Implement support for DNS over TCP fallback in Netty.

src/main/generated/io/vertx/core/dns/AddressResolverOptionsConverter.java

@@ -3,8 +3,6 @@
 import io.vertx.core.json.JsonObject;
 import io.vertx.core.json.JsonArray;
 import io.vertx.core.json.impl.JsonUtil;
-import java.time.Instant;
-import java.time.format.DateTimeFormatter;
 import java.util.Base64;
 
 /**
@@ -105,6 +103,11 @@ static void fromJson(Iterable<java.util.Map.Entry<String, Object>> json, Address
             obj.setServers(list);
           }
           break;
+        case "retryWithTcpOnTimeout":
+          if (member.getValue() instanceof Boolean) {
+            obj.setRetryWithTcpOnTimeout((Boolean)member.getValue());
+          }
+          break;
       }
     }
   }
@@ -141,5 +144,6 @@ static void toJson(AddressResolverOptions obj, java.util.Map<String, Object> jso
       obj.getServers().forEach(item -> array.add(item));
       json.put("servers", array);
     }
+    json.put("retryWithTcpOnTimeout", obj.isRetryWithTcpOnTimeout());
   }
 }

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

@@ -103,6 +103,11 @@ public class AddressResolverOptions {
    */
   public static final boolean DEFAULT_ROUND_ROBIN_INET_ADDRESS = false;
 
+  /**
+   * The default retry with TCP on timeout = false
+   */
+  public static final boolean DEFAULT_RETRY_WITH_TCP_ON_TIMEOUT = false;
+
   private String hostsPath;
   private Buffer hostsValue;
   private int hostsRefreshPeriod;
@@ -118,6 +123,7 @@ public class AddressResolverOptions {
   private int ndots;
   private boolean rotateServers;
   private boolean roundRobinInetAddress;
+  private boolean retryWithTcpOnTimeout;
 
   public AddressResolverOptions() {
     servers = DEFAULT_SERVERS;
@@ -133,6 +139,7 @@ public AddressResolverOptions() {
     rotateServers = DEFAULT_ROTATE_SERVERS;
     roundRobinInetAddress = DEFAULT_ROUND_ROBIN_INET_ADDRESS;
     hostsRefreshPeriod = DEFAULT_HOSTS_REFRESH_PERIOD;
+    retryWithTcpOnTimeout = DEFAULT_RETRY_WITH_TCP_ON_TIMEOUT;
   }
 
   public AddressResolverOptions(AddressResolverOptions other) {
@@ -151,6 +158,7 @@ public AddressResolverOptions(AddressResolverOptions other) {
     this.ndots = other.ndots;
     this.rotateServers = other.rotateServers;
     this.roundRobinInetAddress = other.roundRobinInetAddress;
+    this.retryWithTcpOnTimeout = other.retryWithTcpOnTimeout;
   }
 
   public AddressResolverOptions(JsonObject json) {
@@ -496,6 +504,23 @@ public AddressResolverOptions setRoundRobinInetAddress(boolean roundRobinInetAdd
     return this;
   }
 
+  /**
+   * @return the value of retry with TCP on timeout flag
+   */
+  public boolean isRetryWithTcpOnTimeout() {
+    return retryWithTcpOnTimeout;
+  }
+
+  /**
+   * Set retry with TCP on timeout flag.
+   *
+   * @return a reference to this, so the API can be used fluently
+   */
+  public AddressResolverOptions setRetryWithTcpOnTimeout(boolean retryWithTcpOnTimeout) {
+    this.retryWithTcpOnTimeout = retryWithTcpOnTimeout;
+    return this;
+  }
+
   public JsonObject toJson() {
     JsonObject json = new JsonObject();
     AddressResolverOptionsConverter.toJson(this, json);

src/main/java/io/vertx/core/impl/resolver/DnsResolverProvider.java

@@ -105,7 +105,8 @@ private DnsResolverProvider(VertxInternal vertx, AddressResolverOptions options)
     DnsNameResolverBuilder builder = new DnsNameResolverBuilder();
     builder.hostsFileEntriesResolver(this);
     builder.channelFactory(() -> vertx.transport().datagramChannel());
-    builder.socketChannelFactory(() -> (SocketChannel) vertx.transport().channelFactory(false).newChannel());
+    builder.socketChannelFactory(() ->
+        (SocketChannel) vertx.transport().channelFactory(false).newChannel(), options.isRetryWithTcpOnTimeout());
     builder.nameServerProvider(nameServerAddressProvider);
     builder.optResourceEnabled(options.isOptResourceEnabled());
     builder.resolveCache(resolveCache);