Most proper clean way of using a DnsAddressResolverGroup with AHC

Let us never speak of this again.

proxy/src/main/java/com/velocitypowered/proxy/network/ConnectionManager.java

@@ -6,6 +6,7 @@ import static org.asynchttpclient.Dsl.config;
 import com.google.common.base.Preconditions;
 import com.velocitypowered.natives.util.Natives;
 import com.velocitypowered.proxy.VelocityServer;
+import com.velocitypowered.proxy.network.netty.DnsAddressResolverGroupNameResolverAdapter;
 import com.velocitypowered.proxy.protocol.netty.GS4QueryHandler;
 import io.netty.bootstrap.Bootstrap;
 import io.netty.bootstrap.ServerBootstrap;
@@ -16,6 +17,7 @@ import io.netty.channel.EventLoopGroup;
 import io.netty.channel.WriteBufferWaterMark;
 import io.netty.resolver.dns.DnsAddressResolverGroup;
 import io.netty.resolver.dns.DnsNameResolverBuilder;
+import io.netty.util.concurrent.EventExecutor;
 import java.net.InetSocketAddress;
 import java.util.HashMap;
 import java.util.Map;
@@ -59,13 +61,10 @@ public final class ConnectionManager {
     this.workerGroup = this.transportType.createEventLoopGroup(TransportType.Type.WORKER);
     this.serverChannelInitializer = new ServerChannelInitializerHolder(
         new ServerChannelInitializer(this.server));
-
-    DnsNameResolverBuilder builder = new DnsNameResolverBuilder()
+    this.resolverGroup = new DnsAddressResolverGroup(new DnsNameResolverBuilder()
         .channelType(this.transportType.datagramChannelClass)
         .negativeTtl(15)
-        .ndots(1);
-
-    this.resolverGroup = new DnsAddressResolverGroup(builder);
+        .ndots(1));
     this.httpClient = asyncHttpClient(config()
         .setEventLoopGroup(this.workerGroup)
         .setUserAgent(server.getVersion().getName() + "/" + server.getVersion().getVersion())
@@ -74,7 +73,9 @@ public final class ConnectionManager {
           public <T> FilterContext<T> filter(FilterContext<T> ctx) throws FilterException {
             return new FilterContextBuilder<>(ctx)
                 .request(new RequestBuilder(ctx.getRequest())
-                    .setNameResolver(builder.eventLoop(workerGroup.next()).build())
+                    .setNameResolver(
+                        new DnsAddressResolverGroupNameResolverAdapter(resolverGroup, workerGroup)
+                    )
                     .build())
                 .build();
           }

proxy/src/main/java/com/velocitypowered/proxy/network/netty/DnsAddressResolverGroupNameResolverAdapter.java

@@ -0,0 +1,68 @@
+package com.velocitypowered.proxy.network.netty;
+
+import io.netty.channel.EventLoopGroup;
+import io.netty.resolver.InetNameResolver;
+import io.netty.resolver.dns.DnsAddressResolverGroup;
+import io.netty.util.concurrent.EventExecutor;
+import io.netty.util.concurrent.FutureListener;
+import io.netty.util.concurrent.ImmediateEventExecutor;
+import io.netty.util.concurrent.Promise;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.util.ArrayList;
+import java.util.List;
+
+public class DnsAddressResolverGroupNameResolverAdapter extends InetNameResolver {
+
+  private final DnsAddressResolverGroup resolverGroup;
+  private final EventLoopGroup group;
+
+  public DnsAddressResolverGroupNameResolverAdapter(
+      DnsAddressResolverGroup resolverGroup, EventLoopGroup group) {
+    super(ImmediateEventExecutor.INSTANCE);
+    this.resolverGroup = resolverGroup;
+    this.group = group;
+  }
+
+  @Override
+  protected void doResolve(String inetHost, Promise<InetAddress> promise) throws Exception {
+    EventExecutor executor = this.findExecutor();
+    resolverGroup.getResolver(executor).resolve(InetSocketAddress.createUnresolved(inetHost, 17))
+        .addListener((FutureListener<InetSocketAddress>) future -> {
+          if (future.isSuccess()) {
+            promise.trySuccess(future.getNow().getAddress());
+          } else {
+            promise.tryFailure(future.cause());
+          }
+        });
+  }
+
+  @Override
+  protected void doResolveAll(String inetHost, Promise<List<InetAddress>> promise)
+      throws Exception {
+    EventExecutor executor = this.findExecutor();
+    resolverGroup.getResolver(executor).resolveAll(InetSocketAddress.createUnresolved(inetHost, 17))
+        .addListener((FutureListener<List<InetSocketAddress>>) future -> {
+          if (future.isSuccess()) {
+            List<InetAddress> addresses = new ArrayList<>(future.getNow().size());
+            for (InetSocketAddress address : future.getNow()) {
+              addresses.add(address.getAddress());
+            }
+            promise.trySuccess(addresses);
+          } else {
+            promise.tryFailure(future.cause());
+          }
+        });
+  }
+
+  private EventExecutor findExecutor() {
+    for (EventExecutor executor : group) {
+      if (executor.inEventLoop()) {
+        return executor;
+      }
+    }
+
+    // otherwise, pick one
+    return group.next();
+  }
+}