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package hotline
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"github.com/jhalter/mobius/concat"
"net"
"strconv"
"time"
)
type TrackerRegistration struct {
Port []byte // Server listening port number
UserCount int // Number of users connected to this particular server
PassID []byte // Random number generated by the server
Name string // Server name
Description string // Description of the server
}
func (tr *TrackerRegistration) Payload() []byte {
userCount := make([]byte, 2)
binary.BigEndian.PutUint16(userCount, uint16(tr.UserCount))
return concat.Slices(
[]byte{0x00, 0x01},
tr.Port,
userCount,
[]byte{0x00, 0x00},
tr.PassID,
[]byte{uint8(len(tr.Name))},
[]byte(tr.Name),
[]byte{uint8(len(tr.Description))},
[]byte(tr.Description),
)
}
func register(tracker string, tr *TrackerRegistration) error {
conn, err := net.Dial("udp", tracker)
if err != nil {
return err
}
if _, err := conn.Write(tr.Payload()); err != nil {
return err
}
return nil
}
const trackerTimeout = 5 * time.Second
// 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)
// 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)
}
// Message type 2 1 Sending list of servers
// Message data size 2 Remaining size of this request
// Number of servers 2 Number of servers in the server list
// Number of servers 2 Same as previous field
type ServerInfoHeader struct {
MsgType [2]byte // always has value of 1
MsgDataSize [2]byte // Remaining size of request
SrvCount [2]byte // Number of servers in the server list
SrvCountDup [2]byte // Same as previous field ¯\_(ツ)_/¯
}
type ServerRecord struct {
IPAddr [4]byte
Port [2]byte
NumUsers [2]byte // Number of users connected to this particular server
Unused [2]byte
NameSize byte // Length of name string
Name []byte // Server name
DescriptionSize byte
Description []byte
}
func GetListing(addr string) ([]ServerRecord, error) {
conn, err := net.DialTimeout("tcp", addr, trackerTimeout)
if err != nil {
return []ServerRecord{}, err
}
defer func() { _ = conn.Close() }()
_, err = conn.Write(
[]byte{
0x48, 0x54, 0x52, 0x4B, // HTRK
0x00, 0x01, // Version
},
)
if err != nil {
return nil, err
}
totalRead := 0
buf := make([]byte, 4096)
var readLen int
if readLen, err = conn.Read(buf); err != nil {
return nil, err
}
totalRead += readLen // 1514
var th TrackerHeader
if err := binary.Read(bytes.NewReader(buf[:6]), binary.BigEndian, &th); err != nil {
return nil, err
}
var info ServerInfoHeader
if err := binary.Read(bytes.NewReader(buf[6:14]), binary.BigEndian, &info); err != nil {
return nil, err
}
payloadSize := int(binary.BigEndian.Uint16(info.MsgDataSize[:]))
buf = buf[:readLen]
if totalRead < payloadSize {
for {
tmpBuf := make([]byte, 4096)
if readLen, err = conn.Read(tmpBuf); err != nil {
return nil, err
}
buf = append(buf, tmpBuf[:readLen]...)
totalRead += readLen
if totalRead >= payloadSize {
break
}
}
}
totalSrv := int(binary.BigEndian.Uint16(info.SrvCount[:]))
srvBuf := buf[14:totalRead]
var servers []ServerRecord
for {
var srv ServerRecord
n, _ := srv.Read(srvBuf)
servers = append(servers, srv)
srvBuf = srvBuf[n:]
if len(servers) == totalSrv {
return servers, nil
}
if len(srvBuf) == 0 {
return servers, errors.New("tracker sent too few bytes for server count")
}
}
}
func (s *ServerRecord) Read(b []byte) (n int, err error) {
copy(s.IPAddr[:], b[0:4])
copy(s.Port[:], b[4:6])
copy(s.NumUsers[:], b[6:8])
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) PortInt() int {
data := binary.BigEndian.Uint16(s.Port[:])
return int(data)
}
func (s *ServerRecord) Addr() string {
return fmt.Sprintf("%s:%s",
net.IP(s.IPAddr[:]),
strconv.Itoa(int(binary.BigEndian.Uint16(s.Port[:]))),
)
}
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