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webseed.go
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webseed.go
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package piecepicker
import (
"sort"
"github.com/cenkalti/rain/internal/peer"
"github.com/cenkalti/rain/internal/webseedsource"
)
// WebseedDownloadSpec contains information for downloading torrent data from webseed sources.
type WebseedDownloadSpec struct {
Source *webseedsource.WebseedSource
Begin uint32
End uint32
}
// PickWebseed returns the next spec for downloading files from webseed sources.
func (p *PiecePicker) PickWebseed(src *webseedsource.WebseedSource) *WebseedDownloadSpec {
begin, end := p.findRangeForWebseed()
if begin == end {
return nil
}
// Mark selected range as being downloaded so we won't select it again.
for i := begin; i < end; i++ {
if p.pieces[i].RequestedWebseed != nil {
panic("already downloading from webseed url")
}
p.pieces[i].RequestedWebseed = src
}
return &WebseedDownloadSpec{
Source: src,
Begin: begin,
End: end,
}
}
func (p *PiecePicker) downloadingWebseed() bool {
for _, src := range p.webseedSources {
if src.Downloading() {
return true
}
}
return false
}
func (p *PiecePicker) findRangeForWebseed() (begin, end uint32) {
gaps := p.findGaps()
if len(gaps) == 0 {
gap := p.webseedStealsFromAnotherWebseed()
return gap.Begin, gap.End
}
sort.Slice(gaps, func(i, j int) bool { return gaps[i].Len() > gaps[j].Len() })
return gaps[0].Begin, gaps[0].End
}
func (p *PiecePicker) getDownloadingSources() []*webseedsource.WebseedSource {
ret := make([]*webseedsource.WebseedSource, 0, len(p.webseedSources))
for _, src := range p.webseedSources {
if src.Downloading() {
ret = append(ret, src)
}
}
return ret
}
func (p *PiecePicker) webseedStealsFromAnotherWebseed() (r Range) {
downloading := p.getDownloadingSources()
if len(downloading) == 0 {
return
}
sort.Slice(downloading, func(i, j int) bool { return downloading[i].Remaining() > downloading[j].Remaining() })
src := downloading[0]
r.End = src.Downloader.End
r.Begin = (src.Downloader.ReadCurrent() + src.Downloader.End + 1) / 2
p.WebseedStopAt(src, r.Begin)
return
}
func (p *PiecePicker) peerStealsFromWebseed(pe *peer.Peer) *myPiece {
downloading := p.getDownloadingSources()
for _, src := range downloading {
if src.Remaining() == 0 {
continue
}
for i := src.Downloader.End - 1; i > src.Downloader.ReadCurrent(); i-- {
pi := &p.pieces[i]
if pi.Done || pi.Writing {
continue
}
if !pi.Having.Has(pe) {
continue
}
if pi.Requested.Len() > 0 {
continue
}
p.WebseedStopAt(src, i)
return pi
}
}
return nil
}
func (p *PiecePicker) findGaps() []Range {
gaps := p.findGaps2(false)
if len(gaps) == 0 {
gaps = p.findGaps2(true)
}
return gaps
}
func (p *PiecePicker) findGaps2(duplicate bool) []Range {
a := make([]Range, 0, len(p.pieces)/2)
var inGap bool
var begin uint32
for _, pi := range p.pieces {
if !inGap {
if pi.AvailableForWebseed(duplicate) {
begin = pi.Index
inGap = true
} else {
continue
}
} else {
if pi.AvailableForWebseed(duplicate) {
continue
} else {
a = append(a, Range{Begin: begin, End: pi.Index})
inGap = false
}
}
}
if inGap {
a = append(a, Range{Begin: begin, End: uint32(len(p.pieces))})
}
return a
}
func (p *PiecePicker) pickLastPieceOfSmallestGap(pe *peer.Peer) *myPiece {
gaps := p.findGaps()
if len(gaps) == 0 {
return nil
}
sort.Slice(gaps, func(i, j int) bool { return gaps[i].Len() < gaps[j].Len() })
for _, gap := range gaps {
// Convert index to int because it goes below zero in loop.
for i := int(gap.End - 1); i >= int(gap.Begin); i-- {
mp := &p.pieces[i]
if !mp.Having.Has(pe) {
continue
}
if pe.PeerChoking && !pe.ReceivedAllowedFast.Has(mp.Piece) {
continue
}
return mp
}
}
return nil
}
// Range is a piece range.
// Begin is inclusive, End is exclusive.
type Range struct {
Begin, End uint32
}
// Len returns the number of pieces in the range.
func (r Range) Len() uint32 {
return r.End - r.Begin
}