/*
    * 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.util;
  
  import java.lang.reflect.Method;
  import java.net.UnknownHostException;
  
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * Wrapper around Hadoop's DNS class to hide reflection.
   */
  @InterfaceAudience.Private
  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="REC_CATCH_EXCEPTION",
    justification="If exception, presume HAS_NEW_DNS_GET_DEFAULT_HOST_API false")
  public final class DNS {
    private static boolean HAS_NEW_DNS_GET_DEFAULT_HOST_API;
    private static Method GET_DEFAULT_HOST_METHOD;
  
    static {
      try {
        GET_DEFAULT_HOST_METHOD = org.apache.hadoop.net.DNS.class
            .getMethod("getDefaultHost", String.class, String.class, boolean.class);
        HAS_NEW_DNS_GET_DEFAULT_HOST_API = true;
      } catch (Exception e) {
        HAS_NEW_DNS_GET_DEFAULT_HOST_API = false; // FindBugs: Causes REC_CATCH_EXCEPTION. Suppressed
      }
    }
  
    private DNS() {}
  
    /**
     * Wrapper around DNS.getDefaultHost(String, String), calling
     * DNS.getDefaultHost(String, String, boolean) when available.
     *
     * @param strInterface The network interface to query.
     * @param nameserver The DNS host name.
     * @return The default host names associated with IPs bound to the network interface.
     */
    public static String getDefaultHost(String strInterface, String nameserver)
        throws UnknownHostException {
      if (HAS_NEW_DNS_GET_DEFAULT_HOST_API) {
        try {
          // Hadoop-2.8 includes a String, String, boolean variant of getDefaultHost
          // which properly handles multi-homed systems with Kerberos.
          return (String) GET_DEFAULT_HOST_METHOD.invoke(null, strInterface, nameserver, true);
        } catch (Exception e) {
          // If we can't invoke the method as it should exist, throw an exception
          throw new RuntimeException("Failed to invoke DNS.getDefaultHost via reflection", e);
        }
      } else {
        return org.apache.hadoop.net.DNS.getDefaultHost(strInterface, nameserver);
      }
    }
  
    public static String getMasterHostname(Configuration conf) throws UnknownHostException {
      String hostname = conf.get("hbase.master.hostname", "");
      if (hostname.isEmpty()) {
        return Strings.domainNamePointerToHostName(getDefaultHost(
            conf.get("hbase.master.dns.interface", "default"),
            conf.get("hbase.master.dns.nameserver", "default")));
      }
      return hostname;
    }
  }