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

   1 package hotline
   2
   3 import (
   4         "bufio"
   5         "encoding/binary"
   6         "fmt"
   7         "io"
   8         "net"
   9         "slices"
  10         "strconv"
  11         "time"
  12 )
  13
  14 // TrackerRegistration represents the payload a Hotline server sends to a Tracker to register
  15 type TrackerRegistration struct {
  16         Port        [2]byte // Server's listening TCP port number
  17         UserCount   int     // Number of users connected to this particular server
  18         PassID      [4]byte // Random number generated by the server
  19         Name        string  // Server Name
  20         Description string  // Description of the server
  21
  22         readOffset int // Internal offset to track read progress
  23 }
  24
  25 // Read implements io.Reader to write tracker registration payload bytes to slice
  26 func (tr *TrackerRegistration) Read(p []byte) (int, error) {
  27         userCount := make([]byte, 2)
  28         binary.BigEndian.PutUint16(userCount, uint16(tr.UserCount))
  29
  30         buf := slices.Concat(
  31                 []byte{0x00, 0x01}, // Magic number, always 1
  32                 tr.Port[:],
  33                 userCount,
  34                 []byte{0x00, 0x00}, // Magic number, always 0
  35                 tr.PassID[:],
  36                 []byte{uint8(len(tr.Name))},
  37                 []byte(tr.Name),
  38                 []byte{uint8(len(tr.Description))},
  39                 []byte(tr.Description),
  40         )
  41
  42         if tr.readOffset >= len(buf) {
  43                 return 0, io.EOF // All bytes have been read
  44         }
  45
  46         n := copy(p, buf[tr.readOffset:])
  47         tr.readOffset += n
  48
  49         return n, nil
  50 }
  51
  52 func register(tracker string, tr *TrackerRegistration) error {
  53         conn, err := net.Dial("udp", tracker)
  54         if err != nil {
  55                 return fmt.Errorf("failed to dial tracker: %w", err)
  56         }
  57         defer conn.Close()
  58
  59         if _, err := io.Copy(conn, tr); err != nil {
  60                 return fmt.Errorf("failed to write to connection: %w", err)
  61         }
  62
  63         return nil
  64 }
  65
  66 const trackerTimeout = 5 * time.Second
  67
  68 // All string values use 8-bit ASCII character set encoding.
  69 // Client Interface with Tracker
  70 // After establishing a connection with tracker, the following information is sent:
  71 // Description  Size    Data    Note
  72 // Magic number 4       ‘HTRK’
  73 // Version      2       1 or 2  Old protocol (1) or new (2)
  74
  75 // Reply received from the tracker starts with a header:
  76 type TrackerHeader struct {
  77         Protocol [4]byte // "HTRK" 0x4854524B
  78         Version  [2]byte // Old protocol (1) or new (2)
  79 }
  80
  81 // Message type                 2       1       Sending list of servers
  82 // Message data size    2               Remaining size of this request
  83 // Number of servers    2               Number of servers in the server list
  84 // Number of servers    2               Same as previous field
  85 type ServerInfoHeader struct {
  86         MsgType     [2]byte // always has value of 1
  87         MsgDataSize [2]byte // Remaining size of request
  88         SrvCount    [2]byte // Number of servers in the server list
  89         SrvCountDup [2]byte // Same as previous field ¯\_(ツ)_/¯
  90 }
  91
  92 type ServerRecord struct {
  93         IPAddr          [4]byte
  94         Port            [2]byte
  95         NumUsers        [2]byte // Number of users connected to this particular server
  96         Unused          [2]byte
  97         NameSize        byte   // Length of Name string
  98         Name            []byte // Server Name
  99         DescriptionSize byte
 100         Description     []byte
 101 }
 102
 103 func GetListing(addr string) ([]ServerRecord, error) {
 104         conn, err := net.DialTimeout("tcp", addr, trackerTimeout)
 105         if err != nil {
 106                 return []ServerRecord{}, err
 107         }
 108         defer func() { _ = conn.Close() }()
 109
 110         _, err = conn.Write(
 111                 []byte{
 112                         0x48, 0x54, 0x52, 0x4B, // HTRK
 113                         0x00, 0x01, // Version
 114                 },
 115         )
 116         if err != nil {
 117                 return nil, err
 118         }
 119
 120         var th TrackerHeader
 121         if err := binary.Read(conn, binary.BigEndian, &th); err != nil {
 122                 return nil, err
 123         }
 124
 125         var info ServerInfoHeader
 126         if err := binary.Read(conn, binary.BigEndian, &info); err != nil {
 127                 return nil, err
 128         }
 129
 130         totalSrv := int(binary.BigEndian.Uint16(info.SrvCount[:]))
 131
 132         scanner := bufio.NewScanner(conn)
 133         scanner.Split(serverScanner)
 134
 135         var servers []ServerRecord
 136         for {
 137                 scanner.Scan()
 138                 var srv ServerRecord
 139                 _, err = srv.Write(scanner.Bytes())
 140                 if err != nil {
 141                         return nil, err
 142                 }
 143
 144                 servers = append(servers, srv)
 145                 if len(servers) == totalSrv {
 146                         break
 147                 }
 148         }
 149
 150         return servers, nil
 151 }
 152
 153 // serverScanner implements bufio.SplitFunc for parsing the tracker list into ServerRecords tokens
 154 // Example payload:
 155 // 00000000  18 05 30 63 15 7c 00 02  00 00 10 54 68 65 20 4d  |..0c.|.....The M|
 156 // 00000010  6f 62 69 75 73 20 53 74  72 69 70 40 48 6f 6d 65  |obius Strip@Home|
 157 // 00000020  20 6f 66 20 74 68 65 20  4d 6f 62 69 75 73 20 48  | of the Mobius H|
 158 // 00000030  6f 74 6c 69 6e 65 20 73  65 72 76 65 72 20 61 6e  |otline server an|
 159 // 00000040  64 20 63 6c 69 65 6e 74  20 7c 20 54 52 54 50 48  |d client | TRTPH|
 160 // 00000050  4f 54 4c 2e 63 6f 6d 3a  35 35 30 30 2d 4f 3a b2  |OTL.com:5500-O:.|
 161 // 00000060  15 7c 00 00 00 00 08 53  65 6e 65 63 74 75 73 20  |.|.....Senectus |
 162 func serverScanner(data []byte, _ bool) (advance int, token []byte, err error) {
 163         // The name length field is the 11th byte of the server record.  If we don't have that many bytes,
 164         // return nil token so the Scanner reads more data and continues scanning.
 165         if len(data) < 10 {
 166                 return 0, nil, nil
 167         }
 168
 169         // A server entry has two variable length fields: the name and description.
 170         // To get the token length, we first need the name length from the 10th byte
 171         nameLen := int(data[10])
 172
 173         // The description length field is at the 12th + nameLen byte of the server record.
 174         // If we don't have that many bytes, return nil token so the Scanner reads more data and continues scanning.
 175         if len(data) < 11+nameLen {
 176                 return 0, nil, nil
 177         }
 178
 179         // Next we need the description length from the 11+nameLen byte:
 180         descLen := int(data[11+nameLen])
 181
 182         if len(data) < 12+nameLen+descLen {
 183                 return 0, nil, nil
 184         }
 185
 186         return 12 + nameLen + descLen, data[0 : 12+nameLen+descLen], nil
 187 }
 188
 189 // Write implements io.Writer for ServerRecord
 190 func (s *ServerRecord) Write(b []byte) (n int, err error) {
 191         copy(s.IPAddr[:], b[0:4])
 192         copy(s.Port[:], b[4:6])
 193         copy(s.NumUsers[:], b[6:8])
 194         nameLen := int(b[10])
 195
 196         s.Name = b[11 : 11+nameLen]
 197         s.DescriptionSize = b[11+nameLen]
 198         s.Description = b[12+nameLen : 12+nameLen+int(s.DescriptionSize)]
 199
 200         return 12 + nameLen + int(s.DescriptionSize), nil
 201 }
 202
 203 func (s *ServerRecord) Addr() string {
 204         return fmt.Sprintf("%s:%s",
 205                 net.IP(s.IPAddr[:]),
 206                 strconv.Itoa(int(binary.BigEndian.Uint16(s.Port[:]))),
 207         )
 208 }