Node.js dns.lookupService()方法

原文:https://www . geesforgeks . org/node-js-DNS-lookup service-method/

dns.lookupService()方法是 dns 模块的内置应用程序编程接口，用于使用操作系统的底层 getnameinfo 实现将地址和端口号解析为主机名。

语法:

dns.lookupService( address, port, callback )

参数:该方法有三个参数，如上所述，如下所述:

• Address: It specifies a string representing the address to be resolved.
• Port: It is a number that specifies the port number of the address whose service is to be resolved.
• Callback: Specify the function to be called after the address and port are resolved.
  • Error: The specified generation error.
  • Hostname: String representation of the hostname. For example, geeksforgeeks.org
  • Service: It is a string that specifies the name of the service. E.g. http

返回值:该方法通过回调函数返回错误、主机名和服务。这些数据作为参数传递给回调函数。

下面的例子说明了在 Node.js 中 dns.lookupService()方法的使用:

示例 1: 本地主机的 IP

// Accessing dns module
const dns = require('dns');

// Calling dns.lookupService() method for
// 127.0.0.1 port  number 22
dns.lookupService('127.0.0.1', 22,
         (err, hostname, service) => {

    // Printing hostname and service as callback
    console.log(hostname, service);
});

输出:这里我电脑的名字是 my-lappy

my-lappy ssh

例 2:

// Accessing dns module
const dns = require('dns');

// Setting options for dns.lookup() method
const options = {

    // Setting family as 4 i.e. IPv4
    family: 4,
    hints: dns.ADDRCONFIG | dns.V4MAPPED,
};

dns.lookup('www.geeksforgeeks.org', 
        options, (err, address, family) => {

    console.log('address:', address);
        if(err){
            console.log(err.stack);
        } else{

        // Calling dns.lookupService() method 
        dns.lookupService(address, 80,
                 (err, hostname, service) => {
            if(err){
                console.log(err.stack);
            }

            // Printing hostname and service
            // as callback
            console.log(hostname, service);
        });
    }
});

输出:

address: 42.106.162.241
42-106-162-241.live.vodafone.in http

注意:以上程序使用node filename.js命令编译运行。

参考:https://nodejs . org/API/DNS . html # DNS _ DNS _ lookupservice _ address _ port _ callback

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