/**
    *
    * 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.zookeeper;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.net.InetSocketAddress;
  import java.net.Socket;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Deque;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  
  import javax.security.auth.login.AppConfigurationEntry;
  import javax.security.auth.login.AppConfigurationEntry.LoginModuleControlFlag;
  
  import org.apache.commons.lang.StringUtils;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.AuthUtil;
  import org.apache.hadoop.hbase.HBaseConfiguration;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.exceptions.DeserializationException;
  import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
  import org.apache.hadoop.hbase.protobuf.generated.ClusterStatusProtos;
  import org.apache.hadoop.hbase.protobuf.generated.ClusterStatusProtos.RegionStoreSequenceIds;
  import org.apache.hadoop.hbase.protobuf.generated.ZooKeeperProtos;
  import org.apache.hadoop.hbase.replication.ReplicationStateZKBase;
  import org.apache.hadoop.hbase.security.Superusers;
  import org.apache.hadoop.hbase.util.ByteStringer;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.Threads;
  import org.apache.hadoop.hbase.zookeeper.ZKUtil.ZKUtilOp.CreateAndFailSilent;
  import org.apache.hadoop.hbase.zookeeper.ZKUtil.ZKUtilOp.DeleteNodeFailSilent;
  import org.apache.hadoop.hbase.zookeeper.ZKUtil.ZKUtilOp.SetData;
  import org.apache.hadoop.security.SecurityUtil;
  import org.apache.hadoop.security.authentication.util.KerberosUtil;
  import org.apache.zookeeper.AsyncCallback;
  import org.apache.zookeeper.CreateMode;
  import org.apache.zookeeper.KeeperException;
  import org.apache.zookeeper.KeeperException.NoNodeException;
  import org.apache.zookeeper.Op;
  import org.apache.zookeeper.Watcher;
  import org.apache.zookeeper.ZooDefs.Ids;
  import org.apache.zookeeper.ZooDefs.Perms;
  import org.apache.zookeeper.ZooKeeper;
  import org.apache.zookeeper.client.ZooKeeperSaslClient;
  import org.apache.zookeeper.data.ACL;
  import org.apache.zookeeper.data.Id;
  import org.apache.zookeeper.data.Stat;
  import org.apache.zookeeper.proto.CreateRequest;
  import org.apache.zookeeper.proto.DeleteRequest;
  import org.apache.zookeeper.proto.SetDataRequest;
  import org.apache.zookeeper.server.ZooKeeperSaslServer;
  
  import com.google.protobuf.InvalidProtocolBufferException;
  
  /**
   * Internal HBase utility class for ZooKeeper.
   *
   * <p>Contains only static methods and constants.
   *
   * <p>Methods all throw {@link KeeperException} if there is an unexpected
   * zookeeper exception, so callers of these methods must handle appropriately.
   * If ZK is required for the operation, the server will need to be aborted.
   */
  @InterfaceAudience.Private
  public class ZKUtil {
    private static final Log LOG = LogFactory.getLog(ZKUtil.class);
  
    // TODO: Replace this with ZooKeeper constant when ZOOKEEPER-277 is resolved.
    public static final char ZNODE_PATH_SEPARATOR = '/';
    private static int zkDumpConnectionTimeOut;
  
    /**
    * Creates a new connection to ZooKeeper, pulling settings and ensemble config
    * from the specified configuration object using methods from {@link ZKConfig}.
    *
    * Sets the connection status monitoring watcher to the specified watcher.
    *
    * @param conf configuration to pull ensemble and other settings from
    * @param watcher watcher to monitor connection changes
    * @return connection to zookeeper
    * @throws IOException if unable to connect to zk or config problem
    */
   public static RecoverableZooKeeper connect(Configuration conf, Watcher watcher)
   throws IOException {
     String ensemble = ZKConfig.getZKQuorumServersString(conf);
     return connect(conf, ensemble, watcher);
   }
 
   public static RecoverableZooKeeper connect(Configuration conf, String ensemble,
       Watcher watcher)
   throws IOException {
     return connect(conf, ensemble, watcher, null);
   }
 
   public static RecoverableZooKeeper connect(Configuration conf, String ensemble,
       Watcher watcher, final String identifier)
   throws IOException {
     if(ensemble == null) {
       throw new IOException("Unable to determine ZooKeeper ensemble");
     }
     int timeout = conf.getInt(HConstants.ZK_SESSION_TIMEOUT,
         HConstants.DEFAULT_ZK_SESSION_TIMEOUT);
     if (LOG.isTraceEnabled()) {
       LOG.trace(identifier + " opening connection to ZooKeeper ensemble=" + ensemble);
     }
     int retry = conf.getInt("zookeeper.recovery.retry", 3);
     int retryIntervalMillis =
       conf.getInt("zookeeper.recovery.retry.intervalmill", 1000);
     int maxSleepTime = conf.getInt("zookeeper.recovery.retry.maxsleeptime", 60000);
     zkDumpConnectionTimeOut = conf.getInt("zookeeper.dump.connection.timeout",
         1000);
     return new RecoverableZooKeeper(ensemble, timeout, watcher,
         retry, retryIntervalMillis, maxSleepTime, identifier);
   }
 
   /**
    * Log in the current zookeeper server process using the given configuration
    * keys for the credential file and login principal.
    *
    * <p><strong>This is only applicable when running on secure hbase</strong>
    * On regular HBase (without security features), this will safely be ignored.
    * </p>
    *
    * @param conf The configuration data to use
    * @param keytabFileKey Property key used to configure the path to the credential file
    * @param userNameKey Property key used to configure the login principal
    * @param hostname Current hostname to use in any credentials
    * @throws IOException underlying exception from SecurityUtil.login() call
    */
   public static void loginServer(Configuration conf, String keytabFileKey,
       String userNameKey, String hostname) throws IOException {
     login(conf, keytabFileKey, userNameKey, hostname,
           ZooKeeperSaslServer.LOGIN_CONTEXT_NAME_KEY,
           JaasConfiguration.SERVER_KEYTAB_KERBEROS_CONFIG_NAME);
   }
 
   /**
    * Log in the current zookeeper client using the given configuration
    * keys for the credential file and login principal.
    *
    * <p><strong>This is only applicable when running on secure hbase</strong>
    * On regular HBase (without security features), this will safely be ignored.
    * </p>
    *
    * @param conf The configuration data to use
    * @param keytabFileKey Property key used to configure the path to the credential file
    * @param userNameKey Property key used to configure the login principal
    * @param hostname Current hostname to use in any credentials
    * @throws IOException underlying exception from SecurityUtil.login() call
    */
   public static void loginClient(Configuration conf, String keytabFileKey,
       String userNameKey, String hostname) throws IOException {
     login(conf, keytabFileKey, userNameKey, hostname,
           ZooKeeperSaslClient.LOGIN_CONTEXT_NAME_KEY,
           JaasConfiguration.CLIENT_KEYTAB_KERBEROS_CONFIG_NAME);
   }
 
   /**
    * Log in the current process using the given configuration keys for the
    * credential file and login principal.
    *
    * <p><strong>This is only applicable when running on secure hbase</strong>
    * On regular HBase (without security features), this will safely be ignored.
    * </p>
    *
    * @param conf The configuration data to use
    * @param keytabFileKey Property key used to configure the path to the credential file
    * @param userNameKey Property key used to configure the login principal
    * @param hostname Current hostname to use in any credentials
    * @param loginContextProperty property name to expose the entry name
    * @param loginContextName jaas entry name
    * @throws IOException underlying exception from SecurityUtil.login() call
    */
   private static void login(Configuration conf, String keytabFileKey,
       String userNameKey, String hostname,
       String loginContextProperty, String loginContextName)
       throws IOException {
     if (!isSecureZooKeeper(conf))
       return;
 
     // User has specified a jaas.conf, keep this one as the good one.
     // HBASE_OPTS="-Djava.security.auth.login.config=jaas.conf"
     if (System.getProperty("java.security.auth.login.config") != null)
       return;
 
     // No keytab specified, no auth
     String keytabFilename = conf.get(keytabFileKey);
     if (keytabFilename == null) {
       LOG.warn("no keytab specified for: " + keytabFileKey);
       return;
     }
 
     String principalConfig = conf.get(userNameKey, System.getProperty("user.name"));
     String principalName = SecurityUtil.getServerPrincipal(principalConfig, hostname);
 
     // Initialize the "jaas.conf" for keyTab/principal,
     // If keyTab is not specified use the Ticket Cache.
     // and set the zookeeper login context name.
     JaasConfiguration jaasConf = new JaasConfiguration(loginContextName,
         principalName, keytabFilename);
     javax.security.auth.login.Configuration.setConfiguration(jaasConf);
     System.setProperty(loginContextProperty, loginContextName);
   }
 
   /**
    * A JAAS configuration that defines the login modules that we want to use for login.
    */
   private static class JaasConfiguration extends javax.security.auth.login.Configuration {
     private static final String SERVER_KEYTAB_KERBEROS_CONFIG_NAME =
       "zookeeper-server-keytab-kerberos";
     private static final String CLIENT_KEYTAB_KERBEROS_CONFIG_NAME =
       "zookeeper-client-keytab-kerberos";
 
     private static final Map<String, String> BASIC_JAAS_OPTIONS =
       new HashMap<String,String>();
     static {
       String jaasEnvVar = System.getenv("HBASE_JAAS_DEBUG");
       if (jaasEnvVar != null && "true".equalsIgnoreCase(jaasEnvVar)) {
         BASIC_JAAS_OPTIONS.put("debug", "true");
       }
     }
 
     private static final Map<String,String> KEYTAB_KERBEROS_OPTIONS =
       new HashMap<String,String>();
     static {
       KEYTAB_KERBEROS_OPTIONS.put("doNotPrompt", "true");
       KEYTAB_KERBEROS_OPTIONS.put("storeKey", "true");
       KEYTAB_KERBEROS_OPTIONS.put("refreshKrb5Config", "true");
       KEYTAB_KERBEROS_OPTIONS.putAll(BASIC_JAAS_OPTIONS);
     }
 
     private static final AppConfigurationEntry KEYTAB_KERBEROS_LOGIN =
       new AppConfigurationEntry(KerberosUtil.getKrb5LoginModuleName(),
                                 LoginModuleControlFlag.REQUIRED,
                                 KEYTAB_KERBEROS_OPTIONS);
 
     private static final AppConfigurationEntry[] KEYTAB_KERBEROS_CONF =
       new AppConfigurationEntry[]{KEYTAB_KERBEROS_LOGIN};
 
     private javax.security.auth.login.Configuration baseConfig;
     private final String loginContextName;
     private final boolean useTicketCache;
     private final String keytabFile;
     private final String principal;
 
     public JaasConfiguration(String loginContextName, String principal) {
       this(loginContextName, principal, null, true);
     }
 
     public JaasConfiguration(String loginContextName, String principal, String keytabFile) {
       this(loginContextName, principal, keytabFile, keytabFile == null || keytabFile.length() == 0);
     }
 
     private JaasConfiguration(String loginContextName, String principal,
                              String keytabFile, boolean useTicketCache) {
       try {
         this.baseConfig = javax.security.auth.login.Configuration.getConfiguration();
       } catch (SecurityException e) {
         this.baseConfig = null;
       }
       this.loginContextName = loginContextName;
       this.useTicketCache = useTicketCache;
       this.keytabFile = keytabFile;
       this.principal = principal;
       LOG.info("JaasConfiguration loginContextName=" + loginContextName +
                " principal=" + principal + " useTicketCache=" + useTicketCache +
                " keytabFile=" + keytabFile);
     }
 
     @Override
     public AppConfigurationEntry[] getAppConfigurationEntry(String appName) {
       if (loginContextName.equals(appName)) {
         if (!useTicketCache) {
           KEYTAB_KERBEROS_OPTIONS.put("keyTab", keytabFile);
           KEYTAB_KERBEROS_OPTIONS.put("useKeyTab", "true");
         }
         KEYTAB_KERBEROS_OPTIONS.put("principal", principal);
         KEYTAB_KERBEROS_OPTIONS.put("useTicketCache", useTicketCache ? "true" : "false");
         return KEYTAB_KERBEROS_CONF;
       }
       if (baseConfig != null) return baseConfig.getAppConfigurationEntry(appName);
       return(null);
     }
   }
 
   //
   // Helper methods
   //
 
   /**
    * Join the prefix znode name with the suffix znode name to generate a proper
    * full znode name.
    *
    * Assumes prefix does not end with slash and suffix does not begin with it.
    *
    * @param prefix beginning of znode name
    * @param suffix ending of znode name
    * @return result of properly joining prefix with suffix
    */
   public static String joinZNode(String prefix, String suffix) {
     return prefix + ZNODE_PATH_SEPARATOR + suffix;
   }
 
   /**
    * Returns the full path of the immediate parent of the specified node.
    * @param node path to get parent of
    * @return parent of path, null if passed the root node or an invalid node
    */
   public static String getParent(String node) {
     int idx = node.lastIndexOf(ZNODE_PATH_SEPARATOR);
     return idx <= 0 ? null : node.substring(0, idx);
   }
 
   /**
    * Get the name of the current node from the specified fully-qualified path.
    * @param path fully-qualified path
    * @return name of the current node
    */
   public static String getNodeName(String path) {
     return path.substring(path.lastIndexOf("/")+1);
   }
 
   //
   // Existence checks and watches
   //
 
   /**
    * Watch the specified znode for delete/create/change events.  The watcher is
    * set whether or not the node exists.  If the node already exists, the method
    * returns true.  If the node does not exist, the method returns false.
    *
    * @param zkw zk reference
    * @param znode path of node to watch
    * @return true if znode exists, false if does not exist or error
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static boolean watchAndCheckExists(ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     try {
       Stat s = zkw.getRecoverableZooKeeper().exists(znode, zkw);
       boolean exists = s != null ? true : false;
       if (exists) {
         LOG.debug(zkw.prefix("Set watcher on existing znode=" + znode));
       } else {
         LOG.debug(zkw.prefix("Set watcher on znode that does not yet exist, " + znode));
       }
       return exists;
     } catch (KeeperException e) {
       LOG.warn(zkw.prefix("Unable to set watcher on znode " + znode), e);
       zkw.keeperException(e);
       return false;
     } catch (InterruptedException e) {
       LOG.warn(zkw.prefix("Unable to set watcher on znode " + znode), e);
       zkw.interruptedException(e);
       return false;
     }
   }
 
   /**
    * Watch the specified znode, but only if exists. Useful when watching
    * for deletions. Uses .getData() (and handles NoNodeException) instead
    * of .exists() to accomplish this, as .getData() will only set a watch if
    * the znode exists.
    * @param zkw zk reference
    * @param znode path of node to watch
    * @return true if the watch is set, false if node does not exists
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static boolean setWatchIfNodeExists(ZooKeeperWatcher zkw, String znode)
       throws KeeperException {
     try {
       zkw.getRecoverableZooKeeper().getData(znode, true, null);
       return true;
     } catch (NoNodeException e) {
       return false;
     } catch (InterruptedException e) {
       LOG.warn(zkw.prefix("Unable to set watcher on znode " + znode), e);
       zkw.interruptedException(e);
       return false;
     }
   }
 
   /**
    * Check if the specified node exists.  Sets no watches.
    *
    * @param zkw zk reference
    * @param znode path of node to watch
    * @return version of the node if it exists, -1 if does not exist
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static int checkExists(ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     try {
       Stat s = zkw.getRecoverableZooKeeper().exists(znode, null);
       return s != null ? s.getVersion() : -1;
     } catch (KeeperException e) {
       LOG.warn(zkw.prefix("Unable to set watcher on znode (" + znode + ")"), e);
       zkw.keeperException(e);
       return -1;
     } catch (InterruptedException e) {
       LOG.warn(zkw.prefix("Unable to set watcher on znode (" + znode + ")"), e);
       zkw.interruptedException(e);
       return -1;
     }
   }
 
   //
   // Znode listings
   //
 
   /**
    * Lists the children znodes of the specified znode.  Also sets a watch on
    * the specified znode which will capture a NodeDeleted event on the specified
    * znode as well as NodeChildrenChanged if any children of the specified znode
    * are created or deleted.
    *
    * Returns null if the specified node does not exist.  Otherwise returns a
    * list of children of the specified node.  If the node exists but it has no
    * children, an empty list will be returned.
    *
    * @param zkw zk reference
    * @param znode path of node to list and watch children of
    * @return list of children of the specified node, an empty list if the node
    *          exists but has no children, and null if the node does not exist
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static List<String> listChildrenAndWatchForNewChildren(
       ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     try {
       List<String> children = zkw.getRecoverableZooKeeper().getChildren(znode, zkw);
       return children;
     } catch(KeeperException.NoNodeException ke) {
       LOG.debug(zkw.prefix("Unable to list children of znode " + znode + " " +
           "because node does not exist (not an error)"));
       return null;
     } catch (KeeperException e) {
       LOG.warn(zkw.prefix("Unable to list children of znode " + znode + " "), e);
       zkw.keeperException(e);
       return null;
     } catch (InterruptedException e) {
       LOG.warn(zkw.prefix("Unable to list children of znode " + znode + " "), e);
       zkw.interruptedException(e);
       return null;
     }
   }
 
   /**
    * List all the children of the specified znode, setting a watch for children
    * changes and also setting a watch on every individual child in order to get
    * the NodeCreated and NodeDeleted events.
    * @param zkw zookeeper reference
    * @param znode node to get children of and watch
    * @return list of znode names, null if the node doesn't exist
    * @throws KeeperException
    */
   public static List<String> listChildrenAndWatchThem(ZooKeeperWatcher zkw,
       String znode) throws KeeperException {
     List<String> children = listChildrenAndWatchForNewChildren(zkw, znode);
     if (children == null) {
       return null;
     }
     for (String child : children) {
       watchAndCheckExists(zkw, joinZNode(znode, child));
     }
     return children;
   }
 
   /**
    * Lists the children of the specified znode without setting any watches.
    *
    * Sets no watches at all, this method is best effort.
    *
    * Returns an empty list if the node has no children.  Returns null if the
    * parent node itself does not exist.
    *
    * @param zkw zookeeper reference
    * @param znode node to get children
    * @return list of data of children of specified znode, empty if no children,
    *         null if parent does not exist
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static List<String> listChildrenNoWatch(ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     List<String> children = null;
     try {
       // List the children without watching
       children = zkw.getRecoverableZooKeeper().getChildren(znode, null);
     } catch(KeeperException.NoNodeException nne) {
       return null;
     } catch(InterruptedException ie) {
       zkw.interruptedException(ie);
     }
     return children;
   }
 
   /**
    * Simple class to hold a node path and node data.
    * @deprecated Unused
    */
   @Deprecated
   public static class NodeAndData {
     private String node;
     private byte [] data;
     public NodeAndData(String node, byte [] data) {
       this.node = node;
       this.data = data;
     }
     public String getNode() {
       return node;
     }
     public byte [] getData() {
       return data;
     }
     @Override
     public String toString() {
       return node;
     }
     public boolean isEmpty() {
       return (data == null || data.length == 0);
     }
   }
 
   /**
    * Checks if the specified znode has any children.  Sets no watches.
    *
    * Returns true if the node exists and has children.  Returns false if the
    * node does not exist or if the node does not have any children.
    *
    * Used during master initialization to determine if the master is a
    * failed-over-to master or the first master during initial cluster startup.
    * If the directory for regionserver ephemeral nodes is empty then this is
    * a cluster startup, if not then it is not cluster startup.
    *
    * @param zkw zk reference
    * @param znode path of node to check for children of
    * @return true if node has children, false if not or node does not exist
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static boolean nodeHasChildren(ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     try {
       return !zkw.getRecoverableZooKeeper().getChildren(znode, null).isEmpty();
     } catch(KeeperException.NoNodeException ke) {
       LOG.debug(zkw.prefix("Unable to list children of znode " + znode + " " +
       "because node does not exist (not an error)"));
       return false;
     } catch (KeeperException e) {
       LOG.warn(zkw.prefix("Unable to list children of znode " + znode), e);
       zkw.keeperException(e);
       return false;
     } catch (InterruptedException e) {
       LOG.warn(zkw.prefix("Unable to list children of znode " + znode), e);
       zkw.interruptedException(e);
       return false;
     }
   }
 
   /**
    * Get the number of children of the specified node.
    *
    * If the node does not exist or has no children, returns 0.
    *
    * Sets no watches at all.
    *
    * @param zkw zk reference
    * @param znode path of node to count children of
    * @return number of children of specified node, 0 if none or parent does not
    *         exist
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static int getNumberOfChildren(ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     try {
       Stat stat = zkw.getRecoverableZooKeeper().exists(znode, null);
       return stat == null ? 0 : stat.getNumChildren();
     } catch(KeeperException e) {
       LOG.warn(zkw.prefix("Unable to get children of node " + znode));
       zkw.keeperException(e);
     } catch(InterruptedException e) {
       zkw.interruptedException(e);
     }
     return 0;
   }
 
   //
   // Data retrieval
   //
 
   /**
    * Get znode data. Does not set a watcher.
    * @return ZNode data, null if the node does not exist or if there is an
    *  error.
    */
   public static byte [] getData(ZooKeeperWatcher zkw, String znode)
       throws KeeperException, InterruptedException {
     try {
       byte [] data = zkw.getRecoverableZooKeeper().getData(znode, null, null);
       logRetrievedMsg(zkw, znode, data, false);
       return data;
     } catch (KeeperException.NoNodeException e) {
       LOG.debug(zkw.prefix("Unable to get data of znode " + znode + " " +
           "because node does not exist (not an error)"));
       return null;
     } catch (KeeperException e) {
       LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
       zkw.keeperException(e);
       return null;
     }
   }
 
   /**
    * Get the data at the specified znode and set a watch.
    *
    * Returns the data and sets a watch if the node exists.  Returns null and no
    * watch is set if the node does not exist or there is an exception.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @return data of the specified znode, or null
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static byte [] getDataAndWatch(ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     return getDataInternal(zkw, znode, null, true);
   }
 
   /**
    * Get the data at the specified znode and set a watch.
    *
    * Returns the data and sets a watch if the node exists.  Returns null and no
    * watch is set if the node does not exist or there is an exception.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param stat object to populate the version of the znode
    * @return data of the specified znode, or null
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static byte[] getDataAndWatch(ZooKeeperWatcher zkw, String znode,
       Stat stat) throws KeeperException {
     return getDataInternal(zkw, znode, stat, true);
   }
 
   private static byte[] getDataInternal(ZooKeeperWatcher zkw, String znode, Stat stat,
       boolean watcherSet)
       throws KeeperException {
     try {
       byte [] data = zkw.getRecoverableZooKeeper().getData(znode, zkw, stat);
       logRetrievedMsg(zkw, znode, data, watcherSet);
       return data;
     } catch (KeeperException.NoNodeException e) {
       // This log can get pretty annoying when we cycle on 100ms waits.
       // Enable trace if you really want to see it.
       LOG.trace(zkw.prefix("Unable to get data of znode " + znode + " " +
         "because node does not exist (not an error)"));
       return null;
     } catch (KeeperException e) {
       LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
       zkw.keeperException(e);
       return null;
     } catch (InterruptedException e) {
       LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
       zkw.interruptedException(e);
       return null;
     }
   }
 
   /**
    * Get the data at the specified znode without setting a watch.
    *
    * Returns the data if the node exists.  Returns null if the node does not
    * exist.
    *
    * Sets the stats of the node in the passed Stat object.  Pass a null stat if
    * not interested.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param stat node status to get if node exists
    * @return data of the specified znode, or null if node does not exist
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static byte [] getDataNoWatch(ZooKeeperWatcher zkw, String znode,
       Stat stat)
   throws KeeperException {
     try {
       byte [] data = zkw.getRecoverableZooKeeper().getData(znode, null, stat);
       logRetrievedMsg(zkw, znode, data, false);
       return data;
     } catch (KeeperException.NoNodeException e) {
       LOG.debug(zkw.prefix("Unable to get data of znode " + znode + " " +
           "because node does not exist (not necessarily an error)"));
       return null;
     } catch (KeeperException e) {
       LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
       zkw.keeperException(e);
       return null;
     } catch (InterruptedException e) {
       LOG.warn(zkw.prefix("Unable to get data of znode " + znode), e);
       zkw.interruptedException(e);
       return null;
     }
   }
 
   /**
    * Returns the date of child znodes of the specified znode.  Also sets a watch on
    * the specified znode which will capture a NodeDeleted event on the specified
    * znode as well as NodeChildrenChanged if any children of the specified znode
    * are created or deleted.
    *
    * Returns null if the specified node does not exist.  Otherwise returns a
    * list of children of the specified node.  If the node exists but it has no
    * children, an empty list will be returned.
    *
    * @param zkw zk reference
    * @param baseNode path of node to list and watch children of
    * @return list of data of children of the specified node, an empty list if the node
    *          exists but has no children, and null if the node does not exist
    * @throws KeeperException if unexpected zookeeper exception
    * @deprecated Unused
    */
   public static List<NodeAndData> getChildDataAndWatchForNewChildren(
       ZooKeeperWatcher zkw, String baseNode) throws KeeperException {
     List<String> nodes =
       ZKUtil.listChildrenAndWatchForNewChildren(zkw, baseNode);
     if (nodes != null) {
       List<NodeAndData> newNodes = new ArrayList<NodeAndData>();
       for (String node : nodes) {
         String nodePath = ZKUtil.joinZNode(baseNode, node);
         byte[] data = ZKUtil.getDataAndWatch(zkw, nodePath);
         newNodes.add(new NodeAndData(nodePath, data));
       }
       return newNodes;
     }
     return null;
   }
 
   /**
    * Update the data of an existing node with the expected version to have the
    * specified data.
    *
    * Throws an exception if there is a version mismatch or some other problem.
    *
    * Sets no watches under any conditions.
    *
    * @param zkw zk reference
    * @param znode
    * @param data
    * @param expectedVersion
    * @throws KeeperException if unexpected zookeeper exception
    * @throws KeeperException.BadVersionException if version mismatch
    * @deprecated Unused
    */
   public static void updateExistingNodeData(ZooKeeperWatcher zkw, String znode,
       byte [] data, int expectedVersion)
   throws KeeperException {
     try {
       zkw.getRecoverableZooKeeper().setData(znode, data, expectedVersion);
     } catch(InterruptedException ie) {
       zkw.interruptedException(ie);
     }
   }
 
   //
   // Data setting
   //
 
   /**
    * Sets the data of the existing znode to be the specified data.  Ensures that
    * the current data has the specified expected version.
    *
    * <p>If the node does not exist, a {@link NoNodeException} will be thrown.
    *
    * <p>If their is a version mismatch, method returns null.
    *
    * <p>No watches are set but setting data will trigger other watchers of this
    * node.
    *
    * <p>If there is another problem, a KeeperException will be thrown.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param data data to set for node
    * @param expectedVersion version expected when setting data
    * @return true if data set, false if version mismatch
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static boolean setData(ZooKeeperWatcher zkw, String znode,
       byte [] data, int expectedVersion)
   throws KeeperException, KeeperException.NoNodeException {
     try {
       return zkw.getRecoverableZooKeeper().setData(znode, data, expectedVersion) != null;
     } catch (InterruptedException e) {
       zkw.interruptedException(e);
       return false;
     }
   }
 
   /**
    * Set data into node creating node if it doesn't yet exist.
    * Does not set watch.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param data data to set for node
    * @throws KeeperException
    */
   public static void createSetData(final ZooKeeperWatcher zkw, final String znode,
       final byte [] data)
   throws KeeperException {
     if (checkExists(zkw, znode) == -1) {
       ZKUtil.createWithParents(zkw, znode, data);
     } else {
       ZKUtil.setData(zkw, znode, data);
     }
   }
 
   /**
    * Sets the data of the existing znode to be the specified data.  The node
    * must exist but no checks are done on the existing data or version.
    *
    * <p>If the node does not exist, a {@link NoNodeException} will be thrown.
    *
    * <p>No watches are set but setting data will trigger other watchers of this
    * node.
    *
    * <p>If there is another problem, a KeeperException will be thrown.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param data data to set for node
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static void setData(ZooKeeperWatcher zkw, String znode, byte [] data)
   throws KeeperException, KeeperException.NoNodeException {
     setData(zkw, (SetData)ZKUtilOp.setData(znode, data));
   }
 
   private static void setData(ZooKeeperWatcher zkw, SetData setData)
   throws KeeperException, KeeperException.NoNodeException {
     SetDataRequest sd = (SetDataRequest)toZooKeeperOp(zkw, setData).toRequestRecord();
     setData(zkw, sd.getPath(), sd.getData(), sd.getVersion());
   }
 
   /**
    * Returns whether or not secure authentication is enabled
    * (whether <code>hbase.security.authentication</code> is set to
    * <code>kerberos</code>.
    */
   public static boolean isSecureZooKeeper(Configuration conf) {
     // Detection for embedded HBase client with jaas configuration
     // defined for third party programs.
     try {
       javax.security.auth.login.Configuration testConfig =
           javax.security.auth.login.Configuration.getConfiguration();
       if (testConfig.getAppConfigurationEntry("Client") == null
           && testConfig.getAppConfigurationEntry(
             JaasConfiguration.CLIENT_KEYTAB_KERBEROS_CONFIG_NAME) == null
           && testConfig.getAppConfigurationEntry(
               JaasConfiguration.SERVER_KEYTAB_KERBEROS_CONFIG_NAME) == null
           && conf.get(HConstants.ZK_CLIENT_KERBEROS_PRINCIPAL) == null
           && conf.get(HConstants.ZK_SERVER_KERBEROS_PRINCIPAL) == null) {
 
         return false;
       }
     } catch(Exception e) {
       // No Jaas configuration defined.
       return false;
     }
 
     // Master & RSs uses hbase.zookeeper.client.*
     return "kerberos".equalsIgnoreCase(conf.get("hbase.security.authentication"));
   }
 
   private static ArrayList<ACL> createACL(ZooKeeperWatcher zkw, String node) {
     return createACL(zkw, node, isSecureZooKeeper(zkw.getConfiguration()));
   }
 
   public static ArrayList<ACL> createACL(ZooKeeperWatcher zkw, String node,
     boolean isSecureZooKeeper) {
     if (!node.startsWith(zkw.baseZNode)) {
       return Ids.OPEN_ACL_UNSAFE;
     }
     if (isSecureZooKeeper) {
       ArrayList<ACL> acls = new ArrayList<ACL>();
       // add permission to hbase supper user
       String[] superUsers = zkw.getConfiguration().getStrings(Superusers.SUPERUSER_CONF_KEY);
       if (superUsers != null) {
         List<String> groups = new ArrayList<String>();
         for (String user : superUsers) {
           if (AuthUtil.isGroupPrincipal(user)) {
             // TODO: Set node ACL for groups when ZK supports this feature
             groups.add(user);
           } else {
             acls.add(new ACL(Perms.ALL, new Id("sasl", user)));
           }
         }
         if (!groups.isEmpty()) {
           LOG.warn("Znode ACL setting for group " + groups
               + " is skipped, Zookeeper doesn't support this feature presently.");
         }
       }
       // Certain znodes are accessed directly by the client,
       // so they must be readable by non-authenticated clients
       if (zkw.isClientReadable(node)) {
         acls.addAll(Ids.CREATOR_ALL_ACL);
         acls.addAll(Ids.READ_ACL_UNSAFE);
       } else {
         acls.addAll(Ids.CREATOR_ALL_ACL);
       }
       return acls;
     } else {
       return Ids.OPEN_ACL_UNSAFE;
     }
   }
 
   //
   // Node creation
   //
 
   /**
    *
    * Set the specified znode to be an ephemeral node carrying the specified
    * data.
    *
    * If the node is created successfully, a watcher is also set on the node.
    *
    * If the node is not created successfully because it already exists, this
    * method will also set a watcher on the node.
    *
    * If there is another problem, a KeeperException will be thrown.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param data data of node
    * @return true if node created, false if not, watch set in both cases
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static boolean createEphemeralNodeAndWatch(ZooKeeperWatcher zkw,
       String znode, byte [] data)
   throws KeeperException {
     boolean ret = true;
     try {
       zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
           CreateMode.EPHEMERAL);
     } catch (KeeperException.NodeExistsException nee) {
       ret = false;
     } catch (InterruptedException e) {
       LOG.info("Interrupted", e);
       Thread.currentThread().interrupt();
     }
     if(!watchAndCheckExists(zkw, znode)) {
       // It did exist but now it doesn't, try again
       return createEphemeralNodeAndWatch(zkw, znode, data);
     }
     return ret;
   }
 
   /**
    * Creates the specified znode to be a persistent node carrying the specified
    * data.
    *
    * Returns true if the node was successfully created, false if the node
    * already existed.
    *
    * If the node is created successfully, a watcher is also set on the node.
    *
    * If the node is not created successfully because it already exists, this
    * method will also set a watcher on the node but return false.
    *
    * If there is another problem, a KeeperException will be thrown.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param data data of node
    * @return true if node created, false if not, watch set in both cases
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static boolean createNodeIfNotExistsAndWatch(
       ZooKeeperWatcher zkw, String znode, byte [] data)
   throws KeeperException {
     boolean ret = true;
     try {
       zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
           CreateMode.PERSISTENT);
     } catch (KeeperException.NodeExistsException nee) {
       ret = false;
     } catch (InterruptedException e) {
       zkw.interruptedException(e);
       return false;
     }
     try {
       zkw.getRecoverableZooKeeper().exists(znode, zkw);
     } catch (InterruptedException e) {
       zkw.interruptedException(e);
       return false;
     }
     return ret;
   }
 
   /**
    * Creates the specified znode with the specified data but does not watch it.
    *
    * Returns the znode of the newly created node
    *
    * If there is another problem, a KeeperException will be thrown.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param data data of node
    * @param createMode specifying whether the node to be created is ephemeral and/or sequential
    * @return true name of the newly created znode or null
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static String createNodeIfNotExistsNoWatch(ZooKeeperWatcher zkw, String znode,
       byte[] data, CreateMode createMode) throws KeeperException {
 
     String createdZNode = null;
     try {
       createdZNode = zkw.getRecoverableZooKeeper().create(znode, data,
           createACL(zkw, znode), createMode);
     } catch (KeeperException.NodeExistsException nee) {
       return znode;
     } catch (InterruptedException e) {
       zkw.interruptedException(e);
       return null;
     }
     return createdZNode;
   }
 
   /**
    * Creates the specified node with the specified data and watches it.
    *
    * <p>Throws an exception if the node already exists.
    *
    * <p>The node created is persistent and open access.
    *
    * <p>Returns the version number of the created node if successful.
    *
    * @param zkw zk reference
    * @param znode path of node to create
    * @param data data of node to create
    * @return version of node created
    * @throws KeeperException if unexpected zookeeper exception
    * @throws KeeperException.NodeExistsException if node already exists
    */
   public static int createAndWatch(ZooKeeperWatcher zkw,
       String znode, byte [] data)
   throws KeeperException, KeeperException.NodeExistsException {
     try {
       zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
           CreateMode.PERSISTENT);
       Stat stat = zkw.getRecoverableZooKeeper().exists(znode, zkw);
       if (stat == null){
         // Likely a race condition. Someone deleted the znode.
         throw KeeperException.create(KeeperException.Code.SYSTEMERROR,
             "ZK.exists returned null (i.e.: znode does not exist) for znode=" + znode);
       }
      return stat.getVersion();
     } catch (InterruptedException e) {
       zkw.interruptedException(e);
       return -1;
     }
   }
 
   /**
    * Async creates the specified node with the specified data.
    *
    * <p>Throws an exception if the node already exists.
    *
    * <p>The node created is persistent and open access.
    *
    * @param zkw zk reference
    * @param znode path of node to create
    * @param data data of node to create
    * @param cb
    * @param ctx
    */
   public static void asyncCreate(ZooKeeperWatcher zkw,
       String znode, byte [] data, final AsyncCallback.StringCallback cb,
       final Object ctx) {
     zkw.getRecoverableZooKeeper().getZooKeeper().create(znode, data,
         createACL(zkw, znode), CreateMode.PERSISTENT, cb, ctx);
   }
 
   /**
    * Creates the specified node, iff the node does not exist.  Does not set a
    * watch and fails silently if the node already exists.
    *
    * The node created is persistent and open access.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static void createAndFailSilent(ZooKeeperWatcher zkw,
       String znode) throws KeeperException {
     createAndFailSilent(zkw, znode, new byte[0]);
   }
 
   /**
    * Creates the specified node containing specified data, iff the node does not exist.  Does
    * not set a watch and fails silently if the node already exists.
    *
    * The node created is persistent and open access.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @param data a byte array data to store in the znode
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static void createAndFailSilent(ZooKeeperWatcher zkw,
       String znode, byte[] data)
   throws KeeperException {
     createAndFailSilent(zkw,
         (CreateAndFailSilent)ZKUtilOp.createAndFailSilent(znode, data));
   }
 
   private static void createAndFailSilent(ZooKeeperWatcher zkw, CreateAndFailSilent cafs)
   throws KeeperException {
     CreateRequest create = (CreateRequest)toZooKeeperOp(zkw, cafs).toRequestRecord();
     String znode = create.getPath();
     try {
       RecoverableZooKeeper zk = zkw.getRecoverableZooKeeper();
       if (zk.exists(znode, false) == null) {
         zk.create(znode, create.getData(), create.getAcl(), CreateMode.fromFlag(create.getFlags()));
       }
     } catch(KeeperException.NodeExistsException nee) {
     } catch(KeeperException.NoAuthException nee){
       try {
         if (null == zkw.getRecoverableZooKeeper().exists(znode, false)) {
           // If we failed to create the file and it does not already exist.
           throw(nee);
         }
       } catch (InterruptedException ie) {
         zkw.interruptedException(ie);
       }
     } catch(InterruptedException ie) {
       zkw.interruptedException(ie);
     }
   }
 
   /**
    * Creates the specified node and all parent nodes required for it to exist.
    *
    * No watches are set and no errors are thrown if the node already exists.
    *
    * The nodes created are persistent and open access.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static void createWithParents(ZooKeeperWatcher zkw, String znode)
   throws KeeperException {
     createWithParents(zkw, znode, new byte[0]);
   }
 
   /**
    * Creates the specified node and all parent nodes required for it to exist.  The creation of
    * parent znodes is not atomic with the leafe znode creation but the data is written atomically
    * when the leaf node is created.
    *
    * No watches are set and no errors are thrown if the node already exists.
    *
    * The nodes created are persistent and open access.
    *
    * @param zkw zk reference
    * @param znode path of node
    * @throws KeeperException if unexpected zookeeper exception
    */
   public static void createWithParents(ZooKeeperWatcher zkw, String znode, byte[] data)
   throws KeeperException {
     try {
       if(znode == null) {
         return;
       }
       zkw.getRecoverableZooKeeper().create(znode, data, createACL(zkw, znode),
           CreateMode.PERSISTENT);
     } catch(KeeperException.NodeExistsException nee) {
       return;
     } catch(KeeperException.NoNodeException nne) {
       createWithParents(zkw, getParent(znode));
       createWithParents(zkw, znode, data);
     } catch(InterruptedException ie) {
       zkw.interruptedException(ie);
     }
   }
 
   //
   // Deletes
   //
 
   /**
    * Delete the specified node.  Sets no watches.  Throws all exceptions.
    */
   public static void deleteNode(ZooKeeperWatcher zkw, String node)
   throws KeeperException {
     deleteNode(zkw, node, -1);
   }
 
   /**
    * Delete the specified node with the specified version.  Sets no watches.
    * Throws all exceptions.
    */
   public static boolean deleteNode(ZooKeeperWatcher zkw, String node,
       int version)
   throws KeeperException {
     try {
       zkw.getRecoverableZooKeeper().delete(node, version);
       return true;
     } catch(KeeperException.BadVersionException bve) {
       return false;
     } catch(InterruptedException ie) {
       zkw.interruptedException(ie);
       return false;
     }
   }
 
   /**
    * Deletes the specified node.  Fails silent if the node does not exist.
    * @param zkw
    * @param node
    * @throws KeeperException
    */
   public static void deleteNodeFailSilent(ZooKeeperWatcher zkw, String node)
   throws KeeperException {
     deleteNodeFailSilent(zkw,
       (DeleteNodeFailSilent)ZKUtilOp.deleteNodeFailSilent(node));
   }
 
   private static void deleteNodeFailSilent(ZooKeeperWatcher zkw,
       DeleteNodeFailSilent dnfs) throws KeeperException {
     DeleteRequest delete = (DeleteRequest)toZooKeeperOp(zkw, dnfs).toRequestRecord();
     try {
       zkw.getRecoverableZooKeeper().delete(delete.getPath(), delete.getVersion());
     } catch(KeeperException.NoNodeException nne) {
     } catch(InterruptedException ie) {
       zkw.interruptedException(ie);
     }
   }
 
 
   /**
    * Delete the specified node and all of it's children.
    * <p>
    * If the node does not exist, just returns.
    * <p>
    * Sets no watches. Throws all exceptions besides dealing with deletion of
    * children.
    */
   public static void deleteNodeRecursively(ZooKeeperWatcher zkw, String node)
   throws KeeperException {
     deleteNodeRecursivelyMultiOrSequential(zkw, true, node);
   }
 
   /**
    * Delete all the children of the specified node but not the node itself.
    *
    * Sets no watches.  Throws all exceptions besides dealing with deletion of
    * children.
    *
    * If hbase.zookeeper.useMulti is true, use ZooKeeper's multi-update functionality.
    * Otherwise, run the list of operations sequentially.
    *
    * @throws KeeperException
    */
   public static void deleteChildrenRecursively(ZooKeeperWatcher zkw, String node)
       throws KeeperException {
     deleteChildrenRecursivelyMultiOrSequential(zkw, true, node);
   }
 
   /**
    * Delete all the children of the specified node but not the node itself. This
    * will first traverse the znode tree for listing the children and then delete
    * these znodes using multi-update api or sequential based on the specified
    * configurations.
    * <p>
    * Sets no watches. Throws all exceptions besides dealing with deletion of
    * children.
    * <p>
    * If hbase.zookeeper.useMulti is true, use ZooKeeper's multi-update
    * functionality. Otherwise, run the list of operations sequentially.
    * <p>
    * If all of the following are true:
    * <ul>
    * <li>runSequentialOnMultiFailure is true
    * <li>hbase.zookeeper.useMulti is true
    * </ul>
    * on calling multi, we get a ZooKeeper exception that can be handled by a
    * sequential call(*), we retry the operations one-by-one (sequentially).
    *
    * @param zkw
    *          - zk reference
    * @param runSequentialOnMultiFailure
    *          - if true when we get a ZooKeeper exception that could retry the
    *          operations one-by-one (sequentially)
    * @param pathRoots
    *          - path of the parent node(s)
    * @throws KeeperException.NotEmptyException
    *           if node has children while deleting
    * @throws KeeperException
    *           if unexpected ZooKeeper exception
    * @throws IllegalArgumentException
    *           if an invalid path is specified
    */
   public static void deleteChildrenRecursivelyMultiOrSequential(
       ZooKeeperWatcher zkw, boolean runSequentialOnMultiFailure,
       String... pathRoots) throws KeeperException {
     if (pathRoots == null || pathRoots.length <= 0) {
       LOG.warn("Given path is not valid!");
       return;
     }
     List<ZKUtilOp> ops = new ArrayList<ZKUtil.ZKUtilOp>();
     for (String eachRoot : pathRoots) {
       List<String> children = listChildrenBFSNoWatch(zkw, eachRoot);
       // Delete the leaves first and eventually get rid of the root
       for (int i = children.size() - 1; i >= 0; --i) {
         ops.add(ZKUtilOp.deleteNodeFailSilent(children.get(i)));
       }
     }
     // atleast one element should exist
     if (ops.size() > 0) {
       multiOrSequential(zkw, ops, runSequentialOnMultiFailure);
     }
   }
 
   /**
    * Delete the specified node and its children. This traverse the
    * znode tree for listing the children and then delete
    * these znodes including the parent using multi-update api or
    * sequential based on the specified configurations.
    * <p>
    * Sets no watches. Throws all exceptions besides dealing with deletion of
    * children.
    * <p>
    * If hbase.zookeeper.useMulti is true, use ZooKeeper's multi-update
    * functionality. Otherwise, run the list of operations sequentially.
    * <p>
    * If all of the following are true:
    * <ul>
    * <li>runSequentialOnMultiFailure is true
    * <li>hbase.zookeeper.useMulti is true
    * </ul>
    * on calling multi, we get a ZooKeeper exception that can be handled by a
    * sequential call(*), we retry the operations one-by-one (sequentially).
    *
    * @param zkw
    *          - zk reference
    * @param runSequentialOnMultiFailure
    *          - if true when we get a ZooKeeper exception that could retry the
    *          operations one-by-one (sequentially)
    * @param pathRoots
    *          - path of the parent node(s)
    * @throws KeeperException.NotEmptyException
    *           if node has children while deleting
    * @throws KeeperException
    *           if unexpected ZooKeeper exception
    * @throws IllegalArgumentException
    *           if an invalid path is specified
    */
   public static void deleteNodeRecursivelyMultiOrSequential(ZooKeeperWatcher zkw,
       boolean runSequentialOnMultiFailure, String... pathRoots) throws KeeperException {
     if (pathRoots == null || pathRoots.length <= 0) {
       LOG.warn("Given path is not valid!");
       return;
     }
     List<ZKUtilOp> ops = new ArrayList<ZKUtil.ZKUtilOp>();
     for (String eachRoot : pathRoots) {
       // Zookeeper Watches are one time triggers; When children of parent nodes are deleted
       // recursively, must set another watch, get notified of delete node
       List<String> children = listChildrenBFSAndWatchThem(zkw, eachRoot);
       // Delete the leaves first and eventually get rid of the root
       for (int i = children.size() - 1; i >= 0; --i) {
         ops.add(ZKUtilOp.deleteNodeFailSilent(children.get(i)));
       }
       try {
         if (zkw.getRecoverableZooKeeper().exists(eachRoot, zkw) != null) {
           ops.add(ZKUtilOp.deleteNodeFailSilent(eachRoot));
         }
       } catch (InterruptedException e) {
         zkw.interruptedException(e);
       }
     }
     // atleast one element should exist
     if (ops.size() > 0) {
       multiOrSequential(zkw, ops, runSequentialOnMultiFailure);
     }
   }
 
   /**
    * BFS Traversal of all the children under path, with the entries in the list,
    * in the same order as that of the traversal. Lists all the children without
    * setting any watches.
    *
    * @param zkw
    *          - zk reference
    * @param znode
    *          - path of node
    * @return list of children znodes under the path
    * @throws KeeperException
    *           if unexpected ZooKeeper exception
    */
   private static List<String> listChildrenBFSNoWatch(ZooKeeperWatcher zkw,
       final String znode) throws KeeperException {
     Deque<String> queue = new LinkedList<String>();
     List<String> tree = new ArrayList<String>();
     queue.add(znode);
     while (true) {
       String node = queue.pollFirst();
       if (node == null) {
         break;
       }
       List<String> children = listChildrenNoWatch(zkw, node);
       if (children == null) {
         continue;
       }
       for (final String child : children) {
         final String childPath = node + "/" + child;
         queue.add(childPath);
         tree.add(childPath);
       }
     }
     return tree;
   }
 
   /**
    * BFS Traversal of all the children under path, with the entries in the list,
    * in the same order as that of the traversal.
    * Lists all the children and set watches on to them.
    *
    * @param zkw
    *          - zk reference
    * @param znode
    *          - path of node
    * @return list of children znodes under the path
    * @throws KeeperException
    *           if unexpected ZooKeeper exception
    */
   private static List<String> listChildrenBFSAndWatchThem(ZooKeeperWatcher zkw, final String znode)
       throws KeeperException {
     Deque<String> queue = new LinkedList<String>();
     List<String> tree = new ArrayList<String>();
     queue.add(znode);
     while (true) {
       String node = queue.pollFirst();
       if (node == null) {
         break;
       }
       List<String> children = listChildrenAndWatchThem(zkw, node);
       if (children == null) {
         continue;
       }
       for (final String child : children) {
         final String childPath = node + "/" + child;
         queue.add(childPath);
         tree.add(childPath);
       }
     }
     return tree;
   }
 
   /**
    * Represents an action taken by ZKUtil, e.g. createAndFailSilent.
    * These actions are higher-level than ZKOp actions, which represent
    * individual actions in the ZooKeeper API, like create.
    */
   public abstract static class ZKUtilOp {
     private String path;
 
     private ZKUtilOp(String path) {
       this.path = path;
     }
 
     /**
      * @return a createAndFailSilent ZKUtilOp
      */
     public static ZKUtilOp createAndFailSilent(String path, byte[] data) {
       return new CreateAndFailSilent(path, data);
     }
 
     /**
      * @return a deleteNodeFailSilent ZKUtilOP
      */
     public static ZKUtilOp deleteNodeFailSilent(String path) {
       return new DeleteNodeFailSilent(path);
     }
 
     /**
      * @return a setData ZKUtilOp
      */
     public static ZKUtilOp setData(String path, byte [] data) {
       return new SetData(path, data);
     }
 
     /**
      * @return path to znode where the ZKOp will occur
      */
     public String getPath() {
       return path;
     }
 
     /**
      * ZKUtilOp representing createAndFailSilent in ZooKeeper
      * (attempt to create node, ignore error if already exists)
      */
     public static class CreateAndFailSilent extends ZKUtilOp {
       private byte [] data;
 
       private CreateAndFailSilent(String path, byte [] data) {
         super(path);
         this.data = data;
       }
 
       public byte[] getData() {
         return data;
       }
 
       @Override
       public boolean equals(Object o) {
         if (this == o) return true;
         if (!(o instanceof CreateAndFailSilent)) return false;
 
         CreateAndFailSilent op = (CreateAndFailSilent) o;
         return getPath().equals(op.getPath()) && Arrays.equals(data, op.data);
       }
 
       @Override
       public int hashCode() {
         int ret = 17 + getPath().hashCode() * 31;
         return ret * 31 + Bytes.hashCode(data);
       }
     }
 
     /**
      * ZKUtilOp representing deleteNodeFailSilent in ZooKeeper
      * (attempt to delete node, ignore error if node doesn't exist)
      */
     public static class DeleteNodeFailSilent extends ZKUtilOp {
       private DeleteNodeFailSilent(String path) {
         super(path);
       }
 
       @Override
       public boolean equals(Object o) {
         if (this == o) return true;
         if (!(o instanceof DeleteNodeFailSilent)) return false;
 
         return super.equals(o);
       }
 
       @Override
       public int hashCode() {
         return getPath().hashCode();
       }
     }
 
     /**
      * ZKUtilOp representing setData in ZooKeeper
      */
     public static class SetData extends ZKUtilOp {
       private byte [] data;
 
       private SetData(String path, byte [] data) {
         super(path);
         this.data = data;
       }
 
       public byte[] getData() {
         return data;
       }
 
       @Override
       public boolean equals(Object o) {
         if (this == o) return true;
         if (!(o instanceof SetData)) return false;
 
         SetData op = (SetData) o;
         return getPath().equals(op.getPath()) && Arrays.equals(data, op.data);
       }
 
       @Override
       public int hashCode() {
         int ret = getPath().hashCode();
         return ret * 31 + Bytes.hashCode(data);
       }
     }
   }
 
   /**
    * Convert from ZKUtilOp to ZKOp
    */
   private static Op toZooKeeperOp(ZooKeeperWatcher zkw, ZKUtilOp op)
   throws UnsupportedOperationException {
     if(op == null) return null;
 
     if (op instanceof CreateAndFailSilent) {
       CreateAndFailSilent cafs = (CreateAndFailSilent)op;
       return Op.create(cafs.getPath(), cafs.getData(), createACL(zkw, cafs.getPath()),
         CreateMode.PERSISTENT);
     } else if (op instanceof DeleteNodeFailSilent) {
       DeleteNodeFailSilent dnfs = (DeleteNodeFailSilent)op;
       return Op.delete(dnfs.getPath(), -1);
     } else if (op instanceof SetData) {
       SetData sd = (SetData)op;
       return Op.setData(sd.getPath(), sd.getData(), -1);
     } else {
       throw new UnsupportedOperationException("Unexpected ZKUtilOp type: "
         + op.getClass().getName());
     }
   }
 
   /**
    * If hbase.zookeeper.useMulti is true, use ZooKeeper's multi-update functionality.
    * Otherwise, run the list of operations sequentially.
    *
    * If all of the following are true:
    * - runSequentialOnMultiFailure is true
    * - hbase.zookeeper.useMulti is true
    * - on calling multi, we get a ZooKeeper exception that can be handled by a sequential call(*)
    * Then:
    * - we retry the operations one-by-one (sequentially)
    *
    * Note *: an example is receiving a NodeExistsException from a "create" call.  Without multi,
    * a user could call "createAndFailSilent" to ensure that a node exists if they don't care who
    * actually created the node (i.e. the NodeExistsException from ZooKeeper is caught).
    * This will cause all operations in the multi to fail, however, because
    * the NodeExistsException that zk.create throws will fail the multi transaction.
    * In this case, if the previous conditions hold, the commands are run sequentially, which should
    * result in the correct final state, but means that the operations will not run atomically.
    *
    * @throws KeeperException
    */
   public static void multiOrSequential(ZooKeeperWatcher zkw, List<ZKUtilOp> ops,
       boolean runSequentialOnMultiFailure) throws KeeperException {
     if (ops == null) return;
     boolean useMulti = zkw.getConfiguration().getBoolean(HConstants.ZOOKEEPER_USEMULTI, false);
 
     if (useMulti) {
       List<Op> zkOps = new LinkedList<Op>();
       for (ZKUtilOp op : ops) {
         zkOps.add(toZooKeeperOp(zkw, op));
       }
       try {
         zkw.getRecoverableZooKeeper().multi(zkOps);
       } catch (KeeperException ke) {
        switch (ke.code()) {
          case NODEEXISTS:
          case NONODE:
          case BADVERSION:
          case NOAUTH:
            // if we get an exception that could be solved by running sequentially
            // (and the client asked us to), then break out and run sequentially
            if (runSequentialOnMultiFailure) {
              LOG.info("On call to ZK.multi, received exception: " + ke.toString() + "."
                + "  Attempting to run operations sequentially because"
                + " runSequentialOnMultiFailure is: " + runSequentialOnMultiFailure + ".");
              processSequentially(zkw, ops);
              break;
            }
           default:
             throw ke;
         }
       } catch (InterruptedException ie) {
         zkw.interruptedException(ie);
       }
     } else {
       // run sequentially
       processSequentially(zkw, ops);
     }
 
   }
 
   private static void processSequentially(ZooKeeperWatcher zkw, List<ZKUtilOp> ops)
       throws KeeperException, NoNodeException {
     for (ZKUtilOp op : ops) {
       if (op instanceof CreateAndFailSilent) {
         createAndFailSilent(zkw, (CreateAndFailSilent) op);
       } else if (op instanceof DeleteNodeFailSilent) {
         deleteNodeFailSilent(zkw, (DeleteNodeFailSilent) op);
       } else if (op instanceof SetData) {
         setData(zkw, (SetData) op);
       } else {
         throw new UnsupportedOperationException("Unexpected ZKUtilOp type: "
             + op.getClass().getName());
       }
     }
   }
 
   //
   // ZooKeeper cluster information
   //
 
   /** @return String dump of everything in ZooKeeper. */
   public static String dump(ZooKeeperWatcher zkw) {
     StringBuilder sb = new StringBuilder();
     try {
       sb.append("HBase is rooted at ").append(zkw.baseZNode);
       sb.append("\nActive master address: ");
       try {
         sb.append(MasterAddressTracker.getMasterAddress(zkw));
       } catch (IOException e) {
         sb.append("<<FAILED LOOKUP: " + e.getMessage() + ">>");
       }
       sb.append("\nBackup master addresses:");
       for (String child : listChildrenNoWatch(zkw,
                                               zkw.backupMasterAddressesZNode)) {
         sb.append("\n ").append(child);
       }
       sb.append("\nRegion server holding hbase:meta: "
         + new MetaTableLocator().getMetaRegionLocation(zkw));
       Configuration conf = HBaseConfiguration.create();
       int numMetaReplicas = conf.getInt(HConstants.META_REPLICAS_NUM,
                HConstants.DEFAULT_META_REPLICA_NUM);
       for (int i = 1; i < numMetaReplicas; i++) {
         sb.append("\nRegion server holding hbase:meta, replicaId " + i + " "
                     + new MetaTableLocator().getMetaRegionLocation(zkw, i));
       }
       sb.append("\nRegion servers:");
       for (String child : listChildrenNoWatch(zkw, zkw.rsZNode)) {
         sb.append("\n ").append(child);
       }
       try {
         getReplicationZnodesDump(zkw, sb);
       } catch (KeeperException ke) {
         LOG.warn("Couldn't get the replication znode dump", ke);
       }
       sb.append("\nQuorum Server Statistics:");
       String[] servers = zkw.getQuorum().split(",");
       for (String server : servers) {
         sb.append("\n ").append(server);
         try {
           String[] stat = getServerStats(server, ZKUtil.zkDumpConnectionTimeOut);
 
           if (stat == null) {
             sb.append("[Error] invalid quorum server: " + server);
             break;
           }
 
           for (String s : stat) {
             sb.append("\n  ").append(s);
           }
         } catch (Exception e) {
           sb.append("\n  ERROR: ").append(e.getMessage());
         }
       }
     } catch (KeeperException ke) {
       sb.append("\nFATAL ZooKeeper Exception!\n");
       sb.append("\n" + ke.getMessage());
     }
     return sb.toString();
   }
 
   /**
    * Appends replication znodes to the passed StringBuilder.
    * @param zkw
    * @param sb
    * @throws KeeperException
    */
   private static void getReplicationZnodesDump(ZooKeeperWatcher zkw, StringBuilder sb)
       throws KeeperException {
     String replicationZNodeName = zkw.getConfiguration().get("zookeeper.znode.replication",
       "replication");
     String replicationZnode = joinZNode(zkw.baseZNode, replicationZNodeName);
     if (ZKUtil.checkExists(zkw, replicationZnode) == -1) return;
     // do a ls -r on this znode
     sb.append("\n").append(replicationZnode).append(": ");
     List<String> children = ZKUtil.listChildrenNoWatch(zkw, replicationZnode);
     for (String child : children) {
       String znode = joinZNode(replicationZnode, child);
       if (child.equals(zkw.getConfiguration().get("zookeeper.znode.replication.peers", "peers"))) {
         appendPeersZnodes(zkw, znode, sb);
       } else if (child.equals(zkw.getConfiguration().
           get("zookeeper.znode.replication.rs", "rs"))) {
         appendRSZnodes(zkw, znode, sb);
       } else if (child.equals(zkw.getConfiguration().get(
         ReplicationStateZKBase.ZOOKEEPER_ZNODE_REPLICATION_HFILE_REFS_KEY,
         ReplicationStateZKBase.ZOOKEEPER_ZNODE_REPLICATION_HFILE_REFS_DEFAULT))) {
         appendHFileRefsZnodes(zkw, znode, sb);
       }
     }
   }
 
   private static void appendHFileRefsZnodes(ZooKeeperWatcher zkw, String hfileRefsZnode,
       StringBuilder sb) throws KeeperException {
     sb.append("\n").append(hfileRefsZnode).append(": ");
     for (String peerIdZnode : ZKUtil.listChildrenNoWatch(zkw, hfileRefsZnode)) {
       String znodeToProcess = ZKUtil.joinZNode(hfileRefsZnode, peerIdZnode);
       sb.append("\n").append(znodeToProcess).append(": ");
       List<String> peerHFileRefsZnodes = ZKUtil.listChildrenNoWatch(zkw, znodeToProcess);
       int size = peerHFileRefsZnodes.size();
       for (int i = 0; i < size; i++) {
         sb.append(peerHFileRefsZnodes.get(i));
         if (i != size - 1) {
           sb.append(", ");
         }
       }
     }
   }
 
   /**
    * Returns a string with replication znodes and position of the replication log
    * @param zkw
    * @return aq string of replication znodes and log positions
    */
   public static String getReplicationZnodesDump(ZooKeeperWatcher zkw) throws KeeperException {
     StringBuilder sb = new StringBuilder();
     getReplicationZnodesDump(zkw, sb);
     return sb.toString();
   }
 
   private static void appendRSZnodes(ZooKeeperWatcher zkw, String znode, StringBuilder sb)
       throws KeeperException {
     List<String> stack = new LinkedList<String>();
     stack.add(znode);
     do {
       String znodeToProcess = stack.remove(stack.size() - 1);
       sb.append("\n").append(znodeToProcess).append(": ");
       byte[] data;
       try {
         data = ZKUtil.getData(zkw, znodeToProcess);
       } catch (InterruptedException e) {
         zkw.interruptedException(e);
         return;
       }
       if (data != null && data.length > 0) { // log position
         long position = 0;
         try {
           position = ZKUtil.parseWALPositionFrom(ZKUtil.getData(zkw, znodeToProcess));
           sb.append(position);
         } catch (DeserializationException ignored) {
         } catch (InterruptedException e) {
           zkw.interruptedException(e);
           return;
         }
       }
       for (String zNodeChild : ZKUtil.listChildrenNoWatch(zkw, znodeToProcess)) {
         stack.add(ZKUtil.joinZNode(znodeToProcess, zNodeChild));
       }
     } while (stack.size() > 0);
   }
 
   private static void appendPeersZnodes(ZooKeeperWatcher zkw, String peersZnode,
     StringBuilder sb) throws KeeperException {
     int pblen = ProtobufUtil.lengthOfPBMagic();
     sb.append("\n").append(peersZnode).append(": ");
     for (String peerIdZnode : ZKUtil.listChildrenNoWatch(zkw, peersZnode)) {
       String znodeToProcess = ZKUtil.joinZNode(peersZnode, peerIdZnode);
       byte[] data;
       try {
         data = ZKUtil.getData(zkw, znodeToProcess);
       } catch (InterruptedException e) {
         zkw.interruptedException(e);
         return;
       }
       // parse the data of the above peer znode.
       try {
         ZooKeeperProtos.ReplicationPeer.Builder builder =
           ZooKeeperProtos.ReplicationPeer.newBuilder();
         ProtobufUtil.mergeFrom(builder, data, pblen, data.length - pblen);
         String clusterKey = builder.getClusterkey();
         sb.append("\n").append(znodeToProcess).append(": ").append(clusterKey);
         // add the peer-state.
         appendPeerState(zkw, znodeToProcess, sb);
       } catch (IOException ipbe) {
         LOG.warn("Got Exception while parsing peer: " + znodeToProcess, ipbe);
       }
     }
   }
 
   private static void appendPeerState(ZooKeeperWatcher zkw, String znodeToProcess,
       StringBuilder sb) throws KeeperException, InvalidProtocolBufferException {
     String peerState = zkw.getConfiguration().get("zookeeper.znode.replication.peers.state",
       "peer-state");
     int pblen = ProtobufUtil.lengthOfPBMagic();
     for (String child : ZKUtil.listChildrenNoWatch(zkw, znodeToProcess)) {
       if (!child.equals(peerState)) continue;
       String peerStateZnode = ZKUtil.joinZNode(znodeToProcess, child);
       sb.append("\n").append(peerStateZnode).append(": ");
       byte[] peerStateData;
       try {
         peerStateData = ZKUtil.getData(zkw, peerStateZnode);
         ZooKeeperProtos.ReplicationState.Builder builder =
             ZooKeeperProtos.ReplicationState.newBuilder();
         ProtobufUtil.mergeFrom(builder, peerStateData, pblen, peerStateData.length - pblen);
         sb.append(builder.getState().name());
       } catch (IOException ipbe) {
         LOG.warn("Got Exception while parsing peer: " + znodeToProcess, ipbe);
       } catch (InterruptedException e) {
         zkw.interruptedException(e);
         return;
       }
     }
   }
 
   /**
    * Gets the statistics from the given server.
    *
    * @param server  The server to get the statistics from.
    * @param timeout  The socket timeout to use.
    * @return The array of response strings.
    * @throws IOException When the socket communication fails.
    */
   public static String[] getServerStats(String server, int timeout)
   throws IOException {
     String[] sp = server.split(":");
     if (sp == null || sp.length == 0) {
       return null;
     }
 
     String host = sp[0];
     int port = sp.length > 1 ? Integer.parseInt(sp[1])
         : HConstants.DEFAULT_ZOOKEPER_CLIENT_PORT;
 
     Socket socket = new Socket();
     InetSocketAddress sockAddr = new InetSocketAddress(host, port);
     socket.connect(sockAddr, timeout);
 
     socket.setSoTimeout(timeout);
     PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
     BufferedReader in = new BufferedReader(new InputStreamReader(
       socket.getInputStream()));
     out.println("stat");
     out.flush();
     ArrayList<String> res = new ArrayList<String>();
     while (true) {
       String line = in.readLine();
       if (line != null) {
         res.add(line);
       } else {
         break;
       }
     }
     socket.close();
     return res.toArray(new String[res.size()]);
   }
 
   private static void logRetrievedMsg(final ZooKeeperWatcher zkw,
       final String znode, final byte [] data, final boolean watcherSet) {
     if (!LOG.isTraceEnabled()) return;
     LOG.trace(zkw.prefix("Retrieved " + ((data == null)? 0: data.length) +
       " byte(s) of data from znode " + znode +
       (watcherSet? " and set watcher; ": "; data=") +
       (data == null? "null": data.length == 0? "empty": (
           znode.startsWith(zkw.assignmentZNode)?
             ZKAssign.toString(data): // We should not be doing this reaching into another class
           znode.startsWith(ZooKeeperWatcher.META_ZNODE_PREFIX)?
             getServerNameOrEmptyString(data):
           znode.startsWith(zkw.backupMasterAddressesZNode)?
             getServerNameOrEmptyString(data):
           StringUtils.abbreviate(Bytes.toStringBinary(data), 32)))));
   }
 
   private static String getServerNameOrEmptyString(final byte [] data) {
     try {
       return ServerName.parseFrom(data).toString();
     } catch (DeserializationException e) {
       return "";
     }
   }
 
   /**
    * Waits for HBase installation's base (parent) znode to become available.
    * @throws IOException on ZK errors
    */
   public static void waitForBaseZNode(Configuration conf) throws IOException {
     LOG.info("Waiting until the base znode is available");
     String parentZNode = conf.get(HConstants.ZOOKEEPER_ZNODE_PARENT,
         HConstants.DEFAULT_ZOOKEEPER_ZNODE_PARENT);
     ZooKeeper zk = new ZooKeeper(ZKConfig.getZKQuorumServersString(conf),
         conf.getInt(HConstants.ZK_SESSION_TIMEOUT,
         HConstants.DEFAULT_ZK_SESSION_TIMEOUT), EmptyWatcher.instance);
 
     final int maxTimeMs = 10000;
     final int maxNumAttempts = maxTimeMs / HConstants.SOCKET_RETRY_WAIT_MS;
 
     KeeperException keeperEx = null;
     try {
       try {
         for (int attempt = 0; attempt < maxNumAttempts; ++attempt) {
           try {
             if (zk.exists(parentZNode, false) != null) {
               LOG.info("Parent znode exists: " + parentZNode);
               keeperEx = null;
               break;
             }
           } catch (KeeperException e) {
             keeperEx = e;
           }
           Threads.sleepWithoutInterrupt(HConstants.SOCKET_RETRY_WAIT_MS);
         }
       } finally {
         zk.close();
       }
     } catch (InterruptedException ex) {
       Thread.currentThread().interrupt();
     }
 
     if (keeperEx != null) {
       throw new IOException(keeperEx);
     }
   }
 
 
   public static byte[] blockUntilAvailable(
     final ZooKeeperWatcher zkw, final String znode, final long timeout)
     throws InterruptedException {
     if (timeout < 0) throw new IllegalArgumentException();
     if (zkw == null) throw new IllegalArgumentException();
     if (znode == null) throw new IllegalArgumentException();
 
     byte[] data = null;
     boolean finished = false;
     final long endTime = System.currentTimeMillis() + timeout;
     while (!finished) {
       try {
         data = ZKUtil.getData(zkw, znode);
       } catch(KeeperException e) {
         if (e instanceof KeeperException.SessionExpiredException
             || e instanceof KeeperException.AuthFailedException) {
           // non-recoverable errors so stop here
           throw new InterruptedException("interrupted due to " + e);
         }
         LOG.warn("Unexpected exception handling blockUntilAvailable", e);
       }
 
       if (data == null && (System.currentTimeMillis() +
         HConstants.SOCKET_RETRY_WAIT_MS < endTime)) {
         Thread.sleep(HConstants.SOCKET_RETRY_WAIT_MS);
       } else {
         finished = true;
       }
     }
 
     return data;
   }
 
 
   /**
    * Convert a {@link DeserializationException} to a more palatable {@link KeeperException}.
    * Used when can't let a {@link DeserializationException} out w/o changing public API.
    * @param e Exception to convert
    * @return Converted exception
    */
   public static KeeperException convert(final DeserializationException e) {
     KeeperException ke = new KeeperException.DataInconsistencyException();
     ke.initCause(e);
     return ke;
   }
 
   /**
    * Recursively print the current state of ZK (non-transactional)
    * @param root name of the root directory in zk to print
    */
   public static void logZKTree(ZooKeeperWatcher zkw, String root) {
     if (!LOG.isDebugEnabled()) return;
     LOG.debug("Current zk system:");
     String prefix = "|-";
     LOG.debug(prefix + root);
     try {
       logZKTree(zkw, root, prefix);
     } catch (KeeperException e) {
       throw new RuntimeException(e);
     }
   }
 
   /**
    * Helper method to print the current state of the ZK tree.
    * @see #logZKTree(ZooKeeperWatcher, String)
    * @throws KeeperException if an unexpected exception occurs
    */
   protected static void logZKTree(ZooKeeperWatcher zkw, String root, String prefix)
       throws KeeperException {
     List<String> children = ZKUtil.listChildrenNoWatch(zkw, root);
     if (children == null) return;
     for (String child : children) {
       LOG.debug(prefix + child);
       String node = ZKUtil.joinZNode(root.equals("/") ? "" : root, child);
       logZKTree(zkw, node, prefix + "---");
     }
   }
 
   /**
    * @param position
    * @return Serialized protobuf of <code>position</code> with pb magic prefix prepended suitable
    *         for use as content of an wal position in a replication queue.
    */
   public static byte[] positionToByteArray(final long position) {
     byte[] bytes = ZooKeeperProtos.ReplicationHLogPosition.newBuilder().setPosition(position)
         .build().toByteArray();
     return ProtobufUtil.prependPBMagic(bytes);
   }
 
   /**
    * @param bytes - Content of a WAL position znode.
    * @return long - The current WAL position.
    * @throws DeserializationException
    */
   public static long parseWALPositionFrom(final byte[] bytes) throws DeserializationException {
     if (bytes == null) {
       throw new DeserializationException("Unable to parse null WAL position.");
     }
     if (ProtobufUtil.isPBMagicPrefix(bytes)) {
       int pblen = ProtobufUtil.lengthOfPBMagic();
       ZooKeeperProtos.ReplicationHLogPosition.Builder builder =
           ZooKeeperProtos.ReplicationHLogPosition.newBuilder();
       ZooKeeperProtos.ReplicationHLogPosition position;
       try {
         ProtobufUtil.mergeFrom(builder, bytes, pblen, bytes.length - pblen);
         position = builder.build();
       } catch (IOException e) {
         throw new DeserializationException(e);
       }
       return position.getPosition();
     } else {
       if (bytes.length > 0) {
         return Bytes.toLong(bytes);
       }
       return 0;
     }
   }
 
   /**
    * @param regionLastFlushedSequenceId the flushed sequence id of a region which is the min of its
    *          store max seq ids
    * @param storeSequenceIds column family to sequence Id map
    * @return Serialized protobuf of <code>RegionSequenceIds</code> with pb magic prefix prepended
    *         suitable for use to filter wal edits in distributedLogReplay mode
    */
   public static byte[] regionSequenceIdsToByteArray(final Long regionLastFlushedSequenceId,
       final Map<byte[], Long> storeSequenceIds) {
     ClusterStatusProtos.RegionStoreSequenceIds.Builder regionSequenceIdsBuilder =
         ClusterStatusProtos.RegionStoreSequenceIds.newBuilder();
     ClusterStatusProtos.StoreSequenceId.Builder storeSequenceIdBuilder =
         ClusterStatusProtos.StoreSequenceId.newBuilder();
     if (storeSequenceIds != null) {
       for (Map.Entry<byte[], Long> e : storeSequenceIds.entrySet()){
         byte[] columnFamilyName = e.getKey();
         Long curSeqId = e.getValue();
         storeSequenceIdBuilder.setFamilyName(ByteStringer.wrap(columnFamilyName));
         storeSequenceIdBuilder.setSequenceId(curSeqId);
         regionSequenceIdsBuilder.addStoreSequenceId(storeSequenceIdBuilder.build());
         storeSequenceIdBuilder.clear();
       }
     }
     regionSequenceIdsBuilder.setLastFlushedSequenceId(regionLastFlushedSequenceId);
     byte[] result = regionSequenceIdsBuilder.build().toByteArray();
     return ProtobufUtil.prependPBMagic(result);
   }
 
   /**
    * @param bytes Content of serialized data of RegionStoreSequenceIds
    * @return a RegionStoreSequenceIds object
    * @throws DeserializationException
    */
   public static RegionStoreSequenceIds parseRegionStoreSequenceIds(final byte[] bytes)
       throws DeserializationException {
     if (bytes == null || !ProtobufUtil.isPBMagicPrefix(bytes)) {
       throw new DeserializationException("Unable to parse RegionStoreSequenceIds.");
     }
     RegionStoreSequenceIds.Builder regionSequenceIdsBuilder =
         ClusterStatusProtos.RegionStoreSequenceIds.newBuilder();
     int pblen = ProtobufUtil.lengthOfPBMagic();
     RegionStoreSequenceIds storeIds = null;
     try {
       ProtobufUtil.mergeFrom(regionSequenceIdsBuilder, bytes, pblen, bytes.length - pblen);
       storeIds = regionSequenceIdsBuilder.build();
     } catch (IOException e) {
       throw new DeserializationException(e);
     }
     return storeIds;
   }
 }