NewFile creates a new attachment file with a progress state.

NewMessageUploader creates a new MessageUploader.

NewProgress creates a new upload progress state.

NewReusableReader creates a new reader that is reusable after a read failure or a close.

File represents a middle format that can be used to create a MessageAttachment.

Progress wraps around a ReadCloser and implements a progress state for a reader.

ReusableReader provides an API which allows a reader to be used multiple times.