client.go

   1 package torrent
   2
   3 import (
   4         "bufio"
   5         "bytes"
   6         "crypto/rand"
   7         "encoding/hex"
   8         "errors"
   9         "fmt"
  10         "io"
  11         "log"
  12         mathRand "math/rand"
  13         "net"
  14         "net/url"
  15         "strconv"
  16         "strings"
  17         "time"
  18
  19         "github.com/anacrolix/missinggo"
  20         "github.com/anacrolix/missinggo/pproffd"
  21         "github.com/anacrolix/missinggo/pubsub"
  22         "github.com/anacrolix/missinggo/slices"
  23         "github.com/anacrolix/sync"
  24         "github.com/anacrolix/utp"
  25         "github.com/dustin/go-humanize"
  26
  27         "github.com/anacrolix/torrent/bencode"
  28         "github.com/anacrolix/torrent/dht"
  29         "github.com/anacrolix/torrent/dht/krpc"
  30         "github.com/anacrolix/torrent/iplist"
  31         "github.com/anacrolix/torrent/metainfo"
  32         "github.com/anacrolix/torrent/mse"
  33         pp "github.com/anacrolix/torrent/peer_protocol"
  34         "github.com/anacrolix/torrent/storage"
  35 )
  36
  37 // Currently doesn't really queue, but should in the future.
  38 func (cl *Client) queuePieceCheck(t *Torrent, pieceIndex int) {
  39         piece := &t.pieces[pieceIndex]
  40         if piece.QueuedForHash {
  41                 return
  42         }
  43         piece.QueuedForHash = true
  44         t.publishPieceChange(pieceIndex)
  45         go cl.verifyPiece(t, pieceIndex)
  46 }
  47
  48 // Queue a piece check if one isn't already queued, and the piece has never
  49 // been checked before.
  50 func (cl *Client) queueFirstHash(t *Torrent, piece int) {
  51         p := &t.pieces[piece]
  52         if p.EverHashed || p.Hashing || p.QueuedForHash || t.pieceComplete(piece) {
  53                 return
  54         }
  55         cl.queuePieceCheck(t, piece)
  56 }
  57
  58 // Clients contain zero or more Torrents. A Client manages a blocklist, the
  59 // TCP/UDP protocol ports, and DHT as desired.
  60 type Client struct {
  61         halfOpenLimit int
  62         peerID        [20]byte
  63         // The net.Addr.String part that should be common to all active listeners.
  64         listenAddr     string
  65         tcpListener    net.Listener
  66         utpSock        *utp.Socket
  67         dHT            *dht.Server
  68         ipBlockList    iplist.Ranger
  69         config         Config
  70         extensionBytes peerExtensionBytes
  71         // Set of addresses that have our client ID. This intentionally will
  72         // include ourselves if we end up trying to connect to our own address
  73         // through legitimate channels.
  74         dopplegangerAddrs map[string]struct{}
  75         badPeerIPs        map[string]struct{}
  76
  77         defaultStorage storage.Client
  78
  79         mu     sync.RWMutex
  80         event  sync.Cond
  81         closed missinggo.Event
  82
  83         torrents map[metainfo.Hash]*Torrent
  84 }
  85
  86 func (cl *Client) BadPeerIPs() []string {
  87         cl.mu.RLock()
  88         defer cl.mu.RUnlock()
  89         return slices.FromMapKeys(cl.badPeerIPs).([]string)
  90 }
  91
  92 func (cl *Client) IPBlockList() iplist.Ranger {
  93         cl.mu.Lock()
  94         defer cl.mu.Unlock()
  95         return cl.ipBlockList
  96 }
  97
  98 func (cl *Client) SetIPBlockList(list iplist.Ranger) {
  99         cl.mu.Lock()
 100         defer cl.mu.Unlock()
 101         cl.ipBlockList = list
 102         if cl.dHT != nil {
 103                 cl.dHT.SetIPBlockList(list)
 104         }
 105 }
 106
 107 func (cl *Client) PeerID() string {
 108         return string(cl.peerID[:])
 109 }
 110
 111 type torrentAddr string
 112
 113 func (me torrentAddr) Network() string { return "" }
 114
 115 func (me torrentAddr) String() string { return string(me) }
 116
 117 func (cl *Client) ListenAddr() net.Addr {
 118         if cl.listenAddr == "" {
 119                 return nil
 120         }
 121         return torrentAddr(cl.listenAddr)
 122 }
 123
 124 func (cl *Client) sortedTorrents() (ret []*Torrent) {
 125         return slices.Sort(slices.FromMapElems(cl.torrents), func(l, r metainfo.Hash) bool {
 126                 return l.AsString() < r.AsString()
 127         }).([]*Torrent)
 128 }
 129
 130 // Writes out a human readable status of the client, such as for writing to a
 131 // HTTP status page.
 132 func (cl *Client) WriteStatus(_w io.Writer) {
 133         w := bufio.NewWriter(_w)
 134         defer w.Flush()
 135         if addr := cl.ListenAddr(); addr != nil {
 136                 fmt.Fprintf(w, "Listening on %s\n", addr)
 137         } else {
 138                 fmt.Fprintln(w, "Not listening!")
 139         }
 140         fmt.Fprintf(w, "Peer ID: %+q\n", cl.PeerID())
 141         fmt.Fprintf(w, "Banned IPs: %d\n", len(cl.BadPeerIPs()))
 142         if dht := cl.DHT(); dht != nil {
 143                 dhtStats := dht.Stats()
 144                 fmt.Fprintf(w, "DHT nodes: %d (%d good, %d banned)\n", dhtStats.Nodes, dhtStats.GoodNodes, dhtStats.BadNodes)
 145                 fmt.Fprintf(w, "DHT Server ID: %x\n", dht.ID())
 146                 fmt.Fprintf(w, "DHT port: %d\n", missinggo.AddrPort(dht.Addr()))
 147                 fmt.Fprintf(w, "DHT announces: %d\n", dhtStats.ConfirmedAnnounces)
 148                 fmt.Fprintf(w, "Outstanding transactions: %d\n", dhtStats.OutstandingTransactions)
 149         }
 150         fmt.Fprintf(w, "# Torrents: %d\n", len(cl.Torrents()))
 151         fmt.Fprintln(w)
 152         for _, t := range slices.Sort(append([]*Torrent(nil), cl.Torrents()...), func(l, r *Torrent) bool {
 153                 return l.InfoHash().AsString() < r.InfoHash().AsString()
 154         }).([]*Torrent) {
 155                 if t.Name() == "" {
 156                         fmt.Fprint(w, "<unknown name>")
 157                 } else {
 158                         fmt.Fprint(w, t.Name())
 159                 }
 160                 fmt.Fprint(w, "\n")
 161                 if t.Info() != nil {
 162                         fmt.Fprintf(w, "%f%% of %d bytes (%s)", 100*(1-float64(t.BytesMissing())/float64(t.Info().TotalLength())), t.length, humanize.Bytes(uint64(t.Info().TotalLength())))
 163                 } else {
 164                         w.WriteString("<missing metainfo>")
 165                 }
 166                 fmt.Fprint(w, "\n")
 167                 t.writeStatus(w)
 168                 fmt.Fprintln(w)
 169         }
 170 }
 171
 172 func listenUTP(networkSuffix, addr string) (*utp.Socket, error) {
 173         return utp.NewSocket("udp"+networkSuffix, addr)
 174 }
 175
 176 func listenTCP(networkSuffix, addr string) (net.Listener, error) {
 177         return net.Listen("tcp"+networkSuffix, addr)
 178 }
 179
 180 func listenBothSameDynamicPort(networkSuffix, host string) (tcpL net.Listener, utpSock *utp.Socket, listenedAddr string, err error) {
 181         for {
 182                 tcpL, err = listenTCP(networkSuffix, net.JoinHostPort(host, "0"))
 183                 if err != nil {
 184                         return
 185                 }
 186                 listenedAddr = tcpL.Addr().String()
 187                 utpSock, err = listenUTP(networkSuffix, listenedAddr)
 188                 if err == nil {
 189                         return
 190                 }
 191                 tcpL.Close()
 192                 if !strings.Contains(err.Error(), "address already in use") {
 193                         return
 194                 }
 195         }
 196 }
 197
 198 // Listen to enabled protocols, ensuring ports match.
 199 func listen(tcp, utp bool, networkSuffix, addr string) (tcpL net.Listener, utpSock *utp.Socket, listenedAddr string, err error) {
 200         if addr == "" {
 201                 addr = ":50007"
 202         }
 203         if tcp && utp {
 204                 var host string
 205                 var port int
 206                 host, port, err = missinggo.ParseHostPort(addr)
 207                 if err != nil {
 208                         return
 209                 }
 210                 if port == 0 {
 211                         // If both protocols are active, they need to have the same port.
 212                         return listenBothSameDynamicPort(networkSuffix, host)
 213                 }
 214         }
 215         defer func() {
 216                 if err != nil {
 217                         listenedAddr = ""
 218                 }
 219         }()
 220         if tcp {
 221                 tcpL, err = listenTCP(networkSuffix, addr)
 222                 if err != nil {
 223                         return
 224                 }
 225                 defer func() {
 226                         if err != nil {
 227                                 tcpL.Close()
 228                         }
 229                 }()
 230                 listenedAddr = tcpL.Addr().String()
 231         }
 232         if utp {
 233                 utpSock, err = listenUTP(networkSuffix, addr)
 234                 if err != nil {
 235                         return
 236                 }
 237                 listenedAddr = utpSock.Addr().String()
 238         }
 239         return
 240 }
 241
 242 // Creates a new client.
 243 func NewClient(cfg *Config) (cl *Client, err error) {
 244         if cfg == nil {
 245                 cfg = &Config{}
 246         }
 247
 248         defer func() {
 249                 if err != nil {
 250                         cl = nil
 251                 }
 252         }()
 253         cl = &Client{
 254                 halfOpenLimit:     defaultHalfOpenConnsPerTorrent,
 255                 config:            *cfg,
 256                 defaultStorage:    cfg.DefaultStorage,
 257                 dopplegangerAddrs: make(map[string]struct{}),
 258                 torrents:          make(map[metainfo.Hash]*Torrent),
 259         }
 260         missinggo.CopyExact(&cl.extensionBytes, defaultExtensionBytes)
 261         cl.event.L = &cl.mu
 262         if cl.defaultStorage == nil {
 263                 cl.defaultStorage = storage.NewFile(cfg.DataDir)
 264         }
 265         if cfg.IPBlocklist != nil {
 266                 cl.ipBlockList = cfg.IPBlocklist
 267         }
 268
 269         if cfg.PeerID != "" {
 270                 missinggo.CopyExact(&cl.peerID, cfg.PeerID)
 271         } else {
 272                 o := copy(cl.peerID[:], bep20)
 273                 _, err = rand.Read(cl.peerID[o:])
 274                 if err != nil {
 275                         panic("error generating peer id")
 276                 }
 277         }
 278
 279         cl.tcpListener, cl.utpSock, cl.listenAddr, err = listen(
 280                 !cl.config.DisableTCP,
 281                 !cl.config.DisableUTP,
 282                 func() string {
 283                         if cl.config.DisableIPv6 {
 284                                 return "4"
 285                         } else {
 286                                 return ""
 287                         }
 288                 }(),
 289                 cl.config.ListenAddr)
 290         if err != nil {
 291                 return
 292         }
 293         if cl.tcpListener != nil {
 294                 go cl.acceptConnections(cl.tcpListener, false)
 295         }
 296         if cl.utpSock != nil {
 297                 go cl.acceptConnections(cl.utpSock, true)
 298         }
 299         if !cfg.NoDHT {
 300                 dhtCfg := cfg.DHTConfig
 301                 if dhtCfg.IPBlocklist == nil {
 302                         dhtCfg.IPBlocklist = cl.ipBlockList
 303                 }
 304                 dhtCfg.Addr = firstNonEmptyString(dhtCfg.Addr, cl.listenAddr, cl.config.ListenAddr)
 305                 if dhtCfg.Conn == nil && cl.utpSock != nil {
 306                         dhtCfg.Conn = cl.utpSock
 307                 }
 308                 cl.dHT, err = dht.NewServer(&dhtCfg)
 309                 if err != nil {
 310                         return
 311                 }
 312         }
 313
 314         return
 315 }
 316
 317 func firstNonEmptyString(ss ...string) string {
 318         for _, s := range ss {
 319                 if s != "" {
 320                         return s
 321                 }
 322         }
 323         return ""
 324 }
 325
 326 // Stops the client. All connections to peers are closed and all activity will
 327 // come to a halt.
 328 func (cl *Client) Close() {
 329         cl.mu.Lock()
 330         defer cl.mu.Unlock()
 331         cl.closed.Set()
 332         if cl.dHT != nil {
 333                 cl.dHT.Close()
 334         }
 335         if cl.utpSock != nil {
 336                 cl.utpSock.CloseNow()
 337         }
 338         if cl.tcpListener != nil {
 339                 cl.tcpListener.Close()
 340         }
 341         for _, t := range cl.torrents {
 342                 t.close()
 343         }
 344         cl.event.Broadcast()
 345 }
 346
 347 var ipv6BlockRange = iplist.Range{Description: "non-IPv4 address"}
 348
 349 func (cl *Client) ipBlockRange(ip net.IP) (r iplist.Range, blocked bool) {
 350         if cl.ipBlockList == nil {
 351                 return
 352         }
 353         ip4 := ip.To4()
 354         // If blocklists are enabled, then block non-IPv4 addresses, because
 355         // blocklists do not yet support IPv6.
 356         if ip4 == nil {
 357                 if missinggo.CryHeard() {
 358                         log.Printf("blocking non-IPv4 address: %s", ip)
 359                 }
 360                 r = ipv6BlockRange
 361                 blocked = true
 362                 return
 363         }
 364         return cl.ipBlockList.Lookup(ip4)
 365 }
 366
 367 func (cl *Client) waitAccept() {
 368         for {
 369                 for _, t := range cl.torrents {
 370                         if t.wantConns() {
 371                                 return
 372                         }
 373                 }
 374                 if cl.closed.IsSet() {
 375                         return
 376                 }
 377                 cl.event.Wait()
 378         }
 379 }
 380
 381 func (cl *Client) acceptConnections(l net.Listener, utp bool) {
 382         cl.mu.Lock()
 383         defer cl.mu.Unlock()
 384         for {
 385                 cl.waitAccept()
 386                 cl.mu.Unlock()
 387                 conn, err := l.Accept()
 388                 conn = pproffd.WrapNetConn(conn)
 389                 cl.mu.Lock()
 390                 if cl.closed.IsSet() {
 391                         if conn != nil {
 392                                 conn.Close()
 393                         }
 394                         return
 395                 }
 396                 if err != nil {
 397                         log.Print(err)
 398                         // I think something harsher should happen here? Our accept
 399                         // routine just fucked off.
 400                         return
 401                 }
 402                 if utp {
 403                         acceptUTP.Add(1)
 404                 } else {
 405                         acceptTCP.Add(1)
 406                 }
 407                 reject := cl.badPeerIPPort(
 408                         missinggo.AddrIP(conn.RemoteAddr()),
 409                         missinggo.AddrPort(conn.RemoteAddr()))
 410                 if reject {
 411                         acceptReject.Add(1)
 412                         conn.Close()
 413                         continue
 414                 }
 415                 go cl.incomingConnection(conn, utp)
 416         }
 417 }
 418
 419 func (cl *Client) incomingConnection(nc net.Conn, utp bool) {
 420         defer nc.Close()
 421         if tc, ok := nc.(*net.TCPConn); ok {
 422                 tc.SetLinger(0)
 423         }
 424         c := newConnection(nc, &cl.mu)
 425         c.Discovery = peerSourceIncoming
 426         c.uTP = utp
 427         cl.runReceivedConn(c)
 428 }
 429
 430 // Returns a handle to the given torrent, if it's present in the client.
 431 func (cl *Client) Torrent(ih metainfo.Hash) (t *Torrent, ok bool) {
 432         cl.mu.Lock()
 433         defer cl.mu.Unlock()
 434         t, ok = cl.torrents[ih]
 435         return
 436 }
 437
 438 func (cl *Client) torrent(ih metainfo.Hash) *Torrent {
 439         return cl.torrents[ih]
 440 }
 441
 442 type dialResult struct {
 443         Conn net.Conn
 444         UTP  bool
 445 }
 446
 447 func doDial(dial func(addr string, t *Torrent) (net.Conn, error), ch chan dialResult, utp bool, addr string, t *Torrent) {
 448         conn, err := dial(addr, t)
 449         if err != nil {
 450                 if conn != nil {
 451                         conn.Close()
 452                 }
 453                 conn = nil // Pedantic
 454         }
 455         ch <- dialResult{conn, utp}
 456         if err == nil {
 457                 successfulDials.Add(1)
 458                 return
 459         }
 460         unsuccessfulDials.Add(1)
 461 }
 462
 463 func reducedDialTimeout(max time.Duration, halfOpenLimit int, pendingPeers int) (ret time.Duration) {
 464         ret = max / time.Duration((pendingPeers+halfOpenLimit)/halfOpenLimit)
 465         if ret < minDialTimeout {
 466                 ret = minDialTimeout
 467         }
 468         return
 469 }
 470
 471 // Returns whether an address is known to connect to a client with our own ID.
 472 func (cl *Client) dopplegangerAddr(addr string) bool {
 473         _, ok := cl.dopplegangerAddrs[addr]
 474         return ok
 475 }
 476
 477 // Start the process of connecting to the given peer for the given torrent if
 478 // appropriate.
 479 func (cl *Client) initiateConn(peer Peer, t *Torrent) {
 480         if peer.Id == cl.peerID {
 481                 return
 482         }
 483         if cl.badPeerIPPort(peer.IP, peer.Port) {
 484                 return
 485         }
 486         addr := net.JoinHostPort(peer.IP.String(), fmt.Sprintf("%d", peer.Port))
 487         if t.addrActive(addr) {
 488                 return
 489         }
 490         t.halfOpen[addr] = struct{}{}
 491         go cl.outgoingConnection(t, addr, peer.Source)
 492 }
 493
 494 func (cl *Client) dialTimeout(t *Torrent) time.Duration {
 495         cl.mu.Lock()
 496         pendingPeers := len(t.peers)
 497         cl.mu.Unlock()
 498         return reducedDialTimeout(nominalDialTimeout, cl.halfOpenLimit, pendingPeers)
 499 }
 500
 501 func (cl *Client) dialTCP(addr string, t *Torrent) (c net.Conn, err error) {
 502         c, err = net.DialTimeout("tcp", addr, cl.dialTimeout(t))
 503         if err == nil {
 504                 c.(*net.TCPConn).SetLinger(0)
 505         }
 506         c = pproffd.WrapNetConn(c)
 507         return
 508 }
 509
 510 func (cl *Client) dialUTP(addr string, t *Torrent) (c net.Conn, err error) {
 511         return cl.utpSock.DialTimeout(addr, cl.dialTimeout(t))
 512 }
 513
 514 // Returns a connection over UTP or TCP, whichever is first to connect.
 515 func (cl *Client) dialFirst(addr string, t *Torrent) (conn net.Conn, utp bool) {
 516         // Initiate connections via TCP and UTP simultaneously. Use the first one
 517         // that succeeds.
 518         left := 0
 519         if !cl.config.DisableUTP {
 520                 left++
 521         }
 522         if !cl.config.DisableTCP {
 523                 left++
 524         }
 525         resCh := make(chan dialResult, left)
 526         if !cl.config.DisableUTP {
 527                 go doDial(cl.dialUTP, resCh, true, addr, t)
 528         }
 529         if !cl.config.DisableTCP {
 530                 go doDial(cl.dialTCP, resCh, false, addr, t)
 531         }
 532         var res dialResult
 533         // Wait for a successful connection.
 534         for ; left > 0 && res.Conn == nil; left-- {
 535                 res = <-resCh
 536         }
 537         if left > 0 {
 538                 // There are still incompleted dials.
 539                 go func() {
 540                         for ; left > 0; left-- {
 541                                 conn := (<-resCh).Conn
 542                                 if conn != nil {
 543                                         conn.Close()
 544                                 }
 545                         }
 546                 }()
 547         }
 548         conn = res.Conn
 549         utp = res.UTP
 550         return
 551 }
 552
 553 func (cl *Client) noLongerHalfOpen(t *Torrent, addr string) {
 554         if _, ok := t.halfOpen[addr]; !ok {
 555                 panic("invariant broken")
 556         }
 557         delete(t.halfOpen, addr)
 558         cl.openNewConns(t)
 559 }
 560
 561 // Performs initiator handshakes and returns a connection. Returns nil
 562 // *connection if no connection for valid reasons.
 563 func (cl *Client) handshakesConnection(nc net.Conn, t *Torrent, encrypted, utp bool) (c *connection, err error) {
 564         c = newConnection(nc, &cl.mu)
 565         c.encrypted = encrypted
 566         c.uTP = utp
 567         err = nc.SetDeadline(time.Now().Add(handshakesTimeout))
 568         if err != nil {
 569                 return
 570         }
 571         ok, err := cl.initiateHandshakes(c, t)
 572         if !ok {
 573                 c = nil
 574         }
 575         return
 576 }
 577
 578 // Returns nil connection and nil error if no connection could be established
 579 // for valid reasons.
 580 func (cl *Client) establishOutgoingConn(t *Torrent, addr string) (c *connection, err error) {
 581         nc, utp := cl.dialFirst(addr, t)
 582         if nc == nil {
 583                 return
 584         }
 585         c, err = cl.handshakesConnection(nc, t, !cl.config.DisableEncryption, utp)
 586         if err != nil {
 587                 nc.Close()
 588                 return
 589         } else if c != nil {
 590                 return
 591         }
 592         nc.Close()
 593         if cl.config.DisableEncryption {
 594                 // We already tried without encryption.
 595                 return
 596         }
 597         // Try again without encryption, using whichever protocol type worked last
 598         // time.
 599         if utp {
 600                 nc, err = cl.dialUTP(addr, t)
 601         } else {
 602                 nc, err = cl.dialTCP(addr, t)
 603         }
 604         if err != nil {
 605                 err = fmt.Errorf("error dialing for unencrypted connection: %s", err)
 606                 return
 607         }
 608         c, err = cl.handshakesConnection(nc, t, false, utp)
 609         if err != nil || c == nil {
 610                 nc.Close()
 611         }
 612         return
 613 }
 614
 615 // Called to dial out and run a connection. The addr we're given is already
 616 // considered half-open.
 617 func (cl *Client) outgoingConnection(t *Torrent, addr string, ps peerSource) {
 618         c, err := cl.establishOutgoingConn(t, addr)
 619         cl.mu.Lock()
 620         defer cl.mu.Unlock()
 621         // Don't release lock between here and addConnection, unless it's for
 622         // failure.
 623         cl.noLongerHalfOpen(t, addr)
 624         if err != nil {
 625                 if cl.config.Debug {
 626                         log.Printf("error establishing outgoing connection: %s", err)
 627                 }
 628                 return
 629         }
 630         if c == nil {
 631                 return
 632         }
 633         defer c.Close()
 634         c.Discovery = ps
 635         cl.runInitiatedHandshookConn(c, t)
 636 }
 637
 638 // The port number for incoming peer connections. 0 if the client isn't
 639 // listening.
 640 func (cl *Client) incomingPeerPort() int {
 641         if cl.listenAddr == "" {
 642                 return 0
 643         }
 644         _, port, err := missinggo.ParseHostPort(cl.listenAddr)
 645         if err != nil {
 646                 panic(err)
 647         }
 648         return port
 649 }
 650
 651 // Convert a net.Addr to its compact IP representation. Either 4 or 16 bytes
 652 // per "yourip" field of http://www.bittorrent.org/beps/bep_0010.html.
 653 func addrCompactIP(addr net.Addr) (string, error) {
 654         host, _, err := net.SplitHostPort(addr.String())
 655         if err != nil {
 656                 return "", err
 657         }
 658         ip := net.ParseIP(host)
 659         if v4 := ip.To4(); v4 != nil {
 660                 if len(v4) != 4 {
 661                         panic(v4)
 662                 }
 663                 return string(v4), nil
 664         }
 665         return string(ip.To16()), nil
 666 }
 667
 668 func handshakeWriter(w io.Writer, bb <-chan []byte, done chan<- error) {
 669         var err error
 670         for b := range bb {
 671                 _, err = w.Write(b)
 672                 if err != nil {
 673                         break
 674                 }
 675         }
 676         done <- err
 677 }
 678
 679 type (
 680         peerExtensionBytes [8]byte
 681         peerID             [20]byte
 682 )
 683
 684 func (pex *peerExtensionBytes) SupportsExtended() bool {
 685         return pex[5]&0x10 != 0
 686 }
 687
 688 func (pex *peerExtensionBytes) SupportsDHT() bool {
 689         return pex[7]&0x01 != 0
 690 }
 691
 692 func (pex *peerExtensionBytes) SupportsFast() bool {
 693         return pex[7]&0x04 != 0
 694 }
 695
 696 type handshakeResult struct {
 697         peerExtensionBytes
 698         peerID
 699         metainfo.Hash
 700 }
 701
 702 // ih is nil if we expect the peer to declare the InfoHash, such as when the
 703 // peer initiated the connection. Returns ok if the handshake was successful,
 704 // and err if there was an unexpected condition other than the peer simply
 705 // abandoning the handshake.
 706 func handshake(sock io.ReadWriter, ih *metainfo.Hash, peerID [20]byte, extensions peerExtensionBytes) (res handshakeResult, ok bool, err error) {
 707         // Bytes to be sent to the peer. Should never block the sender.
 708         postCh := make(chan []byte, 4)
 709         // A single error value sent when the writer completes.
 710         writeDone := make(chan error, 1)
 711         // Performs writes to the socket and ensures posts don't block.
 712         go handshakeWriter(sock, postCh, writeDone)
 713
 714         defer func() {
 715                 close(postCh) // Done writing.
 716                 if !ok {
 717                         return
 718                 }
 719                 if err != nil {
 720                         panic(err)
 721                 }
 722                 // Wait until writes complete before returning from handshake.
 723                 err = <-writeDone
 724                 if err != nil {
 725                         err = fmt.Errorf("error writing: %s", err)
 726                 }
 727         }()
 728
 729         post := func(bb []byte) {
 730                 select {
 731                 case postCh <- bb:
 732                 default:
 733                         panic("mustn't block while posting")
 734                 }
 735         }
 736
 737         post([]byte(pp.Protocol))
 738         post(extensions[:])
 739         if ih != nil { // We already know what we want.
 740                 post(ih[:])
 741                 post(peerID[:])
 742         }
 743         var b [68]byte
 744         _, err = io.ReadFull(sock, b[:68])
 745         if err != nil {
 746                 err = nil
 747                 return
 748         }
 749         if string(b[:20]) != pp.Protocol {
 750                 return
 751         }
 752         missinggo.CopyExact(&res.peerExtensionBytes, b[20:28])
 753         missinggo.CopyExact(&res.Hash, b[28:48])
 754         missinggo.CopyExact(&res.peerID, b[48:68])
 755         peerExtensions.Add(hex.EncodeToString(res.peerExtensionBytes[:]), 1)
 756
 757         // TODO: Maybe we can just drop peers here if we're not interested. This
 758         // could prevent them trying to reconnect, falsely believing there was
 759         // just a problem.
 760         if ih == nil { // We were waiting for the peer to tell us what they wanted.
 761                 post(res.Hash[:])
 762                 post(peerID[:])
 763         }
 764
 765         ok = true
 766         return
 767 }
 768
 769 // Wraps a raw connection and provides the interface we want for using the
 770 // connection in the message loop.
 771 type deadlineReader struct {
 772         nc net.Conn
 773         r  io.Reader
 774 }
 775
 776 func (r deadlineReader) Read(b []byte) (n int, err error) {
 777         // Keep-alives should be received every 2 mins. Give a bit of gracetime.
 778         err = r.nc.SetReadDeadline(time.Now().Add(150 * time.Second))
 779         if err != nil {
 780                 err = fmt.Errorf("error setting read deadline: %s", err)
 781         }
 782         n, err = r.r.Read(b)
 783         // Convert common errors into io.EOF.
 784         // if err != nil {
 785         //      if opError, ok := err.(*net.OpError); ok && opError.Op == "read" && opError.Err == syscall.ECONNRESET {
 786         //              err = io.EOF
 787         //      } else if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
 788         //              if n != 0 {
 789         //                      panic(n)
 790         //              }
 791         //              err = io.EOF
 792         //      }
 793         // }
 794         return
 795 }
 796
 797 type readWriter struct {
 798         io.Reader
 799         io.Writer
 800 }
 801
 802 func maybeReceiveEncryptedHandshake(rw io.ReadWriter, skeys [][]byte) (ret io.ReadWriter, encrypted bool, err error) {
 803         var protocol [len(pp.Protocol)]byte
 804         _, err = io.ReadFull(rw, protocol[:])
 805         if err != nil {
 806                 return
 807         }
 808         ret = readWriter{
 809                 io.MultiReader(bytes.NewReader(protocol[:]), rw),
 810                 rw,
 811         }
 812         if string(protocol[:]) == pp.Protocol {
 813                 return
 814         }
 815         encrypted = true
 816         ret, err = mse.ReceiveHandshake(ret, skeys)
 817         return
 818 }
 819
 820 func (cl *Client) receiveSkeys() (ret [][]byte) {
 821         for ih := range cl.torrents {
 822                 ret = append(ret, ih[:])
 823         }
 824         return
 825 }
 826
 827 func (cl *Client) initiateHandshakes(c *connection, t *Torrent) (ok bool, err error) {
 828         if c.encrypted {
 829                 c.rw, err = mse.InitiateHandshake(c.rw, t.infoHash[:], nil)
 830                 if err != nil {
 831                         return
 832                 }
 833         }
 834         ih, ok, err := cl.connBTHandshake(c, &t.infoHash)
 835         if ih != t.infoHash {
 836                 ok = false
 837         }
 838         return
 839 }
 840
 841 // Do encryption and bittorrent handshakes as receiver.
 842 func (cl *Client) receiveHandshakes(c *connection) (t *Torrent, err error) {
 843         cl.mu.Lock()
 844         skeys := cl.receiveSkeys()
 845         cl.mu.Unlock()
 846         if !cl.config.DisableEncryption {
 847                 c.rw, c.encrypted, err = maybeReceiveEncryptedHandshake(c.rw, skeys)
 848                 if err != nil {
 849                         if err == mse.ErrNoSecretKeyMatch {
 850                                 err = nil
 851                         }
 852                         return
 853                 }
 854         }
 855         ih, ok, err := cl.connBTHandshake(c, nil)
 856         if err != nil {
 857                 err = fmt.Errorf("error during bt handshake: %s", err)
 858                 return
 859         }
 860         if !ok {
 861                 return
 862         }
 863         cl.mu.Lock()
 864         t = cl.torrents[ih]
 865         cl.mu.Unlock()
 866         return
 867 }
 868
 869 // Returns !ok if handshake failed for valid reasons.
 870 func (cl *Client) connBTHandshake(c *connection, ih *metainfo.Hash) (ret metainfo.Hash, ok bool, err error) {
 871         res, ok, err := handshake(c.rw, ih, cl.peerID, cl.extensionBytes)
 872         if err != nil || !ok {
 873                 return
 874         }
 875         ret = res.Hash
 876         c.PeerExtensionBytes = res.peerExtensionBytes
 877         c.PeerID = res.peerID
 878         c.completedHandshake = time.Now()
 879         return
 880 }
 881
 882 func (cl *Client) runInitiatedHandshookConn(c *connection, t *Torrent) {
 883         if c.PeerID == cl.peerID {
 884                 connsToSelf.Add(1)
 885                 addr := c.conn.RemoteAddr().String()
 886                 cl.dopplegangerAddrs[addr] = struct{}{}
 887                 return
 888         }
 889         cl.runHandshookConn(c, t)
 890 }
 891
 892 func (cl *Client) runReceivedConn(c *connection) {
 893         err := c.conn.SetDeadline(time.Now().Add(handshakesTimeout))
 894         if err != nil {
 895                 panic(err)
 896         }
 897         t, err := cl.receiveHandshakes(c)
 898         if err != nil {
 899                 if cl.config.Debug {
 900                         log.Printf("error receiving handshakes: %s", err)
 901                 }
 902                 return
 903         }
 904         if t == nil {
 905                 return
 906         }
 907         cl.mu.Lock()
 908         defer cl.mu.Unlock()
 909         if c.PeerID == cl.peerID {
 910                 // Because the remote address is not necessarily the same as its
 911                 // client's torrent listen address, we won't record the remote address
 912                 // as a doppleganger. Instead, the initiator can record *us* as the
 913                 // doppleganger.
 914                 return
 915         }
 916         cl.runHandshookConn(c, t)
 917 }
 918
 919 func (cl *Client) runHandshookConn(c *connection, t *Torrent) {
 920         c.conn.SetWriteDeadline(time.Time{})
 921         c.rw = readWriter{
 922                 deadlineReader{c.conn, c.rw},
 923                 c.rw,
 924         }
 925         completedHandshakeConnectionFlags.Add(c.connectionFlags(), 1)
 926         if !t.addConnection(c) {
 927                 return
 928         }
 929         defer t.dropConnection(c)
 930         go c.writer(time.Minute)
 931         cl.sendInitialMessages(c, t)
 932         err := cl.connectionLoop(t, c)
 933         if err != nil && cl.config.Debug {
 934                 log.Printf("error during connection loop: %s", err)
 935         }
 936 }
 937
 938 func (cl *Client) sendInitialMessages(conn *connection, torrent *Torrent) {
 939         if conn.PeerExtensionBytes.SupportsExtended() && cl.extensionBytes.SupportsExtended() {
 940                 conn.Post(pp.Message{
 941                         Type:       pp.Extended,
 942                         ExtendedID: pp.HandshakeExtendedID,
 943                         ExtendedPayload: func() []byte {
 944                                 d := map[string]interface{}{
 945                                         "m": func() (ret map[string]int) {
 946                                                 ret = make(map[string]int, 2)
 947                                                 ret["ut_metadata"] = metadataExtendedId
 948                                                 if !cl.config.DisablePEX {
 949                                                         ret["ut_pex"] = pexExtendedId
 950                                                 }
 951                                                 return
 952                                         }(),
 953                                         "v": extendedHandshakeClientVersion,
 954                                         // No upload queue is implemented yet.
 955                                         "reqq": 64,
 956                                 }
 957                                 if !cl.config.DisableEncryption {
 958                                         d["e"] = 1
 959                                 }
 960                                 if torrent.metadataSizeKnown() {
 961                                         d["metadata_size"] = torrent.metadataSize()
 962                                 }
 963                                 if p := cl.incomingPeerPort(); p != 0 {
 964                                         d["p"] = p
 965                                 }
 966                                 yourip, err := addrCompactIP(conn.remoteAddr())
 967                                 if err != nil {
 968                                         log.Printf("error calculating yourip field value in extension handshake: %s", err)
 969                                 } else {
 970                                         d["yourip"] = yourip
 971                                 }
 972                                 // log.Printf("sending %v", d)
 973                                 b, err := bencode.Marshal(d)
 974                                 if err != nil {
 975                                         panic(err)
 976                                 }
 977                                 return b
 978                         }(),
 979                 })
 980         }
 981         if torrent.haveAnyPieces() {
 982                 conn.Bitfield(torrent.bitfield())
 983         } else if cl.extensionBytes.SupportsFast() && conn.PeerExtensionBytes.SupportsFast() {
 984                 conn.Post(pp.Message{
 985                         Type: pp.HaveNone,
 986                 })
 987         }
 988         if conn.PeerExtensionBytes.SupportsDHT() && cl.extensionBytes.SupportsDHT() && cl.dHT != nil {
 989                 conn.Post(pp.Message{
 990                         Type: pp.Port,
 991                         Port: uint16(missinggo.AddrPort(cl.dHT.Addr())),
 992                 })
 993         }
 994 }
 995
 996 func (cl *Client) peerUnchoked(torrent *Torrent, conn *connection) {
 997         conn.updateRequests()
 998 }
 999
1000 func (cl *Client) connCancel(t *Torrent, cn *connection, r request) (ok bool) {
1001         ok = cn.Cancel(r)
1002         if ok {
1003                 postedCancels.Add(1)
1004         }
1005         return
1006 }
1007
1008 func (cl *Client) connDeleteRequest(t *Torrent, cn *connection, r request) bool {
1009         if !cn.RequestPending(r) {
1010                 return false
1011         }
1012         delete(cn.Requests, r)
1013         return true
1014 }
1015
1016 // Process incoming ut_metadata message.
1017 func (cl *Client) gotMetadataExtensionMsg(payload []byte, t *Torrent, c *connection) error {
1018         var d map[string]int
1019         err := bencode.Unmarshal(payload, &d)
1020         if err != nil {
1021                 return fmt.Errorf("error unmarshalling payload: %s: %q", err, payload)
1022         }
1023         msgType, ok := d["msg_type"]
1024         if !ok {
1025                 return errors.New("missing msg_type field")
1026         }
1027         piece := d["piece"]
1028         switch msgType {
1029         case pp.DataMetadataExtensionMsgType:
1030                 if !c.requestedMetadataPiece(piece) {
1031                         return fmt.Errorf("got unexpected piece %d", piece)
1032                 }
1033                 c.metadataRequests[piece] = false
1034                 begin := len(payload) - metadataPieceSize(d["total_size"], piece)
1035                 if begin < 0 || begin >= len(payload) {
1036                         return fmt.Errorf("data has bad offset in payload: %d", begin)
1037                 }
1038                 t.saveMetadataPiece(piece, payload[begin:])
1039                 c.UsefulChunksReceived++
1040                 c.lastUsefulChunkReceived = time.Now()
1041                 return t.maybeCompleteMetadata()
1042         case pp.RequestMetadataExtensionMsgType:
1043                 if !t.haveMetadataPiece(piece) {
1044                         c.Post(t.newMetadataExtensionMessage(c, pp.RejectMetadataExtensionMsgType, d["piece"], nil))
1045                         return nil
1046                 }
1047                 start := (1 << 14) * piece
1048                 c.Post(t.newMetadataExtensionMessage(c, pp.DataMetadataExtensionMsgType, piece, t.metadataBytes[start:start+t.metadataPieceSize(piece)]))
1049                 return nil
1050         case pp.RejectMetadataExtensionMsgType:
1051                 return nil
1052         default:
1053                 return errors.New("unknown msg_type value")
1054         }
1055 }
1056
1057 func (cl *Client) upload(t *Torrent, c *connection) {
1058         if cl.config.NoUpload {
1059                 return
1060         }
1061         if !c.PeerInterested {
1062                 return
1063         }
1064         seeding := t.seeding()
1065         if !seeding && !t.connHasWantedPieces(c) {
1066                 return
1067         }
1068 another:
1069         for seeding || c.chunksSent < c.UsefulChunksReceived+6 {
1070                 c.Unchoke()
1071                 for r := range c.PeerRequests {
1072                         err := cl.sendChunk(t, c, r)
1073                         if err != nil {
1074                                 i := int(r.Index)
1075                                 if t.pieceComplete(i) {
1076                                         t.updatePieceCompletion(i)
1077                                         if !t.pieceComplete(i) {
1078                                                 // We had the piece, but not anymore.
1079                                                 break another
1080                                         }
1081                                 }
1082                                 log.Printf("error sending chunk %+v to peer: %s", r, err)
1083                                 // If we failed to send a chunk, choke the peer to ensure they
1084                                 // flush all their requests. We've probably dropped a piece,
1085                                 // but there's no way to communicate this to the peer. If they
1086                                 // ask for it again, we'll kick them to allow us to send them
1087                                 // an updated bitfield.
1088                                 break another
1089                         }
1090                         delete(c.PeerRequests, r)
1091                         goto another
1092                 }
1093                 return
1094         }
1095         c.Choke()
1096 }
1097
1098 func (cl *Client) sendChunk(t *Torrent, c *connection, r request) error {
1099         // Count the chunk being sent, even if it isn't.
1100         b := make([]byte, r.Length)
1101         p := t.info.Piece(int(r.Index))
1102         n, err := t.readAt(b, p.Offset()+int64(r.Begin))
1103         if n != len(b) {
1104                 if err == nil {
1105                         panic("expected error")
1106                 }
1107                 return err
1108         }
1109         c.Post(pp.Message{
1110                 Type:  pp.Piece,
1111                 Index: r.Index,
1112                 Begin: r.Begin,
1113                 Piece: b,
1114         })
1115         c.chunksSent++
1116         uploadChunksPosted.Add(1)
1117         c.lastChunkSent = time.Now()
1118         return nil
1119 }
1120
1121 // Processes incoming bittorrent messages. The client lock is held upon entry
1122 // and exit. Returning will end the connection.
1123 func (cl *Client) connectionLoop(t *Torrent, c *connection) error {
1124         decoder := pp.Decoder{
1125                 R:         bufio.NewReader(c.rw),
1126                 MaxLength: 256 * 1024,
1127         }
1128         for {
1129                 cl.mu.Unlock()
1130                 var msg pp.Message
1131                 err := decoder.Decode(&msg)
1132                 cl.mu.Lock()
1133                 if cl.closed.IsSet() || c.closed.IsSet() || err == io.EOF {
1134                         return nil
1135                 }
1136                 if err != nil {
1137                         return err
1138                 }
1139                 c.readMsg(&msg)
1140                 c.lastMessageReceived = time.Now()
1141                 if msg.Keepalive {
1142                         receivedKeepalives.Add(1)
1143                         continue
1144                 }
1145                 receivedMessageTypes.Add(strconv.FormatInt(int64(msg.Type), 10), 1)
1146                 switch msg.Type {
1147                 case pp.Choke:
1148                         c.PeerChoked = true
1149                         c.Requests = nil
1150                         // We can then reset our interest.
1151                         c.updateRequests()
1152                 case pp.Reject:
1153                         cl.connDeleteRequest(t, c, newRequest(msg.Index, msg.Begin, msg.Length))
1154                         c.updateRequests()
1155                 case pp.Unchoke:
1156                         c.PeerChoked = false
1157                         cl.peerUnchoked(t, c)
1158                 case pp.Interested:
1159                         c.PeerInterested = true
1160                         cl.upload(t, c)
1161                 case pp.NotInterested:
1162                         c.PeerInterested = false
1163                         c.Choke()
1164                 case pp.Have:
1165                         err = c.peerSentHave(int(msg.Index))
1166                 case pp.Request:
1167                         if c.Choked {
1168                                 break
1169                         }
1170                         if !c.PeerInterested {
1171                                 err = errors.New("peer sent request but isn't interested")
1172                                 break
1173                         }
1174                         if !t.havePiece(msg.Index.Int()) {
1175                                 // This isn't necessarily them screwing up. We can drop pieces
1176                                 // from our storage, and can't communicate this to peers
1177                                 // except by reconnecting.
1178                                 requestsReceivedForMissingPieces.Add(1)
1179                                 err = errors.New("peer requested piece we don't have")
1180                                 break
1181                         }
1182                         if c.PeerRequests == nil {
1183                                 c.PeerRequests = make(map[request]struct{}, maxRequests)
1184                         }
1185                         c.PeerRequests[newRequest(msg.Index, msg.Begin, msg.Length)] = struct{}{}
1186                         cl.upload(t, c)
1187                 case pp.Cancel:
1188                         req := newRequest(msg.Index, msg.Begin, msg.Length)
1189                         if !c.PeerCancel(req) {
1190                                 unexpectedCancels.Add(1)
1191                         }
1192                 case pp.Bitfield:
1193                         err = c.peerSentBitfield(msg.Bitfield)
1194                 case pp.HaveAll:
1195                         err = c.peerSentHaveAll()
1196                 case pp.HaveNone:
1197                         err = c.peerSentHaveNone()
1198                 case pp.Piece:
1199                         cl.downloadedChunk(t, c, &msg)
1200                 case pp.Extended:
1201                         switch msg.ExtendedID {
1202                         case pp.HandshakeExtendedID:
1203                                 // TODO: Create a bencode struct for this.
1204                                 var d map[string]interface{}
1205                                 err = bencode.Unmarshal(msg.ExtendedPayload, &d)
1206                                 if err != nil {
1207                                         err = fmt.Errorf("error decoding extended message payload: %s", err)
1208                                         break
1209                                 }
1210                                 // log.Printf("got handshake from %q: %#v", c.Socket.RemoteAddr().String(), d)
1211                                 if reqq, ok := d["reqq"]; ok {
1212                                         if i, ok := reqq.(int64); ok {
1213                                                 c.PeerMaxRequests = int(i)
1214                                         }
1215                                 }
1216                                 if v, ok := d["v"]; ok {
1217                                         c.PeerClientName = v.(string)
1218                                 }
1219                                 m, ok := d["m"]
1220                                 if !ok {
1221                                         err = errors.New("handshake missing m item")
1222                                         break
1223                                 }
1224                                 mTyped, ok := m.(map[string]interface{})
1225                                 if !ok {
1226                                         err = errors.New("handshake m value is not dict")
1227                                         break
1228                                 }
1229                                 if c.PeerExtensionIDs == nil {
1230                                         c.PeerExtensionIDs = make(map[string]byte, len(mTyped))
1231                                 }
1232                                 for name, v := range mTyped {
1233                                         id, ok := v.(int64)
1234                                         if !ok {
1235                                                 log.Printf("bad handshake m item extension ID type: %T", v)
1236                                                 continue
1237                                         }
1238                                         if id == 0 {
1239                                                 delete(c.PeerExtensionIDs, name)
1240                                         } else {
1241                                                 if c.PeerExtensionIDs[name] == 0 {
1242                                                         supportedExtensionMessages.Add(name, 1)
1243                                                 }
1244                                                 c.PeerExtensionIDs[name] = byte(id)
1245                                         }
1246                                 }
1247                                 metadata_sizeUntyped, ok := d["metadata_size"]
1248                                 if ok {
1249                                         metadata_size, ok := metadata_sizeUntyped.(int64)
1250                                         if !ok {
1251                                                 log.Printf("bad metadata_size type: %T", metadata_sizeUntyped)
1252                                         } else {
1253                                                 err = t.setMetadataSize(metadata_size)
1254                                                 if err != nil {
1255                                                         err = fmt.Errorf("error setting metadata size to %d", metadata_size)
1256                                                         break
1257                                                 }
1258                                         }
1259                                 }
1260                                 if _, ok := c.PeerExtensionIDs["ut_metadata"]; ok {
1261                                         c.requestPendingMetadata()
1262                                 }
1263                         case metadataExtendedId:
1264                                 err = cl.gotMetadataExtensionMsg(msg.ExtendedPayload, t, c)
1265                                 if err != nil {
1266                                         err = fmt.Errorf("error handling metadata extension message: %s", err)
1267                                 }
1268                         case pexExtendedId:
1269                                 if cl.config.DisablePEX {
1270                                         break
1271                                 }
1272                                 var pexMsg peerExchangeMessage
1273                                 err = bencode.Unmarshal(msg.ExtendedPayload, &pexMsg)
1274                                 if err != nil {
1275                                         err = fmt.Errorf("error unmarshalling PEX message: %s", err)
1276                                         break
1277                                 }
1278                                 go func() {
1279                                         cl.mu.Lock()
1280                                         t.addPeers(func() (ret []Peer) {
1281                                                 for i, cp := range pexMsg.Added {
1282                                                         p := Peer{
1283                                                                 IP:     make([]byte, 4),
1284                                                                 Port:   cp.Port,
1285                                                                 Source: peerSourcePEX,
1286                                                         }
1287                                                         if i < len(pexMsg.AddedFlags) && pexMsg.AddedFlags[i]&0x01 != 0 {
1288                                                                 p.SupportsEncryption = true
1289                                                         }
1290                                                         missinggo.CopyExact(p.IP, cp.IP[:])
1291                                                         ret = append(ret, p)
1292                                                 }
1293                                                 return
1294                                         }())
1295                                         cl.mu.Unlock()
1296                                 }()
1297                         default:
1298                                 err = fmt.Errorf("unexpected extended message ID: %v", msg.ExtendedID)
1299                         }
1300                         if err != nil {
1301                                 // That client uses its own extension IDs for outgoing message
1302                                 // types, which is incorrect.
1303                                 if bytes.HasPrefix(c.PeerID[:], []byte("-SD0100-")) ||
1304                                         strings.HasPrefix(string(c.PeerID[:]), "-XL0012-") {
1305                                         return nil
1306                                 }
1307                         }
1308                 case pp.Port:
1309                         if cl.dHT == nil {
1310                                 break
1311                         }
1312                         pingAddr, err := net.ResolveUDPAddr("", c.remoteAddr().String())
1313                         if err != nil {
1314                                 panic(err)
1315                         }
1316                         if msg.Port != 0 {
1317                                 pingAddr.Port = int(msg.Port)
1318                         }
1319                         cl.dHT.Ping(pingAddr)
1320                 default:
1321                         err = fmt.Errorf("received unknown message type: %#v", msg.Type)
1322                 }
1323                 if err != nil {
1324                         return err
1325                 }
1326         }
1327 }
1328
1329 func (cl *Client) openNewConns(t *Torrent) {
1330         defer t.updateWantPeersEvent()
1331         for len(t.peers) != 0 {
1332                 if !t.wantConns() {
1333                         return
1334                 }
1335                 if len(t.halfOpen) >= cl.halfOpenLimit {
1336                         return
1337                 }
1338                 var (
1339                         k peersKey
1340                         p Peer
1341                 )
1342                 for k, p = range t.peers {
1343                         break
1344                 }
1345                 delete(t.peers, k)
1346                 cl.initiateConn(p, t)
1347         }
1348 }
1349
1350 func (cl *Client) badPeerIPPort(ip net.IP, port int) bool {
1351         if port == 0 {
1352                 return true
1353         }
1354         if cl.dopplegangerAddr(net.JoinHostPort(ip.String(), strconv.FormatInt(int64(port), 10))) {
1355                 return true
1356         }
1357         if _, ok := cl.ipBlockRange(ip); ok {
1358                 return true
1359         }
1360         if _, ok := cl.badPeerIPs[ip.String()]; ok {
1361                 return true
1362         }
1363         return false
1364 }
1365
1366 // Return a Torrent ready for insertion into a Client.
1367 func (cl *Client) newTorrent(ih metainfo.Hash) (t *Torrent) {
1368         t = &Torrent{
1369                 cl:        cl,
1370                 infoHash:  ih,
1371                 chunkSize: defaultChunkSize,
1372                 peers:     make(map[peersKey]Peer),
1373
1374                 halfOpen:          make(map[string]struct{}),
1375                 pieceStateChanges: pubsub.NewPubSub(),
1376
1377                 storageOpener:       cl.defaultStorage,
1378                 maxEstablishedConns: defaultEstablishedConnsPerTorrent,
1379         }
1380         return
1381 }
1382
1383 func init() {
1384         // For shuffling the tracker tiers.
1385         mathRand.Seed(time.Now().Unix())
1386 }
1387
1388 type trackerTier []string
1389
1390 // The trackers within each tier must be shuffled before use.
1391 // http://stackoverflow.com/a/12267471/149482
1392 // http://www.bittorrent.org/beps/bep_0012.html#order-of-processing
1393 func shuffleTier(tier trackerTier) {
1394         for i := range tier {
1395                 j := mathRand.Intn(i + 1)
1396                 tier[i], tier[j] = tier[j], tier[i]
1397         }
1398 }
1399
1400 // A file-like handle to some torrent data resource.
1401 type Handle interface {
1402         io.Reader
1403         io.Seeker
1404         io.Closer
1405         io.ReaderAt
1406 }
1407
1408 // Specifies a new torrent for adding to a client. There are helpers for
1409 // magnet URIs and torrent metainfo files.
1410 type TorrentSpec struct {
1411         // The tiered tracker URIs.
1412         Trackers  [][]string
1413         InfoHash  metainfo.Hash
1414         InfoBytes []byte
1415         // The name to use if the Name field from the Info isn't available.
1416         DisplayName string
1417         // The chunk size to use for outbound requests. Defaults to 16KiB if not
1418         // set.
1419         ChunkSize int
1420         Storage   storage.Client
1421 }
1422
1423 func TorrentSpecFromMagnetURI(uri string) (spec *TorrentSpec, err error) {
1424         m, err := metainfo.ParseMagnetURI(uri)
1425         if err != nil {
1426                 return
1427         }
1428         spec = &TorrentSpec{
1429                 Trackers:    [][]string{m.Trackers},
1430                 DisplayName: m.DisplayName,
1431                 InfoHash:    m.InfoHash,
1432         }
1433         return
1434 }
1435
1436 func TorrentSpecFromMetaInfo(mi *metainfo.MetaInfo) (spec *TorrentSpec) {
1437         info := mi.UnmarshalInfo()
1438         spec = &TorrentSpec{
1439                 Trackers:    mi.AnnounceList,
1440                 InfoBytes:   mi.InfoBytes,
1441                 DisplayName: info.Name,
1442                 InfoHash:    mi.HashInfoBytes(),
1443         }
1444         if spec.Trackers == nil && mi.Announce != "" {
1445                 spec.Trackers = [][]string{{mi.Announce}}
1446         }
1447         return
1448 }
1449
1450 func (cl *Client) AddTorrentInfoHash(infoHash metainfo.Hash) (t *Torrent, new bool) {
1451         cl.mu.Lock()
1452         defer cl.mu.Unlock()
1453         t, ok := cl.torrents[infoHash]
1454         if ok {
1455                 return
1456         }
1457         new = true
1458         t = cl.newTorrent(infoHash)
1459         if cl.dHT != nil {
1460                 go t.dhtAnnouncer()
1461         }
1462         cl.torrents[infoHash] = t
1463         t.updateWantPeersEvent()
1464         // Tickle Client.waitAccept, new torrent may want conns.
1465         cl.event.Broadcast()
1466         return
1467 }
1468
1469 // Add or merge a torrent spec. If the torrent is already present, the
1470 // trackers will be merged with the existing ones. If the Info isn't yet
1471 // known, it will be set. The display name is replaced if the new spec
1472 // provides one. Returns new if the torrent wasn't already in the client.
1473 func (cl *Client) AddTorrentSpec(spec *TorrentSpec) (t *Torrent, new bool, err error) {
1474         t, new = cl.AddTorrentInfoHash(spec.InfoHash)
1475         if spec.DisplayName != "" {
1476                 t.SetDisplayName(spec.DisplayName)
1477         }
1478         if spec.InfoBytes != nil {
1479                 err = t.SetInfoBytes(spec.InfoBytes)
1480                 if err != nil {
1481                         return
1482                 }
1483         }
1484         cl.mu.Lock()
1485         defer cl.mu.Unlock()
1486         if spec.ChunkSize != 0 {
1487                 t.chunkSize = pp.Integer(spec.ChunkSize)
1488         }
1489         t.addTrackers(spec.Trackers)
1490         t.maybeNewConns()
1491         return
1492 }
1493
1494 func (cl *Client) dropTorrent(infoHash metainfo.Hash) (err error) {
1495         t, ok := cl.torrents[infoHash]
1496         if !ok {
1497                 err = fmt.Errorf("no such torrent")
1498                 return
1499         }
1500         err = t.close()
1501         if err != nil {
1502                 panic(err)
1503         }
1504         delete(cl.torrents, infoHash)
1505         return
1506 }
1507
1508 func (cl *Client) prepareTrackerAnnounceUnlocked(announceURL string) (blocked bool, urlToUse string, host string, err error) {
1509         _url, err := url.Parse(announceURL)
1510         if err != nil {
1511                 return
1512         }
1513         hmp := missinggo.SplitHostMaybePort(_url.Host)
1514         if hmp.Err != nil {
1515                 err = hmp.Err
1516                 return
1517         }
1518         addr, err := net.ResolveIPAddr("ip", hmp.Host)
1519         if err != nil {
1520                 return
1521         }
1522         cl.mu.RLock()
1523         _, blocked = cl.ipBlockRange(addr.IP)
1524         cl.mu.RUnlock()
1525         host = _url.Host
1526         hmp.Host = addr.String()
1527         _url.Host = hmp.String()
1528         urlToUse = _url.String()
1529         return
1530 }
1531
1532 func (cl *Client) allTorrentsCompleted() bool {
1533         for _, t := range cl.torrents {
1534                 if !t.haveInfo() {
1535                         return false
1536                 }
1537                 if t.numPiecesCompleted() != t.numPieces() {
1538                         return false
1539                 }
1540         }
1541         return true
1542 }
1543
1544 // Returns true when all torrents are completely downloaded and false if the
1545 // client is stopped before that.
1546 func (cl *Client) WaitAll() bool {
1547         cl.mu.Lock()
1548         defer cl.mu.Unlock()
1549         for !cl.allTorrentsCompleted() {
1550                 if cl.closed.IsSet() {
1551                         return false
1552                 }
1553                 cl.event.Wait()
1554         }
1555         return true
1556 }
1557
1558 // Handle a received chunk from a peer.
1559 func (cl *Client) downloadedChunk(t *Torrent, c *connection, msg *pp.Message) {
1560         chunksReceived.Add(1)
1561
1562         req := newRequest(msg.Index, msg.Begin, pp.Integer(len(msg.Piece)))
1563
1564         // Request has been satisfied.
1565         if cl.connDeleteRequest(t, c, req) {
1566                 defer c.updateRequests()
1567         } else {
1568                 unexpectedChunksReceived.Add(1)
1569         }
1570
1571         index := int(req.Index)
1572         piece := &t.pieces[index]
1573
1574         // Do we actually want this chunk?
1575         if !t.wantPiece(req) {
1576                 unwantedChunksReceived.Add(1)
1577                 c.UnwantedChunksReceived++
1578                 return
1579         }
1580
1581         c.UsefulChunksReceived++
1582         c.lastUsefulChunkReceived = time.Now()
1583
1584         cl.upload(t, c)
1585
1586         // Need to record that it hasn't been written yet, before we attempt to do
1587         // anything with it.
1588         piece.incrementPendingWrites()
1589         // Record that we have the chunk.
1590         piece.unpendChunkIndex(chunkIndex(req.chunkSpec, t.chunkSize))
1591
1592         // Cancel pending requests for this chunk.
1593         for _, c := range t.conns {
1594                 if cl.connCancel(t, c, req) {
1595                         c.updateRequests()
1596                 }
1597         }
1598
1599         cl.mu.Unlock()
1600         // Write the chunk out. Note that the upper bound on chunk writing
1601         // concurrency will be the number of connections.
1602         err := t.writeChunk(int(msg.Index), int64(msg.Begin), msg.Piece)
1603         cl.mu.Lock()
1604
1605         piece.decrementPendingWrites()
1606
1607         if err != nil {
1608                 log.Printf("%s: error writing chunk %v: %s", t, req, err)
1609                 t.pendRequest(req)
1610                 t.updatePieceCompletion(int(msg.Index))
1611                 return
1612         }
1613
1614         // It's important that the piece is potentially queued before we check if
1615         // the piece is still wanted, because if it is queued, it won't be wanted.
1616         if t.pieceAllDirty(index) {
1617                 cl.queuePieceCheck(t, int(req.Index))
1618         }
1619
1620         if c.peerTouchedPieces == nil {
1621                 c.peerTouchedPieces = make(map[int]struct{})
1622         }
1623         c.peerTouchedPieces[index] = struct{}{}
1624
1625         cl.event.Broadcast()
1626         t.publishPieceChange(int(req.Index))
1627         return
1628 }
1629
1630 // Return the connections that touched a piece, and clear the entry while
1631 // doing it.
1632 func (cl *Client) reapPieceTouches(t *Torrent, piece int) (ret []*connection) {
1633         for _, c := range t.conns {
1634                 if _, ok := c.peerTouchedPieces[piece]; ok {
1635                         ret = append(ret, c)
1636                         delete(c.peerTouchedPieces, piece)
1637                 }
1638         }
1639         return
1640 }
1641
1642 func (cl *Client) pieceHashed(t *Torrent, piece int, correct bool) {
1643         if t.closed.IsSet() {
1644                 return
1645         }
1646         p := &t.pieces[piece]
1647         if p.EverHashed {
1648                 // Don't score the first time a piece is hashed, it could be an
1649                 // initial check.
1650                 if correct {
1651                         pieceHashedCorrect.Add(1)
1652                 } else {
1653                         log.Printf("%s: piece %d (%x) failed hash", t, piece, p.Hash)
1654                         pieceHashedNotCorrect.Add(1)
1655                 }
1656         }
1657         p.EverHashed = true
1658         touchers := cl.reapPieceTouches(t, piece)
1659         if correct {
1660                 for _, c := range touchers {
1661                         c.goodPiecesDirtied++
1662                 }
1663                 err := p.Storage().MarkComplete()
1664                 if err != nil {
1665                         log.Printf("%T: error completing piece %d: %s", t.storage, piece, err)
1666                 }
1667                 t.updatePieceCompletion(piece)
1668         } else if len(touchers) != 0 {
1669                 log.Printf("dropping and banning %d conns that touched piece", len(touchers))
1670                 for _, c := range touchers {
1671                         c.badPiecesDirtied++
1672                         t.cl.banPeerIP(missinggo.AddrIP(c.remoteAddr()))
1673                         t.dropConnection(c)
1674                 }
1675         }
1676         cl.pieceChanged(t, piece)
1677 }
1678
1679 func (cl *Client) onCompletedPiece(t *Torrent, piece int) {
1680         t.pendingPieces.Remove(piece)
1681         t.pendAllChunkSpecs(piece)
1682         for _, conn := range t.conns {
1683                 conn.Have(piece)
1684                 for r := range conn.Requests {
1685                         if int(r.Index) == piece {
1686                                 conn.Cancel(r)
1687                         }
1688                 }
1689                 // Could check here if peer doesn't have piece, but due to caching
1690                 // some peers may have said they have a piece but they don't.
1691                 cl.upload(t, conn)
1692         }
1693 }
1694
1695 func (cl *Client) onFailedPiece(t *Torrent, piece int) {
1696         if t.pieceAllDirty(piece) {
1697                 t.pendAllChunkSpecs(piece)
1698         }
1699         if !t.wantPieceIndex(piece) {
1700                 return
1701         }
1702         cl.openNewConns(t)
1703         for _, conn := range t.conns {
1704                 if conn.PeerHasPiece(piece) {
1705                         conn.updateRequests()
1706                 }
1707         }
1708 }
1709
1710 func (cl *Client) pieceChanged(t *Torrent, piece int) {
1711         correct := t.pieceComplete(piece)
1712         defer cl.event.Broadcast()
1713         if correct {
1714                 cl.onCompletedPiece(t, piece)
1715         } else {
1716                 cl.onFailedPiece(t, piece)
1717         }
1718         if t.updatePiecePriority(piece) {
1719                 t.piecePriorityChanged(piece)
1720         }
1721         t.publishPieceChange(piece)
1722 }
1723
1724 func (cl *Client) verifyPiece(t *Torrent, piece int) {
1725         cl.mu.Lock()
1726         defer cl.mu.Unlock()
1727         p := &t.pieces[piece]
1728         for p.Hashing || t.storage == nil {
1729                 cl.event.Wait()
1730         }
1731         p.QueuedForHash = false
1732         if t.closed.IsSet() || t.pieceComplete(piece) {
1733                 t.updatePiecePriority(piece)
1734                 t.publishPieceChange(piece)
1735                 return
1736         }
1737         p.Hashing = true
1738         t.publishPieceChange(piece)
1739         cl.mu.Unlock()
1740         sum := t.hashPiece(piece)
1741         cl.mu.Lock()
1742         p.Hashing = false
1743         cl.pieceHashed(t, piece, sum == p.Hash)
1744 }
1745
1746 // Returns handles to all the torrents loaded in the Client.
1747 func (cl *Client) Torrents() (ret []*Torrent) {
1748         cl.mu.Lock()
1749         for _, t := range cl.torrents {
1750                 ret = append(ret, t)
1751         }
1752         cl.mu.Unlock()
1753         return
1754 }
1755
1756 func (cl *Client) AddMagnet(uri string) (T *Torrent, err error) {
1757         spec, err := TorrentSpecFromMagnetURI(uri)
1758         if err != nil {
1759                 return
1760         }
1761         T, _, err = cl.AddTorrentSpec(spec)
1762         return
1763 }
1764
1765 func (cl *Client) AddTorrent(mi *metainfo.MetaInfo) (T *Torrent, err error) {
1766         T, _, err = cl.AddTorrentSpec(TorrentSpecFromMetaInfo(mi))
1767         var ss []string
1768         slices.MakeInto(&ss, mi.Nodes)
1769         cl.AddDHTNodes(ss)
1770         return
1771 }
1772
1773 func (cl *Client) AddTorrentFromFile(filename string) (T *Torrent, err error) {
1774         mi, err := metainfo.LoadFromFile(filename)
1775         if err != nil {
1776                 return
1777         }
1778         return cl.AddTorrent(mi)
1779 }
1780
1781 func (cl *Client) DHT() *dht.Server {
1782         return cl.dHT
1783 }
1784
1785 func (cl *Client) AddDHTNodes(nodes []string) {
1786         for _, n := range nodes {
1787                 hmp := missinggo.SplitHostMaybePort(n)
1788                 ip := net.ParseIP(hmp.Host)
1789                 if ip == nil {
1790                         log.Printf("won't add DHT node with bad IP: %q", hmp.Host)
1791                         continue
1792                 }
1793                 ni := krpc.NodeInfo{
1794                         Addr: &net.UDPAddr{
1795                                 IP:   ip,
1796                                 Port: hmp.Port,
1797                         },
1798                 }
1799                 cl.DHT().AddNode(ni)
1800         }
1801 }
1802
1803 func (cl *Client) banPeerIP(ip net.IP) {
1804         if cl.badPeerIPs == nil {
1805                 cl.badPeerIPs = make(map[string]struct{})
1806         }
1807         cl.badPeerIPs[ip.String()] = struct{}{}
1808 }