public interface B2UploadListener
A B2UploadListener is called by periodically by the upload processes to
provide an indication of progress.
This interface is used for both small files and for large files.
In both cases, partIndex is zero-based. (Don't confuse partIndex with
a large file's part's partNumber.) For a small file, you'll only get
updates for partIndex=0 and partCount will always be 1.
For a large file with N parts, partIndex will range from 0 to N-1 and
partCount will always be N.
You may be called with state FAILED more than once in a row as various
layers of the software notice the error. Further, because of the way
the SDK retries, you may see updates indicating progress and perhaps
even failure and then you may see updates showing one or more subsequent
attempts to upload the same content.
THREAD-SAFETY: Listeners will be called from arbitrary threads and may be
called from multiple threads simultaneously. As a result, implementations
of B2UploadListener must be thread-safe.
PERFORMANCE: do not do anything that might block the thread for any appreciable
amount of time. doing so will slow down the upload.