Your IP : 216.73.216.224
package hotline
import (
"bufio"
"encoding/binary"
"errors"
"fmt"
"io"
"net"
"slices"
"strconv"
)
// TrackerRegistration represents the payload a Hotline server sends to a Tracker to register
type TrackerRegistration struct {
Port [2]byte // Server's listening TCP port number
UserCount int // Number of users connected to this particular server
TLSPort [2]byte // TLSPort
PassID [4]byte // Random number generated by the server
Name string // Server Name
Description string // Description of the server
Password string // Tracker password, if required by tracker
readOffset int // Internal offset to track read progress
}
// Read implements io.Reader to write tracker registration payload bytes to slice
func (tr *TrackerRegistration) Read(p []byte) (int, error) {
userCount := make([]byte, 2)
binary.BigEndian.PutUint16(userCount, uint16(tr.UserCount))
buf := slices.Concat(
[]byte{0x00, 0x01}, // Magic number, always 1
tr.Port[:],
userCount,
tr.TLSPort[:],
tr.PassID[:],
[]byte{uint8(len(tr.Name))},
[]byte(tr.Name),
[]byte{uint8(len(tr.Description))},
[]byte(tr.Description),
[]byte{uint8(len(tr.Password))},
[]byte(tr.Password),
)
return readFrom(p, &tr.readOffset, buf)
}
// Dialer interface to abstract the dialing operation
type Dialer interface {
Dial(network, address string) (net.Conn, error)
}
// RealDialer is the real implementation of the Dialer interface
type RealDialer struct{}
func (d *RealDialer) Dial(network, address string) (net.Conn, error) {
return net.Dial(network, address)
}
func register(dialer Dialer, tracker string, tr io.Reader) error {
conn, err := dialer.Dial("udp", tracker)
if err != nil {
return fmt.Errorf("failed to dial tracker: %v", err)
}
defer func() { _ = conn.Close() }()
if _, err := io.Copy(conn, tr); err != nil {
return fmt.Errorf("failed to write to connection: %w", err)
}
return nil
}
// All string values use 8-bit ASCII character set encoding.
// Client Interface with Tracker
// After establishing a connection with tracker, the following information is sent:
// Description Size Data Note
// Magic number 4 ‘HTRK’
// Version 2 1 or 2 Old protocol (1) or new (2)
// TrackerHeader is sent in reply Reply received from the tracker starts with a header:
type TrackerHeader struct {
Protocol [4]byte // "HTRK" 0x4854524B
Version [2]byte // Old protocol (1) or new (2)
}
// ServerInfoHeader represents a batch header in the tracker response.
// The tracker protocol splits large server lists into batches, with each batch
// preceded by its own ServerInfoHeader. The first header indicates the total
// number of servers across all batches, and each header (including the first)
// indicates how many servers are in the current batch.
//
// Example flow for 106 servers split into batches:
// 1. First ServerInfoHeader: SrvCount=106, BatchSize=97
// 2. Read 97 ServerRecords
// 3. Second ServerInfoHeader: SrvCount=106, BatchSize=9
// 4. Read 9 ServerRecords (total: 106)
type ServerInfoHeader struct {
MsgType [2]byte // Always has value of 1
MsgDataSize [2]byte // Remaining size of request
SrvCount [2]byte // Total number of servers across all batches
BatchSize [2]byte // Number of servers in the current batch
}
// ServerRecord is a tracker listing for a single server
type ServerRecord struct {
IPAddr [4]byte
Port [2]byte
NumUsers [2]byte // Number of users connected to this particular server
TLSPort [2]byte
NameSize byte // Length of Name string
Name []byte // Server Name
DescriptionSize byte
Description []byte
}
func GetListing(conn io.ReadWriteCloser) ([]ServerRecord, error) {
defer func() { _ = conn.Close() }()
_, err := conn.Write(
[]byte{
0x48, 0x54, 0x52, 0x4B, // HTRK
0x00, 0x01, // Version
},
)
if err != nil {
return nil, err
}
var th TrackerHeader
if err := binary.Read(conn, binary.BigEndian, &th); err != nil {
return nil, err
}
// Use a buffered reader so we can read both headers and server records from the same buffer
reader := bufio.NewReader(conn)
var info ServerInfoHeader
if err := binary.Read(reader, binary.BigEndian, &info); err != nil {
return nil, err
}
totalSrv := int(binary.BigEndian.Uint16(info.SrvCount[:]))
batchSize := int(binary.BigEndian.Uint16(info.BatchSize[:]))
servers := make([]ServerRecord, 0, totalSrv)
serversInCurrentBatch := 0
for len(servers) < totalSrv {
// Check if we've read all servers in the current batch
if serversInCurrentBatch == batchSize {
// Read the next ServerInfoHeader for the next batch from the buffered reader
if err := binary.Read(reader, binary.BigEndian, &info); err != nil {
return nil, fmt.Errorf("failed to read next ServerInfoHeader after %d servers: %w", len(servers), err)
}
batchSize = int(binary.BigEndian.Uint16(info.BatchSize[:]))
serversInCurrentBatch = 0
}
// Read a server record using our helper function
srv, err := readServerRecord(reader)
if err != nil {
return nil, fmt.Errorf("failed to read server record %d: %w", len(servers)+1, err)
}
servers = append(servers, srv)
serversInCurrentBatch++
}
return servers, nil
}
// readServerRecord reads a single ServerRecord from the reader
func readServerRecord(reader *bufio.Reader) (ServerRecord, error) {
var srv ServerRecord
// Read fixed header: IP (4) + Port (2) + NumUsers (2) + TLSPort (2) = 10 bytes
header := make([]byte, 10)
if _, err := io.ReadFull(reader, header); err != nil {
return srv, fmt.Errorf("failed to read server header: %w", err)
}
copy(srv.IPAddr[:], header[0:4])
copy(srv.Port[:], header[4:6])
copy(srv.NumUsers[:], header[6:8])
copy(srv.TLSPort[:], header[8:10])
// Read name size
nameSizeByte, err := reader.ReadByte()
if err != nil {
return srv, fmt.Errorf("failed to read name size: %w", err)
}
srv.NameSize = nameSizeByte
// Read name
srv.Name = make([]byte, srv.NameSize)
if _, err := io.ReadFull(reader, srv.Name); err != nil {
return srv, fmt.Errorf("failed to read name: %w", err)
}
// Read description size
descSizeByte, err := reader.ReadByte()
if err != nil {
return srv, fmt.Errorf("failed to read description size: %w", err)
}
srv.DescriptionSize = descSizeByte
// Read description
srv.Description = make([]byte, srv.DescriptionSize)
if _, err := io.ReadFull(reader, srv.Description); err != nil {
return srv, fmt.Errorf("failed to read description: %w", err)
}
return srv, nil
}
// Write implements io.Writer for ServerRecord
func (s *ServerRecord) Write(b []byte) (n int, err error) {
if len(b) < 12 {
return 0, errors.New("too few bytes")
}
copy(s.IPAddr[:], b[0:4])
copy(s.Port[:], b[4:6])
copy(s.NumUsers[:], b[6:8])
s.NameSize = b[10]
nameLen := int(b[10])
s.Name = b[11 : 11+nameLen]
s.DescriptionSize = b[11+nameLen]
s.Description = b[12+nameLen : 12+nameLen+int(s.DescriptionSize)]
return 12 + nameLen + int(s.DescriptionSize), nil
}
func (s *ServerRecord) Addr() string {
return fmt.Sprintf("%s:%s",
net.IP(s.IPAddr[:]),
strconv.Itoa(int(binary.BigEndian.Uint16(s.Port[:]))),
)
}