connection.go

   1 package torrent
   2
   3 import (
   4         "bufio"
   5         "bytes"
   6         "fmt"
   7         "io"
   8         "math"
   9         "math/rand"
  10         "net"
  11         "strconv"
  12         "strings"
  13         "sync"
  14         "time"
  15
  16         "github.com/anacrolix/dht/v2"
  17         "github.com/anacrolix/log"
  18         "github.com/anacrolix/missinggo"
  19         "github.com/anacrolix/missinggo/iter"
  20         "github.com/anacrolix/missinggo/v2/bitmap"
  21         "github.com/anacrolix/missinggo/v2/prioritybitmap"
  22         "github.com/anacrolix/multiless"
  23         "github.com/pkg/errors"
  24
  25         "github.com/anacrolix/torrent/bencode"
  26         "github.com/anacrolix/torrent/mse"
  27         pp "github.com/anacrolix/torrent/peer_protocol"
  28 )
  29
  30 type peerSource string
  31
  32 const (
  33         peerSourceTracker         = "Tr"
  34         peerSourceIncoming        = "I"
  35         peerSourceDhtGetPeers     = "Hg" // Peers we found by searching a DHT.
  36         peerSourceDhtAnnouncePeer = "Ha" // Peers that were announced to us by a DHT.
  37         peerSourcePex             = "X"
  38 )
  39
  40 // Maintains the state of a connection with a peer.
  41 type connection struct {
  42         // First to ensure 64-bit alignment for atomics. See #262.
  43         _stats ConnStats
  44
  45         t *Torrent
  46         // The actual Conn, used for closing, and setting socket options.
  47         conn       net.Conn
  48         outgoing   bool
  49         network    string
  50         remoteAddr IpPort
  51         // The Reader and Writer for this Conn, with hooks installed for stats,
  52         // limiting, deadlines etc.
  53         w io.Writer
  54         r io.Reader
  55         // True if the connection is operating over MSE obfuscation.
  56         headerEncrypted bool
  57         cryptoMethod    mse.CryptoMethod
  58         Discovery       peerSource
  59         trusted         bool
  60         closed          missinggo.Event
  61         // Set true after we've added our ConnStats generated during handshake to
  62         // other ConnStat instances as determined when the *Torrent became known.
  63         reconciledHandshakeStats bool
  64
  65         lastMessageReceived     time.Time
  66         completedHandshake      time.Time
  67         lastUsefulChunkReceived time.Time
  68         lastChunkSent           time.Time
  69
  70         // Stuff controlled by the local peer.
  71         Interested           bool
  72         lastBecameInterested time.Time
  73         priorInterest        time.Duration
  74
  75         lastStartedExpectingToReceiveChunks time.Time
  76         cumulativeExpectedToReceiveChunks   time.Duration
  77         _chunksReceivedWhileExpecting       int64
  78
  79         Choked           bool
  80         requests         map[request]struct{}
  81         requestsLowWater int
  82         // Chunks that we might reasonably expect to receive from the peer. Due to
  83         // latency, buffering, and implementation differences, we may receive
  84         // chunks that are no longer in the set of requests actually want.
  85         validReceiveChunks map[request]struct{}
  86         // Indexed by metadata piece, set to true if posted and pending a
  87         // response.
  88         metadataRequests []bool
  89         sentHaves        bitmap.Bitmap
  90
  91         // Stuff controlled by the remote peer.
  92         PeerID             PeerID
  93         PeerInterested     bool
  94         PeerChoked         bool
  95         PeerRequests       map[request]struct{}
  96         PeerExtensionBytes pp.PeerExtensionBits
  97         // The pieces the peer has claimed to have.
  98         _peerPieces bitmap.Bitmap
  99         // The peer has everything. This can occur due to a special message, when
 100         // we may not even know the number of pieces in the torrent yet.
 101         peerSentHaveAll bool
 102         // The highest possible number of pieces the torrent could have based on
 103         // communication with the peer. Generally only useful until we have the
 104         // torrent info.
 105         peerMinPieces pieceIndex
 106         // Pieces we've accepted chunks for from the peer.
 107         peerTouchedPieces map[pieceIndex]struct{}
 108         peerAllowedFast   bitmap.Bitmap
 109
 110         PeerMaxRequests  int // Maximum pending requests the peer allows.
 111         PeerExtensionIDs map[pp.ExtensionName]pp.ExtensionNumber
 112         PeerClientName   string
 113
 114         pieceInclination   []int
 115         _pieceRequestOrder prioritybitmap.PriorityBitmap
 116
 117         writeBuffer *bytes.Buffer
 118         uploadTimer *time.Timer
 119         writerCond  sync.Cond
 120
 121         logger log.Logger
 122 }
 123
 124 func (cn *connection) updateExpectingChunks() {
 125         if cn.expectingChunks() {
 126                 if cn.lastStartedExpectingToReceiveChunks.IsZero() {
 127                         cn.lastStartedExpectingToReceiveChunks = time.Now()
 128                 }
 129         } else {
 130                 if !cn.lastStartedExpectingToReceiveChunks.IsZero() {
 131                         cn.cumulativeExpectedToReceiveChunks += time.Since(cn.lastStartedExpectingToReceiveChunks)
 132                         cn.lastStartedExpectingToReceiveChunks = time.Time{}
 133                 }
 134         }
 135 }
 136
 137 func (cn *connection) expectingChunks() bool {
 138         return cn.Interested && !cn.PeerChoked
 139 }
 140
 141 // Returns true if the connection is over IPv6.
 142 func (cn *connection) ipv6() bool {
 143         ip := cn.remoteAddr.IP
 144         if ip.To4() != nil {
 145                 return false
 146         }
 147         return len(ip) == net.IPv6len
 148 }
 149
 150 // Returns true the dialer has the lower client peer ID. TODO: Find the
 151 // specification for this.
 152 func (cn *connection) isPreferredDirection() bool {
 153         return bytes.Compare(cn.t.cl.peerID[:], cn.PeerID[:]) < 0 == cn.outgoing
 154 }
 155
 156 // Returns whether the left connection should be preferred over the right one,
 157 // considering only their networking properties. If ok is false, we can't
 158 // decide.
 159 func (l *connection) hasPreferredNetworkOver(r *connection) (left, ok bool) {
 160         var ml multiLess
 161         ml.NextBool(l.isPreferredDirection(), r.isPreferredDirection())
 162         ml.NextBool(!l.utp(), !r.utp())
 163         ml.NextBool(l.ipv6(), r.ipv6())
 164         return ml.FinalOk()
 165 }
 166
 167 func (cn *connection) cumInterest() time.Duration {
 168         ret := cn.priorInterest
 169         if cn.Interested {
 170                 ret += time.Since(cn.lastBecameInterested)
 171         }
 172         return ret
 173 }
 174
 175 func (cn *connection) peerHasAllPieces() (all bool, known bool) {
 176         if cn.peerSentHaveAll {
 177                 return true, true
 178         }
 179         if !cn.t.haveInfo() {
 180                 return false, false
 181         }
 182         return bitmap.Flip(cn._peerPieces, 0, bitmap.BitIndex(cn.t.numPieces())).IsEmpty(), true
 183 }
 184
 185 func (cn *connection) mu() sync.Locker {
 186         return cn.t.cl.locker()
 187 }
 188
 189 func (cn *connection) localAddr() net.Addr {
 190         return cn.conn.LocalAddr()
 191 }
 192
 193 func (cn *connection) supportsExtension(ext pp.ExtensionName) bool {
 194         _, ok := cn.PeerExtensionIDs[ext]
 195         return ok
 196 }
 197
 198 // The best guess at number of pieces in the torrent for this peer.
 199 func (cn *connection) bestPeerNumPieces() pieceIndex {
 200         if cn.t.haveInfo() {
 201                 return cn.t.numPieces()
 202         }
 203         return cn.peerMinPieces
 204 }
 205
 206 func (cn *connection) completedString() string {
 207         have := pieceIndex(cn._peerPieces.Len())
 208         if cn.peerSentHaveAll {
 209                 have = cn.bestPeerNumPieces()
 210         }
 211         return fmt.Sprintf("%d/%d", have, cn.bestPeerNumPieces())
 212 }
 213
 214 // Correct the PeerPieces slice length. Return false if the existing slice is
 215 // invalid, such as by receiving badly sized BITFIELD, or invalid HAVE
 216 // messages.
 217 func (cn *connection) setNumPieces(num pieceIndex) error {
 218         cn._peerPieces.RemoveRange(bitmap.BitIndex(num), bitmap.ToEnd)
 219         cn.peerPiecesChanged()
 220         return nil
 221 }
 222
 223 func eventAgeString(t time.Time) string {
 224         if t.IsZero() {
 225                 return "never"
 226         }
 227         return fmt.Sprintf("%.2fs ago", time.Since(t).Seconds())
 228 }
 229
 230 func (cn *connection) connectionFlags() (ret string) {
 231         c := func(b byte) {
 232                 ret += string([]byte{b})
 233         }
 234         if cn.cryptoMethod == mse.CryptoMethodRC4 {
 235                 c('E')
 236         } else if cn.headerEncrypted {
 237                 c('e')
 238         }
 239         ret += string(cn.Discovery)
 240         if cn.utp() {
 241                 c('U')
 242         }
 243         return
 244 }
 245
 246 func (cn *connection) utp() bool {
 247         return parseNetworkString(cn.network).Udp
 248 }
 249
 250 // Inspired by https://github.com/transmission/transmission/wiki/Peer-Status-Text.
 251 func (cn *connection) statusFlags() (ret string) {
 252         c := func(b byte) {
 253                 ret += string([]byte{b})
 254         }
 255         if cn.Interested {
 256                 c('i')
 257         }
 258         if cn.Choked {
 259                 c('c')
 260         }
 261         c('-')
 262         ret += cn.connectionFlags()
 263         c('-')
 264         if cn.PeerInterested {
 265                 c('i')
 266         }
 267         if cn.PeerChoked {
 268                 c('c')
 269         }
 270         return
 271 }
 272
 273 // func (cn *connection) String() string {
 274 //      var buf bytes.Buffer
 275 //      cn.WriteStatus(&buf, nil)
 276 //      return buf.String()
 277 // }
 278
 279 func (cn *connection) downloadRate() float64 {
 280         return float64(cn._stats.BytesReadUsefulData.Int64()) / cn.cumInterest().Seconds()
 281 }
 282
 283 func (cn *connection) WriteStatus(w io.Writer, t *Torrent) {
 284         // \t isn't preserved in <pre> blocks?
 285         fmt.Fprintf(w, "%+-55q %s %s-%s\n", cn.PeerID, cn.PeerExtensionBytes, cn.localAddr(), cn.remoteAddr)
 286         fmt.Fprintf(w, "    last msg: %s, connected: %s, last helpful: %s, itime: %s, etime: %s\n",
 287                 eventAgeString(cn.lastMessageReceived),
 288                 eventAgeString(cn.completedHandshake),
 289                 eventAgeString(cn.lastHelpful()),
 290                 cn.cumInterest(),
 291                 cn.totalExpectingTime(),
 292         )
 293         fmt.Fprintf(w,
 294                 "    %s completed, %d pieces touched, good chunks: %v/%v-%v reqq: (%d,%d,%d]-%d, flags: %s, dr: %.1f KiB/s\n",
 295                 cn.completedString(),
 296                 len(cn.peerTouchedPieces),
 297                 &cn._stats.ChunksReadUseful,
 298                 &cn._stats.ChunksRead,
 299                 &cn._stats.ChunksWritten,
 300                 cn.requestsLowWater,
 301                 cn.numLocalRequests(),
 302                 cn.nominalMaxRequests(),
 303                 len(cn.PeerRequests),
 304                 cn.statusFlags(),
 305                 cn.downloadRate()/(1<<10),
 306         )
 307         fmt.Fprintf(w, "    next pieces: %v%s\n",
 308                 iter.ToSlice(iter.Head(10, cn.iterPendingPiecesUntyped)),
 309                 func() string {
 310                         if cn == t.fastestConn {
 311                                 return " (fastest)"
 312                         } else {
 313                                 return ""
 314                         }
 315                 }(),
 316         )
 317 }
 318
 319 func (cn *connection) Close() {
 320         if !cn.closed.Set() {
 321                 return
 322         }
 323         cn.tickleWriter()
 324         cn.discardPieceInclination()
 325         cn._pieceRequestOrder.Clear()
 326         if cn.conn != nil {
 327                 go cn.conn.Close()
 328         }
 329 }
 330
 331 func (cn *connection) PeerHasPiece(piece pieceIndex) bool {
 332         return cn.peerSentHaveAll || cn._peerPieces.Contains(bitmap.BitIndex(piece))
 333 }
 334
 335 // Writes a message into the write buffer.
 336 func (cn *connection) Post(msg pp.Message) {
 337         torrent.Add(fmt.Sprintf("messages posted of type %s", msg.Type.String()), 1)
 338         // We don't need to track bytes here because a connection.w Writer wrapper
 339         // takes care of that (although there's some delay between us recording
 340         // the message, and the connection writer flushing it out.).
 341         cn.writeBuffer.Write(msg.MustMarshalBinary())
 342         // Last I checked only Piece messages affect stats, and we don't post
 343         // those.
 344         cn.wroteMsg(&msg)
 345         cn.tickleWriter()
 346 }
 347
 348 func (cn *connection) requestMetadataPiece(index int) {
 349         eID := cn.PeerExtensionIDs[pp.ExtensionNameMetadata]
 350         if eID == 0 {
 351                 return
 352         }
 353         if index < len(cn.metadataRequests) && cn.metadataRequests[index] {
 354                 return
 355         }
 356         cn.logger.Printf("requesting metadata piece %d", index)
 357         cn.Post(pp.Message{
 358                 Type:       pp.Extended,
 359                 ExtendedID: eID,
 360                 ExtendedPayload: func() []byte {
 361                         b, err := bencode.Marshal(map[string]int{
 362                                 "msg_type": pp.RequestMetadataExtensionMsgType,
 363                                 "piece":    index,
 364                         })
 365                         if err != nil {
 366                                 panic(err)
 367                         }
 368                         return b
 369                 }(),
 370         })
 371         for index >= len(cn.metadataRequests) {
 372                 cn.metadataRequests = append(cn.metadataRequests, false)
 373         }
 374         cn.metadataRequests[index] = true
 375 }
 376
 377 func (cn *connection) requestedMetadataPiece(index int) bool {
 378         return index < len(cn.metadataRequests) && cn.metadataRequests[index]
 379 }
 380
 381 // The actual value to use as the maximum outbound requests.
 382 func (cn *connection) nominalMaxRequests() (ret int) {
 383         return int(clamp(
 384                 1,
 385                 int64(cn.PeerMaxRequests),
 386                 int64(cn.t.requestStrategy.nominalMaxRequests(cn.requestStrategyConnection())),
 387         ))
 388 }
 389
 390 // The actual value to use as the maximum outbound requests.
 391 func (requestStrategyThree) nominalMaxRequests(cn requestStrategyConnection) (ret int) {
 392         expectingTime := int64(cn.totalExpectingTime())
 393         if expectingTime == 0 {
 394                 expectingTime = math.MaxInt64
 395         } else {
 396                 expectingTime *= 2
 397         }
 398         return int(clamp(
 399                 1,
 400                 int64(cn.peerMaxRequests()),
 401                 max(
 402                         // It makes sense to always pipeline at least one connection, since latency must be
 403                         // non-zero.
 404                         2,
 405                         // Request only as many as we expect to receive in the duplicateRequestTimeout
 406                         // window. We are trying to avoid having to duplicate requests.
 407                         cn.chunksReceivedWhileExpecting()*int64(cn.torrent().duplicateRequestTimeout())/expectingTime,
 408                 ),
 409         ))
 410 }
 411 func defaultNominalMaxRequests(cn requestStrategyConnection) int {
 412         return int(
 413                 max(64,
 414                         cn.stats().ChunksReadUseful.Int64()-(cn.stats().ChunksRead.Int64()-cn.stats().ChunksReadUseful.Int64())))
 415 }
 416 func (rs requestStrategyOne) nominalMaxRequests(cn requestStrategyConnection) int {
 417         return defaultNominalMaxRequests(cn)
 418 }
 419 func (rs requestStrategyTwo) nominalMaxRequests(cn requestStrategyConnection) int {
 420         return defaultNominalMaxRequests(cn)
 421 }
 422
 423 func (cn *connection) totalExpectingTime() (ret time.Duration) {
 424         ret = cn.cumulativeExpectedToReceiveChunks
 425         if !cn.lastStartedExpectingToReceiveChunks.IsZero() {
 426                 ret += time.Since(cn.lastStartedExpectingToReceiveChunks)
 427         }
 428         return
 429
 430 }
 431
 432 func (cn *connection) onPeerSentCancel(r request) {
 433         if _, ok := cn.PeerRequests[r]; !ok {
 434                 torrent.Add("unexpected cancels received", 1)
 435                 return
 436         }
 437         if cn.fastEnabled() {
 438                 cn.reject(r)
 439         } else {
 440                 delete(cn.PeerRequests, r)
 441         }
 442 }
 443
 444 func (cn *connection) Choke(msg messageWriter) (more bool) {
 445         if cn.Choked {
 446                 return true
 447         }
 448         cn.Choked = true
 449         more = msg(pp.Message{
 450                 Type: pp.Choke,
 451         })
 452         if cn.fastEnabled() {
 453                 for r := range cn.PeerRequests {
 454                         // TODO: Don't reject pieces in allowed fast set.
 455                         cn.reject(r)
 456                 }
 457         } else {
 458                 cn.PeerRequests = nil
 459         }
 460         return
 461 }
 462
 463 func (cn *connection) Unchoke(msg func(pp.Message) bool) bool {
 464         if !cn.Choked {
 465                 return true
 466         }
 467         cn.Choked = false
 468         return msg(pp.Message{
 469                 Type: pp.Unchoke,
 470         })
 471 }
 472
 473 func (cn *connection) SetInterested(interested bool, msg func(pp.Message) bool) bool {
 474         if cn.Interested == interested {
 475                 return true
 476         }
 477         cn.Interested = interested
 478         if interested {
 479                 cn.lastBecameInterested = time.Now()
 480         } else if !cn.lastBecameInterested.IsZero() {
 481                 cn.priorInterest += time.Since(cn.lastBecameInterested)
 482         }
 483         cn.updateExpectingChunks()
 484         // log.Printf("%p: setting interest: %v", cn, interested)
 485         return msg(pp.Message{
 486                 Type: func() pp.MessageType {
 487                         if interested {
 488                                 return pp.Interested
 489                         } else {
 490                                 return pp.NotInterested
 491                         }
 492                 }(),
 493         })
 494 }
 495
 496 // The function takes a message to be sent, and returns true if more messages
 497 // are okay.
 498 type messageWriter func(pp.Message) bool
 499
 500 // Proxies the messageWriter's response.
 501 func (cn *connection) request(r request, mw messageWriter) bool {
 502         if _, ok := cn.requests[r]; ok {
 503                 panic("chunk already requested")
 504         }
 505         if !cn.PeerHasPiece(pieceIndex(r.Index)) {
 506                 panic("requesting piece peer doesn't have")
 507         }
 508         if _, ok := cn.t.conns[cn]; !ok {
 509                 panic("requesting but not in active conns")
 510         }
 511         if cn.closed.IsSet() {
 512                 panic("requesting when connection is closed")
 513         }
 514         if cn.PeerChoked {
 515                 if cn.peerAllowedFast.Get(int(r.Index)) {
 516                         torrent.Add("allowed fast requests sent", 1)
 517                 } else {
 518                         panic("requesting while choked and not allowed fast")
 519                 }
 520         }
 521         if cn.t.hashingPiece(pieceIndex(r.Index)) {
 522                 panic("piece is being hashed")
 523         }
 524         if cn.t.pieceQueuedForHash(pieceIndex(r.Index)) {
 525                 panic("piece is queued for hash")
 526         }
 527         if cn.requests == nil {
 528                 cn.requests = make(map[request]struct{})
 529         }
 530         cn.requests[r] = struct{}{}
 531         if cn.validReceiveChunks == nil {
 532                 cn.validReceiveChunks = make(map[request]struct{})
 533         }
 534         cn.validReceiveChunks[r] = struct{}{}
 535         cn.t.pendingRequests[r]++
 536         cn.t.lastRequested[r] = time.AfterFunc(cn.t._duplicateRequestTimeout, func() {
 537                 torrent.Add("duplicate request timeouts", 1)
 538                 cn.mu().Lock()
 539                 defer cn.mu().Unlock()
 540                 delete(cn.t.lastRequested, r)
 541                 for cn := range cn.t.conns {
 542                         if cn.PeerHasPiece(pieceIndex(r.Index)) {
 543                                 cn.updateRequests()
 544                         }
 545                 }
 546         })
 547         cn.updateExpectingChunks()
 548         return mw(pp.Message{
 549                 Type:   pp.Request,
 550                 Index:  r.Index,
 551                 Begin:  r.Begin,
 552                 Length: r.Length,
 553         })
 554 }
 555
 556 func (cn *connection) fillWriteBuffer(msg func(pp.Message) bool) {
 557         if !cn.t.networkingEnabled {
 558                 if !cn.SetInterested(false, msg) {
 559                         return
 560                 }
 561                 if len(cn.requests) != 0 {
 562                         for r := range cn.requests {
 563                                 cn.deleteRequest(r)
 564                                 // log.Printf("%p: cancelling request: %v", cn, r)
 565                                 if !msg(makeCancelMessage(r)) {
 566                                         return
 567                                 }
 568                         }
 569                 }
 570         }
 571         if len(cn.requests) <= cn.requestsLowWater {
 572                 filledBuffer := false
 573                 cn.iterPendingPieces(func(pieceIndex pieceIndex) bool {
 574                         cn.iterPendingRequests(pieceIndex, func(r request) bool {
 575                                 if !cn.SetInterested(true, msg) {
 576                                         filledBuffer = true
 577                                         return false
 578                                 }
 579                                 if len(cn.requests) >= cn.nominalMaxRequests() {
 580                                         return false
 581                                 }
 582                                 // Choking is looked at here because our interest is dependent
 583                                 // on whether we'd make requests in its absence.
 584                                 if cn.PeerChoked {
 585                                         if !cn.peerAllowedFast.Get(bitmap.BitIndex(r.Index)) {
 586                                                 return false
 587                                         }
 588                                 }
 589                                 if _, ok := cn.requests[r]; ok {
 590                                         return true
 591                                 }
 592                                 filledBuffer = !cn.request(r, msg)
 593                                 return !filledBuffer
 594                         })
 595                         return !filledBuffer
 596                 })
 597                 if filledBuffer {
 598                         // If we didn't completely top up the requests, we shouldn't mark
 599                         // the low water, since we'll want to top up the requests as soon
 600                         // as we have more write buffer space.
 601                         return
 602                 }
 603                 cn.requestsLowWater = len(cn.requests) / 2
 604         }
 605
 606         cn.upload(msg)
 607 }
 608
 609 // Routine that writes to the peer. Some of what to write is buffered by
 610 // activity elsewhere in the Client, and some is determined locally when the
 611 // connection is writable.
 612 func (cn *connection) writer(keepAliveTimeout time.Duration) {
 613         var (
 614                 lastWrite      time.Time = time.Now()
 615                 keepAliveTimer *time.Timer
 616         )
 617         keepAliveTimer = time.AfterFunc(keepAliveTimeout, func() {
 618                 cn.mu().Lock()
 619                 defer cn.mu().Unlock()
 620                 if time.Since(lastWrite) >= keepAliveTimeout {
 621                         cn.tickleWriter()
 622                 }
 623                 keepAliveTimer.Reset(keepAliveTimeout)
 624         })
 625         cn.mu().Lock()
 626         defer cn.mu().Unlock()
 627         defer cn.Close()
 628         defer keepAliveTimer.Stop()
 629         frontBuf := new(bytes.Buffer)
 630         for {
 631                 if cn.closed.IsSet() {
 632                         return
 633                 }
 634                 if cn.writeBuffer.Len() == 0 {
 635                         cn.fillWriteBuffer(func(msg pp.Message) bool {
 636                                 cn.wroteMsg(&msg)
 637                                 cn.writeBuffer.Write(msg.MustMarshalBinary())
 638                                 torrent.Add(fmt.Sprintf("messages filled of type %s", msg.Type.String()), 1)
 639                                 return cn.writeBuffer.Len() < 1<<16 // 64KiB
 640                         })
 641                 }
 642                 if cn.writeBuffer.Len() == 0 && time.Since(lastWrite) >= keepAliveTimeout {
 643                         cn.writeBuffer.Write(pp.Message{Keepalive: true}.MustMarshalBinary())
 644                         postedKeepalives.Add(1)
 645                 }
 646                 if cn.writeBuffer.Len() == 0 {
 647                         // TODO: Minimize wakeups....
 648                         cn.writerCond.Wait()
 649                         continue
 650                 }
 651                 // Flip the buffers.
 652                 frontBuf, cn.writeBuffer = cn.writeBuffer, frontBuf
 653                 cn.mu().Unlock()
 654                 n, err := cn.w.Write(frontBuf.Bytes())
 655                 cn.mu().Lock()
 656                 if n != 0 {
 657                         lastWrite = time.Now()
 658                         keepAliveTimer.Reset(keepAliveTimeout)
 659                 }
 660                 if err != nil {
 661                         return
 662                 }
 663                 if n != frontBuf.Len() {
 664                         panic("short write")
 665                 }
 666                 frontBuf.Reset()
 667         }
 668 }
 669
 670 func (cn *connection) Have(piece pieceIndex) {
 671         if cn.sentHaves.Get(bitmap.BitIndex(piece)) {
 672                 return
 673         }
 674         cn.Post(pp.Message{
 675                 Type:  pp.Have,
 676                 Index: pp.Integer(piece),
 677         })
 678         cn.sentHaves.Add(bitmap.BitIndex(piece))
 679 }
 680
 681 func (cn *connection) PostBitfield() {
 682         if cn.sentHaves.Len() != 0 {
 683                 panic("bitfield must be first have-related message sent")
 684         }
 685         if !cn.t.haveAnyPieces() {
 686                 return
 687         }
 688         cn.Post(pp.Message{
 689                 Type:     pp.Bitfield,
 690                 Bitfield: cn.t.bitfield(),
 691         })
 692         cn.sentHaves = cn.t._completedPieces.Copy()
 693 }
 694
 695 func (cn *connection) updateRequests() {
 696         // log.Print("update requests")
 697         cn.tickleWriter()
 698 }
 699
 700 // Emits the indices in the Bitmaps bms in order, never repeating any index.
 701 // skip is mutated during execution, and its initial values will never be
 702 // emitted.
 703 func iterBitmapsDistinct(skip *bitmap.Bitmap, bms ...bitmap.Bitmap) iter.Func {
 704         return func(cb iter.Callback) {
 705                 for _, bm := range bms {
 706                         if !iter.All(
 707                                 func(i interface{}) bool {
 708                                         skip.Add(i.(int))
 709                                         return cb(i)
 710                                 },
 711                                 bitmap.Sub(bm, *skip).Iter,
 712                         ) {
 713                                 return
 714                         }
 715                 }
 716         }
 717 }
 718
 719 func iterUnbiasedPieceRequestOrder(cn requestStrategyConnection, f func(piece pieceIndex) bool) bool {
 720         now, readahead := cn.torrent().readerPiecePriorities()
 721         skip := bitmap.Flip(cn.peerPieces(), 0, cn.torrent().numPieces())
 722         skip.Union(cn.torrent().ignorePieces())
 723         // Return an iterator over the different priority classes, minus the skip pieces.
 724         return iter.All(
 725                 func(_piece interface{}) bool {
 726                         return f(pieceIndex(_piece.(bitmap.BitIndex)))
 727                 },
 728                 iterBitmapsDistinct(&skip, now, readahead),
 729                 // We have to iterate _pendingPieces separately because it isn't a Bitmap.
 730                 func(cb iter.Callback) {
 731                         cn.torrent().pendingPieces().IterTyped(func(piece int) bool {
 732                                 if skip.Contains(piece) {
 733                                         return true
 734                                 }
 735                                 more := cb(piece)
 736                                 skip.Add(piece)
 737                                 return more
 738                         })
 739                 },
 740         )
 741 }
 742
 743 // The connection should download highest priority pieces first, without any inclination toward
 744 // avoiding wastage. Generally we might do this if there's a single connection, or this is the
 745 // fastest connection, and we have active readers that signal an ordering preference. It's
 746 // conceivable that the best connection should do this, since it's least likely to waste our time if
 747 // assigned to the highest priority pieces, and assigning more than one this role would cause
 748 // significant wasted bandwidth.
 749 func (cn *connection) shouldRequestWithoutBias() bool {
 750         return cn.t.requestStrategy.shouldRequestWithoutBias(cn.requestStrategyConnection())
 751 }
 752
 753 func defaultShouldRequestWithoutBias(cn requestStrategyConnection) bool {
 754         return false
 755 }
 756
 757 func (requestStrategyTwo) shouldRequestWithoutBias(cn requestStrategyConnection) bool {
 758         if cn.torrent().numReaders() == 0 {
 759                 return false
 760         }
 761         if cn.torrent().numConns() == 1 {
 762                 return true
 763         }
 764         if cn.fastest() {
 765                 return true
 766         }
 767         return false
 768 }
 769
 770 func (requestStrategyOne) shouldRequestWithoutBias(cn requestStrategyConnection) bool {
 771         return defaultShouldRequestWithoutBias(cn)
 772 }
 773
 774 func (requestStrategyThree) shouldRequestWithoutBias(cn requestStrategyConnection) bool {
 775         return defaultShouldRequestWithoutBias(cn)
 776 }
 777
 778 func (cn *connection) iterPendingPieces(f func(pieceIndex) bool) bool {
 779         if !cn.t.haveInfo() {
 780                 return false
 781         }
 782         return cn.t.requestStrategy.iterPendingPieces(cn, f)
 783 }
 784 func (requestStrategyThree) iterPendingPieces(cn requestStrategyConnection, f func(pieceIndex) bool) bool {
 785         return iterUnbiasedPieceRequestOrder(cn, f)
 786 }
 787 func defaultIterPendingPieces(rs requestStrategy, cn requestStrategyConnection, f func(pieceIndex) bool) bool {
 788         if rs.shouldRequestWithoutBias(cn) {
 789                 return iterUnbiasedPieceRequestOrder(cn, f)
 790         } else {
 791                 return cn.pieceRequestOrder().IterTyped(func(i int) bool {
 792                         return f(pieceIndex(i))
 793                 })
 794         }
 795 }
 796 func (rs requestStrategyOne) iterPendingPieces(cn requestStrategyConnection, cb func(pieceIndex) bool) bool {
 797         return defaultIterPendingPieces(rs, cn, cb)
 798 }
 799 func (rs requestStrategyTwo) iterPendingPieces(cn requestStrategyConnection, cb func(pieceIndex) bool) bool {
 800         return defaultIterPendingPieces(rs, cn, cb)
 801 }
 802
 803 func (cn *connection) iterPendingPiecesUntyped(f iter.Callback) {
 804         cn.iterPendingPieces(func(i pieceIndex) bool { return f(i) })
 805 }
 806
 807 func (cn *connection) iterPendingRequests(piece pieceIndex, f func(request) bool) bool {
 808         return cn.t.requestStrategy.iterUndirtiedChunks(cn.t.piece(piece).requestStrategyPiece(),
 809                 func(cs chunkSpec) bool {
 810                         return f(request{pp.Integer(piece), cs})
 811                 })
 812 }
 813
 814 func (requestStrategyThree) iterUndirtiedChunks(p requestStrategyPiece, f func(chunkSpec) bool) bool {
 815         for i := pp.Integer(0); i < pp.Integer(p.numChunks()); i++ {
 816                 if p.dirtyChunks().Get(bitmap.BitIndex(i)) {
 817                         continue
 818                 }
 819                 ci := p.chunkIndexSpec(i)
 820                 if p.wouldDuplicateRecent(ci) {
 821                         continue
 822                 }
 823                 if !f(p.chunkIndexSpec(i)) {
 824                         return false
 825                 }
 826         }
 827         return true
 828 }
 829
 830 func defaultIterUndirtiedChunks(p requestStrategyPiece, f func(chunkSpec) bool) bool {
 831         chunkIndices := p.dirtyChunks().Copy()
 832         chunkIndices.FlipRange(0, bitmap.BitIndex(p.numChunks()))
 833         return iter.ForPerm(chunkIndices.Len(), func(i int) bool {
 834                 ci, err := chunkIndices.RB.Select(uint32(i))
 835                 if err != nil {
 836                         panic(err)
 837                 }
 838                 return f(p.chunkIndexSpec(pp.Integer(ci)))
 839         })
 840 }
 841
 842 func (rs requestStrategyOne) iterUndirtiedChunks(p requestStrategyPiece, f func(chunkSpec) bool) bool {
 843         return defaultIterUndirtiedChunks(p, f)
 844 }
 845
 846 func (rs requestStrategyTwo) iterUndirtiedChunks(p requestStrategyPiece, f func(chunkSpec) bool) bool {
 847         return defaultIterUndirtiedChunks(p, f)
 848 }
 849
 850 // check callers updaterequests
 851 func (cn *connection) stopRequestingPiece(piece pieceIndex) bool {
 852         return cn._pieceRequestOrder.Remove(bitmap.BitIndex(piece))
 853 }
 854
 855 // This is distinct from Torrent piece priority, which is the user's
 856 // preference. Connection piece priority is specific to a connection and is
 857 // used to pseudorandomly avoid connections always requesting the same pieces
 858 // and thus wasting effort.
 859 func (cn *connection) updatePiecePriority(piece pieceIndex) bool {
 860         tpp := cn.t.piecePriority(piece)
 861         if !cn.PeerHasPiece(piece) {
 862                 tpp = PiecePriorityNone
 863         }
 864         if tpp == PiecePriorityNone {
 865                 return cn.stopRequestingPiece(piece)
 866         }
 867         prio := cn.getPieceInclination()[piece]
 868         prio = cn.t.requestStrategy.piecePriority(cn, piece, tpp, prio)
 869         return cn._pieceRequestOrder.Set(bitmap.BitIndex(piece), prio) || cn.shouldRequestWithoutBias()
 870 }
 871
 872 func (requestStrategyOne) piecePriority(cn requestStrategyConnection, piece pieceIndex, tpp piecePriority, prio int) int {
 873         switch tpp {
 874         case PiecePriorityNormal:
 875         case PiecePriorityReadahead:
 876                 prio -= int(cn.torrent().numPieces())
 877         case PiecePriorityNext, PiecePriorityNow:
 878                 prio -= 2 * int(cn.torrent().numPieces())
 879         default:
 880                 panic(tpp)
 881         }
 882         prio += int(piece / 3)
 883         return prio
 884 }
 885
 886 func defaultPiecePriority(cn requestStrategyConnection, piece pieceIndex, tpp piecePriority, prio int) int {
 887         return prio
 888 }
 889
 890 func (requestStrategyTwo) piecePriority(cn requestStrategyConnection, piece pieceIndex, tpp piecePriority, prio int) int {
 891         return defaultPiecePriority(cn, piece, tpp, prio)
 892 }
 893
 894 func (requestStrategyThree) piecePriority(cn requestStrategyConnection, piece pieceIndex, tpp piecePriority, prio int) int {
 895         return defaultPiecePriority(cn, piece, tpp, prio)
 896 }
 897
 898 func (cn *connection) getPieceInclination() []int {
 899         if cn.pieceInclination == nil {
 900                 cn.pieceInclination = cn.t.getConnPieceInclination()
 901         }
 902         return cn.pieceInclination
 903 }
 904
 905 func (cn *connection) discardPieceInclination() {
 906         if cn.pieceInclination == nil {
 907                 return
 908         }
 909         cn.t.putPieceInclination(cn.pieceInclination)
 910         cn.pieceInclination = nil
 911 }
 912
 913 func (cn *connection) peerPiecesChanged() {
 914         if cn.t.haveInfo() {
 915                 prioritiesChanged := false
 916                 for i := pieceIndex(0); i < cn.t.numPieces(); i++ {
 917                         if cn.updatePiecePriority(i) {
 918                                 prioritiesChanged = true
 919                         }
 920                 }
 921                 if prioritiesChanged {
 922                         cn.updateRequests()
 923                 }
 924         }
 925 }
 926
 927 func (cn *connection) raisePeerMinPieces(newMin pieceIndex) {
 928         if newMin > cn.peerMinPieces {
 929                 cn.peerMinPieces = newMin
 930         }
 931 }
 932
 933 func (cn *connection) peerSentHave(piece pieceIndex) error {
 934         if cn.t.haveInfo() && piece >= cn.t.numPieces() || piece < 0 {
 935                 return errors.New("invalid piece")
 936         }
 937         if cn.PeerHasPiece(piece) {
 938                 return nil
 939         }
 940         cn.raisePeerMinPieces(piece + 1)
 941         cn._peerPieces.Set(bitmap.BitIndex(piece), true)
 942         if cn.updatePiecePriority(piece) {
 943                 cn.updateRequests()
 944         }
 945         return nil
 946 }
 947
 948 func (cn *connection) peerSentBitfield(bf []bool) error {
 949         cn.peerSentHaveAll = false
 950         if len(bf)%8 != 0 {
 951                 panic("expected bitfield length divisible by 8")
 952         }
 953         // We know that the last byte means that at most the last 7 bits are
 954         // wasted.
 955         cn.raisePeerMinPieces(pieceIndex(len(bf) - 7))
 956         if cn.t.haveInfo() && len(bf) > int(cn.t.numPieces()) {
 957                 // Ignore known excess pieces.
 958                 bf = bf[:cn.t.numPieces()]
 959         }
 960         for i, have := range bf {
 961                 if have {
 962                         cn.raisePeerMinPieces(pieceIndex(i) + 1)
 963                 }
 964                 cn._peerPieces.Set(i, have)
 965         }
 966         cn.peerPiecesChanged()
 967         return nil
 968 }
 969
 970 func (cn *connection) onPeerSentHaveAll() error {
 971         cn.peerSentHaveAll = true
 972         cn._peerPieces.Clear()
 973         cn.peerPiecesChanged()
 974         return nil
 975 }
 976
 977 func (cn *connection) peerSentHaveNone() error {
 978         cn._peerPieces.Clear()
 979         cn.peerSentHaveAll = false
 980         cn.peerPiecesChanged()
 981         return nil
 982 }
 983
 984 func (c *connection) requestPendingMetadata() {
 985         if c.t.haveInfo() {
 986                 return
 987         }
 988         if c.PeerExtensionIDs[pp.ExtensionNameMetadata] == 0 {
 989                 // Peer doesn't support this.
 990                 return
 991         }
 992         // Request metadata pieces that we don't have in a random order.
 993         var pending []int
 994         for index := 0; index < c.t.metadataPieceCount(); index++ {
 995                 if !c.t.haveMetadataPiece(index) && !c.requestedMetadataPiece(index) {
 996                         pending = append(pending, index)
 997                 }
 998         }
 999         rand.Shuffle(len(pending), func(i, j int) { pending[i], pending[j] = pending[j], pending[i] })
1000         for _, i := range pending {
1001                 c.requestMetadataPiece(i)
1002         }
1003 }
1004
1005 func (cn *connection) wroteMsg(msg *pp.Message) {
1006         torrent.Add(fmt.Sprintf("messages written of type %s", msg.Type.String()), 1)
1007         cn.allStats(func(cs *ConnStats) { cs.wroteMsg(msg) })
1008 }
1009
1010 func (cn *connection) readMsg(msg *pp.Message) {
1011         cn.allStats(func(cs *ConnStats) { cs.readMsg(msg) })
1012 }
1013
1014 // After handshake, we know what Torrent and Client stats to include for a
1015 // connection.
1016 func (cn *connection) postHandshakeStats(f func(*ConnStats)) {
1017         t := cn.t
1018         f(&t.stats)
1019         f(&t.cl.stats)
1020 }
1021
1022 // All ConnStats that include this connection. Some objects are not known
1023 // until the handshake is complete, after which it's expected to reconcile the
1024 // differences.
1025 func (cn *connection) allStats(f func(*ConnStats)) {
1026         f(&cn._stats)
1027         if cn.reconciledHandshakeStats {
1028                 cn.postHandshakeStats(f)
1029         }
1030 }
1031
1032 func (cn *connection) wroteBytes(n int64) {
1033         cn.allStats(add(n, func(cs *ConnStats) *Count { return &cs.BytesWritten }))
1034 }
1035
1036 func (cn *connection) readBytes(n int64) {
1037         cn.allStats(add(n, func(cs *ConnStats) *Count { return &cs.BytesRead }))
1038 }
1039
1040 // Returns whether the connection could be useful to us. We're seeding and
1041 // they want data, we don't have metainfo and they can provide it, etc.
1042 func (c *connection) useful() bool {
1043         t := c.t
1044         if c.closed.IsSet() {
1045                 return false
1046         }
1047         if !t.haveInfo() {
1048                 return c.supportsExtension("ut_metadata")
1049         }
1050         if t.seeding() && c.PeerInterested {
1051                 return true
1052         }
1053         if c.peerHasWantedPieces() {
1054                 return true
1055         }
1056         return false
1057 }
1058
1059 func (c *connection) lastHelpful() (ret time.Time) {
1060         ret = c.lastUsefulChunkReceived
1061         if c.t.seeding() && c.lastChunkSent.After(ret) {
1062                 ret = c.lastChunkSent
1063         }
1064         return
1065 }
1066
1067 func (c *connection) fastEnabled() bool {
1068         return c.PeerExtensionBytes.SupportsFast() && c.t.cl.extensionBytes.SupportsFast()
1069 }
1070
1071 func (c *connection) reject(r request) {
1072         if !c.fastEnabled() {
1073                 panic("fast not enabled")
1074         }
1075         c.Post(r.ToMsg(pp.Reject))
1076         delete(c.PeerRequests, r)
1077 }
1078
1079 func (c *connection) onReadRequest(r request) error {
1080         requestedChunkLengths.Add(strconv.FormatUint(r.Length.Uint64(), 10), 1)
1081         if _, ok := c.PeerRequests[r]; ok {
1082                 torrent.Add("duplicate requests received", 1)
1083                 return nil
1084         }
1085         if c.Choked {
1086                 torrent.Add("requests received while choking", 1)
1087                 if c.fastEnabled() {
1088                         torrent.Add("requests rejected while choking", 1)
1089                         c.reject(r)
1090                 }
1091                 return nil
1092         }
1093         if len(c.PeerRequests) >= maxRequests {
1094                 torrent.Add("requests received while queue full", 1)
1095                 if c.fastEnabled() {
1096                         c.reject(r)
1097                 }
1098                 // BEP 6 says we may close here if we choose.
1099                 return nil
1100         }
1101         if !c.t.havePiece(pieceIndex(r.Index)) {
1102                 // This isn't necessarily them screwing up. We can drop pieces
1103                 // from our storage, and can't communicate this to peers
1104                 // except by reconnecting.
1105                 requestsReceivedForMissingPieces.Add(1)
1106                 return fmt.Errorf("peer requested piece we don't have: %v", r.Index.Int())
1107         }
1108         // Check this after we know we have the piece, so that the piece length will be known.
1109         if r.Begin+r.Length > c.t.pieceLength(pieceIndex(r.Index)) {
1110                 torrent.Add("bad requests received", 1)
1111                 return errors.New("bad request")
1112         }
1113         if c.PeerRequests == nil {
1114                 c.PeerRequests = make(map[request]struct{}, maxRequests)
1115         }
1116         c.PeerRequests[r] = struct{}{}
1117         c.tickleWriter()
1118         return nil
1119 }
1120
1121 // Processes incoming BitTorrent wire-protocol messages. The client lock is held upon entry and
1122 // exit. Returning will end the connection.
1123 func (c *connection) mainReadLoop() (err error) {
1124         defer func() {
1125                 if err != nil {
1126                         torrent.Add("connection.mainReadLoop returned with error", 1)
1127                 } else {
1128                         torrent.Add("connection.mainReadLoop returned with no error", 1)
1129                 }
1130         }()
1131         t := c.t
1132         cl := t.cl
1133
1134         decoder := pp.Decoder{
1135                 R:         bufio.NewReaderSize(c.r, 1<<17),
1136                 MaxLength: 256 * 1024,
1137                 Pool:      t.chunkPool,
1138         }
1139         for {
1140                 var msg pp.Message
1141                 func() {
1142                         cl.unlock()
1143                         defer cl.lock()
1144                         err = decoder.Decode(&msg)
1145                 }()
1146                 if t.closed.IsSet() || c.closed.IsSet() || err == io.EOF {
1147                         return nil
1148                 }
1149                 if err != nil {
1150                         return err
1151                 }
1152                 c.readMsg(&msg)
1153                 c.lastMessageReceived = time.Now()
1154                 if msg.Keepalive {
1155                         receivedKeepalives.Add(1)
1156                         continue
1157                 }
1158                 messageTypesReceived.Add(msg.Type.String(), 1)
1159                 if msg.Type.FastExtension() && !c.fastEnabled() {
1160                         return fmt.Errorf("received fast extension message (type=%v) but extension is disabled", msg.Type)
1161                 }
1162                 switch msg.Type {
1163                 case pp.Choke:
1164                         c.PeerChoked = true
1165                         c.deleteAllRequests()
1166                         // We can then reset our interest.
1167                         c.updateRequests()
1168                         c.updateExpectingChunks()
1169                 case pp.Unchoke:
1170                         c.PeerChoked = false
1171                         c.tickleWriter()
1172                         c.updateExpectingChunks()
1173                 case pp.Interested:
1174                         c.PeerInterested = true
1175                         c.tickleWriter()
1176                 case pp.NotInterested:
1177                         c.PeerInterested = false
1178                         // We don't clear their requests since it isn't clear in the spec.
1179                         // We'll probably choke them for this, which will clear them if
1180                         // appropriate, and is clearly specified.
1181                 case pp.Have:
1182                         err = c.peerSentHave(pieceIndex(msg.Index))
1183                 case pp.Bitfield:
1184                         err = c.peerSentBitfield(msg.Bitfield)
1185                 case pp.Request:
1186                         r := newRequestFromMessage(&msg)
1187                         err = c.onReadRequest(r)
1188                 case pp.Piece:
1189                         err = c.receiveChunk(&msg)
1190                         if len(msg.Piece) == int(t.chunkSize) {
1191                                 t.chunkPool.Put(&msg.Piece)
1192                         }
1193                         if err != nil {
1194                                 err = fmt.Errorf("receiving chunk: %s", err)
1195                         }
1196                 case pp.Cancel:
1197                         req := newRequestFromMessage(&msg)
1198                         c.onPeerSentCancel(req)
1199                 case pp.Port:
1200                         pingAddr := net.UDPAddr{
1201                                 IP:   c.remoteAddr.IP,
1202                                 Port: int(c.remoteAddr.Port),
1203                         }
1204                         if msg.Port != 0 {
1205                                 pingAddr.Port = int(msg.Port)
1206                         }
1207                         cl.eachDhtServer(func(s *dht.Server) {
1208                                 go s.Ping(&pingAddr, nil)
1209                         })
1210                 case pp.Suggest:
1211                         torrent.Add("suggests received", 1)
1212                         log.Fmsg("peer suggested piece %d", msg.Index).AddValues(c, msg.Index, debugLogValue).Log(c.t.logger)
1213                         c.updateRequests()
1214                 case pp.HaveAll:
1215                         err = c.onPeerSentHaveAll()
1216                 case pp.HaveNone:
1217                         err = c.peerSentHaveNone()
1218                 case pp.Reject:
1219                         c.deleteRequest(newRequestFromMessage(&msg))
1220                         delete(c.validReceiveChunks, newRequestFromMessage(&msg))
1221                 case pp.AllowedFast:
1222                         torrent.Add("allowed fasts received", 1)
1223                         log.Fmsg("peer allowed fast: %d", msg.Index).AddValues(c, debugLogValue).Log(c.t.logger)
1224                         c.peerAllowedFast.Add(int(msg.Index))
1225                         c.updateRequests()
1226                 case pp.Extended:
1227                         err = c.onReadExtendedMsg(msg.ExtendedID, msg.ExtendedPayload)
1228                 default:
1229                         err = fmt.Errorf("received unknown message type: %#v", msg.Type)
1230                 }
1231                 if err != nil {
1232                         return err
1233                 }
1234         }
1235 }
1236
1237 func (c *connection) onReadExtendedMsg(id pp.ExtensionNumber, payload []byte) (err error) {
1238         defer func() {
1239                 // TODO: Should we still do this?
1240                 if err != nil {
1241                         // These clients use their own extension IDs for outgoing message
1242                         // types, which is incorrect.
1243                         if bytes.HasPrefix(c.PeerID[:], []byte("-SD0100-")) || strings.HasPrefix(string(c.PeerID[:]), "-XL0012-") {
1244                                 err = nil
1245                         }
1246                 }
1247         }()
1248         t := c.t
1249         cl := t.cl
1250         switch id {
1251         case pp.HandshakeExtendedID:
1252                 var d pp.ExtendedHandshakeMessage
1253                 if err := bencode.Unmarshal(payload, &d); err != nil {
1254                         c.t.logger.Printf("error parsing extended handshake message %q: %s", payload, err)
1255                         return errors.Wrap(err, "unmarshalling extended handshake payload")
1256                 }
1257                 if d.Reqq != 0 {
1258                         c.PeerMaxRequests = d.Reqq
1259                 }
1260                 c.PeerClientName = d.V
1261                 if c.PeerExtensionIDs == nil {
1262                         c.PeerExtensionIDs = make(map[pp.ExtensionName]pp.ExtensionNumber, len(d.M))
1263                 }
1264                 for name, id := range d.M {
1265                         if _, ok := c.PeerExtensionIDs[name]; !ok {
1266                                 torrent.Add(fmt.Sprintf("peers supporting extension %q", name), 1)
1267                         }
1268                         c.PeerExtensionIDs[name] = id
1269                 }
1270                 if d.MetadataSize != 0 {
1271                         if err = t.setMetadataSize(d.MetadataSize); err != nil {
1272                                 return errors.Wrapf(err, "setting metadata size to %d", d.MetadataSize)
1273                         }
1274                 }
1275                 c.requestPendingMetadata()
1276                 return nil
1277         case metadataExtendedId:
1278                 err := cl.gotMetadataExtensionMsg(payload, t, c)
1279                 if err != nil {
1280                         return fmt.Errorf("handling metadata extension message: %w", err)
1281                 }
1282                 return nil
1283         case pexExtendedId:
1284                 if cl.config.DisablePEX {
1285                         // TODO: Maybe close the connection. Check that we're not
1286                         // advertising that we support PEX if it's disabled.
1287                         return nil
1288                 }
1289                 var pexMsg pp.PexMsg
1290                 err := bencode.Unmarshal(payload, &pexMsg)
1291                 if err != nil {
1292                         return fmt.Errorf("error unmarshalling PEX message: %s", err)
1293                 }
1294                 torrent.Add("pex added6 peers received", int64(len(pexMsg.Added6)))
1295                 var peers Peers
1296                 peers.AppendFromPex(pexMsg.Added6, pexMsg.Added6Flags)
1297                 peers.AppendFromPex(pexMsg.Added, pexMsg.AddedFlags)
1298                 t.addPeers(peers)
1299                 return nil
1300         default:
1301                 return fmt.Errorf("unexpected extended message ID: %v", id)
1302         }
1303 }
1304
1305 // Set both the Reader and Writer for the connection from a single ReadWriter.
1306 func (cn *connection) setRW(rw io.ReadWriter) {
1307         cn.r = rw
1308         cn.w = rw
1309 }
1310
1311 // Returns the Reader and Writer as a combined ReadWriter.
1312 func (cn *connection) rw() io.ReadWriter {
1313         return struct {
1314                 io.Reader
1315                 io.Writer
1316         }{cn.r, cn.w}
1317 }
1318
1319 // Handle a received chunk from a peer.
1320 func (c *connection) receiveChunk(msg *pp.Message) error {
1321         t := c.t
1322         cl := t.cl
1323         torrent.Add("chunks received", 1)
1324
1325         req := newRequestFromMessage(msg)
1326
1327         if c.PeerChoked {
1328                 torrent.Add("chunks received while choked", 1)
1329         }
1330
1331         if _, ok := c.validReceiveChunks[req]; !ok {
1332                 torrent.Add("chunks received unexpected", 1)
1333                 return errors.New("received unexpected chunk")
1334         }
1335         delete(c.validReceiveChunks, req)
1336
1337         if c.PeerChoked && c.peerAllowedFast.Get(int(req.Index)) {
1338                 torrent.Add("chunks received due to allowed fast", 1)
1339         }
1340
1341         // Request has been satisfied.
1342         if c.deleteRequest(req) {
1343                 if c.expectingChunks() {
1344                         c._chunksReceivedWhileExpecting++
1345                 }
1346         } else {
1347                 torrent.Add("chunks received unwanted", 1)
1348         }
1349
1350         // Do we actually want this chunk?
1351         if t.haveChunk(req) {
1352                 torrent.Add("chunks received wasted", 1)
1353                 c.allStats(add(1, func(cs *ConnStats) *Count { return &cs.ChunksReadWasted }))
1354                 return nil
1355         }
1356
1357         piece := &t.pieces[req.Index]
1358
1359         c.allStats(add(1, func(cs *ConnStats) *Count { return &cs.ChunksReadUseful }))
1360         c.allStats(add(int64(len(msg.Piece)), func(cs *ConnStats) *Count { return &cs.BytesReadUsefulData }))
1361         c.lastUsefulChunkReceived = time.Now()
1362         // if t.fastestConn != c {
1363         // log.Printf("setting fastest connection %p", c)
1364         // }
1365         t.fastestConn = c
1366
1367         // Need to record that it hasn't been written yet, before we attempt to do
1368         // anything with it.
1369         piece.incrementPendingWrites()
1370         // Record that we have the chunk, so we aren't trying to download it while
1371         // waiting for it to be written to storage.
1372         piece.unpendChunkIndex(chunkIndex(req.chunkSpec, t.chunkSize))
1373
1374         // Cancel pending requests for this chunk.
1375         for c := range t.conns {
1376                 c.postCancel(req)
1377         }
1378
1379         err := func() error {
1380                 cl.unlock()
1381                 defer cl.lock()
1382                 concurrentChunkWrites.Add(1)
1383                 defer concurrentChunkWrites.Add(-1)
1384                 // Write the chunk out. Note that the upper bound on chunk writing
1385                 // concurrency will be the number of connections. We write inline with
1386                 // receiving the chunk (with this lock dance), because we want to
1387                 // handle errors synchronously and I haven't thought of a nice way to
1388                 // defer any concurrency to the storage and have that notify the
1389                 // client of errors. TODO: Do that instead.
1390                 return t.writeChunk(int(msg.Index), int64(msg.Begin), msg.Piece)
1391         }()
1392
1393         piece.decrementPendingWrites()
1394
1395         if err != nil {
1396                 panic(fmt.Sprintf("error writing chunk: %v", err))
1397                 t.pendRequest(req)
1398                 t.updatePieceCompletion(pieceIndex(msg.Index))
1399                 return nil
1400         }
1401
1402         // It's important that the piece is potentially queued before we check if
1403         // the piece is still wanted, because if it is queued, it won't be wanted.
1404         if t.pieceAllDirty(pieceIndex(req.Index)) {
1405                 t.queuePieceCheck(pieceIndex(req.Index))
1406                 t.pendAllChunkSpecs(pieceIndex(req.Index))
1407         }
1408
1409         c.onDirtiedPiece(pieceIndex(req.Index))
1410
1411         cl.event.Broadcast()
1412         t.publishPieceChange(pieceIndex(req.Index))
1413
1414         return nil
1415 }
1416
1417 func (c *connection) onDirtiedPiece(piece pieceIndex) {
1418         if c.peerTouchedPieces == nil {
1419                 c.peerTouchedPieces = make(map[pieceIndex]struct{})
1420         }
1421         c.peerTouchedPieces[piece] = struct{}{}
1422         ds := &c.t.pieces[piece].dirtiers
1423         if *ds == nil {
1424                 *ds = make(map[*connection]struct{})
1425         }
1426         (*ds)[c] = struct{}{}
1427 }
1428
1429 func (c *connection) uploadAllowed() bool {
1430         if c.t.cl.config.NoUpload {
1431                 return false
1432         }
1433         if c.t.seeding() {
1434                 return true
1435         }
1436         if !c.peerHasWantedPieces() {
1437                 return false
1438         }
1439         // Don't upload more than 100 KiB more than we download.
1440         if c._stats.BytesWrittenData.Int64() >= c._stats.BytesReadData.Int64()+100<<10 {
1441                 return false
1442         }
1443         return true
1444 }
1445
1446 func (c *connection) setRetryUploadTimer(delay time.Duration) {
1447         if c.uploadTimer == nil {
1448                 c.uploadTimer = time.AfterFunc(delay, c.writerCond.Broadcast)
1449         } else {
1450                 c.uploadTimer.Reset(delay)
1451         }
1452 }
1453
1454 // Also handles choking and unchoking of the remote peer.
1455 func (c *connection) upload(msg func(pp.Message) bool) bool {
1456         // Breaking or completing this loop means we don't want to upload to the
1457         // peer anymore, and we choke them.
1458 another:
1459         for c.uploadAllowed() {
1460                 // We want to upload to the peer.
1461                 if !c.Unchoke(msg) {
1462                         return false
1463                 }
1464                 for r := range c.PeerRequests {
1465                         res := c.t.cl.config.UploadRateLimiter.ReserveN(time.Now(), int(r.Length))
1466                         if !res.OK() {
1467                                 panic(fmt.Sprintf("upload rate limiter burst size < %d", r.Length))
1468                         }
1469                         delay := res.Delay()
1470                         if delay > 0 {
1471                                 res.Cancel()
1472                                 c.setRetryUploadTimer(delay)
1473                                 // Hard to say what to return here.
1474                                 return true
1475                         }
1476                         more, err := c.sendChunk(r, msg)
1477                         if err != nil {
1478                                 i := pieceIndex(r.Index)
1479                                 if c.t.pieceComplete(i) {
1480                                         c.t.updatePieceCompletion(i)
1481                                         if !c.t.pieceComplete(i) {
1482                                                 // We had the piece, but not anymore.
1483                                                 break another
1484                                         }
1485                                 }
1486                                 log.Str("error sending chunk to peer").AddValues(c, r, err).Log(c.t.logger)
1487                                 // If we failed to send a chunk, choke the peer to ensure they
1488                                 // flush all their requests. We've probably dropped a piece,
1489                                 // but there's no way to communicate this to the peer. If they
1490                                 // ask for it again, we'll kick them to allow us to send them
1491                                 // an updated bitfield.
1492                                 break another
1493                         }
1494                         delete(c.PeerRequests, r)
1495                         if !more {
1496                                 return false
1497                         }
1498                         goto another
1499                 }
1500                 return true
1501         }
1502         return c.Choke(msg)
1503 }
1504
1505 func (cn *connection) Drop() {
1506         cn.t.dropConnection(cn)
1507 }
1508
1509 func (cn *connection) netGoodPiecesDirtied() int64 {
1510         return cn._stats.PiecesDirtiedGood.Int64() - cn._stats.PiecesDirtiedBad.Int64()
1511 }
1512
1513 func (c *connection) peerHasWantedPieces() bool {
1514         return !c._pieceRequestOrder.IsEmpty()
1515 }
1516
1517 func (c *connection) numLocalRequests() int {
1518         return len(c.requests)
1519 }
1520
1521 func (c *connection) deleteRequest(r request) bool {
1522         if _, ok := c.requests[r]; !ok {
1523                 return false
1524         }
1525         delete(c.requests, r)
1526         c.updateExpectingChunks()
1527         if t, ok := c.t.lastRequested[r]; ok {
1528                 t.Stop()
1529                 delete(c.t.lastRequested, r)
1530         }
1531         pr := c.t.pendingRequests
1532         pr[r]--
1533         n := pr[r]
1534         if n == 0 {
1535                 delete(pr, r)
1536         }
1537         if n < 0 {
1538                 panic(n)
1539         }
1540         c.updateRequests()
1541         for _c := range c.t.conns {
1542                 if !_c.Interested && _c != c && c.PeerHasPiece(pieceIndex(r.Index)) {
1543                         _c.updateRequests()
1544                 }
1545         }
1546         return true
1547 }
1548
1549 func (c *connection) deleteAllRequests() {
1550         for r := range c.requests {
1551                 c.deleteRequest(r)
1552         }
1553         if len(c.requests) != 0 {
1554                 panic(len(c.requests))
1555         }
1556         // for c := range c.t.conns {
1557         //      c.tickleWriter()
1558         // }
1559 }
1560
1561 func (c *connection) tickleWriter() {
1562         c.writerCond.Broadcast()
1563 }
1564
1565 func (c *connection) postCancel(r request) bool {
1566         if !c.deleteRequest(r) {
1567                 return false
1568         }
1569         c.Post(makeCancelMessage(r))
1570         return true
1571 }
1572
1573 func (c *connection) sendChunk(r request, msg func(pp.Message) bool) (more bool, err error) {
1574         // Count the chunk being sent, even if it isn't.
1575         b := make([]byte, r.Length)
1576         p := c.t.info.Piece(int(r.Index))
1577         n, err := c.t.readAt(b, p.Offset()+int64(r.Begin))
1578         if n != len(b) {
1579                 if err == nil {
1580                         panic("expected error")
1581                 }
1582                 return
1583         } else if err == io.EOF {
1584                 err = nil
1585         }
1586         more = msg(pp.Message{
1587                 Type:  pp.Piece,
1588                 Index: r.Index,
1589                 Begin: r.Begin,
1590                 Piece: b,
1591         })
1592         c.lastChunkSent = time.Now()
1593         return
1594 }
1595
1596 func (c *connection) setTorrent(t *Torrent) {
1597         if c.t != nil {
1598                 panic("connection already associated with a torrent")
1599         }
1600         c.t = t
1601         c.logger.Printf("torrent=%v", t)
1602         t.reconcileHandshakeStats(c)
1603 }
1604
1605 func (c *connection) peerPriority() peerPriority {
1606         return bep40PriorityIgnoreError(c.remoteIpPort(), c.t.cl.publicAddr(c.remoteIp()))
1607 }
1608
1609 func (c *connection) remoteIp() net.IP {
1610         return c.remoteAddr.IP
1611 }
1612
1613 func (c *connection) remoteIpPort() IpPort {
1614         return c.remoteAddr
1615 }
1616
1617 func (c *connection) String() string {
1618         return fmt.Sprintf("connection %p", c)
1619 }
1620
1621 func (c *connection) trust() connectionTrust {
1622         return connectionTrust{c.trusted, c.netGoodPiecesDirtied()}
1623 }
1624
1625 type connectionTrust struct {
1626         Implicit            bool
1627         NetGoodPiecesDirted int64
1628 }
1629
1630 func (l connectionTrust) Less(r connectionTrust) bool {
1631         return multiless.New().Bool(l.Implicit, r.Implicit).Int64(l.NetGoodPiecesDirted, r.NetGoodPiecesDirted).Less()
1632 }
1633
1634 func (cn *connection) requestStrategyConnection() requestStrategyConnection {
1635         return cn
1636 }
1637
1638 func (cn *connection) chunksReceivedWhileExpecting() int64 {
1639         return cn._chunksReceivedWhileExpecting
1640 }
1641
1642 func (cn *connection) fastest() bool {
1643         return cn == cn.t.fastestConn
1644 }
1645
1646 func (cn *connection) peerMaxRequests() int {
1647         return cn.PeerMaxRequests
1648 }
1649
1650 func (cn *connection) peerPieces() bitmap.Bitmap {
1651         ret := cn._peerPieces.Copy()
1652         if cn.peerSentHaveAll {
1653                 ret.AddRange(0, cn.t.numPieces())
1654         }
1655         return ret
1656 }
1657
1658 func (cn *connection) pieceRequestOrder() *prioritybitmap.PriorityBitmap {
1659         return &cn._pieceRequestOrder
1660 }
1661
1662 func (cn *connection) stats() *ConnStats {
1663         return &cn._stats
1664 }
1665
1666 func (cn *connection) torrent() requestStrategyTorrent {
1667         return cn.t.requestStrategyTorrent()
1668 }