JavaScript中的文件切片导致空blob [英] File slicing in JavaScript results in empty blob

问题描述

我正在实现一个基于浏览器的分块文件上传器。要打开文件，我使用< input type =fileid =fileSelector/> 和这段代码（简化）：

  $（'＃fileSelector'）。on（'change'，function（）{
 _file = evt.target.files [0 ]; 
}）; 
  

我正在将文件切成块，但不将块读入内存（未明确）。 / p>

问题：偶尔（少于0.1％的上传文件）从基础文件中切出的块是空的。例如。在上传大文件的过程中，事情进展顺利，然后在该文件的中间调用：

  var _blob = _file.slice（ chunk.start，chunk.end，_ file.type）; 
  

产生一个空切片（ _blob.size 是0）。将此blob发送到服务器（.NET 4.6）会导致 Request.InputStream 为空。我发送的是bniary数据：

  _xhr.setRequestHeader（'content-type'，'application / octet-stream'）; 
 _xhr.send（_blob）; 
  

我还应该提到调用 _file.slice 再次产生相同的空斑点。我可以在Chrome 57，Chrome 60（Win和Mac），Mac Safari 10.1.1和Edge 15中观察到这一点。其他浏览器也是可以的。

什么可以错误？我正在考虑的事情：

• 文件正在使用中


• 文件/磁盘已损坏


• 同时使用JavaScript引擎对blob进行GC管理 - 如果可以的话，如何确保它不是GC？


• 浏览器错误（我找到了）这个，但不确定它是否相关： https：//错误。 chromium.org/p/chromium/issues/detail?id=167111 ）

解决方案

答案结果非常简单：当上传的文件消失（重命名，删除）时会发生这种情况。

I am implementing a browser-based chunked file uploader. To open the file I am using <input type="file" id="fileSelector" /> and this piece of code (simplified):

$('#fileSelector').on('change', function () {
    _file = evt.target.files[0];
});

I am slicing the file into chunks, but not reading the chunk into memory (not explicitly).

Problem: occasionally (for less than 0.1% of uploaded files) the chunk sliced from the underlying file is empty. E.g. during uploading a large file things go well, and then in the middle of that file calling:

var _blob = _file.slice(chunk.start, chunk.end, _file.type);

results in an empty slice (_blob.size is 0). Sending such blob to the server (.NET 4.6) results in Request.InputStream being empty. I am sending bniary data:

_xhr.setRequestHeader('content-type', 'application/octet-stream');
_xhr.send(_blob);

I should also mention that calling _file.slice again produces same empty blob. I can observe this in Chrome 57, Chrome 60 (Win and Mac), Mac Safari 10.1.1 and in Edge 15. Other browsers are also possible.

What can be wrong? Things I am considering:

• file is in use
• file/disk is corrupt
• the blob is GCed by JavaScript engine in the meantime - if that can be the case how to make sure it is not GCed?
• browser bug (I found this, but not sure if it is related: https://bugs.chromium.org/p/chromium/issues/detail?id=167111)

解决方案

The answer turned out to be very simple: that's what happens when the file being uploaded is gone (renamed, deleted).

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