/**
    *
    * 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.hadoop.hbase.client;
  
  import java.io.IOException;
  import java.lang.management.ManagementFactory;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.Addressing;
  import org.apache.hadoop.hbase.util.Bytes;
  
  /**
   * The class that is able to determine some unique strings for the client,
   * such as an IP address, PID, and composite deterministic ID.
   */
  @InterfaceAudience.Private
  class ClientIdGenerator {
    private static final Log LOG = LogFactory.getLog(ClientIdGenerator.class);
  
    /**
     * @return a unique ID incorporating IP address, PID, TID and timer. Might be an overkill...
     * Note though that new UUID in java by default is just a random number.
     */
    public static byte[] generateClientId() {
      byte[] selfBytes = getIpAddressBytes();
      Long pid = getPid();
      long tid = Thread.currentThread().getId();
      long ts = System.currentTimeMillis();
  
      byte[] id = new byte[selfBytes.length + ((pid != null ? 1 : 0) + 2) * Bytes.SIZEOF_LONG];
      int offset = Bytes.putBytes(id, 0, selfBytes, 0, selfBytes.length);
      if (pid != null) {
        offset = Bytes.putLong(id, offset, pid);
      }
      offset = Bytes.putLong(id, offset, tid);
      offset = Bytes.putLong(id, offset, ts);
      assert offset == id.length;
      return id;
    }
  
    /**
     * @return PID of the current process, if it can be extracted from JVM name, or null.
     */
    public static Long getPid() {
      String name = ManagementFactory.getRuntimeMXBean().getName();
      String[] nameParts = name.split("@");
      if (nameParts.length == 2) { // 12345@somewhere
        try {
          return Long.parseLong(nameParts[0]);
        } catch (NumberFormatException ex) {
          LOG.warn("Failed to get PID from [" + name + "]", ex);
        }
      } else {
        LOG.warn("Don't know how to get PID from [" + name + "]");
      }
      return null;
    }
  
    /**
     * @return Some IPv4/IPv6 address available on the current machine that is up, not virtual
     *         and not a loopback address. Empty array if none can be found or error occured.
     */
    public static byte[] getIpAddressBytes() {
      try {
        return Addressing.getIpAddress().getAddress();
      } catch (IOException ex) {
        LOG.warn("Failed to get IP address bytes", ex);
      }
      return new byte[0];
    }
  }