hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/net/TestDNSDomainNameResolver.java

/**
 * 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,
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 * See the License for the specific language governing permissions and
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 */
package org.apache.hadoop.net;

import org.junit.Test;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Objects;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotEquals;
import static org.junit.Assume.assumeFalse;


public class TestDNSDomainNameResolver {

  static DNSDomainNameResolver DNR = new DNSDomainNameResolver();

  @Test
  public void testGetHostNameByIP() throws UnknownHostException {
    InetAddress localhost = InetAddress.getLocalHost();
    assumeFalse("IP lookup support required",
        Objects.equals(localhost.getCanonicalHostName(), localhost.getHostAddress()));

    // Precondition: host name and canonical host name for unresolved returns an IP address.
    InetAddress unresolved = InetAddress.getByAddress(localhost.getHostAddress(),
        localhost.getAddress());
    assertEquals(localhost.getHostAddress(), unresolved.getHostName());

    // Test: Get the canonical name despite InetAddress caching
    String canonicalHostName = DNR.getHostnameByIP(unresolved);

    // Verify: The canonical host name doesn't match the host address but does match the localhost.
    assertNotEquals(localhost.getHostAddress(), canonicalHostName);
    assertEquals(localhost.getCanonicalHostName(), canonicalHostName);
  }

}