UTF8 string marshaler

UTF8StringMarshaler.cs

#if !NETSTANDARD2_1_OR_GREATER
using System;
using System.Runtime.InteropServices;
using System.Text;

namespace resvg.net
{
    public sealed class UTF8Marshaler : ICustomMarshaler
    {
        public static readonly UTF8Marshaler Instance = new UTF8Marshaler();

        public object MarshalNativeToManaged(IntPtr pNativeData)
        {
            if (pNativeData == IntPtr.Zero)
            {
                return null;
            }
            int length = 0;
            while (Marshal.ReadByte(pNativeData, length) != 0)
            {
                length++;
            }
            byte[] buffer = new byte[length];
            Marshal.Copy(pNativeData, buffer, 0, length);
            return Encoding.UTF8.GetString(buffer);
        }

        public IntPtr MarshalManagedToNative(object managedObj)
        {
            if (managedObj == null)
            {
                return IntPtr.Zero;
            }

            if (!(managedObj is string str))
            {
                throw new MarshalDirectiveException($"{GetType().Name} must be used on a string.");
            }

            int len = Encoding.UTF8.GetByteCount(str);
            len++; // null terminator
            byte[] buffer = new byte[len];
            Encoding.UTF8.GetBytes(str, 0, str.Length, buffer, 0);
            IntPtr ptr = Marshal.AllocHGlobal(len);
            Marshal.Copy(buffer, 0, ptr, len);
            return ptr;
        }

        public void CleanUpNativeData(IntPtr pNativeData)
        {
            if (pNativeData != IntPtr.Zero)
            {
                Marshal.FreeHGlobal(pNativeData);
            }
        }

        public void CleanUpManagedData(object managedObj)
        {
        }

        public int GetNativeDataSize() => -1;
    }
}
#endif