How can I get an active UNC Path in DFS programatically

Question

Given a DFS path how would I know what is the active path it is currently on programatically.

For exmaple I have 2 Servers shares as "\\Server1\Folder\" and "\\Server2\Folder\" and it has DFS turned on so it can be accessed on "\\DFS_Server\Folder\", how would I know what is the active path currently "\\DFS_Server\Folder\" is on, whether it is "\\Server1\Folder\" or "\\Server2\Folder\".

Answer 1

If I understand your requirement correctly, there's also an API that seems to do what you need:

// mscorlib (no additional assemblies needed)
using System.Runtime.InteropServices;

public static class Dfs
{
    private enum NetDfsInfoLevel
    {
        DfsInfo1 = 1,
        DfsInfo2 = 2,
        DfsInfo3 = 3,
        DfsInfo4 = 4,
        DfsInfo5 = 5,
        DfsInfo6 = 6,
        DfsInfo7 = 7,
        DfsInfo8 = 8,
        DfsInfo9 = 9,
        DfsInfo50 = 50,
        DfsInfo100 = 100,
        DfsInfo150 = 150,
    }

    [DllImport("netapi32.dll", SetLastError = true)]
    private static extern int NetApiBufferFree(IntPtr buffer);

    [DllImport("Netapi32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    private static extern int NetDfsGetInfo(
        [MarshalAs(UnmanagedType.LPWStr)] string DfsEntryPath, // DFS entry path for the volume
        [MarshalAs(UnmanagedType.LPWStr)] string ServerName,   // This parameter is currently ignored and should be NULL
        [MarshalAs(UnmanagedType.LPWStr)] string ShareName,    // This parameter is currently ignored and should be NULL.
        NetDfsInfoLevel Level,                                 // Level of information requested
        out IntPtr Buffer                                      // API allocates and returns buffer with requested info
        );

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    private struct DFS_INFO_3
    {
        [MarshalAs(UnmanagedType.LPWStr)]
        public string EntryPath;
        [MarshalAs(UnmanagedType.LPWStr)]
        public string Comment;
        public int State;
        public int NumberOfStorages;
        public IntPtr Storage;
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    private struct DFS_STORAGE_INFO
    {
        public int State;
        [MarshalAs(UnmanagedType.LPWStr)]
        public string ServerName;
        [MarshalAs(UnmanagedType.LPWStr)]
        public string ShareName;
    }

    private static T GetStruct<T>(IntPtr buffer, int offset=0)where T:struct
    {
        T r = new T();
        r = (T) Marshal.PtrToStructure(buffer + offset * Marshal.SizeOf(r), typeof(T));
        return r;
    }

    public static string GetDfsInfo(string server)
    {
        string rval = null;
        IntPtr b;
        int r = NetDfsGetInfo(server, null, null, NetDfsInfoLevel.DfsInfo3, out b);
        if(r != 0)
        {
            NetApiBufferFree(b);

            // return passed string if not DFS
            return rval;
        }

        DFS_INFO_3 sRes = GetStruct<DFS_INFO_3>(b);
        if(sRes.NumberOfStorages > 0)
        {
            DFS_STORAGE_INFO sResInfo = GetStruct<DFS_STORAGE_INFO>(sRes.Storage);
            rval = string.Concat(@"\\", sResInfo.ServerName, @"\", sResInfo.ShareName, @"\");
        }

        NetApiBufferFree(b);

        return rval;
    }
}

Use it like this:

string dfsPath = @"\\DFS_Server\Folder\";
string share = Dfs.GetDfsInfo(dfsPath)

For an API reference, check msdn on NetDfsGetInfo, DFS_INFO_3, DFS_STORAGE_INFO and NetApiBufferFree.