如何从JS中的ArrayBuffer写入文件 [英] How to write a file from an ArrayBuffer in JS

问题描述

我正在为Meteor框架写一个文件上传器。
原理是将客户端上的文件从ArrayBuffer中分离出来，通过一个Meteor.method发送到服务器的4096位小数据包中。

下面的简化代码是向服务器发送块的客户端的一部分，直到偏移量达到 data.byteLength ： p>

  //数据是一个ArrayBuffer 
 var total = data.byteLength; 
 var offset = 0; 
 
 var upload = function（）{
 var length = 4096; //块大小
 
 //调整最后块大小
 if（offset + length> total）{
 length = total  -  offset; 
} 
 
 //我使用Uint8Array来创建块
 //，因为它可以本地传递给Meteor.method 
 var chunk = new Uint8Array数据，偏移量，长度）; 
 
 if（offset< total）{
 //发送块到服务器并告诉它要附加到
的文件Meteor.call（'uploadFileData'，fileId，如果（！err）{
 offset + = length; $ b $ upload（）; 
} 
} 
 } 
上传（）; //开始上传
  

下面的代码是接收块并将其写入文件系统的服务器上的部分：

  var fs = Npm.require（'fs'）; 
 var Future = Npm.require（'fibers / future'）; 
 
 Meteor.methods（{
 uploadFileData：函数（fileId，chunk）{
 var fut = new Future（）; 
 var path ='/ uploads /'+ fileId; 
 $ b $ //我试过没有成功
 chunk = String.fromCharCode.apply（null，chunk）; 
 
 //如何将Uint8Array的块写入磁盘？
 fs.appendFile（path，块，二进制，函数（ERR）{
如果（ERR）{
 fut.throw（ERR）; 
} else {
 fut.return（chunk.length）; 
} 
}）; 
 return fut.wait（）; 
} 
}）; 
  

我无法将有效的文件写入磁盘，实际上文件已保存，但无法打开，当我看到文本编辑器中的内容，它是类似于原始文件（例如一个JPG），但有些字符是不同的，我认为这可能是一个编码问题，因为文件大小是不一样的，但我不不知道如何解决这个问题...
解决方案

保存文件和使用Uint8Array对象创建一个新的Buffer一样简单：

$ $ p $ code $ chunk是Uint8Array对象
fs.appendFile（path，new Buffer（chunk），function err）{
if（err）{
fut.throw（err）;
} else {
fut.return（chunk.length）;
}
}）;

I am trying to write a file uploader for Meteor framework. The principle is to split the fileon the client from an ArrayBuffer in small packets of 4096 bits that are sent to the server through a Meteor.method.

The simplified code below is the part of the client that sends a chunk to the server, it is repeated until offset reaches data.byteLength :

// data is an ArrayBuffer
var total = data.byteLength;
var offset = 0;

var upload = function() {
  var length = 4096; // chunk size

  // adjust the last chunk size
  if (offset + length > total) {
     length = total - offset;
  }

  // I am using Uint8Array to create the chunk
  // because it can be passed to the Meteor.method natively
  var chunk = new Uint8Array(data, offset, length);

  if (offset < total) {
     // Send the chunk to the server and tell it what file to append to
     Meteor.call('uploadFileData', fileId, chunk, function (err, length) {
        if (!err) {
          offset += length;
          upload();
        }
     }
  }
};
upload(); // start uploading

The simplified code below is the part on the server that receives the chunk and writes it to the file system :

var fs = Npm.require('fs');
var Future = Npm.require('fibers/future');

Meteor.methods({
  uploadFileData: function(fileId, chunk) {
    var fut = new Future();
    var path = '/uploads/' + fileId;

    // I tried that with no success
    chunk = String.fromCharCode.apply(null, chunk);

    // how to write the chunk that is an Uint8Array to the disk ?
    fs.appendFile(path, chunk, 'binary', function (err) {
      if (err) {
        fut.throw(err);
      } else {
        fut.return(chunk.length);
      }
    });
    return fut.wait();
  }
});

I failed to write a valid file to the disk, actually the file is saved but I cannot open it, when I see the content in a text editor, it is similar to the original file (a jpg for example) but some characters are different, I think that could be an encoding problem as the file size is not the same, but I don't know how to fix that...

解决方案

Saving the file was as easy as creating a new Buffer with the Uint8Array object :

// chunk is the Uint8Array object
fs.appendFile(path, new Buffer(chunk), function (err) {
    if (err) {
      fut.throw(err);
    } else {
      fut.return(chunk.length);
    }
});

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