func (f *File) PrioritizeRegion(off, len int64) {
	f.t.DownloadPieces(f.t.byteRegionPieces(f.offset+off, len))
}
Requests that torrent pieces containing bytes in the given region of the
file be downloaded.
package torrent
import (
	"strings"
	"github.com/anacrolix/torrent/metainfo"
)
type File struct {
	t      *Torrent
	path   string
	offset int64
	length int64
	fi     metainfo.FileInfo
}
func (f *File) Torrent() *Torrent {
	return f.t
}
func (f *File) Offset() int64 {
	return f.offset
}
func (f File) FileInfo() metainfo.FileInfo {
	return f.fi
}
func (f File) Path() string {
	return f.path
}
func (f *File) Length() int64 {
	return f.length
}
func (f *File) DisplayPath() string {
	fip := f.FileInfo().Path
	if len(fip) == 0 {
		return f.t.Info().Name
	}
	return strings.Join(fip, "/")
}
type FilePieceState struct {
	Bytes int64  
	PieceState
}
func (f *File) State() (ret []FilePieceState) {
	pieceSize := int64(f.t.usualPieceSize())
	off := f.offset % pieceSize
	remaining := f.length
	for i := int(f.offset / pieceSize); ; i++ {
		if remaining == 0 {
			break
		}
		len1 := pieceSize - off
		if len1 > remaining {
			len1 = remaining
		}
		f.t.cl.mu.RLock()
		ps := f.t.pieceState(i)
		f.t.cl.mu.RUnlock()
		ret = append(ret, FilePieceState{len1, ps})
		off = 0
		remaining -= len1
	}
	return
}
func (f *File) Download() {
	f.t.DownloadPieces(f.t.byteRegionPieces(f.offset, f.length))
}