QuotedStringFormatReader.cs

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using System.Net.Mime;
 
namespace System.Net.Mail;
 
internal static class QuotedStringFormatReader
{
    internal static bool TryReadReverseQuoted(string data, int index, bool permitUnicode, out int outIndex, bool throwExceptionIfFail)
    {
        index--;
        do
        {
            if (!WhitespaceReader.TryReadFwsReverse(data, index, out index, throwExceptionIfFail))
            {
                outIndex = 0;
                return false;
            }
            if (index < 0)
            {
                break;
            }
            if (!QuotedPairReader.TryCountQuotedChars(data, index, permitUnicode, out var outIndex2, throwExceptionIfFail))
            {
                outIndex = 0;
                return false;
            }
            if (outIndex2 > 0)
            {
                index -= outIndex2;
                continue;
            }
            if (data[index] == '"')
            {
                outIndex = index - 1;
                return true;
            }
            if (!IsValidQtext(permitUnicode, data[index]))
            {
                if (throwExceptionIfFail)
                {
                    throw new FormatException(System.SR.Format(System.SR.MailHeaderFieldInvalidCharacter, data[index]));
                }
                outIndex = 0;
                return false;
            }
            index--;
        }
        while (index >= 0);
        if (throwExceptionIfFail)
        {
            throw new FormatException(System.SR.Format(System.SR.MailHeaderFieldInvalidCharacter, '"'));
        }
        outIndex = 0;
        return false;
    }
 
    internal static bool TryReadReverseUnQuoted(string data, int index, bool permitUnicode, bool expectCommaDelimiter, out int outIndex, bool throwExceptionIfFail)
    {
        do
        {
            if (!WhitespaceReader.TryReadFwsReverse(data, index, out index, throwExceptionIfFail))
            {
                outIndex = 0;
                return false;
            }
            if (index < 0)
            {
                break;
            }
            if (!QuotedPairReader.TryCountQuotedChars(data, index, permitUnicode, out var outIndex2, throwExceptionIfFail))
            {
                outIndex = 0;
                return false;
            }
            if (outIndex2 > 0)
            {
                index -= outIndex2;
                continue;
            }
            if (expectCommaDelimiter && data[index] == ',')
            {
                break;
            }
            if (!IsValidQtext(permitUnicode, data[index]))
            {
                if (throwExceptionIfFail)
                {
                    throw new FormatException(System.SR.Format(System.SR.MailHeaderFieldInvalidCharacter, data[index]));
                }
                outIndex = 0;
                return false;
            }
            index--;
        }
        while (index >= 0);
        outIndex = index;
        return true;
    }
 
    private static bool IsValidQtext(bool allowUnicode, char ch)
    {
        if (ch > '\u007f')
        {
            return allowUnicode;
        }
        return MailBnfHelper.Qtext[(uint)ch];
    }
}