"Read" problem for overly large files

I have an app performing uploads of large files, using "read" to extract Base64 chunks and upload them; today found an issue with my uploads freezing beyond a certain point, and it's due to the "position" being larger than int_max, so when cast to (int) seek file to offset fails.
Pretty simple fix (on iOS at least) - instead of casting the variables to integers, they should be cast to longs, which works for NSIntegers. Still working on Android, but will post a pull request (at least for "read") when that's working