Setting Windows internet connection proxy from C#

using System;
using System.Runtime.InteropServices;
using System.ComponentModel;

namespace PoshHttp
{
   public class Proxies
   {
      public static bool UnsetProxy()
      {
         return SetProxy(null, null);
      }
      public static bool SetProxy(string strProxy)
      {
         return SetProxy(strProxy, null);
      }

      public static bool SetProxy(string strProxy, string exceptions)
      {
         InternetPerConnOptionList list = new InternetPerConnOptionList();

         int optionCount = string.IsNullOrEmpty(strProxy) ? 1 : (string.IsNullOrEmpty(exceptions) ? 2 : 3);
         InternetConnectionOption[] options = new InternetConnectionOption[optionCount];
         // USE a proxy server ...
         options[0].m_Option = PerConnOption.INTERNET_PER_CONN_FLAGS;
         options[0].m_Value.m_Int = (int)((optionCount < 2) ? PerConnFlags.PROXY_TYPE_DIRECT : (PerConnFlags.PROXY_TYPE_DIRECT | PerConnFlags.PROXY_TYPE_PROXY));
         // use THIS proxy server
         if (optionCount > 1)
         {
            options[1].m_Option = PerConnOption.INTERNET_PER_CONN_PROXY_SERVER;
            options[1].m_Value.m_StringPtr = Marshal.StringToHGlobalAuto(strProxy);
            // except for these addresses ...
            if (optionCount > 2)
            {
               options[2].m_Option = PerConnOption.INTERNET_PER_CONN_PROXY_BYPASS;
               options[2].m_Value.m_StringPtr = Marshal.StringToHGlobalAuto(exceptions);
            }
         }

         // default stuff
         list.dwSize = Marshal.SizeOf(list);
         list.szConnection = IntPtr.Zero;
         list.dwOptionCount = options.Length;
         list.dwOptionError = 0;


         int optSize = Marshal.SizeOf(typeof(InternetConnectionOption));
         // make a pointer out of all that ...
         IntPtr optionsPtr = Marshal.AllocCoTaskMem(optSize * options.Length);
         // copy the array over into that spot in memory ...
         for (int i = 0; i < options.Length; ++i)
         {
            IntPtr opt = new IntPtr(optionsPtr.ToInt32() + (i * optSize));
            Marshal.StructureToPtr(options[i], opt, false);
         }

         list.options = optionsPtr;

         // and then make a pointer out of the whole list
         IntPtr ipcoListPtr = Marshal.AllocCoTaskMem((Int32)list.dwSize);
         Marshal.StructureToPtr(list, ipcoListPtr, false);

         // and finally, call the API method!
         int returnvalue = NativeMethods.InternetSetOption(IntPtr.Zero,
            InternetOption.INTERNET_OPTION_PER_CONNECTION_OPTION,
            ipcoListPtr, list.dwSize) ? -1 : 0;
         if (returnvalue == 0)
         {  // get the error codes, they might be helpful
            returnvalue = Marshal.GetLastWin32Error();
         }
         // FREE the data ASAP
         Marshal.FreeCoTaskMem(optionsPtr);
         Marshal.FreeCoTaskMem(ipcoListPtr);
         if (returnvalue > 0)
         {  // throw the error codes, they might be helpful
            throw new Win32Exception(Marshal.GetLastWin32Error());
         }

         return (returnvalue < 0);
      }
   }

   #region WinInet structures
   [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
   public struct InternetPerConnOptionList
   {
      public int dwSize;               // size of the INTERNET_PER_CONN_OPTION_LIST struct
      public IntPtr szConnection;         // connection name to set/query options
      public int dwOptionCount;        // number of options to set/query
      public int dwOptionError;           // on error, which option failed
      //[MarshalAs(UnmanagedType.)]
      public IntPtr options;
   };

   [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
   public struct InternetConnectionOption
   {
      static readonly int Size;
      public PerConnOption m_Option;
      public InternetConnectionOptionValue m_Value;
      static InternetConnectionOption()
      {
         InternetConnectionOption.Size = Marshal.SizeOf(typeof(InternetConnectionOption));
      }

      // Nested Types
      [StructLayout(LayoutKind.Explicit)]
      public struct InternetConnectionOptionValue
      {
         // Fields
         [FieldOffset(0)]
         public System.Runtime.InteropServices.ComTypes.FILETIME m_FileTime;
         [FieldOffset(0)]
         public int m_Int;
         [FieldOffset(0)]
         public IntPtr m_StringPtr;
      }
   }
   #endregion

   #region WinInet enums
   //
   // options manifests for Internet{Query|Set}Option
   //
   public enum InternetOption : uint
   {
      INTERNET_OPTION_PER_CONNECTION_OPTION = 75
   }

   //
   // Options used in INTERNET_PER_CONN_OPTON struct
   //
   public enum PerConnOption
   {
      INTERNET_PER_CONN_FLAGS = 1, // Sets or retrieves the connection type. The Value member will contain one or more of the values from PerConnFlags
      INTERNET_PER_CONN_PROXY_SERVER = 2, // Sets or retrieves a string containing the proxy servers.  
      INTERNET_PER_CONN_PROXY_BYPASS = 3, // Sets or retrieves a string containing the URLs that do not use the proxy server.  
      INTERNET_PER_CONN_AUTOCONFIG_URL = 4//, // Sets or retrieves a string containing the URL to the automatic configuration script.  

   }

   //
   // PER_CONN_FLAGS
   //
   [Flags]
   public enum PerConnFlags
   {
      PROXY_TYPE_DIRECT = 0x00000001,  // direct to net
      PROXY_TYPE_PROXY = 0x00000002,  // via named proxy
      PROXY_TYPE_AUTO_PROXY_URL = 0x00000004,  // autoproxy URL
      PROXY_TYPE_AUTO_DETECT = 0x00000008   // use autoproxy detection
   }
   #endregion

   internal static class NativeMethods
   {
      [DllImport("WinInet.dll", SetLastError = true, CharSet = CharSet.Auto)]
      [return: MarshalAs(UnmanagedType.Bool)]
      public static extern bool InternetSetOption(IntPtr hInternet, InternetOption dwOption, IntPtr lpBuffer, int dwBufferLength);
   }
}