Resolve hostnames using netty's DNS resolver #498

Lettuce now defaults to netty's DNS resolution upon connect when using netty 4.1. DnsResolver returns an empty array of addresses to signal an unresolved address. Netty performs a non-blocking DNS lookup.

src/main/java/com/lambdaworks/redis/resource/DefaultClientResources.java

@@ -36,6 +36,7 @@
 
 import io.netty.util.HashedWheelTimer;
 import io.netty.util.Timer;
+import io.netty.util.Version;
 import io.netty.util.concurrent.*;
 import io.netty.util.internal.SystemPropertyUtil;
 import io.netty.util.internal.logging.InternalLogger;
@@ -87,6 +88,8 @@ public class DefaultClientResources implements ClientResources {
      */
     public static final Supplier<Delay> DEFAULT_RECONNECT_DELAY = Delay::exponential;
 
+    private static final boolean NETTY_DNS_RESOLVER_SUPPORTED;
+
     static {
         int threads = Math.max(
                 1,
@@ -98,6 +101,9 @@ public class DefaultClientResources implements ClientResources {
         if (logger.isDebugEnabled()) {
             logger.debug("-Dio.netty.eventLoopThreads: {}", threads);
         }
+
+        Version version = Version.identify().get("netty-common");
+        NETTY_DNS_RESOLVER_SUPPORTED = version != null && version.artifactVersion().startsWith("4.1");
     }
 
     private final boolean sharedEventLoopGroupProvider;
@@ -195,7 +201,7 @@ protected DefaultClientResources(Builder builder) {
         }
 
         if (builder.dnsResolver == null) {
-            dnsResolver = DnsResolvers.JVM_DEFAULT;
+            dnsResolver = NETTY_DNS_RESOLVER_SUPPORTED ? DnsResolvers.UNRESOLVED : DnsResolvers.JVM_DEFAULT;
         } else {
             dnsResolver = builder.dnsResolver;
         }
@@ -235,7 +241,7 @@ public static class Builder {
         private CommandLatencyCollectorOptions commandLatencyCollectorOptions = DefaultCommandLatencyCollectorOptions.create();
         private CommandLatencyCollector commandLatencyCollector;
         private EventPublisherOptions commandLatencyPublisherOptions = DefaultEventPublisherOptions.create();
-        private DnsResolver dnsResolver = DnsResolvers.JVM_DEFAULT;
+        private DnsResolver dnsResolver = NETTY_DNS_RESOLVER_SUPPORTED ? DnsResolvers.UNRESOLVED : DnsResolvers.JVM_DEFAULT;
         private Supplier<Delay> reconnectDelay = DEFAULT_RECONNECT_DELAY;
 
         private Builder() {

src/main/java/com/lambdaworks/redis/resource/DnsResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2016 the original author or authors.
+ * Copyright 2011-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,17 +20,19 @@
 
 /**
  * Users may implement this interface to override the normal DNS lookup offered by the OS.
- * 
+ *
  * @author Mark Paluch
  * @since 4.2
  */
 public interface DnsResolver {
 
     /**
      * Returns the IP address for the specified host name.
-     * 
+     *
      * @param host the hostname, must not be empty or {@literal null}.
-     * @return array of one or more {@link InetAddress adresses}
+     * @return array of one or more {@link InetAddress adresses}. An empty array indicates that DNS resolution is not supported
+     *         by this {@link DnsResolver} and should happen by netty, see
+     *         {@link java.net.InetSocketAddress#createUnresolved(String, int)}.
      * @throws UnknownHostException if the given host is not recognized or the associated IP address cannot be used to build an
      *         {@link InetAddress} instance
      */

src/main/java/com/lambdaworks/redis/resource/DnsResolvers.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2016 the original author or authors.
+ * Copyright 2011-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,9 +19,8 @@
 import java.net.UnknownHostException;
 
 /**
- *
  * Predefined DNS resolvers.
- * 
+ *
  * @author Mark Paluch
  * @since 4.2
  */
@@ -30,10 +29,24 @@ public enum DnsResolvers implements DnsResolver {
     /**
      * Java VM default resolver.
      */
-    JVM_DEFAULT;
+    JVM_DEFAULT {
+        @Override
+        public InetAddress[] resolve(String host) throws UnknownHostException {
+            return InetAddress.getAllByName(host);
+        }
+    },
+
+    /**
+     * Non-resolving {@link DnsResolver}. Returns an empty {@link InetAddress} to indicate an unresolved address.
+     *
+     * @see java.net.InetSocketAddress#createUnresolved(String, int)
+     * @since 4.4
+     */
+    UNRESOLVED {
+        @Override
+        public InetAddress[] resolve(String host) throws UnknownHostException {
+            return new InetAddress[0];
+        }
+    };
 
-    @Override
-    public InetAddress[] resolve(String host) throws UnknownHostException {
-        return InetAddress.getAllByName(host);
-    }
 }

src/main/java/com/lambdaworks/redis/resource/SocketAddressResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2016 the original author or authors.
+ * Copyright 2011-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,14 +24,14 @@
 
 /**
  * Resolves a {@link com.lambdaworks.redis.RedisURI} to a {@link java.net.SocketAddress}.
- * 
+ *
  * @author Mark Paluch
  */
 public class SocketAddressResolver {
 
     /**
      * Resolves a {@link com.lambdaworks.redis.RedisURI} to a {@link java.net.SocketAddress}.
-     * 
+     *
      * @param redisURI must not be {@literal null}
      * @param dnsResolver must not be {@literal null}
      * @return the resolved {@link SocketAddress}
@@ -43,8 +43,13 @@ public static SocketAddress resolve(RedisURI redisURI, DnsResolver dnsResolver)
         }
 
         try {
-            InetAddress inetAddress = dnsResolver.resolve(redisURI.getHost())[0];
-            return new InetSocketAddress(inetAddress, redisURI.getPort());
+            InetAddress[] inetAddress = dnsResolver.resolve(redisURI.getHost());
+
+            if (inetAddress.length == 0) {
+                return InetSocketAddress.createUnresolved(redisURI.getHost(), redisURI.getPort());
+            }
+
+            return new InetSocketAddress(inetAddress[0], redisURI.getPort());
         } catch (UnknownHostException e) {
             return redisURI.getResolvedAddress();
         }