X-Git-Url: https://git.r.bdr.sh/rbdr/mobius/blobdiff_plain/aebc4d3647b9823ae8cbb57b21b1af83bfd011fb..d9bc63a10d0978d9a5222cf7be74044e55f409b7:/hotline/tracker.go

diff --git a/hotline/tracker.go b/hotline/tracker.go
index 0825fc7..2d655d9 100644
--- a/hotline/tracker.go
+++ b/hotline/tracker.go
@@ -1,56 +1,80 @@
 package hotline
 
 import (
-	"bytes"
+	"bufio"
 	"encoding/binary"
 	"errors"
 	"fmt"
-	"github.com/jhalter/mobius/concat"
+	"io"
 	"net"
+	"slices"
 	"strconv"
-	"time"
 )
 
+// TrackerRegistration represents the payload a Hotline server sends to a Tracker to register
 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
+	Port        [2]byte // Server's listening TCP port number
+	UserCount   int     // Number of users connected to this particular server
+	PassID      [4]byte // Random number generated by the server
+	Name        string  // Server Name
+	Description string  // Description of the server
+
+	readOffset int // Internal offset to track read progress
 }
 
-func (tr *TrackerRegistration) Payload() []byte {
+// 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))
 
-	return concat.Slices(
-		[]byte{0x00, 0x01},
-		tr.Port,
+	buf := slices.Concat(
+		[]byte{0x00, 0x01}, // Magic number, always 1
+		tr.Port[:],
 		userCount,
-		[]byte{0x00, 0x00},
-		tr.PassID,
+		[]byte{0x00, 0x00}, // Magic number, always 0
+		tr.PassID[:],
 		[]byte{uint8(len(tr.Name))},
 		[]byte(tr.Name),
 		[]byte{uint8(len(tr.Description))},
 		[]byte(tr.Description),
 	)
+
+	if tr.readOffset >= len(buf) {
+		return 0, io.EOF // All bytes have been read
+	}
+
+	n := copy(p, buf[tr.readOffset:])
+	tr.readOffset += n
+
+	return n, nil
+}
+
+// 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(tracker string, tr TrackerRegistration) error {
-	conn, err := net.Dial("udp", tracker)
+func register(dialer Dialer, tracker string, tr io.Reader) error {
+	conn, err := dialer.Dial("udp", tracker)
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to dial tracker: %v", err)
 	}
+	defer conn.Close()
 
-	if _, err := conn.Write(tr.Payload()); err != nil {
-		return err
+	if _, err := io.Copy(conn, tr); err != nil {
+		return fmt.Errorf("failed to write to connection: %w", 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:
@@ -58,42 +82,35 @@ const trackerTimeout = 5 * time.Second
 // Magic number	4	‘HTRK’
 // Version	2	1 or 2	Old protocol (1) or new (2)
 
-// Reply received from the tracker starts with a header:
+// 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)
 }
 
-// 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
+	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)_/¯
 }
 
+// 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
 	Unused          [2]byte
-	NameSize        byte   // Length of name string
-	Name            []byte // Server name
+	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
-	}
+func GetListing(conn io.ReadWriteCloser) ([]ServerRecord, error) {
 	defer func() { _ = conn.Close() }()
 
-	_, err = conn.Write(
+	_, err := conn.Write(
 		[]byte{
 			0x48, 0x54, 0x52, 0x4B, // HTRK
 			0x00, 0x01, // Version
@@ -103,68 +120,85 @@ func GetListing(addr string) ([]ServerRecord, error) {
 		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 {
+	if err := binary.Read(conn, 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 {
+	if err := binary.Read(conn, 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]
+	scanner := bufio.NewScanner(conn)
+	scanner.Split(serverScanner)
 
 	var servers []ServerRecord
-
 	for {
-		var srv ServerRecord
-		n, _ := srv.Read(srvBuf)
-		servers = append(servers, srv)
+		scanner.Scan()
 
-		srvBuf = srvBuf[n:]
+		var srv ServerRecord
+		_, err = srv.Write(scanner.Bytes())
+		if err != nil {
+			return nil, err
+		}
 
+		servers = append(servers, srv)
 		if len(servers) == totalSrv {
-			return servers, nil
+			break
 		}
+	}
 
-		if len(srvBuf) == 0 {
-			return servers, errors.New("tracker sent too few bytes for server count")
-		}
+	return servers, nil
+}
+
+// serverScanner implements bufio.SplitFunc for parsing the tracker list into ServerRecords tokens
+// Example payload:
+// 00000000  18 05 30 63 15 7c 00 02  00 00 10 54 68 65 20 4d  |..0c.|.....The M|
+// 00000010  6f 62 69 75 73 20 53 74  72 69 70 40 48 6f 6d 65  |obius Strip@Home|
+// 00000020  20 6f 66 20 74 68 65 20  4d 6f 62 69 75 73 20 48  | of the Mobius H|
+// 00000030  6f 74 6c 69 6e 65 20 73  65 72 76 65 72 20 61 6e  |otline server an|
+// 00000040  64 20 63 6c 69 65 6e 74  20 7c 20 54 52 54 50 48  |d client | TRTPH|
+// 00000050  4f 54 4c 2e 63 6f 6d 3a  35 35 30 30 2d 4f 3a b2  |OTL.com:5500-O:.|
+// 00000060  15 7c 00 00 00 00 08 53  65 6e 65 63 74 75 73 20  |.|.....Senectus |
+func serverScanner(data []byte, _ bool) (advance int, token []byte, err error) {
+	// The name length field is the 11th byte of the server record.  If we don't have that many bytes,
+	// return nil token so the Scanner reads more data and continues scanning.
+	if len(data) < 10 {
+		return 0, nil, nil
 	}
+
+	// A server entry has two variable length fields: the name and description.
+	// To get the token length, we first need the name length from the 10th byte
+	nameLen := int(data[10])
+
+	// The description length field is at the 12th + nameLen byte of the server record.
+	// If we don't have that many bytes, return nil token so the Scanner reads more data and continues scanning.
+	if len(data) < 11+nameLen {
+		return 0, nil, nil
+	}
+
+	// Next we need the description length from the 11+nameLen byte:
+	descLen := int(data[11+nameLen])
+
+	if len(data) < 12+nameLen+descLen {
+		return 0, nil, nil
+	}
+
+	return 12 + nameLen + descLen, data[0 : 12+nameLen+descLen], nil
 }
 
-func (s *ServerRecord) Read(b []byte) (n int, err error) {
+// Write implements io.Writer for ServerRecord
+func (s *ServerRecord) Write(b []byte) (n int, err error) {
+	if len(b) < 13 {
+		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]
@@ -174,11 +208,6 @@ func (s *ServerRecord) Read(b []byte) (n int, err error) {
 	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[:]),