The FileProvider module allows users to select files from their online file storage providers and choose which files to upload to ReviewBoard for file attachments. This module consists of the following files

reviewboard/fileproviders/model.py : the Django model for representing file provider accounts for different users and file providers
reviewboard/fileproviders/fileprovider.py : the abstract FileProvider object to interact with the file providers.
reviewboard/fileproviders/tree.py : contains a base Node object, which can be used to represent files and directories found in the online file providers.
reviewboard/fileproviders/errors.py : contains error objects for the FileProvider framework

Anyone who wishes to support a particular file provider can do so by taking creating a derived class from FileProvider and implement the object's methods as neccessary, as well as creating an entry point for the object under reviewboard.file_providers

Test cases for functions and some object method in reviewboard/fileproviders/tests.py