io.grpc.internal.DnsNameResolver Maven / Gradle / Ivy
/*
* Copyright 2015, 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.internal;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import io.grpc.Attributes;
import io.grpc.EquivalentAddressGroup;
import io.grpc.NameResolver;
import io.grpc.Status;
import io.grpc.internal.SharedResourceHolder.Resource;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.URI;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;
import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.InitialDirContext;
/**
* A DNS-based {@link NameResolver}.
*
* Each {@code A} or {@code AAAA} record emits an {@link EquivalentAddressGroup} in the list
* passed to {@link NameResolver.Listener#onUpdate}
*
* @see DnsNameResolverProvider
*/
final class DnsNameResolver extends NameResolver {
private static final Logger logger = Logger.getLogger(DnsNameResolver.class.getName());
private static final boolean JNDI_AVAILABLE = jndiAvailable();
@VisibleForTesting
static boolean enableJndi = false;
private DelegateResolver delegateResolver = pickDelegateResolver();
private final String authority;
private final String host;
private final int port;
private final Resource timerServiceResource;
private final Resource executorResource;
private final ProxyDetector proxyDetector;
@GuardedBy("this")
private boolean shutdown;
@GuardedBy("this")
private ScheduledExecutorService timerService;
@GuardedBy("this")
private ExecutorService executor;
@GuardedBy("this")
private ScheduledFuture resolutionTask;
@GuardedBy("this")
private boolean resolving;
@GuardedBy("this")
private Listener listener;
DnsNameResolver(@Nullable String nsAuthority, String name, Attributes params,
Resource timerServiceResource,
Resource executorResource,
ProxyDetector proxyDetector) {
// TODO: if a DNS server is provided as nsAuthority, use it.
// https://www.captechconsulting.com/blogs/accessing-the-dusty-corners-of-dns-with-java
this.timerServiceResource = timerServiceResource;
this.executorResource = executorResource;
// Must prepend a "//" to the name when constructing a URI, otherwise it will be treated as an
// opaque URI, thus the authority and host of the resulted URI would be null.
URI nameUri = URI.create("//" + name);
authority = Preconditions.checkNotNull(nameUri.getAuthority(),
"nameUri (%s) doesn't have an authority", nameUri);
host = Preconditions.checkNotNull(nameUri.getHost(), "host");
if (nameUri.getPort() == -1) {
Integer defaultPort = params.get(NameResolver.Factory.PARAMS_DEFAULT_PORT);
if (defaultPort != null) {
port = defaultPort;
} else {
throw new IllegalArgumentException(
"name '" + name + "' doesn't contain a port, and default port is not set in params");
}
} else {
port = nameUri.getPort();
}
this.proxyDetector = proxyDetector;
}
@Override
public final String getServiceAuthority() {
return authority;
}
@Override
public final synchronized void start(Listener listener) {
Preconditions.checkState(this.listener == null, "already started");
timerService = SharedResourceHolder.get(timerServiceResource);
executor = SharedResourceHolder.get(executorResource);
this.listener = Preconditions.checkNotNull(listener, "listener");
resolve();
}
@Override
public final synchronized void refresh() {
Preconditions.checkState(listener != null, "not started");
resolve();
}
private final Runnable resolutionRunnable = new Runnable() {
@Override
public void run() {
Listener savedListener;
synchronized (DnsNameResolver.this) {
// If this task is started by refresh(), there might already be a scheduled task.
if (resolutionTask != null) {
resolutionTask.cancel(false);
resolutionTask = null;
}
if (shutdown) {
return;
}
savedListener = listener;
resolving = true;
}
try {
InetSocketAddress destination = InetSocketAddress.createUnresolved(host, port);
ProxyParameters proxy = proxyDetector.proxyFor(destination);
if (proxy != null) {
EquivalentAddressGroup server = new EquivalentAddressGroup(destination);
savedListener.onAddresses(Collections.singletonList(server), Attributes.EMPTY);
return;
}
ResolutionResults resolvedInetAddrs;
try {
resolvedInetAddrs = delegateResolver.resolve(host);
} catch (Exception e) {
synchronized (DnsNameResolver.this) {
if (shutdown) {
return;
}
// Because timerService is the single-threaded GrpcUtil.TIMER_SERVICE in production,
// we need to delegate the blocking work to the executor
resolutionTask =
timerService.schedule(new LogExceptionRunnable(resolutionRunnableOnExecutor),
1, TimeUnit.MINUTES);
}
savedListener.onError(Status.UNAVAILABLE.withCause(e));
return;
}
// Each address forms an EAG
ArrayList servers = new ArrayList();
for (InetAddress inetAddr : resolvedInetAddrs.addresses) {
servers.add(new EquivalentAddressGroup(new InetSocketAddress(inetAddr, port)));
}
savedListener.onAddresses(servers, Attributes.EMPTY);
} finally {
synchronized (DnsNameResolver.this) {
resolving = false;
}
}
}
};
private final Runnable resolutionRunnableOnExecutor = new Runnable() {
@Override
public void run() {
synchronized (DnsNameResolver.this) {
if (!shutdown) {
executor.execute(resolutionRunnable);
}
}
}
};
@GuardedBy("this")
private void resolve() {
if (resolving || shutdown) {
return;
}
executor.execute(resolutionRunnable);
}
@Override
public final synchronized void shutdown() {
if (shutdown) {
return;
}
shutdown = true;
if (resolutionTask != null) {
resolutionTask.cancel(false);
}
if (timerService != null) {
timerService = SharedResourceHolder.release(timerServiceResource, timerService);
}
if (executor != null) {
executor = SharedResourceHolder.release(executorResource, executor);
}
}
final int getPort() {
return port;
}
private DelegateResolver pickDelegateResolver() {
JdkResolver jdkResolver = new JdkResolver();
if (JNDI_AVAILABLE && enableJndi) {
return new CompositeResolver(jdkResolver, new JndiResolver());
}
return jdkResolver;
}
/**
* Forces the resolver. This should only be used by testing code.
*/
@VisibleForTesting
void setDelegateResolver(DelegateResolver delegateResolver) {
this.delegateResolver = delegateResolver;
}
/**
* Returns whether the JNDI DNS resolver is available. This is accomplished by looking up a
* particular class. It is believed to be the default (only?) DNS resolver that will actually be
* used. It is provided by the OpenJDK, but unlikely Android. Actual resolution will be done by
* using a service provider when a hostname query is present, so the {@code DnsContextFactory}
* may not actually be used to perform the query. This is believed to be "okay."
*/
@VisibleForTesting
@SuppressWarnings("LiteralClassName")
static boolean jndiAvailable() {
try {
Class.forName("javax.naming.directory.InitialDirContext");
Class.forName("com.sun.jndi.dns.DnsContextFactory");
} catch (ClassNotFoundException e) {
logger.log(Level.FINE, "Unable to find JNDI DNS resolver, skipping", e);
return false;
}
return true;
}
/**
* Common interface between the delegate resolvers used by DnsNameResolver.
*/
@VisibleForTesting
abstract static class DelegateResolver {
abstract ResolutionResults resolve(String host) throws Exception;
}
/**
* Describes the results from a DNS query.
*/
@VisibleForTesting
static final class ResolutionResults {
final List addresses;
final List txtRecords;
ResolutionResults(List addresses, List txtRecords) {
this.addresses = Collections.unmodifiableList(checkNotNull(addresses, "addresses"));
this.txtRecords = Collections.unmodifiableList(checkNotNull(txtRecords, "txtRecords"));
}
}
/**
* A composite DNS resolver that uses both the JDK and JNDI resolvers as delegate. It is
* expected that two DNS queries will be executed, with the second one being from JNDI.
*/
@VisibleForTesting
static final class CompositeResolver extends DelegateResolver {
private final DelegateResolver jdkResovler;
private final DelegateResolver jndiResovler;
CompositeResolver(DelegateResolver jdkResovler, DelegateResolver jndiResovler) {
this.jdkResovler = jdkResovler;
this.jndiResovler = jndiResovler;
}
@Override
ResolutionResults resolve(String host) throws Exception {
ResolutionResults jdkResults = jdkResovler.resolve(host);
List addresses = jdkResults.addresses;
List txtRecords = Collections.emptyList();
try {
ResolutionResults jdniResults = jndiResovler.resolve(host);
txtRecords = jdniResults.txtRecords;
} catch (Exception e) {
logger.log(Level.SEVERE, "Failed to resolve TXT results", e);
}
return new ResolutionResults(addresses, txtRecords);
}
}
/**
* The default name resolver provided with the JDK. This is unable to lookup TXT records, but
* provides address ordering sorted according to RFC 3484. This is true on OpenJDK, because it
* in turn calls into libc which sorts addresses in order of reachability.
*/
@VisibleForTesting
static final class JdkResolver extends DelegateResolver {
@Override
ResolutionResults resolve(String host) throws Exception {
return new ResolutionResults(
Arrays.asList(InetAddress.getAllByName(host)),
Collections.emptyList());
}
}
/**
* A resolver that uses JNDI. This class is capable of looking up both addresses
* and text records, but does not provide ordering guarantees. It is currently not used for
* address resolution.
*/
@VisibleForTesting
static final class JndiResolver extends DelegateResolver {
private static final String[] rrTypes = new String[]{"TXT"};
@Override
ResolutionResults resolve(String host) throws NamingException {
InitialDirContext dirContext = new InitialDirContext();
javax.naming.directory.Attributes attrs = dirContext.getAttributes("dns:///" + host, rrTypes);
List addresses = new ArrayList();
List txtRecords = new ArrayList();
NamingEnumeration rrGroups = attrs.getAll();
try {
while (rrGroups.hasMore()) {
Attribute rrEntry = rrGroups.next();
assert Arrays.asList(rrTypes).contains(rrEntry.getID());
NamingEnumeration rrValues = rrEntry.getAll();
try {
while (rrValues.hasMore()) {
String rrValue = (String) rrValues.next();
txtRecords.add(rrValue);
}
} finally {
rrValues.close();
}
}
} finally {
rrGroups.close();
}
return new ResolutionResults(addresses, txtRecords);
}
}
}