Add polyfills for Convert.ToHexString[Lower](...) and Convert.FromHexString(...)

PolyShim.Tests/Net50/ConvertTests.cs

@@ -0,0 +1,27 @@
+using System;
+using FluentAssertions;
+using Xunit;
+
+namespace PolyShim.Tests.Net50;
+
+public class ConvertTests
+{
+    [Fact]
+    public void FromHexString_Test()
+    {
+        // Act & assert
+        Convert.FromHexString("4A6F686E").Should().Equal("John"u8.ToArray());
+        Convert.FromHexString("").Should().BeEmpty();
+        Assert.Throws<FormatException>(() => Convert.FromHexString("4A6F686")); // Odd length
+        Assert.Throws<FormatException>(() => Convert.FromHexString("4A6F68GH")); // Invalid character
+    }
+
+    [Fact]
+    public void ToHexString_Test()
+    {
+        // Act & assert
+        Convert.ToHexString("John"u8.ToArray()).Should().Be("4A6F686E");
+        Convert.ToHexString(Array.Empty<byte>()).Should().Be("");
+        Convert.ToHexString("John"u8.ToArray(), 1, 2).Should().Be("6F68");
+    }
+}

PolyShim.Tests/Net90/ConvertTests.cs

@@ -0,0 +1,17 @@
+using System;
+using FluentAssertions;
+using Xunit;
+
+namespace PolyShim.Tests.Net90;
+
+public class ConvertTests
+{
+    [Fact]
+    public void ToHexStringLower_Test()
+    {
+        // Act & assert
+        Convert.ToHexStringLower("John"u8.ToArray()).Should().Be("4a6f686e");
+        Convert.ToHexStringLower(Array.Empty<byte>()).Should().Be("");
+        Convert.ToHexStringLower("John"u8.ToArray(), 1, 2).Should().Be("6f68");
+    }
+}

PolyShim/Net50/Convert.cs

@@ -0,0 +1,66 @@
+#if (NETCOREAPP && !NET5_0_OR_GREATER) || (NETFRAMEWORK) || (NETSTANDARD)
+#nullable enable
+// ReSharper disable RedundantUsingDirective
+// ReSharper disable CheckNamespace
+// ReSharper disable InconsistentNaming
+// ReSharper disable PartialTypeWithSinglePart
+
+using System;
+
+internal static partial class PolyfillExtensions
+{
+    extension(Convert)
+    {
+        // https://learn.microsoft.com/dotnet/api/system.convert.fromhexstring#system-convert-fromhexstring(system-string)
+        public static byte[] FromHexString(string s)
+        {
+            static int GetHexValue(char c)
+            {
+                if (c is >= '0' and <= '9')
+                    return c - '0';
+                if (c is >= 'A' and <= 'F')
+                    return c - 'A' + 10;
+                if (c is >= 'a' and <= 'f')
+                    return c - 'a' + 10;
+
+                throw new FormatException($"Invalid hex character: {c}");
+            }
+
+            if (s.Length % 2 != 0)
+                throw new FormatException("The hex string must have an even length.");
+
+            var byteCount = s.Length / 2;
+            var bytes = new byte[byteCount];
+
+            for (var i = 0; i < byteCount; i++)
+            {
+                var highNibble = s[i * 2];
+                var lowNibble = s[i * 2 + 1];
+
+                bytes[i] = (byte)((GetHexValue(highNibble) << 4) + GetHexValue(lowNibble));
+            }
+
+            return bytes;
+        }
+
+        // https://learn.microsoft.com/dotnet/api/system.convert.tohexstring#system-convert-tohexstring(system-byte()-system-int32-system-int32)
+        public static string ToHexString(byte[] value, int startIndex, int length)
+        {
+            var c = new char[length * 2];
+
+            for (var i = 0; i < length; i++)
+            {
+                var b = value[startIndex + i] >> 4;
+                c[i * 2] = (char)(55 + b + (((b - 10) >> 31) & -7));
+                b = value[startIndex + i] & 0xF;
+                c[i * 2 + 1] = (char)(55 + b + (((b - 10) >> 31) & -7));
+            }
+
+            return new string(c);
+        }
+
+        // https://learn.microsoft.com/dotnet/api/system.convert.tohexstring#system-convert-tohexstring(system-byte())
+        public static string ToHexString(byte[] value) => ToHexString(value, 0, value.Length);
+    }
+}
+#endif

PolyShim/Net90/Convert.cs

@@ -0,0 +1,23 @@
+#if (NETCOREAPP && !NET9_0_OR_GREATER) || (NETFRAMEWORK) || (NETSTANDARD)
+#nullable enable
+// ReSharper disable RedundantUsingDirective
+// ReSharper disable CheckNamespace
+// ReSharper disable InconsistentNaming
+// ReSharper disable PartialTypeWithSinglePart
+
+using System;
+
+internal static partial class PolyfillExtensions
+{
+    extension(Convert)
+    {
+        // https://learn.microsoft.com/dotnet/api/system.convert.tohexstringlower#system-convert-tohexstringlower(system-byte()-system-int32-system-int32)
+        public static string ToHexStringLower(byte[] value, int startIndex, int length) =>
+            Convert.ToHexString(value, startIndex, length).ToLowerInvariant();
+
+        // https://learn.microsoft.com/dotnet/api/system.convert.tohexstringlower#system-convert-tohexstringlower(system-byte())
+        public static string ToHexStringLower(byte[] value) =>
+            ToHexStringLower(value, 0, value.Length);
+    }
+}
+#endif

PolyShim/Signatures.md

@@ -1,8 +1,8 @@
 # Signatures
 
-- **Total:** 259
+- **Total:** 264
 - **Types:** 62
-- **Members:** 197
+- **Members:** 202
 
 ___
 
@@ -26,6 +26,12 @@ ___
   - [`Task CancelAsync()`](https://learn.microsoft.com/dotnet/api/system.threading.cancellationtokensource.cancelasync) <sup><sub>.NET 8.0</sub></sup>
 - `CompilerFeatureRequiredAttribute`
   - [**[class]**](https://learn.microsoft.com/dotnet/api/system.runtime.compilerservices.compilerfeaturerequiredattribute) <sup><sub>.NET 7.0</sub></sup>
+- `Convert`
+  - [`byte[] FromHexString(string)`](https://learn.microsoft.com/dotnet/api/system.convert.fromhexstring#system-convert-fromhexstring(system-string)) <sup><sub>.NET 5.0</sub></sup>
+  - [`string ToHexString(byte[], int, int)`](https://learn.microsoft.com/dotnet/api/system.convert.tohexstring#system-convert-tohexstring(system-byte()-system-int32-system-int32)) <sup><sub>.NET 5.0</sub></sup>
+  - [`string ToHexString(byte[])`](https://learn.microsoft.com/dotnet/api/system.convert.tohexstring#system-convert-tohexstring(system-byte())) <sup><sub>.NET 5.0</sub></sup>
+  - [`string ToHexStringLower(byte[], int, int)`](https://learn.microsoft.com/dotnet/api/system.convert.tohexstringlower#system-convert-tohexstringlower(system-byte()-system-int32-system-int32)) <sup><sub>.NET 9.0</sub></sup>
+  - [`string ToHexStringLower(byte[])`](https://learn.microsoft.com/dotnet/api/system.convert.tohexstringlower#system-convert-tohexstringlower(system-byte())) <sup><sub>.NET 9.0</sub></sup>
 - `DateTime`
   - [`DateTime UnixEpoch`](https://learn.microsoft.com/dotnet/api/system.datetime.unixepoch) <sup><sub>.NET Core 2.1</sub></sup>
 - `DateTimeOffset`