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1   /*
2    * Copyright 2017 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.resolver.dns;
17  
18  import io.netty.util.internal.PlatformDependent;
19  import io.netty.util.internal.logging.InternalLogger;
20  import io.netty.util.internal.logging.InternalLoggerFactory;
21  
22  import java.lang.reflect.Constructor;
23  import java.lang.reflect.InvocationTargetException;
24  import java.security.AccessController;
25  import java.security.PrivilegedAction;
26  import java.util.concurrent.TimeUnit;
27  import java.util.concurrent.atomic.AtomicLong;
28  
29  /**
30   * Utility methods related to {@link DnsServerAddressStreamProvider}.
31   */
32  public final class DnsServerAddressStreamProviders {
33  
34      private static final InternalLogger LOGGER =
35              InternalLoggerFactory.getInstance(DnsServerAddressStreamProviders.class);
36      private static final Constructor<? extends DnsServerAddressStreamProvider> STREAM_PROVIDER_CONSTRUCTOR;
37      private static final String MACOS_PROVIDER_CLASS_NAME =
38              "io.netty.resolver.dns.macos.MacOSDnsServerAddressStreamProvider";
39  
40      static {
41          Constructor<? extends DnsServerAddressStreamProvider> constructor = null;
42          if (PlatformDependent.isOsx()) {
43              try {
44                  // As MacOSDnsServerAddressStreamProvider is contained in another jar which depends on this jar
45                  // we use reflection to use it if its on the classpath.
46                  Object maybeProvider = AccessController.doPrivileged(new PrivilegedAction<Object>() {
47                      @Override
48                      public Object run() {
49                          try {
50                              return Class.forName(
51                                      MACOS_PROVIDER_CLASS_NAME,
52                                      true,
53                                      DnsServerAddressStreamProviders.class.getClassLoader());
54                          } catch (Throwable cause) {
55                              return cause;
56                          }
57                      }
58                  });
59                  if (maybeProvider instanceof Class) {
60                      @SuppressWarnings("unchecked")
61                      Class<? extends DnsServerAddressStreamProvider> providerClass =
62                              (Class<? extends DnsServerAddressStreamProvider>) maybeProvider;
63                      constructor = providerClass.getConstructor();
64                      constructor.newInstance();  // ctor ensures availability
65                      LOGGER.debug("{}: available", MACOS_PROVIDER_CLASS_NAME);
66                  } else {
67                      throw (Throwable) maybeProvider;
68                  }
69              } catch (ClassNotFoundException cause) {
70                  LOGGER.warn("Can not find {} in the classpath, fallback to system defaults. This may result in "
71                          + "incorrect DNS resolutions on MacOS.", MACOS_PROVIDER_CLASS_NAME);
72              } catch (Throwable cause) {
73                  LOGGER.error("Unable to load {}, fallback to system defaults. This may result in "
74                          + "incorrect DNS resolutions on MacOS.", MACOS_PROVIDER_CLASS_NAME, cause);
75                  constructor = null;
76              }
77          }
78          STREAM_PROVIDER_CONSTRUCTOR = constructor;
79      }
80  
81      private DnsServerAddressStreamProviders() {
82      }
83  
84      /**
85       * A {@link DnsServerAddressStreamProvider} which inherits the DNS servers from your local host's configuration.
86       * <p>
87       * Note that only macOS and Linux are currently supported.
88       * @return A {@link DnsServerAddressStreamProvider} which inherits the DNS servers from your local host's
89       * configuration.
90       */
91      public static DnsServerAddressStreamProvider platformDefault() {
92          if (STREAM_PROVIDER_CONSTRUCTOR != null) {
93              try {
94                  return STREAM_PROVIDER_CONSTRUCTOR.newInstance();
95              } catch (IllegalAccessException e) {
96                  // ignore
97              } catch (InstantiationException e) {
98                  // ignore
99              } catch (InvocationTargetException e) {
100                 // ignore
101             }
102         }
103         return unixDefault();
104     }
105 
106     public static DnsServerAddressStreamProvider unixDefault() {
107         return DefaultProviderHolder.DEFAULT_DNS_SERVER_ADDRESS_STREAM_PROVIDER;
108     }
109 
110     // We use a Holder class to only initialize DEFAULT_DNS_SERVER_ADDRESS_STREAM_PROVIDER if we really
111     // need it.
112     private static final class DefaultProviderHolder {
113         // We use 5 minutes which is the same as what OpenJDK is using in sun.net.dns.ResolverConfigurationImpl.
114         private static final long REFRESH_INTERVAL = TimeUnit.MINUTES.toNanos(5);
115 
116         // TODO(scott): how is this done on Windows? This may require a JNI call to GetNetworkParams
117         // https://msdn.microsoft.com/en-us/library/aa365968(VS.85).aspx.
118         static final DnsServerAddressStreamProvider DEFAULT_DNS_SERVER_ADDRESS_STREAM_PROVIDER =
119                 new DnsServerAddressStreamProvider() {
120                     private volatile DnsServerAddressStreamProvider currentProvider = provider();
121                     private final AtomicLong lastRefresh = new AtomicLong(System.nanoTime());
122 
123                     @Override
124                     public DnsServerAddressStream nameServerAddressStream(String hostname) {
125                         long last = lastRefresh.get();
126                         DnsServerAddressStreamProvider current = currentProvider;
127                         if (System.nanoTime() - last > REFRESH_INTERVAL) {
128                             // This is slightly racy which means it will be possible still use the old configuration
129                             // for a small amount of time, but that's ok.
130                             if (lastRefresh.compareAndSet(last, System.nanoTime())) {
131                                 current = currentProvider = provider();
132                             }
133                         }
134                         return current.nameServerAddressStream(hostname);
135                     }
136 
137                     private DnsServerAddressStreamProvider provider() {
138                         // If on windows just use the DefaultDnsServerAddressStreamProvider.INSTANCE as otherwise
139                         // we will log some error which may be confusing.
140                         return PlatformDependent.isWindows() ? DefaultDnsServerAddressStreamProvider.INSTANCE :
141                                 UnixResolverDnsServerAddressStreamProvider.parseSilently();
142                     }
143                 };
144     }
145 }