client.go

   1 /*
   2 Package torrent implements a torrent client.
   3
   4 Simple example:
   5
   6         c := &Client{}
   7         c.Start()
   8         defer c.Stop()
   9         if err := c.AddTorrent(externalMetaInfoPackageSux); err != nil {
  10                 return fmt.Errors("error adding torrent: %s", err)
  11         }
  12         c.WaitAll()
  13         log.Print("erhmahgerd, torrent downloaded")
  14
  15 */
  16 package torrent
  17
  18 import (
  19         "bufio"
  20         "bytes"
  21         "container/heap"
  22         "crypto/rand"
  23         "crypto/sha1"
  24         "errors"
  25         "expvar"
  26         "fmt"
  27         "io"
  28         "log"
  29         "math/big"
  30         mathRand "math/rand"
  31         "net"
  32         "os"
  33         "path/filepath"
  34         "sort"
  35         "strings"
  36         "syscall"
  37         "time"
  38
  39         "bitbucket.org/anacrolix/go.torrent/dht"
  40         "bitbucket.org/anacrolix/go.torrent/internal/pieceordering"
  41         "bitbucket.org/anacrolix/go.torrent/iplist"
  42         pp "bitbucket.org/anacrolix/go.torrent/peer_protocol"
  43         "bitbucket.org/anacrolix/go.torrent/tracker"
  44         _ "bitbucket.org/anacrolix/go.torrent/tracker/udp"
  45         . "bitbucket.org/anacrolix/go.torrent/util"
  46         "bitbucket.org/anacrolix/sync"
  47         "bitbucket.org/anacrolix/utp"
  48         "github.com/anacrolix/libtorgo/bencode"
  49         "github.com/anacrolix/libtorgo/metainfo"
  50 )
  51
  52 var (
  53         unusedDownloadedChunksCount = expvar.NewInt("unusedDownloadedChunksCount")
  54         chunksDownloadedCount       = expvar.NewInt("chunksDownloadedCount")
  55         peersFoundByDHT             = expvar.NewInt("peersFoundByDHT")
  56         peersFoundByPEX             = expvar.NewInt("peersFoundByPEX")
  57         uploadChunksPosted          = expvar.NewInt("uploadChunksPosted")
  58         unexpectedCancels           = expvar.NewInt("unexpectedCancels")
  59         postedCancels               = expvar.NewInt("postedCancels")
  60         duplicateConnsAvoided       = expvar.NewInt("duplicateConnsAvoided")
  61         failedPieceHashes           = expvar.NewInt("failedPieceHashes")
  62         unsuccessfulDials           = expvar.NewInt("unsuccessfulDials")
  63         successfulDials             = expvar.NewInt("successfulDials")
  64         acceptedConns               = expvar.NewInt("acceptedConns")
  65         inboundConnsBlocked         = expvar.NewInt("inboundConnsBlocked")
  66 )
  67
  68 const (
  69         // Justification for set bits follows.
  70         //
  71         // Extension protocol: http://www.bittorrent.org/beps/bep_0010.html
  72         // DHT: http://www.bittorrent.org/beps/bep_0005.html
  73         extensionBytes = "\x00\x00\x00\x00\x00\x10\x00\x01"
  74
  75         socketsPerTorrent     = 40
  76         torrentPeersHighWater = 1000
  77         torrentPeersLowWater  = socketsPerTorrent * 5
  78 )
  79
  80 // Currently doesn't really queue, but should in the future.
  81 func (cl *Client) queuePieceCheck(t *torrent, pieceIndex pp.Integer) {
  82         piece := t.Pieces[pieceIndex]
  83         if piece.QueuedForHash {
  84                 return
  85         }
  86         piece.QueuedForHash = true
  87         go cl.verifyPiece(t, pieceIndex)
  88 }
  89
  90 func (cl *Client) queueFirstHash(t *torrent, piece int) {
  91         p := t.Pieces[piece]
  92         if p.EverHashed || p.Hashing || p.QueuedForHash {
  93                 return
  94         }
  95         cl.queuePieceCheck(t, pp.Integer(piece))
  96 }
  97
  98 // Queues the torrent data for the given region for download. The beginning of
  99 // the region is given highest priority to allow a subsequent read at the same
 100 // offset to return data ASAP.
 101 func (me *Client) PrioritizeDataRegion(ih InfoHash, off, len_ int64) error {
 102         me.mu.Lock()
 103         defer me.mu.Unlock()
 104         t := me.torrent(ih)
 105         if t == nil {
 106                 return errors.New("no such active torrent")
 107         }
 108         if !t.haveInfo() {
 109                 return errors.New("missing metadata")
 110         }
 111         firstIndex := int(off / int64(t.UsualPieceSize()))
 112         for i := 0; i < 5; i++ {
 113                 index := firstIndex + i
 114                 if index >= t.NumPieces() {
 115                         continue
 116                 }
 117                 me.queueFirstHash(t, index)
 118         }
 119         me.downloadStrategy.TorrentPrioritize(t, off, len_)
 120         for _, cn := range t.Conns {
 121                 me.replenishConnRequests(t, cn)
 122         }
 123         me.openNewConns(t)
 124         return nil
 125 }
 126
 127 type dataWait struct {
 128         offset int64
 129         ready  chan struct{}
 130 }
 131
 132 type Client struct {
 133         noUpload         bool
 134         dataDir          string
 135         halfOpenLimit    int
 136         peerID           [20]byte
 137         listeners        []net.Listener
 138         utpSock          *utp.Socket
 139         disableTrackers  bool
 140         downloadStrategy DownloadStrategy
 141         dHT              *dht.Server
 142         disableUTP       bool
 143         disableTCP       bool
 144         ipBlockList      *iplist.IPList
 145         bannedTorrents   map[InfoHash]struct{}
 146
 147         mu    sync.RWMutex
 148         event sync.Cond
 149         quit  chan struct{}
 150
 151         handshaking int
 152
 153         torrents map[InfoHash]*torrent
 154
 155         dataWaits map[*torrent][]dataWait
 156 }
 157
 158 func (me *Client) SetIPBlockList(list *iplist.IPList) {
 159         me.mu.Lock()
 160         defer me.mu.Unlock()
 161         me.ipBlockList = list
 162         if me.dHT != nil {
 163                 me.dHT.SetIPBlockList(list)
 164         }
 165 }
 166
 167 func (me *Client) PeerID() string {
 168         return string(me.peerID[:])
 169 }
 170
 171 func (me *Client) ListenAddr() (addr net.Addr) {
 172         for _, l := range me.listeners {
 173                 if addr != nil && l.Addr().String() != addr.String() {
 174                         panic("listeners exist on different addresses")
 175                 }
 176                 addr = l.Addr()
 177         }
 178         return
 179 }
 180
 181 type hashSorter struct {
 182         Hashes []InfoHash
 183 }
 184
 185 func (me hashSorter) Len() int {
 186         return len(me.Hashes)
 187 }
 188
 189 func (me hashSorter) Less(a, b int) bool {
 190         return (&big.Int{}).SetBytes(me.Hashes[a][:]).Cmp((&big.Int{}).SetBytes(me.Hashes[b][:])) < 0
 191 }
 192
 193 func (me hashSorter) Swap(a, b int) {
 194         me.Hashes[a], me.Hashes[b] = me.Hashes[b], me.Hashes[a]
 195 }
 196
 197 func (cl *Client) sortedTorrents() (ret []*torrent) {
 198         var hs hashSorter
 199         for ih := range cl.torrents {
 200                 hs.Hashes = append(hs.Hashes, ih)
 201         }
 202         sort.Sort(hs)
 203         for _, ih := range hs.Hashes {
 204                 ret = append(ret, cl.torrent(ih))
 205         }
 206         return
 207 }
 208
 209 func (cl *Client) WriteStatus(_w io.Writer) {
 210         cl.mu.RLock()
 211         defer cl.mu.RUnlock()
 212         w := bufio.NewWriter(_w)
 213         defer w.Flush()
 214         fmt.Fprintf(w, "Listening on %s\n", cl.ListenAddr())
 215         fmt.Fprintf(w, "Peer ID: %q\n", cl.peerID)
 216         fmt.Fprintf(w, "Handshaking: %d\n", cl.handshaking)
 217         if cl.dHT != nil {
 218                 dhtStats := cl.dHT.Stats()
 219                 fmt.Fprintf(w, "DHT nodes: %d (%d good)\n", dhtStats.NumNodes, dhtStats.NumGoodNodes)
 220                 fmt.Fprintf(w, "DHT Server ID: %x\n", cl.dHT.IDString())
 221                 fmt.Fprintf(w, "DHT port: %d\n", addrPort(cl.dHT.LocalAddr()))
 222                 fmt.Fprintf(w, "DHT announces: %d\n", cl.dHT.NumConfirmedAnnounces)
 223                 fmt.Fprintf(w, "Outstanding transactions: %d\n", dhtStats.NumOutstandingTransactions)
 224         }
 225         cl.downloadStrategy.WriteStatus(w)
 226         fmt.Fprintln(w)
 227         for _, t := range cl.sortedTorrents() {
 228                 if t.Name() == "" {
 229                         fmt.Fprint(w, "<unknown name>")
 230                 } else {
 231                         fmt.Fprint(w, t.Name())
 232                 }
 233                 if t.haveInfo() {
 234                         fmt.Fprintf(w, ": %f%% of %d bytes", 100*(1-float32(t.BytesLeft())/float32(t.Length())), t.Length())
 235                 }
 236                 fmt.Fprint(w, "\n")
 237                 fmt.Fprint(w, "Blocked reads:")
 238                 for _, dw := range cl.dataWaits[t] {
 239                         fmt.Fprintf(w, " %d", dw.offset)
 240                 }
 241                 fmt.Fprintln(w)
 242                 t.WriteStatus(w)
 243                 fmt.Fprintln(w)
 244         }
 245 }
 246
 247 // Read torrent data at the given offset. Returns ErrDataNotReady if the data
 248 // isn't available.
 249 func (cl *Client) torrentReadAt(t *torrent, off int64, p []byte) (n int, err error) {
 250         cl.mu.Lock()
 251         defer cl.mu.Unlock()
 252         index := int(off / int64(t.UsualPieceSize()))
 253         // Reading outside the bounds of a file is an error.
 254         if index < 0 {
 255                 err = os.ErrInvalid
 256                 return
 257         }
 258         if int(index) >= len(t.Pieces) {
 259                 err = io.EOF
 260                 return
 261         }
 262         piece := t.Pieces[index]
 263         pieceOff := pp.Integer(off % int64(t.UsualPieceSize()))
 264         pieceLeft := int(t.PieceLength(pp.Integer(index)) - pieceOff)
 265         if pieceLeft <= 0 {
 266                 err = io.EOF
 267                 return
 268         }
 269         cl.readRaisePiecePriorities(t, off, int64(len(p)))
 270         if len(p) > pieceLeft {
 271                 p = p[:pieceLeft]
 272         }
 273         if len(p) == 0 {
 274                 panic(len(p))
 275         }
 276         for !piece.Complete() {
 277                 piece.Event.Wait()
 278         }
 279         return t.Data.ReadAt(p, off)
 280 }
 281
 282 func (cl *Client) readRaisePiecePriorities(t *torrent, off, _len int64) {
 283         index := int(off / int64(t.UsualPieceSize()))
 284         cl.raisePiecePriority(t, index, piecePriorityNow)
 285         index++
 286         if index >= t.NumPieces() {
 287                 return
 288         }
 289         cl.raisePiecePriority(t, index, piecePriorityNext)
 290         for i := 0; i < t.numConnsUnchoked()-2; i++ {
 291                 index++
 292                 if index >= t.NumPieces() {
 293                         break
 294                 }
 295                 cl.raisePiecePriority(t, index, piecePriorityReadahead)
 296         }
 297 }
 298
 299 func (cl *Client) configDir() string {
 300         return filepath.Join(os.Getenv("HOME"), ".config/torrent")
 301 }
 302
 303 func (cl *Client) ConfigDir() string {
 304         return cl.configDir()
 305 }
 306
 307 func (t *torrent) connPendPiece(c *connection, piece int) {
 308         c.pendPiece(piece, t.Pieces[piece].Priority)
 309 }
 310
 311 func (cl *Client) raisePiecePriority(t *torrent, piece int, priority piecePriority) {
 312         if t.Pieces[piece].Priority < priority {
 313                 cl.prioritizePiece(t, piece, priority)
 314         }
 315 }
 316
 317 func (cl *Client) prioritizePiece(t *torrent, piece int, priority piecePriority) {
 318         if t.havePiece(piece) {
 319                 return
 320         }
 321         cl.queueFirstHash(t, piece)
 322         t.Pieces[piece].Priority = priority
 323         if t.wantPiece(piece) {
 324                 for _, c := range t.Conns {
 325                         if c.PeerHasPiece(pp.Integer(piece)) {
 326                                 t.connPendPiece(c, piece)
 327                                 cl.replenishConnRequests(t, c)
 328                         }
 329                 }
 330         }
 331 }
 332
 333 func (cl *Client) setEnvBlocklist() (err error) {
 334         filename := os.Getenv("TORRENT_BLOCKLIST_FILE")
 335         defaultBlocklist := filename == ""
 336         if defaultBlocklist {
 337                 filename = filepath.Join(cl.configDir(), "blocklist")
 338         }
 339         f, err := os.Open(filename)
 340         if err != nil {
 341                 if defaultBlocklist {
 342                         err = nil
 343                 }
 344                 return
 345         }
 346         defer f.Close()
 347         var ranges []iplist.Range
 348         scanner := bufio.NewScanner(f)
 349         for scanner.Scan() {
 350                 r, ok, lineErr := iplist.ParseBlocklistP2PLine(scanner.Text())
 351                 if lineErr != nil {
 352                         err = fmt.Errorf("error reading torrent blocklist line: %s", lineErr)
 353                         return
 354                 }
 355                 if !ok {
 356                         continue
 357                 }
 358                 ranges = append(ranges, r)
 359         }
 360         err = scanner.Err()
 361         if err != nil {
 362                 err = fmt.Errorf("error reading torrent blocklist: %s", err)
 363                 return
 364         }
 365         cl.ipBlockList = iplist.New(ranges)
 366         return
 367 }
 368
 369 func (cl *Client) initBannedTorrents() error {
 370         f, err := os.Open(filepath.Join(cl.configDir(), "banned_infohashes"))
 371         if err != nil {
 372                 if os.IsNotExist(err) {
 373                         return nil
 374                 }
 375                 return fmt.Errorf("error opening banned infohashes file: %s", err)
 376         }
 377         defer f.Close()
 378         scanner := bufio.NewScanner(f)
 379         cl.bannedTorrents = make(map[InfoHash]struct{})
 380         for scanner.Scan() {
 381                 var ihs string
 382                 n, err := fmt.Sscanf(scanner.Text(), "%x", &ihs)
 383                 if err != nil {
 384                         return fmt.Errorf("error reading infohash: %s", err)
 385                 }
 386                 if n != 1 {
 387                         continue
 388                 }
 389                 if len(ihs) != 20 {
 390                         return errors.New("bad infohash")
 391                 }
 392                 var ih InfoHash
 393                 CopyExact(&ih, ihs)
 394                 cl.bannedTorrents[ih] = struct{}{}
 395         }
 396         if err := scanner.Err(); err != nil {
 397                 return fmt.Errorf("error scanning file: %s", err)
 398         }
 399         return nil
 400 }
 401
 402 func NewClient(cfg *Config) (cl *Client, err error) {
 403         if cfg == nil {
 404                 cfg = &Config{}
 405         }
 406
 407         cl = &Client{
 408                 noUpload:         cfg.NoUpload,
 409                 disableTrackers:  cfg.DisableTrackers,
 410                 downloadStrategy: cfg.DownloadStrategy,
 411                 halfOpenLimit:    socketsPerTorrent,
 412                 dataDir:          cfg.DataDir,
 413                 disableUTP:       cfg.DisableUTP,
 414                 disableTCP:       cfg.DisableTCP,
 415
 416                 quit:     make(chan struct{}),
 417                 torrents: make(map[InfoHash]*torrent),
 418
 419                 dataWaits: make(map[*torrent][]dataWait),
 420         }
 421         // TODO: Write my own UTP library ಠ_ಠ
 422         // cl.disableUTP = true
 423         cl.event.L = &cl.mu
 424
 425         if !cfg.NoDefaultBlocklist {
 426                 err = cl.setEnvBlocklist()
 427                 if err != nil {
 428                         return
 429                 }
 430         }
 431
 432         if err = cl.initBannedTorrents(); err != nil {
 433                 err = fmt.Errorf("error initing banned torrents: %s", err)
 434                 return
 435         }
 436
 437         if cfg.PeerID != "" {
 438                 CopyExact(&cl.peerID, cfg.PeerID)
 439         } else {
 440                 o := copy(cl.peerID[:], BEP20)
 441                 _, err = rand.Read(cl.peerID[o:])
 442                 if err != nil {
 443                         panic("error generating peer id")
 444                 }
 445         }
 446
 447         if cl.downloadStrategy == nil {
 448                 cl.downloadStrategy = &DefaultDownloadStrategy{}
 449         }
 450
 451         // Returns the laddr string to listen on for the next Listen call.
 452         listenAddr := func() string {
 453                 if addr := cl.ListenAddr(); addr != nil {
 454                         return addr.String()
 455                 }
 456                 if cfg.ListenAddr == "" {
 457                         return ":50007"
 458                 }
 459                 return cfg.ListenAddr
 460         }
 461         if !cl.disableTCP {
 462                 var l net.Listener
 463                 l, err = net.Listen("tcp", listenAddr())
 464                 if err != nil {
 465                         return
 466                 }
 467                 cl.listeners = append(cl.listeners, l)
 468                 go cl.acceptConnections(l, false)
 469         }
 470         if !cl.disableUTP {
 471                 cl.utpSock, err = utp.NewSocket(listenAddr())
 472                 if err != nil {
 473                         return
 474                 }
 475                 cl.listeners = append(cl.listeners, cl.utpSock)
 476                 go cl.acceptConnections(cl.utpSock, true)
 477         }
 478         if !cfg.NoDHT {
 479                 dhtCfg := cfg.DHTConfig
 480                 if dhtCfg == nil {
 481                         dhtCfg = &dht.ServerConfig{}
 482                 }
 483                 if dhtCfg.Addr == "" {
 484                         dhtCfg.Addr = listenAddr()
 485                 }
 486                 if dhtCfg.Conn == nil && cl.utpSock != nil {
 487                         dhtCfg.Conn = cl.utpSock
 488                 }
 489                 cl.dHT, err = dht.NewServer(dhtCfg)
 490                 if cl.ipBlockList != nil {
 491                         cl.dHT.SetIPBlockList(cl.ipBlockList)
 492                 }
 493                 if err != nil {
 494                         return
 495                 }
 496         }
 497
 498         return
 499 }
 500
 501 func (cl *Client) stopped() bool {
 502         select {
 503         case <-cl.quit:
 504                 return true
 505         default:
 506                 return false
 507         }
 508 }
 509
 510 // Stops the client. All connections to peers are closed and all activity will
 511 // come to a halt.
 512 func (me *Client) Stop() {
 513         me.mu.Lock()
 514         close(me.quit)
 515         for _, l := range me.listeners {
 516                 l.Close()
 517         }
 518         me.event.Broadcast()
 519         for _, t := range me.torrents {
 520                 t.Close()
 521         }
 522         me.mu.Unlock()
 523 }
 524
 525 var ipv6BlockRange = iplist.Range{Description: "non-IPv4 address"}
 526
 527 func (cl *Client) ipBlockRange(ip net.IP) (r *iplist.Range) {
 528         if cl.ipBlockList == nil {
 529                 return
 530         }
 531         ip = ip.To4()
 532         if ip == nil {
 533                 log.Printf("saw non-IPv4 address")
 534                 r = &ipv6BlockRange
 535                 return
 536         }
 537         r = cl.ipBlockList.Lookup(ip)
 538         return
 539 }
 540
 541 func (cl *Client) acceptConnections(l net.Listener, utp bool) {
 542         for {
 543                 // We accept all connections immediately, because we don't know what
 544                 // torrent they're for.
 545                 conn, err := l.Accept()
 546                 select {
 547                 case <-cl.quit:
 548                         if conn != nil {
 549                                 conn.Close()
 550                         }
 551                         return
 552                 default:
 553                 }
 554                 if err != nil {
 555                         log.Print(err)
 556                         return
 557                 }
 558                 acceptedConns.Add(1)
 559                 cl.mu.RLock()
 560                 blockRange := cl.ipBlockRange(AddrIP(conn.RemoteAddr()))
 561                 cl.mu.RUnlock()
 562                 if blockRange != nil {
 563                         inboundConnsBlocked.Add(1)
 564                         log.Printf("inbound connection from %s blocked by %s", conn.RemoteAddr(), blockRange)
 565                         conn.Close()
 566                         continue
 567                 }
 568                 go func() {
 569                         if err := cl.runConnection(conn, nil, peerSourceIncoming, utp); err != nil {
 570                                 log.Print(err)
 571                         }
 572                 }()
 573         }
 574 }
 575
 576 func (me *Client) torrent(ih InfoHash) *torrent {
 577         for _, t := range me.torrents {
 578                 if t.InfoHash == ih {
 579                         return t
 580                 }
 581         }
 582         return nil
 583 }
 584
 585 type dialResult struct {
 586         net.Conn
 587         UTP bool
 588 }
 589
 590 func doDial(dial func() (net.Conn, error), ch chan dialResult, utp bool) {
 591         conn, err := dial()
 592         if err != nil {
 593                 if conn != nil {
 594                         conn.Close()
 595                 }
 596                 conn = nil // Pedantic
 597         }
 598         ch <- dialResult{conn, utp}
 599         if err == nil {
 600                 successfulDials.Add(1)
 601                 return
 602         }
 603         unsuccessfulDials.Add(1)
 604         if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
 605                 return
 606         }
 607         if netOpErr, ok := err.(*net.OpError); ok {
 608                 switch netOpErr.Err {
 609                 case syscall.ECONNREFUSED, syscall.EHOSTUNREACH:
 610                         return
 611                 }
 612         }
 613         if err != nil {
 614                 log.Printf("error connecting to peer: %s %#v", err, err)
 615                 return
 616         }
 617 }
 618
 619 func reducedDialTimeout(max time.Duration, halfOpenLimit int, pendingPeers int) (ret time.Duration) {
 620         ret = max / time.Duration((pendingPeers+halfOpenLimit)/halfOpenLimit)
 621         if ret < minDialTimeout {
 622                 ret = minDialTimeout
 623         }
 624         return
 625 }
 626
 627 // Start the process of connecting to the given peer for the given torrent if
 628 // appropriate.
 629 func (me *Client) initiateConn(peer Peer, t *torrent) {
 630         if peer.Id == me.peerID {
 631                 return
 632         }
 633         addr := net.JoinHostPort(peer.IP.String(), fmt.Sprintf("%d", peer.Port))
 634         if t.addrActive(addr) {
 635                 duplicateConnsAvoided.Add(1)
 636                 return
 637         }
 638         if r := me.ipBlockRange(peer.IP); r != nil {
 639                 log.Printf("outbound connect to %s blocked by IP blocklist rule %s", peer.IP, r)
 640                 return
 641         }
 642         dialTimeout := reducedDialTimeout(nominalDialTimeout, me.halfOpenLimit, len(t.Peers))
 643         t.HalfOpen[addr] = struct{}{}
 644         go func() {
 645                 // Binding to the listen address and dialing via net.Dialer gives
 646                 // "address in use" error. It seems it's not possible to dial out from
 647                 // this address so that peers associate our local address with our
 648                 // listen address.
 649
 650                 // Initiate connections via TCP and UTP simultaneously. Use the first
 651                 // one that succeeds.
 652                 left := 0
 653                 if !me.disableUTP {
 654                         left++
 655                 }
 656                 if !me.disableTCP {
 657                         left++
 658                 }
 659                 resCh := make(chan dialResult, left)
 660                 if !me.disableUTP {
 661                         go doDial(func() (net.Conn, error) {
 662                                 return me.utpSock.DialTimeout(addr, dialTimeout)
 663                         }, resCh, true)
 664                 }
 665                 if !me.disableTCP {
 666                         go doDial(func() (net.Conn, error) {
 667                                 // time.Sleep(time.Second) // Give uTP a bit of a head start.
 668                                 return net.DialTimeout("tcp", addr, dialTimeout)
 669                         }, resCh, false)
 670                 }
 671                 var res dialResult
 672                 for ; left > 0 && res.Conn == nil; left-- {
 673                         res = <-resCh
 674                 }
 675                 // Whether or not the connection attempt succeeds, the half open
 676                 // counter should be decremented, and new connection attempts made.
 677                 go func() {
 678                         me.mu.Lock()
 679                         defer me.mu.Unlock()
 680                         if _, ok := t.HalfOpen[addr]; !ok {
 681                                 panic("invariant broken")
 682                         }
 683                         delete(t.HalfOpen, addr)
 684                         me.openNewConns(t)
 685                 }()
 686                 if res.Conn == nil {
 687                         return
 688                 }
 689                 if left > 0 {
 690                         go func() {
 691                                 for ; left > 0; left-- {
 692                                         conn := (<-resCh).Conn
 693                                         if conn != nil {
 694                                                 conn.Close()
 695                                         }
 696                                 }
 697                         }()
 698                 }
 699
 700                 // log.Printf("connected to %s", conn.RemoteAddr())
 701                 err := me.runConnection(res.Conn, t, peer.Source, res.UTP)
 702                 if err != nil {
 703                         log.Print(err)
 704                 }
 705         }()
 706 }
 707
 708 // The port number for incoming peer connections. 0 if the client isn't
 709 // listening.
 710 func (cl *Client) incomingPeerPort() int {
 711         listenAddr := cl.ListenAddr()
 712         if listenAddr == nil {
 713                 return 0
 714         }
 715         return addrPort(listenAddr)
 716 }
 717
 718 // Convert a net.Addr to its compact IP representation. Either 4 or 16 bytes
 719 // per "yourip" field of http://www.bittorrent.org/beps/bep_0010.html.
 720 func addrCompactIP(addr net.Addr) (string, error) {
 721         host, _, err := net.SplitHostPort(addr.String())
 722         if err != nil {
 723                 return "", err
 724         }
 725         ip := net.ParseIP(host)
 726         if v4 := ip.To4(); v4 != nil {
 727                 if len(v4) != 4 {
 728                         panic(v4)
 729                 }
 730                 return string(v4), nil
 731         }
 732         return string(ip.To16()), nil
 733 }
 734
 735 func handshakeWriter(w io.WriteCloser, bb <-chan []byte, done chan<- error) {
 736         var err error
 737         for b := range bb {
 738                 _, err = w.Write(b)
 739                 if err != nil {
 740                         w.Close()
 741                         break
 742                 }
 743         }
 744         done <- err
 745 }
 746
 747 type peerExtensionBytes [8]byte
 748 type peerID [20]byte
 749
 750 type handshakeResult struct {
 751         peerExtensionBytes
 752         peerID
 753         InfoHash
 754 }
 755
 756 func handshake(sock io.ReadWriteCloser, ih *InfoHash, peerID [20]byte) (res handshakeResult, ok bool, err error) {
 757         // Bytes to be sent to the peer. Should never block the sender.
 758         postCh := make(chan []byte, 4)
 759         // A single error value sent when the writer completes.
 760         writeDone := make(chan error, 1)
 761         // Performs writes to the socket and ensures posts don't block.
 762         go handshakeWriter(sock, postCh, writeDone)
 763
 764         defer func() {
 765                 close(postCh) // Done writing.
 766                 if !ok {
 767                         return
 768                 }
 769                 if err != nil {
 770                         panic(err)
 771                 }
 772                 // Wait until writes complete before returning from handshake.
 773                 err = <-writeDone
 774                 if err != nil {
 775                         err = fmt.Errorf("error writing during handshake: %s", err)
 776                 }
 777         }()
 778
 779         post := func(bb []byte) {
 780                 select {
 781                 case postCh <- bb:
 782                 default:
 783                         panic("mustn't block while posting")
 784                 }
 785         }
 786
 787         post([]byte(pp.Protocol))
 788         post([]byte(extensionBytes))
 789         if ih != nil { // We already know what we want.
 790                 post(ih[:])
 791                 post(peerID[:])
 792         }
 793         var b [68]byte
 794         _, err = io.ReadFull(sock, b[:68])
 795         if err != nil {
 796                 err = nil
 797                 return
 798         }
 799         if string(b[:20]) != pp.Protocol {
 800                 return
 801         }
 802         CopyExact(&res.peerExtensionBytes, b[20:28])
 803         CopyExact(&res.InfoHash, b[28:48])
 804         CopyExact(&res.peerID, b[48:68])
 805
 806         if ih == nil { // We were waiting for the peer to tell us what they wanted.
 807                 post(res.InfoHash[:])
 808                 post(peerID[:])
 809         }
 810
 811         ok = true
 812         return
 813 }
 814
 815 type peerConn struct {
 816         net.Conn
 817 }
 818
 819 func (pc peerConn) Read(b []byte) (n int, err error) {
 820         // Keep-alives should be received every 2 mins. Give a bit of gracetime.
 821         err = pc.Conn.SetReadDeadline(time.Now().Add(150 * time.Second))
 822         if err != nil {
 823                 err = fmt.Errorf("error setting read deadline: %s", err)
 824         }
 825         n, err = pc.Conn.Read(b)
 826         if err != nil {
 827                 if opError, ok := err.(*net.OpError); ok && opError.Op == "read" && opError.Err == syscall.ECONNRESET {
 828                         err = io.EOF
 829                 } else if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
 830                         if n != 0 {
 831                                 panic(n)
 832                         }
 833                         err = io.EOF
 834                 }
 835         }
 836         return
 837 }
 838
 839 func (me *Client) runConnection(sock net.Conn, torrent *torrent, discovery peerSource, uTP bool) (err error) {
 840         if tcpConn, ok := sock.(*net.TCPConn); ok {
 841                 tcpConn.SetLinger(0)
 842         }
 843         defer sock.Close()
 844         me.mu.Lock()
 845         me.handshaking++
 846         me.mu.Unlock()
 847         // One minute to complete handshake.
 848         sock.SetDeadline(time.Now().Add(time.Minute))
 849         hsRes, ok, err := handshake(sock, func() *InfoHash {
 850                 if torrent == nil {
 851                         return nil
 852                 } else {
 853                         return &torrent.InfoHash
 854                 }
 855         }(), me.peerID)
 856         me.mu.Lock()
 857         defer me.mu.Unlock()
 858         if me.handshaking == 0 {
 859                 panic("handshake count invariant is broken")
 860         }
 861         me.handshaking--
 862         if err != nil {
 863                 err = fmt.Errorf("error during handshake: %s", err)
 864                 return
 865         }
 866         if !ok {
 867                 return
 868         }
 869         if hsRes.peerID == me.peerID {
 870                 return
 871         }
 872         torrent = me.torrent(hsRes.InfoHash)
 873         if torrent == nil {
 874                 return
 875         }
 876         sock.SetWriteDeadline(time.Time{})
 877         sock = peerConn{sock}
 878         conn := newConnection(sock, hsRes.peerExtensionBytes, hsRes.peerID, uTP)
 879         defer conn.Close()
 880         conn.Discovery = discovery
 881         if !me.addConnection(torrent, conn) {
 882                 return
 883         }
 884         if conn.PeerExtensionBytes[5]&0x10 != 0 {
 885                 conn.Post(pp.Message{
 886                         Type:       pp.Extended,
 887                         ExtendedID: pp.HandshakeExtendedID,
 888                         ExtendedPayload: func() []byte {
 889                                 d := map[string]interface{}{
 890                                         "m": map[string]int{
 891                                                 "ut_metadata": 1,
 892                                                 "ut_pex":      2,
 893                                         },
 894                                         "v": "go.torrent dev 20140825", // Just the date
 895                                         // No upload queue is implemented yet.
 896                                         "reqq": func() int {
 897                                                 if me.noUpload {
 898                                                         // No need to look strange if it costs us nothing.
 899                                                         return 250
 900                                                 } else {
 901                                                         return 1
 902                                                 }
 903                                         }(),
 904                                 }
 905                                 if torrent.metadataSizeKnown() {
 906                                         d["metadata_size"] = torrent.metadataSize()
 907                                 }
 908                                 if p := me.incomingPeerPort(); p != 0 {
 909                                         d["p"] = p
 910                                 }
 911                                 yourip, err := addrCompactIP(conn.Socket.RemoteAddr())
 912                                 if err != nil {
 913                                         log.Printf("error calculating yourip field value in extension handshake: %s", err)
 914                                 } else {
 915                                         d["yourip"] = yourip
 916                                 }
 917                                 // log.Printf("sending %v", d)
 918                                 b, err := bencode.Marshal(d)
 919                                 if err != nil {
 920                                         panic(err)
 921                                 }
 922                                 return b
 923                         }(),
 924                 })
 925         }
 926         if torrent.haveAnyPieces() {
 927                 conn.Post(pp.Message{
 928                         Type:     pp.Bitfield,
 929                         Bitfield: torrent.bitfield(),
 930                 })
 931         }
 932         if conn.PeerExtensionBytes[7]&0x01 != 0 && me.dHT != nil {
 933                 conn.Post(pp.Message{
 934                         Type: pp.Port,
 935                         Port: uint16(AddrPort(me.dHT.LocalAddr())),
 936                 })
 937         }
 938         if torrent.haveInfo() {
 939                 torrent.initRequestOrdering(conn)
 940                 me.replenishConnRequests(torrent, conn)
 941         }
 942         err = me.connectionLoop(torrent, conn)
 943         if err != nil {
 944                 err = fmt.Errorf("during Connection loop with peer %q: %s", conn.PeerID, err)
 945         }
 946         me.dropConnection(torrent, conn)
 947         return
 948 }
 949
 950 func (t *torrent) initRequestOrdering(c *connection) {
 951         if c.pieceRequestOrder != nil || c.piecePriorities != nil {
 952                 panic("double init of request ordering")
 953         }
 954         c.piecePriorities = mathRand.Perm(t.NumPieces())
 955         c.pieceRequestOrder = pieceordering.New()
 956         for i := 0; i < t.NumPieces(); i++ {
 957                 if !c.PeerHasPiece(pp.Integer(i)) {
 958                         continue
 959                 }
 960                 if !t.wantPiece(i) {
 961                         continue
 962                 }
 963                 t.connPendPiece(c, i)
 964         }
 965 }
 966
 967 func (me *Client) peerGotPiece(t *torrent, c *connection, piece int) {
 968         if t.haveInfo() {
 969                 if c.PeerPieces == nil {
 970                         c.PeerPieces = make([]bool, t.NumPieces())
 971                 }
 972         } else {
 973                 for piece >= len(c.PeerPieces) {
 974                         c.PeerPieces = append(c.PeerPieces, false)
 975                 }
 976         }
 977         c.PeerPieces[piece] = true
 978         if t.wantPiece(piece) {
 979                 t.connPendPiece(c, piece)
 980                 me.replenishConnRequests(t, c)
 981         }
 982 }
 983
 984 func (me *Client) peerUnchoked(torrent *torrent, conn *connection) {
 985         me.replenishConnRequests(torrent, conn)
 986 }
 987
 988 func (cl *Client) connCancel(t *torrent, cn *connection, r request) (ok bool) {
 989         ok = cn.Cancel(r)
 990         if ok {
 991                 postedCancels.Add(1)
 992                 cl.downloadStrategy.DeleteRequest(t, r)
 993         }
 994         return
 995 }
 996
 997 func (cl *Client) connDeleteRequest(t *torrent, cn *connection, r request) {
 998         if !cn.RequestPending(r) {
 999                 return
1000         }
1001         cl.downloadStrategy.DeleteRequest(t, r)
1002         delete(cn.Requests, r)
1003 }
1004
1005 func (cl *Client) requestPendingMetadata(t *torrent, c *connection) {
1006         if t.haveInfo() {
1007                 return
1008         }
1009         var pending []int
1010         for index := 0; index < t.MetadataPieceCount(); index++ {
1011                 if !t.HaveMetadataPiece(index) {
1012                         pending = append(pending, index)
1013                 }
1014         }
1015         for _, i := range mathRand.Perm(len(pending)) {
1016                 c.Post(pp.Message{
1017                         Type:       pp.Extended,
1018                         ExtendedID: byte(c.PeerExtensionIDs["ut_metadata"]),
1019                         ExtendedPayload: func() []byte {
1020                                 b, err := bencode.Marshal(map[string]int{
1021                                         "msg_type": 0,
1022                                         "piece":    pending[i],
1023                                 })
1024                                 if err != nil {
1025                                         panic(err)
1026                                 }
1027                                 return b
1028                         }(),
1029                 })
1030         }
1031 }
1032
1033 func (cl *Client) completedMetadata(t *torrent) {
1034         h := sha1.New()
1035         h.Write(t.MetaData)
1036         var ih InfoHash
1037         CopyExact(&ih, h.Sum(nil))
1038         if ih != t.InfoHash {
1039                 log.Print("bad metadata")
1040                 t.InvalidateMetadata()
1041                 return
1042         }
1043         var info metainfo.Info
1044         err := bencode.Unmarshal(t.MetaData, &info)
1045         if err != nil {
1046                 log.Printf("error unmarshalling metadata: %s", err)
1047                 t.InvalidateMetadata()
1048                 return
1049         }
1050         // TODO(anacrolix): If this fails, I think something harsher should be
1051         // done.
1052         err = cl.setMetaData(t, info, t.MetaData)
1053         if err != nil {
1054                 log.Printf("error setting metadata: %s", err)
1055                 t.InvalidateMetadata()
1056                 return
1057         }
1058         log.Printf("%s: got metadata from peers", t)
1059 }
1060
1061 // Process incoming ut_metadata message.
1062 func (cl *Client) gotMetadataExtensionMsg(payload []byte, t *torrent, c *connection) (err error) {
1063         var d map[string]int
1064         err = bencode.Unmarshal(payload, &d)
1065         if err != nil {
1066                 err = fmt.Errorf("error unmarshalling payload: %s: %q", err, payload)
1067                 return
1068         }
1069         msgType, ok := d["msg_type"]
1070         if !ok {
1071                 err = errors.New("missing msg_type field")
1072                 return
1073         }
1074         piece := d["piece"]
1075         switch msgType {
1076         case pp.DataMetadataExtensionMsgType:
1077                 if t.haveInfo() {
1078                         break
1079                 }
1080                 begin := len(payload) - metadataPieceSize(d["total_size"], piece)
1081                 if begin < 0 || begin >= len(payload) {
1082                         log.Printf("got bad metadata piece")
1083                         break
1084                 }
1085                 t.SaveMetadataPiece(piece, payload[begin:])
1086                 c.UsefulChunksReceived++
1087                 c.lastUsefulChunkReceived = time.Now()
1088                 if !t.HaveAllMetadataPieces() {
1089                         break
1090                 }
1091                 cl.completedMetadata(t)
1092         case pp.RequestMetadataExtensionMsgType:
1093                 if !t.HaveMetadataPiece(piece) {
1094                         c.Post(t.NewMetadataExtensionMessage(c, pp.RejectMetadataExtensionMsgType, d["piece"], nil))
1095                         break
1096                 }
1097                 start := (1 << 14) * piece
1098                 c.Post(t.NewMetadataExtensionMessage(c, pp.DataMetadataExtensionMsgType, piece, t.MetaData[start:start+t.metadataPieceSize(piece)]))
1099         case pp.RejectMetadataExtensionMsgType:
1100         default:
1101                 err = errors.New("unknown msg_type value")
1102         }
1103         return
1104 }
1105
1106 type peerExchangeMessage struct {
1107         Added      CompactPeers   `bencode:"added"`
1108         AddedFlags []byte         `bencode:"added.f"`
1109         Dropped    []tracker.Peer `bencode:"dropped"`
1110 }
1111
1112 // Extracts the port as an integer from an address string.
1113 func addrPort(addr net.Addr) int {
1114         return AddrPort(addr)
1115 }
1116
1117 // Processes incoming bittorrent messages. The client lock is held upon entry
1118 // and exit.
1119 func (me *Client) connectionLoop(t *torrent, c *connection) error {
1120         decoder := pp.Decoder{
1121                 R:         bufio.NewReader(c.Socket),
1122                 MaxLength: 256 * 1024,
1123         }
1124         for {
1125                 me.mu.Unlock()
1126                 var msg pp.Message
1127                 err := decoder.Decode(&msg)
1128                 me.mu.Lock()
1129                 c.lastMessageReceived = time.Now()
1130                 select {
1131                 case <-c.closing:
1132                         return nil
1133                 default:
1134                 }
1135                 if err != nil {
1136                         if me.stopped() || err == io.EOF {
1137                                 return nil
1138                         }
1139                         return err
1140                 }
1141                 if msg.Keepalive {
1142                         continue
1143                 }
1144                 switch msg.Type {
1145                 case pp.Choke:
1146                         c.PeerChoked = true
1147                         for r := range c.Requests {
1148                                 me.connDeleteRequest(t, c, r)
1149                         }
1150                         // We can then reset our interest.
1151                         me.replenishConnRequests(t, c)
1152                 case pp.Unchoke:
1153                         c.PeerChoked = false
1154                         me.peerUnchoked(t, c)
1155                 case pp.Interested:
1156                         c.PeerInterested = true
1157                         // TODO: This should be done from a dedicated unchoking routine.
1158                         if me.noUpload {
1159                                 break
1160                         }
1161                         c.Unchoke()
1162                 case pp.NotInterested:
1163                         c.PeerInterested = false
1164                         c.Choke()
1165                 case pp.Have:
1166                         me.peerGotPiece(t, c, int(msg.Index))
1167                 case pp.Request:
1168                         if me.noUpload {
1169                                 break
1170                         }
1171                         if c.PeerRequests == nil {
1172                                 c.PeerRequests = make(map[request]struct{}, maxRequests)
1173                         }
1174                         request := newRequest(msg.Index, msg.Begin, msg.Length)
1175                         // TODO: Requests should be satisfied from a dedicated upload routine.
1176                         // c.PeerRequests[request] = struct{}{}
1177                         p := make([]byte, msg.Length)
1178                         n, err := t.Data.ReadAt(p, int64(t.PieceLength(0))*int64(msg.Index)+int64(msg.Begin))
1179                         if err != nil {
1180                                 return fmt.Errorf("reading t data to serve request %q: %s", request, err)
1181                         }
1182                         if n != int(msg.Length) {
1183                                 return fmt.Errorf("bad request: %v", msg)
1184                         }
1185                         c.Post(pp.Message{
1186                                 Type:  pp.Piece,
1187                                 Index: msg.Index,
1188                                 Begin: msg.Begin,
1189                                 Piece: p,
1190                         })
1191                         uploadChunksPosted.Add(1)
1192                 case pp.Cancel:
1193                         req := newRequest(msg.Index, msg.Begin, msg.Length)
1194                         if !c.PeerCancel(req) {
1195                                 unexpectedCancels.Add(1)
1196                         }
1197                 case pp.Bitfield:
1198                         if c.PeerPieces != nil {
1199                                 err = errors.New("received unexpected bitfield")
1200                                 break
1201                         }
1202                         if t.haveInfo() {
1203                                 if len(msg.Bitfield) < t.NumPieces() {
1204                                         err = errors.New("received invalid bitfield")
1205                                         break
1206                                 }
1207                                 msg.Bitfield = msg.Bitfield[:t.NumPieces()]
1208                         }
1209                         c.PeerPieces = msg.Bitfield
1210                         for index, has := range c.PeerPieces {
1211                                 if has {
1212                                         me.peerGotPiece(t, c, index)
1213                                 }
1214                         }
1215                 case pp.Piece:
1216                         err = me.downloadedChunk(t, c, &msg)
1217                 case pp.Extended:
1218                         switch msg.ExtendedID {
1219                         case pp.HandshakeExtendedID:
1220                                 // TODO: Create a bencode struct for this.
1221                                 var d map[string]interface{}
1222                                 err = bencode.Unmarshal(msg.ExtendedPayload, &d)
1223                                 if err != nil {
1224                                         err = fmt.Errorf("error decoding extended message payload: %s", err)
1225                                         break
1226                                 }
1227                                 // log.Printf("got handshake from %q: %#v", c.Socket.RemoteAddr().String(), d)
1228                                 if reqq, ok := d["reqq"]; ok {
1229                                         if i, ok := reqq.(int64); ok {
1230                                                 c.PeerMaxRequests = int(i)
1231                                         }
1232                                 }
1233                                 if v, ok := d["v"]; ok {
1234                                         c.PeerClientName = v.(string)
1235                                 }
1236                                 m, ok := d["m"]
1237                                 if !ok {
1238                                         err = errors.New("handshake missing m item")
1239                                         break
1240                                 }
1241                                 mTyped, ok := m.(map[string]interface{})
1242                                 if !ok {
1243                                         err = errors.New("handshake m value is not dict")
1244                                         break
1245                                 }
1246                                 if c.PeerExtensionIDs == nil {
1247                                         c.PeerExtensionIDs = make(map[string]int64, len(mTyped))
1248                                 }
1249                                 for name, v := range mTyped {
1250                                         id, ok := v.(int64)
1251                                         if !ok {
1252                                                 log.Printf("bad handshake m item extension ID type: %T", v)
1253                                                 continue
1254                                         }
1255                                         if id == 0 {
1256                                                 delete(c.PeerExtensionIDs, name)
1257                                         } else {
1258                                                 c.PeerExtensionIDs[name] = id
1259                                         }
1260                                 }
1261                                 metadata_sizeUntyped, ok := d["metadata_size"]
1262                                 if ok {
1263                                         metadata_size, ok := metadata_sizeUntyped.(int64)
1264                                         if !ok {
1265                                                 log.Printf("bad metadata_size type: %T", metadata_sizeUntyped)
1266                                         } else {
1267                                                 t.SetMetadataSize(metadata_size)
1268                                         }
1269                                 }
1270                                 if _, ok := c.PeerExtensionIDs["ut_metadata"]; ok {
1271                                         me.requestPendingMetadata(t, c)
1272                                 }
1273                         case 1:
1274                                 err = me.gotMetadataExtensionMsg(msg.ExtendedPayload, t, c)
1275                                 if err != nil {
1276                                         err = fmt.Errorf("error handling metadata extension message: %s", err)
1277                                 }
1278                         case 2:
1279                                 var pexMsg peerExchangeMessage
1280                                 err := bencode.Unmarshal(msg.ExtendedPayload, &pexMsg)
1281                                 if err != nil {
1282                                         err = fmt.Errorf("error unmarshalling PEX message: %s", err)
1283                                         break
1284                                 }
1285                                 go func() {
1286                                         err := me.AddPeers(t.InfoHash, func() (ret []Peer) {
1287                                                 for _, cp := range pexMsg.Added {
1288                                                         p := Peer{
1289                                                                 IP:     make([]byte, 4),
1290                                                                 Port:   int(cp.Port),
1291                                                                 Source: peerSourcePEX,
1292                                                         }
1293                                                         if n := copy(p.IP, cp.IP[:]); n != 4 {
1294                                                                 panic(n)
1295                                                         }
1296                                                         ret = append(ret, p)
1297                                                 }
1298                                                 return
1299                                         }())
1300                                         if err != nil {
1301                                                 log.Printf("error adding PEX peers: %s", err)
1302                                                 return
1303                                         }
1304                                         peersFoundByPEX.Add(int64(len(pexMsg.Added)))
1305                                 }()
1306                         default:
1307                                 err = fmt.Errorf("unexpected extended message ID: %v", msg.ExtendedID)
1308                         }
1309                         if err != nil {
1310                                 // That client uses its own extension IDs for outgoing message
1311                                 // types, which is incorrect.
1312                                 if bytes.HasPrefix(c.PeerID[:], []byte("-SD0100-")) ||
1313                                         strings.HasPrefix(string(c.PeerID[:]), "-XL0012-") {
1314                                         return nil
1315                                 }
1316                                 // log.Printf("peer extension map: %#v", c.PeerExtensionIDs)
1317                         }
1318                 case pp.Port:
1319                         if me.dHT == nil {
1320                                 break
1321                         }
1322                         pingAddr, err := net.ResolveUDPAddr("", c.Socket.RemoteAddr().String())
1323                         if err != nil {
1324                                 panic(err)
1325                         }
1326                         if msg.Port != 0 {
1327                                 pingAddr.Port = int(msg.Port)
1328                         }
1329                         _, err = me.dHT.Ping(pingAddr)
1330                 default:
1331                         err = fmt.Errorf("received unknown message type: %#v", msg.Type)
1332                 }
1333                 if err != nil {
1334                         return err
1335                 }
1336         }
1337 }
1338
1339 func (me *Client) dropConnection(torrent *torrent, conn *connection) {
1340         for r := range conn.Requests {
1341                 me.connDeleteRequest(torrent, conn, r)
1342         }
1343         conn.Close()
1344         for i0, c := range torrent.Conns {
1345                 if c != conn {
1346                         continue
1347                 }
1348                 i1 := len(torrent.Conns) - 1
1349                 if i0 != i1 {
1350                         torrent.Conns[i0] = torrent.Conns[i1]
1351                 }
1352                 torrent.Conns = torrent.Conns[:i1]
1353                 me.openNewConns(torrent)
1354                 return
1355         }
1356         panic("connection not found")
1357 }
1358
1359 func (me *Client) addConnection(t *torrent, c *connection) bool {
1360         if me.stopped() {
1361                 return false
1362         }
1363         select {
1364         case <-t.ceasingNetworking:
1365                 return false
1366         default:
1367         }
1368         if !me.wantConns(t) {
1369                 return false
1370         }
1371         for _, c0 := range t.Conns {
1372                 if c.PeerID == c0.PeerID {
1373                         // Already connected to a client with that ID.
1374                         return false
1375                 }
1376         }
1377         t.Conns = append(t.Conns, c)
1378         // TODO: This should probably be done by a routine that kills off bad
1379         // connections, and extra connections killed here instead.
1380         if len(t.Conns) > socketsPerTorrent {
1381                 wcs := t.worstConnsHeap()
1382                 heap.Pop(wcs).(*connection).Close()
1383         }
1384         return true
1385 }
1386
1387 func (t *torrent) needData() bool {
1388         if !t.haveInfo() {
1389                 return true
1390         }
1391         for i := range t.Pieces {
1392                 if t.wantPiece(i) {
1393                         return true
1394                 }
1395         }
1396         return false
1397 }
1398
1399 // TODO: I'm sure there's something here to do with seeding.
1400 func (t *torrent) badConn(c *connection) bool {
1401         if time.Now().Sub(c.completedHandshake) < 30*time.Second {
1402                 return false
1403         }
1404         if !t.haveInfo() {
1405                 return !c.supportsExtension("ut_metadata")
1406         }
1407         return !t.connHasWantedPieces(c)
1408 }
1409
1410 func (t *torrent) numGoodConns() (num int) {
1411         for _, c := range t.Conns {
1412                 if !t.badConn(c) {
1413                         num++
1414                 }
1415         }
1416         return
1417 }
1418
1419 func (me *Client) wantConns(t *torrent) bool {
1420         if !t.needData() && me.noUpload {
1421                 return false
1422         }
1423         if t.numGoodConns() >= socketsPerTorrent {
1424                 return false
1425         }
1426         return true
1427 }
1428
1429 func (me *Client) openNewConns(t *torrent) {
1430         select {
1431         case <-t.ceasingNetworking:
1432                 return
1433         default:
1434         }
1435         for len(t.Peers) != 0 {
1436                 if !me.wantConns(t) {
1437                         return
1438                 }
1439                 if len(t.HalfOpen) >= me.halfOpenLimit {
1440                         return
1441                 }
1442                 var (
1443                         k peersKey
1444                         p Peer
1445                 )
1446                 for k, p = range t.Peers {
1447                         break
1448                 }
1449                 delete(t.Peers, k)
1450                 me.initiateConn(p, t)
1451         }
1452         t.wantPeers.Broadcast()
1453 }
1454
1455 func (me *Client) addPeers(t *torrent, peers []Peer) {
1456         blocked := 0
1457         for i, p := range peers {
1458                 if me.ipBlockRange(p.IP) == nil {
1459                         continue
1460                 }
1461                 peers[i] = peers[len(peers)-1]
1462                 peers = peers[:len(peers)-1]
1463                 i--
1464                 blocked++
1465         }
1466         if blocked != 0 {
1467                 log.Printf("IP blocklist screened %d peers from being added", blocked)
1468         }
1469         t.AddPeers(peers)
1470         me.openNewConns(t)
1471 }
1472
1473 // Adds peers to the swarm for the torrent corresponding to infoHash.
1474 func (me *Client) AddPeers(infoHash InfoHash, peers []Peer) error {
1475         me.mu.Lock()
1476         defer me.mu.Unlock()
1477         t := me.torrent(infoHash)
1478         if t == nil {
1479                 return errors.New("no such torrent")
1480         }
1481         me.addPeers(t, peers)
1482         return nil
1483 }
1484
1485 func (cl *Client) torrentFileCachePath(ih InfoHash) string {
1486         return filepath.Join(cl.configDir(), "torrents", ih.HexString()+".torrent")
1487 }
1488
1489 func (cl *Client) saveTorrentFile(t *torrent) error {
1490         path := cl.torrentFileCachePath(t.InfoHash)
1491         os.MkdirAll(filepath.Dir(path), 0777)
1492         f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
1493         if err != nil {
1494                 return fmt.Errorf("error opening file: %s", err)
1495         }
1496         defer f.Close()
1497         e := bencode.NewEncoder(f)
1498         err = e.Encode(t.MetaInfo())
1499         if err != nil {
1500                 return fmt.Errorf("error marshalling metainfo: %s", err)
1501         }
1502         mi, _ := cl.torrentCacheMetaInfo(t.InfoHash)
1503         if !bytes.Equal(mi.Info.Hash, t.InfoHash[:]) {
1504                 log.Fatalf("%x != %x", mi.Info.Hash, t.InfoHash[:])
1505         }
1506         return nil
1507 }
1508
1509 func (cl *Client) setMetaData(t *torrent, md metainfo.Info, bytes []byte) (err error) {
1510         err = t.setMetadata(md, cl.dataDir, bytes, &cl.mu)
1511         if err != nil {
1512                 return
1513         }
1514         // If the client intends to upload, it needs to know what state pieces are
1515         // in.
1516         if !cl.noUpload {
1517                 // Queue all pieces for hashing. This is done sequentially to avoid
1518                 // spamming goroutines.
1519                 for _, p := range t.Pieces {
1520                         p.QueuedForHash = true
1521                 }
1522                 go func() {
1523                         for i := range t.Pieces {
1524                                 cl.verifyPiece(t, pp.Integer(i))
1525                         }
1526                 }()
1527         }
1528
1529         cl.downloadStrategy.TorrentStarted(t)
1530         if err := cl.saveTorrentFile(t); err != nil {
1531                 log.Printf("error saving torrent file for %s: %s", t, err)
1532         }
1533         close(t.gotMetainfo)
1534         return
1535 }
1536
1537 // Prepare a Torrent without any attachment to a Client. That means we can
1538 // initialize fields all fields that don't require the Client without locking
1539 // it.
1540 func newTorrent(ih InfoHash, announceList [][]string, halfOpenLimit int) (t *torrent, err error) {
1541         t = &torrent{
1542                 InfoHash: ih,
1543                 Peers:    make(map[peersKey]Peer),
1544
1545                 closing:           make(chan struct{}),
1546                 ceasingNetworking: make(chan struct{}),
1547
1548                 gotMetainfo: make(chan struct{}),
1549
1550                 HalfOpen: make(map[string]struct{}),
1551         }
1552         t.wantPeers.L = &t.stateMu
1553         t.GotMetainfo = t.gotMetainfo
1554         t.addTrackers(announceList)
1555         return
1556 }
1557
1558 func init() {
1559         // For shuffling the tracker tiers.
1560         mathRand.Seed(time.Now().Unix())
1561 }
1562
1563 // The trackers within each tier must be shuffled before use.
1564 // http://stackoverflow.com/a/12267471/149482
1565 // http://www.bittorrent.org/beps/bep_0012.html#order-of-processing
1566 func shuffleTier(tier []tracker.Client) {
1567         for i := range tier {
1568                 j := mathRand.Intn(i + 1)
1569                 tier[i], tier[j] = tier[j], tier[i]
1570         }
1571 }
1572
1573 func copyTrackers(base [][]tracker.Client) (copy [][]tracker.Client) {
1574         for _, tier := range base {
1575                 copy = append(copy, append([]tracker.Client{}, tier...))
1576         }
1577         return
1578 }
1579
1580 func mergeTier(tier []tracker.Client, newURLs []string) []tracker.Client {
1581 nextURL:
1582         for _, url := range newURLs {
1583                 for _, tr := range tier {
1584                         if tr.URL() == url {
1585                                 continue nextURL
1586                         }
1587                 }
1588                 tr, err := tracker.New(url)
1589                 if err != nil {
1590                         log.Printf("error creating tracker client for %q: %s", url, err)
1591                         continue
1592                 }
1593                 tier = append(tier, tr)
1594         }
1595         return tier
1596 }
1597
1598 func (t *torrent) addTrackers(announceList [][]string) {
1599         newTrackers := copyTrackers(t.Trackers)
1600         for tierIndex, tier := range announceList {
1601                 if tierIndex < len(newTrackers) {
1602                         newTrackers[tierIndex] = mergeTier(newTrackers[tierIndex], tier)
1603                 } else {
1604                         newTrackers = append(newTrackers, mergeTier(nil, tier))
1605                 }
1606                 shuffleTier(newTrackers[tierIndex])
1607         }
1608         t.Trackers = newTrackers
1609 }
1610
1611 type Torrent struct {
1612         cl *Client
1613         *torrent
1614 }
1615
1616 type File struct {
1617         t      Torrent
1618         path   string
1619         offset int64
1620         length int64
1621 }
1622
1623 func (f *File) Length() int64 {
1624         return f.length
1625 }
1626
1627 func (f *File) PrioritizeRegion(off, len int64) {
1628         if off < 0 || off >= f.length {
1629                 return
1630         }
1631         if off+len > f.length {
1632                 len = f.length - off
1633         }
1634         off += f.offset
1635         f.t.SetRegionPriority(off, len)
1636 }
1637
1638 // Returns handles to the files in the torrent. This requires the metainfo is
1639 // available first.
1640 func (t Torrent) Files() (ret []File) {
1641         var offset int64
1642         for _, fi := range t.Info.UpvertedFiles() {
1643                 ret = append(ret, File{
1644                         t,
1645                         strings.Join(fi.Path, "/"),
1646                         offset,
1647                         fi.Length,
1648                 })
1649                 offset += fi.Length
1650         }
1651         return
1652 }
1653
1654 func (t Torrent) SetRegionPriority(off, len int64) {
1655         t.cl.mu.Lock()
1656         defer t.cl.mu.Unlock()
1657         pieceSize := int64(t.UsualPieceSize())
1658         for i := off / pieceSize; i*pieceSize < off+len; i++ {
1659                 t.cl.prioritizePiece(t.torrent, int(i), piecePriorityNormal)
1660         }
1661 }
1662
1663 func (t Torrent) MetainfoFilepath() string {
1664         return filepath.Join(t.cl.ConfigDir(), "torrents", t.InfoHash.HexString()+".torrent")
1665 }
1666
1667 func (t Torrent) AddPeers(pp []Peer) error {
1668         return t.cl.AddPeers(t.torrent.InfoHash, pp)
1669 }
1670
1671 func (t Torrent) DownloadAll() {
1672         t.cl.mu.Lock()
1673         for i := 0; i < t.NumPieces(); i++ {
1674                 // TODO: Leave higher priorities as they were?
1675                 t.cl.prioritizePiece(t.torrent, i, piecePriorityNormal)
1676         }
1677         // Nice to have the first and last pieces soon for various interactive
1678         // purposes.
1679         t.cl.prioritizePiece(t.torrent, 0, piecePriorityReadahead)
1680         t.cl.prioritizePiece(t.torrent, t.NumPieces()-1, piecePriorityReadahead)
1681         t.cl.mu.Unlock()
1682 }
1683
1684 func (me Torrent) ReadAt(p []byte, off int64) (n int, err error) {
1685         return me.cl.torrentReadAt(me.torrent, off, p)
1686 }
1687
1688 func (cl *Client) torrentCacheMetaInfo(ih InfoHash) (mi *metainfo.MetaInfo, err error) {
1689         f, err := os.Open(cl.torrentFileCachePath(ih))
1690         if err != nil {
1691                 if os.IsNotExist(err) {
1692                         err = nil
1693                 }
1694                 return
1695         }
1696         defer f.Close()
1697         dec := bencode.NewDecoder(f)
1698         err = dec.Decode(&mi)
1699         if err != nil {
1700                 return
1701         }
1702         if !bytes.Equal(mi.Info.Hash, ih[:]) {
1703                 err = fmt.Errorf("cached torrent has wrong infohash: %x != %x", mi.Info.Hash, ih[:])
1704                 return
1705         }
1706         return
1707 }
1708
1709 func (cl *Client) AddMagnet(uri string) (T Torrent, err error) {
1710         m, err := ParseMagnetURI(uri)
1711         if err != nil {
1712                 return
1713         }
1714         mi, err := cl.torrentCacheMetaInfo(m.InfoHash)
1715         if err != nil {
1716                 log.Printf("error getting cached metainfo for %x: %s", m.InfoHash[:], err)
1717         } else if mi != nil {
1718                 cl.AddTorrent(mi)
1719         }
1720         cl.mu.Lock()
1721         defer cl.mu.Unlock()
1722         T, err = cl.addOrMergeTorrent(m.InfoHash, [][]string{m.Trackers})
1723         if err != nil {
1724                 return
1725         }
1726         if m.DisplayName != "" {
1727                 T.DisplayName = m.DisplayName
1728         }
1729         return
1730 }
1731
1732 // Actively prunes unused connections. This is required to make space to dial
1733 // for replacements.
1734 func (cl *Client) connectionPruner(t *torrent) {
1735         for {
1736                 time.Sleep(15 * time.Second)
1737                 cl.mu.Lock()
1738                 select {
1739                 case <-t.ceasingNetworking:
1740                 default:
1741                 }
1742                 license := len(t.Conns) - (socketsPerTorrent+1)/2
1743                 for _, c := range t.Conns {
1744                         if license <= 0 {
1745                                 break
1746                         }
1747                         if time.Now().Sub(c.lastUsefulChunkReceived) < time.Minute {
1748                                 continue
1749                         }
1750                         if time.Now().Sub(c.completedHandshake) < time.Minute {
1751                                 continue
1752                         }
1753                         c.Close()
1754                         license--
1755                 }
1756                 cl.mu.Unlock()
1757         }
1758 }
1759
1760 func (me *Client) DropTorrent(infoHash InfoHash) (err error) {
1761         me.mu.Lock()
1762         defer me.mu.Unlock()
1763         t, ok := me.torrents[infoHash]
1764         if !ok {
1765                 err = fmt.Errorf("no such torrent")
1766                 return
1767         }
1768         err = t.Close()
1769         if err != nil {
1770                 panic(err)
1771         }
1772         delete(me.torrents, infoHash)
1773         me.downloadStrategy.TorrentStopped(t)
1774         for _, dw := range me.dataWaits[t] {
1775                 close(dw.ready)
1776         }
1777         delete(me.dataWaits, t)
1778         return
1779 }
1780
1781 func (me *Client) addOrMergeTorrent(ih InfoHash, announceList [][]string) (T Torrent, err error) {
1782         if _, ok := me.bannedTorrents[ih]; ok {
1783                 err = errors.New("banned torrent")
1784                 return
1785         }
1786         T.cl = me
1787         var ok bool
1788         T.torrent, ok = me.torrents[ih]
1789         if ok {
1790                 T.torrent.addTrackers(announceList)
1791         } else {
1792                 T.torrent, err = newTorrent(ih, announceList, me.halfOpenLimit)
1793                 if err != nil {
1794                         return
1795                 }
1796                 me.torrents[ih] = T.torrent
1797                 if !me.disableTrackers {
1798                         go me.announceTorrentTrackers(T.torrent)
1799                 }
1800                 if me.dHT != nil {
1801                         go me.announceTorrentDHT(T.torrent, true)
1802                 }
1803                 go me.connectionPruner(T.torrent)
1804         }
1805         return
1806 }
1807
1808 // Adds the torrent to the client.
1809 func (me *Client) AddTorrent(metaInfo *metainfo.MetaInfo) (t Torrent, err error) {
1810         var ih InfoHash
1811         CopyExact(&ih, metaInfo.Info.Hash)
1812         me.mu.Lock()
1813         defer me.mu.Unlock()
1814         t, err = me.addOrMergeTorrent(ih, metaInfo.AnnounceList)
1815         if err != nil {
1816                 return
1817         }
1818         if !t.torrent.haveInfo() {
1819                 err = me.setMetaData(t.torrent, metaInfo.Info.Info, metaInfo.Info.Bytes)
1820                 if err != nil {
1821                         return
1822                 }
1823         }
1824         return
1825 }
1826
1827 func (me *Client) AddTorrentFromFile(name string) (t Torrent, err error) {
1828         mi, err := metainfo.LoadFromFile(name)
1829         if err != nil {
1830                 err = fmt.Errorf("error loading metainfo from file: %s", err)
1831                 return
1832         }
1833         return me.AddTorrent(mi)
1834 }
1835
1836 // Returns true when peers are required, or false if the torrent is closing.
1837 func (cl *Client) waitWantPeers(t *torrent) bool {
1838         cl.mu.Lock()
1839         defer cl.mu.Unlock()
1840         t.stateMu.Lock()
1841         defer t.stateMu.Unlock()
1842         for {
1843                 select {
1844                 case <-t.ceasingNetworking:
1845                         return false
1846                 default:
1847                 }
1848                 if len(t.Peers) < torrentPeersLowWater {
1849                         return true
1850                 }
1851                 cl.mu.Unlock()
1852                 t.wantPeers.Wait()
1853                 t.stateMu.Unlock()
1854                 cl.mu.Lock()
1855                 t.stateMu.Lock()
1856         }
1857 }
1858
1859 func (cl *Client) announceTorrentDHT(t *torrent, impliedPort bool) {
1860         for cl.waitWantPeers(t) {
1861                 log.Printf("getting peers for %q from DHT", t)
1862                 ps, err := cl.dHT.Announce(string(t.InfoHash[:]), cl.incomingPeerPort(), impliedPort)
1863                 if err != nil {
1864                         log.Printf("error getting peers from dht: %s", err)
1865                         return
1866                 }
1867                 allAddrs := make(map[string]struct{})
1868         getPeers:
1869                 for {
1870                         select {
1871                         case v, ok := <-ps.Values:
1872                                 if !ok {
1873                                         break getPeers
1874                                 }
1875                                 peersFoundByDHT.Add(int64(len(v.Peers)))
1876                                 for _, p := range v.Peers {
1877                                         allAddrs[(&net.UDPAddr{
1878                                                 IP:   p.IP[:],
1879                                                 Port: int(p.Port),
1880                                         }).String()] = struct{}{}
1881                                 }
1882                                 // log.Printf("%s: %d new peers from DHT", t, len(v.Peers))
1883                                 cl.mu.Lock()
1884                                 cl.addPeers(t, func() (ret []Peer) {
1885                                         for _, cp := range v.Peers {
1886                                                 ret = append(ret, Peer{
1887                                                         IP:     cp.IP[:],
1888                                                         Port:   int(cp.Port),
1889                                                         Source: peerSourceDHT,
1890                                                 })
1891                                         }
1892                                         return
1893                                 }())
1894                                 numPeers := len(t.Peers)
1895                                 cl.mu.Unlock()
1896                                 if numPeers >= torrentPeersHighWater {
1897                                         break getPeers
1898                                 }
1899                         case <-t.ceasingNetworking:
1900                                 ps.Close()
1901                                 return
1902                         }
1903                 }
1904                 ps.Close()
1905                 log.Printf("finished DHT peer scrape for %s: %d peers", t, len(allAddrs))
1906
1907         }
1908 }
1909
1910 func (cl *Client) announceTorrentSingleTracker(tr tracker.Client, req *tracker.AnnounceRequest, t *torrent) error {
1911         if err := tr.Connect(); err != nil {
1912                 return fmt.Errorf("error connecting: %s", err)
1913         }
1914         resp, err := tr.Announce(req)
1915         if err != nil {
1916                 return fmt.Errorf("error announcing: %s", err)
1917         }
1918         var peers []Peer
1919         for _, peer := range resp.Peers {
1920                 peers = append(peers, Peer{
1921                         IP:   peer.IP,
1922                         Port: peer.Port,
1923                 })
1924         }
1925         err = cl.AddPeers(t.InfoHash, peers)
1926         if err != nil {
1927                 log.Printf("error adding peers to torrent %s: %s", t, err)
1928         } else {
1929                 log.Printf("%s: %d new peers from %s", t, len(peers), tr)
1930         }
1931
1932         time.Sleep(time.Second * time.Duration(resp.Interval))
1933         return nil
1934 }
1935
1936 func (cl *Client) announceTorrentTrackersFastStart(req *tracker.AnnounceRequest, trackers [][]tracker.Client, t *torrent) (atLeastOne bool) {
1937         oks := make(chan bool)
1938         outstanding := 0
1939         for _, tier := range trackers {
1940                 for _, tr := range tier {
1941                         outstanding++
1942                         go func(tr tracker.Client) {
1943                                 err := cl.announceTorrentSingleTracker(tr, req, t)
1944                                 oks <- err == nil
1945                         }(tr)
1946                 }
1947         }
1948         for outstanding > 0 {
1949                 ok := <-oks
1950                 outstanding--
1951                 if ok {
1952                         atLeastOne = true
1953                 }
1954         }
1955         return
1956 }
1957
1958 // Announce torrent to its trackers.
1959 func (cl *Client) announceTorrentTrackers(t *torrent) {
1960         req := tracker.AnnounceRequest{
1961                 Event:    tracker.Started,
1962                 NumWant:  -1,
1963                 Port:     int16(cl.incomingPeerPort()),
1964                 PeerId:   cl.peerID,
1965                 InfoHash: t.InfoHash,
1966         }
1967         cl.mu.RLock()
1968         req.Left = t.BytesLeft()
1969         trackers := t.Trackers
1970         cl.mu.RUnlock()
1971         if cl.announceTorrentTrackersFastStart(&req, trackers, t) {
1972                 req.Event = tracker.None
1973         }
1974 newAnnounce:
1975         for cl.waitWantPeers(t) {
1976                 cl.mu.RLock()
1977                 req.Left = t.BytesLeft()
1978                 trackers = t.Trackers
1979                 cl.mu.RUnlock()
1980                 numTrackersTried := 0
1981                 for _, tier := range trackers {
1982                         for trIndex, tr := range tier {
1983                                 numTrackersTried++
1984                                 err := cl.announceTorrentSingleTracker(tr, &req, t)
1985                                 if err != nil {
1986                                         continue
1987                                 }
1988                                 // Float the successful announce to the top of the tier. If
1989                                 // the trackers list has been changed, we'll be modifying an
1990                                 // old copy so it won't matter.
1991                                 cl.mu.Lock()
1992                                 tier[0], tier[trIndex] = tier[trIndex], tier[0]
1993                                 cl.mu.Unlock()
1994
1995                                 req.Event = tracker.None
1996                                 continue newAnnounce
1997                         }
1998                 }
1999                 if numTrackersTried != 0 {
2000                         log.Printf("%s: all trackers failed", t)
2001                 }
2002                 // TODO: Wait until trackers are added if there are none.
2003                 time.Sleep(10 * time.Second)
2004         }
2005 }
2006
2007 func (cl *Client) allTorrentsCompleted() bool {
2008         for _, t := range cl.torrents {
2009                 if !t.haveInfo() {
2010                         return false
2011                 }
2012                 if t.NumPiecesCompleted() != t.NumPieces() {
2013                         return false
2014                 }
2015         }
2016         return true
2017 }
2018
2019 // Returns true when all torrents are completely downloaded and false if the
2020 // client is stopped before that.
2021 func (me *Client) WaitAll() bool {
2022         me.mu.Lock()
2023         defer me.mu.Unlock()
2024         for !me.allTorrentsCompleted() {
2025                 if me.stopped() {
2026                         return false
2027                 }
2028                 me.event.Wait()
2029         }
2030         return true
2031 }
2032
2033 func (me *Client) replenishConnRequests(t *torrent, c *connection) {
2034         if !t.haveInfo() {
2035                 return
2036         }
2037         me.downloadStrategy.FillRequests(t, c)
2038         if len(c.Requests) == 0 && !c.PeerChoked {
2039                 c.SetInterested(false)
2040         }
2041 }
2042
2043 // Handle a received chunk from a peer.
2044 func (me *Client) downloadedChunk(t *torrent, c *connection, msg *pp.Message) error {
2045         chunksDownloadedCount.Add(1)
2046
2047         req := newRequest(msg.Index, msg.Begin, pp.Integer(len(msg.Piece)))
2048
2049         // Request has been satisfied.
2050         me.connDeleteRequest(t, c, req)
2051
2052         defer me.replenishConnRequests(t, c)
2053
2054         // Do we actually want this chunk?
2055         if _, ok := t.Pieces[req.Index].PendingChunkSpecs[req.chunkSpec]; !ok {
2056                 unusedDownloadedChunksCount.Add(1)
2057                 c.UnwantedChunksReceived++
2058                 return nil
2059         }
2060
2061         c.UsefulChunksReceived++
2062         c.lastUsefulChunkReceived = time.Now()
2063
2064         // Write the chunk out.
2065         err := t.WriteChunk(int(msg.Index), int64(msg.Begin), msg.Piece)
2066         if err != nil {
2067                 return fmt.Errorf("error writing chunk: %s", err)
2068         }
2069
2070         // Record that we have the chunk.
2071         delete(t.Pieces[req.Index].PendingChunkSpecs, req.chunkSpec)
2072         me.dataReady(t, req)
2073         if len(t.Pieces[req.Index].PendingChunkSpecs) == 0 {
2074                 for _, c := range t.Conns {
2075                         c.pieceRequestOrder.DeletePiece(int(req.Index))
2076                 }
2077                 me.queuePieceCheck(t, req.Index)
2078         }
2079
2080         // Unprioritize the chunk.
2081         me.downloadStrategy.TorrentGotChunk(t, req)
2082
2083         // Cancel pending requests for this chunk.
2084         for _, c := range t.Conns {
2085                 if me.connCancel(t, c, req) {
2086                         me.replenishConnRequests(t, c)
2087                 }
2088         }
2089
2090         me.downloadStrategy.AssertNotRequested(t, req)
2091
2092         return nil
2093 }
2094
2095 func (cl *Client) dataReady(t *torrent, r request) {
2096         dws := cl.dataWaits[t]
2097         begin := t.requestOffset(r)
2098         end := begin + int64(r.Length)
2099         for i := 0; i < len(dws); {
2100                 dw := dws[i]
2101                 if begin <= dw.offset && dw.offset < end {
2102                         close(dw.ready)
2103                         dws[i] = dws[len(dws)-1]
2104                         dws = dws[:len(dws)-1]
2105                 } else {
2106                         i++
2107                 }
2108         }
2109         cl.dataWaits[t] = dws
2110 }
2111
2112 // Returns a channel that is closed when new data has become available in the
2113 // client.
2114 func (me *Client) DataWaiter(ih InfoHash, off int64) (ret <-chan struct{}) {
2115         me.mu.Lock()
2116         defer me.mu.Unlock()
2117         ch := make(chan struct{})
2118         ret = ch
2119         t := me.torrents[ih]
2120         if t == nil {
2121                 close(ch)
2122                 return
2123         }
2124         if r, ok := t.offsetRequest(off); !ok || t.haveChunk(r) {
2125                 close(ch)
2126                 return
2127         }
2128         me.dataWaits[t] = append(me.dataWaits[t], dataWait{
2129                 offset: off,
2130                 ready:  ch,
2131         })
2132         return
2133 }
2134
2135 func (me *Client) pieceHashed(t *torrent, piece pp.Integer, correct bool) {
2136         p := t.Pieces[piece]
2137         if p.EverHashed && !correct {
2138                 log.Printf("%s: piece %d failed hash", t, piece)
2139                 failedPieceHashes.Add(1)
2140         }
2141         p.EverHashed = true
2142         if correct {
2143                 p.Priority = piecePriorityNone
2144                 p.PendingChunkSpecs = nil
2145                 p.Event.Broadcast()
2146                 me.downloadStrategy.TorrentGotPiece(t, int(piece))
2147                 me.dataReady(t, request{
2148                         pp.Integer(piece),
2149                         chunkSpec{0, pp.Integer(t.PieceLength(piece))},
2150                 })
2151         } else {
2152                 if len(p.PendingChunkSpecs) == 0 {
2153                         t.pendAllChunkSpecs(piece)
2154                 }
2155                 if p.Priority != piecePriorityNone {
2156                         me.openNewConns(t)
2157                 }
2158         }
2159         for _, conn := range t.Conns {
2160                 if correct {
2161                         conn.Post(pp.Message{
2162                                 Type:  pp.Have,
2163                                 Index: pp.Integer(piece),
2164                         })
2165                         // TODO: Cancel requests for this piece.
2166                         for r := range conn.Requests {
2167                                 if r.Index == piece {
2168                                         panic("wat")
2169                                 }
2170                         }
2171                         conn.pieceRequestOrder.DeletePiece(int(piece))
2172                 }
2173                 if t.wantPiece(int(piece)) && conn.PeerHasPiece(piece) {
2174                         t.connPendPiece(conn, int(piece))
2175                         me.replenishConnRequests(t, conn)
2176                 }
2177         }
2178         if t.haveAllPieces() && me.noUpload {
2179                 t.CeaseNetworking()
2180         }
2181         me.event.Broadcast()
2182 }
2183
2184 func (cl *Client) verifyPiece(t *torrent, index pp.Integer) {
2185         cl.mu.Lock()
2186         defer cl.mu.Unlock()
2187         p := t.Pieces[index]
2188         for p.Hashing {
2189                 cl.event.Wait()
2190         }
2191         if t.isClosed() {
2192                 return
2193         }
2194         p.Hashing = true
2195         p.QueuedForHash = false
2196         cl.mu.Unlock()
2197         sum := t.HashPiece(index)
2198         cl.mu.Lock()
2199         select {
2200         case <-t.closing:
2201                 return
2202         default:
2203         }
2204         p.Hashing = false
2205         cl.pieceHashed(t, index, sum == p.Hash)
2206 }
2207
2208 func (me *Client) Torrents() (ret []Torrent) {
2209         me.mu.Lock()
2210         for _, t := range me.torrents {
2211                 ret = append(ret, Torrent{me, t})
2212         }
2213         me.mu.Unlock()
2214         return
2215 }