code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC 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 org.openqa.selenium.events.zeromq;
  
  import static org.openqa.selenium.events.zeromq.UnboundZmqEventBus.REJECTED_EVENT;
  
  import java.net.URI;
  import java.net.URISyntaxException;
  import java.util.function.Consumer;
  import org.openqa.selenium.events.EventBus;
  import org.openqa.selenium.events.EventListener;
  import org.openqa.selenium.events.EventName;
  import org.openqa.selenium.grid.config.Config;
  import org.openqa.selenium.grid.config.ConfigException;
  import org.openqa.selenium.grid.security.Secret;
  import org.openqa.selenium.grid.security.SecretOptions;
  import org.openqa.selenium.internal.Require;
  import org.openqa.selenium.json.JsonInput;
  import org.openqa.selenium.net.Urls;
  import org.zeromq.ZContext;
  
  /** An {@link EventBus} backed by ZeroMQ. */
  public class ZeroMqEventBus {
  
    private static final String EVENTS_SECTION = "events";
  
    private ZeroMqEventBus() {
      // Use the create method.
    }
  
    public static EventBus create(
        ZContext context, String publish, String subscribe, boolean bind, Secret secret) {
      if (bind) {
        return new BoundZmqEventBus(context, publish, subscribe, secret);
      }
      return new UnboundZmqEventBus(context, publish, subscribe, secret);
    }
  
    public static EventBus create(Config config) {
      String publish =
          config
              .get(EVENTS_SECTION, "publish")
              .orElseGet(
                  () -> {
                    URI uri =
                        config
                            .get("node", "hub")
                            .map(Urls::from)
                            .orElseThrow(
                                () ->
                                    new IllegalArgumentException(
                                        "Unable to find address to publish events to."));
                    return mungeUri(uri, "tcp", 4442);
                  });
  
      String subscribe =
          config
              .get(EVENTS_SECTION, "subscribe")
              .orElseGet(
                  () -> {
                    URI uri =
                        config
                            .get("node", "hub")
                            .map(Urls::from)
                            .orElseThrow(
                                () ->
                                    new IllegalArgumentException(
                                        "Unable to find address to subscribe for events from."));
                    return mungeUri(uri, "tcp", 4443);
                  });
  
      boolean bind = config.getBool(EVENTS_SECTION, "bind").orElse(false);
  
      SecretOptions secretOptions = new SecretOptions(config);
  
      return create(new ZContext(), publish, subscribe, bind, secretOptions.getRegistrationSecret());
    }
  
    private static String mungeUri(URI base, String scheme, int port) {
      try {
        return new URI(scheme, null, base.getHost(), port, null, null, null).toString();
      } catch (URISyntaxException e) {
        throw new ConfigException("Unable to create URI from " + base);
      }
    }
  
    public static EventListener<RejectedEvent> onRejectedEvent(Consumer<RejectedEvent> handler) {
      Require.nonNull("Handler", handler);
      return new EventListener<>(REJECTED_EVENT, RejectedEvent.class, handler);
    }
  
    public static class RejectedEvent {
      private final EventName name;
      private final Object data;
  
      RejectedEvent(EventName name, Object data) {
        this.name = name;
        this.data = data;
      }
  
      private static RejectedEvent fromJson(JsonInput input) {
        EventName name = null;
        Object data = null;
  
        input.beginObject();
        while (input.hasNext()) {
          switch (input.nextName()) {
            case "data":
              data = input.read(Object.class);
              break;
  
            case "name":
              name = input.read(EventName.class);
              break;
  
            default:
              input.skipValue();
              break;
          }
        }
        input.endObject();
  
        return new RejectedEvent(name, data);
      }
  
      public EventName getName() {
        return name;
      }
  
      public Object getData() {
        return data;
      }
    }
  }
  