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16 package io.netty.resolver.dns;
17
18 import io.netty.util.NetUtil;
19 import io.netty.util.internal.SocketUtils;
20 import io.netty.util.internal.UnstableApi;
21 import io.netty.util.internal.logging.InternalLogger;
22 import io.netty.util.internal.logging.InternalLoggerFactory;
23
24 import javax.naming.Context;
25 import javax.naming.NamingException;
26 import javax.naming.directory.DirContext;
27 import javax.naming.directory.InitialDirContext;
28 import java.lang.reflect.Method;
29 import java.net.Inet6Address;
30 import java.net.InetSocketAddress;
31 import java.net.URI;
32 import java.net.URISyntaxException;
33 import java.util.ArrayList;
34 import java.util.Collections;
35 import java.util.Hashtable;
36 import java.util.List;
37
38 import static io.netty.resolver.dns.DnsServerAddresses.sequential;
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45
46 @UnstableApi
47 public final class DefaultDnsServerAddressStreamProvider implements DnsServerAddressStreamProvider {
48 private static final InternalLogger logger =
49 InternalLoggerFactory.getInstance(DefaultDnsServerAddressStreamProvider.class);
50 public static final DefaultDnsServerAddressStreamProvider INSTANCE = new DefaultDnsServerAddressStreamProvider();
51
52 private static final List<InetSocketAddress> DEFAULT_NAME_SERVER_LIST;
53 private static final DnsServerAddresses DEFAULT_NAME_SERVERS;
54 static final int DNS_PORT = 53;
55
56 static {
57 final List<InetSocketAddress> defaultNameServers = new ArrayList<InetSocketAddress>(2);
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64 Hashtable<String, String> env = new Hashtable<String, String>();
65 env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.dns.DnsContextFactory");
66 env.put("java.naming.provider.url", "dns://");
67 try {
68 DirContext ctx = new InitialDirContext(env);
69 String dnsUrls = (String) ctx.getEnvironment().get("java.naming.provider.url");
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71 if (dnsUrls != null && !dnsUrls.isEmpty()) {
72 String[] servers = dnsUrls.split(" ");
73 for (String server : servers) {
74 try {
75 URI uri = new URI(server);
76 String host = new URI(server).getHost();
77
78 if (host == null || host.isEmpty()) {
79 logger.debug(
80 "Skipping a nameserver URI as host portion could not be extracted: {}", server);
81
82 continue;
83 }
84 int port = uri.getPort();
85 defaultNameServers.add(SocketUtils.socketAddress(uri.getHost(), port == -1 ? DNS_PORT : port));
86 } catch (URISyntaxException e) {
87 logger.debug("Skipping a malformed nameserver URI: {}", server, e);
88 }
89 }
90 }
91 } catch (NamingException ignore) {
92
93 }
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95 if (defaultNameServers.isEmpty()) {
96 try {
97 Class<?> configClass = Class.forName("sun.net.dns.ResolverConfiguration");
98 Method open = configClass.getMethod("open");
99 Method nameservers = configClass.getMethod("nameservers");
100 Object instance = open.invoke(null);
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102 @SuppressWarnings("unchecked")
103 final List<String> list = (List<String>) nameservers.invoke(instance);
104 for (String a: list) {
105 if (a != null) {
106 defaultNameServers.add(new InetSocketAddress(SocketUtils.addressByName(a), DNS_PORT));
107 }
108 }
109 } catch (Exception ignore) {
110
111
112 }
113 }
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115 if (!defaultNameServers.isEmpty()) {
116 if (logger.isDebugEnabled()) {
117 logger.debug(
118 "Default DNS servers: {} (sun.net.dns.ResolverConfiguration)", defaultNameServers);
119 }
120 } else {
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124 if (NetUtil.isIpV6AddressesPreferred() ||
125 (NetUtil.LOCALHOST instanceof Inet6Address && !NetUtil.isIpV4StackPreferred())) {
126 Collections.addAll(
127 defaultNameServers,
128 SocketUtils.socketAddress("2001:4860:4860::8888", DNS_PORT),
129 SocketUtils.socketAddress("2001:4860:4860::8844", DNS_PORT));
130 } else {
131 Collections.addAll(
132 defaultNameServers,
133 SocketUtils.socketAddress("8.8.8.8", DNS_PORT),
134 SocketUtils.socketAddress("8.8.4.4", DNS_PORT));
135 }
136
137 if (logger.isWarnEnabled()) {
138 logger.warn(
139 "Default DNS servers: {} (Google Public DNS as a fallback)", defaultNameServers);
140 }
141 }
142
143 DEFAULT_NAME_SERVER_LIST = Collections.unmodifiableList(defaultNameServers);
144 DEFAULT_NAME_SERVERS = sequential(DEFAULT_NAME_SERVER_LIST);
145 }
146
147 private DefaultDnsServerAddressStreamProvider() {
148 }
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150 @Override
151 public DnsServerAddressStream nameServerAddressStream(String hostname) {
152 return DEFAULT_NAME_SERVERS.stream();
153 }
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160 public static List<InetSocketAddress> defaultAddressList() {
161 return DEFAULT_NAME_SERVER_LIST;
162 }
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175 public static DnsServerAddresses defaultAddresses() {
176 return DEFAULT_NAME_SERVERS;
177 }
178 }