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core: NameResolverProvider should use ServiceProviders util (grpc#4005)
1 parent 2996207 commit 2a93e6b

5 files changed

Lines changed: 159 additions & 284 deletions

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‎core/src/main/java/io/grpc/InternalNameResolverProvider.java‎

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/*
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* Copyright 2018, gRPC Authors All rights reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.grpc;
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import com.google.common.annotations.VisibleForTesting;
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public class InternalNameResolverProvider {
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@VisibleForTesting
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public static final Iterable<Class<?>> HARDCODED_CLASSES =
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NameResolverProvider.HARDCODED_CLASSES;
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}

‎core/src/main/java/io/grpc/NameResolverProvider.java‎

Lines changed: 35 additions & 88 deletions
Original file line numberDiff line numberDiff line change
@@ -20,11 +20,8 @@
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import com.google.common.base.Preconditions;
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import java.net.URI;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.Comparator;
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import java.util.Iterator;
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import java.util.List;
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import java.util.ServiceConfigurationError;
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import java.util.ServiceLoader;
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/**
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* Provider of name resolvers for name agnostic consumption.
@@ -41,81 +38,26 @@ public abstract class NameResolverProvider extends NameResolver.Factory {
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*/
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public static final Attributes.Key<Integer> PARAMS_DEFAULT_PORT =
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NameResolver.Factory.PARAMS_DEFAULT_PORT;
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private static final List<NameResolverProvider> providers
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= load(NameResolverProvider.class.getClassLoader());
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private static final NameResolver.Factory factory = new NameResolverFactory(providers);
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@VisibleForTesting
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static List<NameResolverProvider> load(ClassLoader classLoader) {
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Iterable<NameResolverProvider> candidates;
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if (isAndroid()) {
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candidates = getCandidatesViaHardCoded();
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} else {
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candidates = getCandidatesViaServiceLoader(classLoader);
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}
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List<NameResolverProvider> list = new ArrayList<NameResolverProvider>();
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for (NameResolverProvider current : candidates) {
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if (!current.isAvailable()) {
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continue;
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}
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list.add(current);
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}
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// Sort descending based on priority.
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Collections.sort(list, Collections.reverseOrder(new Comparator<NameResolverProvider>() {
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@Override
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public int compare(NameResolverProvider f1, NameResolverProvider f2) {
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return f1.priority() - f2.priority();
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}
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}));
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return Collections.unmodifiableList(list);
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}
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/**
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* Loads service providers for the {@link NameResolverProvider} service using
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* {@link ServiceLoader}.
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*/
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@VisibleForTesting
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public static Iterable<NameResolverProvider> getCandidatesViaServiceLoader(
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ClassLoader classLoader) {
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Iterable<NameResolverProvider> i
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= ServiceLoader.load(NameResolverProvider.class, classLoader);
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// Attempt to load using the context class loader and ServiceLoader.
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// This allows frameworks like http://aries.apache.org/modules/spi-fly.html to plug in.
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if (!i.iterator().hasNext()) {
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i = ServiceLoader.load(NameResolverProvider.class);
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}
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return i;
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}
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static final Iterable<Class<?>> HARDCODED_CLASSES = new HardcodedClasses();
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private static final List<NameResolverProvider> providers = ServiceProviders.loadAll(
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NameResolverProvider.class,
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HARDCODED_CLASSES,
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NameResolverProvider.class.getClassLoader(),
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new ServiceProviders.PriorityAccessor<NameResolverProvider>() {
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@Override
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public boolean isAvailable(NameResolverProvider provider) {
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return provider.isAvailable();
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}
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/**
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* Load providers from a hard-coded list. This avoids using getResource(), which has performance
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* problems on Android (see https://github.com/grpc/grpc-java/issues/2037). Any provider that may
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* be used on Android is free to be added here.
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*/
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@VisibleForTesting
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public static Iterable<NameResolverProvider> getCandidatesViaHardCoded() {
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// Class.forName(String) is used to remove the need for ProGuard configuration. Note that
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// ProGuard does not detect usages of Class.forName(String, boolean, ClassLoader):
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// https://sourceforge.net/p/proguard/bugs/418/
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List<NameResolverProvider> list = new ArrayList<NameResolverProvider>();
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try {
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list.add(create(Class.forName("io.grpc.internal.DnsNameResolverProvider")));
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} catch (ClassNotFoundException ex) {
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// ignore
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}
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return list;
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}
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@Override
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public int getPriority(NameResolverProvider provider) {
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return provider.priority();
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}
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});
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@VisibleForTesting
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static NameResolverProvider create(Class<?> rawClass) {
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try {
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return rawClass.asSubclass(NameResolverProvider.class).getConstructor().newInstance();
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} catch (Throwable t) {
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throw new ServiceConfigurationError(
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"Provider " + rawClass.getName() + " could not be instantiated: " + t, t);
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}
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}
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private static final NameResolver.Factory factory = new NameResolverFactory(providers);
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/**
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* Returns non-{@code null} ClassLoader-wide providers, in preference order.
@@ -133,18 +75,6 @@ static NameResolver.Factory asFactory(List<NameResolverProvider> providers) {
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return new NameResolverFactory(providers);
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}
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private static boolean isAndroid() {
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try {
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// Specify a class loader instead of null because we may be running under Robolectric
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Class.forName("android.app.Application", /*initialize=*/ false,
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NameResolverProvider.class.getClassLoader());
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return true;
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} catch (Exception e) {
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// If Application isn't loaded, it might as well not be Android.
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return false;
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}
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}
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/**
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* Whether this provider is available for use, taking the current environment into consideration.
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* If {@code false}, no other methods are safe to be called.
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+ "This is probably due to a broken build. If using ProGuard, check your configuration");
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}
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}
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@VisibleForTesting
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static final class HardcodedClasses implements Iterable<Class<?>> {
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@Override
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public Iterator<Class<?>> iterator() {
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List<Class<?>> list = new ArrayList<Class<?>>();
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// Class.forName(String) is used to remove the need for ProGuard configuration. Note that
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// ProGuard does not detect usages of Class.forName(String, boolean, ClassLoader):
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// https://sourceforge.net/p/proguard/bugs/418/
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try {
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list.add(Class.forName("io.grpc.internal.DnsNameResolverProvider"));
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} catch (ClassNotFoundException e) {
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// ignore
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}
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return list.iterator();
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}
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}
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}

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