1 /*
2 * ====================================================================
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing,
14 * software distributed under the License is distributed on an
15 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16 * KIND, either express or implied. See the License for the
17 * specific language governing permissions and limitations
18 * under the License.
19 * ====================================================================
20 *
21 * This software consists of voluntary contributions made by many
22 * individuals on behalf of the Apache Software Foundation. For more
23 * information on the Apache Software Foundation, please see
24 * <http://www.apache.org/>.
25 *
26 */
27 package org.apache.hc.client5.http;
28
29 import java.net.InetAddress;
30 import java.net.UnknownHostException;
31
32 /**
33 * DNS resolver that uses the default OS implementation for resolving host names.
34 *
35 * @since 4.2
36 */
37 public class SystemDefaultDnsResolver implements DnsResolver {
38
39 /**
40 * Default instance of {@link SystemDefaultDnsResolver}.
41 */
42 public static final SystemDefaultDnsResolver INSTANCE = new SystemDefaultDnsResolver();
43
44 @Override
45 public InetAddress[] resolve(final String host) throws UnknownHostException {
46 try {
47 // Try resolving using the default resolver
48 return InetAddress.getAllByName(host);
49 } catch (final UnknownHostException e) {
50 // If default resolver fails, try stripping the IPv6 zone ID and resolving again
51 String strippedHost = null;
52 if (host.charAt(0) == '[') {
53 final int i = host.lastIndexOf('%');
54 if (i != -1) {
55 strippedHost = host.substring(0, i) + "]";
56 }
57 }
58 if (strippedHost != null) {
59 return InetAddress.getAllByName(strippedHost);
60 }
61 throw e;
62 }
63 }
64
65 @Override
66 public String resolveCanonicalHostname(final String host) throws UnknownHostException {
67 if (host == null) {
68 return null;
69 }
70 final InetAddress in = InetAddress.getByName(host);
71 final String canonicalServer = in.getCanonicalHostName();
72 if (in.getHostAddress().contentEquals(canonicalServer)) {
73 return host;
74 }
75 return canonicalServer;
76 }
77 }