node.js – 尝试将文件从aws s3下载到nodejs writeStream中

downloadFile = function(bucketName, fileName, localFileName) {
    //Donwload the file
    var bucket = new AWS.S3({
        params: { Bucket: bucketName },
        signatureVersion: 'v4'
    });
    var file = require('fs').createWriteStream(localFileName);
    var request = bucket.getObject({ Key: fileName });
    request.createReadStream().pipe(file);
    request.send();
    return request.promise();
}

运行此函数我收到此错误：

Uncaught Error: write after end

怎么了？写入完成之前文件是否已关闭？为什么？

var s3 = new AWS.S3({
    accessKeyId: accessKeyId,
    secretAccessKey: secretAccessKey
}),
file = fs.createWriteStream(localFileName);
s3
.getObject({
    Bucket: bucketName,
    Key: fileName
})
.on('error', function (err) {
    console.log(err);
})
.on('httpData', function (chunk) {
    file.write(chunk);
})
.on('httpDone', function () {
    file.end();
})
.send();