/*
 * Copyright 2015 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.dns;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufHolder;
import io.netty.channel.AddressedEnvelope;
import io.netty.channel.ChannelFactory;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.EventLoop;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.MultithreadEventLoopGroup;
import io.netty.channel.ReflectiveChannelFactory;
import io.netty.channel.nio.NioHandler;
import io.netty.channel.socket.DatagramChannel;
import io.netty.channel.socket.DatagramPacket;
import io.netty.channel.socket.InternetProtocolFamily;
import io.netty.channel.socket.nio.NioDatagramChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.dns.DefaultDnsQuestion;
import io.netty.handler.codec.dns.DnsQuestion;
import io.netty.handler.codec.dns.DnsRawRecord;
import io.netty.handler.codec.dns.DnsRecord;
import io.netty.handler.codec.dns.DnsRecordType;
import io.netty.handler.codec.dns.DnsResponse;
import io.netty.handler.codec.dns.DnsResponseCode;
import io.netty.handler.codec.dns.DnsSection;
import io.netty.resolver.HostsFileEntriesResolver;
import io.netty.resolver.ResolvedAddressTypes;
import io.netty.util.CharsetUtil;
import io.netty.util.NetUtil;
import io.netty.util.ReferenceCountUtil;
import io.netty.util.concurrent.Future;
import io.netty.util.internal.SocketUtils;
import io.netty.util.internal.StringUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import org.apache.directory.server.dns.DnsException;
import org.apache.directory.server.dns.io.encoder.DnsMessageEncoder;
import org.apache.directory.server.dns.messages.DnsMessage;
import org.apache.directory.server.dns.messages.DnsMessageModifier;
import org.apache.directory.server.dns.messages.QuestionRecord;
import org.apache.directory.server.dns.messages.RecordClass;
import org.apache.directory.server.dns.messages.RecordType;
import org.apache.directory.server.dns.messages.ResourceRecord;
import org.apache.directory.server.dns.messages.ResourceRecordModifier;
import org.apache.directory.server.dns.messages.ResponseCode;
import org.apache.directory.server.dns.store.DnsAttribute;
import org.apache.directory.server.dns.store.RecordStore;
import org.apache.mina.core.buffer.IoBuffer;
import org.hamcrest.Matchers;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

import java.io.IOException;
import java.io.InputStream;
import java.net.DatagramSocket;
import java.net.Inet4Address;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.CompletionException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;

import static io.netty.handler.codec.dns.DnsRecordType.A;
import static io.netty.handler.codec.dns.DnsRecordType.AAAA;
import static io.netty.handler.codec.dns.DnsRecordType.CNAME;
import static io.netty.resolver.dns.DnsServerAddresses.sequential;
import static java.util.Collections.singletonList;
import static org.hamcrest.Matchers.greaterThan;
import static org.hamcrest.Matchers.hasSize;
import static org.hamcrest.Matchers.instanceOf;
import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNotEquals;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.assertSame;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;

public class DnsNameResolverTest {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(DnsNameResolver.class);
    private static final long DEFAULT_TEST_TIMEOUT_MS = 30000;

    // Using the top-100 web sites ranked in Alexa.com (Oct 2014)
    // Please use the following series of shell commands to get this up-to-date:
    // $ curl -O http://s3.amazonaws.com/alexa-static/top-1m.csv.zip
    // $ unzip -o top-1m.csv.zip top-1m.csv
    // $ head -100 top-1m.csv | cut -d, -f2 | cut -d/ -f1 | while read L; do echo '"'"$L"'",'; done > topsites.txt
    private static final Set<String> DOMAINS = Collections.unmodifiableSet(new HashSet<>(Arrays.asList(
            "google.com",
            "youtube.com",
            "facebook.com",
            "baidu.com",
            "wikipedia.org",
            "yahoo.com",
            "reddit.com",
            "google.co.in",
            "qq.com",
            "amazon.com",
            "taobao.com",
            "tmall.com",
            "twitter.com",
            "vk.com",
            "live.com",
            "sohu.com",
            "instagram.com",
            "google.co.jp",
            "sina.com.cn",
            "jd.com",
            "weibo.com",
            "360.cn",
            "google.de",
            "google.co.uk",
            "google.com.br",
            "list.tmall.com",
            "google.ru",
            "google.fr",
            "yandex.ru",
            "netflix.com",
            "google.it",
            "google.com.hk",
            "linkedin.com",
            "pornhub.com",
            "t.co",
            "google.es",
            "twitch.tv",
            "alipay.com",
            "xvideos.com",
            "ebay.com",
            "yahoo.co.jp",
            "google.ca",
            "google.com.mx",
            "bing.com",
            "ok.ru",
            "imgur.com",
            "microsoft.com",
            "mail.ru",
            "imdb.com",
            "aliexpress.com",
            "hao123.com",
            "msn.com",
            "tumblr.com",
            "csdn.net",
            "wikia.com",
            "wordpress.com",
            "office.com",
            "google.com.tr",
            "livejasmin.com",
            "amazon.co.jp",
            "deloton.com",
            "apple.com",
            "google.com.au",
            "paypal.com",
            "google.com.tw",
            "bongacams.com",
            "popads.net",
            "whatsapp.com",
            "blogspot.com",
            "detail.tmall.com",
            "google.pl",
            "microsoftonline.com",
            "xhamster.com",
            "google.co.id",
            "github.com",
            "stackoverflow.com",
            "pinterest.com",
            "amazon.de",
            "diply.com",
            "amazon.co.uk",
            "so.com",
            "google.com.ar",
            "coccoc.com",
            "soso.com",
            "espn.com",
            "adobe.com",
            "google.com.ua",
            "tianya.cn",
            "xnxx.com",
            "googleusercontent.com",
            "savefrom.net",
            "google.com.pk",
            "amazon.in",
            "nicovideo.jp",
            "google.co.th",
            "dropbox.com",
            "thepiratebay.org",
            "google.com.sa",
            "google.com.eg",
            "pixnet.net",
            "localhost")));

    private static final Map<String, String> DOMAINS_PUNYCODE = new HashMap<>();

    static {
        DOMAINS_PUNYCODE.put("büchner.de", "xn--bchner-3ya.de");
        DOMAINS_PUNYCODE.put("müller.de", "xn--mller-kva.de");
    }

    private static final Set<String> DOMAINS_ALL;

    static {
        Set<String> all = new HashSet<>(DOMAINS.size() + DOMAINS_PUNYCODE.size());
        all.addAll(DOMAINS);
        all.addAll(DOMAINS_PUNYCODE.values());
        DOMAINS_ALL = Collections.unmodifiableSet(all);
    }

    /**
     * The list of the domain names to exclude from {@link #testResolveAorAAAA()}.
     */
    private static final Set<String> EXCLUSIONS_RESOLVE_A = new HashSet<>();

    static {
        Collections.addAll(
                EXCLUSIONS_RESOLVE_A,
                "akamaihd.net",
                "googleusercontent.com",
                StringUtil.EMPTY_STRING);
    }

    /**
     * The list of the domain names to exclude from {@link #testResolveAAAA()}.
     * Unfortunately, there are only handful of domain names with IPv6 addresses.
     */
    private static final Set<String> EXCLUSIONS_RESOLVE_AAAA = new HashSet<>();

    static {
        EXCLUSIONS_RESOLVE_AAAA.addAll(EXCLUSIONS_RESOLVE_A);
        EXCLUSIONS_RESOLVE_AAAA.addAll(DOMAINS);
        EXCLUSIONS_RESOLVE_AAAA.removeAll(Arrays.asList(
                "google.com",
                "facebook.com",
                "youtube.com",
                "wikipedia.org",
                "google.co.in",
                "blogspot.com",
                "vk.com",
                "google.de",
                "google.co.jp",
                "google.co.uk",
                "google.fr",
                "google.com.br",
                "google.ru",
                "google.it",
                "google.es",
                "google.com.mx",
                "xhamster.com",
                "google.ca",
                "google.co.id",
                "blogger.com",
                "flipkart.com",
                "google.com.tr",
                "google.com.au",
                "google.pl",
                "google.com.hk",
                "blogspot.in"
        ));
    }

    /**
     * The list of the domain names to exclude from {@link #testQueryMx()}.
     */
    private static final Set<String> EXCLUSIONS_QUERY_MX = new HashSet<>();

    static {
        Collections.addAll(
                EXCLUSIONS_QUERY_MX,
                "hao123.com",
                "blogspot.com",
                "t.co",
                "espn.go.com",
                "people.com.cn",
                "googleusercontent.com",
                "blogspot.in",
                "localhost",
                StringUtil.EMPTY_STRING);
    }

    private static final TestDnsServer dnsServer = new TestDnsServer(DOMAINS_ALL);
    private static final EventLoopGroup group = new MultithreadEventLoopGroup(1, NioHandler.newFactory());

    @Rule
    public ExpectedException expectedException = ExpectedException.none();

    private static DnsNameResolverBuilder newResolver(boolean decodeToUnicode) {
        return newResolver(decodeToUnicode, null);
    }

    private static DnsNameResolverBuilder newResolver(boolean decodeToUnicode,
                                                      DnsServerAddressStreamProvider dnsServerAddressStreamProvider) {
        DnsNameResolverBuilder builder = new DnsNameResolverBuilder(group.next())
                .dnsQueryLifecycleObserverFactory(new TestRecursiveCacheDnsQueryLifecycleObserverFactory())
                .channelType(NioDatagramChannel.class)
                .maxQueriesPerResolve(1)
                .decodeIdn(decodeToUnicode)
                .optResourceEnabled(false)
                .ndots(1);

        if (dnsServerAddressStreamProvider == null) {
            builder.nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer.localAddress()));
        } else {
            builder.nameServerProvider(new MultiDnsServerAddressStreamProvider(dnsServerAddressStreamProvider,
                    new SingletonDnsServerAddressStreamProvider(dnsServer.localAddress())));
        }

        return builder;
    }

    private static DnsNameResolverBuilder newResolver() {
        return newResolver(true);
    }

    private static DnsNameResolverBuilder newResolver(ResolvedAddressTypes resolvedAddressTypes) {
        return newResolver()
                .resolvedAddressTypes(resolvedAddressTypes);
    }

    private static DnsNameResolverBuilder newNonCachedResolver(ResolvedAddressTypes resolvedAddressTypes) {
        return newResolver()
                .resolveCache(NoopDnsCache.INSTANCE)
                .resolvedAddressTypes(resolvedAddressTypes);
    }

    @BeforeClass
    public static void init() throws Exception {
        dnsServer.start();
    }

    @AfterClass
    public static void destroy() {
        dnsServer.stop();
        group.shutdownGracefully();
    }

    @Test
    public void testResolveAorAAAA() throws Exception {
        DnsNameResolver resolver = newResolver(ResolvedAddressTypes.IPV4_PREFERRED).build();
        try {
            testResolve0(resolver, EXCLUSIONS_RESOLVE_A, AAAA);
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testResolveAAAAorA() throws Exception {
        DnsNameResolver resolver = newResolver(ResolvedAddressTypes.IPV6_PREFERRED).build();
        try {
            testResolve0(resolver, EXCLUSIONS_RESOLVE_A, A);
        } finally {
            resolver.close();
        }
    }

    /**
     * This test will start an second DNS test server which returns fixed results that can be easily verified as
     * originating from the second DNS test server. The resolver will put {@link DnsServerAddressStreamProvider} under
     * test to ensure that some hostnames can be directed toward both the primary and secondary DNS test servers
     * simultaneously.
     */
    @Test
    public void testNameServerCache() throws IOException, InterruptedException {
        final String overriddenIP = "12.34.12.34";
        final TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            switch (question.getRecordType()) {
                case A:
                    Map<String, Object> attr = new HashMap<>();
                    attr.put(DnsAttribute.IP_ADDRESS.toLowerCase(Locale.US), overriddenIP);
                    return Collections.singleton(
                            new TestDnsServer.TestResourceRecord(
                                    question.getDomainName(), question.getRecordType(), attr));
                default:
                    return null;
            }
        });
        dnsServer2.start();
        try {
            final Set<String> overriddenHostnames = new HashSet<>();
            for (String name : DOMAINS) {
                if (EXCLUSIONS_RESOLVE_A.contains(name)) {
                    continue;
                }
                if (ThreadLocalRandom.current().nextBoolean()) {
                    overriddenHostnames.add(name);
                }
            }
            DnsNameResolver resolver = newResolver(false, hostname ->
                    overriddenHostnames.contains(hostname) ? sequential(dnsServer2.localAddress()).stream() : null)
                    .build();
            try {
                final Map<String, InetAddress> resultA = testResolve0(resolver, EXCLUSIONS_RESOLVE_A, AAAA);
                for (Entry<String, InetAddress> resolvedEntry : resultA.entrySet()) {
                    if (resolvedEntry.getValue().isLoopbackAddress()) {
                        continue;
                    }
                    if (overriddenHostnames.contains(resolvedEntry.getKey())) {
                        assertEquals("failed to resolve " + resolvedEntry.getKey(),
                                overriddenIP, resolvedEntry.getValue().getHostAddress());
                    } else {
                        assertNotEquals("failed to resolve " + resolvedEntry.getKey(),
                                overriddenIP, resolvedEntry.getValue().getHostAddress());
                    }
                }
            } finally {
                resolver.close();
            }
        } finally {
            dnsServer2.stop();
        }
    }

    @Test
    public void testResolveA() throws Exception {
        DnsNameResolver resolver = newResolver(ResolvedAddressTypes.IPV4_ONLY)
                // Cache for eternity
                .ttl(Integer.MAX_VALUE, Integer.MAX_VALUE)
                .build();
        try {
            final Map<String, InetAddress> resultA = testResolve0(resolver, EXCLUSIONS_RESOLVE_A, null);

            // Now, try to resolve again to see if it's cached.
            // This test works because the DNS servers usually randomizes the order of the records in a response.
            // If cached, the resolved addresses must be always same, because we reuse the same response.

            final Map<String, InetAddress> resultB = testResolve0(resolver, EXCLUSIONS_RESOLVE_A, null);

            // Ensure the result from the cache is identical from the uncached one.
            assertThat(resultB.size(), is(resultA.size()));
            for (Entry<String, InetAddress> e : resultA.entrySet()) {
                InetAddress expected = e.getValue();
                InetAddress actual = resultB.get(e.getKey());
                if (!actual.equals(expected)) {
                    // Print the content of the cache when test failure is expected.
                    System.err.println("Cache for " + e.getKey() + ": " + resolver.resolveAll(e.getKey()).getNow());
                }
                assertThat(actual, is(expected));
            }
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testResolveAAAA() throws Exception {
        DnsNameResolver resolver = newResolver(ResolvedAddressTypes.IPV6_ONLY).build();
        try {
            testResolve0(resolver, EXCLUSIONS_RESOLVE_AAAA, null);
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testNonCachedResolve() throws Exception {
        DnsNameResolver resolver = newNonCachedResolver(ResolvedAddressTypes.IPV4_ONLY).build();
        try {
            testResolve0(resolver, EXCLUSIONS_RESOLVE_A, null);
        } finally {
            resolver.close();
        }
    }

    @Test(timeout = DEFAULT_TEST_TIMEOUT_MS)
    public void testNonCachedResolveEmptyHostName() throws Exception {
        testNonCachedResolveEmptyHostName("");
    }

    @Test(timeout = DEFAULT_TEST_TIMEOUT_MS)
    public void testNonCachedResolveNullHostName() throws Exception {
        testNonCachedResolveEmptyHostName(null);
    }

    private static void testNonCachedResolveEmptyHostName(String inetHost) throws Exception {
        DnsNameResolver resolver = newNonCachedResolver(ResolvedAddressTypes.IPV4_ONLY).build();
        try {
            InetAddress addr = resolver.resolve(inetHost).syncUninterruptibly().getNow();
            assertEquals(SocketUtils.addressByName(inetHost), addr);
        } finally {
            resolver.close();
        }
    }

    @Test(timeout = DEFAULT_TEST_TIMEOUT_MS)
    public void testNonCachedResolveAllEmptyHostName() throws Exception {
        testNonCachedResolveAllEmptyHostName("");
    }

    @Test(timeout = DEFAULT_TEST_TIMEOUT_MS)
    public void testNonCachedResolveAllNullHostName() throws Exception {
        testNonCachedResolveAllEmptyHostName(null);
    }

    private static void testNonCachedResolveAllEmptyHostName(String inetHost) throws UnknownHostException {
        DnsNameResolver resolver = newNonCachedResolver(ResolvedAddressTypes.IPV4_ONLY).build();
        try {
            List<InetAddress> addrs = resolver.resolveAll(inetHost).syncUninterruptibly().getNow();
            assertEquals(Arrays.asList(
                    SocketUtils.allAddressesByName(inetHost)), addrs);
        } finally {
            resolver.close();
        }
    }

    private static Map<String, InetAddress> testResolve0(DnsNameResolver resolver, Set<String> excludedDomains,
                                                         DnsRecordType cancelledType)
            throws InterruptedException {

        assertThat(resolver.isRecursionDesired(), is(true));

        final Map<String, InetAddress> results = new HashMap<>();
        final Map<String, Future<InetAddress>> futures =
                new LinkedHashMap<>();

        for (String name : DOMAINS) {
            if (excludedDomains.contains(name)) {
                continue;
            }

            resolve(resolver, futures, name);
        }

        for (Entry<String, Future<InetAddress>> e : futures.entrySet()) {
            String unresolved = e.getKey();
            InetAddress resolved = e.getValue().sync().getNow();

            logger.info("{}: {}", unresolved, resolved.getHostAddress());

            assertThat(resolved.getHostName(), is(unresolved));

            boolean typeMatches = false;
            for (InternetProtocolFamily f : resolver.resolvedInternetProtocolFamiliesUnsafe()) {
                Class<?> resolvedType = resolved.getClass();
                if (f.addressType().isAssignableFrom(resolvedType)) {
                    typeMatches = true;
                }
            }

            assertThat(typeMatches, is(true));

            results.put(resolved.getHostName(), resolved);
        }

        assertQueryObserver(resolver, cancelledType);

        return results;
    }

    @Test
    public void testQueryMx() {
        DnsNameResolver resolver = newResolver().build();
        try {
            assertThat(resolver.isRecursionDesired(), is(true));

            Map<String, Future<AddressedEnvelope<DnsResponse, InetSocketAddress>>> futures =
                    new LinkedHashMap<>();
            for (String name : DOMAINS) {
                if (EXCLUSIONS_QUERY_MX.contains(name)) {
                    continue;
                }

                queryMx(resolver, futures, name);
            }

            for (Entry<String, Future<AddressedEnvelope<DnsResponse, InetSocketAddress>>> e : futures.entrySet()) {
                String hostname = e.getKey();
                Future<AddressedEnvelope<DnsResponse, InetSocketAddress>> f = e.getValue().awaitUninterruptibly();

                DnsResponse response = f.getNow().content();
                assertThat(response.code(), is(DnsResponseCode.NOERROR));

                final int answerCount = response.count(DnsSection.ANSWER);
                final List<DnsRecord> mxList = new ArrayList<>(answerCount);
                for (int i = 0; i < answerCount; i++) {
                    final DnsRecord r = response.recordAt(DnsSection.ANSWER, i);
                    if (r.type() == DnsRecordType.MX) {
                        mxList.add(r);
                    }
                }

                assertThat(mxList.size(), is(greaterThan(0)));
                StringBuilder buf = new StringBuilder();
                for (DnsRecord r : mxList) {
                    ByteBuf recordContent = ((ByteBufHolder) r).content();

                    buf.append(StringUtil.NEWLINE);
                    buf.append('\t');
                    buf.append(r.name());
                    buf.append(' ');
                    buf.append(r.type().name());
                    buf.append(' ');
                    buf.append(recordContent.readUnsignedShort());
                    buf.append(' ');
                    buf.append(DnsResolveContext.decodeDomainName(recordContent));
                }

                logger.info("{} has the following MX records:{}", hostname, buf);
                response.release();

                // We only track query lifecycle if it is managed by the DnsNameResolverContext, and not direct calls
                // to query.
                assertNoQueriesMade(resolver);
            }
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testNegativeTtl() throws Exception {
        final DnsNameResolver resolver = newResolver().negativeTtl(10).build();
        try {
            resolveNonExistentDomain(resolver);

            final int size = 10000;
            final List<UnknownHostException> exceptions = new ArrayList<>();

            // If negative cache works, this thread should be done really quickly.
            final Thread negativeLookupThread = new Thread() {
                @Override
                public void run() {
                    for (int i = 0; i < size; i++) {
                        exceptions.add(resolveNonExistentDomain(resolver));
                        if (isInterrupted()) {
                            break;
                        }
                    }
                }
            };

            negativeLookupThread.start();
            negativeLookupThread.join(DEFAULT_TEST_TIMEOUT_MS);

            if (negativeLookupThread.isAlive()) {
                negativeLookupThread.interrupt();
                fail("Cached negative lookups did not finish quickly.");
            }

            assertThat(exceptions, hasSize(size));
        } finally {
            resolver.close();
        }
    }

    private static UnknownHostException resolveNonExistentDomain(DnsNameResolver resolver) {
        try {
            resolver.resolve("non-existent.netty.io").syncUninterruptibly();
            fail();
            return null;
        } catch (CompletionException cause) {
            Throwable e = cause.getCause();
            assertThat(e, is(instanceOf(UnknownHostException.class)));

            TestRecursiveCacheDnsQueryLifecycleObserverFactory lifecycleObserverFactory =
                    (TestRecursiveCacheDnsQueryLifecycleObserverFactory) resolver.dnsQueryLifecycleObserverFactory();
            TestDnsQueryLifecycleObserver observer = lifecycleObserverFactory.observers.poll();
            if (observer != null) {
                Object o = observer.events.poll();
                if (o instanceof QueryCancelledEvent) {
                    assertTrue("unexpected type: " + observer.question,
                            observer.question.type() == CNAME || observer.question.type() == AAAA);
                } else if (o instanceof QueryWrittenEvent) {
                    QueryFailedEvent failedEvent = (QueryFailedEvent) observer.events.poll();
                } else if (!(o instanceof QueryFailedEvent)) {
                    fail("unexpected event type: " + o);
                }
                assertTrue(observer.events.isEmpty());
            }
            return (UnknownHostException) e;
        }
    }

    @Test
    public void testResolveIp() {
        DnsNameResolver resolver = newResolver().build();
        try {
            InetAddress address = resolver.resolve("10.0.0.1").syncUninterruptibly().getNow();

            assertEquals("10.0.0.1", address.getHostAddress());

            // This address is already resolved, and so we shouldn't have to query for anything.
            assertNoQueriesMade(resolver);
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testResolveEmptyIpv4() {
        testResolve0(ResolvedAddressTypes.IPV4_ONLY, NetUtil.LOCALHOST4, StringUtil.EMPTY_STRING);
    }

    @Test
    public void testResolveEmptyIpv6() {
        testResolve0(ResolvedAddressTypes.IPV6_ONLY, NetUtil.LOCALHOST6, StringUtil.EMPTY_STRING);
    }

    @Test
    public void testResolveNullIpv4() {
        testResolve0(ResolvedAddressTypes.IPV4_ONLY, NetUtil.LOCALHOST4, null);
    }

    @Test
    public void testResolveNullIpv6() {
        testResolve0(ResolvedAddressTypes.IPV6_ONLY, NetUtil.LOCALHOST6, null);
    }

    private static void testResolve0(ResolvedAddressTypes addressTypes, InetAddress expectedAddr, String name) {
        DnsNameResolver resolver = newResolver(addressTypes).build();
        try {
            InetAddress address = resolver.resolve(name).syncUninterruptibly().getNow();
            assertEquals(expectedAddr, address);

            // We are resolving the local address, so we shouldn't make any queries.
            assertNoQueriesMade(resolver);
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testResolveAllEmptyIpv4() {
        testResolveAll0(ResolvedAddressTypes.IPV4_ONLY, NetUtil.LOCALHOST4, StringUtil.EMPTY_STRING);
    }

    @Test
    public void testResolveAllEmptyIpv6() {
        testResolveAll0(ResolvedAddressTypes.IPV6_ONLY, NetUtil.LOCALHOST6, StringUtil.EMPTY_STRING);
    }

    @Test
    public void testCNAMEResolveAllIpv4() throws IOException {
        testCNAMERecursiveResolve(true);
    }

    @Test
    public void testCNAMEResolveAllIpv6() throws IOException {
        testCNAMERecursiveResolve(false);
    }

    private static void testCNAMERecursiveResolve(boolean ipv4Preferred) throws IOException {
        final String firstName = "firstname.com";
        final String secondName = "secondname.com";
        final String lastName = "lastname.com";
        final String ipv4Addr = "1.2.3.4";
        final String ipv6Addr = "::1";
        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            ResourceRecordModifier rm = new ResourceRecordModifier();
            rm.setDnsClass(RecordClass.IN);
            rm.setDnsName(question.getDomainName());
            rm.setDnsTtl(100);
            rm.setDnsType(RecordType.CNAME);

            if (question.getDomainName().equals(firstName)) {
                rm.put(DnsAttribute.DOMAIN_NAME, secondName);
            } else if (question.getDomainName().equals(secondName)) {
                rm.put(DnsAttribute.DOMAIN_NAME, lastName);
            } else if (question.getDomainName().equals(lastName)) {
                rm.setDnsType(question.getRecordType());
                switch (question.getRecordType()) {
                    case A:
                        rm.put(DnsAttribute.IP_ADDRESS, ipv4Addr);
                        break;
                    case AAAA:
                        rm.put(DnsAttribute.IP_ADDRESS, ipv6Addr);
                        break;
                    default:
                        return null;
                }
            } else {
                return null;
            }
            return Collections.singleton(rm.getEntry());
        });
        dnsServer2.start();
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(true)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));
            if (ipv4Preferred) {
                builder.resolvedAddressTypes(ResolvedAddressTypes.IPV4_PREFERRED);
            } else {
                builder.resolvedAddressTypes(ResolvedAddressTypes.IPV6_PREFERRED);
            }
            resolver = builder.build();
            InetAddress resolvedAddress = resolver.resolve(firstName).syncUninterruptibly().getNow();
            if (ipv4Preferred) {
                assertEquals(ipv4Addr, resolvedAddress.getHostAddress());
            } else {
                assertEquals(ipv6Addr, NetUtil.toAddressString(resolvedAddress));
            }
            assertEquals(firstName, resolvedAddress.getHostName());
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test
    public void testCNAMERecursiveResolveMultipleNameServersIPv4() throws IOException {
        testCNAMERecursiveResolveMultipleNameServers(true);
    }

    @Test
    public void testCNAMERecursiveResolveMultipleNameServersIPv6() throws IOException {
        testCNAMERecursiveResolveMultipleNameServers(false);
    }

    private static void testCNAMERecursiveResolveMultipleNameServers(boolean ipv4Preferred) throws IOException {
        final String firstName = "firstname.nettyfoo.com";
        final String lastName = "lastname.nettybar.com";
        final String ipv4Addr = "1.2.3.4";
        final String ipv6Addr = "::1";
        final AtomicBoolean hitServer2 = new AtomicBoolean();
        final TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            hitServer2.set(true);
            if (question.getDomainName().equals(firstName)) {
                ResourceRecordModifier rm = new ResourceRecordModifier();
                rm.setDnsClass(RecordClass.IN);
                rm.setDnsName(question.getDomainName());
                rm.setDnsTtl(100);
                rm.setDnsType(RecordType.CNAME);
                rm.put(DnsAttribute.DOMAIN_NAME, lastName);
                return Collections.singleton(rm.getEntry());
            } else {
                throw new DnsException(ResponseCode.REFUSED);
            }
        });
        final TestDnsServer dnsServer3 = new TestDnsServer(question -> {
            if (question.getDomainName().equals(lastName)) {
                ResourceRecordModifier rm = new ResourceRecordModifier();
                rm.setDnsClass(RecordClass.IN);
                rm.setDnsName(question.getDomainName());
                rm.setDnsTtl(100);
                rm.setDnsType(question.getRecordType());
                switch (question.getRecordType()) {
                    case A:
                        rm.put(DnsAttribute.IP_ADDRESS, ipv4Addr);
                        break;
                    case AAAA:
                        rm.put(DnsAttribute.IP_ADDRESS, ipv6Addr);
                        break;
                    default:
                        return null;
                }

                return Collections.singleton(rm.getEntry());
            } else {
                throw new DnsException(ResponseCode.REFUSED);
            }
        });
        dnsServer2.start();
        dnsServer3.start();
        DnsNameResolver resolver = null;
        try {
            AuthoritativeDnsServerCache nsCache = new DefaultAuthoritativeDnsServerCache();
            // What we want to test is the following:
            // 1. Do a DNS query.
            // 2. CNAME is returned, we want to lookup that CNAME on multiple DNS servers
            // 3. The first DNS server should fail
            // 4. The second DNS server should succeed
            // This verifies that we do in fact follow multiple DNS servers in the CNAME resolution.
            // The DnsCache is used for the name server cache, but doesn't provide a InetSocketAddress (only InetAddress
            // so no port), so we only specify the name server in the cache, and then specify both name servers in the
            // fallback name server provider.
            nsCache.cache("nettyfoo.com.", dnsServer2.localAddress(), 10000, group.next());
            resolver = new DnsNameResolver(
                    group.next(), new ReflectiveChannelFactory<DatagramChannel>(NioDatagramChannel.class),
                    NoopDnsCache.INSTANCE, nsCache, NoopDnsQueryLifecycleObserverFactory.INSTANCE, 3000,
                    ipv4Preferred ? ResolvedAddressTypes.IPV4_ONLY : ResolvedAddressTypes.IPV6_ONLY, true,
                    10, true, 4096, false, HostsFileEntriesResolver.DEFAULT,
                    new SequentialDnsServerAddressStreamProvider(dnsServer2.localAddress(), dnsServer3.localAddress()),
                    DnsNameResolver.DEFAULT_SEARCH_DOMAINS, 0, true) {
                @Override
                InetSocketAddress newRedirectServerAddress(InetAddress server) {
                    int port = hitServer2.get() ? dnsServer3.localAddress().getPort() :
                            dnsServer2.localAddress().getPort();
                    return new InetSocketAddress(server, port);
                }
            };
            InetAddress resolvedAddress = resolver.resolve(firstName).syncUninterruptibly().getNow();
            if (ipv4Preferred) {
                assertEquals(ipv4Addr, resolvedAddress.getHostAddress());
            } else {
                assertEquals(ipv6Addr, NetUtil.toAddressString(resolvedAddress));
            }
            assertEquals(firstName, resolvedAddress.getHostName());
        } finally {
            dnsServer2.stop();
            dnsServer3.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test
    public void testResolveAllNullIpv4() {
        testResolveAll0(ResolvedAddressTypes.IPV4_ONLY, NetUtil.LOCALHOST4, null);
    }

    @Test
    public void testResolveAllNullIpv6() {
        testResolveAll0(ResolvedAddressTypes.IPV6_ONLY, NetUtil.LOCALHOST6, null);
    }

    private static void testResolveAll0(ResolvedAddressTypes addressTypes, InetAddress expectedAddr, String name) {
        DnsNameResolver resolver = newResolver(addressTypes).build();
        try {
            List<InetAddress> addresses = resolver.resolveAll(name).syncUninterruptibly().getNow();
            assertEquals(1, addresses.size());
            assertEquals(expectedAddr, addresses.get(0));

            // We are resolving the local address, so we shouldn't make any queries.
            assertNoQueriesMade(resolver);
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testResolveAllMx() {
        final DnsNameResolver resolver = newResolver().build();
        try {
            assertThat(resolver.isRecursionDesired(), is(true));

            final Map<String, Future<List<DnsRecord>>> futures = new LinkedHashMap<>();
            for (String name : DOMAINS) {
                if (EXCLUSIONS_QUERY_MX.contains(name)) {
                    continue;
                }

                futures.put(name, resolver.resolveAll(new DefaultDnsQuestion(name, DnsRecordType.MX)));
            }

            for (Entry<String, Future<List<DnsRecord>>> e : futures.entrySet()) {
                String hostname = e.getKey();
                Future<List<DnsRecord>> f = e.getValue().awaitUninterruptibly();

                final List<DnsRecord> mxList = f.getNow();
                assertThat(mxList.size(), is(greaterThan(0)));
                StringBuilder buf = new StringBuilder();
                for (DnsRecord r : mxList) {
                    ByteBuf recordContent = ((ByteBufHolder) r).content();

                    buf.append(StringUtil.NEWLINE);
                    buf.append('\t');
                    buf.append(r.name());
                    buf.append(' ');
                    buf.append(r.type().name());
                    buf.append(' ');
                    buf.append(recordContent.readUnsignedShort());
                    buf.append(' ');
                    buf.append(DnsResolveContext.decodeDomainName(recordContent));

                    ReferenceCountUtil.release(r);
                }

                logger.info("{} has the following MX records:{}", hostname, buf);
            }
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testResolveAllHostsFile() {
        final DnsNameResolver resolver = new DnsNameResolverBuilder(group.next())
                .channelType(NioDatagramChannel.class)
                .hostsFileEntriesResolver((inetHost, resolvedAddressTypes) -> {
                    if ("foo.com.".equals(inetHost)) {
                        try {
                            return InetAddress.getByAddress("foo.com", new byte[] { 1, 2, 3, 4 });
                        } catch (UnknownHostException e) {
                            throw new Error(e);
                        }
                    }
                    return null;
                }).build();

        final List<DnsRecord> records = resolver.resolveAll(new DefaultDnsQuestion("foo.com.", A))
                .syncUninterruptibly().getNow();
        assertThat(records, Matchers.hasSize(1));
        assertThat(records.get(0), Matchers.instanceOf(DnsRawRecord.class));

        final DnsRawRecord record = (DnsRawRecord) records.get(0);
        final ByteBuf content = record.content();
        assertThat(record.name(), is("foo.com."));
        assertThat(record.dnsClass(), is(DnsRecord.CLASS_IN));
        assertThat(record.type(), is(A));
        assertThat(content.readableBytes(), is(4));
        assertThat(content.readInt(), is(0x01020304));
        record.release();
    }

    @Test
    public void testResolveDecodeUnicode() {
        testResolveUnicode(true);
    }

    @Test
    public void testResolveNotDecodeUnicode() {
        testResolveUnicode(false);
    }

    private static void testResolveUnicode(boolean decode) {
        DnsNameResolver resolver = newResolver(decode).build();
        try {
            for (Entry<String, String> entries : DOMAINS_PUNYCODE.entrySet()) {
                InetAddress address = resolver.resolve(entries.getKey()).syncUninterruptibly().getNow();
                assertEquals(decode ? entries.getKey() : entries.getValue(), address.getHostName());
            }

            assertQueryObserver(resolver, AAAA);
        } finally {
            resolver.close();
        }
    }

    @Test(timeout = DEFAULT_TEST_TIMEOUT_MS)
    public void secondDnsServerShouldBeUsedBeforeCNAMEFirstServerNotStarted() throws IOException {
        secondDnsServerShouldBeUsedBeforeCNAME(false);
    }

    @Test(timeout = DEFAULT_TEST_TIMEOUT_MS)
    public void secondDnsServerShouldBeUsedBeforeCNAMEFirstServerFailResolve() throws IOException {
        secondDnsServerShouldBeUsedBeforeCNAME(true);
    }

    private static void secondDnsServerShouldBeUsedBeforeCNAME(boolean startDnsServer1) throws IOException {
        final String knownHostName = "netty.io";
        final TestDnsServer dnsServer1 = new TestDnsServer(Collections.singleton("notnetty.com"));
        final TestDnsServer dnsServer2 = new TestDnsServer(Collections.singleton(knownHostName));
        DnsNameResolver resolver = null;
        try {
            final InetSocketAddress dnsServer1Address;
            if (startDnsServer1) {
                dnsServer1.start();
                dnsServer1Address = dnsServer1.localAddress();
            } else {
                // Some address where a DNS server will not be running.
                dnsServer1Address = new InetSocketAddress("127.0.0.1", 22);
            }
            dnsServer2.start();

            TestRecursiveCacheDnsQueryLifecycleObserverFactory lifecycleObserverFactory =
                    new TestRecursiveCacheDnsQueryLifecycleObserverFactory();

            DnsNameResolverBuilder builder = new DnsNameResolverBuilder(group.next())
                    .dnsQueryLifecycleObserverFactory(lifecycleObserverFactory)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_ONLY)
                    .channelType(NioDatagramChannel.class)
                    .queryTimeoutMillis(1000) // We expect timeouts if startDnsServer1 is false
                    .optResourceEnabled(false)
                    .ndots(1);

            builder.nameServerProvider(new SequentialDnsServerAddressStreamProvider(dnsServer1Address,
                    dnsServer2.localAddress()));
            resolver = builder.build();
            assertNotNull(resolver.resolve(knownHostName).syncUninterruptibly().getNow());

            TestDnsQueryLifecycleObserver observer = lifecycleObserverFactory.observers.poll();
            assertNotNull(observer);
            assertEquals(1, lifecycleObserverFactory.observers.size());
            assertEquals(2, observer.events.size());
            QueryWrittenEvent writtenEvent = (QueryWrittenEvent) observer.events.poll();
            assertEquals(dnsServer1Address, writtenEvent.dnsServerAddress);
            QueryFailedEvent failedEvent = (QueryFailedEvent) observer.events.poll();

            observer = lifecycleObserverFactory.observers.poll();
            assertEquals(2, observer.events.size());
            writtenEvent = (QueryWrittenEvent) observer.events.poll();
            assertEquals(dnsServer2.localAddress(), writtenEvent.dnsServerAddress);
            QuerySucceededEvent succeededEvent = (QuerySucceededEvent) observer.events.poll();
        } finally {
            if (resolver != null) {
                resolver.close();
            }
            dnsServer1.stop();
            dnsServer2.stop();
        }
    }

    @Test(timeout = DEFAULT_TEST_TIMEOUT_MS)
    public void aAndAAAAQueryShouldTryFirstDnsServerBeforeSecond() throws IOException {
        final String knownHostName = "netty.io";
        final TestDnsServer dnsServer1 = new TestDnsServer(Collections.singleton("notnetty.com"));
        final TestDnsServer dnsServer2 = new TestDnsServer(Collections.singleton(knownHostName));
        DnsNameResolver resolver = null;
        try {
            dnsServer1.start();
            dnsServer2.start();

            TestRecursiveCacheDnsQueryLifecycleObserverFactory lifecycleObserverFactory =
                    new TestRecursiveCacheDnsQueryLifecycleObserverFactory();

            DnsNameResolverBuilder builder = new DnsNameResolverBuilder(group.next())
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_ONLY)
                    .dnsQueryLifecycleObserverFactory(lifecycleObserverFactory)
                    .channelType(NioDatagramChannel.class)
                    .optResourceEnabled(false)
                    .ndots(1);

            builder.nameServerProvider(new SequentialDnsServerAddressStreamProvider(dnsServer1.localAddress(),
                    dnsServer2.localAddress()));
            resolver = builder.build();
            assertNotNull(resolver.resolve(knownHostName).syncUninterruptibly().getNow());

            TestDnsQueryLifecycleObserver observer = lifecycleObserverFactory.observers.poll();
            assertNotNull(observer);
            assertEquals(1, lifecycleObserverFactory.observers.size());
            assertEquals(2, observer.events.size());
            QueryWrittenEvent writtenEvent = (QueryWrittenEvent) observer.events.poll();
            assertEquals(dnsServer1.localAddress(), writtenEvent.dnsServerAddress);
            QueryFailedEvent failedEvent = (QueryFailedEvent) observer.events.poll();

            observer = lifecycleObserverFactory.observers.poll();
            assertEquals(2, observer.events.size());
            writtenEvent = (QueryWrittenEvent) observer.events.poll();
            assertEquals(dnsServer2.localAddress(), writtenEvent.dnsServerAddress);
            QuerySucceededEvent succeededEvent = (QuerySucceededEvent) observer.events.poll();
        } finally {
            if (resolver != null) {
                resolver.close();
            }
            dnsServer1.stop();
            dnsServer2.stop();
        }
    }

    @Test
    public void testRecursiveResolveNoCache() throws Exception {
        testRecursiveResolveCache(false);
    }

    @Test
    public void testRecursiveResolveCache() throws Exception {
        testRecursiveResolveCache(true);
    }

    @Test
    public void testIpv4PreferredWhenIpv6First() throws Exception {
        testResolvesPreferredWhenNonPreferredFirst0(ResolvedAddressTypes.IPV4_PREFERRED);
    }

    @Test
    public void testIpv6PreferredWhenIpv4First() throws Exception {
        testResolvesPreferredWhenNonPreferredFirst0(ResolvedAddressTypes.IPV6_PREFERRED);
    }

    private static void testResolvesPreferredWhenNonPreferredFirst0(ResolvedAddressTypes types) throws Exception {
        final String name = "netty.com";
        // This store is non-compliant, returning records of the wrong type for a query.
        // It works since we don't verify the type of the result when resolving to deal with
        // non-compliant servers in the wild.
        List<Set<ResourceRecord>> records = new ArrayList<>();
        final String ipv6Address = "0:0:0:0:0:0:1:1";
        final String ipv4Address = "1.1.1.1";
        if (types == ResolvedAddressTypes.IPV4_PREFERRED) {
            records.add(Collections.singleton(TestDnsServer.newAddressRecord(name, RecordType.AAAA, ipv6Address)));
            records.add(Collections.singleton(TestDnsServer.newAddressRecord(name, RecordType.A, ipv4Address)));
        } else {
            records.add(Collections.singleton(TestDnsServer.newAddressRecord(name, RecordType.A, ipv4Address)));
            records.add(Collections.singleton(TestDnsServer.newAddressRecord(name, RecordType.AAAA, ipv6Address)));
        }
        final Iterator<Set<ResourceRecord>> recordsIterator = records.iterator();
        RecordStore arbitrarilyOrderedStore = questionRecord -> recordsIterator.next();
        TestDnsServer nonCompliantDnsServer = new TestDnsServer(arbitrarilyOrderedStore);
        nonCompliantDnsServer.start();
        try {
            DnsNameResolver resolver = newResolver(types)
                    .maxQueriesPerResolve(2)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(
                            nonCompliantDnsServer.localAddress()))
                    .build();
            InetAddress resolved = resolver.resolve("netty.com").syncUninterruptibly().getNow();
            if (types == ResolvedAddressTypes.IPV4_PREFERRED) {
                assertEquals(ipv4Address, resolved.getHostAddress());
            } else {
                assertEquals(ipv6Address, resolved.getHostAddress());
            }
            InetAddress ipv4InetAddress = InetAddress.getByAddress("netty.com",
                    InetAddress.getByName(ipv4Address).getAddress());
            InetAddress ipv6InetAddress = InetAddress.getByAddress("netty.com",
                    InetAddress.getByName(ipv6Address).getAddress());

            List<InetAddress> resolvedAll = resolver.resolveAll("netty.com").syncUninterruptibly().getNow();
            List<InetAddress> expected = types == ResolvedAddressTypes.IPV4_PREFERRED ?
                    Arrays.asList(ipv4InetAddress, ipv6InetAddress) :  Arrays.asList(ipv6InetAddress, ipv4InetAddress);
            assertEquals(expected, resolvedAll);
        } finally {
            nonCompliantDnsServer.stop();
        }
    }

    private static void testRecursiveResolveCache(boolean cache)
            throws Exception {
        final String hostname = "some.record.netty.io";
        final String hostname2 = "some2.record.netty.io";

        final TestDnsServer dnsServerAuthority = new TestDnsServer(new HashSet<>(
                Arrays.asList(hostname, hostname2)));
        dnsServerAuthority.start();

        TestDnsServer dnsServer = new RedirectingTestDnsServer(hostname,
                dnsServerAuthority.localAddress().getAddress().getHostAddress());
        dnsServer.start();

        TestAuthoritativeDnsServerCache nsCache = new TestAuthoritativeDnsServerCache(
                cache ? new DefaultAuthoritativeDnsServerCache() : NoopAuthoritativeDnsServerCache.INSTANCE);
        TestRecursiveCacheDnsQueryLifecycleObserverFactory lifecycleObserverFactory =
                new TestRecursiveCacheDnsQueryLifecycleObserverFactory();
        EventLoopGroup group = new MultithreadEventLoopGroup(1, NioHandler.newFactory());
        final DnsNameResolver resolver = new DnsNameResolver(
                group.next(), new ReflectiveChannelFactory<DatagramChannel>(NioDatagramChannel.class),
                NoopDnsCache.INSTANCE, nsCache, lifecycleObserverFactory, 3000, ResolvedAddressTypes.IPV4_ONLY, true,
                10, true, 4096, false, HostsFileEntriesResolver.DEFAULT,
                new SingletonDnsServerAddressStreamProvider(dnsServer.localAddress()),
                DnsNameResolver.DEFAULT_SEARCH_DOMAINS, 0, true) {
            @Override
            InetSocketAddress newRedirectServerAddress(InetAddress server) {
                if (server.equals(dnsServerAuthority.localAddress().getAddress())) {
                    return new InetSocketAddress(server, dnsServerAuthority.localAddress().getPort());
                }
                return super.newRedirectServerAddress(server);
            }
        };

        // Java7 will strip of the "." so we need to adjust the expected dnsname. Both are valid in terms of the RFC
        // so its ok.
        String expectedDnsName = "dns4.some.record.netty.io.";

        try {
            resolver.resolveAll(hostname).syncUninterruptibly();

            TestDnsQueryLifecycleObserver observer = lifecycleObserverFactory.observers.poll();
            assertNotNull(observer);
            assertTrue(lifecycleObserverFactory.observers.isEmpty());
            assertEquals(4, observer.events.size());
            QueryWrittenEvent writtenEvent1 = (QueryWrittenEvent) observer.events.poll();
            assertEquals(dnsServer.localAddress(), writtenEvent1.dnsServerAddress);
            QueryRedirectedEvent redirectedEvent = (QueryRedirectedEvent) observer.events.poll();

            assertEquals(expectedDnsName, redirectedEvent.nameServers.get(0).getHostName());
            assertEquals(dnsServerAuthority.localAddress(), redirectedEvent.nameServers.get(0));
            QueryWrittenEvent writtenEvent2 = (QueryWrittenEvent) observer.events.poll();
            assertEquals(dnsServerAuthority.localAddress(), writtenEvent2.dnsServerAddress);
            QuerySucceededEvent succeededEvent = (QuerySucceededEvent) observer.events.poll();

            if (cache) {
                assertNull(nsCache.cache.get("io."));
                assertNull(nsCache.cache.get("netty.io."));
                DnsServerAddressStream entries = nsCache.cache.get("record.netty.io.");

                // First address should be resolved (as we received a matching additional record), second is unresolved.
                assertEquals(2, entries.size());
                assertFalse(entries.next().isUnresolved());
                assertTrue(entries.next().isUnresolved());

                assertNull(nsCache.cache.get(hostname));

                // Test again via cache.
                resolver.resolveAll(hostname).syncUninterruptibly();

                observer = lifecycleObserverFactory.observers.poll();
                assertNotNull(observer);
                assertTrue(lifecycleObserverFactory.observers.isEmpty());
                assertEquals(2, observer.events.size());
                writtenEvent1 = (QueryWrittenEvent) observer.events.poll();
                assertEquals(expectedDnsName, writtenEvent1.dnsServerAddress.getHostName());
                assertEquals(dnsServerAuthority.localAddress(), writtenEvent1.dnsServerAddress);
                succeededEvent = (QuerySucceededEvent) observer.events.poll();

                resolver.resolveAll(hostname2).syncUninterruptibly();

                observer = lifecycleObserverFactory.observers.poll();
                assertNotNull(observer);
                assertTrue(lifecycleObserverFactory.observers.isEmpty());
                assertEquals(2, observer.events.size());
                writtenEvent1 = (QueryWrittenEvent) observer.events.poll();
                assertEquals(expectedDnsName, writtenEvent1.dnsServerAddress.getHostName());
                assertEquals(dnsServerAuthority.localAddress(), writtenEvent1.dnsServerAddress);
                succeededEvent = (QuerySucceededEvent) observer.events.poll();

                // Check that it only queried the cache for record.netty.io.
                assertNull(nsCache.cacheHits.get("io."));
                assertNull(nsCache.cacheHits.get("netty.io."));
                assertNotNull(nsCache.cacheHits.get("record.netty.io."));
                assertNull(nsCache.cacheHits.get("some.record.netty.io."));
            }
        } finally {
            resolver.close();
            group.shutdownGracefully(0, 0, TimeUnit.SECONDS);
            dnsServer.stop();
            dnsServerAuthority.stop();
        }
    }

    @Test
    public void testFollowNsRedirectsNoopCaches() throws Exception {
        testFollowNsRedirects(NoopDnsCache.INSTANCE, NoopAuthoritativeDnsServerCache.INSTANCE, false);
    }

    @Test
    public void testFollowNsRedirectsNoopDnsCache() throws Exception {
        testFollowNsRedirects(NoopDnsCache.INSTANCE, new DefaultAuthoritativeDnsServerCache(), false);
    }

    @Test
    public void testFollowNsRedirectsNoopAuthoritativeDnsServerCache() throws Exception {
        testFollowNsRedirects(new DefaultDnsCache(), NoopAuthoritativeDnsServerCache.INSTANCE, false);
    }

    @Test
    public void testFollowNsRedirectsDefaultCaches() throws Exception {
        testFollowNsRedirects(new DefaultDnsCache(), new DefaultAuthoritativeDnsServerCache(), false);
    }

    @Test
    public void testFollowNsRedirectAndTrySecondNsOnTimeout() throws Exception {
        testFollowNsRedirects(NoopDnsCache.INSTANCE, NoopAuthoritativeDnsServerCache.INSTANCE, true);
    }

    @Test
    public void testFollowNsRedirectAndTrySecondNsOnTimeoutDefaultCaches() throws Exception {
        testFollowNsRedirects(new DefaultDnsCache(), new DefaultAuthoritativeDnsServerCache(), true);
    }

    private void testFollowNsRedirects(DnsCache cache, AuthoritativeDnsServerCache authoritativeDnsServerCache,
            final boolean invalidNsFirst) throws Exception {
        final String domain = "netty.io";
        final String ns1Name = "ns1." + domain;
        final String ns2Name = "ns2." + domain;
        final InetAddress expected = InetAddress.getByAddress("some.record." + domain, new byte[] { 10, 10, 10, 10 });

        // This is used to simulate a query timeout...
        final DatagramSocket socket = new DatagramSocket(new InetSocketAddress(0));

        final TestDnsServer dnsServerAuthority = new TestDnsServer(question -> {
            if (question.getDomainName().equals(expected.getHostName())) {
                return Collections.singleton(TestDnsServer.newARecord(
                        expected.getHostName(), expected.getHostAddress()));
            }
            return Collections.emptySet();
        });
        dnsServerAuthority.start();

        TestDnsServer redirectServer = new TestDnsServer(new HashSet<>(
                Arrays.asList(expected.getHostName(), ns1Name, ns2Name))) {
            @Override
            protected DnsMessage filterMessage(DnsMessage message) {
                for (QuestionRecord record: message.getQuestionRecords()) {
                    if (record.getDomainName().equals(expected.getHostName())) {
                        message.getAdditionalRecords().clear();
                        message.getAnswerRecords().clear();
                        if (invalidNsFirst) {
                            message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns2Name));
                            message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns1Name));
                        } else {
                            message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns1Name));
                            message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns2Name));
                        }
                        return message;
                    }
                }
                return message;
            }
        };
        redirectServer.start();
        EventLoopGroup group = new MultithreadEventLoopGroup(1, NioHandler.newFactory());
        final DnsNameResolver resolver = new DnsNameResolver(
                group.next(), new ReflectiveChannelFactory<DatagramChannel>(NioDatagramChannel.class),
                cache, authoritativeDnsServerCache, NoopDnsQueryLifecycleObserverFactory.INSTANCE, 2000,
                ResolvedAddressTypes.IPV4_ONLY, true, 10, true, 4096,
                false, HostsFileEntriesResolver.DEFAULT,
                new SingletonDnsServerAddressStreamProvider(redirectServer.localAddress()),
                DnsNameResolver.DEFAULT_SEARCH_DOMAINS, 0, true) {

            @Override
            InetSocketAddress newRedirectServerAddress(InetAddress server) {
                try {
                    if (server.getHostName().startsWith(ns1Name)) {
                        return new InetSocketAddress(InetAddress.getByAddress(ns1Name,
                                dnsServerAuthority.localAddress().getAddress().getAddress()),
                                dnsServerAuthority.localAddress().getPort());
                    }
                    if (server.getHostName().startsWith(ns2Name)) {
                        return new InetSocketAddress(InetAddress.getByAddress(ns2Name,
                                NetUtil.LOCALHOST.getAddress()), socket.getLocalPort());
                    }
                } catch (UnknownHostException e) {
                    throw new IllegalStateException(e);
                }
                return super.newRedirectServerAddress(server);
            }
        };

        try {
            List<InetAddress> resolved = resolver.resolveAll(expected.getHostName()).syncUninterruptibly().getNow();
            assertEquals(1, resolved.size());
            assertEquals(expected, resolved.get(0));

            List<InetAddress> resolved2 = resolver.resolveAll(expected.getHostName()).syncUninterruptibly().getNow();
            assertEquals(1, resolved2.size());
            assertEquals(expected, resolved2.get(0));

            if (authoritativeDnsServerCache != NoopAuthoritativeDnsServerCache.INSTANCE) {
                DnsServerAddressStream cached = authoritativeDnsServerCache.get(domain + '.');
                assertEquals(2, cached.size());
                InetSocketAddress ns1Address = InetSocketAddress.createUnresolved(
                        ns1Name + '.', DefaultDnsServerAddressStreamProvider.DNS_PORT);
                InetSocketAddress ns2Address = InetSocketAddress.createUnresolved(
                        ns2Name + '.', DefaultDnsServerAddressStreamProvider.DNS_PORT);

                if (invalidNsFirst) {
                    assertEquals(ns2Address, cached.next());
                    assertEquals(ns1Address, cached.next());
                } else {
                    assertEquals(ns1Address, cached.next());
                    assertEquals(ns2Address, cached.next());
                }
            }
            if (cache != NoopDnsCache.INSTANCE) {
                List<? extends DnsCacheEntry> ns1Cached = cache.get(ns1Name + '.', null);
                assertEquals(1, ns1Cached.size());
                DnsCacheEntry nsEntry = ns1Cached.get(0);
                assertNotNull(nsEntry.address());
                assertNull(nsEntry.cause());

                List<? extends DnsCacheEntry> ns2Cached = cache.get(ns2Name + '.', null);
                if (invalidNsFirst) {
                    assertEquals(1, ns2Cached.size());
                    DnsCacheEntry ns2Entry = ns2Cached.get(0);
                    assertNotNull(ns2Entry.address());
                    assertNull(ns2Entry.cause());
                } else {
                    // We should not even have tried to resolve the DNS name so this should be null.
                    assertNull(ns2Cached);
                }

                List<? extends DnsCacheEntry> expectedCached = cache.get(expected.getHostName(), null);
                assertEquals(1, expectedCached.size());
                DnsCacheEntry expectedEntry = expectedCached.get(0);
                assertEquals(expected, expectedEntry.address());
                assertNull(expectedEntry.cause());
            }
        } finally {
            resolver.close();
            group.shutdownGracefully(0, 0, TimeUnit.SECONDS);
            redirectServer.stop();
            dnsServerAuthority.stop();
            socket.close();
        }
    }

    @Test
    public void testMultipleAdditionalRecordsForSameNSRecord() throws Exception {
        testMultipleAdditionalRecordsForSameNSRecord(false);
    }

    @Test
    public void testMultipleAdditionalRecordsForSameNSRecordReordered() throws Exception {
        testMultipleAdditionalRecordsForSameNSRecord(true);
    }

    private static void testMultipleAdditionalRecordsForSameNSRecord(final boolean reversed) throws Exception {
        final String domain = "netty.io";
        final String hostname = "test.netty.io";
        final String ns1Name = "ns1." + domain;
        final InetSocketAddress ns1Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 1 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns2Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 2 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns3Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 3 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns4Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 4 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);

        TestDnsServer redirectServer = new TestDnsServer(new HashSet<>(Arrays.asList(hostname, ns1Name))) {
            @Override
            protected DnsMessage filterMessage(DnsMessage message) {
                for (QuestionRecord record: message.getQuestionRecords()) {
                    if (record.getDomainName().equals(hostname)) {
                        message.getAdditionalRecords().clear();
                        message.getAnswerRecords().clear();
                        message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns1Name));
                        message.getAdditionalRecords().add(newARecord(ns1Address));
                        message.getAdditionalRecords().add(newARecord(ns2Address));
                        message.getAdditionalRecords().add(newARecord(ns3Address));
                        message.getAdditionalRecords().add(newARecord(ns4Address));
                        return message;
                    }
                }
                return message;
            }

            private ResourceRecord newARecord(InetSocketAddress address) {
                return TestDnsServer.newARecord(address.getHostName(), address.getAddress().getHostAddress());
            }
        };
        redirectServer.start();
        EventLoopGroup group = new MultithreadEventLoopGroup(1, NioHandler.newFactory());

        final List<InetSocketAddress> cached = new CopyOnWriteArrayList<>();
        final AuthoritativeDnsServerCache authoritativeDnsServerCache = new AuthoritativeDnsServerCache() {
            @Override
            public DnsServerAddressStream get(String hostname) {
                return null;
            }

            @Override
            public void cache(String hostname, InetSocketAddress address, long originalTtl, EventLoop loop) {
                cached.add(address);
            }

            @Override
            public void clear() {
                // NOOP
            }

            @Override
            public boolean clear(String hostname) {
                return false;
            }
        };

        final AtomicReference<DnsServerAddressStream> redirectedRef = new AtomicReference<>();
        final DnsNameResolver resolver = new DnsNameResolver(
                group.next(), new ReflectiveChannelFactory<DatagramChannel>(NioDatagramChannel.class),
                NoopDnsCache.INSTANCE, authoritativeDnsServerCache,
                NoopDnsQueryLifecycleObserverFactory.INSTANCE, 2000, ResolvedAddressTypes.IPV4_ONLY,
                true, 10, true, 4096,
                false, HostsFileEntriesResolver.DEFAULT,
                new SingletonDnsServerAddressStreamProvider(redirectServer.localAddress()),
                DnsNameResolver.DEFAULT_SEARCH_DOMAINS, 0, true) {

            @Override
            protected DnsServerAddressStream newRedirectDnsServerStream(
                    String hostname, List<InetSocketAddress> nameservers) {
                if (reversed) {
                    Collections.reverse(nameservers);
                }
                DnsServerAddressStream stream = new SequentialDnsServerAddressStream(nameservers, 0);
                redirectedRef.set(stream);
                return stream;
            }
        };

        try {
            Throwable cause = resolver.resolveAll(hostname).await().cause();
            assertTrue(cause instanceof UnknownHostException);
            DnsServerAddressStream redirected = redirectedRef.get();
            assertNotNull(redirected);
            assertEquals(4, redirected.size());
            assertEquals(4, cached.size());

            if (reversed) {
                assertEquals(ns4Address, redirected.next());
                assertEquals(ns3Address, redirected.next());
                assertEquals(ns2Address, redirected.next());
                assertEquals(ns1Address, redirected.next());
            } else {
                assertEquals(ns1Address, redirected.next());
                assertEquals(ns2Address, redirected.next());
                assertEquals(ns3Address, redirected.next());
                assertEquals(ns4Address, redirected.next());
            }

            // We should always have the same order in the cache.
            assertEquals(ns1Address, cached.get(0));
            assertEquals(ns2Address, cached.get(1));
            assertEquals(ns3Address, cached.get(2));
            assertEquals(ns4Address, cached.get(3));
        } finally {
            resolver.close();
            group.shutdownGracefully(0, 0, TimeUnit.SECONDS);
            redirectServer.stop();
        }
    }

    @Test
    public void testNSRecordsFromCache() throws Exception {
        final String domain = "netty.io";
        final String hostname = "test.netty.io";
        final String ns0Name = "ns0." + domain + '.';
        final String ns1Name = "ns1." + domain + '.';
        final String ns2Name = "ns2." + domain + '.';

        final InetSocketAddress ns0Address = new InetSocketAddress(
                InetAddress.getByAddress(ns0Name, new byte[] { 10, 1, 0, 1 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns1Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 1 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns2Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 2 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns3Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 3 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns4Address = new InetSocketAddress(
                InetAddress.getByAddress(ns1Name, new byte[] { 10, 0, 0, 4 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        final InetSocketAddress ns5Address = new InetSocketAddress(
                InetAddress.getByAddress(ns2Name, new byte[] { 10, 0, 0, 5 }),
                DefaultDnsServerAddressStreamProvider.DNS_PORT);
        TestDnsServer redirectServer = new TestDnsServer(new HashSet<>(Arrays.asList(hostname, ns1Name))) {
            @Override
            protected DnsMessage filterMessage(DnsMessage message) {
                for (QuestionRecord record: message.getQuestionRecords()) {
                    if (record.getDomainName().equals(hostname)) {
                        message.getAdditionalRecords().clear();
                        message.getAnswerRecords().clear();
                        message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns0Name));
                        message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns1Name));
                        message.getAuthorityRecords().add(TestDnsServer.newNsRecord(domain, ns2Name));

                        message.getAdditionalRecords().add(newARecord(ns0Address));
                        message.getAdditionalRecords().add(newARecord(ns5Address));

                        return message;
                    }
                }
                return message;
            }

            private ResourceRecord newARecord(InetSocketAddress address) {
                return TestDnsServer.newARecord(address.getHostName(), address.getAddress().getHostAddress());
            }
        };
        redirectServer.start();
        EventLoopGroup group = new MultithreadEventLoopGroup(1, NioHandler.newFactory());

        final List<InetSocketAddress> cached = new CopyOnWriteArrayList<>();
        final AuthoritativeDnsServerCache authoritativeDnsServerCache = new AuthoritativeDnsServerCache() {
            @Override
            public DnsServerAddressStream get(String hostname) {
                return null;
            }

            @Override
            public void cache(String hostname, InetSocketAddress address, long originalTtl, EventLoop loop) {
                cached.add(address);
            }

            @Override
            public void clear() {
                // NOOP
            }

            @Override
            public boolean clear(String hostname) {
                return false;
            }
        };

        EventLoop loop = group.next();
        DefaultDnsCache cache = new DefaultDnsCache();
        cache.cache(ns1Name, null, ns1Address.getAddress(), 10000, loop);
        cache.cache(ns1Name, null, ns2Address.getAddress(), 10000, loop);
        cache.cache(ns1Name, null, ns3Address.getAddress(), 10000, loop);
        cache.cache(ns1Name, null, ns4Address.getAddress(), 10000, loop);

        final AtomicReference<DnsServerAddressStream> redirectedRef = new AtomicReference<>();
        final DnsNameResolver resolver = new DnsNameResolver(
                loop, new ReflectiveChannelFactory<DatagramChannel>(NioDatagramChannel.class),
                cache, authoritativeDnsServerCache,
                NoopDnsQueryLifecycleObserverFactory.INSTANCE, 2000, ResolvedAddressTypes.IPV4_ONLY,
                true, 10, true, 4096,
                false, HostsFileEntriesResolver.DEFAULT,
                new SingletonDnsServerAddressStreamProvider(redirectServer.localAddress()),
                DnsNameResolver.DEFAULT_SEARCH_DOMAINS, 0, true) {

            @Override
            protected DnsServerAddressStream newRedirectDnsServerStream(
                    String hostname, List<InetSocketAddress> nameservers) {
                DnsServerAddressStream stream = new SequentialDnsServerAddressStream(nameservers, 0);
                redirectedRef.set(stream);
                return stream;
            }
        };

        try {
            Throwable cause = resolver.resolveAll(hostname).await().cause();
            assertTrue(cause instanceof UnknownHostException);
            DnsServerAddressStream redirected = redirectedRef.get();
            assertNotNull(redirected);
            assertEquals(6, redirected.size());
            assertEquals(3, cached.size());

            // The redirected addresses should have been retrieven from the DnsCache if not resolved, so these are
            // fully resolved.
            assertEquals(ns0Address, redirected.next());
            assertEquals(ns1Address, redirected.next());
            assertEquals(ns2Address, redirected.next());
            assertEquals(ns3Address, redirected.next());
            assertEquals(ns4Address, redirected.next());
            assertEquals(ns5Address, redirected.next());

            // As this address was supplied as ADDITIONAL we should put it resolved into the cache.
            assertEquals(ns0Address, cached.get(0));
            assertEquals(ns5Address, cached.get(1));

            // We should have put the unresolved address in the AuthoritativeDnsServerCache (but only 1 time)
            assertEquals(unresolved(ns1Address), cached.get(2));
        } finally {
            resolver.close();
            group.shutdownGracefully(0, 0, TimeUnit.SECONDS);
            redirectServer.stop();
        }
    }

    private static InetSocketAddress unresolved(InetSocketAddress address) {
        return InetSocketAddress.createUnresolved(address.getHostString(), address.getPort());
    }

    private static void resolve(DnsNameResolver resolver, Map<String, Future<InetAddress>> futures, String hostname) {
        futures.put(hostname, resolver.resolve(hostname));
    }

    private static void queryMx(
            DnsNameResolver resolver,
            Map<String, Future<AddressedEnvelope<DnsResponse, InetSocketAddress>>> futures,
            String hostname) {
        futures.put(hostname, resolver.query(new DefaultDnsQuestion(hostname, DnsRecordType.MX)));
    }

    private static void assertNoQueriesMade(DnsNameResolver resolver) {
        TestRecursiveCacheDnsQueryLifecycleObserverFactory lifecycleObserverFactory =
                (TestRecursiveCacheDnsQueryLifecycleObserverFactory) resolver.dnsQueryLifecycleObserverFactory();
        assertTrue(lifecycleObserverFactory.observers.isEmpty());
    }

    private static void assertQueryObserver(DnsNameResolver resolver, DnsRecordType cancelledType) {
        TestRecursiveCacheDnsQueryLifecycleObserverFactory lifecycleObserverFactory =
                (TestRecursiveCacheDnsQueryLifecycleObserverFactory) resolver.dnsQueryLifecycleObserverFactory();
        TestDnsQueryLifecycleObserver observer;
        while ((observer = lifecycleObserverFactory.observers.poll()) != null) {
            Object o = observer.events.poll();
            if (o instanceof QueryCancelledEvent) {
                assertEquals(cancelledType, observer.question.type());
            } else if (o instanceof QueryWrittenEvent) {
                QuerySucceededEvent succeededEvent = (QuerySucceededEvent) observer.events.poll();
            } else {
                fail("unexpected event type: " + o);
            }
            assertTrue(observer.events.isEmpty());
        }
    }

    private static final class TestRecursiveCacheDnsQueryLifecycleObserverFactory
            implements DnsQueryLifecycleObserverFactory {
        final Queue<TestDnsQueryLifecycleObserver> observers =
                new ConcurrentLinkedQueue<>();
        @Override
        public DnsQueryLifecycleObserver newDnsQueryLifecycleObserver(DnsQuestion question) {
            TestDnsQueryLifecycleObserver observer = new TestDnsQueryLifecycleObserver(question);
            observers.add(observer);
            return observer;
        }
    }

    private static final class QueryWrittenEvent {
        final InetSocketAddress dnsServerAddress;

        QueryWrittenEvent(InetSocketAddress dnsServerAddress) {
            this.dnsServerAddress = dnsServerAddress;
        }
    }

    private static final class QueryCancelledEvent {
        final int queriesRemaining;

        QueryCancelledEvent(int queriesRemaining) {
            this.queriesRemaining = queriesRemaining;
        }
    }

    private static final class QueryRedirectedEvent {
        final List<InetSocketAddress> nameServers;

        QueryRedirectedEvent(List<InetSocketAddress> nameServers) {
            this.nameServers = nameServers;
        }
    }

    private static final class QueryCnamedEvent {
        final DnsQuestion question;

        QueryCnamedEvent(DnsQuestion question) {
            this.question = question;
        }
    }

    private static final class QueryNoAnswerEvent {
        final DnsResponseCode code;

        QueryNoAnswerEvent(DnsResponseCode code) {
            this.code = code;
        }
    }

    private static final class QueryFailedEvent {
        final Throwable cause;

        QueryFailedEvent(Throwable cause) {
            this.cause = cause;
        }
    }

    private static final class QuerySucceededEvent {
    }

    private static final class TestDnsQueryLifecycleObserver implements DnsQueryLifecycleObserver {
        final Queue<Object> events = new ArrayDeque<>();
        final DnsQuestion question;

        TestDnsQueryLifecycleObserver(DnsQuestion question) {
            this.question = question;
        }

        @Override
        public void queryWritten(InetSocketAddress dnsServerAddress, ChannelFuture future) {
            events.add(new QueryWrittenEvent(dnsServerAddress));
        }

        @Override
        public void queryCancelled(int queriesRemaining) {
            events.add(new QueryCancelledEvent(queriesRemaining));
        }

        @Override
        public DnsQueryLifecycleObserver queryRedirected(List<InetSocketAddress> nameServers) {
            events.add(new QueryRedirectedEvent(nameServers));
            return this;
        }

        @Override
        public DnsQueryLifecycleObserver queryCNAMEd(DnsQuestion cnameQuestion) {
            events.add(new QueryCnamedEvent(cnameQuestion));
            return this;
        }

        @Override
        public DnsQueryLifecycleObserver queryNoAnswer(DnsResponseCode code) {
            events.add(new QueryNoAnswerEvent(code));
            return this;
        }

        @Override
        public void queryFailed(Throwable cause) {
            events.add(new QueryFailedEvent(cause));
        }

        @Override
        public void querySucceed() {
            events.add(new QuerySucceededEvent());
        }
    }

    private static final class TestAuthoritativeDnsServerCache implements AuthoritativeDnsServerCache {
        final AuthoritativeDnsServerCache cache;
        final Map<String, DnsServerAddressStream> cacheHits = new HashMap<>();

        TestAuthoritativeDnsServerCache(AuthoritativeDnsServerCache cache) {
            this.cache = cache;
        }

        @Override
        public void clear() {
            cache.clear();
        }

        @Override
        public boolean clear(String hostname) {
            return cache.clear(hostname);
        }

        @Override
        public DnsServerAddressStream get(String hostname) {
            DnsServerAddressStream cached = cache.get(hostname);
            if (cached != null) {
                cacheHits.put(hostname, cached.duplicate());
            }
            return cached;
        }

        @Override
        public void cache(String hostname, InetSocketAddress address, long originalTtl, EventLoop loop) {
            cache.cache(hostname, address, originalTtl, loop);
        }
    }

    private static final class TestDnsCache implements DnsCache {
        final DnsCache cache;
        final Map<String, List<? extends DnsCacheEntry>> cacheHits =
                new HashMap<>();

        TestDnsCache(DnsCache cache) {
            this.cache = cache;
        }

        @Override
        public void clear() {
            cache.clear();
        }

        @Override
        public boolean clear(String hostname) {
            return cache.clear(hostname);
        }

        @Override
        public List<? extends DnsCacheEntry> get(String hostname, DnsRecord[] additionals) {
            List<? extends DnsCacheEntry> cached = cache.get(hostname, additionals);
            cacheHits.put(hostname, cached);
            return cached;
        }

        @Override
        public DnsCacheEntry cache(String hostname, DnsRecord[] additionals, InetAddress address,
                                   long originalTtl, EventLoop loop) {
            return cache.cache(hostname, additionals, address, originalTtl, loop);
        }

        @Override
        public DnsCacheEntry cache(String hostname, DnsRecord[] additionals, Throwable cause, EventLoop loop) {
            return cache.cache(hostname, additionals, cause, loop);
        }
    }

    private static class RedirectingTestDnsServer extends TestDnsServer {

        private final String dnsAddress;
        private final String domain;

        RedirectingTestDnsServer(String domain, String dnsAddress) {
            super(Collections.singleton(domain));
            this.domain = domain;
            this.dnsAddress = dnsAddress;
        }

        @Override
        protected DnsMessage filterMessage(DnsMessage message) {
            // Clear the answers as we want to add our own stuff to test dns redirects.
            message.getAnswerRecords().clear();
            message.getAuthorityRecords().clear();
            message.getAdditionalRecords().clear();

            String name = domain;
            for (int i = 0 ;; i++) {
                int idx = name.indexOf('.');
                if (idx <= 0) {
                    break;
                }
                name = name.substring(idx + 1); // skip the '.' as well.
                String dnsName = "dns" + idx + '.' + domain;
                message.getAuthorityRecords().add(newNsRecord(name, dnsName));
                message.getAdditionalRecords().add(newARecord(dnsName, i == 0 ? dnsAddress : "1.2.3." + idx));

                // Add an unresolved NS record (with no additionals as well)
                message.getAuthorityRecords().add(newNsRecord(name, "unresolved." + dnsName));
            }

            return message;
        }
    }

    @Test(timeout = 3000)
    public void testTimeoutNotCached() {
        DnsCache cache = new DnsCache() {
            @Override
            public void clear() {
                // NOOP
            }

            @Override
            public boolean clear(String hostname) {
                return false;
            }

            @Override
            public List<? extends DnsCacheEntry> get(String hostname, DnsRecord[] additionals) {
                return Collections.emptyList();
            }

            @Override
            public DnsCacheEntry cache(String hostname, DnsRecord[] additionals, InetAddress address,
                                       long originalTtl, EventLoop loop) {
                fail("Should not be cached");
                return null;
            }

            @Override
            public DnsCacheEntry cache(String hostname, DnsRecord[] additionals, Throwable cause, EventLoop loop) {
                fail("Should not be cached");
                return null;
            }
        };
        DnsNameResolverBuilder builder = newResolver();
        builder.queryTimeoutMillis(100)
                .authoritativeDnsServerCache(cache)
                .resolveCache(cache)
                .nameServerProvider(new SingletonDnsServerAddressStreamProvider(
                        new InetSocketAddress(NetUtil.LOCALHOST, 12345)));
        DnsNameResolver resolver = builder.build();
        Future<InetAddress> result = resolver.resolve("doesnotexist.netty.io").awaitUninterruptibly();
        Throwable cause = result.cause();
        assertTrue(cause instanceof UnknownHostException);
        assertTrue(cause.getCause() instanceof DnsNameResolverTimeoutException);
        assertTrue(DnsNameResolver.isTimeoutError(cause));
        assertTrue(DnsNameResolver.isTransportOrTimeoutError(cause));
        resolver.close();
    }

    @Test
    public void testDnsNameResolverBuilderCopy() {
        ChannelFactory<DatagramChannel> channelFactory =
                new ReflectiveChannelFactory<>(NioDatagramChannel.class);
        DnsNameResolverBuilder builder = new DnsNameResolverBuilder(group.next())
                .channelFactory(channelFactory);
        DnsNameResolverBuilder copiedBuilder = builder.copy();

        // change channel factory does not propagate to previously made copy
        ChannelFactory<DatagramChannel> newChannelFactory =
                new ReflectiveChannelFactory<>(NioDatagramChannel.class);
        builder.channelFactory(newChannelFactory);
        assertEquals(channelFactory, copiedBuilder.channelFactory());
        assertEquals(newChannelFactory, builder.channelFactory());
    }

    @Test
    public void testFollowCNAMEEvenIfARecordIsPresent() throws IOException {
        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            if (question.getDomainName().equals("cname.netty.io")) {
                Map<String, Object> map1 = new HashMap<>();
                map1.put(DnsAttribute.IP_ADDRESS.toLowerCase(), "10.0.0.99");
                return Collections.singleton(
                        new TestDnsServer.TestResourceRecord(question.getDomainName(), RecordType.A, map1));
            } else {
                Set<ResourceRecord> records = new LinkedHashSet<>(2);
                Map<String, Object> map = new HashMap<>();
                map.put(DnsAttribute.DOMAIN_NAME.toLowerCase(), "cname.netty.io");
                records.add(new TestDnsServer.TestResourceRecord(
                        question.getDomainName(), RecordType.CNAME, map));

                Map<String, Object> map1 = new HashMap<>();
                map1.put(DnsAttribute.IP_ADDRESS.toLowerCase(), "10.0.0.2");
                records.add(new TestDnsServer.TestResourceRecord(
                        question.getDomainName(), RecordType.A, map1));
                return records;
            }
        });
        dnsServer2.start();
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(true)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_ONLY)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));

            resolver = builder.build();
            List<InetAddress> resolvedAddresses =
                    resolver.resolveAll("somehost.netty.io").syncUninterruptibly().getNow();
            assertEquals(2, resolvedAddresses.size());
            assertTrue(resolvedAddresses.contains(InetAddress.getByAddress(new byte[] { 10, 0, 0, 99 })));
            assertTrue(resolvedAddresses.contains(InetAddress.getByAddress(new byte[] { 10, 0, 0, 2 })));
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test
    public void testFollowCNAMELoop() throws Throwable {
        expectedException.expect(UnknownHostException.class);
        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            Set<ResourceRecord> records = new LinkedHashSet<>(4);

            records.add(new TestDnsServer.TestResourceRecord("x." + question.getDomainName(),
                    RecordType.A, Collections.singletonMap(
                            DnsAttribute.IP_ADDRESS.toLowerCase(), "10.0.0.99")));
            records.add(new TestDnsServer.TestResourceRecord(
                    "cname2.netty.io", RecordType.CNAME,
                    Collections.singletonMap(
                            DnsAttribute.DOMAIN_NAME.toLowerCase(), "cname.netty.io")));
            records.add(new TestDnsServer.TestResourceRecord(
                    "cname.netty.io", RecordType.CNAME,
                    Collections.singletonMap(
                            DnsAttribute.DOMAIN_NAME.toLowerCase(), "cname2.netty.io")));
            records.add(new TestDnsServer.TestResourceRecord(
                    question.getDomainName(), RecordType.CNAME,
                    Collections.singletonMap(
                            DnsAttribute.DOMAIN_NAME.toLowerCase(), "cname.netty.io")));
            return records;
        });
        dnsServer2.start();
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(false)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_ONLY)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));

            resolver = builder.build();
            resolver.resolveAll("somehost.netty.io").syncUninterruptibly().getNow();
        } catch (CompletionException e) {
            throw e.getCause();
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test
    public void testSearchDomainQueryFailureForSingleAddressTypeCompletes() throws Throwable {
        expectedException.expect(UnknownHostException.class);
        testSearchDomainQueryFailureCompletes(ResolvedAddressTypes.IPV4_ONLY);
    }

    @Test
    public void testSearchDomainQueryFailureForMultipleAddressTypeCompletes() throws Throwable {
        expectedException.expect(UnknownHostException.class);
        testSearchDomainQueryFailureCompletes(ResolvedAddressTypes.IPV4_PREFERRED);
    }

    private void testSearchDomainQueryFailureCompletes(ResolvedAddressTypes types) throws Throwable {
        DnsNameResolver resolver = newResolver()
                .resolvedAddressTypes(types)
                .ndots(1)
                .searchDomains(singletonList(".")).build();
        try {
            resolver.resolve("invalid.com").syncUninterruptibly();
        } catch (CompletionException cause) {
            throw cause.getCause();
        } finally {
            resolver.close();
        }
    }

    @Test(timeout = 2000L)
    public void testCachesClearedOnClose() throws Exception {
        final CountDownLatch resolveLatch = new CountDownLatch(1);
        final CountDownLatch authoritativeLatch = new CountDownLatch(1);

        DnsNameResolver resolver = newResolver().resolveCache(new DnsCache() {
            @Override
            public void clear() {
                resolveLatch.countDown();
            }

            @Override
            public boolean clear(String hostname) {
                return false;
            }

            @Override
            public List<? extends DnsCacheEntry> get(String hostname, DnsRecord[] additionals) {
                return null;
            }

            @Override
            public DnsCacheEntry cache(
                    String hostname, DnsRecord[] additionals, InetAddress address, long originalTtl, EventLoop loop) {
                return null;
            }

            @Override
            public DnsCacheEntry cache(
                    String hostname, DnsRecord[] additionals, Throwable cause, EventLoop loop) {
                return null;
            }
        }).authoritativeDnsServerCache(new DnsCache() {
            @Override
            public void clear() {
                authoritativeLatch.countDown();
            }

            @Override
            public boolean clear(String hostname) {
                return false;
            }

            @Override
            public List<? extends DnsCacheEntry> get(String hostname, DnsRecord[] additionals) {
                return null;
            }

            @Override
            public DnsCacheEntry cache(
                    String hostname, DnsRecord[] additionals, InetAddress address, long originalTtl, EventLoop loop) {
                return null;
            }

            @Override
            public DnsCacheEntry cache(String hostname, DnsRecord[] additionals, Throwable cause, EventLoop loop) {
                return null;
            }
        }).build();

        resolver.close();
        resolveLatch.await();
        authoritativeLatch.await();
    }

    @Test
    public void testResolveACachedWithDot() {
        final DnsCache cache = new DefaultDnsCache();
        DnsNameResolver resolver = newResolver(ResolvedAddressTypes.IPV4_ONLY)
                .resolveCache(cache).build();

        try {
            String domain = DOMAINS.iterator().next();
            String domainWithDot = domain + '.';

            resolver.resolve(domain).syncUninterruptibly();
            List<? extends DnsCacheEntry> cached = cache.get(domain, null);
            List<? extends DnsCacheEntry> cached2 = cache.get(domainWithDot, null);

            assertEquals(1, cached.size());
            assertSame(cached, cached2);
        } finally {
            resolver.close();
        }
    }

    @Test
    public void testResolveACachedWithDotSearchDomain() throws Exception {
        final TestDnsCache cache = new TestDnsCache(new DefaultDnsCache());
        TestDnsServer server = new TestDnsServer(Collections.singleton("test.netty.io"));
        server.start();
        DnsNameResolver resolver = newResolver(ResolvedAddressTypes.IPV4_ONLY)
                .searchDomains(Collections.singletonList("netty.io"))
                .nameServerProvider(new SingletonDnsServerAddressStreamProvider(server.localAddress()))
                .resolveCache(cache).build();
        try {
            resolver.resolve("test").syncUninterruptibly();

            assertNull(cache.cacheHits.get("test.netty.io"));

            List<? extends DnsCacheEntry> cached = cache.cache.get("test.netty.io", null);
            List<? extends DnsCacheEntry> cached2 = cache.cache.get("test.netty.io.", null);
            assertEquals(1, cached.size());
            assertSame(cached, cached2);

            resolver.resolve("test").syncUninterruptibly();
            List<? extends DnsCacheEntry> entries = cache.cacheHits.get("test.netty.io");
            assertFalse(entries.isEmpty());
        } finally {
            resolver.close();
            server.stop();
        }
    }

    @Test
    public void testChannelFactoryException() {
        final IllegalStateException exception = new IllegalStateException();
        try {
            newResolver().channelFactory(eventLoop -> {
                throw exception;
            }).build();
            fail();
        } catch (Exception e) {
            assertSame(exception, e);
        }
    }

    @Test
    public void testCNameCached() throws Exception {
        final Map<String, String> cache = new ConcurrentHashMap<>();
        final AtomicInteger cnameQueries = new AtomicInteger();
        final AtomicInteger aQueries = new AtomicInteger();

        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            if ("cname.netty.io".equals(question.getDomainName())) {
                aQueries.incrementAndGet();

                return Collections.singleton(new TestDnsServer.TestResourceRecord(
                        question.getDomainName(), RecordType.A,
                        Collections.singletonMap(
                                DnsAttribute.IP_ADDRESS.toLowerCase(), "10.0.0.99")));
            }
            if ("x.netty.io".equals(question.getDomainName())) {
                cnameQueries.incrementAndGet();

                return Collections.singleton(new TestDnsServer.TestResourceRecord(
                        question.getDomainName(), RecordType.CNAME,
                        Collections.singletonMap(
                                DnsAttribute.DOMAIN_NAME.toLowerCase(), "cname.netty.io")));
            }
            if ("y.netty.io".equals(question.getDomainName())) {
                cnameQueries.incrementAndGet();

                return Collections.singleton(new TestDnsServer.TestResourceRecord(
                        question.getDomainName(), RecordType.CNAME,
                        Collections.singletonMap(
                                DnsAttribute.DOMAIN_NAME.toLowerCase(), "x.netty.io")));
            }
            return Collections.emptySet();
        });
        dnsServer2.start();
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(true)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_ONLY)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()))
                    .resolveCache(NoopDnsCache.INSTANCE)
                    .cnameCache(new DnsCnameCache() {
                        @Override
                        public String get(String hostname) {
                            assertTrue(hostname, hostname.endsWith("."));
                            return cache.get(hostname);
                        }

                        @Override
                        public void cache(String hostname, String cname, long originalTtl, EventLoop loop) {
                            assertTrue(hostname, hostname.endsWith("."));
                            cache.put(hostname, cname);
                        }

                        @Override
                        public void clear() {
                            // NOOP
                        }

                        @Override
                        public boolean clear(String hostname) {
                            return false;
                        }
                    });
            resolver = builder.build();
            List<InetAddress> resolvedAddresses =
                    resolver.resolveAll("x.netty.io").syncUninterruptibly().getNow();
            assertEquals(1, resolvedAddresses.size());
            assertTrue(resolvedAddresses.contains(InetAddress.getByAddress(new byte[] { 10, 0, 0, 99 })));

            assertEquals("cname.netty.io.", cache.get("x.netty.io."));
            assertEquals(1, cnameQueries.get());
            assertEquals(1, aQueries.get());

            resolvedAddresses =
                    resolver.resolveAll("x.netty.io").syncUninterruptibly().getNow();
            assertEquals(1, resolvedAddresses.size());
            assertTrue(resolvedAddresses.contains(InetAddress.getByAddress(new byte[] { 10, 0, 0, 99 })));

            // Should not have queried for the CNAME again.
            assertEquals(1, cnameQueries.get());
            assertEquals(2, aQueries.get());

            resolvedAddresses =
                    resolver.resolveAll("y.netty.io").syncUninterruptibly().getNow();
            assertEquals(1, resolvedAddresses.size());
            assertTrue(resolvedAddresses.contains(InetAddress.getByAddress(new byte[] { 10, 0, 0, 99 })));

            assertEquals("x.netty.io.", cache.get("y.netty.io."));

            // Will only query for one CNAME
            assertEquals(2, cnameQueries.get());
            assertEquals(3, aQueries.get());

            resolvedAddresses =
                    resolver.resolveAll("y.netty.io").syncUninterruptibly().getNow();
            assertEquals(1, resolvedAddresses.size());
            assertTrue(resolvedAddresses.contains(InetAddress.getByAddress(new byte[] { 10, 0, 0, 99 })));

            // Should not have queried for the CNAME again.
            assertEquals(2, cnameQueries.get());
            assertEquals(4, aQueries.get());
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test
    public void testInstanceWithNullPreferredAddressType() {
        new DnsNameResolver(
                group.next(), // eventLoop
                new ReflectiveChannelFactory<DatagramChannel>(NioDatagramChannel.class), // channelFactory
                NoopDnsCache.INSTANCE, // resolveCache
                NoopAuthoritativeDnsServerCache.INSTANCE, // authoritativeDnsServerCache
                NoopDnsQueryLifecycleObserverFactory.INSTANCE, // dnsQueryLifecycleObserverFactory
                100, // queryTimeoutMillis
                null, // resolvedAddressTypes, see https://github.com/netty/netty/pull/8445
                true, // recursionDesired
                1, // maxQueriesPerResolve
                false, // traceEnabled
                4096, // maxPayloadSize
                true, // optResourceEnabled
                HostsFileEntriesResolver.DEFAULT, // hostsFileEntriesResolver
                DnsServerAddressStreamProviders.platformDefault(), // dnsServerAddressStreamProvider
                null, // searchDomains
                1, // ndots
                true // decodeIdn
        ).close();
    }

    @Test
    public void testQueryTxt() throws Exception {
        final String hostname = "txt.netty.io";
        final String txt1 = "some text";
        final String txt2 = "some more text";

        TestDnsServer server = new TestDnsServer(question -> {
            if (question.getDomainName().equals(hostname)) {
                Map<String, Object> map1 = new HashMap<String, Object>();
                map1.put(DnsAttribute.CHARACTER_STRING.toLowerCase(), txt1);

                Map<String, Object> map2 = new HashMap<String, Object>();
                map2.put(DnsAttribute.CHARACTER_STRING.toLowerCase(), txt2);

                Set<ResourceRecord> records = new HashSet<ResourceRecord>();
                records.add(new TestDnsServer.TestResourceRecord(question.getDomainName(), RecordType.TXT, map1));
                records.add(new TestDnsServer.TestResourceRecord(question.getDomainName(), RecordType.TXT, map2));
                return records;
            }
            return Collections.emptySet();
        });
        server.start();
        DnsNameResolver resolver = newResolver(ResolvedAddressTypes.IPV4_ONLY)
                .nameServerProvider(new SingletonDnsServerAddressStreamProvider(server.localAddress()))
                .build();
        try {
            AddressedEnvelope<DnsResponse, InetSocketAddress> envelope = resolver.query(
                    new DefaultDnsQuestion(hostname, DnsRecordType.TXT)).syncUninterruptibly().getNow();
            assertNotNull(envelope.sender());

            DnsResponse response = envelope.content();
            assertNotNull(response);

            assertEquals(DnsResponseCode.NOERROR, response.code());
            int count = response.count(DnsSection.ANSWER);

            assertEquals(2, count);
            List<String> txts = new ArrayList<String>();

            for (int i = 0; i < 2; i++) {
                txts.addAll(decodeTxt(response.recordAt(DnsSection.ANSWER, i)));
            }
            assertTrue(txts.contains(txt1));
            assertTrue(txts.contains(txt2));
            envelope.release();
        } finally {
            resolver.close();
            server.stop();
        }
    }

    private static List<String> decodeTxt(DnsRecord record) {
        if (!(record instanceof DnsRawRecord)) {
            return Collections.emptyList();
        }
        List<String> list = new ArrayList<String>();
        ByteBuf data = ((DnsRawRecord) record).content();
        int idx = data.readerIndex();
        int wIdx = data.writerIndex();
        while (idx < wIdx) {
            int len = data.getUnsignedByte(idx++);
            list.add(data.toString(idx, len, CharsetUtil.UTF_8));
            idx += len;
        }
        return list;
    }

    @Test
    public void testNotIncludeDuplicates() throws IOException {
        final String name = "netty.io";
        final String ipv4Addr = "1.2.3.4";
        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            Set<ResourceRecord> records = new LinkedHashSet<ResourceRecord>(4);
            String qName = question.getDomainName().toLowerCase();
            if (qName.equals(name)) {
                records.add(new TestDnsServer.TestResourceRecord(
                        qName, RecordType.CNAME,
                        Collections.<String, Object>singletonMap(
                                DnsAttribute.DOMAIN_NAME.toLowerCase(), "cname.netty.io")));
                records.add(new TestDnsServer.TestResourceRecord(qName,
                        RecordType.A, Collections.<String, Object>singletonMap(
                        DnsAttribute.IP_ADDRESS.toLowerCase(), ipv4Addr)));
            } else {
                records.add(new TestDnsServer.TestResourceRecord(qName,
                        RecordType.A, Collections.<String, Object>singletonMap(
                        DnsAttribute.IP_ADDRESS.toLowerCase(), ipv4Addr)));
            }
            return records;
        });
        dnsServer2.start();
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(true)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));
            builder.resolvedAddressTypes(ResolvedAddressTypes.IPV4_ONLY);

            resolver = builder.build();
            List<InetAddress> resolvedAddresses = resolver.resolveAll(name).syncUninterruptibly().getNow();
            assertEquals(Collections.singletonList(InetAddress.getByAddress(name, new byte[] { 1, 2, 3, 4 })),
                    resolvedAddresses);
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test
    public void testIncludeDuplicates() throws IOException {
        final String name = "netty.io";
        final String ipv4Addr = "1.2.3.4";
        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            Set<ResourceRecord> records = new LinkedHashSet<ResourceRecord>(2);
            String qName = question.getDomainName().toLowerCase();
            records.add(new TestDnsServer.TestResourceRecord(qName,
                    RecordType.A, Collections.<String, Object>singletonMap(
                    DnsAttribute.IP_ADDRESS.toLowerCase(), ipv4Addr)));
            records.add(new TestDnsServer.TestResourceRecord(qName,
                    RecordType.A, Collections.<String, Object>singletonMap(
                    DnsAttribute.IP_ADDRESS.toLowerCase(), ipv4Addr)));
            return records;
        });
        dnsServer2.start();
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(true)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));
            builder.resolvedAddressTypes(ResolvedAddressTypes.IPV4_ONLY);

            resolver = builder.build();
            List<DnsRecord> resolvedAddresses = resolver.resolveAll(new DefaultDnsQuestion(name, A))
                    .syncUninterruptibly().getNow();
            assertEquals(2, resolvedAddresses.size());
            for (DnsRecord record: resolvedAddresses) {
                ReferenceCountUtil.release(record);
            }
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test
    public void testDropAAAA() throws IOException {
        String host = "somehost.netty.io";
        TestDnsServer dnsServer2 = new TestDnsServer(Collections.singleton(host));
        dnsServer2.start(true);
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(false)
                    .queryTimeoutMillis(500)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_PREFERRED)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));

            resolver = builder.build();
            List<InetAddress> addressList = resolver.resolveAll(host).syncUninterruptibly().getNow();
            assertEquals(1, addressList.size());
            assertEquals(host, addressList.get(0).getHostName());
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test(timeout = 2000)
    public void testDropAAAAResolveFast() throws IOException {
        String host = "somehost.netty.io";
        TestDnsServer dnsServer2 = new TestDnsServer(Collections.singleton(host));
        dnsServer2.start(true);
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(false)
                    .queryTimeoutMillis(10000)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_PREFERRED)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));

            resolver = builder.build();
            InetAddress address = resolver.resolve(host).syncUninterruptibly().getNow();
            assertEquals(host, address.getHostName());
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test(timeout = 2000)
    public void testDropAAAAResolveAllFast() throws IOException {
        final String host = "somehost.netty.io";
        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            String name = question.getDomainName();
            if (name.equals(host)) {
                Set<ResourceRecord> records = new HashSet<ResourceRecord>(2);
                records.add(new TestDnsServer.TestResourceRecord(name, RecordType.A,
                        Collections.<String, Object>singletonMap(DnsAttribute.IP_ADDRESS.toLowerCase(),
                                "10.0.0.1")));
                records.add(new TestDnsServer.TestResourceRecord(name, RecordType.A,
                        Collections.<String, Object>singletonMap(DnsAttribute.IP_ADDRESS.toLowerCase(),
                                "10.0.0.2")));
                return records;
            }
            return null;
        });
        dnsServer2.start(true);
        DnsNameResolver resolver = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .recursionDesired(false)
                    .queryTimeoutMillis(10000)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_PREFERRED)
                    .completeOncePreferredResolved(true)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));

            resolver = builder.build();
            List<InetAddress> addresses = resolver.resolveAll(host).syncUninterruptibly().getNow();
            assertEquals(2, addresses.size());
            for (InetAddress address: addresses) {
                assertThat(address, instanceOf(Inet4Address.class));
                assertEquals(host, address.getHostName());
            }
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }

    @Test(timeout = 5000)
    public void testTruncatedWithoutTcpFallback() throws IOException {
        testTruncated0(false, false);
    }

    @Test(timeout = 5000)
    public void testTruncatedWithTcpFallback() throws IOException {
        testTruncated0(true, false);
    }

    @Test(timeout = 5000)
    public void testTruncatedWithTcpFallbackBecauseOfMtu() throws IOException {
        testTruncated0(true, true);
    }

    private static DnsMessageModifier modifierFrom(DnsMessage message) {
        DnsMessageModifier modifier = new DnsMessageModifier();
        modifier.setAcceptNonAuthenticatedData(message.isAcceptNonAuthenticatedData());
        modifier.setAdditionalRecords(message.getAdditionalRecords());
        modifier.setAnswerRecords(message.getAnswerRecords());
        modifier.setAuthoritativeAnswer(message.isAuthoritativeAnswer());
        modifier.setAuthorityRecords(message.getAuthorityRecords());
        modifier.setMessageType(message.getMessageType());
        modifier.setOpCode(message.getOpCode());
        modifier.setQuestionRecords(message.getQuestionRecords());
        modifier.setRecursionAvailable(message.isRecursionAvailable());
        modifier.setRecursionDesired(message.isRecursionDesired());
        modifier.setReserved(message.isReserved());
        modifier.setResponseCode(message.getResponseCode());
        modifier.setTransactionId(message.getTransactionId());
        modifier.setTruncated(message.isTruncated());
        return modifier;
    }

    private static void testTruncated0(boolean tcpFallback, final boolean truncatedBecauseOfMtu) throws IOException {
        final String host = "somehost.netty.io";
        final String txt = "this is a txt record";
        final AtomicReference<DnsMessage> messageRef = new AtomicReference<DnsMessage>();

        TestDnsServer dnsServer2 = new TestDnsServer(question -> {
            String name = question.getDomainName();
            if (name.equals(host)) {
                return Collections.<ResourceRecord>singleton(
                        new TestDnsServer.TestResourceRecord(name, RecordType.TXT,
                                Collections.<String, Object>singletonMap(
                                        DnsAttribute.CHARACTER_STRING.toLowerCase(), txt)));
            }
            return null;
        }) {
            @Override
            protected DnsMessage filterMessage(DnsMessage message) {
                // Store a original message so we can replay it later on.
                messageRef.set(message);

                if (!truncatedBecauseOfMtu) {
                    // Create a copy of the message but set the truncated flag.
                    DnsMessageModifier modifier = modifierFrom(message);
                    modifier.setTruncated(true);
                    return modifier.getDnsMessage();
                }
                return message;
            }
        };
        dnsServer2.start();
        DnsNameResolver resolver = null;
        ServerSocket serverSocket = null;
        try {
            DnsNameResolverBuilder builder = newResolver()
                    .queryTimeoutMillis(10000)
                    .resolvedAddressTypes(ResolvedAddressTypes.IPV4_PREFERRED)
                    .maxQueriesPerResolve(16)
                    .nameServerProvider(new SingletonDnsServerAddressStreamProvider(dnsServer2.localAddress()));

            if (tcpFallback) {
                // If we are configured to use TCP as a fallback also bind a TCP socket
                serverSocket = new ServerSocket(dnsServer2.localAddress().getPort());
                serverSocket.setReuseAddress(true);

                builder.socketChannelType(NioSocketChannel.class);
            }
            resolver = builder.build();
            if (truncatedBecauseOfMtu) {
                resolver.ch.pipeline().addFirst(new ChannelHandler() {
                    @Override
                    public void channelRead(ChannelHandlerContext ctx, Object msg) {
                        if (msg instanceof DatagramPacket) {
                            // Truncate the packet by 1 byte.
                            DatagramPacket packet = (DatagramPacket) msg;
                            packet.content().writerIndex(packet.content().writerIndex() - 1);
                        }
                        ctx.fireChannelRead(msg);
                    }
                });
            }
            Future<AddressedEnvelope<DnsResponse, InetSocketAddress>> envelopeFuture = resolver.query(
                    new DefaultDnsQuestion(host, DnsRecordType.TXT));

            if (tcpFallback) {
                // If we are configured to use TCP as a fallback lets replay the dns message over TCP
                Socket socket = serverSocket.accept();

                InputStream in = socket.getInputStream();
                assertTrue((in.read() << 8 | (in.read() & 0xff)) > 2); // skip length field
                int txnId = in.read() << 8 | (in.read() & 0xff);

                IoBuffer ioBuffer = IoBuffer.allocate(1024);
                // Must replace the transactionId with the one from the TCP request
                DnsMessageModifier modifier = modifierFrom(messageRef.get());
                modifier.setTransactionId(txnId);
                new DnsMessageEncoder().encode(ioBuffer, modifier.getDnsMessage());
                ioBuffer.flip();

                ByteBuffer lenBuffer = ByteBuffer.allocate(2);
                lenBuffer.putShort((short) ioBuffer.remaining());
                lenBuffer.flip();

                while (lenBuffer.hasRemaining()) {
                    socket.getOutputStream().write(lenBuffer.get());
                }

                while (ioBuffer.hasRemaining()) {
                    socket.getOutputStream().write(ioBuffer.get());
                }
                socket.getOutputStream().flush();
                // Let's wait until we received the envelope before closing the socket.
                envelopeFuture.syncUninterruptibly();

                socket.close();
                serverSocket.close();
            }

            AddressedEnvelope<DnsResponse, InetSocketAddress> envelope = envelopeFuture.syncUninterruptibly().getNow();
            assertNotNull(envelope.sender());

            DnsResponse response = envelope.content();
            assertNotNull(response);

            assertEquals(DnsResponseCode.NOERROR, response.code());
            int count = response.count(DnsSection.ANSWER);

            assertEquals(1, count);
            List<String> texts = decodeTxt(response.recordAt(DnsSection.ANSWER, 0));
            assertEquals(1, texts.size());
            assertEquals(txt, texts.get(0));

            if (tcpFallback) {
                assertFalse(envelope.content().isTruncated());
            } else {
                assertTrue(envelope.content().isTruncated());
            }
            assertTrue(envelope.release());
        } finally {
            dnsServer2.stop();
            if (resolver != null) {
                resolver.close();
            }
        }
    }
}
