FileError in Samsung Internet Browser

[marcoow]

Unfortunately this is a pretty vague bug report but at this point I don't really know how to debug it better 😞

We have an SPA that uses fetch (through https://github.com/stefanpenner/ember-fetch) and we're seeing a lot of FileErrors in production, all coming from Samsung Galaxies (6 and 7). The specific error is

The requested file could not be read, typically due to permission problems that have occurred after a reference to a file was acquired.

which seems to be related to Chrome's FileReader implementation (see here and e.g. here). This is also the only indication I have for this being related to fetch at all since the only usage of the FileReader API in our app bundle is within this library. Unfortunately we're not seeing any stack traces for this error in Sentry and I currently don't have an actual device to test this on.

More specifically, all of these errors (we have about 13000 events for 3000 users) are on Android 6 with Samsung Browser5.0/Chrome 51.

[mislav]

Ouch; thanks for letting us know.

Unfortunately, it's not possible to avoid using FileReader within our polyfill right now. It's automatically used whenever you call the response.text() method. I'm guessing that is how you're using the polyfill?

The only workaround right now that I can suggest is to trick the broken browsers into thinking that they don't have support for FileReader while the polyfill is loading:

<script>
if (samsungGalax) {
  BrokenFileReader = FileReader
  window.FileReader = undefined
}
</script>
<script src="./fetch.js"></script>
<script>
if (samsungGalax) {
  window.FileReader = BrokenFileReader
  delete window.BrokenFileReader
}
</script>

After this, the polyfill will continue to assume that the FileReader interface is unavailable (even though you've restored it) and will not try to use it.

[marcoow]

Unfortunately, it's not possible to avoid using FileReader within our polyfill right now. It's automatically used whenever you call the response.text() method. I'm guessing that is how you're using the polyfill?

Yes, we do use response.text().

The only workaround right now that I can suggest is to trick the broken browsers into thinking that they don't have support for FileReader while the polyfill is loading:

Hadn't even though of just forcing fetch to use the Polyfill… That should fix it of course - thanks for the hint!

BTW: your code is missing semicolons

[wichert]

@mislav I am hitting this as well. We happen to use response.json(), but I suspect that follows a very similar code path internally.

It is not just Samsung: the LG-D855 is hit by this as well. Affected Android versions include Android 4.1 though 6.0 based on the data I see in Sentry.

[nikcorg]

@wichert yep. .json() invokes .text() internally.

I'm also seeing this bug manifesting itself on Chrome Mobile 38.0.1025 on Android 4.2 devices.