| /* |
| * Copyright 2016, Google Inc. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are |
| * met: |
| * |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * Redistributions in binary form must reproduce the above |
| * copyright notice, this list of conditions and the following disclaimer |
| * in the documentation and/or other materials provided with the |
| * distribution. |
| * |
| * * Neither the name of Google Inc. nor the names of its |
| * contributors may be used to endorse or promote products derived from |
| * this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| package io.grpc; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| import com.google.common.base.Preconditions; |
| |
| import java.net.URI; |
| import java.util.ArrayList; |
| import java.util.Collections; |
| import java.util.Comparator; |
| import java.util.List; |
| import java.util.ServiceConfigurationError; |
| import java.util.ServiceLoader; |
| |
| /** |
| * Provider of name resolvers for name agnostic consumption. |
| * |
| * <p>Implementations <em>should not</em> throw. If they do, it may interrupt class loading. If |
| * exceptions may reasonably occur for implementation-specific reasons, implementations should |
| * generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}. |
| */ |
| @Internal |
| public abstract class NameResolverProvider extends NameResolver.Factory { |
| /** |
| * The port number used in case the target or the underlying naming system doesn't provide a |
| * port number. |
| */ |
| public static final Attributes.Key<Integer> PARAMS_DEFAULT_PORT = |
| NameResolver.Factory.PARAMS_DEFAULT_PORT; |
| |
| private static final List<NameResolverProvider> providers |
| = load(getCorrectClassLoader()); |
| private static final NameResolver.Factory factory = new NameResolverFactory(providers); |
| |
| @VisibleForTesting |
| static List<NameResolverProvider> load(ClassLoader classLoader) { |
| Iterable<NameResolverProvider> candidates; |
| if (isAndroid()) { |
| candidates = getCandidatesViaHardCoded(classLoader); |
| } else { |
| candidates = getCandidatesViaServiceLoader(classLoader); |
| } |
| List<NameResolverProvider> list = new ArrayList<NameResolverProvider>(); |
| for (NameResolverProvider current : candidates) { |
| if (!current.isAvailable()) { |
| continue; |
| } |
| list.add(current); |
| } |
| // Sort descending based on priority. |
| Collections.sort(list, Collections.reverseOrder(new Comparator<NameResolverProvider>() { |
| @Override |
| public int compare(NameResolverProvider f1, NameResolverProvider f2) { |
| return f1.priority() - f2.priority(); |
| } |
| })); |
| return Collections.unmodifiableList(list); |
| } |
| |
| @VisibleForTesting |
| public static Iterable<NameResolverProvider> getCandidatesViaServiceLoader( |
| ClassLoader classLoader) { |
| return ServiceLoader.load(NameResolverProvider.class, classLoader); |
| } |
| |
| /** |
| * Load providers from a hard-coded list. This avoids using getResource(), which has performance |
| * problems on Android (see https://github.com/grpc/grpc-java/issues/2037). Any provider that may |
| * be used on Android is free to be added here. |
| */ |
| @VisibleForTesting |
| public static Iterable<NameResolverProvider> getCandidatesViaHardCoded(ClassLoader classLoader) { |
| List<NameResolverProvider> list = new ArrayList<NameResolverProvider>(); |
| try { |
| list.add(create( |
| Class.forName("io.grpc.internal.DnsNameResolverProvider", true, classLoader))); |
| } catch (ClassNotFoundException ex) { |
| // ignore |
| } |
| return list; |
| } |
| |
| @VisibleForTesting |
| static NameResolverProvider create(Class<?> rawClass) { |
| try { |
| return rawClass.asSubclass(NameResolverProvider.class).getConstructor().newInstance(); |
| } catch (Throwable t) { |
| throw new ServiceConfigurationError( |
| "Provider " + rawClass.getName() + " could not be instantiated: " + t, t); |
| } |
| } |
| |
| /** |
| * Returns non-{@code null} ClassLoader-wide providers, in preference order. |
| */ |
| public static List<NameResolverProvider> providers() { |
| return providers; |
| } |
| |
| public static NameResolver.Factory asFactory() { |
| return factory; |
| } |
| |
| @VisibleForTesting |
| static NameResolver.Factory asFactory(List<NameResolverProvider> providers) { |
| return new NameResolverFactory(providers); |
| } |
| |
| private static ClassLoader getCorrectClassLoader() { |
| if (isAndroid()) { |
| // When android:sharedUserId or android:process is used, Android will setup a dummy |
| // ClassLoader for the thread context (http://stackoverflow.com/questions/13407006), |
| // instead of letting users to manually set context class loader, we choose the |
| // correct class loader here. |
| return NameResolverProvider.class.getClassLoader(); |
| } |
| return Thread.currentThread().getContextClassLoader(); |
| } |
| |
| private static boolean isAndroid() { |
| try { |
| Class.forName("android.app.Application", /*initialize=*/ false, null); |
| return true; |
| } catch (Exception e) { |
| // If Application isn't loaded, it might as well not be Android. |
| return false; |
| } |
| } |
| |
| /** |
| * Whether this provider is available for use, taking the current environment into consideration. |
| * If {@code false}, no other methods are safe to be called. |
| */ |
| protected abstract boolean isAvailable(); |
| |
| /** |
| * A priority, from 0 to 10 that this provider should be used, taking the current environment into |
| * consideration. 5 should be considered the default, and then tweaked based on environment |
| * detection. A priority of 0 does not imply that the provider wouldn't work; just that it should |
| * be last in line. |
| */ |
| protected abstract int priority(); |
| |
| private static class NameResolverFactory extends NameResolver.Factory { |
| private final List<NameResolverProvider> providers; |
| |
| public NameResolverFactory(List<NameResolverProvider> providers) { |
| this.providers = providers; |
| } |
| |
| @Override |
| public NameResolver newNameResolver(URI targetUri, Attributes params) { |
| checkForProviders(); |
| for (NameResolverProvider provider : providers) { |
| NameResolver resolver = provider.newNameResolver(targetUri, params); |
| if (resolver != null) { |
| return resolver; |
| } |
| } |
| return null; |
| } |
| |
| @Override |
| public String getDefaultScheme() { |
| checkForProviders(); |
| return providers.get(0).getDefaultScheme(); |
| } |
| |
| private void checkForProviders() { |
| Preconditions.checkState(!providers.isEmpty(), |
| "No NameResolverProviders found via ServiceLoader, including for DNS. " |
| + "This is probably due to a broken build. If using ProGuard, check your configuration"); |
| } |
| } |
| } |