DNSUtil.java
/**
*
* Copyright 2003-2005 Jive Software.
*
* 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 org.jivesoftware.smack.util;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.jivesoftware.smack.util.dns.DNSResolver;
import org.jivesoftware.smack.util.dns.HostAddress;
import org.jivesoftware.smack.util.dns.SRVRecord;
/**
* Utility class to perform DNS lookups for XMPP services.
*
* @author Matt Tucker
*/
public class DNSUtil {
private static final Logger LOGGER = Logger.getLogger(DNSUtil.class.getName());
private static DNSResolver dnsResolver = null;
/**
* International Domain Name transformer.
* <p>
* Used to transform Unicode representations of the Domain Name to ASCII in
* order to perform a DNS request with the ASCII representation.
* 'java.net.IDN' is available since Android API 9, but as long as Smack
* requires API 8, we are going to need this. This part is going to get
* removed once Smack depends on Android API 9 or higher.
* </p>
*/
private static StringTransformer idnaTransformer = new StringTransformer() {
@Override
public String transform(String string) {
return string;
}
};
/**
* Set the DNS resolver that should be used to perform DNS lookups.
*
* @param resolver
*/
public static void setDNSResolver(DNSResolver resolver) {
dnsResolver = resolver;
}
/**
* Returns the current DNS resolved used to perform DNS lookups.
*
* @return the active DNSResolver
*/
public static DNSResolver getDNSResolver() {
return dnsResolver;
}
/**
* Set the IDNA (Internationalizing Domain Names in Applications, RFC 3490) transformer.
* <p>
* You usually want to wrap 'java.net.IDN.toASCII()' into a StringTransformer here.
* </p>
* @param idnaTransformer
*/
public static void setIdnaTransformer(StringTransformer idnaTransformer) {
if (idnaTransformer == null) {
throw new NullPointerException();
}
DNSUtil.idnaTransformer = idnaTransformer;
}
private static enum DomainType {
Server,
Client,
;
}
/**
* Returns a list of HostAddresses under which 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 3.2.1 of RFC 6120. 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:5269".
* </p>
*
* @param domain the domain.
* @param failedAddresses on optional list that will be populated with host addresses that failed to resolve.
* @return List of HostAddress, which encompasses the hostname and port that the
* XMPP server can be reached at for the specified domain.
*/
public static List<HostAddress> resolveXMPPDomain(String domain, List<HostAddress> failedAddresses) {
domain = idnaTransformer.transform(domain);
if (dnsResolver == null) {
LOGGER.warning("No DNS Resolver active in Smack, will be unable to perform DNS SRV lookups");
List<HostAddress> addresses = new ArrayList<HostAddress>(1);
addresses.add(new HostAddress(domain, 5222));
return addresses;
}
return resolveDomain(domain, DomainType.Client, failedAddresses);
}
/**
* Returns a list of HostAddresses under which 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 3.2.1 of RFC 6120. 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 5269.
* <p>
* As an example, a lookup for "example.com" may return "im.example.com:5269".
* </p>
*
* @param domain the domain.
* @param failedAddresses on optional list that will be populated with host addresses that failed to resolve.
* @return List of HostAddress, which encompasses the hostname and port that the
* XMPP server can be reached at for the specified domain.
*/
public static List<HostAddress> resolveXMPPServerDomain(String domain, List<HostAddress> failedAddresses) {
domain = idnaTransformer.transform(domain);
if (dnsResolver == null) {
LOGGER.warning("No DNS Resolver active in Smack, will be unable to perform DNS SRV lookups");
List<HostAddress> addresses = new ArrayList<HostAddress>(1);
addresses.add(new HostAddress(domain, 5269));
return addresses;
}
return resolveDomain(domain, DomainType.Server, failedAddresses);
}
/**
*
* @param domain the domain.
* @param domainType the XMPP domain type, server or client.
* @param failedAddresses on optional list that will be populated with host addresses that failed to resolve.
* @return a list of resolver host addresses for this domain.
*/
private static List<HostAddress> resolveDomain(String domain, DomainType domainType, List<HostAddress> failedAddresses) {
List<HostAddress> addresses = new ArrayList<HostAddress>();
// Step one: Do SRV lookups
String srvDomain;
switch (domainType) {
case Server:
srvDomain = "_xmpp-server._tcp." + domain;
break;
case Client:
srvDomain = "_xmpp-client._tcp." + domain;
break;
default:
throw new AssertionError();
}
try {
List<SRVRecord> srvRecords = dnsResolver.lookupSRVRecords(srvDomain);
if (LOGGER.isLoggable(Level.FINE)) {
String logMessage = "Resolved SRV RR for " + srvDomain + ":";
for (SRVRecord r : srvRecords)
logMessage += " " + r;
LOGGER.fine(logMessage);
}
List<HostAddress> sortedRecords = sortSRVRecords(srvRecords);
addresses.addAll(sortedRecords);
}
catch (Exception e) {
LOGGER.log(Level.WARNING, "Exception while resovling SRV records for " + domain
+ ". Consider adding '_xmpp-(server|client)._tcp' DNS SRV Records", e);
if (failedAddresses != null) {
HostAddress failedHostAddress = new HostAddress(srvDomain);
failedHostAddress.setException(e);
failedAddresses.add(failedHostAddress);
}
}
// Step two: Add the hostname to the end of the list
addresses.add(new HostAddress(domain));
return addresses;
}
/**
* Sort a given list of SRVRecords as described in RFC 2782
* Note that we follow the RFC with one exception. In a group of the same priority, only the first entry
* is calculated by random. The others are ore simply ordered by their priority.
*
* @param records
* @return the list of resolved HostAddresses
*/
private static List<HostAddress> sortSRVRecords(List<SRVRecord> records) {
// RFC 2782, Usage rules: "If there is precisely one SRV RR, and its Target is "."
// (the root domain), abort."
if (records.size() == 1 && records.get(0).getFQDN().equals("."))
return Collections.emptyList();
// sorting the records improves the performance of the bisection later
Collections.sort(records);
// create the priority buckets
SortedMap<Integer, List<SRVRecord>> buckets = new TreeMap<Integer, List<SRVRecord>>();
for (SRVRecord r : records) {
Integer priority = r.getPriority();
List<SRVRecord> bucket = buckets.get(priority);
// create the list of SRVRecords if it doesn't exist
if (bucket == null) {
bucket = new LinkedList<SRVRecord>();
buckets.put(priority, bucket);
}
bucket.add(r);
}
List<HostAddress> res = new ArrayList<HostAddress>(records.size());
for (Integer priority : buckets.keySet()) {
List<SRVRecord> bucket = buckets.get(priority);
int bucketSize;
while ((bucketSize = bucket.size()) > 0) {
int[] totals = new int[bucket.size()];
int running_total = 0;
int count = 0;
int zeroWeight = 1;
for (SRVRecord r : bucket) {
if (r.getWeight() > 0)
zeroWeight = 0;
}
for (SRVRecord r : bucket) {
running_total += (r.getWeight() + zeroWeight);
totals[count] = running_total;
count++;
}
int selectedPos;
if (running_total == 0) {
// If running total is 0, then all weights in this priority
// group are 0. So we simply select one of the weights randomly
// as the other 'normal' algorithm is unable to handle this case
selectedPos = (int) (Math.random() * bucketSize);
} else {
double rnd = Math.random() * running_total;
selectedPos = bisect(totals, rnd);
}
// add the SRVRecord that was randomly chosen on it's weight
// to the start of the result list
SRVRecord chosenSRVRecord = bucket.remove(selectedPos);
res.add(chosenSRVRecord);
}
}
return res;
}
// TODO this is not yet really bisection just a stupid linear search
private static int bisect(int[] array, double value) {
int pos = 0;
for (int element : array) {
if (value < element)
break;
pos++;
}
return pos;
}
}