io.grpc.NameResolverProvider Maven / Gradle / Ivy
/*
* Copyright 2016, gRPC Authors All rights reserved.
*
* 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 com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import java.net.URI;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
/**
* Provider of name resolvers for name agnostic consumption.
*
* Implementations should not 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()}.
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/4159")
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 PARAMS_DEFAULT_PORT =
NameResolver.Factory.PARAMS_DEFAULT_PORT;
@VisibleForTesting
static final Iterable> HARDCODED_CLASSES = new HardcodedClasses();
private static final List providers = ServiceProviders.loadAll(
NameResolverProvider.class,
HARDCODED_CLASSES,
NameResolverProvider.class.getClassLoader(),
new ServiceProviders.PriorityAccessor() {
@Override
public boolean isAvailable(NameResolverProvider provider) {
return provider.isAvailable();
}
@Override
public int getPriority(NameResolverProvider provider) {
return provider.priority();
}
});
private static final NameResolver.Factory factory = new NameResolverFactory(providers);
/**
* Returns non-{@code null} ClassLoader-wide providers, in preference order.
*/
public static List providers() {
return providers;
}
public static NameResolver.Factory asFactory() {
return factory;
}
@VisibleForTesting
static NameResolver.Factory asFactory(List providers) {
return new NameResolverFactory(providers);
}
/**
* 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 providers;
public NameResolverFactory(List 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");
}
}
@VisibleForTesting
static final class HardcodedClasses implements Iterable> {
@Override
public Iterator> iterator() {
List> list = new ArrayList>();
// 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/
try {
list.add(Class.forName("io.grpc.internal.DnsNameResolverProvider"));
} catch (ClassNotFoundException e) {
// ignore
}
return list.iterator();
}
}
}