package tracker import ( "bytes" "encoding" "encoding/binary" "fmt" "math/rand" "net" "github.com/anacrolix/dht/krpc" "github.com/anacrolix/missinggo" ) type torrent struct { Leechers int32 Seeders int32 Peers []krpc.NodeAddr } type server struct { pc net.PacketConn conns map[int64]struct{} t map[[20]byte]torrent } func marshal(parts ...interface{}) (ret []byte, err error) { var buf bytes.Buffer for _, p := range parts { err = binary.Write(&buf, binary.BigEndian, p) if err != nil { return } } ret = buf.Bytes() return } func (s *server) respond(addr net.Addr, rh ResponseHeader, parts ...interface{}) (err error) { b, err := marshal(append([]interface{}{rh}, parts...)...) if err != nil { return } _, err = s.pc.WriteTo(b, addr) return } func (s *server) newConn() (ret int64) { ret = rand.Int63() if s.conns == nil { s.conns = make(map[int64]struct{}) } s.conns[ret] = struct{}{} return } func (s *server) serveOne() (err error) { b := make([]byte, 0x10000) n, addr, err := s.pc.ReadFrom(b) if err != nil { return } r := bytes.NewReader(b[:n]) var h RequestHeader err = readBody(r, &h) if err != nil { return } switch h.Action { case ActionConnect: if h.ConnectionId != connectRequestConnectionId { return } connId := s.newConn() err = s.respond(addr, ResponseHeader{ ActionConnect, h.TransactionId, }, ConnectionResponse{ connId, }) return case ActionAnnounce: if _, ok := s.conns[h.ConnectionId]; !ok { s.respond(addr, ResponseHeader{ TransactionId: h.TransactionId, Action: ActionError, }, []byte("not connected")) return } var ar AnnounceRequest err = readBody(r, &ar) if err != nil { return } t := s.t[ar.InfoHash] bm := func() encoding.BinaryMarshaler { ip := missinggo.AddrIP(addr) if ip.To4() != nil { return krpc.CompactIPv4NodeAddrs(t.Peers) } return krpc.CompactIPv6NodeAddrs(t.Peers) }() b, err = bm.MarshalBinary() if err != nil { panic(err) } err = s.respond(addr, ResponseHeader{ TransactionId: h.TransactionId, Action: ActionAnnounce, }, AnnounceResponseHeader{ Interval: 900, Leechers: t.Leechers, Seeders: t.Seeders, }, b) return default: err = fmt.Errorf("unhandled action: %d", h.Action) s.respond(addr, ResponseHeader{ TransactionId: h.TransactionId, Action: ActionError, }, []byte("unhandled action")) return } }