Add BaseDirectoey.root

[781flyingdutchman]

Allows upload/download to any destination, with the risk related to app sandbox moving to the developer.

Not ideal, but there are so many questions about this that I think it's worth adding in V8

[FluffyDiscord]

I really need to be able to download and upload files directly to/from somewhere in user created folders on Android. There is already package, that can read/write anywhere that user permits using Android's SAF. Would you consider enabling/adding support to download anywhere? https://github.com/alexrintt/shared-storage / https://developer.android.com/training/data-storage/manage-all-files

Right now it's impossible to do so with background_download. We can only move files to some predefined shared folders. Uploading is in even worse state. We have to copy the file to the scoped storage in order to not lose it, since renaming/moving makes the file disappear in the span of the uploading time.

Maybe this could be worked around by adding save/read callbacks where we could handle the IO ourselves? Not sure if possible, or if that would be harder to implement.

[781flyingdutchman]

Yes, I'm planning this for V8, which is what I'm worrying right now. The way this would work is:

1. Set baseDirectory to BaseDirectory.root (a new value in the BaseDirectory enum
2. The task's directory field then becomes the absolute path to a directory on the system, and filename completes that path to point to a specific file
3. Provided you have access to that path, you can download to or upload from that path

You should still use the other BaseDirectory values whenever possible to avoid issues with unstable application directories. If you use .root you're "on your own" w.r.t. stability and permissions.

[781flyingdutchman]

@FluffyDiscord I've added this to branch V8-dev. Do you mind checking it out before this is released as V8?

From the readme: You can also pass an absolute path to the downloader by using BaseDirectory.root combined with the path in directory. This allows you to reach any file destination on your platform. However, be careful: the reason you should not normally do this (and use e.g. BaseDirectory.applicationDocuments instead) is that the location of the app's documents directory may change between application starts (on iOS, and on Android in some cases), and may therefore fail for downloads that complete while the app is suspended. You should therefore never store permanently, or hard-code, an absolute path, unless you are absolutely sure that that path is 'stable'.

[FluffyDiscord]

I will test it later today.

[FluffyDiscord]

Works, but I think you should enable to have the leading / when BaseDirectory.root is being used, so we don't have to always strip the first slash (basically the check at package:background_downloader/src/task.dart:296:7)

[781flyingdutchman]

Good suggestion, I'll change that

[781flyingdutchman]

Included in V8, and the leading path separator is now always stripped from the directory field.