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1   /*
2    * Copyright 2017 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.resolver.dns;
17  
18  import io.netty.util.internal.UnstableApi;
19  
20  /**
21   * Provides an opportunity to override which {@link DnsServerAddressStream} is used to resolve a specific hostname.
22   * <p>
23   * For example this can be used to represent <a href="https://linux.die.net/man/5/resolver">/etc/resolv.conf</a> and
24   * <a href="https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/resolver.5.html">
25   * /etc/resolver</a>.
26   */
27  @UnstableApi
28  public interface DnsServerAddressStreamProvider {
29      /**
30       * Ask this provider for the name servers to query for {@code hostname}.
31       * @param hostname The hostname for which to lookup the DNS server addressed to use.
32       *                 If this is the final {@link DnsServerAddressStreamProvider} to be queried then generally empty
33       *                 string or {@code '.'} correspond to the default {@link DnsServerAddressStream}.
34       * @return The {@link DnsServerAddressStream} which should be used to resolve {@code hostname}.
35       */
36      DnsServerAddressStream nameServerAddressStream(String hostname);
37  }