io.grpc.NameResolverRegistry Maven / Gradle / Ivy
/*
* Copyright 2019 The gRPC Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.grpc;
import static com.google.common.base.Preconditions.checkArgument;
import com.google.common.annotations.VisibleForTesting;
import java.net.URI;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;
/**
* Registry of {@link NameResolverProvider}s. The {@link #getDefaultRegistry default instance}
* loads providers at runtime through the Java service provider mechanism.
*
* @since 1.21.0
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/4159")
@ThreadSafe
public final class NameResolverRegistry {
private static final Logger logger = Logger.getLogger(NameResolverRegistry.class.getName());
private static NameResolverRegistry instance;
private final NameResolver.Factory factory = new NameResolverFactory();
@GuardedBy("this")
private final LinkedHashSet allProviders = new LinkedHashSet<>();
/** Immutable, sorted version of {@code allProviders}. Is replaced instead of mutating. */
@GuardedBy("this")
private List effectiveProviders = Collections.emptyList();
/**
* Register a provider.
*
* If the provider's {@link NameResolverProvider#isAvailable isAvailable()} returns
* {@code false}, this method will throw {@link IllegalArgumentException}.
*
*
Providers will be used in priority order. In case of ties, providers are used in
* registration order.
*/
public synchronized void register(NameResolverProvider provider) {
addProvider(provider);
refreshProviders();
}
private synchronized void addProvider(NameResolverProvider provider) {
checkArgument(provider.isAvailable(), "isAvailable() returned false");
allProviders.add(provider);
}
/**
* Deregisters a provider. No-op if the provider is not in the registry.
*
* @param provider the provider that was added to the register via {@link #register}.
*/
public synchronized void deregister(NameResolverProvider provider) {
allProviders.remove(provider);
refreshProviders();
}
private synchronized void refreshProviders() {
List providers = new ArrayList<>(allProviders);
// Sort descending based on priority.
// sort() must be stable, as we prefer first-registered providers
Collections.sort(providers, Collections.reverseOrder(new Comparator() {
@Override
public int compare(NameResolverProvider o1, NameResolverProvider o2) {
return o1.priority() - o2.priority();
}
}));
effectiveProviders = Collections.unmodifiableList(providers);
}
/**
* Returns the default registry that loads providers via the Java service loader mechanism.
*/
public static synchronized NameResolverRegistry getDefaultRegistry() {
if (instance == null) {
List providerList = ServiceProviders.loadAll(
NameResolverProvider.class,
getHardCodedClasses(),
NameResolverProvider.class.getClassLoader(),
new NameResolverPriorityAccessor());
if (providerList.isEmpty()) {
logger.warning("No NameResolverProviders found via ServiceLoader, including for DNS. This "
+ "is probably due to a broken build. If using ProGuard, check your configuration");
}
instance = new NameResolverRegistry();
for (NameResolverProvider provider : providerList) {
logger.fine("Service loader found " + provider);
if (provider.isAvailable()) {
instance.addProvider(provider);
}
}
instance.refreshProviders();
}
return instance;
}
/**
* Returns effective providers, in priority order.
*/
@VisibleForTesting
synchronized List providers() {
return effectiveProviders;
}
public NameResolver.Factory asFactory() {
return factory;
}
@VisibleForTesting
static List> getHardCodedClasses() {
// Class.forName(String) is used to remove the need for ProGuard configuration. Note that
// ProGuard does not detect usages of Class.forName(String, boolean, ClassLoader):
// https://sourceforge.net/p/proguard/bugs/418/
ArrayList> list = new ArrayList<>();
try {
list.add(Class.forName("io.grpc.internal.DnsNameResolverProvider"));
} catch (ClassNotFoundException e) {
logger.log(Level.FINE, "Unable to find DNS NameResolver", e);
}
return Collections.unmodifiableList(list);
}
private final class NameResolverFactory extends NameResolver.Factory {
@Override
@Nullable
public NameResolver newNameResolver(URI targetUri, NameResolver.Args args) {
List providers = providers();
for (NameResolverProvider provider : providers) {
NameResolver resolver = provider.newNameResolver(targetUri, args);
if (resolver != null) {
return resolver;
}
}
return null;
}
@Override
public String getDefaultScheme() {
List providers = providers();
if (providers.isEmpty()) {
return "unknown";
}
return providers.get(0).getDefaultScheme();
}
}
private static final class NameResolverPriorityAccessor
implements ServiceProviders.PriorityAccessor {
@Override
public boolean isAvailable(NameResolverProvider provider) {
return provider.isAvailable();
}
@Override
public int getPriority(NameResolverProvider provider) {
return provider.priority();
}
}
}