content: /*
   * Copyright (c) 2024, Alibaba Cloud;
   * Licensed 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 com.aliyun.dataworks.migrationx.transformer.core.spark.command;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.net.InetAddress;
  import java.net.InetSocketAddress;
  import java.net.ServerSocket;
  import java.net.Socket;
  import java.security.SecureRandom;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Map;
  import java.util.TimerTask;
  import java.util.concurrent.*;
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  /**
   * A server that listens locally for connections from client launched by the library. Each client has a secret that it
   * needs to send to the server to identify itself and establish the session.
   * <p>
   * I/O is currently blocking (one thread per client). Clients have a limited time to connect back to the server,
   * otherwise the server will ignore the connection.
   * <p>
   * === Architecture Overview ===
   * <p>
   * The launcher server is used when Spark apps are launched as separate processes than the calling app. It looks more or
   * less like the following:
   * <p>
   * -----------------------                       ----------------------- |      User App       |     spark-submit      |
   * Spark App      | |                     |  -------------------> |                     | |         ------------|
   * |-------------        | |         |           |        hello          |            |        | | | L. Server
   * |<----------------------| L. Backend |        | |         |           |                       | |        | |
   * -------------                       ----------------------- |               |     | ^ |               v     |
   *                      | |        -------------| | |        |            |      <per-app channel>       | |        |
   * App Handle |<------------------------------ |        |            | -----------------------
   * <p>
   * The server is started on demand and remains active while there are active or outstanding clients, to avoid opening
   * too many ports when multiple clients are launched. Each client is given a unique secret, and have a limited amount of
   * time to connect back ({@link SparkLauncher#CHILD_CONNECTION_TIMEOUT}), at which point the server will throw away that
   * client's state. A client is only allowed to connect back to the server once.
   * <p>
   * The launcher server listens on the localhost only, so it doesn't need access controls (aside from the per-app secret)
   * nor encryption. It thus requires that the launched app has a local process that communicates with the server. In
   * cluster mode, this means that the client that launches the application must remain alive for the duration of the
   * application (or until the app handle is disconnected).
   */
  class LauncherServer implements Closeable {
  
      private static final Logger LOG = Logger.getLogger(LauncherServer.class.getName());
      private static final String THREAD_NAME_FMT = "LauncherServer-%d";
      private static final long DEFAULT_CONNECT_TIMEOUT = 10000L;
  
      /**
       * For creating secrets used for communication with child processes.
       */
      private static final SecureRandom RND = new SecureRandom();
  
      private static volatile LauncherServer serverInstance;
  
      static synchronized LauncherServer getOrCreateServer() throws IOException {
          LauncherServer server;
          do {
              server = serverInstance != null ? serverInstance : new LauncherServer();
          } while (!server.running);
  
          server.ref();
          serverInstance = server;
          return server;
      }
  
      // For testing.
      static synchronized LauncherServer getServer() {
          return serverInstance;
      }
  
      private final AtomicLong refCount;
      private final AtomicLong threadIds;
      private final ConcurrentMap<String, AbstractAppHandle> secretToPendingApps;
      private final List<ServerConnection> clients;
      private final ServerSocket server;
      private final Thread serverThread;
      private final ThreadFactory factory;
      private final ScheduledExecutorService scheduledExecutorService;
  
      private volatile boolean running;
  
      private LauncherServer() throws IOException {
          this.refCount = new AtomicLong(0);
  
          ServerSocket server = new ServerSocket();
          try {
              server.setReuseAddress(true);
              server.bind(new InetSocketAddress(InetAddress.getLoopbackAddress(), 0));
  
              this.clients = new ArrayList<>();
              this.threadIds = new AtomicLong();
              this.factory = new NamedThreadFactory(THREAD_NAME_FMT);
              this.secretToPendingApps = new ConcurrentHashMap<>();
              this.scheduledExecutorService = Executors.newScheduledThreadPool(5);
              this.server = server;
              this.running = true;
  
              this.serverThread = factory.newThread(this::acceptConnections);
              serverThread.start();
          } catch (IOException ioe) {
              close();
              throw ioe;
          } catch (Exception e) {
              close();
              throw new IOException(e);
          }
      }
  
      /**
       * Registers a handle with the server, and returns the secret the child app needs to connect back.
       */
      synchronized String registerHandle(AbstractAppHandle handle) {
          String secret = createSecret();
          secretToPendingApps.put(secret, handle);
          return secret;
      }
  
      @Override
      public void close() throws IOException {
          synchronized (this) {
              if (!running) {
                  return;
              }
              running = false;
          }
  
          synchronized (LauncherServer.class) {
              serverInstance = null;
          }
  
          scheduledExecutorService.shutdownNow();
  
          server.close();
          synchronized (clients) {
              List<ServerConnection> copy = new ArrayList<>(clients);
              clients.clear();
              for (ServerConnection client : copy) {
                  client.close();
              }
          }
  
          if (serverThread != null) {
              try {
                  serverThread.join();
              } catch (InterruptedException ie) {
                  // no-op
              }
          }
      }
  
      void ref() {
          refCount.incrementAndGet();
      }
  
      void unref() {
          synchronized (LauncherServer.class) {
              if (refCount.decrementAndGet() == 0) {
                  try {
                      close();
                  } catch (IOException ioe) {
                      // no-op.
                  }
              }
          }
      }
  
      int getPort() {
          return server.getLocalPort();
      }
  
      /**
       * Removes the client handle from the pending list (in case it's still there), and unrefs the server.
       */
      void unregister(AbstractAppHandle handle) {
          for (Map.Entry<String, AbstractAppHandle> e : secretToPendingApps.entrySet()) {
              if (e.getValue().equals(handle)) {
                  String secret = e.getKey();
                  secretToPendingApps.remove(secret);
                  break;
              }
          }
  
          unref();
      }
  
      private void acceptConnections() {
          try {
              while (running) {
                  final Socket client = server.accept();
                  TimerTask timeout = new TimerTask() {
                      @Override
                      public void run() {
                          LOG.warning("Timed out waiting for hello message from client.");
                          try {
                              client.close();
                          } catch (IOException ioe) {
                              // no-op.
                          }
                      }
                  };
                  ServerConnection clientConnection = new ServerConnection(client, timeout);
                  Thread clientThread = factory.newThread(clientConnection);
                  clientConnection.setConnectionThread(clientThread);
                  synchronized (clients) {
                      clients.add(clientConnection);
                  }
  
                  long timeoutMs = getConnectionTimeout();
                  // 0 is used for testing to avoid issues with clock resolution / thread scheduling,
                  // and force an immediate timeout.
                  if (timeoutMs > 0) {
                      scheduledExecutorService.schedule(timeout, timeoutMs, TimeUnit.MILLISECONDS);
                  } else {
                      timeout.run();
                  }
  
                  clientThread.start();
              }
          } catch (IOException ioe) {
              if (running) {
                  LOG.log(Level.SEVERE, "Error in accept loop.", ioe);
              }
          }
      }
  
      private long getConnectionTimeout() {
          String value = SparkLauncher.launcherConfig.get(SparkLauncher.CHILD_CONNECTION_TIMEOUT);
          return (value != null) ? Long.parseLong(value) : DEFAULT_CONNECT_TIMEOUT;
      }
  
      private String createSecret() {
          while (true) {
              byte[] secret = new byte[128];
              RND.nextBytes(secret);
  
              StringBuilder sb = new StringBuilder();
              for (byte b : secret) {
                  int ival = b >= 0 ? b : Byte.MAX_VALUE - b;
                  if (ival < 0x10) {
                      sb.append("0");
                  }
                  sb.append(Integer.toHexString(ival));
              }
  
              String secretStr = sb.toString();
              if (!secretToPendingApps.containsKey(secretStr)) {
                  return secretStr;
              }
          }
      }
  
      class ServerConnection extends LauncherConnection {
  
          private TimerTask timeout;
          private volatile Thread connectionThread;
          private volatile AbstractAppHandle handle;
  
          ServerConnection(Socket socket, TimerTask timeout) throws IOException {
              super(socket);
              this.timeout = timeout;
          }
  
          void setConnectionThread(Thread t) {
              this.connectionThread = t;
          }
  
          @Override
          protected void handle(LauncherProtocol.Message msg) throws IOException {
              try {
                  if (msg instanceof LauncherProtocol.Hello) {
                      timeout.cancel();
                      timeout = null;
                      LauncherProtocol.Hello hello = (LauncherProtocol.Hello)msg;
                      AbstractAppHandle handle = secretToPendingApps.remove(hello.secret);
                      if (handle != null) {
                          handle.setConnection(this);
                          handle.setState(SparkAppHandle.State.CONNECTED);
                          this.handle = handle;
                      } else {
                          throw new IllegalArgumentException("Received Hello for unknown client.");
                      }
                  } else {
                      String msgClassName = msg != null ? msg.getClass().getName() : "no message";
                      if (handle == null) {
                          throw new IllegalArgumentException("Expected hello, got: " + msgClassName);
                      }
                      if (msg instanceof LauncherProtocol.SetAppId) {
                          LauncherProtocol.SetAppId set = (LauncherProtocol.SetAppId)msg;
                          handle.setAppId(set.appId);
                      } else if (msg instanceof LauncherProtocol.SetState) {
                          handle.setState(((LauncherProtocol.SetState)msg).state);
                      } else {
                          throw new IllegalArgumentException("Invalid message: " + msgClassName);
                      }
                  }
              } catch (Exception e) {
                  LOG.log(Level.INFO, "Error handling message from client.", e);
                  if (timeout != null) {
                      timeout.cancel();
                  }
                  close();
                  if (handle != null) {
                      handle.dispose();
                  }
              }
          }
  
          @Override
          public void close() throws IOException {
              if (!isOpen()) {
                  return;
              }
  
              synchronized (clients) {
                  clients.remove(this);
              }
  
              super.close();
          }
  
          /**
           * Wait for the remote side to close the connection so that any pending data is processed. This ensures any
           * changes reported by the child application take effect.
           * <p>
           * This method allows a short period for the above to happen (same amount of time as the connection timeout,
           * which is configurable). This should be fine for well-behaved applications, where they close the connection
           * arond the same time the app handle detects the app has finished.
           * <p>
           * In case the connection is not closed within the grace period, this method forcefully closes it and any
           * subsequent data that may arrive will be ignored.
           */
          public void waitForClose() throws IOException {
              Thread connThread = this.connectionThread;
              if (Thread.currentThread() != connThread) {
                  try {
                      connThread.join(getConnectionTimeout());
                  } catch (InterruptedException ie) {
                      // Ignore.
                  }
  
                  if (connThread.isAlive()) {
                      LOG.log(Level.WARNING, "Timed out waiting for child connection to close.");
                      close();
                  }
              }
          }
  
      }
  
  }
  