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package com.sun.jndi.dns;


import java.lang.ref.SoftReference;
import java.util.Date;
import java.util.Vector;


ZoneNode extends NameNode to represent a tree of the zones in the DNS namespace, along with any intermediate nodes between zones. A ZoneNode that represents a zone may be "populated" with a NameNode tree containing the zone's contents.

A populated zone's contents will be flagged as having expired after the time specified by the minimum TTL value in the zone's SOA record.

Since zone cuts aren't directly modeled by a tree of ZoneNodes, ZoneNode.isZoneCut() always returns false.

The synchronization strategy is documented in DnsContext.java.

The zone's contents are accessed via a soft reference, so its heap space may be reclaimed when necessary. The zone may be repopulated later.

Author:Scott Seligman
/** * ZoneNode extends NameNode to represent a tree of the zones in the * DNS namespace, along with any intermediate nodes between zones. * A ZoneNode that represents a zone may be "populated" with a * NameNode tree containing the zone's contents. * * <p> A populated zone's contents will be flagged as having expired after * the time specified by the minimum TTL value in the zone's SOA record. * * <p> Since zone cuts aren't directly modeled by a tree of ZoneNodes, * ZoneNode.isZoneCut() always returns false. * * <p> The synchronization strategy is documented in DnsContext.java. * * <p> The zone's contents are accessed via a soft reference, so its * heap space may be reclaimed when necessary. The zone may be * repopulated later. * * @author Scott Seligman */
class ZoneNode extends NameNode { private SoftReference<NameNode> contentsRef = null; // the zone's namespace private long serialNumber = -1; // the zone data's serial number private Date expiration = null; // time when the zone's data expires ZoneNode(String label) { super(label); } protected NameNode newNameNode(String label) { return new ZoneNode(label); } /* * Clears the contents of this node. If the node was flagged as * expired, it remains so. */ synchronized void depopulate() { contentsRef = null; serialNumber = -1; } /* * Is this node currently populated? */ synchronized boolean isPopulated() { return (getContents() != null); } /* * Returns the zone's contents, or null if the zone is not populated. */ synchronized NameNode getContents() { return (contentsRef != null) ? contentsRef.get() : null; } /* * Has this zone's data expired? */ synchronized boolean isExpired() { return ((expiration != null) && expiration.before(new Date())); } /* * Returns the deepest populated zone on the path specified by a * fully-qualified domain name, or null if there is no populated * zone on that path. Note that a node may be depopulated after * being returned. */ ZoneNode getDeepestPopulated(DnsName fqdn) { ZoneNode znode = this; ZoneNode popNode = isPopulated() ? this : null; for (int i = 1; i < fqdn.size(); i++) { // "i=1" to skip root label znode = (ZoneNode) znode.get(fqdn.getKey(i)); if (znode == null) { break; } else if (znode.isPopulated()) { popNode = znode; } } return popNode; } /* * Populates (or repopulates) a zone given its own fully-qualified * name and its resource records. Returns the zone's new contents. */ NameNode populate(DnsName zone, ResourceRecords rrs) { // assert zone.get(0).isEmpty(); // zone has root label // assert (zone.size() == (depth() + 1)); // +1 due to root label NameNode newContents = new NameNode(null); for (int i = 0; i < rrs.answer.size(); i++) { ResourceRecord rr = rrs.answer.elementAt(i); DnsName n = rr.getName(); // Ignore resource records whose names aren't within the zone's // domain. Also skip records of the zone's top node, since // the zone's root NameNode is already in place. if ((n.size() > zone.size()) && n.startsWith(zone)) { NameNode nnode = newContents.add(n, zone.size()); if (rr.getType() == ResourceRecord.TYPE_NS) { nnode.setZoneCut(true); } } } // The zone's SOA record is the first record in the answer section. ResourceRecord soa = rrs.answer.firstElement(); synchronized (this) { contentsRef = new SoftReference<NameNode>(newContents); serialNumber = getSerialNumber(soa); setExpiration(getMinimumTtl(soa)); return newContents; } } /* * Set this zone's data to expire in {@code secsToExpiration} seconds. */ private void setExpiration(long secsToExpiration) { expiration = new Date(System.currentTimeMillis() + 1000 * secsToExpiration); } /* * Returns an SOA record's minimum TTL field. */ private static long getMinimumTtl(ResourceRecord soa) { String rdata = (String) soa.getRdata(); int pos = rdata.lastIndexOf(' ') + 1; return Long.parseLong(rdata.substring(pos)); } /* * Compares this zone's serial number with that of an SOA record. * Zone must be populated. * Returns a negative, zero, or positive integer as this zone's * serial number is less than, equal to, or greater than the SOA * record's. * See ResourceRecord.compareSerialNumbers() for a description of * serial number arithmetic. */ int compareSerialNumberTo(ResourceRecord soa) { // assert isPopulated(); return ResourceRecord.compareSerialNumbers(serialNumber, getSerialNumber(soa)); } /* * Returns an SOA record's serial number. */ private static long getSerialNumber(ResourceRecord soa) { String rdata = (String) soa.getRdata(); // An SOA record ends with: serial refresh retry expire minimum. // Set "beg" to the space before serial, and "end" to the space after. // We go "backward" to avoid dealing with escaped spaces in names. int beg = rdata.length(); int end = -1; for (int i = 0; i < 5; i++) { end = beg; beg = rdata.lastIndexOf(' ', end - 1); } return Long.parseLong(rdata.substring(beg + 1, end)); } }