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

   1 package hotline
   2
   3 import (
   4         "bufio"
   5         "encoding/binary"
   6         "errors"
   7         "fmt"
   8         "io"
   9         "net"
  10         "slices"
  11         "strconv"
  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 // Dialer interface to abstract the dialing operation
  53 type Dialer interface {
  54         Dial(network, address string) (net.Conn, error)
  55 }
  56
  57 // RealDialer is the real implementation of the Dialer interface
  58 type RealDialer struct{}
  59
  60 func (d *RealDialer) Dial(network, address string) (net.Conn, error) {
  61         return net.Dial(network, address)
  62 }
  63
  64 func register(dialer Dialer, tracker string, tr io.Reader) error {
  65         conn, err := dialer.Dial("udp", tracker)
  66         if err != nil {
  67                 return fmt.Errorf("failed to dial tracker: %w", err)
  68         }
  69         defer conn.Close()
  70
  71         if _, err := io.Copy(conn, tr); err != nil {
  72                 return fmt.Errorf("failed to write to connection: %w", err)
  73         }
  74
  75         return nil
  76 }
  77
  78 // All string values use 8-bit ASCII character set encoding.
  79 // Client Interface with Tracker
  80 // After establishing a connection with tracker, the following information is sent:
  81 // Description  Size    Data    Note
  82 // Magic number 4       ‘HTRK’
  83 // Version      2       1 or 2  Old protocol (1) or new (2)
  84
  85 // TrackerHeader is sent in reply Reply received from the tracker starts with a header:
  86 type TrackerHeader struct {
  87         Protocol [4]byte // "HTRK" 0x4854524B
  88         Version  [2]byte // Old protocol (1) or new (2)
  89 }
  90
  91 type ServerInfoHeader struct {
  92         MsgType     [2]byte // Always has value of 1
  93         MsgDataSize [2]byte // Remaining size of request
  94         SrvCount    [2]byte // Number of servers in the server list
  95         SrvCountDup [2]byte // Same as previous field ¯\_(ツ)_/¯
  96 }
  97
  98 // ServerRecord is a tracker listing for a single server
  99 type ServerRecord struct {
 100         IPAddr          [4]byte
 101         Port            [2]byte
 102         NumUsers        [2]byte // Number of users connected to this particular server
 103         Unused          [2]byte
 104         NameSize        byte   // Length of Name string
 105         Name            []byte // Server Name
 106         DescriptionSize byte
 107         Description     []byte
 108 }
 109
 110 func GetListing(conn io.ReadWriteCloser) ([]ServerRecord, error) {
 111         defer func() { _ = conn.Close() }()
 112
 113         _, err := conn.Write(
 114                 []byte{
 115                         0x48, 0x54, 0x52, 0x4B, // HTRK
 116                         0x00, 0x01, // Version
 117                 },
 118         )
 119         if err != nil {
 120                 return nil, err
 121         }
 122
 123         var th TrackerHeader
 124         if err := binary.Read(conn, binary.BigEndian, &th); err != nil {
 125                 return nil, err
 126         }
 127
 128         var info ServerInfoHeader
 129         if err := binary.Read(conn, binary.BigEndian, &info); err != nil {
 130                 return nil, err
 131         }
 132
 133         totalSrv := int(binary.BigEndian.Uint16(info.SrvCount[:]))
 134
 135         scanner := bufio.NewScanner(conn)
 136         scanner.Split(serverScanner)
 137
 138         var servers []ServerRecord
 139         for {
 140                 scanner.Scan()
 141
 142                 var srv ServerRecord
 143                 _, err = srv.Write(scanner.Bytes())
 144                 if err != nil {
 145                         return nil, err
 146                 }
 147
 148                 servers = append(servers, srv)
 149                 if len(servers) == totalSrv {
 150                         break
 151                 }
 152         }
 153
 154         return servers, nil
 155 }
 156
 157 // serverScanner implements bufio.SplitFunc for parsing the tracker list into ServerRecords tokens
 158 // Example payload:
 159 // 00000000  18 05 30 63 15 7c 00 02  00 00 10 54 68 65 20 4d  |..0c.|.....The M|
 160 // 00000010  6f 62 69 75 73 20 53 74  72 69 70 40 48 6f 6d 65  |obius Strip@Home|
 161 // 00000020  20 6f 66 20 74 68 65 20  4d 6f 62 69 75 73 20 48  | of the Mobius H|
 162 // 00000030  6f 74 6c 69 6e 65 20 73  65 72 76 65 72 20 61 6e  |otline server an|
 163 // 00000040  64 20 63 6c 69 65 6e 74  20 7c 20 54 52 54 50 48  |d client | TRTPH|
 164 // 00000050  4f 54 4c 2e 63 6f 6d 3a  35 35 30 30 2d 4f 3a b2  |OTL.com:5500-O:.|
 165 // 00000060  15 7c 00 00 00 00 08 53  65 6e 65 63 74 75 73 20  |.|.....Senectus |
 166 func serverScanner(data []byte, _ bool) (advance int, token []byte, err error) {
 167         // The name length field is the 11th byte of the server record.  If we don't have that many bytes,
 168         // return nil token so the Scanner reads more data and continues scanning.
 169         if len(data) < 10 {
 170                 return 0, nil, nil
 171         }
 172
 173         // A server entry has two variable length fields: the name and description.
 174         // To get the token length, we first need the name length from the 10th byte
 175         nameLen := int(data[10])
 176
 177         // The description length field is at the 12th + nameLen byte of the server record.
 178         // If we don't have that many bytes, return nil token so the Scanner reads more data and continues scanning.
 179         if len(data) < 11+nameLen {
 180                 return 0, nil, nil
 181         }
 182
 183         // Next we need the description length from the 11+nameLen byte:
 184         descLen := int(data[11+nameLen])
 185
 186         if len(data) < 12+nameLen+descLen {
 187                 return 0, nil, nil
 188         }
 189
 190         return 12 + nameLen + descLen, data[0 : 12+nameLen+descLen], nil
 191 }
 192
 193 // Write implements io.Writer for ServerRecord
 194 func (s *ServerRecord) Write(b []byte) (n int, err error) {
 195         if len(b) < 13 {
 196                 return 0, errors.New("too few bytes")
 197         }
 198         copy(s.IPAddr[:], b[0:4])
 199         copy(s.Port[:], b[4:6])
 200         copy(s.NumUsers[:], b[6:8])
 201         s.NameSize = b[10]
 202         nameLen := int(b[10])
 203
 204         s.Name = b[11 : 11+nameLen]
 205         s.DescriptionSize = b[11+nameLen]
 206         s.Description = b[12+nameLen : 12+nameLen+int(s.DescriptionSize)]
 207
 208         return 12 + nameLen + int(s.DescriptionSize), nil
 209 }
 210
 211 func (s *ServerRecord) Addr() string {
 212         return fmt.Sprintf("%s:%s",
 213                 net.IP(s.IPAddr[:]),
 214                 strconv.Itoa(int(binary.BigEndian.Uint16(s.Port[:]))),
 215         )
 216 }