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	/*
	* Copyright (c) 2000, 2011, 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.dns;


	import java.net.MalformedURLException;
	import java.util.ArrayList;
	import java.util.Hashtable;
	import java.util.List;

	import javax.naming.*;
	import javax.naming.spi.*;

	import com.sun.jndi.toolkit.url.UrlUtil;
	import sun.net.dns.ResolverConfiguration; // available since 1.4.1


	/**
	* A DnsContextFactory serves as the initial context factory for DNS.
	*
	* <p> When an initial context is being created, the environment
	* property "java.naming.provider.url" should contain a DNS pseudo-URL
	* (see DnsUrl) or a space-separated list of them. Multiple URLs must
	* all have the same domain value.
	* If the property is not set, the default "dns:" is used.
	*
	* @author Scott Seligman
	*/


	public class DnsContextFactory implements InitialContextFactory {

	private static final String DEFAULT_URL = "dns:";
	private static final int DEFAULT_PORT = 53;


	public Context getInitialContext(Hashtable<?,?> env) throws NamingException {
	if (env == null) {
	env = new Hashtable<>(5);
	}
	return urlToContext(getInitCtxUrl(env), env);
	}

	public static DnsContext getContext(String domain,
	String[] servers, Hashtable<?,?> env)
	throws NamingException {
	return new DnsContext(domain, servers, env);
	}

	/*
	* "urls" are used to determine the servers, but any domain
	* components are overridden by "domain".
	*/
	public static DnsContext getContext(String domain,
	DnsUrl[] urls, Hashtable<?,?> env)
	throws NamingException {

	String[] servers = serversForUrls(urls);
	DnsContext ctx = getContext(domain, servers, env);
	if (platformServersUsed(urls)) {
	ctx.setProviderUrl(constructProviderUrl(domain, servers));
	}
	return ctx;
	}

	/*
	* Public for use by product test suite.
	*/
	public static boolean platformServersAvailable() {
	return !filterNameServers(
	ResolverConfiguration.open().nameservers(), true
	).isEmpty();
	}

	private static Context urlToContext(String url, Hashtable<?,?> env)
	throws NamingException {

	DnsUrl[] urls;
	try {
	urls = DnsUrl.fromList(url);
	} catch (MalformedURLException e) {
	throw new ConfigurationException(e.getMessage());
	}
	if (urls.length == 0) {
	throw new ConfigurationException(
	"Invalid DNS pseudo-URL(s): " + url);
	}
	String domain = urls[0].getDomain();

	// If multiple urls, all must have the same domain.
	for (int i = 1; i < urls.length; i++) {
	if (!domain.equalsIgnoreCase(urls[i].getDomain())) {
	throw new ConfigurationException(
	"Conflicting domains: " + url);
	}
	}
	return getContext(domain, urls, env);
	}

	/*
	* Returns all the servers specified in a set of URLs.
	* If a URL has no host (or port), the servers configured on the
	* underlying platform are used if possible. If no configured
	* servers can be found, then fall back to the old behavior of
	* using "localhost".
	* There must be at least one URL.
	*/
	private static String[] serversForUrls(DnsUrl[] urls)
	throws NamingException {

	if (urls.length == 0) {
	throw new ConfigurationException("DNS pseudo-URL required");
	}

	List<String> servers = new ArrayList<>();

	for (int i = 0; i < urls.length; i++) {
	String server = urls[i].getHost();
	int port = urls[i].getPort();

	if (server == null && port < 0) {
	// No server or port given, so look to underlying platform.
	// ResolverConfiguration does some limited caching, so the
	// following is reasonably efficient even if called rapid-fire.
	List<String> platformServers = filterNameServers(
	ResolverConfiguration.open().nameservers(), false);
	if (!platformServers.isEmpty()) {
	servers.addAll(platformServers);
	continue; // on to next URL (if any, which is unlikely)
	}
	}

	if (server == null) {
	server = "localhost";
	}
	servers.add((port < 0)
	? server
	: server + ":" + port);
	}
	return servers.toArray(new String[servers.size()]);
	}

	/*
	* Returns true if serversForUrls(urls) would make use of servers
	* from the underlying platform.
	*/
	private static boolean platformServersUsed(DnsUrl[] urls) {
	if (!platformServersAvailable()) {
	return false;
	}
	for (int i = 0; i < urls.length; i++) {
	if (urls[i].getHost() == null &&
	urls[i].getPort() < 0) {
	return true;
	}
	}
	return false;
	}

	/*
	* Returns a value for the PROVIDER_URL property (space-separated URL
	* Strings) that reflects the given domain and servers.
	* Each server is of the form "server[:port]".
	* There must be at least one server.
	* IPv6 literal host names include delimiting brackets.
	*/
	private static String constructProviderUrl(String domain,
	String[] servers) {
	String path = "";
	if (!domain.equals(".")) {
	try {
	path = "/" + UrlUtil.encode(domain, "ISO-8859-1");
	} catch (java.io.UnsupportedEncodingException e) {
	// assert false : "ISO-Latin-1 charset unavailable";
	}
	}

	StringBuffer buf = new StringBuffer();
	for (int i = 0; i < servers.length; i++) {
	if (i > 0) {
	buf.append(' ');
	}
	buf.append("dns://").append(servers[i]).append(path);
	}
	return buf.toString();
	}

	/*
	* Reads environment to find URL(s) of initial context.
	* Default URL is "dns:".
	*/
	private static String getInitCtxUrl(Hashtable<?,?> env) {
	String url = (String) env.get(Context.PROVIDER_URL);
	return ((url != null) ? url : DEFAULT_URL);
	}

	/**
	* Removes any DNS server that's not permitted to access
	* @param input the input server[:port] list, must not be null
	* @param oneIsEnough return output once there exists one ok
	* @return the filtered list, all non-permitted input removed
	*/
	private static List<String> filterNameServers(List<String> input, boolean oneIsEnough) {
	SecurityManager security = System.getSecurityManager();
	if (security == null \|\| input == null \|\| input.isEmpty()) {
	return input;
	} else {
	List<String> output = new ArrayList<>();
	for (String platformServer: input) {
	int colon = platformServer.indexOf(':',
	platformServer.indexOf(']') + 1);

	int p = (colon < 0)
	? DEFAULT_PORT
	: Integer.parseInt(
	platformServer.substring(colon + 1));
	String s = (colon < 0)
	? platformServer
	: platformServer.substring(0, colon);
	try {
	security.checkConnect(s, p);
	output.add(platformServer);
	if (oneIsEnough) {
	return output;
	}
	} catch (SecurityException se) {
	continue;
	}
	}
	return output;
	}
	}
	}

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