io.netty.resolver.RoundRobinInetAddressResolver Maven / Gradle / Ivy
/*
* Copyright 2016 The Netty Project
*
* The Netty Project licenses this file to you 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.netty.resolver;
import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.FutureListener;
import io.netty.util.concurrent.Promise;
import io.netty.util.internal.PlatformDependent;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* A {@link NameResolver} that resolves {@link InetAddress} and force Round Robin by choosing a single address
* randomly in {@link #resolve(String)} and {@link #resolve(String, Promise)}
* if multiple are returned by the {@link NameResolver}.
* Use {@link #asAddressResolver()} to create a {@link InetSocketAddress} resolver
*/
public class RoundRobinInetAddressResolver extends InetNameResolver {
private final NameResolver nameResolver;
/**
* @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned by
* {@link #resolve(String)}
* @param nameResolver the {@link NameResolver} used for name resolution
*/
public RoundRobinInetAddressResolver(EventExecutor executor, NameResolver nameResolver) {
super(executor);
this.nameResolver = nameResolver;
}
@Override
protected void doResolve(final String inetHost, final Promise promise) throws Exception {
// hijack the doResolve request, but do a doResolveAll request under the hood.
// Note that InetSocketAddress.getHostName() will never incur a reverse lookup here,
// because an unresolved address always has a host name.
nameResolver.resolveAll(inetHost).addListener(new FutureListener>() {
@Override
public void operationComplete(Future> future) throws Exception {
if (future.isSuccess()) {
List inetAddresses = future.getNow();
int numAddresses = inetAddresses.size();
if (numAddresses > 0) {
// if there are multiple addresses: we shall pick one by one
// to support the round robin distribution
promise.setSuccess(inetAddresses.get(randomIndex(numAddresses)));
} else {
promise.setFailure(new UnknownHostException(inetHost));
}
} else {
promise.setFailure(future.cause());
}
}
});
}
@Override
protected void doResolveAll(String inetHost, final Promise> promise) throws Exception {
nameResolver.resolveAll(inetHost).addListener(new FutureListener>() {
@Override
public void operationComplete(Future> future) throws Exception {
if (future.isSuccess()) {
List inetAddresses = future.getNow();
if (!inetAddresses.isEmpty()) {
// create a copy to make sure that it's modifiable random access collection
List result = new ArrayList(inetAddresses);
// rotate by different distance each time to force round robin distribution
Collections.rotate(result, randomIndex(inetAddresses.size()));
promise.setSuccess(result);
} else {
promise.setSuccess(inetAddresses);
}
} else {
promise.setFailure(future.cause());
}
}
});
}
private static int randomIndex(int numAddresses) {
return numAddresses == 1 ? 0 : PlatformDependent.threadLocalRandom().nextInt(numAddresses);
}
@Override
public void close() {
nameResolver.close();
}
}