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         Password    string  // Tracker password, if required by tracker
  22
  23         readOffset int // Internal offset to track read progress
  24 }
  25
  26 // Read implements io.Reader to write tracker registration payload bytes to slice
  27 func (tr *TrackerRegistration) Read(p []byte) (int, error) {
  28         userCount := make([]byte, 2)
  29         binary.BigEndian.PutUint16(userCount, uint16(tr.UserCount))
  30
  31         buf := slices.Concat(
  32                 []byte{0x00, 0x01}, // Magic number, always 1
  33                 tr.Port[:],
  34                 userCount,
  35                 []byte{0x00, 0x00}, // Magic number, always 0
  36                 tr.PassID[:],
  37                 []byte{uint8(len(tr.Name))},
  38                 []byte(tr.Name),
  39                 []byte{uint8(len(tr.Description))},
  40                 []byte(tr.Description),
  41                 []byte{uint8(len(tr.Password))},
  42                 []byte(tr.Password),
  43         )
  44
  45         if tr.readOffset >= len(buf) {
  46                 return 0, io.EOF // All bytes have been read
  47         }
  48
  49         n := copy(p, buf[tr.readOffset:])
  50         tr.readOffset += n
  51
  52         return n, nil
  53 }
  54
  55 // Dialer interface to abstract the dialing operation
  56 type Dialer interface {
  57         Dial(network, address string) (net.Conn, error)
  58 }
  59
  60 // RealDialer is the real implementation of the Dialer interface
  61 type RealDialer struct{}
  62
  63 func (d *RealDialer) Dial(network, address string) (net.Conn, error) {
  64         return net.Dial(network, address)
  65 }
  66
  67 func register(dialer Dialer, tracker string, tr io.Reader) error {
  68         conn, err := dialer.Dial("udp", tracker)
  69         if err != nil {
  70                 return fmt.Errorf("failed to dial tracker: %v", err)
  71         }
  72         defer conn.Close()
  73
  74         if _, err := io.Copy(conn, tr); err != nil {
  75                 return fmt.Errorf("failed to write to connection: %w", err)
  76         }
  77
  78         return nil
  79 }
  80
  81 // All string values use 8-bit ASCII character set encoding.
  82 // Client Interface with Tracker
  83 // After establishing a connection with tracker, the following information is sent:
  84 // Description  Size    Data    Note
  85 // Magic number 4       ‘HTRK’
  86 // Version      2       1 or 2  Old protocol (1) or new (2)
  87
  88 // TrackerHeader is sent in reply Reply received from the tracker starts with a header:
  89 type TrackerHeader struct {
  90         Protocol [4]byte // "HTRK" 0x4854524B
  91         Version  [2]byte // Old protocol (1) or new (2)
  92 }
  93
  94 type ServerInfoHeader struct {
  95         MsgType     [2]byte // Always has value of 1
  96         MsgDataSize [2]byte // Remaining size of request
  97         SrvCount    [2]byte // Number of servers in the server list
  98         SrvCountDup [2]byte // Same as previous field ¯\_(ツ)_/¯
  99 }
 100
 101 // ServerRecord is a tracker listing for a single server
 102 type ServerRecord struct {
 103         IPAddr          [4]byte
 104         Port            [2]byte
 105         NumUsers        [2]byte // Number of users connected to this particular server
 106         Unused          [2]byte
 107         NameSize        byte   // Length of Name string
 108         Name            []byte // Server Name
 109         DescriptionSize byte
 110         Description     []byte
 111 }
 112
 113 func GetListing(conn io.ReadWriteCloser) ([]ServerRecord, error) {
 114         defer func() { _ = conn.Close() }()
 115
 116         _, err := conn.Write(
 117                 []byte{
 118                         0x48, 0x54, 0x52, 0x4B, // HTRK
 119                         0x00, 0x01, // Version
 120                 },
 121         )
 122         if err != nil {
 123                 return nil, err
 124         }
 125
 126         var th TrackerHeader
 127         if err := binary.Read(conn, binary.BigEndian, &th); err != nil {
 128                 return nil, err
 129         }
 130
 131         var info ServerInfoHeader
 132         if err := binary.Read(conn, binary.BigEndian, &info); err != nil {
 133                 return nil, err
 134         }
 135
 136         totalSrv := int(binary.BigEndian.Uint16(info.SrvCount[:]))
 137
 138         scanner := bufio.NewScanner(conn)
 139         scanner.Split(serverScanner)
 140
 141         var servers []ServerRecord
 142         for {
 143                 scanner.Scan()
 144
 145                 // Make a new []byte slice and copy the scanner bytes to it.  This is critical as the
 146                 // scanner re-uses the buffer for subsequent scans.
 147                 buf := make([]byte, len(scanner.Bytes()))
 148                 copy(buf, scanner.Bytes())
 149
 150                 var srv ServerRecord
 151                 _, err = srv.Write(buf)
 152                 if err != nil {
 153                         return nil, err
 154                 }
 155
 156                 servers = append(servers, srv)
 157                 if len(servers) == totalSrv {
 158                         break
 159                 }
 160         }
 161
 162         return servers, nil
 163 }
 164
 165 // serverScanner implements bufio.SplitFunc for parsing the tracker list into ServerRecords tokens
 166 // Example payload:
 167 // 00000000  18 05 30 63 15 7c 00 02  00 00 10 54 68 65 20 4d  |..0c.|.....The M|
 168 // 00000010  6f 62 69 75 73 20 53 74  72 69 70 40 48 6f 6d 65  |obius Strip@Home|
 169 // 00000020  20 6f 66 20 74 68 65 20  4d 6f 62 69 75 73 20 48  | of the Mobius H|
 170 // 00000030  6f 74 6c 69 6e 65 20 73  65 72 76 65 72 20 61 6e  |otline server an|
 171 // 00000040  64 20 63 6c 69 65 6e 74  20 7c 20 54 52 54 50 48  |d client | TRTPH|
 172 // 00000050  4f 54 4c 2e 63 6f 6d 3a  35 35 30 30 2d 4f 3a b2  |OTL.com:5500-O:.|
 173 // 00000060  15 7c 00 00 00 00 08 53  65 6e 65 63 74 75 73 20  |.|.....Senectus |
 174 func serverScanner(data []byte, _ bool) (advance int, token []byte, err error) {
 175         // The name length field is the 11th byte of the server record.  If we don't have that many bytes,
 176         // return nil token so the Scanner reads more data and continues scanning.
 177         if len(data) < 10 {
 178                 return 0, nil, nil
 179         }
 180
 181         // A server entry has two variable length fields: the name and description.
 182         // To get the token length, we first need the name length from the 10th byte
 183         nameLen := int(data[10])
 184
 185         // The description length field is at the 12th + nameLen byte of the server record.
 186         // If we don't have that many bytes, return nil token so the Scanner reads more data and continues scanning.
 187         if len(data) < 11+nameLen {
 188                 return 0, nil, nil
 189         }
 190
 191         // Next we need the description length from the 11+nameLen byte:
 192         descLen := int(data[11+nameLen])
 193
 194         if len(data) < 12+nameLen+descLen {
 195                 return 0, nil, nil
 196         }
 197
 198         return 12 + nameLen + descLen, data[0 : 12+nameLen+descLen], nil
 199 }
 200
 201 // Write implements io.Writer for ServerRecord
 202 func (s *ServerRecord) Write(b []byte) (n int, err error) {
 203         if len(b) < 13 {
 204                 return 0, errors.New("too few bytes")
 205         }
 206         copy(s.IPAddr[:], b[0:4])
 207         copy(s.Port[:], b[4:6])
 208         copy(s.NumUsers[:], b[6:8])
 209         s.NameSize = b[10]
 210         nameLen := int(b[10])
 211
 212         s.Name = b[11 : 11+nameLen]
 213         s.DescriptionSize = b[11+nameLen]
 214         s.Description = b[12+nameLen : 12+nameLen+int(s.DescriptionSize)]
 215
 216         return 12 + nameLen + int(s.DescriptionSize), nil
 217 }
 218
 219 func (s *ServerRecord) Addr() string {
 220         return fmt.Sprintf("%s:%s",
 221                 net.IP(s.IPAddr[:]),
 222                 strconv.Itoa(int(binary.BigEndian.Uint16(s.Port[:]))),
 223         )
 224 }