DNSUtil.java
/**
*
* Copyright 2003-2005 Jive Software, 2016-2018 Florian Schmaus.
*
* 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.ConnectionConfiguration.DnssecMode;
import org.jivesoftware.smack.util.dns.DNSResolver;
import org.jivesoftware.smack.util.dns.HostAddress;
import org.jivesoftware.smack.util.dns.SRVRecord;
import org.jivesoftware.smack.util.dns.SmackDaneProvider;
import org.minidns.dnsname.DnsName;
/**
* Utility class to perform DNS lookups for XMPP services.
*
* @author Matt Tucker
* @author Florian Schmaus
*/
public class DNSUtil {
public static final String XMPP_CLIENT_DNS_SRV_PREFIX = "_xmpp-client._tcp";
public static final String XMPP_SERVER_DNS_SRV_PREFIX = "_xmpp-server._tcp";
private static final Logger LOGGER = Logger.getLogger(DNSUtil.class.getName());
private static DNSResolver dnsResolver = null;
private static SmackDaneProvider daneProvider;
/**
* Set the DNS resolver that should be used to perform DNS lookups.
*
* @param resolver
*/
public static void setDNSResolver(DNSResolver resolver) {
dnsResolver = Objects.requireNonNull(resolver);
}
/**
* Returns the current DNS resolved used to perform DNS lookups.
*
* @return the active DNSResolver
*/
public static DNSResolver getDNSResolver() {
return dnsResolver;
}
/**
* Set the DANE provider that should be used when DANE is enabled.
*
* @param daneProvider
*/
public static void setDaneProvider(SmackDaneProvider daneProvider) {
DNSUtil.daneProvider = Objects.requireNonNull(daneProvider);
}
/**
* Returns the currently active DANE provider used when DANE is enabled.
*
* @return the active DANE provider
*/
public static SmackDaneProvider getDaneProvider() {
return daneProvider;
}
@SuppressWarnings("ImmutableEnumChecker")
enum DomainType {
server(XMPP_SERVER_DNS_SRV_PREFIX),
client(XMPP_CLIENT_DNS_SRV_PREFIX),
;
public final DnsName srvPrefix;
DomainType(String srvPrefixString) {
srvPrefix = DnsName.from(srvPrefixString);
}
}
/**
* 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.
* @param dnssecMode DNSSec mode.
* @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> resolveXMPPServiceDomain(DnsName domain, List<HostAddress> failedAddresses, DnssecMode dnssecMode) {
return resolveDomain(domain, DomainType.client, failedAddresses, dnssecMode);
}
/**
* 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.
* @param dnssecMode DNSSec mode.
* @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(DnsName domain, List<HostAddress> failedAddresses, DnssecMode dnssecMode) {
return resolveDomain(domain, DomainType.server, failedAddresses, dnssecMode);
}
/**
*
* @param domain the domain.
* @param domainType the XMPP domain type, server or client.
* @param failedAddresses a 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(DnsName domain, DomainType domainType,
List<HostAddress> failedAddresses, DnssecMode dnssecMode) {
if (dnsResolver == null) {
throw new IllegalStateException("No DNS Resolver active in Smack");
}
List<HostAddress> addresses = new ArrayList<HostAddress>();
// Step one: Do SRV lookups
DnsName srvDomain = DnsName.from(domainType.srvPrefix, domain);
List<SRVRecord> srvRecords = dnsResolver.lookupSRVRecords(srvDomain, failedAddresses, dnssecMode);
if (srvRecords != null && !srvRecords.isEmpty()) {
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);
} else {
LOGGER.info("Could not resolve DNS SRV resource records for " + srvDomain + ". Consider adding those.");
}
int defaultPort = -1;
switch (domainType) {
case client:
defaultPort = 5222;
break;
case server:
defaultPort = 5269;
break;
}
// Step two: Add the hostname to the end of the list
HostAddress hostAddress = dnsResolver.lookupHostAddress(domain, defaultPort, failedAddresses, dnssecMode);
if (hostAddress != null) {
addresses.add(hostAddress);
}
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().isRootLabel())
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[bucketSize];
int running_total = 0;
int count = 0;
int zeroWeight = 1;
for (SRVRecord r : bucket) {
if (r.getWeight() > 0) {
zeroWeight = 0;
break;
}
}
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;
}
}