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git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@10961 b35dd754-fafc-0310-a699-88a17e54d16e
256 lines
No EOL
9.1 KiB
Java
256 lines
No EOL
9.1 KiB
Java
/**
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* $Revision: 1456 $
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* $Date: 2005-06-01 22:04:54 -0700 (Wed, 01 Jun 2005) $
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*
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* Copyright 2003-2005 Jive Software.
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*
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* All rights reserved. Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.jivesoftware.smack.util;
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import java.util.Hashtable;
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import java.util.Map;
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import javax.naming.NamingEnumeration;
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import javax.naming.directory.Attribute;
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import javax.naming.directory.Attributes;
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import javax.naming.directory.DirContext;
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import javax.naming.directory.InitialDirContext;
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/**
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* Utilty class to perform DNS lookups for XMPP services.
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*
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* @author Matt Tucker
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*/
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public class DNSUtil {
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/**
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* Create a cache to hold the 100 most recently accessed DNS lookups for a period of
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* 10 minutes.
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*/
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private static Map cache = new Cache(100, 1000*60*10);
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private static DirContext context;
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static {
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try {
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Hashtable env = new Hashtable();
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env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
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context = new InitialDirContext(env);
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}
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catch (Exception e) {
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// Ignore.
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}
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}
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/**
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* Returns the host name and port that the specified XMPP server can be
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* reached at for client-to-server communication. A DNS lookup for a SRV
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* record in the form "_xmpp-client._tcp.example.com" is attempted, according
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* to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
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* of "_jabber._tcp.example.com" is attempted since servers that implement an
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* older version of the protocol may be listed using that notation. If that
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* lookup fails as well, it's assumed that the XMPP server lives at the
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* host resolved by a DNS lookup at the specified domain on the default port
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* of 5222.<p>
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*
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* As an example, a lookup for "example.com" may return "im.example.com:5269".
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*
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* Note on SRV record selection.
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* We now check priority and weight, but we still don't do this correctly.
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* The missing behavior is this: if we fail to reach a host based on its SRV
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* record then we need to select another host from the other SRV records.
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* In Smack 3.1.1 we're not going to be able to do the major system redesign to
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* correct this.
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*
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* @param domain the domain.
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* @return a HostAddress, which encompasses the hostname and port that the XMPP
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* server can be reached at for the specified domain.
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*/
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public static HostAddress resolveXMPPDomain(String domain) {
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if (context == null) {
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return new HostAddress(domain, 5222);
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}
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String key = "c" + domain;
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// Return item from cache if it exists.
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if (cache.containsKey(key)) {
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HostAddress address = (HostAddress)cache.get(key);
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if (address != null) {
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return address;
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}
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}
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String bestHost = domain;
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int bestPort = 5222;
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int bestPriority = 0;
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int bestWeight = 0;
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try {
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Attributes dnsLookup = context.getAttributes("_xmpp-client._tcp." + domain, new String[]{"SRV"});
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Attribute srvAttribute = dnsLookup.get("SRV");
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NamingEnumeration srvRecords = srvAttribute.getAll();
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while(srvRecords.hasMore()) {
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String srvRecord = (String) srvRecords.next();
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String [] srvRecordEntries = srvRecord.split(" ");
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int priority = Integer.parseInt(srvRecordEntries[srvRecordEntries.length - 4]);
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int port = Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
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int weight = Integer.parseInt(srvRecordEntries[srvRecordEntries.length - 3]);
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String host = srvRecordEntries[srvRecordEntries.length-1];
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// Randomize the weight.
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weight *= Math.random() * weight;
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if ((bestPriority == 0) || (priority < bestPriority)) {
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// Choose a server with the lowest priority.
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bestPriority = priority;
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bestWeight = weight;
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bestHost = host;
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bestPort = port;
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} else if (priority == bestPriority) {
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// When we have like priorities then randomly choose a server based on its weight
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// The weights were randomized above.
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if (weight > bestWeight) {
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bestWeight = weight;
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bestHost = host;
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bestPort = port;
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}
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}
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}
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}
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catch (Exception e) {
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// Ignore.
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}
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// Host entries in DNS should end with a ".".
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if (bestHost.endsWith(".")) {
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bestHost = bestHost.substring(0, bestHost.length()-1);
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}
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HostAddress address = new HostAddress(bestHost, bestPort);
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// Add item to cache.
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cache.put(key, address);
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return address;
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}
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/**
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* Returns the host name and port that the specified XMPP server can be
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* reached at for server-to-server communication. A DNS lookup for a SRV
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* record in the form "_xmpp-server._tcp.example.com" is attempted, according
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* to section 14.4 of RFC 3920. If that lookup fails, a lookup in the older form
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* of "_jabber._tcp.example.com" is attempted since servers that implement an
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* older version of the protocol may be listed using that notation. If that
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* lookup fails as well, it's assumed that the XMPP server lives at the
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* host resolved by a DNS lookup at the specified domain on the default port
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* of 5269.<p>
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*
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* As an example, a lookup for "example.com" may return "im.example.com:5269".
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*
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* @param domain the domain.
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* @return a HostAddress, which encompasses the hostname and port that the XMPP
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* server can be reached at for the specified domain.
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*/
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public static HostAddress resolveXMPPServerDomain(String domain) {
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if (context == null) {
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return new HostAddress(domain, 5269);
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}
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String key = "s" + domain;
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// Return item from cache if it exists.
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if (cache.containsKey(key)) {
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HostAddress address = (HostAddress)cache.get(key);
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if (address != null) {
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return address;
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}
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}
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String host = domain;
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int port = 5269;
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try {
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Attributes dnsLookup =
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context.getAttributes("_xmpp-server._tcp." + domain, new String[]{"SRV"});
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String srvRecord = (String)dnsLookup.get("SRV").get();
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String [] srvRecordEntries = srvRecord.split(" ");
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port = Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
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host = srvRecordEntries[srvRecordEntries.length-1];
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}
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catch (Exception e) {
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// Attempt lookup with older "jabber" name.
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try {
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Attributes dnsLookup =
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context.getAttributes("_jabber._tcp." + domain, new String[]{"SRV"});
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String srvRecord = (String)dnsLookup.get("SRV").get();
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String [] srvRecordEntries = srvRecord.split(" ");
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port = Integer.parseInt(srvRecordEntries[srvRecordEntries.length-2]);
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host = srvRecordEntries[srvRecordEntries.length-1];
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}
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catch (Exception e2) {
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// Ignore.
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}
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}
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// Host entries in DNS should end with a ".".
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if (host.endsWith(".")) {
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host = host.substring(0, host.length()-1);
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}
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HostAddress address = new HostAddress(host, port);
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// Add item to cache.
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cache.put(key, address);
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return address;
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}
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/**
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* Encapsulates a hostname and port.
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*/
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public static class HostAddress {
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private String host;
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private int port;
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private HostAddress(String host, int port) {
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this.host = host;
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this.port = port;
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}
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/**
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* Returns the hostname.
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*
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* @return the hostname.
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*/
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public String getHost() {
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return host;
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}
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/**
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* Returns the port.
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*
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* @return the port.
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*/
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public int getPort() {
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return port;
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}
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public String toString() {
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return host + ":" + port;
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}
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public boolean equals(Object o) {
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if (this == o) {
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return true;
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}
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if (!(o instanceof HostAddress)) {
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return false;
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}
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final HostAddress address = (HostAddress) o;
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if (!host.equals(address.host)) {
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return false;
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}
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return port == address.port;
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}
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}
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} |