Implement piece request ordering with retained state

[btrtrc.git] / torrent.go

package torrent

import (
        "bytes"
        "container/heap"
        "context"
        "crypto/sha1"
        "errors"
        "fmt"
        "io"
        "net/url"
        "sort"
        "strings"
        "text/tabwriter"
        "time"
        "unsafe"

        "github.com/RoaringBitmap/roaring"
        "github.com/anacrolix/chansync"
        "github.com/anacrolix/chansync/events"
        "github.com/anacrolix/dht/v2"
        "github.com/anacrolix/log"
        "github.com/anacrolix/missinggo/perf"
        "github.com/anacrolix/missinggo/pubsub"
        "github.com/anacrolix/missinggo/slices"
        "github.com/anacrolix/missinggo/v2"
        "github.com/anacrolix/missinggo/v2/bitmap"
        "github.com/anacrolix/multiless"
        "github.com/anacrolix/sync"
        request_strategy "github.com/anacrolix/torrent/request-strategy"
        "github.com/davecgh/go-spew/spew"
        "github.com/pion/datachannel"

        "github.com/anacrolix/torrent/bencode"
        "github.com/anacrolix/torrent/common"
        "github.com/anacrolix/torrent/metainfo"
        pp "github.com/anacrolix/torrent/peer_protocol"
        "github.com/anacrolix/torrent/segments"
        "github.com/anacrolix/torrent/storage"
        "github.com/anacrolix/torrent/tracker"
        "github.com/anacrolix/torrent/webseed"
        "github.com/anacrolix/torrent/webtorrent"
)

// Maintains state of torrent within a Client. Many methods should not be called before the info is
// available, see .Info and .GotInfo.
type Torrent struct {
        // Torrent-level aggregate statistics. First in struct to ensure 64-bit
        // alignment. See #262.
        stats  ConnStats
        cl     *Client
        logger log.Logger

        networkingEnabled      chansync.Flag
        dataDownloadDisallowed chansync.Flag
        dataUploadDisallowed   bool
        userOnWriteChunkErr    func(error)

        closed   chansync.SetOnce
        infoHash metainfo.Hash
        pieces   []Piece
        // Values are the piece indices that changed.
        pieceStateChanges *pubsub.PubSub
        // The size of chunks to request from peers over the wire. This is
        // normally 16KiB by convention these days.
        chunkSize pp.Integer
        chunkPool sync.Pool
        // Total length of the torrent in bytes. Stored because it's not O(1) to
        // get this from the info dict.
        length *int64

        // The storage to open when the info dict becomes available.
        storageOpener *storage.Client
        // Storage for torrent data.
        storage *storage.Torrent
        // Read-locked for using storage, and write-locked for Closing.
        storageLock sync.RWMutex

        // TODO: Only announce stuff is used?
        metainfo metainfo.MetaInfo

        // The info dict. nil if we don't have it (yet).
        info      *metainfo.Info
        fileIndex segments.Index
        files     *[]*File

        webSeeds map[string]*Peer

        // Active peer connections, running message stream loops. TODO: Make this
        // open (not-closed) connections only.
        conns               map[*PeerConn]struct{}
        maxEstablishedConns int
        // Set of addrs to which we're attempting to connect. Connections are
        // half-open until all handshakes are completed.
        halfOpen map[string]PeerInfo

        // Reserve of peers to connect to. A peer can be both here and in the
        // active connections if were told about the peer after connecting with
        // them. That encourages us to reconnect to peers that are well known in
        // the swarm.
        peers prioritizedPeers
        // Whether we want to know to know more peers.
        wantPeersEvent missinggo.Event
        // An announcer for each tracker URL.
        trackerAnnouncers map[string]torrentTrackerAnnouncer
        // How many times we've initiated a DHT announce. TODO: Move into stats.
        numDHTAnnounces int

        // Name used if the info name isn't available. Should be cleared when the
        // Info does become available.
        nameMu      sync.RWMutex
        displayName string

        // The bencoded bytes of the info dict. This is actively manipulated if
        // the info bytes aren't initially available, and we try to fetch them
        // from peers.
        metadataBytes []byte
        // Each element corresponds to the 16KiB metadata pieces. If true, we have
        // received that piece.
        metadataCompletedChunks []bool
        metadataChanged         sync.Cond

        // Closed when .Info is obtained.
        gotMetainfoC chan struct{}

        readers                map[*reader]struct{}
        _readerNowPieces       bitmap.Bitmap
        _readerReadaheadPieces bitmap.Bitmap

        // A cache of pieces we need to get. Calculated from various piece and
        // file priorities and completion states elsewhere.
        _pendingPieces roaring.Bitmap
        // A cache of completed piece indices.
        _completedPieces roaring.Bitmap
        // Pieces that need to be hashed.
        piecesQueuedForHash       bitmap.Bitmap
        activePieceHashes         int
        initialPieceCheckDisabled bool

        // Count of each request across active connections.
        pendingRequests pendingRequests
        // Chunks we've written to since the corresponding piece was last checked.
        dirtyChunks roaring.Bitmap

        pex pexState

        // Is On when all pieces are complete.
        Complete chansync.Flag
}

func (t *Torrent) pieceAvailabilityFromPeers(i pieceIndex) (count int) {
        t.iterPeers(func(peer *Peer) {
                if peer.peerHasPiece(i) {
                        count++
                }
        })
        return
}

func (t *Torrent) decPieceAvailability(i pieceIndex) {
        if !t.haveInfo() {
                return
        }
        p := t.piece(i)
        if p.availability <= 0 {
                panic(p.availability)
        }
        p.availability--
        t.updatePieceRequestOrder(i)
}

func (t *Torrent) incPieceAvailability(i pieceIndex) {
        // If we don't the info, this should be reconciled when we do.
        if t.haveInfo() {
                p := t.piece(i)
                p.availability++
                t.updatePieceRequestOrder(i)
        }
}

func (t *Torrent) readerNowPieces() bitmap.Bitmap {
        return t._readerNowPieces
}

func (t *Torrent) readerReadaheadPieces() bitmap.Bitmap {
        return t._readerReadaheadPieces
}

func (t *Torrent) ignorePieceForRequests(i pieceIndex) bool {
        return !t.wantPieceIndex(i)
}

// Returns a channel that is closed when the Torrent is closed.
func (t *Torrent) Closed() events.Done {
        return t.closed.Done()
}

// KnownSwarm returns the known subset of the peers in the Torrent's swarm, including active,
// pending, and half-open peers.
func (t *Torrent) KnownSwarm() (ks []PeerInfo) {
        // Add pending peers to the list
        t.peers.Each(func(peer PeerInfo) {
                ks = append(ks, peer)
        })

        // Add half-open peers to the list
        for _, peer := range t.halfOpen {
                ks = append(ks, peer)
        }

        // Add active peers to the list
        for conn := range t.conns {
                ks = append(ks, PeerInfo{
                        Id:     conn.PeerID,
                        Addr:   conn.RemoteAddr,
                        Source: conn.Discovery,
                        // > If the connection is encrypted, that's certainly enough to set SupportsEncryption.
                        // > But if we're not connected to them with an encrypted connection, I couldn't say
                        // > what's appropriate. We can carry forward the SupportsEncryption value as we
                        // > received it from trackers/DHT/PEX, or just use the encryption state for the
                        // > connection. It's probably easiest to do the latter for now.
                        // https://github.com/anacrolix/torrent/pull/188
                        SupportsEncryption: conn.headerEncrypted,
                })
        }

        return
}

func (t *Torrent) setChunkSize(size pp.Integer) {
        t.chunkSize = size
        t.chunkPool = sync.Pool{
                New: func() interface{} {
                        b := make([]byte, size)
                        return &b
                },
        }
}

func (t *Torrent) pieceComplete(piece pieceIndex) bool {
        return t._completedPieces.Contains(bitmap.BitIndex(piece))
}

func (t *Torrent) pieceCompleteUncached(piece pieceIndex) storage.Completion {
        return t.pieces[piece].Storage().Completion()
}

// There's a connection to that address already.
func (t *Torrent) addrActive(addr string) bool {
        if _, ok := t.halfOpen[addr]; ok {
                return true
        }
        for c := range t.conns {
                ra := c.RemoteAddr
                if ra.String() == addr {
                        return true
                }
        }
        return false
}

func (t *Torrent) appendUnclosedConns(ret []*PeerConn) []*PeerConn {
        return t.appendConns(ret, func(conn *PeerConn) bool {
                return !conn.closed.IsSet()
        })
}

func (t *Torrent) appendConns(ret []*PeerConn, f func(*PeerConn) bool) []*PeerConn {
        for c := range t.conns {
                if f(c) {
                        ret = append(ret, c)
                }
        }
        return ret
}

func (t *Torrent) addPeer(p PeerInfo) (added bool) {
        cl := t.cl
        torrent.Add(fmt.Sprintf("peers added by source %q", p.Source), 1)
        if t.closed.IsSet() {
                return false
        }
        if ipAddr, ok := tryIpPortFromNetAddr(p.Addr); ok {
                if cl.badPeerIPPort(ipAddr.IP, ipAddr.Port) {
                        torrent.Add("peers not added because of bad addr", 1)
                        // cl.logger.Printf("peers not added because of bad addr: %v", p)
                        return false
                }
        }
        if replaced, ok := t.peers.AddReturningReplacedPeer(p); ok {
                torrent.Add("peers replaced", 1)
                if !replaced.equal(p) {
                        t.logger.WithDefaultLevel(log.Debug).Printf("added %v replacing %v", p, replaced)
                        added = true
                }
        } else {
                added = true
        }
        t.openNewConns()
        for t.peers.Len() > cl.config.TorrentPeersHighWater {
                _, ok := t.peers.DeleteMin()
                if ok {
                        torrent.Add("excess reserve peers discarded", 1)
                }
        }
        return
}

func (t *Torrent) invalidateMetadata() {
        for i := 0; i < len(t.metadataCompletedChunks); i++ {
                t.metadataCompletedChunks[i] = false
        }
        t.nameMu.Lock()
        t.gotMetainfoC = make(chan struct{})
        t.info = nil
        t.nameMu.Unlock()
}

func (t *Torrent) saveMetadataPiece(index int, data []byte) {
        if t.haveInfo() {
                return
        }
        if index >= len(t.metadataCompletedChunks) {
                t.logger.Printf("%s: ignoring metadata piece %d", t, index)
                return
        }
        copy(t.metadataBytes[(1<<14)*index:], data)
        t.metadataCompletedChunks[index] = true
}

func (t *Torrent) metadataPieceCount() int {
        return (len(t.metadataBytes) + (1 << 14) - 1) / (1 << 14)
}

func (t *Torrent) haveMetadataPiece(piece int) bool {
        if t.haveInfo() {
                return (1<<14)*piece < len(t.metadataBytes)
        } else {
                return piece < len(t.metadataCompletedChunks) && t.metadataCompletedChunks[piece]
        }
}

func (t *Torrent) metadataSize() int {
        return len(t.metadataBytes)
}

func infoPieceHashes(info *metainfo.Info) (ret [][]byte) {
        for i := 0; i < len(info.Pieces); i += sha1.Size {
                ret = append(ret, info.Pieces[i:i+sha1.Size])
        }
        return
}

func (t *Torrent) makePieces() {
        hashes := infoPieceHashes(t.info)
        t.pieces = make([]Piece, len(hashes))
        for i, hash := range hashes {
                piece := &t.pieces[i]
                piece.t = t
                piece.index = pieceIndex(i)
                piece.noPendingWrites.L = &piece.pendingWritesMutex
                piece.hash = (*metainfo.Hash)(unsafe.Pointer(&hash[0]))
                files := *t.files
                beginFile := pieceFirstFileIndex(piece.torrentBeginOffset(), files)
                endFile := pieceEndFileIndex(piece.torrentEndOffset(), files)
                piece.files = files[beginFile:endFile]
                piece.undirtiedChunksIter = undirtiedChunksIter{
                        TorrentDirtyChunks: &t.dirtyChunks,
                        StartRequestIndex:  piece.requestIndexOffset(),
                        EndRequestIndex:    piece.requestIndexOffset() + piece.numChunks(),
                }
        }
}

// Returns the index of the first file containing the piece. files must be
// ordered by offset.
func pieceFirstFileIndex(pieceOffset int64, files []*File) int {
        for i, f := range files {
                if f.offset+f.length > pieceOffset {
                        return i
                }
        }
        return 0
}

// Returns the index after the last file containing the piece. files must be
// ordered by offset.
func pieceEndFileIndex(pieceEndOffset int64, files []*File) int {
        for i, f := range files {
                if f.offset+f.length >= pieceEndOffset {
                        return i + 1
                }
        }
        return 0
}

func (t *Torrent) cacheLength() {
        var l int64
        for _, f := range t.info.UpvertedFiles() {
                l += f.Length
        }
        t.length = &l
}

// TODO: This shouldn't fail for storage reasons. Instead we should handle storage failure
// separately.
func (t *Torrent) setInfo(info *metainfo.Info) error {
        if err := validateInfo(info); err != nil {
                return fmt.Errorf("bad info: %s", err)
        }
        if t.storageOpener != nil {
                var err error
                t.storage, err = t.storageOpener.OpenTorrent(info, t.infoHash)
                if err != nil {
                        return fmt.Errorf("error opening torrent storage: %s", err)
                }
        }
        t.nameMu.Lock()
        t.info = info
        t.nameMu.Unlock()
        t.updateComplete()
        t.fileIndex = segments.NewIndex(common.LengthIterFromUpvertedFiles(info.UpvertedFiles()))
        t.displayName = "" // Save a few bytes lol.
        t.initFiles()
        t.cacheLength()
        t.makePieces()
        return nil
}

func (t *Torrent) pieceRequestOrderKey(i int) request_strategy.PieceRequestOrderKey {
        return request_strategy.PieceRequestOrderKey{
                InfoHash: t.infoHash,
                Index:    i,
        }
}

// This seems to be all the follow-up tasks after info is set, that can't fail.
func (t *Torrent) onSetInfo() {
        if t.cl.pieceRequestOrder == nil {
                t.cl.pieceRequestOrder = make(map[storage.TorrentCapacity]*request_strategy.PieceRequestOrder)
        }
        if t.cl.pieceRequestOrder[t.storage.Capacity] == nil {
                t.cl.pieceRequestOrder[t.storage.Capacity] = request_strategy.NewPieceOrder()
        }
        for i := range t.pieces {
                p := &t.pieces[i]
                // Need to add availability before updating piece completion, as that may result in conns
                // being dropped.
                if p.availability != 0 {
                        panic(p.availability)
                }
                p.availability = int64(t.pieceAvailabilityFromPeers(i))
                t.cl.pieceRequestOrder[t.storage.Capacity].Add(
                        t.pieceRequestOrderKey(i),
                        t.requestStrategyPieceOrderState(i))
                t.updatePieceCompletion(pieceIndex(i))
                if !t.initialPieceCheckDisabled && !p.storageCompletionOk {
                        // t.logger.Printf("piece %s completion unknown, queueing check", p)
                        t.queuePieceCheck(pieceIndex(i))
                }
        }
        t.cl.event.Broadcast()
        close(t.gotMetainfoC)
        t.updateWantPeersEvent()
        t.pendingRequests.Init(t.numRequests())
        t.tryCreateMorePieceHashers()
        t.iterPeers(func(p *Peer) {
                p.onGotInfo(t.info)
                p.updateRequests("onSetInfo")
        })
}

// Called when metadata for a torrent becomes available.
func (t *Torrent) setInfoBytesLocked(b []byte) error {
        if metainfo.HashBytes(b) != t.infoHash {
                return errors.New("info bytes have wrong hash")
        }
        var info metainfo.Info
        if err := bencode.Unmarshal(b, &info); err != nil {
                return fmt.Errorf("error unmarshalling info bytes: %s", err)
        }
        t.metadataBytes = b
        t.metadataCompletedChunks = nil
        if t.info != nil {
                return nil
        }
        if err := t.setInfo(&info); err != nil {
                return err
        }
        t.onSetInfo()
        return nil
}

func (t *Torrent) haveAllMetadataPieces() bool {
        if t.haveInfo() {
                return true
        }
        if t.metadataCompletedChunks == nil {
                return false
        }
        for _, have := range t.metadataCompletedChunks {
                if !have {
                        return false
                }
        }
        return true
}

// TODO: Propagate errors to disconnect peer.
func (t *Torrent) setMetadataSize(size int) (err error) {
        if t.haveInfo() {
                // We already know the correct metadata size.
                return
        }
        if uint32(size) > maxMetadataSize {
                return errors.New("bad size")
        }
        if len(t.metadataBytes) == size {
                return
        }
        t.metadataBytes = make([]byte, size)
        t.metadataCompletedChunks = make([]bool, (size+(1<<14)-1)/(1<<14))
        t.metadataChanged.Broadcast()
        for c := range t.conns {
                c.requestPendingMetadata()
        }
        return
}

// The current working name for the torrent. Either the name in the info dict,
// or a display name given such as by the dn value in a magnet link, or "".
func (t *Torrent) name() string {
        t.nameMu.RLock()
        defer t.nameMu.RUnlock()
        if t.haveInfo() {
                return t.info.Name
        }
        if t.displayName != "" {
                return t.displayName
        }
        return "infohash:" + t.infoHash.HexString()
}

func (t *Torrent) pieceState(index pieceIndex) (ret PieceState) {
        p := &t.pieces[index]
        ret.Priority = t.piecePriority(index)
        ret.Completion = p.completion()
        ret.QueuedForHash = p.queuedForHash()
        ret.Hashing = p.hashing
        ret.Checking = ret.QueuedForHash || ret.Hashing
        ret.Marking = p.marking
        if !ret.Complete && t.piecePartiallyDownloaded(index) {
                ret.Partial = true
        }
        return
}

func (t *Torrent) metadataPieceSize(piece int) int {
        return metadataPieceSize(len(t.metadataBytes), piece)
}

func (t *Torrent) newMetadataExtensionMessage(c *PeerConn, msgType pp.ExtendedMetadataRequestMsgType, piece int, data []byte) pp.Message {
        return pp.Message{
                Type:       pp.Extended,
                ExtendedID: c.PeerExtensionIDs[pp.ExtensionNameMetadata],
                ExtendedPayload: append(bencode.MustMarshal(pp.ExtendedMetadataRequestMsg{
                        Piece:     piece,
                        TotalSize: len(t.metadataBytes),
                        Type:      msgType,
                }), data...),
        }
}

type pieceAvailabilityRun struct {
        count        pieceIndex
        availability int64
}

func (me pieceAvailabilityRun) String() string {
        return fmt.Sprintf("%v(%v)", me.count, me.availability)
}

func (t *Torrent) pieceAvailabilityRuns() (ret []pieceAvailabilityRun) {
        rle := missinggo.NewRunLengthEncoder(func(el interface{}, count uint64) {
                ret = append(ret, pieceAvailabilityRun{availability: el.(int64), count: int(count)})
        })
        for i := range t.pieces {
                rle.Append(t.pieces[i].availability, 1)
        }
        rle.Flush()
        return
}

func (t *Torrent) pieceStateRuns() (ret PieceStateRuns) {
        rle := missinggo.NewRunLengthEncoder(func(el interface{}, count uint64) {
                ret = append(ret, PieceStateRun{
                        PieceState: el.(PieceState),
                        Length:     int(count),
                })
        })
        for index := range t.pieces {
                rle.Append(t.pieceState(pieceIndex(index)), 1)
        }
        rle.Flush()
        return
}

// Produces a small string representing a PieceStateRun.
func (psr PieceStateRun) String() (ret string) {
        ret = fmt.Sprintf("%d", psr.Length)
        ret += func() string {
                switch psr.Priority {
                case PiecePriorityNext:
                        return "N"
                case PiecePriorityNormal:
                        return "."
                case PiecePriorityReadahead:
                        return "R"
                case PiecePriorityNow:
                        return "!"
                case PiecePriorityHigh:
                        return "H"
                default:
                        return ""
                }
        }()
        if psr.Hashing {
                ret += "H"
        }
        if psr.QueuedForHash {
                ret += "Q"
        }
        if psr.Marking {
                ret += "M"
        }
        if psr.Partial {
                ret += "P"
        }
        if psr.Complete {
                ret += "C"
        }
        if !psr.Ok {
                ret += "?"
        }
        return
}

func (t *Torrent) writeStatus(w io.Writer) {
        fmt.Fprintf(w, "Infohash: %s\n", t.infoHash.HexString())
        fmt.Fprintf(w, "Metadata length: %d\n", t.metadataSize())
        if !t.haveInfo() {
                fmt.Fprintf(w, "Metadata have: ")
                for _, h := range t.metadataCompletedChunks {
                        fmt.Fprintf(w, "%c", func() rune {
                                if h {
                                        return 'H'
                                } else {
                                        return '.'
                                }
                        }())
                }
                fmt.Fprintln(w)
        }
        fmt.Fprintf(w, "Piece length: %s\n",
                func() string {
                        if t.haveInfo() {
                                return fmt.Sprintf("%v (%v chunks)",
                                        t.usualPieceSize(),
                                        float64(t.usualPieceSize())/float64(t.chunkSize))
                        } else {
                                return "no info"
                        }
                }(),
        )
        if t.info != nil {
                fmt.Fprintf(w, "Num Pieces: %d (%d completed)\n", t.numPieces(), t.numPiecesCompleted())
                fmt.Fprintf(w, "Piece States: %s\n", t.pieceStateRuns())
                fmt.Fprintf(w, "Piece availability: %v\n", strings.Join(func() (ret []string) {
                        for _, run := range t.pieceAvailabilityRuns() {
                                ret = append(ret, run.String())
                        }
                        return
                }(), " "))
        }
        fmt.Fprintf(w, "Reader Pieces:")
        t.forReaderOffsetPieces(func(begin, end pieceIndex) (again bool) {
                fmt.Fprintf(w, " %d:%d", begin, end)
                return true
        })
        fmt.Fprintln(w)

        fmt.Fprintf(w, "Enabled trackers:\n")
        func() {
                tw := tabwriter.NewWriter(w, 0, 0, 2, ' ', 0)
                fmt.Fprintf(tw, "    URL\tExtra\n")
                for _, ta := range slices.Sort(slices.FromMapElems(t.trackerAnnouncers), func(l, r torrentTrackerAnnouncer) bool {
                        lu := l.URL()
                        ru := r.URL()
                        var luns, runs url.URL = *lu, *ru
                        luns.Scheme = ""
                        runs.Scheme = ""
                        var ml missinggo.MultiLess
                        ml.StrictNext(luns.String() == runs.String(), luns.String() < runs.String())
                        ml.StrictNext(lu.String() == ru.String(), lu.String() < ru.String())
                        return ml.Less()
                }).([]torrentTrackerAnnouncer) {
                        fmt.Fprintf(tw, "    %q\t%v\n", ta.URL(), ta.statusLine())
                }
                tw.Flush()
        }()

        fmt.Fprintf(w, "DHT Announces: %d\n", t.numDHTAnnounces)

        spew.NewDefaultConfig()
        spew.Fdump(w, t.statsLocked())

        peers := t.peersAsSlice()
        sort.Slice(peers, func(_i, _j int) bool {
                i := peers[_i]
                j := peers[_j]
                if less, ok := multiless.New().EagerSameLess(
                        i.downloadRate() == j.downloadRate(), i.downloadRate() < j.downloadRate(),
                ).LessOk(); ok {
                        return less
                }
                return worseConn(i, j)
        })
        for i, c := range peers {
                fmt.Fprintf(w, "%2d. ", i+1)
                c.writeStatus(w, t)
        }
}

func (t *Torrent) haveInfo() bool {
        return t.info != nil
}

// Returns a run-time generated MetaInfo that includes the info bytes and
// announce-list as currently known to the client.
func (t *Torrent) newMetaInfo() metainfo.MetaInfo {
        return metainfo.MetaInfo{
                CreationDate: time.Now().Unix(),
                Comment:      "dynamic metainfo from client",
                CreatedBy:    "go.torrent",
                AnnounceList: t.metainfo.UpvertedAnnounceList().Clone(),
                InfoBytes: func() []byte {
                        if t.haveInfo() {
                                return t.metadataBytes
                        } else {
                                return nil
                        }
                }(),
                UrlList: func() []string {
                        ret := make([]string, 0, len(t.webSeeds))
                        for url := range t.webSeeds {
                                ret = append(ret, url)
                        }
                        return ret
                }(),
        }
}

// Get bytes left
func (t *Torrent) BytesMissing() (n int64) {
        t.cl.rLock()
        n = t.bytesMissingLocked()
        t.cl.rUnlock()
        return
}

func (t *Torrent) bytesMissingLocked() int64 {
        return t.bytesLeft()
}

func iterFlipped(b *roaring.Bitmap, end uint64, cb func(uint32) bool) {
        roaring.Flip(b, 0, end).Iterate(cb)
}

func (t *Torrent) bytesLeft() (left int64) {
        iterFlipped(&t._completedPieces, uint64(t.numPieces()), func(x uint32) bool {
                p := t.piece(pieceIndex(x))
                left += int64(p.length() - p.numDirtyBytes())
                return true
        })
        return
}

// Bytes left to give in tracker announces.
func (t *Torrent) bytesLeftAnnounce() int64 {
        if t.haveInfo() {
                return t.bytesLeft()
        } else {
                return -1
        }
}

func (t *Torrent) piecePartiallyDownloaded(piece pieceIndex) bool {
        if t.pieceComplete(piece) {
                return false
        }
        if t.pieceAllDirty(piece) {
                return false
        }
        return t.pieces[piece].hasDirtyChunks()
}

func (t *Torrent) usualPieceSize() int {
        return int(t.info.PieceLength)
}

func (t *Torrent) numPieces() pieceIndex {
        return pieceIndex(t.info.NumPieces())
}

func (t *Torrent) numPiecesCompleted() (num pieceIndex) {
        return pieceIndex(t._completedPieces.GetCardinality())
}

func (t *Torrent) deletePieceRequestOrder() {
        for i := 0; i < t.numPieces(); i++ {
                t.cl.pieceRequestOrder[t.storage.Capacity].Delete(t.pieceRequestOrderKey(i))
        }
}

func (t *Torrent) close(wg *sync.WaitGroup) (err error) {
        t.closed.Set()
        if t.storage != nil {
                wg.Add(1)
                go func() {
                        defer wg.Done()
                        t.storageLock.Lock()
                        defer t.storageLock.Unlock()
                        if f := t.storage.Close; f != nil {
                                err1 := f()
                                if err1 != nil {
                                        t.logger.WithDefaultLevel(log.Warning).Printf("error closing storage: %v", err1)
                                }
                        }
                }()
        }
        t.iterPeers(func(p *Peer) {
                p.close()
        })
        if t.storage != nil {
                t.deletePieceRequestOrder()
        }
        t.pex.Reset()
        t.cl.event.Broadcast()
        t.pieceStateChanges.Close()
        t.updateWantPeersEvent()
        return
}

func (t *Torrent) requestOffset(r Request) int64 {
        return torrentRequestOffset(*t.length, int64(t.usualPieceSize()), r)
}

// Return the request that would include the given offset into the torrent data. Returns !ok if
// there is no such request.
func (t *Torrent) offsetRequest(off int64) (req Request, ok bool) {
        return torrentOffsetRequest(*t.length, t.info.PieceLength, int64(t.chunkSize), off)
}

func (t *Torrent) writeChunk(piece int, begin int64, data []byte) (err error) {
        defer perf.ScopeTimerErr(&err)()
        n, err := t.pieces[piece].Storage().WriteAt(data, begin)
        if err == nil && n != len(data) {
                err = io.ErrShortWrite
        }
        return err
}

func (t *Torrent) bitfield() (bf []bool) {
        bf = make([]bool, t.numPieces())
        t._completedPieces.Iterate(func(piece uint32) (again bool) {
                bf[piece] = true
                return true
        })
        return
}

func (t *Torrent) pieceNumChunks(piece pieceIndex) chunkIndexType {
        return chunkIndexType((t.pieceLength(piece) + t.chunkSize - 1) / t.chunkSize)
}

func (t *Torrent) chunksPerRegularPiece() uint32 {
        return uint32((pp.Integer(t.usualPieceSize()) + t.chunkSize - 1) / t.chunkSize)
}

func (t *Torrent) numRequests() RequestIndex {
        if t.numPieces() == 0 {
                return 0
        }
        return uint32(t.numPieces()-1)*t.chunksPerRegularPiece() + t.pieceNumChunks(t.numPieces()-1)
}

func (t *Torrent) pendAllChunkSpecs(pieceIndex pieceIndex) {
        t.dirtyChunks.RemoveRange(
                uint64(t.pieceRequestIndexOffset(pieceIndex)),
                uint64(t.pieceRequestIndexOffset(pieceIndex+1)))
}

func (t *Torrent) pieceLength(piece pieceIndex) pp.Integer {
        if t.info.PieceLength == 0 {
                // There will be no variance amongst pieces. Only pain.
                return 0
        }
        if piece == t.numPieces()-1 {
                ret := pp.Integer(*t.length % t.info.PieceLength)
                if ret != 0 {
                        return ret
                }
        }
        return pp.Integer(t.info.PieceLength)
}

func (t *Torrent) hashPiece(piece pieceIndex) (ret metainfo.Hash, err error) {
        p := t.piece(piece)
        p.waitNoPendingWrites()
        storagePiece := t.pieces[piece].Storage()

        // Does the backend want to do its own hashing?
        if i, ok := storagePiece.PieceImpl.(storage.SelfHashing); ok {
                var sum metainfo.Hash
                // log.Printf("A piece decided to self-hash: %d", piece)
                sum, err = i.SelfHash()
                missinggo.CopyExact(&ret, sum)
                return
        }

        hash := pieceHash.New()
        const logPieceContents = false
        if logPieceContents {
                var examineBuf bytes.Buffer
                _, err = storagePiece.WriteTo(io.MultiWriter(hash, &examineBuf))
                log.Printf("hashed %q with copy err %v", examineBuf.Bytes(), err)
        } else {
                _, err = storagePiece.WriteTo(hash)
        }
        missinggo.CopyExact(&ret, hash.Sum(nil))
        return
}

func (t *Torrent) haveAnyPieces() bool {
        return !t._completedPieces.IsEmpty()
}

func (t *Torrent) haveAllPieces() bool {
        if !t.haveInfo() {
                return false
        }
        return t._completedPieces.GetCardinality() == bitmap.BitRange(t.numPieces())
}

func (t *Torrent) havePiece(index pieceIndex) bool {
        return t.haveInfo() && t.pieceComplete(index)
}

func (t *Torrent) maybeDropMutuallyCompletePeer(
        // I'm not sure about taking peer here, not all peer implementations actually drop. Maybe that's
        // okay?
        p *Peer,
) {
        if !t.cl.config.DropMutuallyCompletePeers {
                return
        }
        if !t.haveAllPieces() {
                return
        }
        if all, known := p.peerHasAllPieces(); !(known && all) {
                return
        }
        if p.useful() {
                return
        }
        t.logger.WithDefaultLevel(log.Debug).Printf("dropping %v, which is mutually complete", p)
        p.drop()
}

func (t *Torrent) haveChunk(r Request) (ret bool) {
        // defer func() {
        //      log.Println("have chunk", r, ret)
        // }()
        if !t.haveInfo() {
                return false
        }
        if t.pieceComplete(pieceIndex(r.Index)) {
                return true
        }
        p := &t.pieces[r.Index]
        return !p.pendingChunk(r.ChunkSpec, t.chunkSize)
}

func chunkIndexFromChunkSpec(cs ChunkSpec, chunkSize pp.Integer) chunkIndexType {
        return chunkIndexType(cs.Begin / chunkSize)
}

func (t *Torrent) wantPieceIndex(index pieceIndex) bool {
        return t._pendingPieces.Contains(uint32(index))
}

// A pool of []*PeerConn, to reduce allocations in functions that need to index or sort Torrent
// conns (which is a map).
var peerConnSlices sync.Pool

func getPeerConnSlice(cap int) []*PeerConn {
        getInterface := peerConnSlices.Get()
        if getInterface == nil {
                return make([]*PeerConn, 0, cap)
        } else {
                return getInterface.([]*PeerConn)[:0]
        }
}

// The worst connection is one that hasn't been sent, or sent anything useful for the longest. A bad
// connection is one that usually sends us unwanted pieces, or has been in the worse half of the
// established connections for more than a minute. This is O(n log n). If there was a way to not
// consider the position of a conn relative to the total number, it could be reduced to O(n).
func (t *Torrent) worstBadConn() (ret *PeerConn) {
        wcs := worseConnSlice{conns: t.appendUnclosedConns(getPeerConnSlice(len(t.conns)))}
        defer peerConnSlices.Put(wcs.conns)
        wcs.initKeys()
        heap.Init(&wcs)
        for wcs.Len() != 0 {
                c := heap.Pop(&wcs).(*PeerConn)
                if c._stats.ChunksReadWasted.Int64() >= 6 && c._stats.ChunksReadWasted.Int64() > c._stats.ChunksReadUseful.Int64() {
                        return c
                }
                // If the connection is in the worst half of the established
                // connection quota and is older than a minute.
                if wcs.Len() >= (t.maxEstablishedConns+1)/2 {
                        // Give connections 1 minute to prove themselves.
                        if time.Since(c.completedHandshake) > time.Minute {
                                return c
                        }
                }
        }
        return nil
}

type PieceStateChange struct {
        Index int
        PieceState
}

func (t *Torrent) publishPieceChange(piece pieceIndex) {
        t.cl._mu.Defer(func() {
                cur := t.pieceState(piece)
                p := &t.pieces[piece]
                if cur != p.publicPieceState {
                        p.publicPieceState = cur
                        t.pieceStateChanges.Publish(PieceStateChange{
                                int(piece),
                                cur,
                        })
                }
        })
}

func (t *Torrent) pieceNumPendingChunks(piece pieceIndex) pp.Integer {
        if t.pieceComplete(piece) {
                return 0
        }
        return pp.Integer(t.pieceNumChunks(piece) - t.pieces[piece].numDirtyChunks())
}

func (t *Torrent) pieceAllDirty(piece pieceIndex) bool {
        return t.pieces[piece].allChunksDirty()
}

func (t *Torrent) readersChanged() {
        t.updateReaderPieces()
        t.updateAllPiecePriorities("Torrent.readersChanged")
}

func (t *Torrent) updateReaderPieces() {
        t._readerNowPieces, t._readerReadaheadPieces = t.readerPiecePriorities()
}

func (t *Torrent) readerPosChanged(from, to pieceRange) {
        if from == to {
                return
        }
        t.updateReaderPieces()
        // Order the ranges, high and low.
        l, h := from, to
        if l.begin > h.begin {
                l, h = h, l
        }
        if l.end < h.begin {
                // Two distinct ranges.
                t.updatePiecePriorities(l.begin, l.end, "Torrent.readerPosChanged")
                t.updatePiecePriorities(h.begin, h.end, "Torrent.readerPosChanged")
        } else {
                // Ranges overlap.
                end := l.end
                if h.end > end {
                        end = h.end
                }
                t.updatePiecePriorities(l.begin, end, "Torrent.readerPosChanged")
        }
}

func (t *Torrent) maybeNewConns() {
        // Tickle the accept routine.
        t.cl.event.Broadcast()
        t.openNewConns()
}

func (t *Torrent) piecePriorityChanged(piece pieceIndex, reason string) {
        if t._pendingPieces.Contains(uint32(piece)) {
                t.iterPeers(func(c *Peer) {
                        if c.actualRequestState.Interested {
                                return
                        }
                        if !c.isLowOnRequests() {
                                return
                        }
                        if !c.peerHasPiece(piece) {
                                return
                        }
                        if c.peerChoking && !c.peerAllowedFast.Contains(uint32(piece)) {
                                return
                        }
                        c.updateRequests(reason)
                })
        }
        t.maybeNewConns()
        t.publishPieceChange(piece)
}

func (t *Torrent) updatePiecePriority(piece pieceIndex, reason string) {
        if !t.closed.IsSet() {
                // It would be possible to filter on pure-priority changes here to avoid churning the piece
                // request order.
                t.updatePieceRequestOrder(piece)
        }
        p := &t.pieces[piece]
        newPrio := p.uncachedPriority()
        // t.logger.Printf("torrent %p: piece %d: uncached priority: %v", t, piece, newPrio)
        if newPrio == PiecePriorityNone {
                if !t._pendingPieces.CheckedRemove(uint32(piece)) {
                        return
                }
        } else {
                if !t._pendingPieces.CheckedAdd(uint32(piece)) {
                        return
                }
        }
        t.piecePriorityChanged(piece, reason)
}

func (t *Torrent) updateAllPiecePriorities(reason string) {
        t.updatePiecePriorities(0, t.numPieces(), reason)
}

// Update all piece priorities in one hit. This function should have the same
// output as updatePiecePriority, but across all pieces.
func (t *Torrent) updatePiecePriorities(begin, end pieceIndex, reason string) {
        for i := begin; i < end; i++ {
                t.updatePiecePriority(i, reason)
        }
}

// Returns the range of pieces [begin, end) that contains the extent of bytes.
func (t *Torrent) byteRegionPieces(off, size int64) (begin, end pieceIndex) {
        if off >= *t.length {
                return
        }
        if off < 0 {
                size += off
                off = 0
        }
        if size <= 0 {
                return
        }
        begin = pieceIndex(off / t.info.PieceLength)
        end = pieceIndex((off + size + t.info.PieceLength - 1) / t.info.PieceLength)
        if end > pieceIndex(t.info.NumPieces()) {
                end = pieceIndex(t.info.NumPieces())
        }
        return
}

// Returns true if all iterations complete without breaking. Returns the read regions for all
// readers. The reader regions should not be merged as some callers depend on this method to
// enumerate readers.
func (t *Torrent) forReaderOffsetPieces(f func(begin, end pieceIndex) (more bool)) (all bool) {
        for r := range t.readers {
                p := r.pieces
                if p.begin >= p.end {
                        continue
                }
                if !f(p.begin, p.end) {
                        return false
                }
        }
        return true
}

func (t *Torrent) piecePriority(piece pieceIndex) piecePriority {
        return t.piece(piece).uncachedPriority()
}

func (t *Torrent) pendRequest(req RequestIndex) {
        t.piece(int(req / t.chunksPerRegularPiece())).pendChunkIndex(req % t.chunksPerRegularPiece())
}

func (t *Torrent) pieceCompletionChanged(piece pieceIndex, reason string) {
        t.cl.event.Broadcast()
        if t.pieceComplete(piece) {
                t.onPieceCompleted(piece)
        } else {
                t.onIncompletePiece(piece)
        }
        t.updatePiecePriority(piece, reason)
}

func (t *Torrent) numReceivedConns() (ret int) {
        for c := range t.conns {
                if c.Discovery == PeerSourceIncoming {
                        ret++
                }
        }
        return
}

func (t *Torrent) maxHalfOpen() int {
        // Note that if we somehow exceed the maximum established conns, we want
        // the negative value to have an effect.
        establishedHeadroom := int64(t.maxEstablishedConns - len(t.conns))
        extraIncoming := int64(t.numReceivedConns() - t.maxEstablishedConns/2)
        // We want to allow some experimentation with new peers, and to try to
        // upset an oversupply of received connections.
        return int(min(max(5, extraIncoming)+establishedHeadroom, int64(t.cl.config.HalfOpenConnsPerTorrent)))
}

func (t *Torrent) openNewConns() (initiated int) {
        defer t.updateWantPeersEvent()
        for t.peers.Len() != 0 {
                if !t.wantConns() {
                        return
                }
                if len(t.halfOpen) >= t.maxHalfOpen() {
                        return
                }
                if len(t.cl.dialers) == 0 {
                        return
                }
                if t.cl.numHalfOpen >= t.cl.config.TotalHalfOpenConns {
                        return
                }
                p := t.peers.PopMax()
                t.initiateConn(p)
                initiated++
        }
        return
}

func (t *Torrent) updatePieceCompletion(piece pieceIndex) bool {
        p := t.piece(piece)
        uncached := t.pieceCompleteUncached(piece)
        cached := p.completion()
        changed := cached != uncached
        complete := uncached.Complete
        p.storageCompletionOk = uncached.Ok
        x := uint32(piece)
        if complete {
                t._completedPieces.Add(x)
                t.openNewConns()
        } else {
                t._completedPieces.Remove(x)
        }
        p.t.updatePieceRequestOrder(piece)
        t.updateComplete()
        if complete && len(p.dirtiers) != 0 {
                t.logger.Printf("marked piece %v complete but still has dirtiers", piece)
        }
        if changed {
                log.Fstr("piece %d completion changed: %+v -> %+v", piece, cached, uncached).SetLevel(log.Debug).Log(t.logger)
                t.pieceCompletionChanged(piece, "Torrent.updatePieceCompletion")
        }
        return changed
}

// Non-blocking read. Client lock is not required.
func (t *Torrent) readAt(b []byte, off int64) (n int, err error) {
        for len(b) != 0 {
                p := &t.pieces[off/t.info.PieceLength]
                p.waitNoPendingWrites()
                var n1 int
                n1, err = p.Storage().ReadAt(b, off-p.Info().Offset())
                if n1 == 0 {
                        break
                }
                off += int64(n1)
                n += n1
                b = b[n1:]
        }
        return
}

// Returns an error if the metadata was completed, but couldn't be set for some reason. Blame it on
// the last peer to contribute. TODO: Actually we shouldn't blame peers for failure to open storage
// etc. Also we should probably cached metadata pieces per-Peer, to isolate failure appropriately.
func (t *Torrent) maybeCompleteMetadata() error {
        if t.haveInfo() {
                // Nothing to do.
                return nil
        }
        if !t.haveAllMetadataPieces() {
                // Don't have enough metadata pieces.
                return nil
        }
        err := t.setInfoBytesLocked(t.metadataBytes)
        if err != nil {
                t.invalidateMetadata()
                return fmt.Errorf("error setting info bytes: %s", err)
        }
        if t.cl.config.Debug {
                t.logger.Printf("%s: got metadata from peers", t)
        }
        return nil
}

func (t *Torrent) readerPiecePriorities() (now, readahead bitmap.Bitmap) {
        t.forReaderOffsetPieces(func(begin, end pieceIndex) bool {
                if end > begin {
                        now.Add(bitmap.BitIndex(begin))
                        readahead.AddRange(bitmap.BitRange(begin)+1, bitmap.BitRange(end))
                }
                return true
        })
        return
}

func (t *Torrent) needData() bool {
        if t.closed.IsSet() {
                return false
        }
        if !t.haveInfo() {
                return true
        }
        return !t._pendingPieces.IsEmpty()
}

func appendMissingStrings(old, new []string) (ret []string) {
        ret = old
new:
        for _, n := range new {
                for _, o := range old {
                        if o == n {
                                continue new
                        }
                }
                ret = append(ret, n)
        }
        return
}

func appendMissingTrackerTiers(existing [][]string, minNumTiers int) (ret [][]string) {
        ret = existing
        for minNumTiers > len(ret) {
                ret = append(ret, nil)
        }
        return
}

func (t *Torrent) addTrackers(announceList [][]string) {
        fullAnnounceList := &t.metainfo.AnnounceList
        t.metainfo.AnnounceList = appendMissingTrackerTiers(*fullAnnounceList, len(announceList))
        for tierIndex, trackerURLs := range announceList {
                (*fullAnnounceList)[tierIndex] = appendMissingStrings((*fullAnnounceList)[tierIndex], trackerURLs)
        }
        t.startMissingTrackerScrapers()
        t.updateWantPeersEvent()
}

// Don't call this before the info is available.
func (t *Torrent) bytesCompleted() int64 {
        if !t.haveInfo() {
                return 0
        }
        return *t.length - t.bytesLeft()
}

func (t *Torrent) SetInfoBytes(b []byte) (err error) {
        t.cl.lock()
        defer t.cl.unlock()
        return t.setInfoBytesLocked(b)
}

// Returns true if connection is removed from torrent.Conns.
func (t *Torrent) deletePeerConn(c *PeerConn) (ret bool) {
        if !c.closed.IsSet() {
                panic("connection is not closed")
                // There are behaviours prevented by the closed state that will fail
                // if the connection has been deleted.
        }
        _, ret = t.conns[c]
        delete(t.conns, c)
        // Avoid adding a drop event more than once. Probably we should track whether we've generated
        // the drop event against the PexConnState instead.
        if ret {
                if !t.cl.config.DisablePEX {
                        t.pex.Drop(c)
                }
        }
        torrent.Add("deleted connections", 1)
        c.deleteAllRequests()
        t.assertPendingRequests()
        return
}

func (t *Torrent) decPeerPieceAvailability(p *Peer) {
        if !t.haveInfo() {
                return
        }
        p.newPeerPieces().Iterate(func(i uint32) bool {
                p.t.decPieceAvailability(pieceIndex(i))
                return true
        })
}

func (t *Torrent) assertPendingRequests() {
        if !check {
                return
        }
        // var actual pendingRequests
        // if t.haveInfo() {
        //      actual.m = make([]int, t.numRequests())
        // }
        // t.iterPeers(func(p *Peer) {
        //      p.actualRequestState.Requests.Iterate(func(x uint32) bool {
        //              actual.Inc(x)
        //              return true
        //      })
        // })
        // diff := cmp.Diff(actual.m, t.pendingRequests.m)
        // if diff != "" {
        //      panic(diff)
        // }
}

func (t *Torrent) dropConnection(c *PeerConn) {
        t.cl.event.Broadcast()
        c.close()
        if t.deletePeerConn(c) {
                t.openNewConns()
        }
}

// Peers as in contact information for dialing out.
func (t *Torrent) wantPeers() bool {
        if t.closed.IsSet() {
                return false
        }
        if t.peers.Len() > t.cl.config.TorrentPeersLowWater {
                return false
        }
        return t.wantConns()
}

func (t *Torrent) updateWantPeersEvent() {
        if t.wantPeers() {
                t.wantPeersEvent.Set()
        } else {
                t.wantPeersEvent.Clear()
        }
}

// Returns whether the client should make effort to seed the torrent.
func (t *Torrent) seeding() bool {
        cl := t.cl
        if t.closed.IsSet() {
                return false
        }
        if t.dataUploadDisallowed {
                return false
        }
        if cl.config.NoUpload {
                return false
        }
        if !cl.config.Seed {
                return false
        }
        if cl.config.DisableAggressiveUpload && t.needData() {
                return false
        }
        return true
}

func (t *Torrent) onWebRtcConn(
        c datachannel.ReadWriteCloser,
        dcc webtorrent.DataChannelContext,
) {
        defer c.Close()
        pc, err := t.cl.initiateProtocolHandshakes(
                context.Background(),
                webrtcNetConn{c, dcc},
                t,
                dcc.LocalOffered,
                false,
                webrtcNetAddr{dcc.Remote},
                webrtcNetwork,
                fmt.Sprintf("webrtc offer_id %x", dcc.OfferId),
        )
        if err != nil {
                t.logger.WithDefaultLevel(log.Error).Printf("error in handshaking webrtc connection: %v", err)
                return
        }
        if dcc.LocalOffered {
                pc.Discovery = PeerSourceTracker
        } else {
                pc.Discovery = PeerSourceIncoming
        }
        pc.conn.SetWriteDeadline(time.Time{})
        t.cl.lock()
        defer t.cl.unlock()
        err = t.cl.runHandshookConn(pc, t)
        if err != nil {
                t.logger.WithDefaultLevel(log.Critical).Printf("error running handshook webrtc conn: %v", err)
        }
}

func (t *Torrent) logRunHandshookConn(pc *PeerConn, logAll bool, level log.Level) {
        err := t.cl.runHandshookConn(pc, t)
        if err != nil || logAll {
                t.logger.WithDefaultLevel(level).Printf("error running handshook conn: %v", err)
        }
}

func (t *Torrent) runHandshookConnLoggingErr(pc *PeerConn) {
        t.logRunHandshookConn(pc, false, log.Debug)
}

func (t *Torrent) startWebsocketAnnouncer(u url.URL) torrentTrackerAnnouncer {
        wtc, release := t.cl.websocketTrackers.Get(u.String())
        go func() {
                <-t.closed.Done()
                release()
        }()
        wst := websocketTrackerStatus{u, wtc}
        go func() {
                err := wtc.Announce(tracker.Started, t.infoHash)
                if err != nil {
                        t.logger.WithDefaultLevel(log.Warning).Printf(
                                "error in initial announce to %q: %v",
                                u.String(), err,
                        )
                }
        }()
        return wst
}

func (t *Torrent) startScrapingTracker(_url string) {
        if _url == "" {
                return
        }
        u, err := url.Parse(_url)
        if err != nil {
                // URLs with a leading '*' appear to be a uTorrent convention to
                // disable trackers.
                if _url[0] != '*' {
                        log.Str("error parsing tracker url").AddValues("url", _url).Log(t.logger)
                }
                return
        }
        if u.Scheme == "udp" {
                u.Scheme = "udp4"
                t.startScrapingTracker(u.String())
                u.Scheme = "udp6"
                t.startScrapingTracker(u.String())
                return
        }
        if _, ok := t.trackerAnnouncers[_url]; ok {
                return
        }
        sl := func() torrentTrackerAnnouncer {
                switch u.Scheme {
                case "ws", "wss":
                        if t.cl.config.DisableWebtorrent {
                                return nil
                        }
                        return t.startWebsocketAnnouncer(*u)
                case "udp4":
                        if t.cl.config.DisableIPv4Peers || t.cl.config.DisableIPv4 {
                                return nil
                        }
                case "udp6":
                        if t.cl.config.DisableIPv6 {
                                return nil
                        }
                }
                newAnnouncer := &trackerScraper{
                        u:               *u,
                        t:               t,
                        lookupTrackerIp: t.cl.config.LookupTrackerIp,
                }
                go newAnnouncer.Run()
                return newAnnouncer
        }()
        if sl == nil {
                return
        }
        if t.trackerAnnouncers == nil {
                t.trackerAnnouncers = make(map[string]torrentTrackerAnnouncer)
        }
        t.trackerAnnouncers[_url] = sl
}

// Adds and starts tracker scrapers for tracker URLs that aren't already
// running.
func (t *Torrent) startMissingTrackerScrapers() {
        if t.cl.config.DisableTrackers {
                return
        }
        t.startScrapingTracker(t.metainfo.Announce)
        for _, tier := range t.metainfo.AnnounceList {
                for _, url := range tier {
                        t.startScrapingTracker(url)
                }
        }
}

// Returns an AnnounceRequest with fields filled out to defaults and current
// values.
func (t *Torrent) announceRequest(event tracker.AnnounceEvent) tracker.AnnounceRequest {
        // Note that IPAddress is not set. It's set for UDP inside the tracker code, since it's
        // dependent on the network in use.
        return tracker.AnnounceRequest{
                Event: event,
                NumWant: func() int32 {
                        if t.wantPeers() && len(t.cl.dialers) > 0 {
                                return -1
                        } else {
                                return 0
                        }
                }(),
                Port:     uint16(t.cl.incomingPeerPort()),
                PeerId:   t.cl.peerID,
                InfoHash: t.infoHash,
                Key:      t.cl.announceKey(),

                // The following are vaguely described in BEP 3.

                Left:     t.bytesLeftAnnounce(),
                Uploaded: t.stats.BytesWrittenData.Int64(),
                // There's no mention of wasted or unwanted download in the BEP.
                Downloaded: t.stats.BytesReadUsefulData.Int64(),
        }
}

// Adds peers revealed in an announce until the announce ends, or we have
// enough peers.
func (t *Torrent) consumeDhtAnnouncePeers(pvs <-chan dht.PeersValues) {
        cl := t.cl
        for v := range pvs {
                cl.lock()
                added := 0
                for _, cp := range v.Peers {
                        if cp.Port == 0 {
                                // Can't do anything with this.
                                continue
                        }
                        if t.addPeer(PeerInfo{
                                Addr:   ipPortAddr{cp.IP, cp.Port},
                                Source: PeerSourceDhtGetPeers,
                        }) {
                                added++
                        }
                }
                cl.unlock()
                // if added != 0 {
                //      log.Printf("added %v peers from dht for %v", added, t.InfoHash().HexString())
                // }
        }
}

// Announce using the provided DHT server. Peers are consumed automatically. done is closed when the
// announce ends. stop will force the announce to end.
func (t *Torrent) AnnounceToDht(s DhtServer) (done <-chan struct{}, stop func(), err error) {
        ps, err := s.Announce(t.infoHash, t.cl.incomingPeerPort(), true)
        if err != nil {
                return
        }
        _done := make(chan struct{})
        done = _done
        stop = ps.Close
        go func() {
                t.consumeDhtAnnouncePeers(ps.Peers())
                close(_done)
        }()
        return
}

func (t *Torrent) timeboxedAnnounceToDht(s DhtServer) error {
        _, stop, err := t.AnnounceToDht(s)
        if err != nil {
                return err
        }
        select {
        case <-t.closed.Done():
        case <-time.After(5 * time.Minute):
        }
        stop()
        return nil
}

func (t *Torrent) dhtAnnouncer(s DhtServer) {
        cl := t.cl
        cl.lock()
        defer cl.unlock()
        for {
                for {
                        if t.closed.IsSet() {
                                return
                        }
                        // We're also announcing ourselves as a listener, so we don't just want peer addresses.
                        // TODO: We can include the announce_peer step depending on whether we can receive
                        // inbound connections. We should probably only announce once every 15 mins too.
                        if !t.wantConns() {
                                goto wait
                        }
                        // TODO: Determine if there's a listener on the port we're announcing.
                        if len(cl.dialers) == 0 && len(cl.listeners) == 0 {
                                goto wait
                        }
                        break
                wait:
                        cl.event.Wait()
                }
                func() {
                        t.numDHTAnnounces++
                        cl.unlock()
                        defer cl.lock()
                        err := t.timeboxedAnnounceToDht(s)
                        if err != nil {
                                t.logger.WithDefaultLevel(log.Warning).Printf("error announcing %q to DHT: %s", t, err)
                        }
                }()
        }
}

func (t *Torrent) addPeers(peers []PeerInfo) (added int) {
        for _, p := range peers {
                if t.addPeer(p) {
                        added++
                }
        }
        return
}

// The returned TorrentStats may require alignment in memory. See
// https://github.com/anacrolix/torrent/issues/383.
func (t *Torrent) Stats() TorrentStats {
        t.cl.rLock()
        defer t.cl.rUnlock()
        return t.statsLocked()
}

func (t *Torrent) statsLocked() (ret TorrentStats) {
        ret.ActivePeers = len(t.conns)
        ret.HalfOpenPeers = len(t.halfOpen)
        ret.PendingPeers = t.peers.Len()
        ret.TotalPeers = t.numTotalPeers()
        ret.ConnectedSeeders = 0
        for c := range t.conns {
                if all, ok := c.peerHasAllPieces(); all && ok {
                        ret.ConnectedSeeders++
                }
        }
        ret.ConnStats = t.stats.Copy()
        ret.PiecesComplete = t.numPiecesCompleted()
        return
}

// The total number of peers in the torrent.
func (t *Torrent) numTotalPeers() int {
        peers := make(map[string]struct{})
        for conn := range t.conns {
                ra := conn.conn.RemoteAddr()
                if ra == nil {
                        // It's been closed and doesn't support RemoteAddr.
                        continue
                }
                peers[ra.String()] = struct{}{}
        }
        for addr := range t.halfOpen {
                peers[addr] = struct{}{}
        }
        t.peers.Each(func(peer PeerInfo) {
                peers[peer.Addr.String()] = struct{}{}
        })
        return len(peers)
}

// Reconcile bytes transferred before connection was associated with a
// torrent.
func (t *Torrent) reconcileHandshakeStats(c *PeerConn) {
        if c._stats != (ConnStats{
                // Handshakes should only increment these fields:
                BytesWritten: c._stats.BytesWritten,
                BytesRead:    c._stats.BytesRead,
        }) {
                panic("bad stats")
        }
        c.postHandshakeStats(func(cs *ConnStats) {
                cs.BytesRead.Add(c._stats.BytesRead.Int64())
                cs.BytesWritten.Add(c._stats.BytesWritten.Int64())
        })
        c.reconciledHandshakeStats = true
}

// Returns true if the connection is added.
func (t *Torrent) addPeerConn(c *PeerConn) (err error) {
        defer func() {
                if err == nil {
                        torrent.Add("added connections", 1)
                }
        }()
        if t.closed.IsSet() {
                return errors.New("torrent closed")
        }
        for c0 := range t.conns {
                if c.PeerID != c0.PeerID {
                        continue
                }
                if !t.cl.config.DropDuplicatePeerIds {
                        continue
                }
                if left, ok := c.hasPreferredNetworkOver(c0); ok && left {
                        c0.close()
                        t.deletePeerConn(c0)
                } else {
                        return errors.New("existing connection preferred")
                }
        }
        if len(t.conns) >= t.maxEstablishedConns {
                c := t.worstBadConn()
                if c == nil {
                        return errors.New("don't want conns")
                }
                c.close()
                t.deletePeerConn(c)
        }
        if len(t.conns) >= t.maxEstablishedConns {
                panic(len(t.conns))
        }
        t.conns[c] = struct{}{}
        if !t.cl.config.DisablePEX && !c.PeerExtensionBytes.SupportsExtended() {
                t.pex.Add(c) // as no further extended handshake expected
        }
        return nil
}

func (t *Torrent) wantConns() bool {
        if !t.networkingEnabled.Bool() {
                return false
        }
        if t.closed.IsSet() {
                return false
        }
        if !t.needData() && (!t.seeding() || !t.haveAnyPieces()) {
                return false
        }
        return len(t.conns) < t.maxEstablishedConns || t.worstBadConn() != nil
}

func (t *Torrent) SetMaxEstablishedConns(max int) (oldMax int) {
        t.cl.lock()
        defer t.cl.unlock()
        oldMax = t.maxEstablishedConns
        t.maxEstablishedConns = max
        wcs := worseConnSlice{
                conns: t.appendConns(nil, func(*PeerConn) bool {
                        return true
                }),
        }
        wcs.initKeys()
        heap.Init(&wcs)
        for len(t.conns) > t.maxEstablishedConns && wcs.Len() > 0 {
                t.dropConnection(heap.Pop(&wcs).(*PeerConn))
        }
        t.openNewConns()
        return oldMax
}

func (t *Torrent) pieceHashed(piece pieceIndex, passed bool, hashIoErr error) {
        t.logger.Log(log.Fstr("hashed piece %d (passed=%t)", piece, passed).SetLevel(log.Debug))
        p := t.piece(piece)
        p.numVerifies++
        t.cl.event.Broadcast()
        if t.closed.IsSet() {
                return
        }

        // Don't score the first time a piece is hashed, it could be an initial check.
        if p.storageCompletionOk {
                if passed {
                        pieceHashedCorrect.Add(1)
                } else {
                        log.Fmsg(
                                "piece %d failed hash: %d connections contributed", piece, len(p.dirtiers),
                        ).AddValues(t, p).SetLevel(log.Debug).Log(t.logger)
                        pieceHashedNotCorrect.Add(1)
                }
        }

        p.marking = true
        t.publishPieceChange(piece)
        defer func() {
                p.marking = false
                t.publishPieceChange(piece)
        }()

        if passed {
                if len(p.dirtiers) != 0 {
                        // Don't increment stats above connection-level for every involved connection.
                        t.allStats((*ConnStats).incrementPiecesDirtiedGood)
                }
                for c := range p.dirtiers {
                        c._stats.incrementPiecesDirtiedGood()
                }
                t.clearPieceTouchers(piece)
                t.cl.unlock()
                err := p.Storage().MarkComplete()
                if err != nil {
                        t.logger.Printf("%T: error marking piece complete %d: %s", t.storage, piece, err)
                }
                t.cl.lock()

                if t.closed.IsSet() {
                        return
                }
                t.pendAllChunkSpecs(piece)
        } else {
                if len(p.dirtiers) != 0 && p.allChunksDirty() && hashIoErr == nil {
                        // Peers contributed to all the data for this piece hash failure, and the failure was
                        // not due to errors in the storage (such as data being dropped in a cache).

                        // Increment Torrent and above stats, and then specific connections.
                        t.allStats((*ConnStats).incrementPiecesDirtiedBad)
                        for c := range p.dirtiers {
                                // Y u do dis peer?!
                                c.stats().incrementPiecesDirtiedBad()
                        }

                        bannableTouchers := make([]*Peer, 0, len(p.dirtiers))
                        for c := range p.dirtiers {
                                if !c.trusted {
                                        bannableTouchers = append(bannableTouchers, c)
                                }
                        }
                        t.clearPieceTouchers(piece)
                        slices.Sort(bannableTouchers, connLessTrusted)

                        if t.cl.config.Debug {
                                t.logger.Printf(
                                        "bannable conns by trust for piece %d: %v",
                                        piece,
                                        func() (ret []connectionTrust) {
                                                for _, c := range bannableTouchers {
                                                        ret = append(ret, c.trust())
                                                }
                                                return
                                        }(),
                                )
                        }

                        if len(bannableTouchers) >= 1 {
                                c := bannableTouchers[0]
                                t.cl.banPeerIP(c.remoteIp())
                                c.drop()
                        }
                }
                t.onIncompletePiece(piece)
                p.Storage().MarkNotComplete()
        }
        t.updatePieceCompletion(piece)
}

func (t *Torrent) cancelRequestsForPiece(piece pieceIndex) {
        // TODO: Make faster
        for cn := range t.conns {
                cn.tickleWriter()
        }
}

func (t *Torrent) onPieceCompleted(piece pieceIndex) {
        t.pendAllChunkSpecs(piece)
        t.cancelRequestsForPiece(piece)
        t.piece(piece).readerCond.Broadcast()
        for conn := range t.conns {
                conn.have(piece)
                t.maybeDropMutuallyCompletePeer(&conn.Peer)
        }
}

// Called when a piece is found to be not complete.
func (t *Torrent) onIncompletePiece(piece pieceIndex) {
        if t.pieceAllDirty(piece) {
                t.pendAllChunkSpecs(piece)
        }
        if !t.wantPieceIndex(piece) {
                // t.logger.Printf("piece %d incomplete and unwanted", piece)
                return
        }
        // We could drop any connections that we told we have a piece that we
        // don't here. But there's a test failure, and it seems clients don't care
        // if you request pieces that you already claim to have. Pruning bad
        // connections might just remove any connections that aren't treating us
        // favourably anyway.

        // for c := range t.conns {
        //      if c.sentHave(piece) {
        //              c.drop()
        //      }
        // }
        t.iterPeers(func(conn *Peer) {
                if conn.peerHasPiece(piece) {
                        conn.updateRequests("piece incomplete")
                }
        })
}

func (t *Torrent) tryCreateMorePieceHashers() {
        for !t.closed.IsSet() && t.activePieceHashes < 2 && t.tryCreatePieceHasher() {
        }
}

func (t *Torrent) tryCreatePieceHasher() bool {
        if t.storage == nil {
                return false
        }
        pi, ok := t.getPieceToHash()
        if !ok {
                return false
        }
        p := t.piece(pi)
        t.piecesQueuedForHash.Remove(bitmap.BitIndex(pi))
        p.hashing = true
        t.publishPieceChange(pi)
        t.updatePiecePriority(pi, "Torrent.tryCreatePieceHasher")
        t.storageLock.RLock()
        t.activePieceHashes++
        go t.pieceHasher(pi)
        return true
}

func (t *Torrent) getPieceToHash() (ret pieceIndex, ok bool) {
        t.piecesQueuedForHash.IterTyped(func(i pieceIndex) bool {
                if t.piece(i).hashing {
                        return true
                }
                ret = i
                ok = true
                return false
        })
        return
}

func (t *Torrent) pieceHasher(index pieceIndex) {
        p := t.piece(index)
        sum, copyErr := t.hashPiece(index)
        correct := sum == *p.hash
        switch copyErr {
        case nil, io.EOF:
        default:
                log.Fmsg("piece %v (%s) hash failure copy error: %v", p, p.hash.HexString(), copyErr).Log(t.logger)
        }
        t.storageLock.RUnlock()
        t.cl.lock()
        defer t.cl.unlock()
        p.hashing = false
        t.pieceHashed(index, correct, copyErr)
        t.updatePiecePriority(index, "Torrent.pieceHasher")
        t.activePieceHashes--
        t.tryCreateMorePieceHashers()
}

// Return the connections that touched a piece, and clear the entries while doing it.
func (t *Torrent) clearPieceTouchers(pi pieceIndex) {
        p := t.piece(pi)
        for c := range p.dirtiers {
                delete(c.peerTouchedPieces, pi)
                delete(p.dirtiers, c)
        }
}

func (t *Torrent) peersAsSlice() (ret []*Peer) {
        t.iterPeers(func(p *Peer) {
                ret = append(ret, p)
        })
        return
}

func (t *Torrent) queuePieceCheck(pieceIndex pieceIndex) {
        piece := t.piece(pieceIndex)
        if piece.queuedForHash() {
                return
        }
        t.piecesQueuedForHash.Add(bitmap.BitIndex(pieceIndex))
        t.publishPieceChange(pieceIndex)
        t.updatePiecePriority(pieceIndex, "Torrent.queuePieceCheck")
        t.tryCreateMorePieceHashers()
}

// Forces all the pieces to be re-hashed. See also Piece.VerifyData. This should not be called
// before the Info is available.
func (t *Torrent) VerifyData() {
        for i := pieceIndex(0); i < t.NumPieces(); i++ {
                t.Piece(i).VerifyData()
        }
}

// Start the process of connecting to the given peer for the given torrent if appropriate.
func (t *Torrent) initiateConn(peer PeerInfo) {
        if peer.Id == t.cl.peerID {
                return
        }
        if t.cl.badPeerAddr(peer.Addr) && !peer.Trusted {
                return
        }
        addr := peer.Addr
        if t.addrActive(addr.String()) {
                return
        }
        t.cl.numHalfOpen++
        t.halfOpen[addr.String()] = peer
        go t.cl.outgoingConnection(t, addr, peer.Source, peer.Trusted)
}

// Adds a trusted, pending peer for each of the given Client's addresses. Typically used in tests to
// quickly make one Client visible to the Torrent of another Client.
func (t *Torrent) AddClientPeer(cl *Client) int {
        return t.AddPeers(func() (ps []PeerInfo) {
                for _, la := range cl.ListenAddrs() {
                        ps = append(ps, PeerInfo{
                                Addr:    la,
                                Trusted: true,
                        })
                }
                return
        }())
}

// All stats that include this Torrent. Useful when we want to increment ConnStats but not for every
// connection.
func (t *Torrent) allStats(f func(*ConnStats)) {
        f(&t.stats)
        f(&t.cl.stats)
}

func (t *Torrent) hashingPiece(i pieceIndex) bool {
        return t.pieces[i].hashing
}

func (t *Torrent) pieceQueuedForHash(i pieceIndex) bool {
        return t.piecesQueuedForHash.Get(bitmap.BitIndex(i))
}

func (t *Torrent) dialTimeout() time.Duration {
        return reducedDialTimeout(t.cl.config.MinDialTimeout, t.cl.config.NominalDialTimeout, t.cl.config.HalfOpenConnsPerTorrent, t.peers.Len())
}

func (t *Torrent) piece(i int) *Piece {
        return &t.pieces[i]
}

func (t *Torrent) onWriteChunkErr(err error) {
        if t.userOnWriteChunkErr != nil {
                go t.userOnWriteChunkErr(err)
                return
        }
        t.logger.WithDefaultLevel(log.Critical).Printf("default chunk write error handler: disabling data download")
        t.disallowDataDownloadLocked()
}

func (t *Torrent) DisallowDataDownload() {
        t.disallowDataDownloadLocked()
}

func (t *Torrent) disallowDataDownloadLocked() {
        t.dataDownloadDisallowed.Set()
}

func (t *Torrent) AllowDataDownload() {
        t.dataDownloadDisallowed.Clear()
}

// Enables uploading data, if it was disabled.
func (t *Torrent) AllowDataUpload() {
        t.cl.lock()
        defer t.cl.unlock()
        t.dataUploadDisallowed = false
        for c := range t.conns {
                c.updateRequests("allow data upload")
        }
}

// Disables uploading data, if it was enabled.
func (t *Torrent) DisallowDataUpload() {
        t.cl.lock()
        defer t.cl.unlock()
        t.dataUploadDisallowed = true
        for c := range t.conns {
                c.updateRequests("disallow data upload")
        }
}

// Sets a handler that is called if there's an error writing a chunk to local storage. By default,
// or if nil, a critical message is logged, and data download is disabled.
func (t *Torrent) SetOnWriteChunkError(f func(error)) {
        t.cl.lock()
        defer t.cl.unlock()
        t.userOnWriteChunkErr = f
}

func (t *Torrent) iterPeers(f func(p *Peer)) {
        for pc := range t.conns {
                f(&pc.Peer)
        }
        for _, ws := range t.webSeeds {
                f(ws)
        }
}

func (t *Torrent) callbacks() *Callbacks {
        return &t.cl.config.Callbacks
}

func (t *Torrent) addWebSeed(url string) {
        if t.cl.config.DisableWebseeds {
                return
        }
        if _, ok := t.webSeeds[url]; ok {
                return
        }
        // I don't think Go http supports pipelining requests. However, we can have more ready to go
        // right away. This value should be some multiple of the number of connections to a host. I
        // would expect that double maxRequests plus a bit would be appropriate. This value is based on
        // downloading Sintel (08ada5a7a6183aae1e09d831df6748d566095a10) from
        // "https://webtorrent.io/torrents/".
        const maxRequests = 16
        ws := webseedPeer{
                peer: Peer{
                        t:                        t,
                        outgoing:                 true,
                        Network:                  "http",
                        reconciledHandshakeStats: true,
                        // This should affect how often we have to recompute requests for this peer. Note that
                        // because we can request more than 1 thing at a time over HTTP, we will hit the low
                        // requests mark more often, so recomputation is probably sooner than with regular peer
                        // conns. ~4x maxRequests would be about right.
                        PeerMaxRequests: 128,
                        RemoteAddr:      remoteAddrFromUrl(url),
                        callbacks:       t.callbacks(),
                },
                client: webseed.Client{
                        HttpClient: t.cl.webseedHttpClient,
                        Url:        url,
                },
                activeRequests: make(map[Request]webseed.Request, maxRequests),
                maxRequests:    maxRequests,
        }
        ws.peer.initUpdateRequestsTimer()
        ws.requesterCond.L = t.cl.locker()
        for i := 0; i < maxRequests; i += 1 {
                go ws.requester(i)
        }
        for _, f := range t.callbacks().NewPeer {
                f(&ws.peer)
        }
        ws.peer.logger = t.logger.WithContextValue(&ws)
        ws.peer.peerImpl = &ws
        if t.haveInfo() {
                ws.onGotInfo(t.info)
        }
        t.webSeeds[url] = &ws.peer
}

func (t *Torrent) peerIsActive(p *Peer) (active bool) {
        t.iterPeers(func(p1 *Peer) {
                if p1 == p {
                        active = true
                }
        })
        return
}

func (t *Torrent) requestIndexToRequest(ri RequestIndex) Request {
        index := ri / t.chunksPerRegularPiece()
        return Request{
                pp.Integer(index),
                t.piece(int(index)).chunkIndexSpec(ri % t.chunksPerRegularPiece()),
        }
}

func (t *Torrent) requestIndexFromRequest(r Request) RequestIndex {
        return t.pieceRequestIndexOffset(pieceIndex(r.Index)) + uint32(r.Begin/t.chunkSize)
}

func (t *Torrent) pieceRequestIndexOffset(piece pieceIndex) RequestIndex {
        return RequestIndex(piece) * t.chunksPerRegularPiece()
}

func (t *Torrent) updateComplete() {
        t.Complete.SetBool(t.haveAllPieces())
}