Improve overwriting files

[charlesbaynham]

Changes from @dHutchings in PR #4:

Previously, if you tried to write a new file, while overwriting a previous one, it would return the FILE_ALREADY_EXISTS error if the filesizes weren't the same.

This doesn't make sense, espescially since the user explititly set the overwrite flag true.

This new behaviour returns FILE_ALREADY_EXISTS only if overwrite is false.

If overwrite is true and it encounters an identically named file, it either uses it (if the sizes are identical) or deletes it and moves on.

(cherry picked from commit f62b6cb050f94f5e71fc10d63834acd2827a75f0)

[charlesbaynham]

In general, the way OSFS handles overwriting is a bit shaky at the moment. For example, we can end up with duplicate files on the filesystem (#5) and there's duplication of logic.

I think a bit of a refactor is in order. How about:

• [x] If overwrite == false, newFile should use getFileInfo to ensure that the file does not exist before writing it.
• [x] If overwrite == true, newFile should use deleteFile to ensure that the file does not exist before writing it.
• [x] Since the result of these checks will mean that newFile should have the same conditions for overwrite == true or false, we can remove all overwriting-related logic from the search loop: the normal check for fitting into a deleted file will work whether that file used to have the same name or not

[charlesbaynham]

@dHutchings I've done the refactor I mentioned above: this code should now support adding larger / smaller files and it shouldn't create duplicates on the filesystem under any circumstances.

I haven't got access to a microcontroller (stuck at home...), would you mind trying these changes out and seeing if they work for your case?

[dHutchings]

@charlesbaynham tested changes (not that rigorously). Seems to work.

Platform was a teensy 3.2 microcontroller.

Thank you! This library is great.

[charlesbaynham]

Brilliant! Glad you like it