管道文件流的输出是什么？ [英] What is the output of a piped file stream?

问题描述

也许这个问题没有以最好的方式措辞，但这里有更多的背景。使用GridFSBucket，我可以在mongo中存储文件并获取该文件的下载流。这是我的问题。假设我想将该文件作为对我的http请求的回复发送回去。

我这样做：

  downloadStream.pipe（RES）; 
  

在我打印responseText的客户端，我得到一些带有一些时髦字符的长字符串看起来是加密的。这个字符串/流的格式/类型是什么？如何设置我的响应，以便我可以在客户端将流数据作为ArrayBuffer获取？

谢谢

更新：

我还没有解决问题，但是@Jekrb的建议提供了与执行控制台完全相同的输出.LOG（this.responseText）。看起来字符串不是缓冲区。以下是这两行的输出：

console.log（this.responseText.toString（'utf8'））

var byteArray = new Uint8Array（arrayBuffer）;

更新2 - 代码信息

前端：

  var savePDF = function（blob）{
 //fs.writeFile(\"test.pdf  BLOB）; 
 var xhr = new XMLHttpRequest（）; 
 xhr.onreadystatechange = function（）{
 if（this.readyState === XMLHttpRequest.DONE&& this.status === 200）{
 
 //待办事项：处理我们将要显示的响应中的文件。 
 console.log（this.responseText.toString（'utf8'））; 
 var arrayBuffer = this.responseText; 
 if（arrayBuffer）{
 var byteArray = new Uint8Array（arrayBuffer）; 
} 
 console.log（arrayBuffer）; 
 
} 
}; 
 xhr.open（POST，/ pdf，true）; 
 xhr.responseType ='arrayBuffer'; 
 xhr.send（blob）; 
 
}; 
  

BACKEND：

  app.post（'/ pdf'，function（req，res）{
 
 MongoClient.connect（mongodb：// localhost：27017 / test，function（err，db） ）{
 if（err）return console.dir（err）; 
 console.log（Connected to Database）; 
 
 var bucket = new GridFSBucket（db，{ bucketName：'pdfs'}）; 
 var CHUNKS_COLL ='pdfs.chunks'; 
 var FILES_COLL ='pdfs.files'; 
 //插入文件
 var uploadStream = bucket .openUploadStream（'test.pdf'）; 
 var id = uploadStream.id; 
 
 uploadStream.once（'finish'，function（）{
 
 console .log（upload finished！）
 
 var downloadStream = bucket.openDownloadStream（id）; 
 downloadStream.pipe（res）; 
}）; 
 
 //这将POST数据传递给文件
 req.pipe（uploadStream）; 
}）; 
}）; 
  

解决方案

我解决了!!!

在您使用
req.responseType =arraybuffer <发出请求之前，基本上将响应类型预设为arraybuffer / p>

现在，一旦收到回复，请不要使用 responseText ，而是使用回复。 response 包含带有文件数据的arraybuffer。

Perhaps the question is not worded in the greatest way but here's some more context. Using GridFSBucket, I'm able to store a file in mongo and obtain a download stream for that file. Here's my question. Let's say I wanted to send that file back as a response to my http request.

I do:

downloadStream.pipe(res);

On the client side now when I print the responseText, I get some long string with some funky characters that look to be encrypted. What is the format/type of this string/stream? How do I setup my response so that I can get the streamed data as an ArrayBuffer on my client side?

Thanks

UPDATE:

I haven't solved the problem yet, however the suggestion by @Jekrb, gives exactly the same output as doing console.log(this.responseText). It looks like the string is not a buffer. Here is the output from these 2 lines:

console.log(this.responseText.toString('utf8'))

var byteArray = new Uint8Array(arrayBuffer);

UPDATE 2 - THE CODE SNIPPETS

Frontend:

    var savePDF = function(blob){
      //fs.writeFile("test.pdf",blob);
      var xhr = new XMLHttpRequest();
      xhr.onreadystatechange = function() {
        if (this.readyState === XMLHttpRequest.DONE && this.status === 200){

            //TO DO: Handle the file in the response which we will be displayed.
            console.log(this.responseText.toString('utf8'));
            var arrayBuffer = this.responseText;
            if (arrayBuffer) {
              var byteArray = new Uint8Array(arrayBuffer);
            }
            console.log(arrayBuffer);

          }
      };
      xhr.open("POST","/pdf",true);
      xhr.responseType = 'arrayBuffer';
      xhr.send(blob);

    };

BACKEND:

app.post('/pdf',function(req,res){

  MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
  if(err) return console.dir(err);
  console.log("Connected to Database");

  var bucket = new GridFSBucket(db, { bucketName: 'pdfs' });
  var CHUNKS_COLL = 'pdfs.chunks';
  var FILES_COLL = 'pdfs.files';
  // insert file
  var uploadStream = bucket.openUploadStream('test.pdf');
  var id = uploadStream.id;

  uploadStream.once('finish', function() {

     console.log("upload finished!")

     var downloadStream = bucket.openDownloadStream(id);
     downloadStream.pipe(res);
  });

  // This pipes the POST data to the file
  req.pipe(uploadStream);
});
});

解决方案

I solved it!!!

Basically preset the response type to "arraybuffer" before you make the request using req.responseType = "arraybuffer"

Now, once you receive the response, don't use responseText, instead use response. response contains the arraybuffer with the data for the file.

这篇关于管道文件流的输出是什么？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！