using System;

public static class Program

{

    const string ShareExtUNCFullPrefix = @"\\?\UNC\";  

    const string ShareExtPrefix = @"\\?\";      

    const string SharePrefix = @"\\";           

    const string DIR = @"\";

    const char  cDIR = '\\';

    const string DIRDOUBLE = @"\\";

    const string COLONDIR = @":\";

    const string COLON = @":";

    const char cCOLON = ':';

    const string DIRSPACE = @"\ ";

    const string SPACEDIR = @" \";

    const string SPACE = @" ";

​

    public static int IndexOfOccurence(this string s, char match, int occurence)

    {

        int i = 1;

        int index = -1;

​

        while (i <= occurence && (index = s.IndexOf(match, index + 1)) != -1)

        {

            if (i == occurence)

                return index;

​

            i++;

        }

​

        return -1;

    }

    /// <summary>

    /// Gets UNC Host and Share from a full UNC path. Cuts 4th backslash from start of path, must have least 1 char between or digit between. Support IPv4 and IPv6.

    /// </summary>

    /// <param name="UNCFullPath">\\host\share returns empty, must end in a backslash</param>

    /// <returns>\\host\share from \\host\share\tail\, \\8.8.8.8\DNS\ also \\?\UNC\ and \\?\ work</returns>

    /// <warn>//fails for one case when "\\?\UNC\share\tail\file.txt", UNC Server Name is named "UNC"</warn>

    /// <author>Metadataconsulting.blogspot.com</warn>

    public static string GetUNCHostIPAddressShare(this string UNCFullPath)

    {

        if (UNCFullPath.StartsWith(DIRDOUBLE))

        {

            string p = UNCFullPath; //local working copy

            if (p.StartsWith(ShareExtPrefix))

            {

                p = p.Substring(3, p.Length - 3);

                if (p.StartsWith(@"\UNC\")) //fails for "\\?\UNC\share\tail\file.txt" one case

                    p = DIRDOUBLE + p.Substring(5, p.Length - 5);

                else

                    p = DIR + p;

            } 

            //starts with \\h\s is min 

            int idx3rd = (p.Length >= 5 ) ? p.IndexOf(cDIR, 3) : -1; //4th position zero index 

​

            //Console.WriteLine("p = " + p + " idx3rd=" + idx3rd); //DEBUG

​

            if (p[0]==cDIR && p[1]==cDIR && Char.IsLetterOrDigit(p[2]) && p.Length >= 5 &&idx3rd > -1 && Char.IsLetter(p[idx3rd+1]) && p.IndexOf(cDIR, idx3rd + 2) > -1)

            {

                int i = p.IndexOfOccurence(cDIR, 4);

​

                if (i > -1)

                    return p.Substring(0, i); //returns empty if i=0

                else

                    return string.Empty;

​

            }

            else

                return string.Empty;

​

        }

        else

            return string.Empty;

​

    }

​

    public static void Main()

    {

         Console.WriteLine(@"\\2001:4860:4860::8888\share\tail\dir1".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\8.8.8.8\share\tail\dir1".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\host\share\tail\dir1".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\host\share\tail\file.txt".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\\?\UNC\share\tail\file.txt".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\h\s\file.txt".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\h\s\".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\\s\".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\h\\".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\\\\\\\".GetUNCHostIPAddressShare());

         Console.WriteLine(@"\\?\UNC\share\tail\file.txt".GetUNCHostIPAddressShare() + ", 1 failed case - UNC is Server Name");

    }

}