 },
+                attributes.GetBytes());
+
+
+            // Permissions change
+            attributes.IsUIDBitSet = true;
+            attributes.OwnerCanExecute = true;
+
+            CollectionAssert.AreEqual(
+                new byte[] { 0, 0, 0, 0x4, 0, 0, 0x89, 0xe4 },
+                attributes.GetBytes());
+
+            Assert.AreEqual("-rwsr--r--", attributes.ToString());
+
+            // Size change
+            attributes.Size = 123;
+
+            CollectionAssert.AreEqual(
+                new byte[] {
+                    0, 0, 0, 0x1 | 0x4,
+                    0, 0, 0, 0, 0, 0, 0, 123,
+                    0, 0, 0x89, 0xe4 },
+                attributes.GetBytes());
+
+            Assert.IsTrue(attributes.ToString().StartsWith("-rwsr--r-- Size: ", StringComparison.Ordinal));
+
+            // Uid/gid change
+            attributes.UserId = 99;
+            attributes.GroupId = 66;
+
+            CollectionAssert.AreEqual(
+                new byte[] {
+                    0, 0, 0, 0x1 | 0x2 | 0x4,
+                    0, 0, 0, 0, 0, 0, 0, 123,
+                    0, 0, 0, 99, 0, 0, 0, 66,
+                    0, 0, 0x89, 0xe4 },
+                attributes.GetBytes());
+
+
+            // Access/mod time change
+            attributes.LastAccessTimeUtc = new DateTime(2025, 08, 10, 17, 51, 37, DateTimeKind.Unspecified);
+            attributes.LastWriteTime = new DateTimeOffset(2016, 12, 02, 13, 18, 20, TimeSpan.FromHours(3)).LocalDateTime;
+
+            var expectedTimeBytes = new byte[8];
+            BinaryPrimitives.WriteUInt32BigEndian(expectedTimeBytes, 1754848297);
+            BinaryPrimitives.WriteUInt32BigEndian(expectedTimeBytes.AsSpan(4), 1480673900);
+
+            CollectionAssert.AreEqual(
+                new byte[] {
+                    0, 0, 0, 0x1 | 0x2 | 0x4 | 0x8,
+                    0, 0, 0, 0, 0, 0, 0, 123,
+                    0, 0, 0, 99, 0, 0, 0, 66,
+                    0, 0, 0x89, 0xe4
+                }.Concat(expectedTimeBytes),
+                attributes.GetBytes());
+
+            Assert.AreEqual(new DateTime(2016, 12, 02, 10, 18, 20, DateTimeKind.Utc), attributes.LastWriteTimeUtc);
+            Assert.AreEqual(DateTimeKind.Utc, attributes.LastWriteTimeUtc.Kind);
+
+            var attributesString = attributes.ToString();
+            Assert.IsTrue(attributesString.StartsWith("-rwsr--r-- Size: ", StringComparison.Ordinal));
+            Assert.Contains(" LastWriteTime: ", attributesString, StringComparison.CurrentCulture);
+        }
+
+        [TestMethod]
+        [DataRow((short)8888)]
+        [DataRow((short)10000)]
+        [DataRow((short)8000)]
+        [DataRow((short)0080)]
+        [DataRow((short)0008)]
+        [DataRow((short)1797)]
+        [DataRow((short)-1)]
+        [DataRow(short.MaxValue)]
+        public void SetPermissions_InvalidMode_ThrowsArgumentOutOfRangeException(short mode)
+        {
+            var attributes = SftpFileAttributes.FromBytes([0, 0, 0, 0]);
+
+            var ex = Assert.Throws<ArgumentOutOfRangeException>(() => attributes.SetPermissions(mode));
+            Assert.AreEqual("mode", ex.ParamName);
+        }
+
+        [TestMethod]
+        [DataRow((short)0777, false, false, false, true, true, true, true, true, true, true, true, true)]
+        [DataRow((short)0755, false, false, false, true, true, true, true, false, true, true, false, true)]
+        [DataRow((short)0644, false, false, false, true, true, false, true, false, false, true, false, false)]
+        [DataRow((short)0444, false, false, false, true, false, false, true, false, false, true, false, false)]
+        [DataRow((short)0000, false, false, false, false, false, false, false, false, false, false, false, false)]
+        [DataRow((short)4700, true, false, false, true, true, true, false, false, false, false, false, false)]
+        [DataRow((short)3001, false, true, true, false, false, false, false, false, false, false, false, true)]
+        [DataRow((short)7777, true, true, true, true, true, true, true, true, true, true, true, true)]
+        public void SetPermissions_ValidMode(
+            short mode,
+            bool setUid, bool setGid, bool sticky,
+            bool ownerRead, bool ownerWrite, bool ownerExec,
+            bool groupRead, bool groupWrite, bool groupExec,
+            bool othersRead, bool othersWrite, bool othersExec)
+        {
+            var attributes = SftpFileAttributes.FromBytes([0, 0, 0, 0]);
+
+            attributes.SetPermissions(mode);
+
+            Assert.AreEqual(setUid, attributes.IsUIDBitSet);
+            Assert.AreEqual(setGid, attributes.IsGroupIDBitSet);
+            Assert.AreEqual(sticky, attributes.IsStickyBitSet);
+            Assert.AreEqual(ownerRead, attributes.OwnerCanRead);
+            Assert.AreEqual(ownerWrite, attributes.OwnerCanWrite);
+            Assert.AreEqual(ownerExec, attributes.OwnerCanExecute);
+            Assert.AreEqual(groupRead, attributes.GroupCanRead);
+            Assert.AreEqual(groupWrite, attributes.GroupCanWrite);
+            Assert.AreEqual(groupExec, attributes.GroupCanExecute);
+            Assert.AreEqual(othersRead, attributes.OthersCanRead);
+            Assert.AreEqual(othersWrite, attributes.OthersCanWrite);
+            Assert.AreEqual(othersExec, attributes.OthersCanExecute);
+        }
+
+        [TestMethod]
+        [DataRow(0xC000u, (short)1770, "srwxrwx--T")] // Socket
+        [DataRow(0xA000u, (short)2707, "lrwx--Srwx")] // Symbolic link
+        [DataRow(0x8000u, (short)4755, "-rwsr-xr-x")] // Regular file
+        [DataRow(0x8000u, (short)4644, "-rwSr--r--")] // Regular file
+        [DataRow(0x6000u, (short)2711, "brwx--s--x")] // Block device
+        [DataRow(0x4000u, (short)1777, "drwxrwxrwt")] // Directory
+        [DataRow(0x4000u, (short)1776, "drwxrwxrwT")] // Directory
+        [DataRow(0x2000u, (short)0660, "crw-rw----")] // Character device
+        [DataRow(0x1000u, (short)0022, "p----w--w-")] // Named pipe
+        public void ToStringWithPermissions(
+            uint fileType,
+            short permissions,
+            string expected)
+        {
+            var attributeBytes = new byte[8];
+            attributeBytes[3] = 0x4; // SSH_FILEXFER_ATTR_PERMISSIONS
+            BinaryPrimitives.WriteUInt32BigEndian(attributeBytes.AsSpan(4), fileType);
+
+            var attributes = SftpFileAttributes.FromBytes(attributeBytes);
+
+            attributes.SetPermissions(permissions);
+
+            Assert.AreEqual(expected, attributes.ToString());
+        }
+    }
+}

test/Renci.SshNet.Tests/Classes/Sftp/SftpFileReaderTestBase.cs

@@ -41,12 +41,6 @@ namespace Renci.SshNet.Tests.Classes.Sftp
 
         protected abstract void Act();
 
-        protected static SftpFileAttributes CreateSftpFileAttributes(long size)
-        {
-            var utcDefault = DateTime.SpecifyKind(default, DateTimeKind.Utc);
-            return new SftpFileAttributes(utcDefault, utcDefault, size, default, default, default, null);
-        }
-
         protected static byte[] CreateByteArray(Random random, int length)
         {
             var chunk = new byte[length];

test/Renci.SshNet.Tests/Classes/Sftp/SftpSessionTest_Connected_RequestRead.cs

@@ -12,6 +12,7 @@ using Renci.SshNet.Channels;
 using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp
 {
@@ -73,7 +74,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp
             _sftpNameResponse = new SftpNameResponseBuilder().WithProtocolVersion(_protocolVersion)
                                                              .WithResponseId(1)
                                                              .WithEncoding(_encoding)
-                                                             .WithFile("XYZ", SftpFileAttributes.Empty)
+                                                             .WithFile("XYZ", SftpFileAttributesBuilder.Empty)
                                                              .Build();
 
             #endregion SftpSession.Connect()

test/Renci.SshNet.Tests/Classes/Sftp/SftpSessionTest_Connected_RequestStatVfs.cs

@@ -10,6 +10,7 @@ using Renci.SshNet.Channels;
 using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp
 {
@@ -70,7 +71,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp
             _sftpNameResponse = new SftpNameResponseBuilder().WithProtocolVersion(_protocolVersion)
                                                              .WithResponseId(1U)
                                                              .WithEncoding(_encoding)
-                                                             .WithFile("ABC", SftpFileAttributes.Empty)
+                                                             .WithFile("ABC", SftpFileAttributesBuilder.Empty)
                                                              .Build();
 
             #endregion SftpSession.Connect()

test/Renci.SshNet.Tests/Classes/Sftp/SftpSessionTest_DataReceived_MultipleSftpMessagesInSingleSshDataMessage.cs

@@ -11,6 +11,7 @@ using Renci.SshNet.Channels;
 using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp
 {
@@ -75,7 +76,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp
             _sftpNameResponse = new SftpNameResponseBuilder().WithProtocolVersion(_protocolVersion)
                                                              .WithResponseId(1)
                                                              .WithEncoding(_encoding)
-                                                             .WithFile("/ABC", SftpFileAttributes.Empty)
+                                                             .WithFile("/ABC", SftpFileAttributesBuilder.Empty)
                                                              .Build();
 
             #endregion SftpSession.Connect()

test/Renci.SshNet.Tests/Classes/Sftp/SftpSessionTest_DataReceived_MultipleSftpMessagesSplitOverMultipleSshDataMessages.cs

@@ -11,6 +11,7 @@ using Renci.SshNet.Channels;
 using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp
 {
@@ -75,7 +76,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp
             _sftpNameResponse = new SftpNameResponseBuilder().WithProtocolVersion(_protocolVersion)
                                                              .WithResponseId(1)
                                                              .WithEncoding(_encoding)
-                                                             .WithFile("/ABC", SftpFileAttributes.Empty)
+                                                             .WithFile("/ABC", SftpFileAttributesBuilder.Empty)
                                                              .Build();
 
             #endregion SftpSession.Connect()

test/Renci.SshNet.Tests/Classes/Sftp/SftpSessionTest_DataReceived_SingleSftpMessageInSshDataMessage.cs

@@ -11,6 +11,7 @@ using Renci.SshNet.Channels;
 using Renci.SshNet.Common;
 using Renci.SshNet.Sftp;
 using Renci.SshNet.Sftp.Responses;
+using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes.Sftp
 {
@@ -71,7 +72,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp
             _sftpNameResponse = new SftpNameResponseBuilder().WithProtocolVersion(_protocolVersion)
                                                              .WithResponseId(1)
                                                              .WithEncoding(_encoding)
-                                                             .WithFile("/ABC", SftpFileAttributes.Empty)
+                                                             .WithFile("/ABC", SftpFileAttributesBuilder.Empty)
                                                              .Build();
 
             #endregion SftpSession.Connect()

test/Renci.SshNet.Tests/Classes/Sftp/SftpVersionResponseBuilder.cs

@@ -31,7 +31,7 @@ namespace Renci.SshNet.Tests.Classes.Sftp
             var sftpVersionResponse = new SftpVersionResponse()
             {
                 Version = _version,
-                Extentions = _extensions
+                Extensions = _extensions
             };
             return sftpVersionResponse;
         }

test/Renci.SshNet.Tests/Classes/ShellStreamTest_Write_WriteBufferNotEmptyAndWriteMoreBytesThanBufferCanContain.cs

@@ -10,7 +10,6 @@ using Moq;
 
 using Renci.SshNet.Channels;
 using Renci.SshNet.Common;
-using Renci.SshNet.Tests.Common;
 
 namespace Renci.SshNet.Tests.Classes
 {
@@ -60,9 +59,7 @@ namespace Renci.SshNet.Tests.Classes
             _offset = 0;
             _count = _data.Length;
 
-            _expectedBytesSent = new ArrayBuilder<byte>().Add(_bufferData)
-                                                         .Add(_data, 0, _bufferSize - _bufferData.Length)
-                                                         .Build();
+            _expectedBytesSent = [.. _bufferData, .. _data.Take(0, _bufferSize - _bufferData.Length)];
         }
 
         private void CreateMocks()

test/Renci.SshNet.Tests/Common/ArrayBuilder`1.cs

@@ -1,34 +0,0 @@
-using System.Collections.Generic;
-
-namespace Renci.SshNet.Tests.Common
-{
-    public class ArrayBuilder<T>
-    {
-        private readonly List<T> _buffer;
-
-        public ArrayBuilder()
-        {
-            _buffer = new List<T>();
-        }
-
-        public ArrayBuilder<T> Add(T[] array)
-        {
-            return Add(array, 0, array.Length);
-        }
-
-        public ArrayBuilder<T> Add(T[] array, int index, int length)
-        {
-            for (var i = 0; i < length; i++)
-            {
-                _buffer.Add(array[index + i]);
-            }
-
-            return this;
-        }
-
-        public T[] Build()
-        {
-            return _buffer.ToArray();
-        }
-    }
-}

test/Renci.SshNet.Tests/Common/Extensions.cs

@@ -1,8 +1,6 @@
-using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
 
 using Renci.SshNet.Common;
-using Renci.SshNet.Sftp;
 
 namespace Renci.SshNet.Tests.Common
 {
@@ -23,44 +21,5 @@ namespace Renci.SshNet.Tests.Common
 
             return reportedExceptions;
         }
-
-        public static byte[] Copy(this byte[] buffer)
-        {
-            var copy = new byte[buffer.Length];
-            Buffer.BlockCopy(buffer, 0, copy, 0, buffer.Length);
-            return copy;
-        }
-
-        /// <summary>
-        /// Creates a deep clone of the current instance.
-        /// </summary>
-        /// <returns>
-        /// A deep clone of the current instance.
-        /// </returns>
-        internal static SftpFileAttributes Clone(this SftpFileAttributes value)
-        {
-            Dictionary<string, string> clonedExtensions;
-
-            if (value.Extensions != null)
-            {
-                clonedExtensions = new Dictionary<string, string>(value.Extensions.Count);
-                foreach (var entry in value.Extensions)
-                {
-                    clonedExtensions.Add(entry.Key, entry.Value);
-                }
-            }
-            else
-            {
-                clonedExtensions = null;
-            }
-
-            return new SftpFileAttributes(value.LastAccessTimeUtc,
-                                          value.LastWriteTimeUtc,
-                                          value.Size,
-                                          value.UserId,
-                                          value.GroupId,
-                                          value.Permissions,
-                                          clonedExtensions);
-        }
     }
 }

test/Renci.SshNet.Tests/Common/SftpFileAttributesBuilder.cs

@@ -1,4 +1,5 @@
-using System;
+#nullable enable
+using System;
 using System.Collections.Generic;
 
 using Renci.SshNet.Sftp;
@@ -7,18 +8,21 @@ namespace Renci.SshNet.Tests.Common
 {
     public class SftpFileAttributesBuilder
     {
+        public static SftpFileAttributes Empty
+        {
+            get
+            {
+                return new SftpFileAttributesBuilder().Build();
+            }
+        }
+
         private DateTime? _lastAccessTime;
         private DateTime? _lastWriteTime;
         private long? _size;
         private int? _userId;
         private int? _groupId;
         private uint? _permissions;
-        private readonly IDictionary<string, string> _extensions;
-
-        public SftpFileAttributesBuilder()
-        {
-            _extensions = new Dictionary<string, string>();
-        }
+        private Dictionary<string, string>? _extensions;
 
         public SftpFileAttributesBuilder WithLastAccessTime(DateTime lastAccessTime)
         {
@@ -58,6 +62,7 @@ namespace Renci.SshNet.Tests.Common
 
         public SftpFileAttributesBuilder WithExtension(string name, string value)
         {
+            _extensions ??= [];
             _extensions.Add(name, value);
             return this;
         }