Reimplement DnsClient with DnsNameResolver

src/main/java/io/vertx/core/dns/DnsClient.java

@@ -15,8 +15,13 @@
 import io.vertx.core.Future;
 import io.vertx.codegen.annotations.VertxGen;
 
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
 import java.util.List;
 
+import static io.vertx.core.dns.impl.DnsClientImpl.HEX_TABLE;
+
 /**
  * Provides a way to asynchronously lookup information from DNS servers.
  * <p>
@@ -139,7 +144,38 @@ public interface DnsClient {
    * @return a future notified with the resolved {@link String} if a record was found. If none was found it will
    *                 get notified with {@code null}. If an error occurs it will get failed.
    */
-  Future<@Nullable String> reverseLookup(String ipaddress);
+  default Future<@Nullable String> reverseLookup(String ipaddress) {
+    try {
+      InetAddress inetAddress = InetAddress.getByName(ipaddress);
+      byte[] addr = inetAddress.getAddress();
+
+      StringBuilder reverseName = new StringBuilder(64);
+      if (inetAddress instanceof Inet4Address) {
+        // reverse ipv4 address
+        reverseName.append(addr[3] & 0xff).append(".")
+          .append(addr[2]& 0xff).append(".")
+          .append(addr[1]& 0xff).append(".")
+          .append(addr[0]& 0xff);
+      } else {
+        // It is an ipv 6 address time to reverse it
+        for (int i = 0; i < 16; i++) {
+          reverseName.append(HEX_TABLE[(addr[15 - i] & 0xf)]);
+          reverseName.append(".");
+          reverseName.append(HEX_TABLE[(addr[15 - i] >> 4) & 0xf]);
+          if (i != 15) {
+            reverseName.append(".");
+          }
+        }
+      }
+      reverseName.append(".in-addr.arpa");
+
+      return resolvePTR(reverseName.toString());
+    } catch (UnknownHostException e) {
+      // Should never happen as we work with ip addresses as input
+      // anyway just in case notify the handler
+      return Future.failedFuture(e);
+    }
+  }
 
   /**
    * Close the client.

src/main/java/io/vertx/core/dns/impl/DnsAddressResolverProvider.java

@@ -47,6 +47,7 @@ public static DnsAddressResolverProvider create(VertxInternal vertx, AddressReso
 
   private final VertxInternal vertx;
   private final List<ResolverRegistration> resolvers = Collections.synchronizedList(new ArrayList<>());
+  private final DnsNameResolverBuilder dnsNameResolverBuilder;
   private AddressResolverGroup<InetSocketAddress> resolverGroup;
   private final List<InetSocketAddress> serverList = new ArrayList<>();
   private final String hostsPath;
@@ -113,6 +114,9 @@ private DnsAddressResolverProvider(VertxInternal vertx, AddressResolverOptions o
     builder.queryTimeoutMillis(options.getQueryTimeout());
     builder.maxQueriesPerResolve(options.getMaxQueries());
     builder.recursionDesired(options.getRdFlag());
+    builder.completeOncePreferredResolved(true);
+    builder.consolidateCacheSize(1024);
+    builder.ndots(1);
     if (options.getSearchDomains() != null) {
       builder.searchDomains(options.getSearchDomains());
       int ndots = options.getNdots();
@@ -122,6 +126,7 @@ private DnsAddressResolverProvider(VertxInternal vertx, AddressResolverOptions o
       builder.ndots(ndots);
     }
 
+    this.dnsNameResolverBuilder = builder;
     this.resolverGroup = new DnsAddressResolverGroup(builder) {
       @Override
       protected io.netty.resolver.AddressResolver<InetSocketAddress> newAddressResolver(EventLoop eventLoop, NameResolver<InetAddress> resolver) throws Exception {
@@ -168,6 +173,10 @@ InetAddress lookup(String inetHost, ResolvedAddressTypes resolvedAddressTypes) {
     }
   }
 
+  public DnsNameResolverBuilder getDnsNameResolverBuilder() {
+    return dnsNameResolverBuilder;
+  }
+
   /**
    * @return a list of DNS servers available to use
    */