Question

How do I convert a structure to a byte array in C#?

I have defined a structure like this:

public struct CIFSPacket
{
    public uint protocolIdentifier; //The value must be "0xFF+'SMB'".
    public byte command;

    public byte errorClass;
    public byte reserved;
    public ushort error;

    public byte flags;

    //Here there are 14 bytes of data which is used differently among different dialects.
    //I do want the flags2. However, so I'll try parsing them.
    public ushort flags2;

    public ushort treeId;
    public ushort processId;
    public ushort userId;
    public ushort multiplexId;

    //Trans request
    public byte wordCount;//Count of parameter words defining the data portion of the packet.
    //From here it might be undefined...

    public int parametersStartIndex;

    public ushort byteCount; //Buffer length
    public int bufferStartIndex;

    public string Buffer;
}

In my main method, I create an instance of it and assign values to it:

CIFSPacket packet = new CIFSPacket();
packet.protocolIdentifier = 0xff;
packet.command = (byte)CommandTypes.SMB_COM_NEGOTIATE;
packet.errorClass = 0xff;
packet.error = 0;
packet.flags = 0x00;
packet.flags2 = 0x0001;
packet.multiplexId = 22;
packet.wordCount = 0;
packet.byteCount = 119;

packet.Buffer = "NT LM 0.12";

Now I want to send this Packet by socket. For that, I need to convert the structure to a byte array. How can I do it?

My full code is as follows.

static void Main(string[] args)
{

  Socket MyPing = new Socket(AddressFamily.InterNetwork,
  SocketType.Stream , ProtocolType.Unspecified ) ;


  MyPing.Connect("172.24.18.240", 139);

    //Fake an IP Address so I can send with SendTo
    IPAddress IP = new IPAddress(new byte[] { 172,24,18,240 });
    IPEndPoint IPEP = new IPEndPoint(IP, 139);

    //Local IP for Receiving
    IPEndPoint Local = new IPEndPoint(IPAddress.Any, 0);
    EndPoint EP = (EndPoint)Local;

    CIFSPacket packet = new CIFSPacket();
    packet.protocolIdentifier = 0xff;
    packet.command = (byte)CommandTypes.SMB_COM_NEGOTIATE;
    packet.errorClass = 0xff;
    packet.error = 0;
    packet.flags = 0x00;
    packet.flags2 = 0x0001;
    packet.multiplexId = 22;
    packet.wordCount = 0;
    packet.byteCount = 119;

    packet.Buffer = "NT LM 0.12";

    MyPing.SendTo(It takes byte array as parameter);
}

What would a code snippet be?

Answer 1

This is fairly easy, using marshalling.

Top of file

using System.Runtime.InteropServices

Function

byte[] getBytes(CIFSPacket str) {
    int size = Marshal.SizeOf(str);
    byte[] arr = new byte[size];

    IntPtr ptr = IntPtr.Zero;
    try
    {
        ptr = Marshal.AllocHGlobal(size);
        Marshal.StructureToPtr(str, ptr, true);
        Marshal.Copy(ptr, arr, 0, size);
    }
    finally
    {
        Marshal.FreeHGlobal(ptr);
    }
    return arr;
}

And to convert it back:

CIFSPacket fromBytes(byte[] arr)
{
    CIFSPacket str = new CIFSPacket();

    int size = Marshal.SizeOf(str);
    IntPtr ptr = IntPtr.Zero;
    try
    {
        ptr = Marshal.AllocHGlobal(size);

        Marshal.Copy(arr, 0, ptr, size);

        str = (CIFSPacket)Marshal.PtrToStructure(ptr, str.GetType());
    }
    finally
    {
        Marshal.FreeHGlobal(ptr);
    }
    return str;
}

In your structure, you will need to put this before a string

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 100)]
public string Buffer;

And make sure SizeConst is as big as your biggest possible string.

And you should probably read this:
http://msdn.microsoft.com/en-us/library/4ca6d5z7.aspx