public static byte[] RewriteUdpHeader(byte[] packet, UInt16 port, RewriteType type)
{
byte IHL = (byte)(packet[0] << 4);
IHL = (byte)(IHL >> 4);
int ip_header_len;
if (IHL > 5)
{
ip_header_len = (IHL * 32) / 8;
}
else
{
ip_header_len = 20;
}
int port_index = ip_header_len + 0;
if (type == RewriteType.Source)
{
port_index = ip_header_len + 0;
}
if (type == RewriteType.Destination)
{
port_index = ip_header_len + 2;
}
byte[] bdst_port = BitConverter.GetBytes(port);
packet[port_index] = bdst_port[1];
packet[port_index + 1] = bdst_port[0];
return(RewriteIpUdpChecksum(packet));
}
//******************************************************************************//
public static byte[] RewriteIpHeader(byte[] packet, IPAddress ip_address, RewriteType type)
{
int repl_index = 12;
if (type == RewriteType.Source)
{
repl_index = 12;
}
if (type == RewriteType.Destination)
{
repl_index = 16;
}
byte IHL = (byte)(packet[0] << 4);
IHL = (byte)(IHL >> 4);
int ip_header_len;
if (IHL > 5)
{
ip_header_len = (IHL * 32) / 8;
}
else
{
ip_header_len = 20;
}
byte[] source_ip = ip_address.GetAddressBytes();
byte[] checksum = new byte[2];
Array.Copy(source_ip, 0, packet, repl_index, 4);
Array.Copy(checksum, 0, packet, 10, 2);
byte[] header = new byte[ip_header_len];
Array.Copy(packet, 0, header, 0, ip_header_len);
ushort ip_checksum = ComputeChecksum(header, 0, ip_header_len);
checksum = BitConverter.GetBytes(ip_checksum);
Array.Reverse(checksum);
Array.Copy(checksum, 0, packet, 10, 2);
return(packet);
}
