udpheader.java

来自「纯java操作系统jnode,安装简单和操作简单的个人使用的Java操作系统」· Java 代码 · 共 167 行

/*
 * $Id: UDPHeader.java,v 1.1 2003/11/25 11:52:26 epr Exp $
 */
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 final Logger log = Logger.getLogger(getClass());
	private final int srcPort;
	private final int dstPort;
	private final int udpLength;
	private final boolean checksumOk;

	/**
	 * Create a new instance
	 * @param srcPort
	 * @param dstPort
	 * @param dataLength
	 */
	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
	 */
	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 ccs1 = IPv4Utils.calcChecksum(phdr, 0, 12);
			final int ccs2 = IPv4Utils.calcChecksum(skbuf, 0, udpLength, ccs1);
			*/
			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);
		//log.debug("ccs=0x" + NumberUtils.hex(ccs, 4));
		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;
		/*for (int i = 0; i < csLength; i++) {
			System.out.print(NumberUtils.hex(phdr.get(i), 2) + " ");
		}
		System.out.println();*/
		
		return IPv4Utils.calcChecksum(phdr, 0, csLength);
	}
}