downloadFileAsync

function downloadFileAsync(url, dest) {
    return new Promise((resolve, reject) => {
        const file = fs.createWriteStream(dest);

        http.get(url, (res) => {
            if (res.statusCode !== 200) {
                reject(response.statusCode);
                return;
            }

            // 进度、超时等
            file.on('finish', () => {
                console.log('downloaded: ' + url);
                file.close(resolve);
            }).on('error', (err) => {
                fs.unlink(dest);
                reject(err.message);
            })

            res.pipe(file);
        });
    });
}

readRemoteFileAsync

function readRemoteFileAsync(url) {
    return new Promise((resolve, reject) => {
        http.get(url, (res) => {
            if (res.statusCode !== 200) {
                reject(response.statusCode);
                return;
            }
            let rawData = '';
            res.on('data', (chunk) => {
                rawData += chunk;
            });
            res.on('end', () => {
                resolve(rawData);
            });
        });
    });
}