Nonzero offset implies a ranged request. Must also specify size.
A size > 0 implies a ranged request.
Callback for successful fetch.
Callback for fetch failure.
use IFetchHandler instead (more flexible).
This provides a hook for the client application to intercept requests for resources if they have to be fetched in a way different than a simple HTTP get request.
If size = 0, a regular fetch of as much as possible is requested. In this case, offset != 0 should not happen and is an error. If size > 0, a fetch of a specific range is requested.
Url to load