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	/*
	* Copyright (c) 2002, 2018, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code 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 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package com.sun.jndi.ldap;

	import java.util.*;

	import javax.naming.*;
	import javax.naming.directory.*;
	import javax.naming.spi.NamingManager;
	import javax.naming.ldap.LdapName;
	import javax.naming.ldap.Rdn;

	/**
	* This class discovers the location of LDAP services by querying DNS.
	* See http://www.ietf.org/internet-drafts/draft-ietf-ldapext-locate-07.txt
	*/

	class ServiceLocator {

	private static final String SRV_RR = "SRV";

	private static final String[] SRV_RR_ATTR = new String[]{SRV_RR};

	private static final Random random = new Random();

	private ServiceLocator() {
	}

	/**
	* Maps a distinguished name (RFC 2253) to a fully qualified domain name.
	* Processes a sequence of RDNs having a DC attribute.
	* The special RDN "DC=." denotes the root of the domain tree.
	* Multi-valued RDNs, non-DC attributes, binary-valued attributes and the
	* RDN "DC=." all reset the domain name and processing continues.
	*
	* @param dn A string distinguished name (RFC 2253).
	* @return A domain name or null if none can be derived.
	* @throw InvalidNameException If the distinugished name is invalid.
	*/
	static String mapDnToDomainName(String dn) throws InvalidNameException {
	if (dn == null) {
	return null;
	}
	StringBuffer domain = new StringBuffer();
	LdapName ldapName = new LdapName(dn);

	// process RDNs left-to-right
	//List<Rdn> rdnList = ldapName.getRdns();

	List<Rdn> rdnList = ldapName.getRdns();
	for (int i = rdnList.size() - 1; i >= 0; i--) {
	//Rdn rdn = rdnList.get(i);
	Rdn rdn = rdnList.get(i);

	// single-valued RDN with a DC attribute
	if ((rdn.size() == 1) &&
	("dc".equalsIgnoreCase(rdn.getType()) )) {
	Object attrval = rdn.getValue();
	if (attrval instanceof String) {
	if (attrval.equals(".") \|\|
	(domain.length() == 1 && domain.charAt(0) == '.')) {
	domain.setLength(0); // reset (when current or previous
	// RDN value is "DC=.")
	}
	if (domain.length() > 0) {
	domain.append('.');
	}
	domain.append(attrval);
	} else {
	domain.setLength(0); // reset (when binary-valued attribute)
	}
	} else {
	domain.setLength(0); // reset (when multi-valued RDN or non-DC)
	}
	}
	return (domain.length() != 0) ? domain.toString() : null;
	}

	/**
	* Locates the LDAP service for a given domain.
	* Queries DNS for a list of LDAP Service Location Records (SRV) for a
	* given domain name.
	*
	* @param domainName A string domain name.
	* @param environment The possibly null environment of the context.
	* @return An ordered list of hostports for the LDAP service or null if
	* the service has not been located.
	*/
	static String[] getLdapService(String domainName, Map<?,?> environment) {
	if (environment instanceof Hashtable) {
	return getLdapService(domainName, (Hashtable)environment);
	}
	return getLdapService(domainName, new Hashtable<>(environment));
	}

	/**
	* Locates the LDAP service for a given domain.
	* Queries DNS for a list of LDAP Service Location Records (SRV) for a
	* given domain name.
	*
	* @param domainName A string domain name.
	* @param environment The possibly null environment of the context.
	* @return An ordered list of hostports for the LDAP service or null if
	* the service has not been located.
	*/
	static String[] getLdapService(String domainName, Hashtable<?,?> environment) {

	if (domainName == null \|\| domainName.length() == 0) {
	return null;
	}

	String dnsUrl = "dns:///_ldap._tcp." + domainName;
	String[] hostports = null;

	try {
	// Create the DNS context using NamingManager rather than using
	// the initial context constructor. This avoids having the initial
	// context constructor call itself (when processing the URL
	// argument in the getAttributes call).
	Context ctx = NamingManager.getURLContext("dns", environment);
	if (!(ctx instanceof DirContext)) {
	return null; // cannot create a DNS context
	}
	Attributes attrs =
	((DirContext)ctx).getAttributes(dnsUrl, SRV_RR_ATTR);
	Attribute attr;

	if (attrs != null && ((attr = attrs.get(SRV_RR)) != null)) {
	int numValues = attr.size();
	int numRecords = 0;
	SrvRecord[] srvRecords = new SrvRecord[numValues];

	// create the service records
	int i = 0;
	int j = 0;
	while (i < numValues) {
	try {
	srvRecords[j] = new SrvRecord((String) attr.get(i));
	j++;
	} catch (Exception e) {
	// ignore bad value
	}
	i++;
	}
	numRecords = j;

	// trim
	if (numRecords < numValues) {
	SrvRecord[] trimmed = new SrvRecord[numRecords];
	System.arraycopy(srvRecords, 0, trimmed, 0, numRecords);
	srvRecords = trimmed;
	}

	// Sort the service records in ascending order of their
	// priority value. For records with equal priority, move
	// those with weight 0 to the top of the list.
	if (numRecords > 1) {
	Arrays.sort(srvRecords);
	}

	// extract the host and port number from each service record
	hostports = extractHostports(srvRecords);
	}
	} catch (NamingException e) {
	// ignore
	}
	return hostports;
	}

	/**
	* Extract hosts and port numbers from a list of SRV records.
	* An array of hostports is returned or null if none were found.
	*/
	private static String[] extractHostports(SrvRecord[] srvRecords) {
	String[] hostports = null;

	int head = 0;
	int tail = 0;
	int sublistLength = 0;
	int k = 0;
	for (int i = 0; i < srvRecords.length; i++) {
	if (hostports == null) {
	hostports = new String[srvRecords.length];
	}
	// find the head and tail of the list of records having the same
	// priority value.
	head = i;
	while (i < srvRecords.length - 1 &&
	srvRecords[i].priority == srvRecords[i + 1].priority) {
	i++;
	}
	tail = i;

	// select hostports from the sublist
	sublistLength = (tail - head) + 1;
	for (int j = 0; j < sublistLength; j++) {
	hostports[k++] = selectHostport(srvRecords, head, tail);
	}
	}
	return hostports;
	}

	/*
	* Randomly select a service record in the range [head, tail] and return
	* its hostport value. Follows the algorithm in RFC 2782.
	*/
	private static String selectHostport(SrvRecord[] srvRecords, int head,
	int tail) {
	if (head == tail) {
	return srvRecords[head].hostport;
	}

	// compute the running sum for records between head and tail
	int sum = 0;
	for (int i = head; i <= tail; i++) {
	if (srvRecords[i] != null) {
	sum += srvRecords[i].weight;
	srvRecords[i].sum = sum;
	}
	}
	String hostport = null;

	// If all records have zero weight, select first available one;
	// otherwise, randomly select a record according to its weight
	int target = (sum == 0 ? 0 : random.nextInt(sum + 1));
	for (int i = head; i <= tail; i++) {
	if (srvRecords[i] != null && srvRecords[i].sum >= target) {
	hostport = srvRecords[i].hostport;
	srvRecords[i] = null; // make this record unavailable
	break;
	}
	}
	return hostport;
	}

	/**
	* This class holds a DNS service (SRV) record.
	* See http://www.ietf.org/rfc/rfc2782.txt
	*/

	static class SrvRecord implements Comparable<SrvRecord> {

	int priority;
	int weight;
	int sum;
	String hostport;

	/**
	* Creates a service record object from a string record.
	* DNS supplies the string record in the following format:
	* <pre>
	* <Priority> " " <Weight> " " <Port> " " <Host>
	* </pre>
	*/
	SrvRecord(String srvRecord) throws Exception {
	StringTokenizer tokenizer = new StringTokenizer(srvRecord, " ");
	String port;

	if (tokenizer.countTokens() == 4) {
	priority = Integer.parseInt(tokenizer.nextToken());
	weight = Integer.parseInt(tokenizer.nextToken());
	port = tokenizer.nextToken();
	hostport = tokenizer.nextToken() + ":" + port;
	} else {
	throw new IllegalArgumentException();
	}
	}

	/*
	* Sort records in ascending order of priority value. For records with
	* equal priority move those with weight 0 to the top of the list.
	*/
	public int compareTo(SrvRecord that) {
	if (priority > that.priority) {
	return 1; // this > that
	} else if (priority < that.priority) {
	return -1; // this < that
	} else if (weight == 0 && that.weight != 0) {
	return -1; // this < that
	} else if (weight != 0 && that.weight == 0) {
	return 1; // this > that
	} else {
	return 0; // this == that
	}
	}
	}
	}

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