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/*********************************************************************************
 *                                                                               *
 * The MIT License (MIT)                                                         *
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 * Copyright (c) 2015-2022 aoju.org and other contributors.                      *
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package org.aoju.bus.http;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
import java.util.List;

/**
 * 解析主机名的IP地址的域名服务。大多数应用程序将使用默认的
 * {@linkplain #SYSTEM SYSTEM DNS服务}，应用程序可能提供
 * 它们自己的实现来使用不同的DNS服务器
 * 选择IPv6地址、选择IPv4地址或强制使用特定的已知IP地址
 *
 * @author Kimi Liu
 * @since Java 17+
 */
public interface DnsX {

    /**
     * 使用{@link InetAddress#getAllByName(String)}请求底层操作系统
     * 查找IP地址的DNS。大多数自定义{@link DnsX}实现应该委托给这个实例.
     */
    DnsX SYSTEM = hostname -> {
        if (null == hostname) throw new UnknownHostException("hostname == null");
        try {
            return Arrays.asList(InetAddress.getAllByName(hostname));
        } catch (NullPointerException e) {
            UnknownHostException unknownHostException =
                    new UnknownHostException("Broken system behaviour for dns lookup of " + hostname);
            unknownHostException.initCause(e);
            throw unknownHostException;
        }
    };

    /**
     * 返回{@code hostname}的IP地址，按Httpd尝试的顺序排列。如果到地址的连接
     * 失败，Httpd将重试下一个地址的连接，直到建立连接、耗尽IP地址集或超出限制
     *
     * @param hostname 主机名信息
     * @return ip地址信息
     * @throws UnknownHostException 异常信息
     */
    List lookup(String hostname) throws UnknownHostException;

}