From 73917356b2f46ccd1cf4d209120b1978ad594b8c Mon Sep 17 00:00:00 2001
From: Robert Hague <rh@johnstreetcapital.com>
Date: Sun, 4 Jun 2023 16:31:31 +0200
Subject: [PATCH] Add a few spans on net6.0 or greater

---
 src/Renci.SshNet/Common/Extensions.cs    |  4 +++
 src/Renci.SshNet/Common/SshDataStream.cs | 44 ++++++++++++++++++++++++
 src/Renci.SshNet/Session.cs              | 13 +++++--
 3 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/src/Renci.SshNet/Common/Extensions.cs b/src/Renci.SshNet/Common/Extensions.cs
index 8fed310c1..0305e17d5 100644
--- a/src/Renci.SshNet/Common/Extensions.cs
+++ b/src/Renci.SshNet/Common/Extensions.cs
@@ -245,6 +245,9 @@ public static bool IsEqualTo(this byte[] left, byte[] right)
                 return true;
             }
 
+#if NET6_0_OR_GREATER
+            return left.AsSpan().SequenceEqual(right);
+#else
             if (left.Length != right.Length)
             {
                 return false;
@@ -259,6 +262,7 @@ public static bool IsEqualTo(this byte[] left, byte[] right)
             }
 
             return true;
+#endif
         }
 
         /// <summary>
diff --git a/src/Renci.SshNet/Common/SshDataStream.cs b/src/Renci.SshNet/Common/SshDataStream.cs
index 1eedd3ffc..656485a76 100644
--- a/src/Renci.SshNet/Common/SshDataStream.cs
+++ b/src/Renci.SshNet/Common/SshDataStream.cs
@@ -1,4 +1,7 @@
 using System;
+#if NET6_0_OR_GREATER
+using System.Buffers.Binary;
+#endif
 using System.Globalization;
 using System.IO;
 using System.Text;
@@ -62,8 +65,14 @@ public bool IsEndOfData
         /// <param name="value"><see cref="uint"/> data to write.</param>
         public void Write(uint value)
         {
+#if NET6_0_OR_GREATER
+            Span<byte> bytes = stackalloc byte[4];
+            BinaryPrimitives.WriteUInt32BigEndian(bytes, value);
+            Write(bytes);
+#else
             var bytes = Pack.UInt32ToBigEndian(value);
             Write(bytes, 0, bytes.Length);
+#endif
         }
 
         /// <summary>
@@ -72,8 +81,14 @@ public void Write(uint value)
         /// <param name="value"><see cref="ulong"/> data to write.</param>
         public void Write(ulong value)
         {
+#if NET6_0_OR_GREATER
+            Span<byte> bytes = stackalloc byte[8];
+            BinaryPrimitives.WriteUInt64BigEndian(bytes, value);
+            Write(bytes);
+#else
             var bytes = Pack.UInt64ToBigEndian(value);
             Write(bytes, 0, bytes.Length);
+#endif
         }
 
         /// <summary>
@@ -188,8 +203,14 @@ public BigInteger ReadBigInt()
         /// </returns>
         public uint ReadUInt32()
         {
+#if NET6_0_OR_GREATER
+            Span<byte> bytes = stackalloc byte[4];
+            ReadBytes(bytes);
+            return BinaryPrimitives.ReadUInt32BigEndian(bytes);
+#else
             var data = ReadBytes(4);
             return Pack.BigEndianToUInt32(data);
+#endif
         }
 
         /// <summary>
@@ -200,8 +221,14 @@ public uint ReadUInt32()
         /// </returns>
         public ulong ReadUInt64()
         {
+#if NET6_0_OR_GREATER
+            Span<byte> bytes = stackalloc byte[8];
+            ReadBytes(bytes);
+            return BinaryPrimitives.ReadUInt64BigEndian(bytes);
+#else
             var data = ReadBytes(8);
             return Pack.BigEndianToUInt64(data);
+#endif
         }
 
         /// <summary>
@@ -264,5 +291,22 @@ private byte[] ReadBytes(int length)
 
             return data;
         }
+
+#if NET6_0_OR_GREATER
+        /// <summary>
+        /// Fills the specified span with bytes from the internal buffer.
+        /// </summary>
+        /// <param name="destination">The span to fill.</param>
+        /// <exception cref="ArgumentException">The Length of <paramref name="destination"/> is greater than the actual number of bytes read.</exception>
+        private void ReadBytes(Span<byte> destination)
+        {
+            var bytesRead = Read(destination);
+
+            if (bytesRead < destination.Length)
+            {
+                throw new ArgumentException(nameof(destination), string.Format(CultureInfo.InvariantCulture, "The requested length ({0}) is greater than the actual number of bytes read ({1}).", destination.Length, bytesRead));
+            }
+        }
+#endif
     }
 }
diff --git a/src/Renci.SshNet/Session.cs b/src/Renci.SshNet/Session.cs
index 9fec6bd7e..ced015563 100644
--- a/src/Renci.SshNet/Session.cs
+++ b/src/Renci.SshNet/Session.cs
@@ -1254,11 +1254,18 @@ private Message ReceiveMessage(Socket socket)
             if (_serverMac != null)
             {
                 var clientHash = _serverMac.ComputeHash(data, 0, data.Length - serverMacLength);
+
+                bool serverHashEqualsClientHash;
+
+#if NET6_0_OR_GREATER
+                var serverHash = data.AsSpan(data.Length - serverMacLength);
+                serverHashEqualsClientHash = serverHash.SequenceEqual(clientHash); 
+#else
                 var serverHash = data.Take(data.Length - serverMacLength, serverMacLength);
+                serverHashEqualsClientHash = serverHash.IsEqualTo(clientHash);
+#endif
 
-                // TODO add IsEqualTo overload that takes left+right index and number of bytes to compare;
-                // TODO that way we can eliminate the extra allocation of the Take above
-                if (!serverHash.IsEqualTo(clientHash))
+                if (!serverHashEqualsClientHash)
                 {
                     throw new SshConnectionException("MAC error", DisconnectReason.MacError);
                 }