torrent/torrent.go

package torrent

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

	"github.com/anacrolix/torrent/common"
	"github.com/anacrolix/torrent/segments"
	"github.com/anacrolix/torrent/webseed"
	"github.com/davecgh/go-spew/spew"
	"github.com/pion/datachannel"

	"github.com/anacrolix/dht/v2"
	"github.com/anacrolix/log"
	"github.com/anacrolix/missinggo"
	"github.com/anacrolix/missinggo/perf"
	"github.com/anacrolix/missinggo/pubsub"
	"github.com/anacrolix/missinggo/slices"
	"github.com/anacrolix/missinggo/v2/bitmap"
	"github.com/anacrolix/missinggo/v2/prioritybitmap"

	"github.com/anacrolix/torrent/bencode"
	"github.com/anacrolix/torrent/metainfo"
	pp "github.com/anacrolix/torrent/peer_protocol"
	"github.com/anacrolix/torrent/storage"
	"github.com/anacrolix/torrent/tracker"
	"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      bool
	dataDownloadDisallowed bool
	dataUploadDisallowed   bool
	userOnWriteChunkErr    func(error)

	// Determines what chunks to request from peers.
	requestStrategy requestStrategy

	closed   missinggo.Event
	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
	fastestPeer *peer

	// 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

	// Set when .Info is obtained.
	gotMetainfo missinggo.Event

	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 prioritybitmap.PriorityBitmap
	// A cache of completed piece indices.
	_completedPieces bitmap.Bitmap
	// Pieces that need to be hashed.
	piecesQueuedForHash bitmap.Bitmap
	activePieceHashes   int

	// A pool of piece priorities []int for assignment to new connections.
	// These "inclinations" are used to give connections preference for
	// different pieces.
	connPieceInclinationPool sync.Pool

	// Count of each request across active connections.
	pendingRequests map[request]int

	pex pexState
}

func (t *Torrent) numConns() int {
	return len(t.conns)
}

func (t *Torrent) numReaders() int {
	return len(t.readers)
}

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

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

func (t *Torrent) ignorePieces() bitmap.Bitmap {
	ret := t._completedPieces.Copy()
	ret.Union(t.piecesQueuedForHash)
	for i := 0; i < t.numPieces(); i++ {
		if t.piece(i).hashing {
			ret.Set(i, true)
		}
	}
	return ret
}

func (t *Torrent) pendingPieces() *prioritybitmap.PriorityBitmap {
	return &t._pendingPieces
}

func (t *Torrent) tickleReaders() {
	t.cl.event.Broadcast()
}

// Returns a channel that is closed when the Torrent is closed.
func (t *Torrent) Closed() <-chan struct{} {
	return t.closed.LockedChan(t.cl.locker())
}

// 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.Get(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) unclosedConnsAsSlice() (ret []*PeerConn) {
	ret = make([]*PeerConn, 0, len(t.conns))
	for c := range t.conns {
		if !c.closed.IsSet() {
			ret = append(ret, c)
		}
	}
	return
}

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 := range t.metadataCompletedChunks {
		t.metadataCompletedChunks[i] = false
	}
	t.nameMu.Lock()
	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]
	}
}

// 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
}

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.fileIndex = segments.NewIndex(common.LengthIterFromUpvertedFiles(info.UpvertedFiles()))
	t.displayName = "" // Save a few bytes lol.
	t.initFiles()
	t.cacheLength()
	t.makePieces()
	return nil
}

// This seems to be all the follow-up tasks after info is set, that can't fail.
func (t *Torrent) onSetInfo() {
	t.iterPeers(func(p *peer) {
		p.onGotInfo(t.info)
	})
	for i := range t.pieces {
		t.updatePieceCompletion(pieceIndex(i))
		p := &t.pieces[i]
		if !p.storageCompletionOk {
			// t.logger.Printf("piece %s completion unknown, queueing check", p)
			t.queuePieceCheck(pieceIndex(i))
		}
	}
	t.cl.event.Broadcast()
	t.gotMetainfo.Set()
	t.updateWantPeersEvent()
	t.pendingRequests = make(map[request]int)
	t.tryCreateMorePieceHashers()
}

// Called when metadata for a torrent becomes available.
func (t *Torrent) setInfoBytes(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(bytes int) (err error) {
	if t.haveInfo() {
		// We already know the correct metadata size.
		return
	}
	if bytes <= 0 || bytes > 10000000 { // 10MB, pulled from my ass.
		return errors.New("bad size")
	}
	if t.metadataBytes != nil && len(t.metadataBytes) == int(bytes) {
		return
	}
	t.metadataBytes = make([]byte, bytes)
	t.metadataCompletedChunks = make([]bool, (bytes+(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
	}
	return t.displayName
}

func (t *Torrent) pieceState(index pieceIndex) (ret PieceState) {
	p := &t.pieces[index]
	ret.Priority = t.piecePriority(index)
	ret.Completion = p.completion()
	if p.queuedForHash() || p.hashing {
		ret.Checking = true
	}
	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 int, piece int, data []byte) pp.Message {
	d := map[string]int{
		"msg_type": msgType,
		"piece":    piece,
	}
	if data != nil {
		d["total_size"] = len(t.metadataBytes)
	}
	p := bencode.MustMarshal(d)
	return pp.Message{
		Type:            pp.Extended,
		ExtendedID:      c.PeerExtensionIDs[pp.ExtensionNameMetadata],
		ExtendedPayload: append(p, data...),
	}
}

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.Checking {
		ret += "H"
	}
	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.Sprint(t.usualPieceSize())
		} else {
			return "?"
		}
	}())
	if t.info != nil {
		fmt.Fprintf(w, "Num Pieces: %d (%d completed)\n", t.numPieces(), t.numPiecesCompleted())
		fmt.Fprintf(w, "Piece States: %s", t.pieceStateRuns())
		fmt.Fprintln(w)
	}
	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 {
		return worseConn(peers[i], peers[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
			}
		}(),
	}
}

func (t *Torrent) BytesMissing() int64 {
	t.cl.rLock()
	defer t.cl.rUnlock()
	return t.bytesMissingLocked()
}

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

func (t *Torrent) bytesLeft() (left int64) {
	bitmap.Flip(t._completedPieces, 0, bitmap.BitIndex(t.numPieces())).IterTyped(func(piece int) bool {
		p := &t.pieces[piece]
		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 int) {
	return t._completedPieces.Len()
}

func (t *Torrent) close() (err error) {
	t.closed.Set()
	t.tickleReaders()
	if t.storage != nil {
		t.storageLock.Lock()
		t.storage.Close()
		t.storageLock.Unlock()
	}
	for conn := range t.conns {
		conn.close()
	}
	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.IterTyped(func(piece int) (again bool) {
		bf[piece] = true
		return true
	})
	return
}

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

func (t *Torrent) pendAllChunkSpecs(pieceIndex pieceIndex) {
	t.pieces[pieceIndex]._dirtyChunks.Clear()
}

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, copyErr error) {
	hash := pieceHash.New()
	p := t.piece(piece)
	p.waitNoPendingWrites()
	ip := t.info.Piece(int(piece))
	pl := ip.Length()
	pieceReader := io.NewSectionReader(t.pieces[piece].Storage(), 0, pl)
	var hashSource io.Reader
	doCopy := func() {
		// Return no error iff pl bytes are copied.
		_, copyErr = io.CopyN(hash, hashSource, pl)
	}
	const logPieceContents = false
	if logPieceContents {
		var examineBuf bytes.Buffer
		hashSource = io.TeeReader(pieceReader, &examineBuf)
		doCopy()
		log.Printf("hashed %q with copy err %v", examineBuf.Bytes(), copyErr)
	} else {
		hashSource = pieceReader
		doCopy()
	}
	missinggo.CopyExact(&ret, hash.Sum(nil))
	return
}

func (t *Torrent) haveAnyPieces() bool {
	return t._completedPieces.Len() != 0
}

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

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

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 chunkIndex(cs chunkSpec, chunkSize pp.Integer) int {
	return int(cs.Begin / chunkSize)
}

func (t *Torrent) wantPieceIndex(index pieceIndex) bool {
	if !t.haveInfo() {
		return false
	}
	if index < 0 || index >= t.numPieces() {
		return false
	}
	p := &t.pieces[index]
	if p.queuedForHash() {
		return false
	}
	if p.hashing {
		return false
	}
	if t.pieceComplete(index) {
		return false
	}
	if t._pendingPieces.Contains(bitmap.BitIndex(index)) {
		return true
	}
	// t.logger.Printf("piece %d not pending", index)
	return !t.forReaderOffsetPieces(func(begin, end pieceIndex) bool {
		return index < begin || index >= end
	})
}

// 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 worser half of the
// established connections for more than a minute.
func (t *Torrent) worstBadConn() *PeerConn {
	wcs := worseConnSlice{t.unclosedConnsAsSlice()}
	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 t.pieceNumChunks(piece) - t.pieces[piece].numDirtyChunks()
}

func (t *Torrent) pieceAllDirty(piece pieceIndex) bool {
	return t.pieces[piece]._dirtyChunks.Len() == int(t.pieceNumChunks(piece))
}

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

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)
		t.updatePiecePriorities(h.begin, h.end)
	} else {
		// Ranges overlap.
		end := l.end
		if h.end > end {
			end = h.end
		}
		t.updatePiecePriorities(l.begin, end)
	}
}

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

func (t *Torrent) piecePriorityChanged(piece pieceIndex) {
	// t.logger.Printf("piece %d priority changed", piece)
	t.iterPeers(func(c *peer) {
		if c.updatePiecePriority(piece) {
			// log.Print("conn piece priority changed")
			c.updateRequests()
		}
	})
	t.maybeNewConns()
	t.publishPieceChange(piece)
}

func (t *Torrent) updatePiecePriority(piece pieceIndex) {
	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.Remove(bitmap.BitIndex(piece)) {
			return
		}
	} else {
		if !t._pendingPieces.Set(bitmap.BitIndex(piece), newPrio.BitmapPriority()) {
			return
		}
	}
	t.piecePriorityChanged(piece)
}

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

// 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) {
	for i := begin; i < end; i++ {
		t.updatePiecePriority(i)
	}
}

// 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 {
	prio, ok := t._pendingPieces.GetPriority(bitmap.BitIndex(piece))
	if !ok {
		return PiecePriorityNone
	}
	if prio > 0 {
		panic(prio)
	}
	ret := piecePriority(-prio)
	if ret == PiecePriorityNone {
		panic(piece)
	}
	return ret
}

func (t *Torrent) pendRequest(req request) {
	ci := chunkIndex(req.chunkSpec, t.chunkSize)
	t.pieces[req.Index].pendChunkIndex(ci)
}

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

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) getConnPieceInclination() []int {
	_ret := t.connPieceInclinationPool.Get()
	if _ret == nil {
		pieceInclinationsNew.Add(1)
		return rand.Perm(int(t.numPieces()))
	}
	pieceInclinationsReused.Add(1)
	return *_ret.(*[]int)
}

func (t *Torrent) putPieceInclination(pi []int) {
	t.connPieceInclinationPool.Put(&pi)
	pieceInclinationsPut.Add(1)
}

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
	t._completedPieces.Set(bitmap.BitIndex(piece), complete)
	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)
	}
	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.
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.setInfoBytes(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.BitIndex(begin)+1, bitmap.BitIndex(end))
		}
		return true
	})
	return
}

func (t *Torrent) needData() bool {
	if t.closed.IsSet() {
		return false
	}
	if !t.haveInfo() {
		return true
	}
	return t._pendingPieces.Len() != 0
}

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.info.TotalLength() - t.bytesLeft()
}

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

// Returns true if connection is removed from torrent.Conns.
func (t *Torrent) deleteConnection(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()
	if t.numActivePeers() == 0 {
		t.assertNoPendingRequests()
	}
	return
}

func (t *Torrent) numActivePeers() (num int) {
	t.iterPeers(func(*peer) {
		num++
	})
	return
}

func (t *Torrent) assertNoPendingRequests() {
	if len(t.pendingRequests) != 0 {
		panic(t.pendingRequests)
	}
	//if len(t.lastRequested) != 0 {
	//	panic(t.lastRequested)
	//}
}

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

func (t *Torrent) wantPeers() bool {
	if t.closed.IsSet() {
		return false
	}
	if t.peers.Len() > t.cl.config.TorrentPeersLowWater {
		return false
	}
	return t.needData() || t.seeding()
}

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
	}
	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.LockedChan(t.cl.locker())
		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
			}
		}
		urlString := (*u).String()
		cl := t.cl
		newAnnouncer := &trackerScraper{
			u: *u,
			t: t,
			allow: func() {
				cl.lock()
				defer cl.unlock()
				if cl.activeAnnounces == nil {
					cl.activeAnnounces = make(map[string]struct{})
				}
				for {
					if _, ok := cl.activeAnnounces[urlString]; ok {
						cl.event.Wait()
					} else {
						break
					}
				}
				cl.activeAnnounces[urlString] = struct{}{}
			},
			done: func(slowdown bool) {
				cl.lock()
				defer cl.unlock()
				delete(cl.activeAnnounces, urlString)
				cl.event.Broadcast()
			},
		}
		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()
		for _, cp := range v.Peers {
			if cp.Port == 0 {
				// Can't do anything with this.
				continue
			}
			t.addPeer(PeerInfo{
				Addr:   ipPortAddr{cp.IP, cp.Port},
				Source: PeerSourceDhtGetPeers,
			})
		}
		cl.unlock()
	}
}

func (t *Torrent) announceToDht(impliedPort bool, s DhtServer) error {
	ps, err := s.Announce(t.infoHash, t.cl.incomingPeerPort(), impliedPort)
	if err != nil {
		return err
	}
	go t.consumeDhtAnnouncePeers(ps.Peers())
	select {
	case <-t.closed.LockedChan(t.cl.locker()):
	case <-time.After(5 * time.Minute):
	}
	ps.Close()
	return nil
}

func (t *Torrent) dhtAnnouncer(s DhtServer) {
	cl := t.cl
	cl.lock()
	defer cl.unlock()
	for {
		for {
			if t.closed.IsSet() {
				return
			}
			if !t.wantPeers() {
				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.announceToDht(true, 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()
	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) addConnection(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.deleteConnection(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.deleteConnection(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 {
		return false
	}
	if t.closed.IsSet() {
		return false
	}
	if !t.seeding() && !t.needData() {
		return false
	}
	if len(t.conns) < t.maxEstablishedConns {
		return true
	}
	return 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 := slices.HeapInterface(slices.FromMapKeys(t.conns), func(l, r *PeerConn) bool {
		return worseConn(&l.peer, &r.peer)
	})
	for len(t.conns) > t.maxEstablishedConns && wcs.Len() > 0 {
		t.dropConnection(wcs.Pop().(*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).Log(t.logger)
			pieceHashedNotCorrect.Add(1)
		}
	}

	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)
		err := p.Storage().MarkComplete()
		if err != nil {
			t.logger.Printf("%T: error marking piece complete %d: %s", t.storage, piece, err)
		}
		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)
	for conn := range t.conns {
		conn.have(piece)
	}
}

// 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()
		}
	})
}

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(pi)
	p.hashing = true
	t.publishPieceChange(pi)
	t.updatePiecePriority(pi)
	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.updatePiecePriority(index)
	t.pieceHashed(index, correct, copyErr)
	t.publishPieceChange(index)
	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)
	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) requestStrategyTorrent() requestStrategyTorrent {
	return t
}

type torrentRequestStrategyCallbacks struct {
	t *Torrent
}

func (cb torrentRequestStrategyCallbacks) requestTimedOut(r request) {
	torrent.Add("request timeouts", 1)
	cb.t.cl.lock()
	defer cb.t.cl.unlock()
	cb.t.iterPeers(func(cn *peer) {
		if cn.peerHasPiece(pieceIndex(r.Index)) {
			cn.updateRequests()
		}
	})

}

func (t *Torrent) requestStrategyCallbacks() requestStrategyCallbacks {
	return torrentRequestStrategyCallbacks{t}
}

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.cl.lock()
	defer t.cl.unlock()
	t.disallowDataDownloadLocked()
}

func (t *Torrent) disallowDataDownloadLocked() {
	t.dataDownloadDisallowed = true
	t.iterPeers(func(c *peer) {
		c.updateRequests()
	})
	t.tickleReaders()
}

func (t *Torrent) AllowDataDownload() {
	t.cl.lock()
	defer t.cl.unlock()
	t.dataDownloadDisallowed = false
	t.tickleReaders()
	t.iterPeers(func(c *peer) {
		c.updateRequests()
	})
}

func (t *Torrent) AllowDataUpload() {
	t.cl.lock()
	defer t.cl.unlock()
	t.dataUploadDisallowed = false
	for c := range t.conns {
		c.updateRequests()
	}
}

func (t *Torrent) DisallowDataUpload() {
	t.cl.lock()
	defer t.cl.unlock()
	t.dataUploadDisallowed = true
	for c := range t.conns {
		c.updateRequests()
	}
}

func (t *Torrent) SetOnWriteChunkError(f func(error)) {
	t.cl.lock()
	defer t.cl.unlock()
	t.userOnWriteChunkErr = f
}

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

func (t *Torrent) addWebSeed(url string) {
	if t.cl.config.DisableWebseeds {
		return
	}
	if _, ok := t.webSeeds[url]; ok {
		return
	}
	const maxRequests = 10
	ws := webseedPeer{
		peer: peer{
			t:                        t,
			outgoing:                 true,
			network:                  "http",
			reconciledHandshakeStats: true,
			peerSentHaveAll:          true,
			PeerMaxRequests:          maxRequests,
		},
		client: webseed.Client{
			HttpClient: http.DefaultClient,
			Url:        url,
		},
		requests: make(map[request]webseed.Request, maxRequests),
	}
	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
}