Optimize AWSSDKUtils.ToHex() for speed and memory

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

@@ -20,13 +20,10 @@
     <GenerateAssemblyFileVersionAttribute>false</GenerateAssemblyFileVersionAttribute>
     <GenerateAssemblyDescriptionAttribute>false</GenerateAssemblyDescriptionAttribute>
 
+    <LangVersion>9.0</LangVersion>
     <NoWarn>$(NoWarn);CS1591;CA1822</NoWarn>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <SignAssembly>True</SignAssembly>
-  </PropertyGroup>
-    <!-- Async Enumerable Compatibility -->
-  <PropertyGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
-    <LangVersion>8.0</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)' == 'net8.0'">
     <WarningsAsErrors>IL2026,IL2075</WarningsAsErrors>

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

@@ -20,6 +20,7 @@
 
 using Amazon.Runtime.Internal.Util;
 using System;
+using System.Buffers;
 using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
@@ -755,14 +756,32 @@ public static long ConvertTimeSpanToMilliseconds(TimeSpan timeSpan)
         /// <returns>String version of the data</returns>
         public static string ToHex(byte[] data, bool lowercase)
         {
-            StringBuilder sb = new StringBuilder();
-
-            for (int i = 0; i < data.Length; i++)
+#if NET8_0_OR_GREATER
+            if (!lowercase)
             {
-                sb.Append(data[i].ToString(lowercase ? "x2" : "X2", CultureInfo.InvariantCulture));
+                return Convert.ToHexString(data);
             }
+#endif
 
-            return sb.ToString();
+#if NETCOREAPP3_1_OR_GREATER
+            return string.Create(data.Length * 2, (data, lowercase), static (chars, state) =>
+            {
+                ToHexString(state.data, chars, state.lowercase);
+            });
+#else
+            char[] chars = ArrayPool<char>.Shared.Rent(data.Length * 2);
+
+            try
+            {
+                ToHexString(data, chars, lowercase);
+
+                return new string(chars, 0, data.Length * 2);
+            }
+            finally
+            {
+                ArrayPool<char>.Shared.Return(chars);
+            }
+#endif
         }
 
         /// <summary>
@@ -1144,6 +1163,23 @@ public static string UrlEncode(int rfcNumber, string data, bool path)
             return encoded.ToString();
         }
 
+        private static void ToHexString(Span<byte> source, Span<char> destination, bool lowercase)
+        {
+            Func<int, char> converter = lowercase ? (Func<int, char>)ToLowerHex : (Func<int, char>)ToUpperHex;
+
+            for (int i = source.Length - 1; i >= 0; i--)
+            {
+                // Break apart the byte into two four-bit components and
+                // then convert each into their hexadecimal equivalent.
+                byte b = source[i];
+                int hiNibble = b >> 4;
+                int loNibble = b & 0xF;
+
+                destination[i * 2] = converter(hiNibble);
+                destination[i * 2 + 1] = converter(loNibble);
+            }
+        }
+
         private static char ToUpperHex(int value)
         {
             // Maps 0-9 to the Unicode range of '0' - '9' (0x30 - 0x39).
@@ -1154,7 +1190,18 @@ private static char ToUpperHex(int value)
             // Maps 10-15 to the Unicode range of 'A' - 'F' (0x41 - 0x46).
             return (char)(value - 10 + 'A');
         }
-
+
+        private static char ToLowerHex(int value)
+        {
+            // Maps 0-9 to the Unicode range of '0' - '9' (0x30 - 0x39).
+            if (value <= 9)
+            {
+                return (char)(value + '0');
+            }
+            // Maps 10-15 to the Unicode range of 'a' - 'f' (0x61 - 0x66).
+            return (char)(value - 10 + 'a');
+        }
+
         internal static string UrlEncodeSlash(string data)
         {
             if (string.IsNullOrEmpty(data))
@@ -1311,18 +1358,6 @@ public static void Sleep(TimeSpan ts)
             Sleep((int)ts.TotalMilliseconds);
         }
 
-        /// <summary>
-        /// Convert bytes to a hex string
-        /// </summary>
-        /// <param name="value">Bytes to convert.</param>
-        /// <returns>Hexadecimal string representing the byte array.</returns>
-        public static string BytesToHexString(byte[] value)
-        {
-            string hex = BitConverter.ToString(value);
-            hex = hex.Replace("-", string.Empty);
-            return hex;
-        }
-
         /// <summary>
         /// Convert a hex string to bytes
         /// </summary>

sdk/src/Services/S3/Custom/Internal/AmazonS3ResponseHandler.cs

@@ -191,8 +191,8 @@ private static void CompareHashes(string etag, byte[] hash)
                 return;
 
             etag = etag.Trim(etagTrimChars);
-
-            string hexHash = AWSSDKUtils.BytesToHexString(hash);
+            
+            string hexHash = AWSSDKUtils.ToHex(hash, false);
             if (!string.Equals(etag, hexHash, StringComparison.OrdinalIgnoreCase))
                 throw new AmazonClientException("Expected hash not equal to calculated hash");
         }

sdk/test/NetStandard/UnitTests/AWSSDK.UnitTests.Custom.NetStandard.csproj

@@ -23,10 +23,10 @@ This project file should not be used as part of a release pipeline.
         <GenerateAssemblyFileVersionAttribute>false</GenerateAssemblyFileVersionAttribute>
         <GenerateAssemblyDescriptionAttribute>false</GenerateAssemblyDescriptionAttribute>
 
+        <LangVersion>9.0</LangVersion>
         <NoWarn>CS1591,CS0612,CS0618,NU1701</NoWarn>
-		<TreatWarningsAsErrors>true</TreatWarningsAsErrors>	
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>	
 		<SignAssembly>true</SignAssembly>
-        <LangVersion Condition="'$(TargetFramework)' == 'netstandard2.0'">8.0</LangVersion>
     </PropertyGroup>
 	<Choose>
 		<When Condition=" '$(AWSKeyFile)' == '' ">

sdk/test/NetStandard/UnitTests/Core/AWSSDKUtilsTests.cs

@@ -0,0 +1,28 @@
+using Amazon.Util;
+using System.Text;
+using Xunit;
+
+namespace UnitTests.NetStandard.Core
+{
+    [Trait("Category", "Core")]
+    public class AWSSDKUtilsTests
+    {
+        [Fact]
+        public void ToHexUppercase()
+        {
+            var bytes = Encoding.UTF8.GetBytes("Hello World");
+            var hexString = AWSSDKUtils.ToHex(bytes, false);
+
+            Assert.Equal("48656C6C6F20576F726C64", hexString);
+        }
+
+        [Fact]
+        public void ToHexLowercase()
+        {
+            var bytes = Encoding.UTF8.GetBytes("Hello World");
+            var hexString = AWSSDKUtils.ToHex(bytes, true);
+
+            Assert.Equal("48656c6c6f20576f726c64", hexString);
+        }
+    }
+}

sdk/test/UnitTests/Custom/Util/AWSSDKUtilsTests.cs

@@ -19,6 +19,7 @@
 using System.Reflection;
 using Moq;
 using Amazon.Util.Internal;
+using System.Text;
 
 namespace AWSSDK.UnitTests
 {
@@ -164,5 +165,18 @@ public void ConvertFromUnixEpochMilliseconds()
 
             Assert.AreEqual(expectedDateTime, dateTime);
         }
+
+        [TestCategory("UnitTest")]
+        [TestCategory("Util")]
+        [DataRow("Hello World", true, "48656c6c6f20576f726c64")]
+        [DataRow("Hello World", false, "48656C6C6F20576F726C64")]
+        [DataTestMethod]
+        public void ToHex(string input, bool lowercase, string expectedResult)
+        {
+            var bytes = Encoding.UTF8.GetBytes(input);
+            var hexString = AWSSDKUtils.ToHex(bytes, lowercase);
+
+            Assert.AreEqual(expectedResult, hexString);
+        }
     }
 }