Question

This is maybe a stupid question, but since I am relatively new to UDP here it goes… If I am having two separate byte arrays that I need the receiving side to get as one big array, for example:

byte[] Array1 = {1,1,1}
byte[] Array2 = {2,2,2}

Can I avoid having to create a buffer and copy each array into it, and then send that buffer, like this:

byte[] Buffer= new byte[Array1.Length + Array2.Length];
Buffer.BlockCopy(Array1, 0, Buffer, 0, Array1.Length);
Buffer.BlockCopy(Array2, 0, Buffer, Array1.Length, Array2.Length);

udpClient.Send(Buffer, Buffer.Length);

Because if the two are big, and data rate is high, copying uses up much system resources…
So can I somehow tell the udpClient that I am starting the UDP fragmentation, and then do like this:

udpClient.ImStartingOneBigDatagram();

udpClient.Send(Array1, Array1.Length);
udpClient.Send(Array2, Array2.Length);

udpClient.ThatsAllFolks();

And be sure that the receiving side would get:

byte[] recv = {1,1,1,2,2,2}

I am using C# for this, and I dont need to use UdpClient, I was just making my point.

Answer 1

Use the equivalent of Win32 API’s WSASendMsg:

public int Send(
    IList<ArraySegment<byte>> buffers,
    SocketFlags socketFlags,
    out SocketError errorCode
)

http://msdn.microsoft.com/en-us/library/ms145161.aspx

But ultimately this is premature optimisation, if you perform some testing you will see that to use I/O scatter gather arrays you need at least 9KB of data to get performance improvement. For small buffers, i.e. less than a page size (4KB on x86) it is faster to build a contiguous buffer yourself before passing to the socket API.