content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF 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.apache.spark.launcher;
  
  import java.io.Serializable;
  
  /**
   * Message definitions for the launcher communication protocol. These messages must remain
   * backwards-compatible, so that the launcher can talk to older versions of Spark that support
   * the protocol.
   */
  final class LauncherProtocol {
  
    /** Environment variable where the server port is stored. */
    static final String ENV_LAUNCHER_PORT = "_SPARK_LAUNCHER_PORT";
  
    /** Environment variable where the secret for connecting back to the server is stored. */
    static final String ENV_LAUNCHER_SECRET = "_SPARK_LAUNCHER_SECRET";
  
    static class Message implements Serializable {
  
    }
  
    /**
     * Hello message, sent from client to server.
     */
    static class Hello extends Message {
  
      final String secret;
      final String sparkVersion;
  
      Hello(String secret, String version) {
        this.secret = secret;
        this.sparkVersion = version;
      }
  
    }
  
    /**
     * SetAppId message, sent from client to server.
     */
    static class SetAppId extends Message {
  
      final String appId;
  
      SetAppId(String appId) {
        this.appId = appId;
      }
  
    }
  
    /**
     * SetState message, sent from client to server.
     */
    static class SetState extends Message {
  
      final SparkAppHandle.State state;
  
      SetState(SparkAppHandle.State state) {
        this.state = state;
      }
  
    }
  
    /**
     * Stop message, send from server to client to stop the application.
     */
    static class Stop extends Message {
  
    }
  
  }
  