icmpheader.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 102 行

/*
 * $Id: ICMPHeader.java,v 1.1 2003/11/25 11:52:20 epr Exp $
 */
package org.jnode.net.ipv4.icmp;

import org.jnode.net.SocketBuffer;
import org.jnode.net.TransportLayerHeader;
import org.jnode.net.ipv4.IPv4Header;
import org.jnode.net.ipv4.IPv4Utils;

/**
 * @author epr
 */
public abstract class ICMPHeader implements TransportLayerHeader, ICMPConstants {
	
	private final int type;
	private final int code;
	private final boolean checksumOk;
	
	/**
	 * Create a new instance
	 * @param type
	 * @param code
	 */
	public ICMPHeader(int type, int code) {
		if ((type < 0) || (type > NR_ICMP_TYPES)) {
			throw new IllegalArgumentException("Invalid type " + type);
		}
		if (code < 0) {
			throw new IllegalArgumentException("Invalid code " + code);
		}
		this.type = type;
		this.code = code;
		this.checksumOk = true;
	}
	
	/**
	 * Read an ICMP header for the given buffer
	 * @param skbuf
	 */
	public ICMPHeader(SocketBuffer skbuf) {
		this.type = skbuf.get(0);
		this.code = skbuf.get(1);
		final int dataLength = ((IPv4Header)skbuf.getNetworkLayerHeader()).getDataLength();
		final int ccs = IPv4Utils.calcChecksum(skbuf, 0, dataLength);
		this.checksumOk = (ccs == 0);
	}

	/**
	 * @see org.jnode.net.LayerHeader#prefixTo(org.jnode.net.SocketBuffer)
	 */
	public void prefixTo(SocketBuffer skbuf) {
		skbuf.insert(getLength());
		skbuf.set(0, type);
		skbuf.set(1, code);
		skbuf.set16(2, 0); // Checksum, overwritten later
		doPrefixTo(skbuf);
		final int dataLength = skbuf.getSize();
		final int ccs = IPv4Utils.calcChecksum(skbuf, 0, dataLength);
		skbuf.set16(2, ccs);
	}

	/**
	 * 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) {
		// Do nothing
	}
	
	/**
	 * Do the header specific prefixing.
	 */
	protected abstract void doPrefixTo(SocketBuffer skbuf);

	/**
	 * Is the checksum valid?
	 */
	public boolean isChecksumOk() {
		return checksumOk;
	}

	/**
	 * Gets the code field
	 */
	public int getCode() {
		return code;
	}

	/**
	 * Gets the type field
	 */
	public int getType() {
		return type;
	}
	
}