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 public static final SystemDefaultDnsResolver INSTANCE = new SystemDefaultDnsResolver();
40
41 @Override
42 public InetAddress[] resolve(final String host) throws UnknownHostException {
43 try {
44 // Try resolving using the default resolver
45 return InetAddress.getAllByName(host);
46 } catch (final UnknownHostException e) {
47 // If default resolver fails, try stripping the IPv6 zone ID and resolving again
48 String strippedHost = null;
49 if (host.charAt(0) == '[') {
50 final int i = host.lastIndexOf('%');
51 if (i != -1) {
52 strippedHost = host.substring(0, i) + "]";
53 }
54 }
55 if (strippedHost != null) {
56 return InetAddress.getAllByName(strippedHost);
57 }
58 throw e;
59 }
60 }
61
62 @Override
63 public String resolveCanonicalHostname(final String host) throws UnknownHostException {
64 if (host == null) {
65 return null;
66 }
67 final InetAddress in = InetAddress.getByName(host);
68 final String canonicalServer = in.getCanonicalHostName();
69 if (in.getHostAddress().contentEquals(canonicalServer)) {
70 return host;
71 }
72 return canonicalServer;
73 }
74 }