/**
* $Revision: 1456 $ $Date: 2005-06-01 22:04:54 -0700 (Wed, 01 Jun 2005) $
*
* Copyright 2003-2005 Jive Software.
*
* All rights reserved. Licensed under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package info.guardianproject.util;
import java.util.Map;
import org.jivesoftware.smack.util.Cache;
import org.xbill.DNS.Lookup;
import org.xbill.DNS.Record;
import org.xbill.DNS.SRVRecord;
import org.xbill.DNS.TextParseException;
import org.xbill.DNS.Type;
/**
* Utilty class to perform DNS lookups for XMPP services.
*
* @author Matt Tucker
*/
public class DNSUtil {
/**
* Create a cache to hold the 100 most recently accessed DNS lookups for a
* period of 10 minutes.
*/
private static Map<String, HostAddress> ccache = new Cache<String, HostAddress>(100,
1000 * 60 * 10);
private static Map<String, HostAddress> scache = new Cache<String, HostAddress>(100,
1000 * 60 * 10);
private static HostAddress resolveSRV(String domain) {
String bestHost = null;
int bestPort = -1;
int bestPriority = Integer.MAX_VALUE;
int bestWeight = 0;
Lookup lookup;
try {
lookup = new Lookup(domain, Type.SRV);
Record recs[] = lookup.run();
if (recs == null) {
return null;
}
for (Record rec : recs) {
SRVRecord record = (SRVRecord) rec;
if (record != null && record.getTarget() != null) {
int weight = (int) (record.getWeight() * record.getWeight() * Math.random());
if (record.getPriority() < bestPriority) {
bestPriority = record.getPriority();
bestWeight = weight;
bestHost = record.getTarget().toString();
bestPort = record.getPort();
} else if (record.getPriority() == bestPriority) {
if (weight > bestWeight) {
bestPriority = record.getPriority();
bestWeight = weight;
bestHost = record.getTarget().toString();
bestPort = record.getPort();
}
}
}
}
} catch (TextParseException e) {
} catch (NullPointerException e) {
}
if (bestHost == null) {
return null;
}
// Host entries in DNS should end with a ".".
if (bestHost.endsWith(".")) {
bestHost = bestHost.substring(0, bestHost.length() - 1);
}
return new HostAddress(bestHost, bestPort);
}
/**
* Returns the host name and port that the specified XMPP server can be
* reached at for client-to-server communication. A DNS lookup for a SRV
* record in the form "_xmpp-client._tcp.example.com" is attempted,
* according to section 14.4 of RFC 3920.
*
* If that lookup fails, it's assumed that the XMPP server lives at the host
* resolved by a DNS lookup at the specified domain on the default port of
* 5222. <p>
*
* As an example, a lookup for "example.com" may return
* "im.example.com:5222".
*
* Note on SRV record selection. We now check priority and weight, but we
* still don't do this correctly. The missing behavior is this: if we fail
* to reach a host based on its SRV record then we need to select another
* host from the other SRV records. In Smack 3.1.1 we're not going to be
* able to do the major system redesign to correct this.
*
* @param domain the domain.
* @return a HostAddress, which encompasses the hostname and port that the
* XMPP server can be reached at for the specified domain.
*/
public static HostAddress resolveXMPPDomain(String domain) {
// Return item from cache if it exists.
synchronized (ccache) {
if (ccache.containsKey(domain)) {
HostAddress address = (HostAddress) ccache.get(domain);
if (address != null) {
return address;
}
}
}
HostAddress result = resolveSRV("_xmpp-client._tcp." + domain);
if (result != null) {
// Add item to cache.
synchronized (ccache) {
ccache.put(domain, result);
}
} else {
result = new HostAddress(domain, 5222);
}
return result;
}
/**
* Returns the host name and port that the specified XMPP server can be
* reached at for server-to-server communication. A DNS lookup for a SRV
* record in the form "_xmpp-server._tcp.example.com" is attempted,
* according to section 14.4 of RFC 3920. If that lookup fails, a lookup in
* the older form of "_jabber._tcp.example.com" is attempted since servers
* that implement an older version of the protocol may be listed using that
* notation. If that lookup fails as well, it's assumed that the XMPP server
* lives at the host resolved by a DNS lookup at the specified domain on the
* default port of 5269. <p>
*
* As an example, a lookup for "example.com" may return
* "im.example.com:5269".
*
* @param domain the domain.
* @return a HostAddress, which encompasses the hostname and port that the
* XMPP server can be reached at for the specified domain.
*/
public static HostAddress resolveXMPPServerDomain(String domain) {
// Return item from cache if it exists.
synchronized (scache) {
if (scache.containsKey(domain)) {
HostAddress address = (HostAddress) scache.get(domain);
if (address != null) {
return address;
}
}
}
HostAddress result = resolveSRV("_xmpp-server._tcp." + domain);
if (result == null) {
result = resolveSRV("_jabber._tcp." + domain);
}
if (result == null) {
result = new HostAddress(domain, 5269);
}
// Add item to cache.
synchronized (scache) {
scache.put(domain, result);
}
return result;
}
/** Encapsulates a hostname and port. */
public static class HostAddress {
private String host;
private int port;
private HostAddress(String host, int port) {
this.host = host;
this.port = port;
}
/**
* Returns the hostname.
*
* @return the hostname.
*/
public String getHost() {
return host;
}
/**
* Returns the port.
*
* @return the port.
*/
public int getPort() {
return port;
}
public String toString() {
return host + ":" + port;
}
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (!(o instanceof HostAddress)) {
return false;
}
final HostAddress address = (HostAddress) o;
if (!host.equals(address.host)) {
return false;
}
return port == address.port;
}
}
}