1 /*
2 * Copyright 2016 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package io.netty5.resolver;
17
18 import io.netty5.util.concurrent.EventExecutor;
19 import io.netty5.util.concurrent.Future;
20 import io.netty5.util.concurrent.Promise;
21
22 import java.net.InetAddress;
23 import java.net.InetSocketAddress;
24 import java.net.UnknownHostException;
25 import java.util.ArrayList;
26 import java.util.Collections;
27 import java.util.List;
28 import java.util.concurrent.ThreadLocalRandom;
29
30 /**
31 * A {@link NameResolver} that resolves {@link InetAddress} and force Round Robin by choosing a single address
32 * randomly in {@link #resolve(String)} and {@link #resolve(String, Promise)}
33 * if multiple are returned by the {@link NameResolver}.
34 * Use {@link #asAddressResolver()} to create a {@link InetSocketAddress} resolver
35 */
36 public class RoundRobinInetAddressResolver extends InetNameResolver {
37 private final NameResolver<InetAddress> nameResolver;
38
39 /**
40 * @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned by
41 * {@link #resolve(String)}
42 * @param nameResolver the {@link NameResolver} used for name resolution
43 */
44 public RoundRobinInetAddressResolver(EventExecutor executor, NameResolver<InetAddress> nameResolver) {
45 super(executor);
46 this.nameResolver = nameResolver;
47 }
48
49 @Override
50 protected void doResolve(final String inetHost, final Promise<InetAddress> promise) throws Exception {
51 // hijack the doResolve request, but do a doResolveAll request under the hood.
52 // Note that InetSocketAddress.getHostName() will never incur a reverse lookup here,
53 // because an unresolved address always has a host name.
54 nameResolver.resolveAll(inetHost).addListener(future -> {
55 if (future.isSuccess()) {
56 List<InetAddress> inetAddresses = future.getNow();
57 int numAddresses = inetAddresses.size();
58 if (numAddresses > 0) {
59 // if there are multiple addresses: we shall pick one by one
60 // to support the round robin distribution
61 promise.setSuccess(inetAddresses.get(randomIndex(numAddresses)));
62 } else {
63 promise.setFailure(new UnknownHostException(inetHost));
64 }
65 } else {
66 promise.setFailure(future.cause());
67 }
68 });
69 }
70
71 @Override
72 protected void doResolveAll(String inetHost, final Promise<List<InetAddress>> promise) throws Exception {
73 nameResolver.resolveAll(inetHost).addListener(future -> {
74 if (future.isSuccess()) {
75 List<InetAddress> inetAddresses = future.getNow();
76 if (!inetAddresses.isEmpty()) {
77 // create a copy to make sure that it's modifiable random access collection
78 List<InetAddress> result = new ArrayList<>(inetAddresses);
79 // rotate by different distance each time to force round robin distribution
80 Collections.rotate(result, randomIndex(inetAddresses.size()));
81 promise.setSuccess(result);
82 } else {
83 promise.setSuccess(inetAddresses);
84 }
85 } else {
86 promise.setFailure(future.cause());
87 }
88 });
89 }
90
91 private static int randomIndex(int numAddresses) {
92 return numAddresses == 1 ? 0 : ThreadLocalRandom.current().nextInt(numAddresses);
93 }
94
95 @Override
96 public void close() {
97 nameResolver.close();
98 }
99 }