node . js dnspromses . lookup service()方法

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

dnsPromises.lookupService()方法是 dns 模块 Promises 对象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和服务。

语法:

dnsPromises.lookupService( address, port )

参数:该方法有两个参数，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.

返回值:此方法返回错误、主机名和服务。

下面的例子说明了在 Node.js 中使用方法:

例 1:

// Node.js program to demonstrate the   
// dnsPromises.lookupService() method

// Accessing promises object from dns module
const dns = require('dns');
const dnsPromises = dns.promises;

// Calling dnsPromises.lookupService() method
// for 127.0.0.1 port  number 22
dnsPromises.lookupService('127.0.0.1', 22).then((res) => {
    console.log(res.hostname, res.service);
});

输出:这里我电脑的名字是 my-lappy

my-lappy ssh

例 2:

// Node.js program to demonstrate the   
// dnsPromises.lookupService() method

// Accessing promises object from dns module
const dns = require('dns');
const dnsPromises = dns.promises;;

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

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

dnsPromises.lookup('geeksforgeeks.org', options).then((response) => {
    if(response){
        console.log(response);

        // Calling dnsPromises.lookupService() method 
        dnsPromises.lookupService(response.address, 80).then((res) => {
            console.log(res.hostname, res.service);
        });
    }
});

输出:

{ address: '34.218.62.116', family: 4 }
ec2-34-218-62-116.us-west-2.compute.amazonaws.com 334

注意:以上程序使用node index.js命令编译运行。

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

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