From b400a7215aa4726a756bac125f638c88231cab01 Mon Sep 17 00:00:00 2001
From: Peter Butzhammer <peter.butzhammer@evopro-ag.de>
Date: Thu, 25 Apr 2024 12:16:49 +0200
Subject: [PATCH] Switch ReadFromBuffer to span

---
 .../ValueConverterTests/ConverterTestBase.cs  | 15 +++++++----
 Sharp7.Rx/ValueConverter.cs                   | 26 +++++++++----------
 2 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/Sharp7.Rx.Tests/ValueConverterTests/ConverterTestBase.cs b/Sharp7.Rx.Tests/ValueConverterTests/ConverterTestBase.cs
index d09c3ed..41fe7ac 100644
--- a/Sharp7.Rx.Tests/ValueConverterTests/ConverterTestBase.cs
+++ b/Sharp7.Rx.Tests/ValueConverterTests/ConverterTestBase.cs
@@ -9,7 +9,7 @@ internal abstract class ConverterTestBase
 
     public static MethodInfo CreateReadMethod(ConverterTestCase tc)
     {
-        var convertMi = typeof(ValueConverter).GetMethod(nameof(ValueConverter.ReadFromBuffer));
+        var convertMi = typeof(ConverterTestBase).GetMethod(nameof(ReadFromBuffer));
         var convert = convertMi!.MakeGenericMethod(tc.Value.GetType());
         return convert;
     }
@@ -67,12 +67,17 @@ internal abstract class ConverterTestBase
 
     /// <summary>
     ///     This helper method exists, since I could not manage to invoke a generic method
-    ///     accepring a Span&lt;T&gt; as parameter.
+    ///     with a Span&lt;T&gt; parameter.
     /// </summary>
-    public static void WriteToBuffer<TValue>(byte[] buffer, TValue value, VariableAddress address)
-    {
+    public static void WriteToBuffer<TValue>(byte[] buffer, TValue value, VariableAddress address) =>
         ValueConverter.WriteToBuffer(buffer, value, address);
-    }
+
+    /// <summary>
+    ///     This helper method exists, since I could not manage to invoke a generic method
+    ///     with a Span&lt;T&gt; parameter.
+    /// </summary>
+    public static TValue ReadFromBuffer<TValue>(byte[] buffer, VariableAddress address) =>
+        ValueConverter.ReadFromBuffer<TValue>(buffer, address);
 
     public record ConverterTestCase(object Value, string Address, byte[] Data)
     {
diff --git a/Sharp7.Rx/ValueConverter.cs b/Sharp7.Rx/ValueConverter.cs
index 83078c2..42c65b5 100644
--- a/Sharp7.Rx/ValueConverter.cs
+++ b/Sharp7.Rx/ValueConverter.cs
@@ -143,42 +143,40 @@ internal static class ValueConverter
             {
                 return address.Type switch
                 {
-                    DbType.String => ParseString(),
-                    DbType.WString => ParseWString(),
-                    DbType.Byte => Encoding.ASCII.GetString(buffer.ToArray()),
+                    DbType.String => ParseString(buffer),
+                    DbType.WString => ParseWString(buffer),
+                    DbType.Byte => Encoding.ASCII.GetString(buffer),
                     _ => throw new DataTypeMissmatchException($"Cannot read string from {address.Type}", typeof(string), address)
                 };
 
-                string ParseString()
+                string ParseString(Span<byte> data)
                 {
                     // First byte is maximal length
                     // Second byte is actual length
                     // https://support.industry.siemens.com/cs/mdm/109747174?c=94063831435&lc=de-DE
 
-                    var length = Math.Min(address.Length, buffer[1]);
+                    var length = Math.Min(address.Length, data[1]);
 
-                    return Encoding.ASCII.GetString(buffer, 2, length);
+                    return Encoding.ASCII.GetString(data.Slice(2, length));
                 }
 
-                string ParseWString()
+                string ParseWString(Span<byte> data)
                 {
                     // First 2 bytes are maximal length
                     // Second 2 bytes are actual length
                     // https://support.industry.siemens.com/cs/mdm/109747174?c=94063855243&lc=de-DE
 
-                    // the length of the string is two bytes per 
-                    var length = Math.Min(address.Length, BinaryPrimitives.ReadUInt16BigEndian(buffer.AsSpan(2, 2))) * 2;
+                    // the length of the string is two bytes per character
+                    var length = Math.Min(address.Length, BinaryPrimitives.ReadUInt16BigEndian(data.Slice(2, 2))) * 2;
 
-                    return Encoding.BigEndianUnicode.GetString(buffer, 4, length);
+                    return Encoding.BigEndianUnicode.GetString(data.Slice(4, length));
                 }
             }
         },
     };
 
-    public static TValue ReadFromBuffer<TValue>(byte[] buffer, VariableAddress address)
+    public static TValue ReadFromBuffer<TValue>(Span<byte> buffer, VariableAddress address)
     {
-        // Todo: Change to Span<byte> when switched to newer .net
-
         if (buffer.Length < address.BufferLength)
             throw new ArgumentException($"Buffer must be at least {address.BufferLength} bytes long for {address}", nameof(buffer));
 
@@ -204,7 +202,7 @@ internal static class ValueConverter
         writeFunc(buffer, address, value);
     }
 
-    delegate object ReadFunc(byte[] data, VariableAddress address);
+    delegate object ReadFunc(Span<byte> data, VariableAddress address);
 
     [StructLayout(LayoutKind.Explicit)]
     private struct UInt32SingleMap