Internet Magic (Proxy Server) Windows Application

using System;
using System.Runtime.InteropServices;
using System.Security;
using System.Collections;
using System.Windows.Forms;

namespace ListNetworkComputers
{
    
    public sealed class NetworkBrowser
    {
       
        //declare the Netapi32 : NetServerEnum method import
        [DllImport("Netapi32", CharSet = CharSet.Auto, SetLastError = true),
        SuppressUnmanagedCodeSecurityAttribute]

        /// <summary>
        /// Netapi32.dll : The NetServerEnum function lists all servers
        /// of the specified type that are visible in a domain. For example, an 
        /// application can call NetServerEnum to list all domain controllers only
        /// or all SQL servers only.
        ///	You can combine bit masks to list several types. For example, a value 
        /// of 0x00000003  combines the bit masks for SV_TYPE_WORKSTATION 
        /// (0x00000001) and SV_TYPE_SERVER (0x00000002)
        /// </summary>
        public static extern int NetServerEnum(
            string ServerNane, // must be null
            int dwLevel,
            ref IntPtr pBuf,
            int dwPrefMaxLen,
            out int dwEntriesRead,
            out int dwTotalEntries,
            int dwServerType,
            string domain, // null for login domain
            out int dwResumeHandle
            );

        //declare the Netapi32 : NetApiBufferFree method import
        [DllImport("Netapi32", SetLastError = true),
        SuppressUnmanagedCodeSecurityAttribute]

        /// <summary>
        /// Netapi32.dll : The NetApiBufferFree function frees 
        /// the memory that the NetApiBufferAllocate function allocates. 
        /// Call NetApiBufferFree to free the memory that other network 
        /// management functions return.
        /// </summary>
        public static extern int NetApiBufferFree(
            IntPtr pBuf);

        //create a _SERVER_INFO_100 STRUCTURE
        [StructLayout(LayoutKind.Sequential)]
        public struct _SERVER_INFO_100
        {
            internal int sv100_platform_id;
            [MarshalAs(UnmanagedType.LPWStr)]
            internal string sv100_name;
        }
        /// <summary>
        /// Constructor, simply creates a new NetworkBrowser object
        /// </summary>
        public NetworkBrowser()
        {

        }
        /// <summary>
        /// Uses the DllImport : NetServerEnum with all its required parameters
        /// </summary>
        /// <returns>Arraylist that represents all the SV_TYPE_WORKSTATION and SV_TYPE_SERVER
        /// PC's in the Domain</returns>
        public ArrayList getNetworkComputers(string dmn)
        {
            //local fields
            ArrayList networkComputers = new ArrayList();
            const int MAX_PREFERRED_LENGTH = -1;
            int SV_TYPE_WORKSTATION = 1;
            int SV_TYPE_SERVER = 2;
            IntPtr buffer = IntPtr.Zero;
            IntPtr tmpBuffer = IntPtr.Zero;
            int entriesRead = 0;
            int totalEntries = 0;
            int resHandle = 0;
            int sizeofINFO = Marshal.SizeOf(typeof(_SERVER_INFO_100));


            try
            {
                //call the DllImport : NetServerEnum with all its required parameters
                
                int ret = NetServerEnum(null, 100, ref buffer, MAX_PREFERRED_LENGTH,
                    out entriesRead,
                    out totalEntries, SV_TYPE_WORKSTATION | SV_TYPE_SERVER, dmn, out 
					resHandle);
                //if the returned with a NERR_Success (C++ term), =0 for C#
                if (ret == 0)
                {
                    //loop through all SV_TYPE_WORKSTATION and SV_TYPE_SERVER PC's
                    for (int i = 0; i < totalEntries; i++)
                    {
                        //get pointer to, Pointer to the buffer that received the data from
                        //the call to NetServerEnum. Must ensure to use correct size of 
                        //STRUCTURE to ensure correct location in memory is pointed to
                        tmpBuffer = new IntPtr((int)buffer + (i * sizeofINFO));
                        //Have now got a pointer to the list of SV_TYPE_WORKSTATION and 
                        //SV_TYPE_SERVER PC's, which is unmanaged memory
                        //Needs to Marshal data from an unmanaged block of memory to a 
                        //managed object, again using STRUCTURE to ensure the correct data
                        //is marshalled 
                        _SERVER_INFO_100 svrInfo = (_SERVER_INFO_100)
                            Marshal.PtrToStructure(tmpBuffer, typeof(_SERVER_INFO_100));

                        //add the PC names to the ArrayList
                        networkComputers.Add(svrInfo.sv100_name);
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("Problem with acessing network computers in NetworkBrowser " +
                    "\r\n\r\n\r\n" + ex.Message,
                    "Error", MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                return null;
            }
            finally
            {
                //The NetApiBufferFree function frees 
                //the memory that the NetApiBufferAllocate function allocates
                NetApiBufferFree(buffer);
            }
            //return entries found
            return networkComputers;

        }
        
    }
    
}