//下载参数

var http = require("http");

var fs = require("fs");

var path = require("path");

var downFlag = false;

var downUrl = '';

var downFileName = '';

/**

 * 下载回调

 */

function getHttpReqCallback (imgSrc, dirName, fileName) {

    var callback = function(res) {

        console.log("request: " + imgSrc + " return status: " + res.statusCode);

        var contentLength = parseInt(res.headers['content-length']);

        var downLength = ;

        var out = fs.createWriteStream(dirName + "/" + fileName);

        res.on('data', function (chunk) {

            downLength += chunk.length;

            var progress =  Math.floor(downLength* / contentLength);

            var str = "下载："+ progress +"%";

            console.log(str);

            //写文件

            out.write(chunk, function () {

                //console.log(chunk.length);

            });

        });

        res.on('end', function() {

            downFlag = false;

            console.log("end downloading " + imgSrc);

            if (isNaN(contentLength)) {

                console.log(imgSrc + " content length error");

                return;

            }

            if (downLength < contentLength) {

                console.log(imgSrc + " download error, try again");

                return;

            }

        });

    };

    return callback;

}

/**

 * 下载开始

 */

function startDownloadTask (imgSrc, dirName,fileName) {

    console.log("start downloading " + imgSrc);

    var req = http.request(imgSrc, getHttpReqCallback(imgSrc, dirName, fileName));

    req.on('error', function(e){

        console.log("request " + imgSrc + " error, try again");

    });

    req.end();

}

startDownloadTask('http://mirrors.tuna.tsinghua.edu.cn/apache/tomcat/tomcat-8/v8.5.41/bin/apache-tomcat-8.5.41.tar.gz','D://1024Workspace//extension','apache-tomcat-8.5.41.tar.gz');

//startDownloadTask('下载地址','本地存储路径','文件名');