Share via

Establish a GPRS connection with TcpClient

  • Article

NETCF's HttpWebRequest automatically sets up a GPRS connection for web requests/web services when a wired/wi-fi connection is not available. Therefore, when you do a web request or consume a web service, developers do not need special coding to handle the GPRS connection case. This does not apply to lower level socket classes like TcpClient and UdpClient. With these classes, you would need to use the Connection Manager APIs to establish/release the connections.

To allow users to more easily setup/release a GPRS connection, I have written a managed representation of the connection manager APIs that we need when we establish a GPRS connection with TcpClient:

     public class GPRSConnection
    {
        const int S_OK = 0;
        const uint CONNMGR_PARAM_GUIDDESTNET = 0x1;
        const uint CONNMGR_FLAG_PROXY_HTTP = 0x1;
        const uint CONNMGR_PRIORITY_USERINTERACTIVE = 0x08000;
        const uint INFINITE = 0xffffffff;
        const uint CONNMGR_STATUS_CONNECTED = 0x10;
        static Hashtable ht = new Hashtable();

        static GPRSConnection()
        {
            ManualResetEvent mre = new ManualResetEvent(false);
            mre.Handle = ConnMgrApiReadyEvent();
            mre.WaitOne();
            CloseHandle(mre.Handle);
        }

        ~GPRSConnection()
        {
            ReleaseAll();
        }

        public static bool Setup(Uri url)
        {
            return Setup(url.ToString());
        }

        public static bool Setup(string urlStr)
        {
            ConnectionInfo ci = new ConnectionInfo();
            IntPtr phConnection = IntPtr.Zero;
            uint status = 0;

            if (ht[urlStr] != null)
                return true;

            if (ConnMgrMapURL(urlStr, ref ci.guidDestNet, IntPtr.Zero) != S_OK)
                return false;
            
            ci.cbSize = (uint) Marshal.SizeOf(ci);
            ci.dwParams = CONNMGR_PARAM_GUIDDESTNET;
            ci.dwFlags = CONNMGR_FLAG_PROXY_HTTP;
            ci.dwPriority = CONNMGR_PRIORITY_USERINTERACTIVE;
            ci.bExclusive = 0;
            ci.bDisabled = 0;
            ci.hWnd = IntPtr.Zero;
            ci.uMsg = 0;
            ci.lParam = 0;

            if (ConnMgrEstablishConnectionSync(ref ci, ref phConnection, INFINITE, ref status) != S_OK &&
                status != CONNMGR_STATUS_CONNECTED)
                return false;

            ht[urlStr] = phConnection;
            return true;
        }

        public static bool Release(Uri url)
        {
            return Release(url.ToString());
        }

        public static bool Release(string urlStr)
        {
            return Release(urlStr, true);
        }

        private static bool Release(string urlStr, bool removeNode)
        {
            bool res = true;
            IntPtr ph = IntPtr.Zero;
            if (ht[urlStr] == null)
                return true;
            ph = (IntPtr)ht[urlStr];
            if (ConnMgrReleaseConnection(ph, 1) != S_OK)
                res = false;
            CloseHandle(ph);
            if (removeNode)
                ht.Remove(urlStr);
            return res;
        }

        public static void ReleaseAll()
        {
           foreach(DictionaryEntry de in ht)
           {
               Release((string)de.Key, false);
           }
           ht.Clear();
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct ConnectionInfo
        {
            public uint cbSize;
            public uint dwParams;
            public uint dwFlags;
            public uint dwPriority;
            public int bExclusive;
            public int bDisabled;
            public Guid guidDestNet;
            public IntPtr hWnd;
            public uint uMsg;
            public uint lParam;
            public uint ulMaxCost;
            public uint ulMinRcvBw;
            public uint ulMaxConnLatency;
        }

        [DllImport("cellcore.dll")]
        private static extern int ConnMgrMapURL(string pwszURL, ref Guid pguid, IntPtr pdwIndex);

        [DllImport("cellcore.dll")]
        private static extern int ConnMgrEstablishConnectionSync(ref ConnectionInfo ci, ref IntPtr phConnection, uint dwTimeout, ref uint pdwStatus);

        [DllImport("cellcore.dll")]
        private static extern IntPtr ConnMgrApiReadyEvent();

        [DllImport("cellcore.dll")]
        private static extern int ConnMgrReleaseConnection(IntPtr hConnection, int bCache);

        [DllImport("coredll.dll")]
        private static extern int CloseHandle(IntPtr hObject);
    }

 To use the GPRSConnection class, simply call the Setup method prior to creating a connection with the TcpClient() class. You may use the following sample as a reference to see how the class is used:

 

         public void DoTcpConnection()
        {
            string url = "www.msn.com";
            bool res = GPRSConnection.Setup("https://" + url + "/");
            if (res)
            {
                TcpClient tc = new TcpClient(url, 80);
                NetworkStream ns = tc.GetStream();
                byte[] buf = new byte[100];
                ns.Write(buf, 0, 100);
                tc.Client.Shutdown(SocketShutdown.Both);
                ns.Close();
                tc.Close();
                MessageBox.Show("Wrote 100 bytes");
            }
            else
            {
                MessageBox.Show("Connection establishment failed");
            }
        }

Enjoy,

Anthony Wong [MSFT]

This posting is provided "AS IS" with no warranties, and confers no rights.

Comments