Using GetExtendedTcpTable function to Get Active TCP endpoints List

The GetExtendedTcpTable function retrieves a table that contains a list of TCP endpoints available to the application.

C# Signature:

[DllImport("iphlpapi.dll", SetLastError=true)]
static extern uint GetExtendedTcpTable(IntPtr pTcpTable, ref int dwOutBufLen, bool sort, int ipVersion, TCP_TABLE_CLASS tblClass,int reserved);

  [StructLayout(LayoutKind.Sequential)]
    public struct MIB_TCPROW_OWNER_PID
    {
        public TcpState state;
        public uint localAddr;
        public byte localPort1;
        public byte localPort2;
        public byte localPort3;
        public byte localPort4;
        public uint remoteAddr;
        public byte remotePort1;
        public byte remotePort2;
        public byte remotePort3;
        public byte remotePort4;
        public int owningPid;
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct MIB_TCPTABLE_OWNER_PID
    {
        public uint dwNumEntries;
        MIB_TCPROW_OWNER_PID table;
    }

    //public TcpRow[] GetAllTcpConnections()
    public MIB_TCPROW_OWNER_PID[] GetAllTcpConnections()
    {
    //  TcpRow is my own class to display returned rows in a nice manner.
    //    TcpRow[] tTable;
        MIB_TCPROW_OWNER_PID[] tTable;
        int AF_INET = 2;    // IP_v4
        int buffSize = 0;

        // how much memory do we need?
        uint ret = GetExtendedTcpTable(IntPtr.Zero, ref buffSize, true, AF_INET, TCP_TABLE_CLASS.TCP_TABLE_OWNER_PID_ALL,0);        
        IntPtr buffTable = Marshal.AllocHGlobal(buffSize);

        try
        {
        ret = GetExtendedTcpTable(buffTable, ref buffSize, true, AF_INET, TCP_TABLE_CLASS.TCP_TABLE_OWNER_PID_ALL, 0);
        if (ret != 0)
        {
            return null;
        }

        // get the number of entries in the table
        //MibTcpTable tab = (MibTcpTable)Marshal.PtrToStructure(buffTable, typeof(MibTcpTable));
        MIB_TCPTABLE_OWNER_PID tab = (MIB_TCPTABLE_OWNER_PID)Marshal.PtrToStructure(buffTable, typeof(MIB_TCPTABLE_OWNER_PID));
        //IntPtr rowPtr = (IntPtr)((long)buffTable + Marshal.SizeOf(tab.numberOfEntries) );
        IntPtr rowPtr = (IntPtr)((long)buffTable + Marshal.SizeOf(tab.dwNumEntries));
        // buffer we will be returning
        //tTable = new TcpRow[tab.numberOfEntries];
        tTable = new MIB_TCPROW_OWNER_PID[tab.dwNumEntries];

        //for (int i = 0; i < tab.numberOfEntries; i++)        
        for (int i = 0; i < tab.dwNumEntries; i++)
        {
            //MibTcpRow_Owner_Pid tcpRow = (MibTcpRow_Owner_Pid)Marshal.PtrToStructure(rowPtr, typeof(MibTcpRow_Owner_Pid));
            MIB_TCPROW_OWNER_PID tcpRow = (MIB_TCPROW_OWNER_PID)Marshal.PtrToStructure(rowPtr, typeof(MIB_TCPROW_OWNER_PID));
            //tTable[i] = new TcpRow(tcpRow);
            tTable[i] = tcpRow;
            rowPtr = (IntPtr)((long)rowPtr + Marshal.SizeOf(tcpRow));   // next entry
        }

        }
        finally
        {
        // Free the Memory
        Marshal.FreeHGlobal(buffTable);
        }



        return tTable;
    }