code: func (p *deviceFolderDownloadState) GetBlockCounts() map[string]int {
  	p.mut.RLock()
  	res := make(map[string]int, len(p.files))
  	for name, state := range p.files {
  		res[name] = len(state.blockIndexes)
  	}
  	p.mut.RUnlock()
  	return res
  }
docs: // GetBlockCounts returns a map filename -> number of blocks downloaded.