Download file using nodejs

nodownload.js

/**
 * nodejs下载文件
 */

var fs = require('fs');
var url = require('url');
var http;

/**
 * @param  opts
 *         opts.url 下载链接
 *         opts.savePath 下载地址
 *         opts.callback 回调方法
 *
 * 回调方法的参数
 * state: 1成功 2正在下载 3失败
 * finished: 已下载
 * total 文件总大小
 */
module.exports = function(opts) {
    var http, protocol;
    protocol = url.parse(opts.url).protocol;
    if(protocol === 'https:') {
        http = require('https');
    } else {
        http = require('http');
    }
    var file = fs.createWriteStream(opts.savePath);

    // 下载超时失败后 会先进入错误处理timeoutWrapper
    // 然后触发 end事件
    var isError = false;
    // abort 会触发 end
    var isAbort = false;

    var timeoutWrapper = function(req) {
        return function() {
            console.log('timeout! abort');
            isError = true;
            req.abort();
            opts.callback.call(null, {
                state: 3
            });
        }
    }

    var requestSave = http.get(opts.url, function(res) {
        var len = 0;
        if(res.headers['content-length']) {
            len = parseInt(res.headers['content-length'], 10);
        } else {
            len = parseInt(res.headers['entries-size'], 10);
        }
        var downloaded = 0;

        res.on('data', function(chunk) {
            file.write(chunk);
            downloaded += chunk.length;

            opts.callback.call(null, {
                state: 1,
                finished: downloaded,
                total: len
            });

            // reset timout
            clearTimeout(timeoutId);
            timeoutId = setTimeout(fn, timeout);
        });

        res.on('end', function() {
            clearTimeout(timeoutId);
            if(!isError && !isAbort) {
                file.end();
                opts.callback.call(null, {
                    state: 2,
                    finished: downloaded,
                    total: len
                });
            } else {
                fs.unlink(opts.savePath);
            }
        });

        res.on('error', function(err) {
            clearTimeout(timeoutId);
            opts.callback.call(null, {
                state: 3,
                finished: downloaded,
                total: len
            });
        });

        var fn = timeoutWrapper(requestSave);
        var timeoutId = setTimeout(fn, timeout);
    });

    requestSave.on('error', function(err) {
        opts.callback.call(null, {
            state: 3
        });
    });

    requestSave.on('close', function(err) {
        isAbort = true;
    });

    return requestSave;
}