ByTeArray AS3 function from C# function help needed

ByTeArray AS3 function from C# function help needed

I am a noob with ByteArray use in as3 and would need some help. I am
trying to reproduce this "Header" function in as3 returning a ByteArray
from a C# function (code provided bellow). Can anyone point me in the
right direction?
I got to this point and not sure how to continue:
private function header():ByteArray
{
var header:ByteArray = new ByteArray();
header.writeUTFBytes("A");
header.writeUTFBytes("B");
header.writeUTFBytes("C");
header.writeUTFBytes("D");
...
}
Thank you
private enum PacketType
{
PtHelo = 0x01,
PtBye = 0x02,
PtButton = 0x03,
PtMouse = 0x04,
}
private const byte bv = 2;
private const byte mv = 0;
private byte[] Header(PacketType packetType, int numberOfPackets, int
currentPacket, int payloadSize)
{
var header = new byte[HeaderSize];
header[0] = (byte)'A';
header[1] = (byte)'B';
header[2] = (byte)'C';
header[3] = (byte)'D';
header[4] = bv;
header[5] = mv;
if (currentPacket == 1)
{
header[6] = (byte)(((ushort)packetType & 0xff00) >> 8);
header[7] = (byte)((ushort)packetType & 0x00ff);
}
else
{
header[6] = ((ushort)PacketType.PtBlob & 0xff00) >> 8;
header[7] = (ushort)PacketType.PtBlob & 0x00ff;
}
header[8] = (byte)((currentPacket & 0xff000000) >> 24);
header[9] = (byte)((currentPacket & 0x00ff0000) >> 16);
header[10] = (byte)((currentPacket & 0x0000ff00) >> 8);
header[11] = (byte)(currentPacket & 0x000000ff);
header[12] = (byte)((numberOfPackets & 0xff000000) >> 24);
header[13] = (byte)((numberOfPackets & 0x00ff0000) >> 16);
header[14] = (byte)((numberOfPackets & 0x0000ff00) >> 8);
header[15] = (byte)(numberOfPackets & 0x000000ff);
header[16] = (byte)((payloadSize & 0xff00) >> 8);
header[17] = (byte)(payloadSize & 0x00ff);
return header;
}