Minimize changes to the non-netcore31 path

Author: stevenaw

sdk/src/Core/AWSSDK.Core.NetStandard.csproj

@@ -74,6 +74,5 @@
 
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="1.1.0" />
-    <PackageReference Include="System.Buffers" Version="4.3.0" />
   </ItemGroup>
 </Project>

sdk/src/Core/Amazon.Util/CryptoUtil.cs

@@ -17,7 +17,9 @@
 using Amazon.Util.Internal;
 using AWSSDK.Runtime.Internal.Util;
 using System;
+#if NETCOREAPP3_1_OR_GREATER
 using System.Buffers;
+#endif
 using System.IO;
 using System.Security.Cryptography;
 using System.Text;
@@ -100,21 +102,26 @@ internal CryptoUtil()
             /// <returns>Computed hash code</returns>
             public string HMACSign(string data, string key, SigningAlgorithm algorithmName)
             {
+#if NETCOREAPP3_1_OR_GREATER
                 Encoding encoding = Encoding.UTF8;
                 int maxSize = encoding.GetMaxByteCount(data.Length);
                 byte[] buffer = ArrayPool<byte>.Shared.Rent(maxSize);
 
                 try
                 {
                     int size = encoding.GetBytes(data, buffer);
-                    ArraySegment<byte> segment = new ArraySegment<byte>(buffer, 0, size);
+                    ArraySegment<byte> binaryData = new ArraySegment<byte>(buffer, 0, size);
 
-                    return HMACSign(segment, key, algorithmName);
+                    return HMACSign(binaryData, key, algorithmName);
                 }
                 finally
                 {
                     ArrayPool<byte>.Shared.Return(buffer);
                 }
+#else
+                byte[] binaryData = Encoding.UTF8.GetBytes(data);
+                return HMACSign(binaryData, key, algorithmName);
+#endif
             }
 
             /// <summary>

sdk/src/Core/Amazon.Util/_netstandard/CryptoUtil.netstandard.cs

@@ -80,7 +80,7 @@ public byte[] HMACSignBinary(byte[] data, byte[] key, SigningAlgorithm algorithm
                 }
             }
 
-            KeyedHashAlgorithm CreateKeyedHashAlgorithm(SigningAlgorithm algorithmName)
+            static KeyedHashAlgorithm CreateKeyedHashAlgorithm(SigningAlgorithm algorithmName)
             {
                 KeyedHashAlgorithm algorithm;
                 switch (algorithmName)

sdk/src/Core/Amazon.Util/_netstandard/Extensions.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Collections.Generic;
 using System.Globalization;
-using System.Text;
+using System.Linq;
+using System.Threading.Tasks;
 
 namespace Amazon.Util
 {
@@ -12,10 +14,5 @@ internal static string ToUpper(this String str, CultureInfo culture)
                 throw new ArgumentException("The extension method ToUpper only works for invariant culture");
             return str.ToUpperInvariant();
         }
-
-#if !NETCOREAPP3_1_OR_GREATER
-        internal static int GetBytes(this Encoding encoding, string chars, byte[] bytes)
-            => encoding.GetBytes(chars, 0, chars.Length, bytes, 0);
-#endif
     }
 }