001/** 002 * 003 * Copyright 2013-2017 Florian Schmaus 004 * 005 * Licensed under the Apache License, Version 2.0 (the "License"); 006 * you may not use this file except in compliance with the License. 007 * You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.jivesoftware.smack.util.dns; 018 019import java.net.InetAddress; 020import java.net.UnknownHostException; 021import java.util.Arrays; 022import java.util.List; 023import java.util.logging.Level; 024import java.util.logging.Logger; 025 026import org.jivesoftware.smack.ConnectionConfiguration.DnssecMode; 027 028/** 029 * Implementations of this interface define a class that is capable of resolving DNS addresses. 030 * 031 */ 032public abstract class DNSResolver { 033 034 protected static final Logger LOGGER = Logger.getLogger(DNSResolver.class.getName()); 035 036 private final boolean supportsDnssec; 037 038 protected DNSResolver(boolean supportsDnssec) { 039 this.supportsDnssec = supportsDnssec; 040 } 041 042 /** 043 * Gets a list of service records for the specified service. 044 * @param name The symbolic name of the service. 045 * @param failedAddresses list of failed addresses. 046 * @param dnssecMode security mode. 047 * @return The list of SRV records mapped to the service name. 048 */ 049 public final List<SRVRecord> lookupSRVRecords(String name, List<HostAddress> failedAddresses, DnssecMode dnssecMode) { 050 checkIfDnssecRequestedAndSupported(dnssecMode); 051 return lookupSRVRecords0(name, failedAddresses, dnssecMode); 052 } 053 054 protected abstract List<SRVRecord> lookupSRVRecords0(String name, List<HostAddress> failedAddresses, DnssecMode dnssecMode); 055 056 public final HostAddress lookupHostAddress(String name, int port, List<HostAddress> failedAddresses, DnssecMode dnssecMode) { 057 checkIfDnssecRequestedAndSupported(dnssecMode); 058 List<InetAddress> inetAddresses = lookupHostAddress0(name, failedAddresses, dnssecMode); 059 if (inetAddresses == null || inetAddresses.isEmpty()) { 060 return null; 061 } 062 return new HostAddress(name, port, inetAddresses); 063 } 064 065 /** 066 * Lookup the IP addresses of a given host name. Returns <code>null</code> if there was an error, in which the error 067 * reason will be added in form of a <code>HostAddress</code> to <code>failedAddresses</code>. Returns a empty list 068 * in case the DNS name exists but has no associated A or AAAA resource records. Otherwise, if the resolution was 069 * successful <em>and</em> there is at least one A or AAAA resource record, then a non-empty list will be returned. 070 * <p> 071 * Concrete DNS resolver implementations are free to overwrite this, but have to stick to the interface contract. 072 * </p> 073 * 074 * @param name the DNS name to lookup 075 * @param failedAddresses a list with the failed addresses 076 * @param dnssecMode the selected DNSSEC mode 077 * @return A list, either empty or non-empty, or <code>null</code> 078 */ 079 protected List<InetAddress> lookupHostAddress0(String name, List<HostAddress> failedAddresses, DnssecMode dnssecMode) { 080 // Default implementation of a DNS name lookup for A/AAAA records. It is assumed that this method does never 081 // support DNSSEC. Subclasses are free to override this method. 082 if (dnssecMode != DnssecMode.disabled) { 083 throw new UnsupportedOperationException("This resolver does not support DNSSEC"); 084 } 085 086 InetAddress[] inetAddressArray; 087 try { 088 inetAddressArray = InetAddress.getAllByName(name); 089 } catch (UnknownHostException e) { 090 failedAddresses.add(new HostAddress(name, e)); 091 return null; 092 } 093 094 return Arrays.asList(inetAddressArray); 095 } 096 097 protected final boolean shouldContinue(CharSequence name, CharSequence hostname, List<InetAddress> hostAddresses) { 098 if (hostAddresses == null) { 099 return true; 100 } 101 102 // If hostAddresses is not null but empty, then the DNS resolution was successful but the domain did not 103 // have any A or AAAA resource records. 104 if (hostAddresses.isEmpty()) { 105 LOGGER.log(Level.INFO, "The DNS name " + name + ", points to a hostname (" + hostname 106 + ") which has neither A or AAAA resource records. This is an indication of a broken DNS setup."); 107 return true; 108 } 109 110 return false; 111 } 112 113 private final void checkIfDnssecRequestedAndSupported(DnssecMode dnssecMode) { 114 if (dnssecMode != DnssecMode.disabled && !supportsDnssec) { 115 throw new UnsupportedOperationException("This resolver does not support DNSSEC"); 116 } 117 } 118}