/*
* Copyright 2010 NCHOVY
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.krakenapps.pcap.decoder.tcp;
import java.net.Inet4Address;
import java.nio.ByteBuffer;
import org.krakenapps.pcap.util.Buffer;
import org.krakenapps.pcap.util.Checksum;
import org.krakenapps.pcap.util.IpConverter;
/**
* @author mindori
*/
public class TcpChecksum {
private TcpChecksum() {
}
public static int sum(TcpPacket s) {
ByteBuffer buf = build(s);
Buffer data = s.getData();
int length = buf.limit();
if (data != null)
length += data.readableBytes();
short[] checksumBytes = new short[length / 2];
int i = 0;
for (; i < checksumBytes.length; i++) {
checksumBytes[i] = buf.getShort();
}
/* add payload to checksum */
if (data != null) {
while (data.isEOB()) {
// TODO: buffer underflow handling (padding)
checksumBytes[i++] = data.getShort();
}
}
if (data != null)
data.rewind();
return Checksum.sum(checksumBytes);
}
private static ByteBuffer build(TcpPacket s) {
/* except option and padding: 16 shorts */
ByteBuffer bb = ByteBuffer.allocate(12 + s.getTotalLength());
// TODO: IPv6 handling
// pseudo header
bb.putInt(IpConverter.toInt((Inet4Address) s.getSourceAddress()));
bb.putInt(IpConverter.toInt((Inet4Address) s.getDestinationAddress()));
bb.put((byte) 0); // padding
bb.put((byte) 6); // tcp
bb.putShort((short) (s.getTotalLength()));
//
bb.putShort((short) s.getSourcePort());
bb.putShort((short) s.getDestinationPort());
bb.putInt(s.getSeq());
bb.putInt(s.getAck());
bb.put((byte) (s.getDataOffset() << 4));
bb.put((byte) s.getFlags());
bb.putShort((short) s.getWindow());
bb.putShort((short) 0); // checksum
bb.putShort((short) s.getUrgentPointer());
if (s.getOptions() != null)
bb.put(s.getOptions());
if (s.getPadding() != null)
bb.put(s.getPadding());
bb.flip();
return bb;
}
}