Add TLS port field to tracker registration protocol

Repurpose the previously unused 2-byte field in the tracker protocol to advertise the server's TLS port. This allows clients to discover which servers support TLS connections.

Note: currently only the official, original, 1990's Tracker software sends this server provided 2-byte field to tracker clients.  I'm adding this to Mobius in the hope that the modern day trackers might update their behavior to match the original software, which would put these unused 2 bytes to a useful purpose.

3 files changed, 51 insertions, 49 deletions

diff --git a/hotline/server.go b/hotline/server.go
index 2c25e93..9b74d99 100644
--- a/hotline/server.go
+++ b/hotline/server.go
@@ -368,6 +368,7 @@ func (s *Server) registerWithAllTrackers() {
 			Description: s.Config.Description,
 		}
 		binary.BigEndian.PutUint16(tr.Port[:], uint16(s.Port))
+		binary.BigEndian.PutUint16(tr.TLSPort[:], uint16(s.TLSPort))
 
 		tr.Password = parseTrackerPassword(t)
 
diff --git a/hotline/tracker.go b/hotline/tracker.go
index bfba69d..ee4fc05 100644
--- a/hotline/tracker.go
+++ b/hotline/tracker.go
@@ -15,6 +15,7 @@ import (
 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
@@ -32,7 +33,7 @@ func (tr *TrackerRegistration) Read(p []byte) (int, error) {
 		[]byte{0x00, 0x01}, // Magic number, always 1
 		tr.Port[:],
 		userCount,
-		[]byte{0x00, 0x00}, // Magic number, always 0
+		tr.TLSPort[:],
 		tr.PassID[:],
 		[]byte{uint8(len(tr.Name))},
 		[]byte(tr.Name),
@@ -114,7 +115,7 @@ type ServerRecord struct {
 	IPAddr          [4]byte
 	Port            [2]byte
 	NumUsers        [2]byte // Number of users connected to this particular server
-	Unused          [2]byte
+	TLSPort         [2]byte
 	NameSize        byte   // Length of Name string
 	Name            []byte // Server Name
 	DescriptionSize byte
@@ -182,7 +183,7 @@ func GetListing(conn io.ReadWriteCloser) ([]ServerRecord, error) {
 func readServerRecord(reader *bufio.Reader) (ServerRecord, error) {
 	var srv ServerRecord
 
-	// Read fixed header: IP (4) + Port (2) + NumUsers (2) + Unused (2) = 10 bytes
+	// 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)
@@ -191,7 +192,7 @@ func readServerRecord(reader *bufio.Reader) (ServerRecord, error) {
 	copy(srv.IPAddr[:], header[0:4])
 	copy(srv.Port[:], header[4:6])
 	copy(srv.NumUsers[:], header[6:8])
-	copy(srv.Unused[:], header[8:10])
+	copy(srv.TLSPort[:], header[8:10])
 
 	// Read name size
 	nameSizeByte, err := reader.ReadByte()
diff --git a/hotline/tracker_test.go b/hotline/tracker_test.go
index 8295582..242deb1 100644
--- a/hotline/tracker_test.go
+++ b/hotline/tracker_test.go
@@ -104,7 +104,7 @@ func TestGetListing(t *testing.T) {
 					192, 168, 1, 1, // IP address
 					0x1F, 0x90, // Port 8080
 					0x00, 0x10, // NumUsers 16
-					0x00, 0x00, // Unused
+					0x00, 0x00, // TLSPort
 					0x04,               // NameSize
 					'S', 'e', 'r', 'v', // Name
 					0x0B,                                                  // DescriptionSize
@@ -113,7 +113,7 @@ func TestGetListing(t *testing.T) {
 					10, 0, 0, 1, // IP address
 					0x1F, 0x91, // Port 8081
 					0x00, 0x05, // NumUsers 5
-					0x00, 0x00, // Unused
+					0x00, 0x00, // TLSPort
 					0x04,               // NameSize
 					'S', 'e', 'r', 'v', // Name
 					0x0B,                                                  // DescriptionSize
@@ -127,7 +127,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 1},
 					Port:            [2]byte{0x1F, 0x90},
 					NumUsers:        [2]byte{0x00, 0x10},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        4,
 					Name:            []byte("Serv"),
 					DescriptionSize: 11,
@@ -137,7 +137,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{10, 0, 0, 1},
 					Port:            [2]byte{0x1F, 0x91},
 					NumUsers:        [2]byte{0x00, 0x05},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        4,
 					Name:            []byte("Serv"),
 					DescriptionSize: 11,
@@ -217,19 +217,19 @@ func TestGetListing(t *testing.T) {
 					192, 168, 1, 1, // IP address
 					0x1F, 0x90, // Port 8080
 					0x00, 0x0A, // NumUsers 10
-					0x00, 0x00, // Unused
-					0x07,                             // NameSize
+					0x00, 0x00, // TLSPort
+					0x07,                              // NameSize
 					'S', 'e', 'r', 'v', 'e', 'r', '1', // Name
-					0x0C,                                                      // DescriptionSize
+					0x0C,                                                       // DescriptionSize
 					'F', 'i', 'r', 's', 't', ' ', 'b', 'a', 't', 'c', 'h', '1', // Description
 					// ServerRecord 2
 					192, 168, 1, 2, // IP address
 					0x1F, 0x91, // Port 8081
 					0x00, 0x14, // NumUsers 20
-					0x00, 0x00, // Unused
-					0x07,                             // NameSize
+					0x00, 0x00, // TLSPort
+					0x07,                              // NameSize
 					'S', 'e', 'r', 'v', 'e', 'r', '2', // Name
-					0x0C,                                                      // DescriptionSize
+					0x0C,                                                       // DescriptionSize
 					'F', 'i', 'r', 's', 't', ' ', 'b', 'a', 't', 'c', 'h', '2', // Description
 					// Second ServerInfoHeader (next batch)
 					0x00, 0x01, // MsgType (1)
@@ -240,10 +240,10 @@ func TestGetListing(t *testing.T) {
 					192, 168, 1, 3, // IP address
 					0x1F, 0x92, // Port 8082
 					0x00, 0x1E, // NumUsers 30
-					0x00, 0x00, // Unused
-					0x07,                             // NameSize
+					0x00, 0x00, // TLSPort
+					0x07,                              // NameSize
 					'S', 'e', 'r', 'v', 'e', 'r', '3', // Name
-					0x0D,                                                           // DescriptionSize
+					0x0D,                                                            // DescriptionSize
 					'S', 'e', 'c', 'o', 'n', 'd', ' ', 'b', 'a', 't', 'c', 'h', '1', // Description
 				}),
 				writeBuffer: &bytes.Buffer{},
@@ -254,7 +254,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 1},
 					Port:            [2]byte{0x1F, 0x90},
 					NumUsers:        [2]byte{0x00, 0x0A},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        7,
 					Name:            []byte("Server1"),
 					DescriptionSize: 12,
@@ -264,7 +264,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 2},
 					Port:            [2]byte{0x1F, 0x91},
 					NumUsers:        [2]byte{0x00, 0x14},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        7,
 					Name:            []byte("Server2"),
 					DescriptionSize: 12,
@@ -274,7 +274,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 3},
 					Port:            [2]byte{0x1F, 0x92},
 					NumUsers:        [2]byte{0x00, 0x1E},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        7,
 					Name:            []byte("Server3"),
 					DescriptionSize: 13,
@@ -298,20 +298,20 @@ func TestGetListing(t *testing.T) {
 					192, 168, 1, 1, // IP
 					0x15, 0x7c, // Port 5500
 					0x00, 0x01, // NumUsers 1
-					0x00, 0x00, // Unused
-					0x01,       // NameSize
-					'A',        // Name
-					0x01,       // DescriptionSize
-					'1',        // Description
+					0x00, 0x00, // TLSPort
+					0x01, // NameSize
+					'A',  // Name
+					0x01, // DescriptionSize
+					'1',  // Description
 					// ServerRecord 2
 					192, 168, 1, 2, // IP
 					0x15, 0x7c, // Port 5500
 					0x00, 0x02, // NumUsers 2
-					0x00, 0x00, // Unused
-					0x01,       // NameSize
-					'B',        // Name
-					0x01,       // DescriptionSize
-					'2',        // Description
+					0x00, 0x00, // TLSPort
+					0x01, // NameSize
+					'B',  // Name
+					0x01, // DescriptionSize
+					'2',  // Description
 					// Second ServerInfoHeader
 					0x00, 0x01, // MsgType (1)
 					0x00, 0x0A, // MsgDataSize
@@ -321,11 +321,11 @@ func TestGetListing(t *testing.T) {
 					192, 168, 1, 3, // IP
 					0x15, 0x7c, // Port 5500
 					0x00, 0x03, // NumUsers 3
-					0x00, 0x00, // Unused
-					0x01,       // NameSize
-					'C',        // Name
-					0x01,       // DescriptionSize
-					'3',        // Description
+					0x00, 0x00, // TLSPort
+					0x01, // NameSize
+					'C',  // Name
+					0x01, // DescriptionSize
+					'3',  // Description
 					// Third ServerInfoHeader
 					0x00, 0x01, // MsgType (1)
 					0x00, 0x0A, // MsgDataSize
@@ -335,11 +335,11 @@ func TestGetListing(t *testing.T) {
 					192, 168, 1, 4, // IP
 					0x15, 0x7c, // Port 5500
 					0x00, 0x04, // NumUsers 4
-					0x00, 0x00, // Unused
-					0x01,       // NameSize
-					'D',        // Name
-					0x01,       // DescriptionSize
-					'4',        // Description
+					0x00, 0x00, // TLSPort
+					0x01, // NameSize
+					'D',  // Name
+					0x01, // DescriptionSize
+					'4',  // Description
 				}),
 				writeBuffer: &bytes.Buffer{},
 			},
@@ -349,7 +349,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 1},
 					Port:            [2]byte{0x15, 0x7c},
 					NumUsers:        [2]byte{0x00, 0x01},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        1,
 					Name:            []byte("A"),
 					DescriptionSize: 1,
@@ -359,7 +359,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 2},
 					Port:            [2]byte{0x15, 0x7c},
 					NumUsers:        [2]byte{0x00, 0x02},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        1,
 					Name:            []byte("B"),
 					DescriptionSize: 1,
@@ -369,7 +369,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 3},
 					Port:            [2]byte{0x15, 0x7c},
 					NumUsers:        [2]byte{0x00, 0x03},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        1,
 					Name:            []byte("C"),
 					DescriptionSize: 1,
@@ -379,7 +379,7 @@ func TestGetListing(t *testing.T) {
 					IPAddr:          [4]byte{192, 168, 1, 4},
 					Port:            [2]byte{0x15, 0x7c},
 					NumUsers:        [2]byte{0x00, 0x04},
-					Unused:          [2]byte{0x00, 0x00},
+					TLSPort:         [2]byte{0x00, 0x00},
 					NameSize:        1,
 					Name:            []byte("D"),
 					DescriptionSize: 1,
@@ -403,11 +403,11 @@ func TestGetListing(t *testing.T) {
 					192, 168, 1, 1, // IP
 					0x15, 0x7c, // Port 5500
 					0x00, 0x01, // NumUsers 1
-					0x00, 0x00, // Unused
-					0x01,       // NameSize
-					'A',        // Name
-					0x01,       // DescriptionSize
-					'1',        // Description
+					0x00, 0x00, // TLSPort
+					0x01, // NameSize
+					'A',  // Name
+					0x01, // DescriptionSize
+					'1',  // Description
 					// Incomplete second ServerInfoHeader
 					0x00, 0x01, // MsgType only
 				}),