cache.java

DNS Java 是java实现的DNS

// Copyright (c) 1999-2004 Brian Wellington ([e-mail])

package org.xbill.DNS;

import java.io.*;
import java.util.*;

/**
 * A cache of DNS records.  The cache obeys TTLs, so items are purged after
 * their validity period is complete.  Negative answers are cached, to
 * avoid repeated failed DNS queries.  The credibility of each RRset is
 * maintained, so that more credible records replace less credible records,
 * and lookups can specify the minimum credibility of data they are requesting.
 * @see RRset
 * @see Credibility
 *
 * @author Brian Wellington
 */

public class Cache {

private interface Element {
	public boolean expired();
	public int compareCredibility(int cred);
	public int getType();
}

private static int
limitExpire(long ttl, long maxttl) {
	if (maxttl >= 0 && maxttl < ttl)
		ttl = maxttl;
	int expire = (int)((System.currentTimeMillis() / 1000) + ttl);
	if (expire < 0 || expire > Integer.MAX_VALUE)
		return Integer.MAX_VALUE;
	return expire;
}

private static class CacheRRset extends RRset implements Element {
	int credibility;
	int expire;

	public
	CacheRRset(Record rec, int cred, long maxttl) {
		super();
		this.credibility = cred;
		this.expire = limitExpire(rec.getTTL(), maxttl);
		addRR(rec);
	}

	public
	CacheRRset(RRset rrset, int cred, long maxttl) {
		super(rrset);
		this.credibility = cred;
		this.expire = limitExpire(rrset.getTTL(), maxttl);
	}

	public final boolean
	expired() {
		int now = (int)(System.currentTimeMillis() / 1000);
		return (now >= expire);
	}

	public final int
	compareCredibility(int cred) {
		return credibility - cred;
	}

	public String
	toString() {
		StringBuffer sb = new StringBuffer();
		sb.append(super.toString());
		sb.append(" cl = ");
		sb.append(credibility);
		return sb.toString();
	}
}

private static class NegativeElement implements Element {
	int type;
	Name name;
	SOARecord soa;
	int credibility;
	int expire;

	public
	NegativeElement(Name name, int type, SOARecord soa, int cred,
			long maxttl)
	{
		this.name = name;
		this.type = type;
		this.soa = soa;
		long cttl = 0;
		if (soa != null)
			cttl = soa.getMinimum();
		this.credibility = cred;
		this.expire = limitExpire(cttl, maxttl);
	}

	public int
	getType() {
		return type;
	}

	public final boolean
	expired() {
		int now = (int)(System.currentTimeMillis() / 1000);
		return (now >= expire);
	}

	public final int
	compareCredibility(int cred) {
		return credibility - cred;
	}

	public String
	toString() {
		StringBuffer sb = new StringBuffer();
		if (type == 0)
			sb.append("NXDOMAIN " + name);
		else
			sb.append("NXRRSET " + name + " " + Type.string(type));
		sb.append(" cl = ");
		sb.append(credibility);
		return sb.toString();
	}
}

private static class CacheMap extends LinkedHashMap {
	private int maxsize = -1;

	CacheMap(int maxsize) {
		super(16, (float) 0.75, true);
		this.maxsize = maxsize;
	}

	int
	getMaxSize() {
		return maxsize;
	}

	void
	setMaxSize(int maxsize) {
		/*
		 * Note that this doesn't shrink the size of the map if
		 * the maximum size is lowered, but it should shrink as
		 * entries expire.
		 */
		this.maxsize = maxsize;
	}

	protected boolean removeEldestEntry(Map.Entry eldest) {
		return maxsize >= 0 && size() > maxsize;
	}
}

private CacheMap data;
private int maxncache = -1;
private int maxcache = -1;
private int dclass;

private static final int defaultMaxEntries = 50000;

/**
 * Creates an empty Cache
 *
 * @param dclass The DNS class of this cache
 * @see DClass
 */
public
Cache(int dclass) {
	this.dclass = dclass;
	data = new CacheMap(defaultMaxEntries);
}

/**
 * Creates an empty Cache for class IN.
 * @see DClass
 */
public
Cache() {
	this(DClass.IN);
}

/**
 * Creates a Cache which initially contains all records in the specified file.
 */
public
Cache(String file) throws IOException {
	data = new CacheMap(defaultMaxEntries);
	Master m = new Master(file);
	Record record;
	while ((record = m.nextRecord()) != null)
		addRecord(record, Credibility.HINT, m);
}

private synchronized Object
exactName(Name name) {
	return data.get(name);
}

private synchronized void
removeName(Name name) {
	data.remove(name);
}

private synchronized Element []
allElements(Object types) {
	if (types instanceof List) {
		List typelist = (List) types;
		int size = typelist.size();
		return (Element []) typelist.toArray(new Element[size]);
	} else {
		Element set = (Element) types;
		return new Element[] {set};
	}
}

private synchronized Element
oneElement(Name name, Object types, int type, int minCred) {
	Element found = null;

	if (type == Type.ANY)
		throw new IllegalArgumentException("oneElement(ANY)");
	if (types instanceof List) {
		List list = (List) types;
		for (int i = 0; i < list.size(); i++) {
			Element set = (Element) list.get(i);
			if (set.getType() == type) {
				found = set;
				break;
			}
		}
	} else {
		Element set = (Element) types;
		if (set.getType() == type)
			found = set;
	}
	if (found == null)
		return null;
	if (found.expired()) {
		removeElement(name, type);
		return null;
	}
	if (found.compareCredibility(minCred) < 0)
		return null;
	return found;
}

private synchronized Element
findElement(Name name, int type, int minCred) {
	Object types = exactName(name);
	if (types == null)
		return null;
	return oneElement(name, types, type, minCred);
}

private synchronized void
addElement(Name name, Element element) {
	Object types = data.get(name);
	if (types == null) {
		data.put(name, element);
		return;
	}
	int type = element.getType();
	if (types instanceof List) {
		List list = (List) types;
		for (int i = 0; i < list.size(); i++) {
			Element elt = (Element) list.get(i);
			if (elt.getType() == type) {
				list.set(i, element);
				return;
			}
		}
		list.add(element);
	} else {
		Element elt = (Element) types;
		if (elt.getType() == type)
			data.put(name, element);
		else {
			LinkedList list = new LinkedList();
			list.add(elt);
			list.add(element);
			data.put(name, list);
		}
	}
}

private synchronized void
removeElement(Name name, int type) {
	Object types = data.get(name);
	if (types == null) {
		return;
	}
	if (types instanceof List) {
		List list = (List) types;
		for (int i = 0; i < list.size(); i++) {
			Element elt = (Element) list.get(i);
			if (elt.getType() == type) {
				list.remove(i);
				if (list.size() == 0)
					data.remove(name);
				return;
			}
		}
	} else {
		Element elt = (Element) types;
		if (elt.getType() != type)
			return;
		data.remove(name);
	}
}

/** Empties the Cache. */
public synchronized void
clearCache() {
	data.clear();
}

/**
 * Adds a record to the Cache.
 * @param r The record to be added
 * @param cred The credibility of the record
 * @param o The source of the record (this could be a Message, for example)
 * @see Record
 */
public synchronized void
addRecord(Record r, int cred, Object o) {
	Name name = r.getName();
	int type = r.getRRsetType();
	if (!Type.isRR(type))
		return;
	Element element = findElement(name, type, cred);
	if (element == null) {
		CacheRRset crrset = new CacheRRset(r, cred, maxcache);
		addRRset(crrset, cred);
	} else if (element.compareCredibility(cred) == 0) {
		if (element instanceof CacheRRset) {
			CacheRRset crrset = (CacheRRset) element;
			crrset.addRR(r);
		}
	}
}

/**
 * Adds an RRset to the Cache.
 * @param rrset The RRset to be added
 * @param cred The credibility of these records
 * @see RRset
 */
public synchronized void
addRRset(RRset rrset, int cred) {
	long ttl = rrset.getTTL();
	Name name = rrset.getName();
	int type = rrset.getType();
	Element element = findElement(name, type, 0);
	if (ttl == 0) {
		if (element != null && element.compareCredibility(cred) <= 0)
			removeElement(name, type);
	} else {
		if (element != null && element.compareCredibility(cred) <= 0)
			element = null;
		if (element == null) {
			CacheRRset crrset;
			if (rrset instanceof CacheRRset)
				crrset = (CacheRRset) rrset;
			else
				crrset = new CacheRRset(rrset, cred, maxcache);
			addElement(name, crrset);
		}
	}
}

/**
 * Adds a negative entry to the Cache.
 * @param name The name of the negative entry
 * @param type The type of the negative entry
 * @param soa The SOA record to add to the negative cache entry, or null.
 * The negative cache ttl is derived from the SOA.
 * @param cred The credibility of the negative entry
 */
public synchronized void
addNegative(Name name, int type, SOARecord soa, int cred) {
	long ttl = 0;
	if (soa != null)
		ttl = soa.getTTL();
	Element element = findElement(name, type, 0);
	if (ttl == 0) {
		if (element != null && element.compareCredibility(cred) <= 0)
			removeElement(name, type);
	} else {
		if (element != null && element.compareCredibility(cred) <= 0)
			element = null;
		if (element == null)
			addElement(name, new NegativeElement(name, type,
							     soa, cred,
							     maxncache));
	}
}

/**
 * Finds all matching sets or something that causes the lookup to stop.
 */
protected synchronized SetResponse
lookup(Name name, int type, int minCred) {
	int labels;
	int tlabels;
	Element element;
	CacheRRset crrset;
	Name tname;
	Object types;
	SetResponse sr;

	labels = name.labels();

	for (tlabels = labels; tlabels >= 1; tlabels--) {
		boolean isRoot = (tlabels == 1);
		boolean isExact = (tlabels == labels);

		if (isRoot)
			tname = Name.root;
		else if (isExact)
			tname = name;
		else
			tname = new Name(name, labels - tlabels);

		types = data.get(tname);
		if (types == null)