code: func (b *Backend) SetStateSuccess(signature *tasks.Signature, results []*tasks.TaskResult) error {
  	decodedResults := b.decodeResults(results)
  	update := bson.M{
  		"state":   tasks.StateSuccess,
  		"results": decodedResults,
  	}
  	return b.updateState(signature, update)
  }
docs: // SetStateSuccess updates task state to SUCCESS