/*
* $Id$
*
* Copyright (C) 2003-2014 JNode.org
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; If not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
package org.jnode.net.ipv4.udp;
import org.apache.log4j.Logger;
import org.jnode.net.SocketBuffer;
import org.jnode.net.TransportLayerHeader;
import org.jnode.net.ipv4.IPv4Header;
import org.jnode.net.ipv4.IPv4Utils;
import org.jnode.util.NumberUtils;
/**
* Header of an UDP packet
*
* @author epr
*/
public class UDPHeader implements TransportLayerHeader, UDPConstants {
/** My logger */
private static final Logger log = Logger.getLogger(UDPHeader.class);
/** The port of the sending process or 0 if not used. */
private final int srcPort;
/** The destination port within the context of a particular internet address */
private final int dstPort;
/** The length in octet. It include the header and the data. Minimum value of the length is 8 */
private final int udpLength;
private final boolean checksumOk;
/**
* Create a new instance
*
* @param srcPort The port of the sending process.
* @param dstPort The destination port.
* @param dataLength The length of the data.
*/
public UDPHeader(int srcPort, int dstPort, int dataLength) {
this.srcPort = srcPort;
this.dstPort = dstPort;
this.udpLength = UDP_HLEN + dataLength;
this.checksumOk = true;
}
/**
* Create a new instance and read the contents from the given buffer
*
* @param skbuf The socket buffer.
*/
public UDPHeader(SocketBuffer skbuf) {
this.srcPort = skbuf.get16(0);
this.dstPort = skbuf.get16(2);
this.udpLength = skbuf.get16(4);
final int checksum = skbuf.get16(6);
if (checksum == 0) {
log.debug("No checksum set");
this.checksumOk = true;
} else {
// Create the pseudo header for checksum calculation
final IPv4Header ipHdr = (IPv4Header) skbuf.getNetworkLayerHeader();
final SocketBuffer phdr = new SocketBuffer(12);
phdr.insert(12);
ipHdr.getSource().writeTo(phdr, 0);
ipHdr.getDestination().writeTo(phdr, 4);
phdr.set(8, 0);
phdr.set(9, ipHdr.getProtocol());
phdr.set16(10, udpLength);
phdr.append(skbuf);
final int ccs2 = IPv4Utils.calcChecksum(phdr, 0, udpLength + 12);
this.checksumOk = (ccs2 == 0);
if (!checksumOk) {
log.debug("Found invalid UDP checksum 0x" + NumberUtils.hex(ccs2, 4));
}
}
}
/**
* @see org.jnode.net.LayerHeader#getLength()
*/
public int getLength() {
return UDP_HLEN;
}
/**
* @see org.jnode.net.LayerHeader#prefixTo(org.jnode.net.SocketBuffer)
*/
public void prefixTo(SocketBuffer skbuf) {
skbuf.insert(UDP_HLEN);
skbuf.set16(0, srcPort);
skbuf.set16(2, dstPort);
skbuf.set16(4, udpLength);
skbuf.set16(6, 0); // Checksum, calculate and overwrite later
}
/**
* Finalize the header in the given buffer. This method is called when all
* layers have set their header data and can be used e.g. to update checksum
* values.
*
* @param skbuf The buffer
* @param offset The offset to the first byte (in the buffer) of this header
* (since low layer headers are already prefixed)
*/
public void finalizeHeader(SocketBuffer skbuf, int offset) {
final int ccs = calcChecksum(skbuf, offset);
skbuf.set16(offset + 6, ccs);
}
/**
* Is the checksum valid?
*/
public boolean isChecksumOk() {
return checksumOk;
}
/**
* Gets the destination port
*/
public int getDstPort() {
return dstPort;
}
/**
* Gets the source port
*/
public int getSrcPort() {
return srcPort;
}
/**
* Gets the length of the UDP packet (header + data)
*/
public int getUdpLength() {
return udpLength;
}
/**
* Gets the length of the UDP data.
*/
public int getDataLength() {
return udpLength - UDP_HLEN;
}
/**
* @see java.lang.Object#toString()
*/
public String toString() {
return "UDP srcPort=" + srcPort + ", dstPort=" + dstPort + ", dataLength=" + getDataLength();
}
private int calcChecksum(SocketBuffer skbuf, int offset) {
final IPv4Header ipHdr = (IPv4Header) skbuf.getNetworkLayerHeader();
final SocketBuffer phdr = new SocketBuffer(12);
phdr.insert(12);
ipHdr.getSource().writeTo(phdr, 0);
ipHdr.getDestination().writeTo(phdr, 4);
phdr.set(8, 0);
phdr.set(9, ipHdr.getProtocol());
phdr.set16(10, udpLength);
phdr.append(offset, skbuf);
final int csLength = udpLength + 12;
return IPv4Utils.calcChecksum(phdr, 0, csLength);
}
}