[jira] [Created] (CB-12085) FileReader#readAsArrayBuffer reads whole file

["Damian Senn (JIRA)" <ji...@apache.org>]

Damian Senn created CB-12085:
--------------------------------

             Summary: FileReader#readAsArrayBuffer reads whole file
                 Key: CB-12085
                 URL: https://issues.apache.org/jira/browse/CB-12085
             Project: Apache Cordova
          Issue Type: Bug
          Components: Plugin File
    Affects Versions: 4.3.0
         Environment: Android
            Reporter: Damian Senn
            Priority: Critical


Reading a File with

```js
let fr = new FileReader

fr.onload = () => done(fs.result)
fr.readAsArrayBuffer(blob)
```

Is very slow, I'm assuming this is because it reads the whole file, then transfers this via base64 to the JS world, where it is converted to an ArrayBuffer. My use-case involves reading some media metadata in JS-World, this usually involves reading several bytes of 2mb to 50mb files.

I noticed this by profiling via Chrome-DevTools where the most time is being spent in the `atob` function in `cordova/base64.toArrayBuffer`.

So parsing some hundreds of bytes on a 3mb file may take around 3 to 4 seconds.

My guess is that this also has a very negative impact on memory usage and garbage collection.



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