git.r.bdr.sh - rbdr/mobius/blob - hotline/tracker.go

   1 package hotline
   2
   3 import (
   4         "bufio"
   5         "encoding/binary"
   6         "fmt"
   7         "github.com/jhalter/mobius/concat"
   8         "net"
   9         "strconv"
  10         "time"
  11 )
  12
  13 // TrackerRegistration represents the payload a Hotline server sends to a Tracker to register
  14 type TrackerRegistration struct {
  15         Port        [2]byte // Server listening port number
  16         UserCount   int     // Number of users connected to this particular server
  17         PassID      []byte  // Random number generated by the server
  18         Name        string  // Server name
  19         Description string  // Description of the server
  20 }
  21
  22 // TODO: reimplement as io.Reader
  23 func (tr *TrackerRegistration) Read() []byte {
  24         userCount := make([]byte, 2)
  25         binary.BigEndian.PutUint16(userCount, uint16(tr.UserCount))
  26
  27         return concat.Slices(
  28                 []byte{0x00, 0x01},
  29                 tr.Port[:],
  30                 userCount,
  31                 []byte{0x00, 0x00},
  32                 tr.PassID,
  33                 []byte{uint8(len(tr.Name))},
  34                 []byte(tr.Name),
  35                 []byte{uint8(len(tr.Description))},
  36                 []byte(tr.Description),
  37         )
  38 }
  39
  40 func register(tracker string, tr *TrackerRegistration) error {
  41         conn, err := net.Dial("udp", tracker)
  42         if err != nil {
  43                 return err
  44         }
  45
  46         b := tr.Read()
  47
  48         if _, err := conn.Write(b); err != nil {
  49                 return err
  50         }
  51
  52         return nil
  53 }
  54
  55 const trackerTimeout = 5 * time.Second
  56
  57 // All string values use 8-bit ASCII character set encoding.
  58 // Client Interface with Tracker
  59 // After establishing a connection with tracker, the following information is sent:
  60 // Description  Size    Data    Note
  61 // Magic number 4       ‘HTRK’
  62 // Version      2       1 or 2  Old protocol (1) or new (2)
  63
  64 // Reply received from the tracker starts with a header:
  65 type TrackerHeader struct {
  66         Protocol [4]byte // "HTRK" 0x4854524B
  67         Version  [2]byte // Old protocol (1) or new (2)
  68 }
  69
  70 // Message type 2       1       Sending list of servers
  71 // Message data size    2               Remaining size of this request
  72 // Number of servers    2               Number of servers in the server list
  73 // Number of servers    2               Same as previous field
  74 type ServerInfoHeader struct {
  75         MsgType     [2]byte // always has value of 1
  76         MsgDataSize [2]byte // Remaining size of request
  77         SrvCount    [2]byte // Number of servers in the server list
  78         SrvCountDup [2]byte // Same as previous field ¯\_(ツ)_/¯
  79 }
  80
  81 type ServerRecord struct {
  82         IPAddr          [4]byte
  83         Port            [2]byte
  84         NumUsers        [2]byte // Number of users connected to this particular server
  85         Unused          [2]byte
  86         NameSize        byte   // Length of name string
  87         Name            []byte // Server name
  88         DescriptionSize byte
  89         Description     []byte
  90 }
  91
  92 func GetListing(addr string) ([]ServerRecord, error) {
  93         conn, err := net.DialTimeout("tcp", addr, trackerTimeout)
  94         if err != nil {
  95                 return []ServerRecord{}, err
  96         }
  97         defer func() { _ = conn.Close() }()
  98
  99         _, err = conn.Write(
 100                 []byte{
 101                         0x48, 0x54, 0x52, 0x4B, // HTRK
 102                         0x00, 0x01, // Version
 103                 },
 104         )
 105         if err != nil {
 106                 return nil, err
 107         }
 108
 109         var th TrackerHeader
 110         if err := binary.Read(conn, binary.BigEndian, &th); err != nil {
 111                 return nil, err
 112         }
 113
 114         var info ServerInfoHeader
 115         if err := binary.Read(conn, binary.BigEndian, &info); err != nil {
 116                 return nil, err
 117         }
 118
 119         totalSrv := int(binary.BigEndian.Uint16(info.SrvCount[:]))
 120
 121         scanner := bufio.NewScanner(conn)
 122         scanner.Split(serverScanner)
 123
 124         var servers []ServerRecord
 125         for {
 126                 scanner.Scan()
 127                 var srv ServerRecord
 128                 _, _ = srv.Read(scanner.Bytes())
 129
 130                 servers = append(servers, srv)
 131                 if len(servers) == totalSrv {
 132                         break
 133                 }
 134         }
 135
 136         return servers, nil
 137 }
 138
 139 // serverScanner implements bufio.SplitFunc for parsing the tracker list into ServerRecords tokens
 140 // Example payload:
 141 // 00000000  18 05 30 63 15 7c 00 02  00 00 10 54 68 65 20 4d  |..0c.|.....The M|
 142 // 00000010  6f 62 69 75 73 20 53 74  72 69 70 40 48 6f 6d 65  |obius Strip@Home|
 143 // 00000020  20 6f 66 20 74 68 65 20  4d 6f 62 69 75 73 20 48  | of the Mobius H|
 144 // 00000030  6f 74 6c 69 6e 65 20 73  65 72 76 65 72 20 61 6e  |otline server an|
 145 // 00000040  64 20 63 6c 69 65 6e 74  20 7c 20 54 52 54 50 48  |d client | TRTPH|
 146 // 00000050  4f 54 4c 2e 63 6f 6d 3a  35 35 30 30 2d 4f 3a b2  |OTL.com:5500-O:.|
 147 // 00000060  15 7c 00 00 00 00 08 53  65 6e 65 63 74 75 73 20  |.|.....Senectus |
 148 func serverScanner(data []byte, _ bool) (advance int, token []byte, err error) {
 149         if len(data) < 10 {
 150                 return 0, nil, nil
 151         }
 152
 153         // A server entry has two variable length fields: the name and description.
 154         // To get the token length, we first need the name length from the 10th byte:
 155         nameLen := int(data[10])
 156
 157         // Next we need the description length from the 11+nameLen byte:
 158         descLen := int(data[11+nameLen])
 159
 160         return 12 + nameLen + descLen, data[0 : 12+nameLen+descLen], nil
 161 }
 162
 163 // Read implements io.Reader for ServerRecord
 164 func (s *ServerRecord) Read(b []byte) (n int, err error) {
 165         copy(s.IPAddr[:], b[0:4])
 166         copy(s.Port[:], b[4:6])
 167         copy(s.NumUsers[:], b[6:8])
 168         nameLen := int(b[10])
 169
 170         s.Name = b[11 : 11+nameLen]
 171         s.DescriptionSize = b[11+nameLen]
 172         s.Description = b[12+nameLen : 12+nameLen+int(s.DescriptionSize)]
 173
 174         return 12 + nameLen + int(s.DescriptionSize), nil
 175 }
 176
 177 func (s *ServerRecord) Addr() string {
 178         return fmt.Sprintf("%s:%s",
 179                 net.IP(s.IPAddr[:]),
 180                 strconv.Itoa(int(binary.BigEndian.Uint16(s.Port[:]))),
 181         )
 182 }