X-Git-Url: http://www.git.stargrave.org/?a=blobdiff_plain;f=peerconn.go;h=e2d944ff269bb94426772d60f267bb359582d156;hb=HEAD;hp=2b27706a20e9f4fea9310dc88685741e76ab2eab;hpb=e51accb3e2eee6206b4f6a1b3844bc3fd00649ae;p=btrtrc.git

diff --git a/peerconn.go b/peerconn.go
index 2b27706a..e2d944ff 100644
--- a/peerconn.go
+++ b/peerconn.go
@@ -3,134 +3,35 @@ package torrent
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"errors"
 	"fmt"
 	"io"
 	"math/rand"
 	"net"
-	"sort"
+	"net/netip"
 	"strconv"
 	"strings"
+	"sync/atomic"
 	"time"
 
 	"github.com/RoaringBitmap/roaring"
+	"github.com/anacrolix/generics"
+	. "github.com/anacrolix/generics"
 	"github.com/anacrolix/log"
-	"github.com/anacrolix/missinggo/iter"
 	"github.com/anacrolix/missinggo/v2/bitmap"
 	"github.com/anacrolix/multiless"
+	"golang.org/x/exp/maps"
+	"golang.org/x/time/rate"
 
-	"github.com/anacrolix/chansync"
 	"github.com/anacrolix/torrent/bencode"
+	"github.com/anacrolix/torrent/internal/alloclim"
 	"github.com/anacrolix/torrent/metainfo"
 	"github.com/anacrolix/torrent/mse"
 	pp "github.com/anacrolix/torrent/peer_protocol"
-	request_strategy "github.com/anacrolix/torrent/request-strategy"
+	utHolepunch "github.com/anacrolix/torrent/peer_protocol/ut-holepunch"
 )
 
-type PeerSource string
-
-const (
-	PeerSourceTracker         = "Tr"
-	PeerSourceIncoming        = "I"
-	PeerSourceDhtGetPeers     = "Hg" // Peers we found by searching a DHT.
-	PeerSourceDhtAnnouncePeer = "Ha" // Peers that were announced to us by a DHT.
-	PeerSourcePex             = "X"
-	// The peer was given directly, such as through a magnet link.
-	PeerSourceDirect = "M"
-)
-
-type peerRequestState struct {
-	data []byte
-}
-
-type PeerRemoteAddr interface {
-	String() string
-}
-
-// Since we have to store all the requests in memory, we can't reasonably exceed what would be
-// indexable with the memory space available.
-type (
-	maxRequests  = int
-	requestState = request_strategy.PeerNextRequestState
-)
-
-type Peer struct {
-	// First to ensure 64-bit alignment for atomics. See #262.
-	_stats ConnStats
-
-	t *Torrent
-
-	peerImpl
-	callbacks *Callbacks
-
-	outgoing   bool
-	Network    string
-	RemoteAddr PeerRemoteAddr
-	// True if the connection is operating over MSE obfuscation.
-	headerEncrypted bool
-	cryptoMethod    mse.CryptoMethod
-	Discovery       PeerSource
-	trusted         bool
-	closed          chansync.SetOnce
-	// Set true after we've added our ConnStats generated during handshake to
-	// other ConnStat instances as determined when the *Torrent became known.
-	reconciledHandshakeStats bool
-
-	lastMessageReceived     time.Time
-	completedHandshake      time.Time
-	lastUsefulChunkReceived time.Time
-	lastChunkSent           time.Time
-
-	// Stuff controlled by the local peer.
-	needRequestUpdate    string
-	actualRequestState   requestState
-	updateRequestsTimer  *time.Timer
-	cancelledRequests    roaring.Bitmap
-	lastBecameInterested time.Time
-	priorInterest        time.Duration
-
-	lastStartedExpectingToReceiveChunks time.Time
-	cumulativeExpectedToReceiveChunks   time.Duration
-	_chunksReceivedWhileExpecting       int64
-
-	choking                                bool
-	piecesReceivedSinceLastRequestUpdate   maxRequests
-	maxPiecesReceivedBetweenRequestUpdates maxRequests
-	// Chunks that we might reasonably expect to receive from the peer. Due to
-	// latency, buffering, and implementation differences, we may receive
-	// chunks that are no longer in the set of requests actually want.
-	validReceiveChunks map[RequestIndex]int
-	// Indexed by metadata piece, set to true if posted and pending a
-	// response.
-	metadataRequests []bool
-	sentHaves        bitmap.Bitmap
-
-	// Stuff controlled by the remote peer.
-	peerInterested        bool
-	peerChoking           bool
-	peerRequests          map[Request]*peerRequestState
-	PeerPrefersEncryption bool // as indicated by 'e' field in extension handshake
-	PeerListenPort        int
-	// The pieces the peer has claimed to have.
-	_peerPieces roaring.Bitmap
-	// The peer has everything. This can occur due to a special message, when
-	// we may not even know the number of pieces in the torrent yet.
-	peerSentHaveAll bool
-	// The highest possible number of pieces the torrent could have based on
-	// communication with the peer. Generally only useful until we have the
-	// torrent info.
-	peerMinPieces pieceIndex
-	// Pieces we've accepted chunks for from the peer.
-	peerTouchedPieces map[pieceIndex]struct{}
-	peerAllowedFast   roaring.Bitmap
-
-	PeerMaxRequests  maxRequests // Maximum pending requests the peer allows.
-	PeerExtensionIDs map[pp.ExtensionName]pp.ExtensionNumber
-	PeerClientName   string
-
-	logger log.Logger
-}
-
 // Maintains the state of a BitTorrent-protocol based connection with a peer.
 type PeerConn struct {
 	Peer
@@ -142,8 +43,10 @@ type PeerConn struct {
 	// See BEP 3 etc.
 	PeerID             PeerID
 	PeerExtensionBytes pp.PeerExtensionBits
+	PeerListenPort     int
 
-	// The actual Conn, used for closing, and setting socket options.
+	// The actual Conn, used for closing, and setting socket options. Do not use methods on this
+	// while holding any mutexes.
 	conn net.Conn
 	// The Reader and Writer for this Conn, with hooks installed for stats,
 	// limiting, deadlines etc.
@@ -152,51 +55,60 @@ type PeerConn struct {
 
 	messageWriter peerConnMsgWriter
 
-	uploadTimer *time.Timer
-	pex         pexConnState
-}
+	PeerExtensionIDs map[pp.ExtensionName]pp.ExtensionNumber
+	PeerClientName   atomic.Value
+	uploadTimer      *time.Timer
+	pex              pexConnState
 
-func (cn *PeerConn) connStatusString() string {
-	return fmt.Sprintf("%+-55q %s %s", cn.PeerID, cn.PeerExtensionBytes, cn.connString)
-}
+	// The pieces the peer has claimed to have.
+	_peerPieces roaring.Bitmap
+	// The peer has everything. This can occur due to a special message, when
+	// we may not even know the number of pieces in the torrent yet.
+	peerSentHaveAll bool
 
-func (cn *Peer) updateExpectingChunks() {
-	if cn.expectingChunks() {
-		if cn.lastStartedExpectingToReceiveChunks.IsZero() {
-			cn.lastStartedExpectingToReceiveChunks = time.Now()
-		}
-	} else {
-		if !cn.lastStartedExpectingToReceiveChunks.IsZero() {
-			cn.cumulativeExpectedToReceiveChunks += time.Since(cn.lastStartedExpectingToReceiveChunks)
-			cn.lastStartedExpectingToReceiveChunks = time.Time{}
-		}
-	}
+	peerRequestDataAllocLimiter alloclim.Limiter
+
+	outstandingHolepunchingRendezvous map[netip.AddrPort]struct{}
 }
 
-func (cn *Peer) expectingChunks() bool {
-	if cn.actualRequestState.Requests.IsEmpty() {
-		return false
+func (cn *PeerConn) pexStatus() string {
+	if !cn.bitExtensionEnabled(pp.ExtensionBitLtep) {
+		return "extended protocol disabled"
 	}
-	if !cn.actualRequestState.Interested {
-		return false
+	if cn.PeerExtensionIDs == nil {
+		return "pending extended handshake"
 	}
-	if !cn.peerChoking {
-		return true
+	if !cn.supportsExtension(pp.ExtensionNamePex) {
+		return "unsupported"
+	}
+	if true {
+		return fmt.Sprintf(
+			"%v conns, %v unsent events",
+			len(cn.pex.remoteLiveConns),
+			cn.pex.numPending(),
+		)
+	} else {
+		// This alternative branch prints out the remote live conn addresses.
+		return fmt.Sprintf(
+			"%v conns, %v unsent events",
+			strings.Join(generics.SliceMap(
+				maps.Keys(cn.pex.remoteLiveConns),
+				func(from netip.AddrPort) string {
+					return from.String()
+				}), ","),
+			cn.pex.numPending(),
+		)
 	}
-	haveAllowedFastRequests := false
-	cn.peerAllowedFast.Iterate(func(i uint32) bool {
-		haveAllowedFastRequests = roaringBitmapRangeCardinality(
-			&cn.actualRequestState.Requests,
-			cn.t.pieceRequestIndexOffset(pieceIndex(i)),
-			cn.t.pieceRequestIndexOffset(pieceIndex(i+1)),
-		) == 0
-		return !haveAllowedFastRequests
-	})
-	return haveAllowedFastRequests
 }
 
-func (cn *Peer) remoteChokingPiece(piece pieceIndex) bool {
-	return cn.peerChoking && !cn.peerAllowedFast.Contains(bitmap.BitIndex(piece))
+func (cn *PeerConn) peerImplStatusLines() []string {
+	return []string{
+		cn.connString,
+		fmt.Sprintf("peer id: %+q", cn.PeerID),
+		fmt.Sprintf("extensions: %v", cn.PeerExtensionBytes),
+		fmt.Sprintf("ltep extensions: %v", cn.PeerExtensionIDs),
+		fmt.Sprintf("pex: %s", cn.pexStatus()),
+	}
 }
 
 // Returns true if the connection is over IPv6.
@@ -208,64 +120,33 @@ func (cn *PeerConn) ipv6() bool {
 	return len(ip) == net.IPv6len
 }
 
-// Returns true the if the dialer/initiator has the lower client peer ID. TODO: Find the
-// specification for this.
+// Returns true the if the dialer/initiator has the higher client peer ID. See
+// https://github.com/arvidn/libtorrent/blame/272828e1cc37b042dfbbafa539222d8533e99755/src/bt_peer_connection.cpp#L3536-L3557.
+// As far as I can tell, Transmission just keeps the oldest connection.
 func (cn *PeerConn) isPreferredDirection() bool {
-	return bytes.Compare(cn.t.cl.peerID[:], cn.PeerID[:]) < 0 == cn.outgoing
+	// True if our client peer ID is higher than the remote's peer ID.
+	return bytes.Compare(cn.PeerID[:], cn.t.cl.peerID[:]) < 0 == cn.outgoing
 }
 
 // Returns whether the left connection should be preferred over the right one,
 // considering only their networking properties. If ok is false, we can't
 // decide.
-func (l *PeerConn) hasPreferredNetworkOver(r *PeerConn) (left, ok bool) {
-	var ml multiLess
-	ml.NextBool(l.isPreferredDirection(), r.isPreferredDirection())
-	ml.NextBool(!l.utp(), !r.utp())
-	ml.NextBool(l.ipv6(), r.ipv6())
-	return ml.FinalOk()
+func (l *PeerConn) hasPreferredNetworkOver(r *PeerConn) bool {
+	var ml multiless.Computation
+	ml = ml.Bool(r.isPreferredDirection(), l.isPreferredDirection())
+	ml = ml.Bool(l.utp(), r.utp())
+	ml = ml.Bool(r.ipv6(), l.ipv6())
+	return ml.Less()
 }
 
-func (cn *Peer) cumInterest() time.Duration {
-	ret := cn.priorInterest
-	if cn.actualRequestState.Interested {
-		ret += time.Since(cn.lastBecameInterested)
-	}
-	return ret
-}
-
-func (cn *Peer) peerHasAllPieces() (all bool, known bool) {
+func (cn *PeerConn) peerHasAllPieces() (all, known bool) {
 	if cn.peerSentHaveAll {
 		return true, true
 	}
 	if !cn.t.haveInfo() {
 		return false, false
 	}
-	return roaring.Flip(&cn._peerPieces, 0, bitmap.BitRange(cn.t.numPieces())).IsEmpty(), true
-}
-
-func (cn *PeerConn) locker() *lockWithDeferreds {
-	return cn.t.cl.locker()
-}
-
-func (cn *Peer) supportsExtension(ext pp.ExtensionName) bool {
-	_, ok := cn.PeerExtensionIDs[ext]
-	return ok
-}
-
-// The best guess at number of pieces in the torrent for this peer.
-func (cn *Peer) bestPeerNumPieces() pieceIndex {
-	if cn.t.haveInfo() {
-		return cn.t.numPieces()
-	}
-	return cn.peerMinPieces
-}
-
-func (cn *Peer) completedString() string {
-	have := pieceIndex(cn._peerPieces.GetCardinality())
-	if cn.peerSentHaveAll {
-		have = cn.bestPeerNumPieces()
-	}
-	return fmt.Sprintf("%d/%d", have, cn.bestPeerNumPieces())
+	return cn._peerPieces.GetCardinality() == uint64(cn.t.numPieces()), true
 }
 
 func (cn *PeerConn) onGotInfo(info *metainfo.Info) {
@@ -279,11 +160,8 @@ func (cn *PeerConn) setNumPieces(num pieceIndex) {
 	cn.peerPiecesChanged()
 }
 
-func eventAgeString(t time.Time) string {
-	if t.IsZero() {
-		return "never"
-	}
-	return fmt.Sprintf("%.2fs ago", time.Since(t).Seconds())
+func (cn *PeerConn) peerPieces() *roaring.Bitmap {
+	return &cn._peerPieces
 }
 
 func (cn *PeerConn) connectionFlags() (ret string) {
@@ -306,136 +184,19 @@ func (cn *PeerConn) utp() bool {
 	return parseNetworkString(cn.Network).Udp
 }
 
-// Inspired by https://github.com/transmission/transmission/wiki/Peer-Status-Text.
-func (cn *Peer) statusFlags() (ret string) {
-	c := func(b byte) {
-		ret += string([]byte{b})
-	}
-	if cn.actualRequestState.Interested {
-		c('i')
-	}
-	if cn.choking {
-		c('c')
-	}
-	c('-')
-	ret += cn.connectionFlags()
-	c('-')
-	if cn.peerInterested {
-		c('i')
-	}
-	if cn.peerChoking {
-		c('c')
-	}
-	return
-}
-
-func (cn *Peer) downloadRate() float64 {
-	num := cn._stats.BytesReadUsefulData.Int64()
-	if num == 0 {
-		return 0
-	}
-	return float64(num) / cn.totalExpectingTime().Seconds()
-}
-
-func (cn *Peer) numRequestsByPiece() (ret map[pieceIndex]int) {
-	ret = make(map[pieceIndex]int)
-	cn.actualRequestState.Requests.Iterate(func(x uint32) bool {
-		ret[pieceIndex(x/cn.t.chunksPerRegularPiece())]++
-		return true
-	})
-	return
-}
-
-func (cn *Peer) writeStatus(w io.Writer, t *Torrent) {
-	// \t isn't preserved in <pre> blocks?
-	if cn.closed.IsSet() {
-		fmt.Fprint(w, "CLOSED: ")
-	}
-	fmt.Fprintln(w, cn.connStatusString())
-	prio, err := cn.peerPriority()
-	prioStr := fmt.Sprintf("%08x", prio)
-	if err != nil {
-		prioStr += ": " + err.Error()
-	}
-	fmt.Fprintf(w, "    bep40-prio: %v\n", prioStr)
-	fmt.Fprintf(w, "    last msg: %s, connected: %s, last helpful: %s, itime: %s, etime: %s\n",
-		eventAgeString(cn.lastMessageReceived),
-		eventAgeString(cn.completedHandshake),
-		eventAgeString(cn.lastHelpful()),
-		cn.cumInterest(),
-		cn.totalExpectingTime(),
-	)
-	fmt.Fprintf(w,
-		"    %s completed, %d pieces touched, good chunks: %v/%v:%v reqq: %d-%v/(%d/%d):%d/%d, flags: %s, dr: %.1f KiB/s\n",
-		cn.completedString(),
-		len(cn.peerTouchedPieces),
-		&cn._stats.ChunksReadUseful,
-		&cn._stats.ChunksRead,
-		&cn._stats.ChunksWritten,
-		cn.actualRequestState.Requests.GetCardinality(),
-		cn.cancelledRequests.GetCardinality(),
-		cn.nominalMaxRequests(),
-		cn.PeerMaxRequests,
-		len(cn.peerRequests),
-		localClientReqq,
-		cn.statusFlags(),
-		cn.downloadRate()/(1<<10),
-	)
-	fmt.Fprintf(w, "    requested pieces:")
-	type pieceNumRequestsType struct {
-		piece       pieceIndex
-		numRequests int
-	}
-	var pieceNumRequests []pieceNumRequestsType
-	for piece, count := range cn.numRequestsByPiece() {
-		pieceNumRequests = append(pieceNumRequests, pieceNumRequestsType{piece, count})
-	}
-	sort.Slice(pieceNumRequests, func(i, j int) bool {
-		return pieceNumRequests[i].piece < pieceNumRequests[j].piece
-	})
-	for _, elem := range pieceNumRequests {
-		fmt.Fprintf(w, " %v(%v)", elem.piece, elem.numRequests)
-	}
-	fmt.Fprintf(w, "\n")
-}
-
-func (p *Peer) close() {
-	if !p.closed.Set() {
-		return
-	}
-	p.peerImpl.onClose()
-	if p.t != nil {
-		p.t.decPeerPieceAvailability(p)
-	}
-	for _, f := range p.callbacks.PeerClosed {
-		f(p)
-	}
-}
-
 func (cn *PeerConn) onClose() {
 	if cn.pex.IsEnabled() {
 		cn.pex.Close()
 	}
-	if cn.updateRequestsTimer != nil {
-		cn.updateRequestsTimer.Stop()
-	}
 	cn.tickleWriter()
 	if cn.conn != nil {
-		cn.conn.Close()
+		go cn.conn.Close()
 	}
 	if cb := cn.callbacks.PeerConnClosed; cb != nil {
 		cb(cn)
 	}
 }
 
-func (cn *Peer) peerHasPiece(piece pieceIndex) bool {
-	return cn.peerSentHaveAll || cn._peerPieces.Contains(bitmap.BitIndex(piece))
-}
-
-// 64KiB, but temporarily less to work around an issue with WebRTC. TODO: Update when
-// https://github.com/pion/datachannel/issues/59 is fixed.
-const writeBufferHighWaterLen = 1 << 15
-
 // Writes a message into the write buffer. Returns whether it's okay to keep writing. Writing is
 // done asynchronously, so it may be that we're not able to honour backpressure from this method.
 func (cn *PeerConn) write(msg pp.Message) bool {
@@ -470,20 +231,6 @@ func (cn *PeerConn) requestedMetadataPiece(index int) bool {
 	return index < len(cn.metadataRequests) && cn.metadataRequests[index]
 }
 
-// The actual value to use as the maximum outbound requests.
-func (cn *Peer) nominalMaxRequests() (ret maxRequests) {
-	return maxRequests(clamp(1, int64(cn.PeerMaxRequests), 2048))
-}
-
-func (cn *Peer) totalExpectingTime() (ret time.Duration) {
-	ret = cn.cumulativeExpectedToReceiveChunks
-	if !cn.lastStartedExpectingToReceiveChunks.IsZero() {
-		ret += time.Since(cn.lastStartedExpectingToReceiveChunks)
-	}
-	return
-
-}
-
 func (cn *PeerConn) onPeerSentCancel(r Request) {
 	if _, ok := cn.peerRequests[r]; !ok {
 		torrent.Add("unexpected cancels received", 1)
@@ -504,17 +251,19 @@ func (cn *PeerConn) choke(msg messageWriter) (more bool) {
 	more = msg(pp.Message{
 		Type: pp.Choke,
 	})
-	if cn.fastEnabled() {
-		for r := range cn.peerRequests {
-			// TODO: Don't reject pieces in allowed fast set.
-			cn.reject(r)
-		}
-	} else {
-		cn.peerRequests = nil
+	if !cn.fastEnabled() {
+		cn.deleteAllPeerRequests()
 	}
 	return
 }
 
+func (cn *PeerConn) deleteAllPeerRequests() {
+	for _, state := range cn.peerRequests {
+		state.allocReservation.Drop()
+	}
+	cn.peerRequests = nil
+}
+
 func (cn *PeerConn) unchoke(msg func(pp.Message) bool) bool {
 	if !cn.choking {
 		return true
@@ -525,21 +274,6 @@ func (cn *PeerConn) unchoke(msg func(pp.Message) bool) bool {
 	})
 }
 
-func (cn *Peer) setInterested(interested bool) bool {
-	if cn.actualRequestState.Interested == interested {
-		return true
-	}
-	cn.actualRequestState.Interested = interested
-	if interested {
-		cn.lastBecameInterested = time.Now()
-	} else if !cn.lastBecameInterested.IsZero() {
-		cn.priorInterest += time.Since(cn.lastBecameInterested)
-	}
-	cn.updateExpectingChunks()
-	// log.Printf("%p: setting interest: %v", cn, interested)
-	return cn.writeInterested(interested)
-}
-
 func (pc *PeerConn) writeInterested(interested bool) bool {
 	return pc.write(pp.Message{
 		Type: func() pp.MessageType {
@@ -552,57 +286,6 @@ func (pc *PeerConn) writeInterested(interested bool) bool {
 	})
 }
 
-// The function takes a message to be sent, and returns true if more messages
-// are okay.
-type messageWriter func(pp.Message) bool
-
-func (cn *Peer) shouldRequest(r RequestIndex) error {
-	pi := pieceIndex(r / cn.t.chunksPerRegularPiece())
-	if !cn.peerHasPiece(pi) {
-		return errors.New("requesting piece peer doesn't have")
-	}
-	if !cn.t.peerIsActive(cn) {
-		panic("requesting but not in active conns")
-	}
-	if cn.closed.IsSet() {
-		panic("requesting when connection is closed")
-	}
-	if cn.t.hashingPiece(pi) {
-		panic("piece is being hashed")
-	}
-	if cn.t.pieceQueuedForHash(pi) {
-		panic("piece is queued for hash")
-	}
-	if cn.peerChoking && !cn.peerAllowedFast.Contains(bitmap.BitIndex(pi)) {
-		panic("peer choking and piece not allowed fast")
-	}
-	return nil
-}
-
-func (cn *Peer) request(r RequestIndex) (more bool, err error) {
-	if err := cn.shouldRequest(r); err != nil {
-		panic(err)
-	}
-	if cn.actualRequestState.Requests.Contains(r) {
-		return true, nil
-	}
-	if maxRequests(cn.actualRequestState.Requests.GetCardinality()) >= cn.nominalMaxRequests() {
-		return true, errors.New("too many outstanding requests")
-	}
-	cn.actualRequestState.Requests.Add(r)
-	if cn.validReceiveChunks == nil {
-		cn.validReceiveChunks = make(map[RequestIndex]int)
-	}
-	cn.validReceiveChunks[r]++
-	cn.t.pendingRequests.Inc(r)
-	cn.updateExpectingChunks()
-	ppReq := cn.t.requestIndexToRequest(r)
-	for _, f := range cn.callbacks.SentRequest {
-		f(PeerRequestEvent{cn, ppReq})
-	}
-	return cn.peerImpl._request(ppReq), nil
-}
-
 func (me *PeerConn) _request(r Request) bool {
 	return me.write(pp.Message{
 		Type:   pp.Request,
@@ -612,35 +295,23 @@ func (me *PeerConn) _request(r Request) bool {
 	})
 }
 
-func (me *Peer) cancel(r RequestIndex) bool {
-	if !me.actualRequestState.Requests.Contains(r) {
-		return true
-	}
-	return me._cancel(r)
-}
-
 func (me *PeerConn) _cancel(r RequestIndex) bool {
-	if me.cancelledRequests.Contains(r) {
-		// Already cancelled and waiting for a response.
-		return true
-	}
-	if me.fastEnabled() {
-		me.cancelledRequests.Add(r)
-	} else {
-		if !me.deleteRequest(r) {
-			panic("request not existing should have been guarded")
-		}
-		if me.actualRequestState.Requests.IsEmpty() {
-			me.updateRequests("Peer.cancel")
-		}
-	}
-	return me.write(makeCancelMessage(me.t.requestIndexToRequest(r)))
+	me.write(makeCancelMessage(me.t.requestIndexToRequest(r)))
+	// Transmission does not send rejects for received cancels. See
+	// https://github.com/transmission/transmission/pull/2275.
+	return me.fastEnabled() && !me.remoteIsTransmission()
 }
 
 func (cn *PeerConn) fillWriteBuffer() {
-	if !cn.applyNextRequestState() {
-		return
-	}
+	if cn.messageWriter.writeBuffer.Len() > writeBufferLowWaterLen {
+		// Fully committing to our max requests requires sufficient space (see
+		// maxLocalToRemoteRequests). Flush what we have instead. We also prefer always to make
+		// requests than to do PEX or upload, so we short-circuit before handling those. Any update
+		// request reason will not be cleared, so we'll come right back here when there's space. We
+		// can't do this in maybeUpdateActualRequestState because it's a method on Peer and has no
+		// knowledge of write buffers.
+	}
+	cn.maybeUpdateActualRequestState()
 	if cn.pex.IsEnabled() {
 		if flow := cn.pex.Share(cn.write); !flow {
 			return
@@ -674,41 +345,11 @@ func (cn *PeerConn) postBitfield() {
 	cn.sentHaves = bitmap.Bitmap{cn.t._completedPieces.Clone()}
 }
 
-func (cn *PeerConn) updateRequests(reason string) {
-	if cn.needRequestUpdate != "" {
-		return
-	}
-	cn.needRequestUpdate = reason
+func (cn *PeerConn) handleUpdateRequests() {
+	// The writer determines the request state as needed when it can write.
 	cn.tickleWriter()
 }
 
-// Emits the indices in the Bitmaps bms in order, never repeating any index.
-// skip is mutated during execution, and its initial values will never be
-// emitted.
-func iterBitmapsDistinct(skip *bitmap.Bitmap, bms ...bitmap.Bitmap) iter.Func {
-	return func(cb iter.Callback) {
-		for _, bm := range bms {
-			if !iter.All(
-				func(_i interface{}) bool {
-					i := _i.(int)
-					if skip.Contains(bitmap.BitIndex(i)) {
-						return true
-					}
-					skip.Add(bitmap.BitIndex(i))
-					return cb(i)
-				},
-				bm.Iter,
-			) {
-				return
-			}
-		}
-	}
-}
-
-func (cn *Peer) peerPiecesChanged() {
-	cn.t.maybeDropMutuallyCompletePeer(cn)
-}
-
 func (cn *PeerConn) raisePeerMinPieces(newMin pieceIndex) {
 	if newMin > cn.peerMinPieces {
 		cn.peerMinPieces = newMin
@@ -744,42 +385,62 @@ func (cn *PeerConn) peerSentBitfield(bf []bool) error {
 		// Ignore known excess pieces.
 		bf = bf[:cn.t.numPieces()]
 	}
-	pp := cn.newPeerPieces()
+	bm := boolSliceToBitmap(bf)
+	if cn.t.haveInfo() && pieceIndex(bm.GetCardinality()) == cn.t.numPieces() {
+		cn.onPeerHasAllPieces()
+		return nil
+	}
+	if !bm.IsEmpty() {
+		cn.raisePeerMinPieces(pieceIndex(bm.Maximum()) + 1)
+	}
+	shouldUpdateRequests := false
+	if cn.peerSentHaveAll {
+		if !cn.t.deleteConnWithAllPieces(&cn.Peer) {
+			panic(cn)
+		}
+		cn.peerSentHaveAll = false
+		if !cn._peerPieces.IsEmpty() {
+			panic("if peer has all, we expect no individual peer pieces to be set")
+		}
+	} else {
+		bm.Xor(&cn._peerPieces)
+	}
 	cn.peerSentHaveAll = false
-	for i, have := range bf {
-		if have {
-			cn.raisePeerMinPieces(pieceIndex(i) + 1)
-			if !pp.Contains(bitmap.BitIndex(i)) {
-				cn.t.incPieceAvailability(i)
-			}
+	// bm is now 'on' for pieces that are changing
+	bm.Iterate(func(x uint32) bool {
+		pi := pieceIndex(x)
+		if cn._peerPieces.Contains(x) {
+			// Then we must be losing this piece
+			cn.t.decPieceAvailability(pi)
 		} else {
-			if pp.Contains(bitmap.BitIndex(i)) {
-				cn.t.decPieceAvailability(i)
+			if !shouldUpdateRequests && cn.t.wantPieceIndex(pieceIndex(x)) {
+				shouldUpdateRequests = true
 			}
+			// We must be gaining this piece
+			cn.t.incPieceAvailability(pieceIndex(x))
 		}
-		if have {
-			cn._peerPieces.Add(uint32(i))
-			if cn.t.wantPieceIndex(i) {
-				cn.updateRequests("bitfield")
-			}
-		} else {
-			cn._peerPieces.Remove(uint32(i))
-		}
+		return true
+	})
+	// Apply the changes. If we had everything previously, this should be empty, so xor is the same
+	// as or.
+	cn._peerPieces.Xor(&bm)
+	if shouldUpdateRequests {
+		cn.updateRequests("bitfield")
 	}
+	// We didn't guard this before, I see no reason to do it now.
 	cn.peerPiecesChanged()
 	return nil
 }
 
-func (cn *Peer) onPeerHasAllPieces() {
+func (cn *PeerConn) onPeerHasAllPieces() {
 	t := cn.t
 	if t.haveInfo() {
-		npp, pc := cn.newPeerPieces(), t.numPieces()
-		for i := 0; i < pc; i += 1 {
-			if !npp.Contains(bitmap.BitIndex(i)) {
-				t.incPieceAvailability(i)
-			}
-		}
+		cn._peerPieces.Iterate(func(x uint32) bool {
+			t.decPieceAvailability(pieceIndex(x))
+			return true
+		})
 	}
+	t.addConnWithAllPieces(&cn.Peer)
 	cn.peerSentHaveAll = true
 	cn._peerPieces.Clear()
 	if !cn.t._pendingPieces.IsEmpty() {
@@ -794,7 +455,9 @@ func (cn *PeerConn) onPeerSentHaveAll() error {
 }
 
 func (cn *PeerConn) peerSentHaveNone() error {
-	cn.t.decPeerPieceAvailability(&cn.Peer)
+	if !cn.peerSentHaveAll {
+		cn.t.decPeerPieceAvailability(&cn.Peer)
+	}
 	cn._peerPieces.Clear()
 	cn.peerSentHaveAll = false
 	cn.peerPiecesChanged()
@@ -835,59 +498,10 @@ func (cn *PeerConn) wroteMsg(msg *pp.Message) {
 	cn.allStats(func(cs *ConnStats) { cs.wroteMsg(msg) })
 }
 
-// After handshake, we know what Torrent and Client stats to include for a
-// connection.
-func (cn *Peer) postHandshakeStats(f func(*ConnStats)) {
-	t := cn.t
-	f(&t.stats)
-	f(&t.cl.stats)
-}
-
-// All ConnStats that include this connection. Some objects are not known
-// until the handshake is complete, after which it's expected to reconcile the
-// differences.
-func (cn *Peer) allStats(f func(*ConnStats)) {
-	f(&cn._stats)
-	if cn.reconciledHandshakeStats {
-		cn.postHandshakeStats(f)
-	}
-}
-
 func (cn *PeerConn) wroteBytes(n int64) {
 	cn.allStats(add(n, func(cs *ConnStats) *Count { return &cs.BytesWritten }))
 }
 
-func (cn *PeerConn) readBytes(n int64) {
-	cn.allStats(add(n, func(cs *ConnStats) *Count { return &cs.BytesRead }))
-}
-
-// Returns whether the connection could be useful to us. We're seeding and
-// they want data, we don't have metainfo and they can provide it, etc.
-func (c *Peer) useful() bool {
-	t := c.t
-	if c.closed.IsSet() {
-		return false
-	}
-	if !t.haveInfo() {
-		return c.supportsExtension("ut_metadata")
-	}
-	if t.seeding() && c.peerInterested {
-		return true
-	}
-	if c.peerHasWantedPieces() {
-		return true
-	}
-	return false
-}
-
-func (c *Peer) lastHelpful() (ret time.Time) {
-	ret = c.lastUsefulChunkReceived
-	if c.t.seeding() && c.lastChunkSent.After(ret) {
-		ret = c.lastChunkSent
-	}
-	return
-}
-
 func (c *PeerConn) fastEnabled() bool {
 	return c.PeerExtensionBytes.SupportsFast() && c.t.cl.config.Extensions.SupportsFast()
 }
@@ -897,13 +511,29 @@ func (c *PeerConn) reject(r Request) {
 		panic("fast not enabled")
 	}
 	c.write(r.ToMsg(pp.Reject))
-	delete(c.peerRequests, r)
+	// It is possible to reject a request before it is added to peer requests due to being invalid.
+	if state, ok := c.peerRequests[r]; ok {
+		state.allocReservation.Drop()
+		delete(c.peerRequests, r)
+	}
 }
 
-func (c *PeerConn) onReadRequest(r Request) error {
+func (c *PeerConn) maximumPeerRequestChunkLength() (_ Option[int]) {
+	uploadRateLimiter := c.t.cl.config.UploadRateLimiter
+	if uploadRateLimiter.Limit() == rate.Inf {
+		return
+	}
+	return Some(uploadRateLimiter.Burst())
+}
+
+// startFetch is for testing purposes currently.
+func (c *PeerConn) onReadRequest(r Request, startFetch bool) error {
 	requestedChunkLengths.Add(strconv.FormatUint(r.Length.Uint64(), 10), 1)
 	if _, ok := c.peerRequests[r]; ok {
 		torrent.Add("duplicate requests received", 1)
+		if c.fastEnabled() {
+			return errors.New("received duplicate request with fast enabled")
+		}
 		return nil
 	}
 	if c.choking {
@@ -923,30 +553,52 @@ func (c *PeerConn) onReadRequest(r Request) error {
 		// BEP 6 says we may close here if we choose.
 		return nil
 	}
+	if opt := c.maximumPeerRequestChunkLength(); opt.Ok && int(r.Length) > opt.Value {
+		err := fmt.Errorf("peer requested chunk too long (%v)", r.Length)
+		c.logger.Levelf(log.Warning, err.Error())
+		if c.fastEnabled() {
+			c.reject(r)
+			return nil
+		} else {
+			return err
+		}
+	}
 	if !c.t.havePiece(pieceIndex(r.Index)) {
-		// This isn't necessarily them screwing up. We can drop pieces
-		// from our storage, and can't communicate this to peers
-		// except by reconnecting.
+		// TODO: Tell the peer we don't have the piece, and reject this request.
 		requestsReceivedForMissingPieces.Add(1)
 		return fmt.Errorf("peer requested piece we don't have: %v", r.Index.Int())
 	}
+	pieceLength := c.t.pieceLength(pieceIndex(r.Index))
 	// Check this after we know we have the piece, so that the piece length will be known.
-	if r.Begin+r.Length > c.t.pieceLength(pieceIndex(r.Index)) {
+	if chunkOverflowsPiece(r.ChunkSpec, pieceLength) {
 		torrent.Add("bad requests received", 1)
-		return errors.New("bad Request")
+		return errors.New("chunk overflows piece")
 	}
 	if c.peerRequests == nil {
 		c.peerRequests = make(map[Request]*peerRequestState, localClientReqq)
 	}
-	value := &peerRequestState{}
+	value := &peerRequestState{
+		allocReservation: c.peerRequestDataAllocLimiter.Reserve(int64(r.Length)),
+	}
 	c.peerRequests[r] = value
-	go c.peerRequestDataReader(r, value)
-	//c.tickleWriter()
+	if startFetch {
+		// TODO: Limit peer request data read concurrency.
+		go c.peerRequestDataReader(r, value)
+	}
 	return nil
 }
 
 func (c *PeerConn) peerRequestDataReader(r Request, prs *peerRequestState) {
-	b, err := readPeerRequestData(r, c)
+	// Should we depend on Torrent closure here? I think it's okay to get cancelled from elsewhere,
+	// or fail to read and then cleanup. Also, we used to hang here if the reservation was never
+	// dropped, that was fixed.
+	ctx := context.Background()
+	err := prs.allocReservation.Wait(ctx)
+	if err != nil {
+		c.logger.WithDefaultLevel(log.Debug).Levelf(log.ErrorLevel(err), "waiting for alloc limit reservation: %v", err)
+		return
+	}
+	b, err := c.readPeerRequestData(r)
 	c.locker().Lock()
 	defer c.locker().Unlock()
 	if err != nil {
@@ -955,7 +607,9 @@ func (c *PeerConn) peerRequestDataReader(r Request, prs *peerRequestState) {
 		if b == nil {
 			panic("data must be non-nil to trigger send")
 		}
+		torrent.Add("peer request data read successes", 1)
 		prs.data = b
+		// This might be required for the error case too (#752 and #753).
 		c.tickleWriter()
 	}
 }
@@ -963,7 +617,17 @@ func (c *PeerConn) peerRequestDataReader(r Request, prs *peerRequestState) {
 // If this is maintained correctly, we might be able to support optional synchronous reading for
 // chunk sending, the way it used to work.
 func (c *PeerConn) peerRequestDataReadFailed(err error, r Request) {
-	c.logger.WithDefaultLevel(log.Warning).Printf("error reading chunk for peer Request %v: %v", r, err)
+	torrent.Add("peer request data read failures", 1)
+	logLevel := log.Warning
+	if c.t.hasStorageCap() {
+		// It's expected that pieces might drop. See
+		// https://github.com/anacrolix/torrent/issues/702#issuecomment-1000953313.
+		logLevel = log.Debug
+	}
+	c.logger.Levelf(logLevel, "error reading chunk for peer Request %v: %v", r, err)
+	if c.t.closed.IsSet() {
+		return
+	}
 	i := pieceIndex(r.Index)
 	if c.t.pieceComplete(i) {
 		// There used to be more code here that just duplicated the following break. Piece
@@ -972,17 +636,26 @@ func (c *PeerConn) peerRequestDataReadFailed(err error, r Request) {
 		// here.
 		c.t.updatePieceCompletion(i)
 	}
-	// If we failed to send a chunk, choke the peer to ensure they flush all their requests. We've
-	// probably dropped a piece from storage, but there's no way to communicate this to the peer. If
-	// they ask for it again, we'll kick them to allow us to send them an updated bitfield on the
-	// next connect. TODO: Support rejecting here too.
-	if c.choking {
-		c.logger.WithDefaultLevel(log.Warning).Printf("already choking peer, requests might not be rejected correctly")
+	// We've probably dropped a piece from storage, but there's no way to communicate this to the
+	// peer. If they ask for it again, we kick them allowing us to send them updated piece states if
+	// we reconnect. TODO: Instead, we could just try to update them with Bitfield or HaveNone and
+	// if they kick us for breaking protocol, on reconnect we will be compliant again (at least
+	// initially).
+	if c.fastEnabled() {
+		c.reject(r)
+	} else {
+		if c.choking {
+			// If fast isn't enabled, I think we would have wiped all peer requests when we last
+			// choked, and requests while we're choking would be ignored. It could be possible that
+			// a peer request data read completed concurrently to it being deleted elsewhere.
+			c.logger.WithDefaultLevel(log.Warning).Printf("already choking peer, requests might not be rejected correctly")
+		}
+		// Choking a non-fast peer should cause them to flush all their requests.
+		c.choke(c.write)
 	}
-	c.choke(c.write)
 }
 
-func readPeerRequestData(r Request, c *PeerConn) ([]byte, error) {
+func (c *PeerConn) readPeerRequestData(r Request) ([]byte, error) {
 	b := make([]byte, r.Length)
 	p := c.t.info.Piece(int(r.Index))
 	n, err := c.t.readAt(b, p.Offset()+int64(r.Begin))
@@ -998,18 +671,10 @@ func readPeerRequestData(r Request, c *PeerConn) ([]byte, error) {
 	return b, err
 }
 
-func runSafeExtraneous(f func()) {
-	if true {
-		go f()
-	} else {
-		f()
-	}
-}
-
 func (c *PeerConn) logProtocolBehaviour(level log.Level, format string, arg ...interface{}) {
-	c.logger.WithLevel(level).WithContextText(fmt.Sprintf(
-		"peer id %q, ext v %q", c.PeerID, c.PeerClientName,
-	)).Printf(format, arg...)
+	c.logger.WithContextText(fmt.Sprintf(
+		"peer id %q, ext v %q", c.PeerID, c.PeerClientName.Load(),
+	)).SkipCallers(1).Levelf(level, format, arg...)
 }
 
 // Processes incoming BitTorrent wire-protocol messages. The client lock is held upon entry and
@@ -1027,7 +692,7 @@ func (c *PeerConn) mainReadLoop() (err error) {
 
 	decoder := pp.Decoder{
 		R:         bufio.NewReaderSize(c.r, 1<<17),
-		MaxLength: 256 * 1024,
+		MaxLength: 4 * pp.Integer(max(int64(t.chunkSize), defaultChunkSize)),
 		Pool:      &t.chunkPool,
 	}
 	for {
@@ -1062,45 +727,45 @@ func (c *PeerConn) mainReadLoop() (err error) {
 				break
 			}
 			if !c.fastEnabled() {
-				c.deleteAllRequests()
+				c.deleteAllRequests("choked by non-fast PeerConn")
 			} else {
-				c.actualRequestState.Requests.Iterate(func(x uint32) bool {
-					if !c.peerAllowedFast.Contains(x / c.t.chunksPerRegularPiece()) {
-						c.t.pendingRequests.Dec(x)
-					}
-					return true
-				})
+				// We don't decrement pending requests here, let's wait for the peer to either
+				// reject or satisfy the outstanding requests. Additionally, some peers may unchoke
+				// us and resume where they left off, we don't want to have piled on to those chunks
+				// in the meanwhile. I think a peer's ability to abuse this should be limited: they
+				// could let us request a lot of stuff, then choke us and never reject, but they're
+				// only a single peer, our chunk balancing should smooth over this abuse.
 			}
 			c.peerChoking = true
-			// We can then reset our interest.
-			c.updateRequests("choked")
 			c.updateExpectingChunks()
 		case pp.Unchoke:
 			if !c.peerChoking {
 				// Some clients do this for some reason. Transmission doesn't error on this, so we
 				// won't for consistency.
-				c.logProtocolBehaviour(log.Info, "received unchoke when already unchoked")
+				c.logProtocolBehaviour(log.Debug, "received unchoke when already unchoked")
 				break
 			}
 			c.peerChoking = false
 			preservedCount := 0
-			c.actualRequestState.Requests.Iterate(func(x uint32) bool {
-				if !c.peerAllowedFast.Contains(x / c.t.chunksPerRegularPiece()) {
+			c.requestState.Requests.Iterate(func(x RequestIndex) bool {
+				if !c.peerAllowedFast.Contains(c.t.pieceIndexOfRequestIndex(x)) {
 					preservedCount++
-					c.t.pendingRequests.Inc(x)
 				}
 				return true
 			})
 			if preservedCount != 0 {
 				// TODO: Yes this is a debug log but I'm not happy with the state of the logging lib
 				// right now.
-				log.Printf(
+				c.logger.Levelf(log.Debug,
 					"%v requests were preserved while being choked (fast=%v)",
 					preservedCount,
 					c.fastEnabled())
+
 				torrent.Add("requestsPreservedThroughChoking", int64(preservedCount))
 			}
-			c.updateRequests("unchoked")
+			if !c.t._pendingPieces.IsEmpty() {
+				c.updateRequests("unchoked")
+			}
 			c.updateExpectingChunks()
 		case pp.Interested:
 			c.peerInterested = true
@@ -1116,7 +781,10 @@ func (c *PeerConn) mainReadLoop() (err error) {
 			err = c.peerSentBitfield(msg.Bitfield)
 		case pp.Request:
 			r := newRequestFromMessage(&msg)
-			err = c.onReadRequest(r)
+			err = c.onReadRequest(r, true)
+			if err != nil {
+				err = fmt.Errorf("on reading request %v: %w", r, err)
+			}
 		case pp.Piece:
 			c.doChunkReadStats(int64(len(msg.Piece)))
 			err = c.receiveChunk(&msg)
@@ -1146,35 +814,21 @@ func (c *PeerConn) mainReadLoop() (err error) {
 			})
 		case pp.Suggest:
 			torrent.Add("suggests received", 1)
-			log.Fmsg("peer suggested piece %d", msg.Index).AddValues(c, msg.Index).SetLevel(log.Debug).Log(c.t.logger)
+			log.Fmsg("peer suggested piece %d", msg.Index).AddValues(c, msg.Index).LogLevel(log.Debug, c.t.logger)
 			c.updateRequests("suggested")
 		case pp.HaveAll:
 			err = c.onPeerSentHaveAll()
 		case pp.HaveNone:
 			err = c.peerSentHaveNone()
 		case pp.Reject:
-			c.remoteRejectedRequest(c.t.requestIndexFromRequest(newRequestFromMessage(&msg)))
+			req := newRequestFromMessage(&msg)
+			if !c.remoteRejectedRequest(c.t.requestIndexFromRequest(req)) {
+				err = fmt.Errorf("received invalid reject for request %v", req)
+				c.logger.Levelf(log.Debug, "%v", err)
+			}
 		case pp.AllowedFast:
 			torrent.Add("allowed fasts received", 1)
-			log.Fmsg("peer allowed fast: %d", msg.Index).AddValues(c).SetLevel(log.Debug).Log(c.t.logger)
-			pieceIndex := msg.Index.Int()
-			// If we have outstanding requests that aren't currently counted toward the combined
-			// outstanding request count, increment them.
-			if c.peerAllowedFast.CheckedAdd(msg.Index.Uint32()) && c.peerChoking &&
-				// The check here could be against having the info, but really what we need to know
-				// is if there are any existing requests.
-				!c.actualRequestState.Requests.IsEmpty() {
-
-				i := c.actualRequestState.Requests.Iterator()
-				i.AdvanceIfNeeded(t.pieceRequestIndexOffset(pieceIndex))
-				for i.HasNext() {
-					r := i.Next()
-					if r >= t.pieceRequestIndexOffset(pieceIndex+1) {
-						break
-					}
-					c.t.pendingRequests.Inc(r)
-				}
-			}
+			log.Fmsg("peer allowed fast: %d", msg.Index).AddValues(c).LogLevel(log.Debug, c.t.logger)
 			c.updateRequests("PeerConn.mainReadLoop allowed fast")
 		case pp.Extended:
 			err = c.onReadExtendedMsg(msg.ExtendedID, msg.ExtendedPayload)
@@ -1187,26 +841,6 @@ func (c *PeerConn) mainReadLoop() (err error) {
 	}
 }
 
-func (c *Peer) remoteRejectedRequest(r RequestIndex) {
-	if c.deleteRequest(r) {
-		if c.actualRequestState.Requests.IsEmpty() {
-			c.updateRequests("Peer.remoteRejectedRequest")
-		}
-		c.decExpectedChunkReceive(r)
-	}
-}
-
-func (c *Peer) decExpectedChunkReceive(r RequestIndex) {
-	count := c.validReceiveChunks[r]
-	if count == 1 {
-		delete(c.validReceiveChunks, r)
-	} else if count > 1 {
-		c.validReceiveChunks[r] = count - 1
-	} else {
-		panic(r)
-	}
-}
-
 func (c *PeerConn) onReadExtendedMsg(id pp.ExtensionNumber, payload []byte) (err error) {
 	defer func() {
 		// TODO: Should we still do this?
@@ -1230,11 +864,11 @@ func (c *PeerConn) onReadExtendedMsg(id pp.ExtensionNumber, payload []byte) (err
 		if cb := c.callbacks.ReadExtendedHandshake; cb != nil {
 			cb(c, &d)
 		}
-		//c.logger.WithDefaultLevel(log.Debug).Printf("received extended handshake message:\n%s", spew.Sdump(d))
+		// c.logger.WithDefaultLevel(log.Debug).Printf("received extended handshake message:\n%s", spew.Sdump(d))
 		if d.Reqq != 0 {
 			c.PeerMaxRequests = d.Reqq
 		}
-		c.PeerClientName = d.V
+		c.PeerClientName.Store(d.V)
 		if c.PeerExtensionIDs == nil {
 			c.PeerExtensionIDs = make(map[pp.ExtensionName]pp.ExtensionNumber, len(d.M))
 		}
@@ -1242,7 +876,11 @@ func (c *PeerConn) onReadExtendedMsg(id pp.ExtensionNumber, payload []byte) (err
 		c.PeerPrefersEncryption = d.Encryption
 		for name, id := range d.M {
 			if _, ok := c.PeerExtensionIDs[name]; !ok {
-				peersSupportingExtension.Add(string(name), 1)
+				peersSupportingExtension.Add(
+					// expvar.Var.String must produce valid JSON. "ut_payme\xeet_address" was being
+					// entered here which caused problems later when unmarshalling.
+					strconv.Quote(string(name)),
+					1)
 			}
 			c.PeerExtensionIDs[name] = id
 		}
@@ -1254,6 +892,7 @@ func (c *PeerConn) onReadExtendedMsg(id pp.ExtensionNumber, payload []byte) (err
 		c.requestPendingMetadata()
 		if !t.cl.config.DisablePEX {
 			t.pex.Add(c) // we learnt enough now
+			// This checks the extension is supported internally.
 			c.pex.Init(c)
 		}
 		return nil
@@ -1267,7 +906,20 @@ func (c *PeerConn) onReadExtendedMsg(id pp.ExtensionNumber, payload []byte) (err
 		if !c.pex.IsEnabled() {
 			return nil // or hang-up maybe?
 		}
-		return c.pex.Recv(payload)
+		err = c.pex.Recv(payload)
+		if err != nil {
+			err = fmt.Errorf("receiving pex message: %w", err)
+		}
+		return
+	case utHolepunchExtendedId:
+		var msg utHolepunch.Msg
+		err = msg.UnmarshalBinary(payload)
+		if err != nil {
+			err = fmt.Errorf("unmarshalling ut_holepunch message: %w", err)
+			return
+		}
+		err = c.t.handleReceivedUtHolepunchMsg(msg, c)
+		return
 	default:
 		return fmt.Errorf("unexpected extended message ID: %v", id)
 	}
@@ -1287,149 +939,6 @@ func (cn *PeerConn) rw() io.ReadWriter {
 	}{cn.r, cn.w}
 }
 
-func (c *Peer) doChunkReadStats(size int64) {
-	c.allStats(func(cs *ConnStats) { cs.receivedChunk(size) })
-}
-
-// Handle a received chunk from a peer.
-func (c *Peer) receiveChunk(msg *pp.Message) error {
-	chunksReceived.Add("total", 1)
-
-	ppReq := newRequestFromMessage(msg)
-	req := c.t.requestIndexFromRequest(ppReq)
-
-	if c.peerChoking {
-		chunksReceived.Add("while choked", 1)
-	}
-
-	if c.validReceiveChunks[req] <= 0 {
-		chunksReceived.Add("unexpected", 1)
-		return errors.New("received unexpected chunk")
-	}
-	c.decExpectedChunkReceive(req)
-
-	if c.peerChoking && c.peerAllowedFast.Contains(bitmap.BitIndex(ppReq.Index)) {
-		chunksReceived.Add("due to allowed fast", 1)
-	}
-
-	// The request needs to be deleted immediately to prevent cancels occurring asynchronously when
-	// have actually already received the piece, while we have the Client unlocked to write the data
-	// out.
-	deletedRequest := false
-	{
-		if c.actualRequestState.Requests.Contains(req) {
-			for _, f := range c.callbacks.ReceivedRequested {
-				f(PeerMessageEvent{c, msg})
-			}
-		}
-		// Request has been satisfied.
-		if c.deleteRequest(req) {
-			deletedRequest = true
-			if !c.peerChoking {
-				c._chunksReceivedWhileExpecting++
-			}
-			if c.actualRequestState.Requests.IsEmpty() {
-				c.updateRequests("Peer.receiveChunk deleted request")
-			}
-		} else {
-			chunksReceived.Add("unwanted", 1)
-		}
-	}
-
-	t := c.t
-	cl := t.cl
-
-	// Do we actually want this chunk?
-	if t.haveChunk(ppReq) {
-		chunksReceived.Add("wasted", 1)
-		c.allStats(add(1, func(cs *ConnStats) *Count { return &cs.ChunksReadWasted }))
-		return nil
-	}
-
-	piece := &t.pieces[ppReq.Index]
-
-	c.allStats(add(1, func(cs *ConnStats) *Count { return &cs.ChunksReadUseful }))
-	c.allStats(add(int64(len(msg.Piece)), func(cs *ConnStats) *Count { return &cs.BytesReadUsefulData }))
-	if deletedRequest {
-		c.piecesReceivedSinceLastRequestUpdate++
-		c.allStats(add(int64(len(msg.Piece)), func(cs *ConnStats) *Count { return &cs.BytesReadUsefulIntendedData }))
-	}
-	for _, f := range c.t.cl.config.Callbacks.ReceivedUsefulData {
-		f(ReceivedUsefulDataEvent{c, msg})
-	}
-	c.lastUsefulChunkReceived = time.Now()
-
-	// Need to record that it hasn't been written yet, before we attempt to do
-	// anything with it.
-	piece.incrementPendingWrites()
-	// Record that we have the chunk, so we aren't trying to download it while
-	// waiting for it to be written to storage.
-	piece.unpendChunkIndex(chunkIndexFromChunkSpec(ppReq.ChunkSpec, t.chunkSize))
-
-	// Cancel pending requests for this chunk from *other* peers.
-	t.iterPeers(func(p *Peer) {
-		if p == c {
-			return
-		}
-		p.cancel(req)
-	})
-
-	err := func() error {
-		cl.unlock()
-		defer cl.lock()
-		concurrentChunkWrites.Add(1)
-		defer concurrentChunkWrites.Add(-1)
-		// Write the chunk out. Note that the upper bound on chunk writing concurrency will be the
-		// number of connections. We write inline with receiving the chunk (with this lock dance),
-		// because we want to handle errors synchronously and I haven't thought of a nice way to
-		// defer any concurrency to the storage and have that notify the client of errors. TODO: Do
-		// that instead.
-		return t.writeChunk(int(msg.Index), int64(msg.Begin), msg.Piece)
-	}()
-
-	piece.decrementPendingWrites()
-
-	if err != nil {
-		c.logger.WithDefaultLevel(log.Error).Printf("writing received chunk %v: %v", req, err)
-		t.pendRequest(req)
-		// Necessary to pass TestReceiveChunkStorageFailureSeederFastExtensionDisabled. I think a
-		// request update runs while we're writing the chunk that just failed. Then we never do a
-		// fresh update after pending the failed request.
-		c.updateRequests("Peer.receiveChunk error writing chunk")
-		t.onWriteChunkErr(err)
-		return nil
-	}
-
-	c.onDirtiedPiece(pieceIndex(ppReq.Index))
-
-	// We need to ensure the piece is only queued once, so only the last chunk writer gets this job.
-	if t.pieceAllDirty(pieceIndex(ppReq.Index)) && piece.pendingWrites == 0 {
-		t.queuePieceCheck(pieceIndex(ppReq.Index))
-		// We don't pend all chunks here anymore because we don't want code dependent on the dirty
-		// chunk status (such as the haveChunk call above) to have to check all the various other
-		// piece states like queued for hash, hashing etc. This does mean that we need to be sure
-		// that chunk pieces are pended at an appropriate time later however.
-	}
-
-	cl.event.Broadcast()
-	// We do this because we've written a chunk, and may change PieceState.Partial.
-	t.publishPieceChange(pieceIndex(ppReq.Index))
-
-	return nil
-}
-
-func (c *Peer) onDirtiedPiece(piece pieceIndex) {
-	if c.peerTouchedPieces == nil {
-		c.peerTouchedPieces = make(map[pieceIndex]struct{})
-	}
-	c.peerTouchedPieces[piece] = struct{}{}
-	ds := &c.t.pieces[piece].dirtiers
-	if *ds == nil {
-		*ds = make(map[*Peer]struct{})
-	}
-	(*ds)[c] = struct{}{}
-}
-
 func (c *PeerConn) uploadAllowed() bool {
 	if c.t.cl.config.NoUpload {
 		return false
@@ -1499,46 +1008,8 @@ func (cn *PeerConn) drop() {
 	cn.t.dropConnection(cn)
 }
 
-func (cn *Peer) netGoodPiecesDirtied() int64 {
-	return cn._stats.PiecesDirtiedGood.Int64() - cn._stats.PiecesDirtiedBad.Int64()
-}
-
-func (c *Peer) peerHasWantedPieces() bool {
-	if c.peerSentHaveAll {
-		return !c.t.haveAllPieces()
-	}
-	if !c.t.haveInfo() {
-		return !c._peerPieces.IsEmpty()
-	}
-	return c._peerPieces.Intersects(&c.t._pendingPieces)
-}
-
-func (c *Peer) deleteRequest(r RequestIndex) bool {
-	if !c.actualRequestState.Requests.CheckedRemove(r) {
-		return false
-	}
-	c.cancelledRequests.Remove(r)
-	for _, f := range c.callbacks.DeletedRequest {
-		f(PeerRequestEvent{c, c.t.requestIndexToRequest(r)})
-	}
-	c.updateExpectingChunks()
-	if !c.peerChoking || c.peerAllowedFast.Contains(r/c.t.chunksPerRegularPiece()) {
-		c.t.pendingRequests.Dec(r)
-	}
-	return true
-}
-
-func (c *Peer) deleteAllRequests() {
-	c.actualRequestState.Requests.Clone().Iterate(func(x uint32) bool {
-		c.deleteRequest(x)
-		return true
-	})
-	if !c.actualRequestState.Requests.IsEmpty() {
-		panic(c.actualRequestState.Requests.GetCardinality())
-	}
-	// for c := range c.t.conns {
-	// 	c.tickleWriter()
-	// }
+func (cn *PeerConn) ban() {
+	cn.t.cl.banPeerIP(cn.remoteIp())
 }
 
 // This is called when something has changed that should wake the writer, such as putting stuff into
@@ -1549,6 +1020,7 @@ func (c *PeerConn) tickleWriter() {
 
 func (c *PeerConn) sendChunk(r Request, msg func(pp.Message) bool, state *peerRequestState) (more bool) {
 	c.lastChunkSent = time.Now()
+	state.allocReservation.Release()
 	return msg(pp.Message{
 		Type:  pp.Piece,
 		Index: r.Index,
@@ -1566,20 +1038,6 @@ func (c *PeerConn) setTorrent(t *Torrent) {
 	t.reconcileHandshakeStats(c)
 }
 
-func (c *Peer) peerPriority() (peerPriority, error) {
-	return bep40Priority(c.remoteIpPort(), c.t.cl.publicAddr(c.remoteIp()))
-}
-
-func (c *Peer) remoteIp() net.IP {
-	host, _, _ := net.SplitHostPort(c.RemoteAddr.String())
-	return net.ParseIP(host)
-}
-
-func (c *Peer) remoteIpPort() IpPort {
-	ipa, _ := tryIpPortFromNetAddr(c.RemoteAddr)
-	return IpPort{ipa.IP, uint16(ipa.Port)}
-}
-
 func (c *PeerConn) pexPeerFlags() pp.PexPeerFlags {
 	f := pp.PexPeerFlags(0)
 	if c.PeerPrefersEncryption {
@@ -1597,42 +1055,35 @@ func (c *PeerConn) pexPeerFlags() pp.PexPeerFlags {
 // This returns the address to use if we want to dial the peer again. It incorporates the peer's
 // advertised listen port.
 func (c *PeerConn) dialAddr() PeerRemoteAddr {
-	if !c.outgoing && c.PeerListenPort != 0 {
-		switch addr := c.RemoteAddr.(type) {
-		case *net.TCPAddr:
-			dialAddr := *addr
-			dialAddr.Port = c.PeerListenPort
-			return &dialAddr
-		case *net.UDPAddr:
-			dialAddr := *addr
-			dialAddr.Port = c.PeerListenPort
-			return &dialAddr
-		}
+	if c.outgoing || c.PeerListenPort == 0 {
+		return c.RemoteAddr
 	}
-	return c.RemoteAddr
+	addrPort, err := addrPortFromPeerRemoteAddr(c.RemoteAddr)
+	if err != nil {
+		c.logger.Levelf(
+			log.Warning,
+			"error parsing %q for alternate dial port: %v",
+			c.RemoteAddr,
+			err,
+		)
+		return c.RemoteAddr
+	}
+	return netip.AddrPortFrom(addrPort.Addr(), uint16(c.PeerListenPort))
 }
 
-func (c *PeerConn) pexEvent(t pexEventType) pexEvent {
+func (c *PeerConn) pexEvent(t pexEventType) (_ pexEvent, err error) {
 	f := c.pexPeerFlags()
-	addr := c.dialAddr()
-	return pexEvent{t, addr, f}
+	dialAddr := c.dialAddr()
+	addr, err := addrPortFromPeerRemoteAddr(dialAddr)
+	if err != nil || !addr.IsValid() {
+		err = fmt.Errorf("parsing dial addr %q: %w", dialAddr, err)
+		return
+	}
+	return pexEvent{t, addr, f, nil}, nil
 }
 
 func (c *PeerConn) String() string {
-	return fmt.Sprintf("connection %p", c)
-}
-
-func (c *Peer) trust() connectionTrust {
-	return connectionTrust{c.trusted, c.netGoodPiecesDirtied()}
-}
-
-type connectionTrust struct {
-	Implicit            bool
-	NetGoodPiecesDirted int64
-}
-
-func (l connectionTrust) Less(r connectionTrust) bool {
-	return multiless.New().Bool(l.Implicit, r.Implicit).Int64(l.NetGoodPiecesDirted, r.NetGoodPiecesDirted).Less()
+	return fmt.Sprintf("%T %p [id=%+q, exts=%v, v=%q]", c, c, c.PeerID, c.PeerExtensionBytes, c.PeerClientName.Load())
 }
 
 // Returns the pieces the peer could have based on their claims. If we don't know how many pieces
@@ -1643,29 +1094,38 @@ func (cn *PeerConn) PeerPieces() *roaring.Bitmap {
 	return cn.newPeerPieces()
 }
 
-// Returns a new Bitmap that includes bits for all pieces the peer could have based on their claims.
-func (cn *Peer) newPeerPieces() *roaring.Bitmap {
-	// TODO: Can we use copy on write?
-	ret := cn._peerPieces.Clone()
-	if cn.peerSentHaveAll {
-		if cn.t.haveInfo() {
-			ret.AddRange(0, bitmap.BitRange(cn.t.numPieces()))
-		} else {
-			ret.AddRange(0, bitmap.ToEnd)
-		}
-	}
-	return ret
+func (pc *PeerConn) remoteIsTransmission() bool {
+	return bytes.HasPrefix(pc.PeerID[:], []byte("-TR")) && pc.PeerID[7] == '-'
 }
 
-func (cn *Peer) stats() *ConnStats {
-	return &cn._stats
+func (pc *PeerConn) remoteDialAddrPort() (netip.AddrPort, error) {
+	dialAddr := pc.dialAddr()
+	return addrPortFromPeerRemoteAddr(dialAddr)
 }
 
-func (p *Peer) TryAsPeerConn() (*PeerConn, bool) {
-	pc, ok := p.peerImpl.(*PeerConn)
-	return pc, ok
+func (pc *PeerConn) bitExtensionEnabled(bit pp.ExtensionBit) bool {
+	return pc.t.cl.config.Extensions.GetBit(bit) && pc.PeerExtensionBytes.GetBit(bit)
+}
+
+func (cn *PeerConn) peerPiecesChanged() {
+	cn.t.maybeDropMutuallyCompletePeer(cn)
 }
 
-func (p *PeerConn) onNextRequestStateChanged() {
-	p.tickleWriter()
+// Returns whether the connection could be useful to us. We're seeding and
+// they want data, we don't have metainfo and they can provide it, etc.
+func (c *PeerConn) useful() bool {
+	t := c.t
+	if c.closed.IsSet() {
+		return false
+	}
+	if !t.haveInfo() {
+		return c.supportsExtension("ut_metadata")
+	}
+	if t.seeding() && c.peerInterested {
+		return true
+	}
+	if c.peerHasWantedPieces() {
+		return true
+	}
+	return false
 }