Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2016, Google Inc. All rights reserved. |
| 3 | * |
| 4 | * Redistribution and use in source and binary forms, with or without |
| 5 | * modification, are permitted provided that the following conditions are |
| 6 | * met: |
| 7 | * |
| 8 | * * Redistributions of source code must retain the above copyright |
| 9 | * notice, this list of conditions and the following disclaimer. |
| 10 | * * Redistributions in binary form must reproduce the above |
| 11 | * copyright notice, this list of conditions and the following disclaimer |
| 12 | * in the documentation and/or other materials provided with the |
| 13 | * distribution. |
| 14 | * |
| 15 | * * Neither the name of Google Inc. nor the names of its |
| 16 | * contributors may be used to endorse or promote products derived from |
| 17 | * this software without specific prior written permission. |
| 18 | * |
| 19 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 20 | * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 21 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| 22 | * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| 23 | * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| 24 | * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| 25 | * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 26 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 27 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 28 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| 29 | * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| 30 | */ |
| 31 | |
| 32 | package io.grpc; |
| 33 | |
| 34 | import com.google.common.annotations.VisibleForTesting; |
Eric Anderson | fe5b7e3 | 2016-06-27 12:02:09 -0700 | [diff] [blame] | 35 | import com.google.common.base.Preconditions; |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 36 | |
| 37 | import java.net.URI; |
| 38 | import java.util.ArrayList; |
| 39 | import java.util.Collections; |
| 40 | import java.util.Comparator; |
| 41 | import java.util.List; |
Eric Anderson | 4289aaf | 2016-07-19 17:52:43 -0700 | [diff] [blame] | 42 | import java.util.ServiceConfigurationError; |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 43 | import java.util.ServiceLoader; |
| 44 | |
| 45 | /** |
| 46 | * Provider of name resolvers for name agnostic consumption. |
| 47 | * |
| 48 | * <p>Implementations <em>should not</em> throw. If they do, it may interrupt class loading. If |
| 49 | * exceptions may reasonably occur for implementation-specific reasons, implementations should |
| 50 | * generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}. |
| 51 | */ |
| 52 | @Internal |
| 53 | public abstract class NameResolverProvider extends NameResolver.Factory { |
| 54 | /** |
| 55 | * The port number used in case the target or the underlying naming system doesn't provide a |
| 56 | * port number. |
| 57 | */ |
| 58 | public static final Attributes.Key<Integer> PARAMS_DEFAULT_PORT = |
| 59 | NameResolver.Factory.PARAMS_DEFAULT_PORT; |
| 60 | |
| 61 | private static final List<NameResolverProvider> providers |
| 62 | = load(getCorrectClassLoader()); |
| 63 | private static final NameResolver.Factory factory = new NameResolverFactory(providers); |
| 64 | |
| 65 | @VisibleForTesting |
| 66 | static List<NameResolverProvider> load(ClassLoader classLoader) { |
Eric Anderson | 4289aaf | 2016-07-19 17:52:43 -0700 | [diff] [blame] | 67 | Iterable<NameResolverProvider> candidates; |
| 68 | if (isAndroid()) { |
| 69 | candidates = getCandidatesViaHardCoded(classLoader); |
| 70 | } else { |
| 71 | candidates = getCandidatesViaServiceLoader(classLoader); |
| 72 | } |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 73 | List<NameResolverProvider> list = new ArrayList<NameResolverProvider>(); |
Eric Anderson | 4289aaf | 2016-07-19 17:52:43 -0700 | [diff] [blame] | 74 | for (NameResolverProvider current : candidates) { |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 75 | if (!current.isAvailable()) { |
| 76 | continue; |
| 77 | } |
| 78 | list.add(current); |
| 79 | } |
| 80 | // Sort descending based on priority. |
| 81 | Collections.sort(list, Collections.reverseOrder(new Comparator<NameResolverProvider>() { |
| 82 | @Override |
| 83 | public int compare(NameResolverProvider f1, NameResolverProvider f2) { |
| 84 | return f1.priority() - f2.priority(); |
| 85 | } |
| 86 | })); |
| 87 | return Collections.unmodifiableList(list); |
| 88 | } |
| 89 | |
Eric Anderson | 4289aaf | 2016-07-19 17:52:43 -0700 | [diff] [blame] | 90 | @VisibleForTesting |
| 91 | public static Iterable<NameResolverProvider> getCandidatesViaServiceLoader( |
| 92 | ClassLoader classLoader) { |
| 93 | return ServiceLoader.load(NameResolverProvider.class, classLoader); |
| 94 | } |
| 95 | |
| 96 | /** |
| 97 | * Load providers from a hard-coded list. This avoids using getResource(), which has performance |
| 98 | * problems on Android (see https://github.com/grpc/grpc-java/issues/2037). Any provider that may |
| 99 | * be used on Android is free to be added here. |
| 100 | */ |
| 101 | @VisibleForTesting |
| 102 | public static Iterable<NameResolverProvider> getCandidatesViaHardCoded(ClassLoader classLoader) { |
| 103 | List<NameResolverProvider> list = new ArrayList<NameResolverProvider>(); |
| 104 | try { |
| 105 | list.add(create( |
| 106 | Class.forName("io.grpc.internal.DnsNameResolverProvider", true, classLoader))); |
| 107 | } catch (ClassNotFoundException ex) { |
| 108 | // ignore |
| 109 | } |
| 110 | return list; |
| 111 | } |
| 112 | |
| 113 | @VisibleForTesting |
| 114 | static NameResolverProvider create(Class<?> rawClass) { |
| 115 | try { |
ZHANG Dapeng | e70f7b4 | 2016-11-16 19:15:16 -0800 | [diff] [blame] | 116 | return rawClass.asSubclass(NameResolverProvider.class).getConstructor().newInstance(); |
Eric Anderson | 4289aaf | 2016-07-19 17:52:43 -0700 | [diff] [blame] | 117 | } catch (Throwable t) { |
| 118 | throw new ServiceConfigurationError( |
| 119 | "Provider " + rawClass.getName() + " could not be instantiated: " + t, t); |
| 120 | } |
| 121 | } |
| 122 | |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 123 | /** |
| 124 | * Returns non-{@code null} ClassLoader-wide providers, in preference order. |
| 125 | */ |
| 126 | public static List<NameResolverProvider> providers() { |
| 127 | return providers; |
| 128 | } |
| 129 | |
| 130 | public static NameResolver.Factory asFactory() { |
| 131 | return factory; |
| 132 | } |
| 133 | |
| 134 | @VisibleForTesting |
| 135 | static NameResolver.Factory asFactory(List<NameResolverProvider> providers) { |
| 136 | return new NameResolverFactory(providers); |
| 137 | } |
| 138 | |
| 139 | private static ClassLoader getCorrectClassLoader() { |
Eric Anderson | b7ed883 | 2016-06-20 14:35:21 -0700 | [diff] [blame] | 140 | if (isAndroid()) { |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 141 | // When android:sharedUserId or android:process is used, Android will setup a dummy |
| 142 | // ClassLoader for the thread context (http://stackoverflow.com/questions/13407006), |
| 143 | // instead of letting users to manually set context class loader, we choose the |
| 144 | // correct class loader here. |
| 145 | return NameResolverProvider.class.getClassLoader(); |
| 146 | } |
| 147 | return Thread.currentThread().getContextClassLoader(); |
| 148 | } |
| 149 | |
Eric Anderson | b7ed883 | 2016-06-20 14:35:21 -0700 | [diff] [blame] | 150 | private static boolean isAndroid() { |
| 151 | try { |
| 152 | Class.forName("android.app.Application", /*initialize=*/ false, null); |
| 153 | return true; |
| 154 | } catch (Exception e) { |
| 155 | // If Application isn't loaded, it might as well not be Android. |
| 156 | return false; |
| 157 | } |
| 158 | } |
| 159 | |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 160 | /** |
| 161 | * Whether this provider is available for use, taking the current environment into consideration. |
| 162 | * If {@code false}, no other methods are safe to be called. |
| 163 | */ |
| 164 | protected abstract boolean isAvailable(); |
| 165 | |
| 166 | /** |
| 167 | * A priority, from 0 to 10 that this provider should be used, taking the current environment into |
| 168 | * consideration. 5 should be considered the default, and then tweaked based on environment |
| 169 | * detection. A priority of 0 does not imply that the provider wouldn't work; just that it should |
| 170 | * be last in line. |
| 171 | */ |
| 172 | protected abstract int priority(); |
| 173 | |
| 174 | private static class NameResolverFactory extends NameResolver.Factory { |
| 175 | private final List<NameResolverProvider> providers; |
| 176 | |
| 177 | public NameResolverFactory(List<NameResolverProvider> providers) { |
| 178 | this.providers = providers; |
| 179 | } |
| 180 | |
| 181 | @Override |
| 182 | public NameResolver newNameResolver(URI targetUri, Attributes params) { |
Eric Anderson | fe5b7e3 | 2016-06-27 12:02:09 -0700 | [diff] [blame] | 183 | checkForProviders(); |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 184 | for (NameResolverProvider provider : providers) { |
| 185 | NameResolver resolver = provider.newNameResolver(targetUri, params); |
| 186 | if (resolver != null) { |
| 187 | return resolver; |
| 188 | } |
| 189 | } |
| 190 | return null; |
| 191 | } |
| 192 | |
| 193 | @Override |
| 194 | public String getDefaultScheme() { |
Eric Anderson | fe5b7e3 | 2016-06-27 12:02:09 -0700 | [diff] [blame] | 195 | checkForProviders(); |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 196 | return providers.get(0).getDefaultScheme(); |
| 197 | } |
Eric Anderson | fe5b7e3 | 2016-06-27 12:02:09 -0700 | [diff] [blame] | 198 | |
| 199 | private void checkForProviders() { |
| 200 | Preconditions.checkState(!providers.isEmpty(), |
| 201 | "No NameResolverProviders found via ServiceLoader, including for DNS. " |
| 202 | + "This is probably due to a broken build. If using ProGuard, check your configuration"); |
| 203 | } |
Eric Anderson | 56a2938 | 2016-06-11 11:55:49 -0700 | [diff] [blame] | 204 | } |
| 205 | } |