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DnsSrvNameResolver.java
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DnsSrvNameResolver.java
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/*
* Copyright 2016-2020 The jetcd 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.etcd.jetcd.resolver;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.net.URI;
import java.util.ArrayList;
import java.util.Hashtable;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.Executor;
import javax.annotation.concurrent.GuardedBy;
import javax.naming.NamingEnumeration;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
import com.google.common.base.Preconditions;
import com.google.common.base.Splitter;
import io.etcd.jetcd.common.exception.ErrorCode;
import io.etcd.jetcd.common.exception.EtcdExceptionFactory;
import io.grpc.EquivalentAddressGroup;
import io.grpc.NameResolver;
import io.grpc.Status;
import io.grpc.internal.GrpcUtil;
import io.grpc.internal.SharedResourceHolder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class DnsSrvNameResolver extends NameResolver {
public static final String SCHEME = "dns+srv";
private static final Logger LOGGER = LoggerFactory.getLogger(DnsSrvNameResolver.class);
private static final String[] ATTRIBUTE_IDS;
private static final Hashtable<String, String> ENV;
static {
ATTRIBUTE_IDS = new String[] { "SRV" };
ENV = new Hashtable<>();
ENV.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
ENV.put("java.naming.provider.url", "dns:");
}
private final Object lock;
private final String authority;
private final URI targetUri;
private volatile boolean shutdown;
private volatile boolean resolving;
@GuardedBy("lock")
private Executor executor;
@GuardedBy("lock")
private Listener listener;
public DnsSrvNameResolver(URI targetUri) {
this.lock = new Object();
this.targetUri = targetUri;
this.authority = targetUri.getAuthority() != null ? targetUri.getAuthority() : SCHEME;
}
@Override
public String getServiceAuthority() {
return authority;
}
@Override
public void start(Listener listener) {
synchronized (lock) {
Preconditions.checkState(this.listener == null, "already started");
this.executor = SharedResourceHolder.get(GrpcUtil.SHARED_CHANNEL_EXECUTOR);
this.listener = Preconditions.checkNotNull(listener, "listener");
resolve();
}
}
@Override
public final synchronized void refresh() {
resolve();
}
@Override
public void shutdown() {
if (shutdown) {
return;
}
shutdown = true;
synchronized (lock) {
if (executor != null) {
executor = SharedResourceHolder.release(GrpcUtil.SHARED_CHANNEL_EXECUTOR, executor);
}
}
}
private void resolve() {
if (resolving || shutdown) {
return;
}
synchronized (lock) {
executor.execute(this::doResolve);
}
}
private void doResolve() {
Listener savedListener;
synchronized (lock) {
if (shutdown) {
return;
}
resolving = true;
savedListener = listener;
}
try {
List<EquivalentAddressGroup> groups = new ArrayList<>();
for (SocketAddress address : resolveAddresses()) {
//
// if the authority is not explicit set on the builder
// then it will be computed from the URI
//
groups.add(new EquivalentAddressGroup(
address,
io.grpc.Attributes.EMPTY));
}
if (groups.isEmpty()) {
throw EtcdExceptionFactory.newEtcdException(
ErrorCode.INVALID_ARGUMENT,
"Unable to resolve endpoint " + targetUri);
}
savedListener.onAddresses(groups, io.grpc.Attributes.EMPTY);
} catch (Exception e) {
LOGGER.warn("Error wile getting list of servers", e);
savedListener.onError(Status.NOT_FOUND);
} finally {
resolving = false;
}
}
private List<SocketAddress> resolveAddresses() {
List<SocketAddress> addresses = new LinkedList<>();
try {
String address = targetUri.getPath();
if (address.startsWith("/")) {
address = address.substring(1);
}
DirContext ctx = new InitialDirContext(ENV);
Attributes attributes = ctx.getAttributes(address, ATTRIBUTE_IDS);
NamingEnumeration<?> resolved = attributes.get("srv").getAll();
while (resolved.hasMore()) {
String record = (String) resolved.next();
List<String> split = Splitter.on(' ').splitToList(record);
if (split.size() >= 4) {
String host = split.get(3).trim();
String port = split.get(2).trim();
addresses.add(new InetSocketAddress(host, Integer.parseInt(port)));
}
}
} catch (Exception e) {
throw EtcdExceptionFactory.toEtcdException(e);
}
return addresses;
}
}