AWS S3下载的pdf writestream在下载时变为零字节

Question

我从node.js express服务器中的aws s3存储桶下载pdf，然后将该pdf写入uploads文件夹中的文件：

var s3 = new aws.S3();
var params = {
    Bucket: 'aliro-pdf-assets',
    Key: req.body.query
};
var out = fs.createWriteStream(__dirname + '/public/uploads/' + req.body.query);
s3.getObject(params).
  on('httpData', function(chunk) { out.write(chunk); }).
  on('httpDone', function() {
    out.end();
    res.send('http done');
  }).send();

之后（在前端ajax调用下载此pdf的回调中），我尝试在前端渲染它，如下所示：

<object data="/uploads/' + pdata.pdf + '" width="98%" height="1300" type="application/pdf">
  <p>You don\'nt have a PDF plugin for this browser. Click Download PDF up in the top left to view the PDF anyway!</p>\
</object>

也是这样的：

<a id="pdfDown" href="/uploads/' + pdata.pdf + '" class= "btn btn-danger btn-sm downloadPDF"><img src="images/pdfIcon.png">Download PDF</a>\

（pdata.pdf是pdf的名称，与服务器中的req.body.query相同）

问题是，这两个渲染都不起作用。 PDF.JS给了我这个错误：

Error: stream must have data pdf.worker.js:237:5
assert@resource://pdf.js/build/pdf.worker.js:254:5
init@resource://pdf.js/build/pdf.worker.js:2343:5
PDFDocument@resource://pdf.js/build/pdf.worker.js:2334:7
NetworkPdfManager@resource://pdf.js/build/pdf.worker.js:1996:24
getPdfManager@resource://pdf.js/build/pdf.worker.js:33775:24
wphSetupDoc@resource://pdf.js/build/pdf.worker.js:33979:7
messageHandlerComObjOnMessage@resource://pdf.js/build/pdf.worker.js:1247:9
 pdf.worker.js:238:1
Warning: Unsupported feature "unknown" pdf.worker.js:224:5
Warning: Unsupported feature "unknown" pdf.js:224:5
An error occurred while loading the PDF.
PDF.js v1.1.551 (build: 2a5616c)
Message: stream must have data

怎么了？我知道我正在访问s3中的正确文件，但我在前端实际收到的pdf是零字节！