如何用空字符填充Byte标头？

Question

Im currently trying to add additional bytes to a byte array.

Im trying to send a header to a server that contains the computer name. However because the computer name could change for every machine im trying to create a byte array that is a specific length like 100 bytes.

Which means once i have my string header "rdmstream§" + Dns.GetHostName()" I need to add x amounts of bytes at the end or start as padding so the overall byte length = 100.

I was wondering if this was possible?

Below is an example of my code for having a set header length:

 public static void SendMultiScreen(byte[] img)
    {
        try
        {

            //string command = ("rdmstream§" + Dns.GetHostName()); //This is what I want to add.

            byte[] send = new byte[img.Length + 16]; //Create a new buffer to send to the server
            byte[] header = Encoding.Unicode.GetBytes("rdmstrea"); //Get the bytes of the header
            Buffer.BlockCopy(header, 0, send, 0, header.Length); //Copy the header to the main buffer
            fps = 800;
            Buffer.BlockCopy(img, 0, send, header.Length, img.Length); //Copy the image to the main buffer
            _clientSocket.Send(send, 0, send.Length, SocketFlags.None); //Send the image to the server


        }

As you can see as long as the message is only 8 Characters long this works fine. However I want the characters in the message to be variable.

I don't have much knowledge on bytes if im honest so any additional help would be much appreciated.

Thankyou in advance.

Answer 1

One can argue about it if padding is the right way to go, but you could pad the name of your host

string hostName = "OhWhatEver".PadRight(100)

then use this as input for your GetBytes call.

Edit: If you can't live with the spaces use that:

byte[] header = new byte[100];
byte[] hostname = System.Text.Encoding.Unicode.GetBytes("rdmstream§" + System.Net.Dns.GetHostName());
Array.Copy(hostname, header, hostname.Length);

Answer 2

If your concern is packet fragmentation: Socket has overloads to send a list of buffer segments in a single operation. That means you can do something like:

var segments = new List<ArraySegment<byte>>();
segments.Add(header);
segments.Add(img);

Note that it is not necessary for the header to be the full array; you can send a part of an array, which allows you to re-use the same buffer; for example:

byte[] buffer = new byte[MaxLength];
var segments = new List<ArraySegment<byte>>();
segments.Add(default); // placeholder
segments.Add(img);
foreach(...) {
    string val = ...
    int len = encoding.GetBytes(val, 0, val.Length, buffer, 0);
    segments[0] = new ArraySegment<byte>(buffer, 0, len);
    thisSocket.Send(segments);
}

However! to do this usually requires some kind of framing on the header - either a sentinel value (perhaps a trailing CR/LF/CRLF), or a prefix of the number of bytes that are the string - len here.

---

If that really isn't possible... just loop over the unused part of the array and set it to what you want, or use Array.Clear if zero is OK.