Utf16StringValidator.cs

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namespace System.Web.Util;
 
internal static class Utf16StringValidator
{
    internal static string ValidateString(string input)
    {
        if (string.IsNullOrEmpty(input))
        {
            return input;
        }
        int num = -1;
        for (int i = 0; i < input.Length; i++)
        {
            if (char.IsSurrogate(input[i]))
            {
                num = i;
                break;
            }
        }
        if (num < 0)
        {
            return input;
        }
        return string.Create(input.Length, (input, num), delegate(Span<char> chars, (string input, int idxOfFirstSurrogate) state)
        {
            state.input.CopyTo(chars);
            for (int j = state.idxOfFirstSurrogate; j < chars.Length; j++)
            {
                char c = chars[j];
                if (char.IsLowSurrogate(c))
                {
                    chars[j] = '\ufffd';
                }
                else if (char.IsHighSurrogate(c))
                {
                    if (j + 1 < chars.Length && char.IsLowSurrogate(chars[j + 1]))
                    {
                        j++;
                    }
                    else
                    {
                        chars[j] = '\ufffd';
                    }
                }
            }
        });
    }
}