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

["Vladimir Kotikov (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CB-12085?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vladimir Kotikov reopened CB-12085:
-----------------------------------
      Assignee:     (was: Nikita Matrosov)

Reopening as it's probably still an issue

> FileReader#readAsArrayBuffer reads whole file
> ---------------------------------------------
>
>                 Key: CB-12085
>                 URL: https://issues.apache.org/jira/browse/CB-12085
>             Project: Apache Cordova
>          Issue Type: Bug
>          Components: cordova-plugin-file
>    Affects Versions: 4.3.0
>         Environment: Android
>            Reporter: Damian Senn
>            Priority: Critical
>              Labels: performance
>
> 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 (maybe around 100b to 1kb) 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 on my Samsung Galaxy S4 and around 1 second on my Samsung Galaxy S6. (This is without trying to read the actual metadata from the file).
> My guess is that this also has a very negative impact on memory usage and garbage collection.



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