public IP4Header(ByteBuffer buffer)
{
try
{
byte versionAndIHL = (byte)buffer.Get();
this.version = (byte)(versionAndIHL >> 4);
this.IHL = (byte)(versionAndIHL & 0x0F);
this.headerLength = this.IHL << 2;
this.typeOfService = BitUtils.GetUnsignedByte((byte)buffer.Get());
this.totalLength = BitUtils.GetUnsignedShort(buffer.Short);
this.identificationAndFlagsAndFragmentOffset = buffer.Int;
this.TTL = BitUtils.GetUnsignedByte((byte)buffer.Get());
this.protocolNum = BitUtils.GetUnsignedByte((byte)buffer.Get());
this.protocol = (TransportProtocol)protocolNum;
this.headerChecksum = BitUtils.GetUnsignedShort(buffer.Short);
byte[] addressBytes = new byte[4];
buffer.Get(addressBytes, 0, 4);
this.sourceAddress = InetAddress.GetByAddress(addressBytes);
buffer.Get(addressBytes, 0, 4);
this.destinationAddress = InetAddress.GetByAddress(addressBytes);
//this.optionsAndPadding = buffer.getInt();
}
catch
{
throw new UnknownHostException();
}
}
private void updateTCPChecksum(int payloadSize)
{
int sum = 0;
int tcpLength = TCP_HEADER_SIZE + payloadSize;
// Calculate pseudo-header checksum
ByteBuffer buffer = ByteBuffer.Wrap(ip4Header.sourceAddress.GetAddress());
sum = BitUtils.GetUnsignedShort(buffer.Short) + BitUtils.GetUnsignedShort(buffer.Short);
buffer = ByteBuffer.Wrap(ip4Header.destinationAddress.GetAddress());
sum += BitUtils.GetUnsignedShort(buffer.Short) + BitUtils.GetUnsignedShort(buffer.Short);
sum += ((int)IP4Header.TransportProtocol.TCP) + tcpLength;
buffer = backingBuffer.Duplicate();
// Clear previous checksum
buffer.PutShort(IP4_HEADER_SIZE + 16, (short)0);
// Calculate TCP segment checksum
buffer.Position(IP4_HEADER_SIZE);
while (tcpLength > 1)
{
sum += BitUtils.GetUnsignedShort(buffer.Short);
tcpLength -= 2;
}
if (tcpLength > 0)
{
sum += BitUtils.GetUnsignedByte((byte)buffer.Get()) << 8;
}
while (sum >> 16 > 0)
{
sum = (sum & 0xFFFF) + (sum >> 16);
}
sum = ~sum;
tcpHeader.checksum = sum;
backingBuffer.PutShort(IP4_HEADER_SIZE + 16, (short)sum);
}
