String Public Key (#395)

* Handle public key being string on older versions

* Update version comment

* One more comment

LibCpp2IL/Metadata/Il2CppAssemblyNameDefinition.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 namespace LibCpp2IL.Metadata;
@@ -28,8 +30,100 @@ public byte[]? PublicKey
     {
         get
         {
-            var result = LibCpp2IlMain.TheMetadata!.GetByteArrayFromIndex(publicKeyIndex);
-            return result.Length == 0 ? null : result;
+            // The difference between these two options can be seen in the header files.
+            // const uint8_t* public_key;
+            // const char* public_key;
+
+            if (IsAtLeast(24.4f) || Is(24.15f))
+            {
+                // 2018.4.34 until 2019 (24.15)
+                // 2019.4.15 until 2020 (24.4)
+                // 2020.1.11 until 2020.2.0 (24.4)
+                // 2020.2.0b7 and later (27+)
+                var result = LibCpp2IlMain.TheMetadata!.GetByteArrayFromIndex(publicKeyIndex);
+                return result.Length == 0 ? null : result;
+            }
+            else
+            {
+                var str = LibCpp2IlMain.TheMetadata!.GetStringFromIndex(publicKeyIndex);
+
+                if (str is "NULL")
+                    return null; // No public key
+
+                // mscorlib example:
+                // "\x0\x0\x0\x0\x0\x0\x0\x0\x4\x0\x0\x0\x0\x0\x0\x0"
+                // The string above is verbatim, so the backslashes are not escape characters and the quotes are part of the string.
+                if (str.Length > 2 && str[0] is '"' && str[^1] is '"' && TryParseByteArray(str.AsSpan()[1..^1], out var result))
+                    return result;
+
+                return null; // Parsing failed
+            }
+
+            static bool IsHexDigit(char c) => c is (>= '0' and <= '9') or (>= 'A' and <= 'F') or (>= 'a' and <= 'f');
+
+            static bool TryParseByte(ReadOnlySpan<char> characters, out byte result)
+            {
+#if NET6_0_OR_GREATER
+                return byte.TryParse(characters, System.Globalization.NumberStyles.HexNumber, null, out result);
+#else
+                return byte.TryParse(characters.ToString(), System.Globalization.NumberStyles.HexNumber, null, out result);
+#endif
+            }
+
+            static bool TryParseByteArray(ReadOnlySpan<char> characters, [NotNullWhen(true)] out byte[]? result)
+            {
+                var bytes = new List<byte>();
+
+                var i = 0;
+                while (i < characters.Length)
+                {
+                    // Each byte is represented by 3 or 4 characters.
+                    // The first one is backslash.
+                    // The second one is 'x'.
+                    // The third and fourth (if present) ones are the hexadecimal representation of the byte.
+                    if (i > characters.Length - 3 || characters[i] is not '\\' || characters[i + 1] is not 'x')
+                    {
+                        result = null;
+                        return false;
+                    }
+
+                    i += 2;
+
+                    if (!IsHexDigit(characters[i]))
+                    {
+                        result = null;
+                        return false;
+                    }
+
+                    ReadOnlySpan<char> hexCharacters;
+                    if (i + 1 < characters.Length && characters[i + 1] is not '\\')
+                    {
+                        if (!IsHexDigit(characters[i + 1]))
+                        {
+                            result = null;
+                            return false;
+                        }
+                        hexCharacters = characters.Slice(i, 2);
+                        i += 2;
+                    }
+                    else
+                    {
+                        hexCharacters = characters.Slice(i, 1);
+                        i += 1;
+                    }
+
+                    if (!TryParseByte(hexCharacters, out var b))
+                    {
+                        result = null;
+                        return false;
+                    }
+
+                    bytes.Add(b);
+                }
+
+                result = bytes.ToArray();
+                return true;
+            }
         }
     }
 

LibCpp2IL/ReadableClass.cs

@@ -1,13 +1,14 @@
-using System;
+using System;
 
 namespace LibCpp2IL;
 
 public abstract class ReadableClass
 {
-    protected bool IsAtLeast(float vers) => LibCpp2IlMain.MetadataVersion >= vers;
-    protected bool IsLessThan(float vers) => LibCpp2IlMain.MetadataVersion < vers;
-    protected bool IsAtMost(float vers) => LibCpp2IlMain.MetadataVersion <= vers;
-    protected bool IsNot(float vers) => Math.Abs(LibCpp2IlMain.MetadataVersion - vers) > 0.001f;
+    protected static bool IsAtLeast(float vers) => LibCpp2IlMain.MetadataVersion >= vers;
+    protected static bool IsLessThan(float vers) => LibCpp2IlMain.MetadataVersion < vers;
+    protected static bool IsAtMost(float vers) => LibCpp2IlMain.MetadataVersion <= vers;
+    protected static bool IsNot(float vers) => Math.Abs(LibCpp2IlMain.MetadataVersion - vers) > 0.001f;
+    protected static bool Is(float vers) => Math.Abs(LibCpp2IlMain.MetadataVersion - vers) < 0.001f;
 
     public abstract void Read(ClassReadingBinaryReader reader);
 }