Return an interface which can be converted to `io.Reader` as well as
report payload size and hash.
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
1. Make it easier to change new parameters.
2. Fix a bug where the generator was created even for read-only
scenarios.
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
