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/*
* Copyright (c) 2019, 2020, Oracle and/or its affiliates.
*
* This program is free software; you can redistribute it and/or modify it under
* the terms of the GNU General Public License, version 2.0, as published by the
* Free Software Foundation.
*
* This program is also distributed with certain software (including but not
* limited to OpenSSL) that is licensed under separate terms, as designated in a
* particular file or component or in included license documentation. The
* authors of MySQL hereby grant you an additional permission to link the
* program and your derivative works with the separately licensed software that
* they have included with MySQL.
*
* Without limiting anything contained in the foregoing, this file, which is
* part of MySQL Connector/J, is also subject to the Universal FOSS Exception,
* version 1.0, a copy of which can be found at
* http://oss.oracle.com/licenses/universal-foss-exception.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License, version 2.0,
* for more details.
*
* You should have received a copy of the GNU General Public License along with
* this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package com.mysql.cj.util;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.Random;
import java.util.stream.Collectors;
import javax.naming.Context;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
public class DnsSrv {
public static class SrvRecord implements Comparable {
private final int priority;
private final int weight;
private final int port;
private final String target;
public static SrvRecord buildFrom(String srvLine) {
String[] srvParts = srvLine.split("\\s+");
if (srvParts.length == 4) {
int priority = Integer.parseInt(srvParts[0]);
int weight = Integer.parseInt(srvParts[1]);
int port = Integer.parseInt(srvParts[2]);
String target = srvParts[3].replaceFirst("\\.$", "");
return new SrvRecord(priority, weight, port, target);
}
return null;
}
public SrvRecord(int priority, int weight, int port, String target) {
this.priority = priority;
this.weight = weight;
this.port = port;
this.target = target;
}
public int getPriority() {
return this.priority;
}
public int getWeight() {
return this.weight;
}
public int getPort() {
return this.port;
}
public String getTarget() {
return this.target;
}
@Override
public String toString() {
return String.format("{\"Priority\": %d, \"Weight\": %d, \"Port\": %d, \"Target\": \"%s\"}", getPriority(), getWeight(), getPort(), getTarget());
}
@Override
public int compareTo(SrvRecord o) {
int priorityDiff = getPriority() - o.getPriority();
return priorityDiff == 0 ? getWeight() - o.getWeight() : priorityDiff;
}
}
public static List lookupSrvRecords(String serviceName) throws NamingException {
List srvRecords = new ArrayList<>();
Properties environment = new Properties();
environment.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
DirContext context = new InitialDirContext(environment);
Attributes dnsEntries = context.getAttributes(serviceName, new String[] { "SRV" });
if (dnsEntries != null) {
Attribute hosts = dnsEntries.get("SRV");
if (hosts != null) {
for (int i = 0; i < hosts.size(); i++) {
srvRecords.add(SrvRecord.buildFrom((String) hosts.get(i)));
}
}
}
return sortSrvRecords(srvRecords);
}
/**
* Sort a list of DNS SRV records according to the sorting rules described in rfc2782.
*
* @param srvRecords
* the list of {@link SrvRecord}s to sort.
* @return
* a new list of sorted {@link SrvRecord}s.
*/
public static List sortSrvRecords(List srvRecords) {
// Sort srv records by their natural order, i.e., first by priority then by weight.
List srvRecordsSortedNatural = srvRecords.stream().sorted().collect(Collectors.toList());
// Sort records with equal priority by weight using a categorical distribution.
Random random = new Random(System.nanoTime());
List srvRecordsSortedRfc2782 = new ArrayList<>();
List priorities = srvRecordsSortedNatural.stream().map(SrvRecord::getPriority).distinct().collect(Collectors.toList());
for (Integer priority : priorities) {
List srvRecordsSamePriority = srvRecordsSortedNatural.stream().filter(s -> s.getPriority() == priority).collect(Collectors.toList());
while (srvRecordsSamePriority.size() > 1) {
int recCount = srvRecordsSamePriority.size();
int sumOfWeights = 0;
int[] weights = new int[recCount];
for (int i = 0; i < recCount; i++) {
sumOfWeights += srvRecordsSamePriority.get(i).getWeight();
weights[i] = sumOfWeights;
}
int selection = random.nextInt(sumOfWeights + 1);
int pos = 0;
for (; pos < recCount && weights[pos] < selection; pos++) {
}
srvRecordsSortedRfc2782.add(srvRecordsSamePriority.remove(pos));
}
srvRecordsSortedRfc2782.add(srvRecordsSamePriority.get(0));
}
return srvRecordsSortedRfc2782;
}
}
