Fix 26.2 login_success protocol handling and add convertibility tests

- Server sends v26_2 login_success with SessionId for protocol >= 776

- Client adds v26_2 login_success handler and scopes v1_21_8 handler to <= 26.1

- Fix WithOtherAccount guard in login server

- Add smart-convert assumption tests for login server/client

- Improve translatePacketVersion error messages

mc/client/login.go

@@ -14,6 +14,7 @@ import (
 	"github.com/admin-else/strom/mc/proto"
 	"github.com/admin-else/strom/mc/proto_base"
 	"github.com/admin-else/strom/mc/proto_generated/v1_21_8"
+	"github.com/admin-else/strom/mc/proto_generated/v26_2"
 	"github.com/admin-else/strom/mc/text"
 )
 
@@ -121,6 +122,14 @@ func (s *LoginClient) OnSuccess(success *v1_21_8.LoginToClientPacketSuccess) (er
 	return
 }
 
+func (s *LoginClient) OnSuccess26_2(success *v26_2.LoginToClientPacketSuccess) (err error) {
+	return s.OnSuccess(&v1_21_8.LoginToClientPacketSuccess{
+		Uuid:       success.Uuid,
+		Username:   success.Username,
+		Properties: success.Properties,
+	})
+}
+
 func (s *LoginClient) OnStart() (err error) {
 	return
 }
@@ -135,7 +144,8 @@ func LoginRaw(c *proto.Conn, account *api.Account) (err error) {
 	lc.RegisterCriticalUntilLatest(lc.OnCompress)
 	lc.RegisterCriticalUntilLatest(lc.OnEncrypt)
 	lc.RegisterCriticalUntilLatest(lc.OnDisconnect)
-	lc.RegisterCriticalUntilLatest(lc.OnSuccess)
+	lc.RegisterCriticalUntil("26.1", lc.OnSuccess)
+	lc.RegisterCriticalUntilLatest(lc.OnSuccess26_2)
 
 	p, err := MakeHandshakePacket(lc.Conn, proto_base.Login)
 	if err != nil {

mc/client/login_test.go

@@ -0,0 +1,55 @@
+package client_test
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/admin-else/strom/mc/data"
+	"github.com/admin-else/strom/mc/proto"
+	"github.com/admin-else/strom/mc/proto_base"
+	"github.com/admin-else/strom/mc/proto_generated/v1_21_8"
+)
+
+func assertClientSendConvertible(t *testing.T, srcType reflect.Type, name string, state proto_base.State, direction proto_base.Direction, targetVersion int32) {
+	t.Helper()
+	targetInfo, ok := proto.LookupPacketInfoByNameProtocolVersionStateAndDirection(name, targetVersion, state, direction)
+	if !ok {
+		t.Fatalf("packet %s not found for version %d", name, targetVersion)
+	}
+	targetType := reflect.TypeOf(targetInfo.Type)
+	if !proto.SmartConvertibleTo(srcType, targetType) {
+		t.Fatalf("%s is not smart-convertible from v1_21_8 to version %d", name, targetVersion)
+	}
+}
+
+func assertClientReceiveConvertible(t *testing.T, dstType reflect.Type, name string, state proto_base.State, direction proto_base.Direction, targetVersion int32) {
+	t.Helper()
+	targetInfo, ok := proto.LookupPacketInfoByNameProtocolVersionStateAndDirection(name, targetVersion, state, direction)
+	if !ok {
+		t.Fatalf("packet %s not found for version %d", name, targetVersion)
+	}
+	targetType := reflect.TypeOf(targetInfo.Type)
+	if !proto.SmartConvertibleTo(targetType, dstType) {
+		t.Fatalf("%s is not smart-convertible from version %d to v1_21_8", name, targetVersion)
+	}
+}
+
+func TestLoginClientSendAssumptions(t *testing.T) {
+	v26_1Version := data.MustLookupProtocolVersion("26.1")
+
+	// Packets sent by LoginClient as v1_21_8.
+	assertClientSendConvertible(t, reflect.TypeFor[*v1_21_8.HandshakingToServerPacketSetProtocol](), "set_protocol", proto_base.Handshaking, proto_base.ToServer, v26_1Version)
+	assertClientSendConvertible(t, reflect.TypeFor[*v1_21_8.LoginToServerPacketLoginStart](), "login_start", proto_base.Login, proto_base.ToServer, v26_1Version)
+	assertClientSendConvertible(t, reflect.TypeFor[*v1_21_8.LoginToServerPacketLoginAcknowledged](), "login_acknowledged", proto_base.Login, proto_base.ToServer, v26_1Version)
+	assertClientSendConvertible(t, reflect.TypeFor[*v1_21_8.LoginToServerPacketEncryptionBegin](), "encryption_begin", proto_base.Login, proto_base.ToServer, v26_1Version)
+}
+
+func TestLoginClientReceiveAssumptions(t *testing.T) {
+	v26_1Version := data.MustLookupProtocolVersion("26.1")
+
+	// Packets received by LoginClient via RegisterCriticalUntilLatest.
+	// login_success is excluded because 26.2 is not convertible.
+	assertClientReceiveConvertible(t, reflect.TypeFor[*v1_21_8.LoginToClientPacketCompress](), "compress", proto_base.Login, proto_base.ToClient, v26_1Version)
+	assertClientReceiveConvertible(t, reflect.TypeFor[*v1_21_8.LoginToClientPacketEncryptionBegin](), "encryption_begin", proto_base.Login, proto_base.ToClient, v26_1Version)
+	assertClientReceiveConvertible(t, reflect.TypeFor[*v1_21_8.LoginToClientPacketDisconnect](), "disconnect", proto_base.Login, proto_base.ToClient, v26_1Version)
+}

mc/proto/connection.go

@@ -166,13 +166,14 @@ func (c *Conn) ActivateReceiveRoutine() (chSending <-chan any) {
 func (c *Conn) translatePacketVersion(packet proto_base.EncodeDecodeAble, packetInfo proto_base.PacketInfo) (convertedPacket proto_base.EncodeDecodeAble, packetInfoReal proto_base.PacketInfo, err error) {
 	packetInfoReal, found := LookupPacketInfoByNameProtocolVersionStateAndDirection(packetInfo.Name, c.ProtocolVersion, c.State(), packetInfo.Direction)
 	if !found {
-		err = PacketDoesntExistInFutureVersionErr
+		err = fmt.Errorf("%w: %s from pv%d to pv%d in %s/%s not found", PacketDoesntExistInFutureVersionErr, packetInfo.Name, packetInfo.ProtocolVersion, c.ProtocolVersion, packetInfo.State, packetInfo.Direction)
 		return
 	}
 
 	dstType := reflect.TypeOf(packetInfoReal.Type)
-	if !SmartConvertibleTo(reflect.TypeOf(packetInfo.Type), dstType) {
+	srcType := reflect.TypeOf(packetInfo.Type)
-		err = CantTranslateErr
+	if !SmartConvertibleTo(srcType, dstType) {
+		err = fmt.Errorf("%w: %s from pv%d to pv%d in %s/%s (src=%s dst=%s)", CantTranslateErr, packetInfo.Name, packetInfo.ProtocolVersion, c.ProtocolVersion, packetInfo.State, packetInfo.Direction, srcType, dstType)
 		return
 	}
 	// can't fail cause pacetinfo.type is proto_base.EncodeDecodeAble

mc/proto/smart_convert_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/admin-else/strom/mc/proto_generated/v1_21_11"
 	"github.com/admin-else/strom/mc/proto_generated/v1_21_8"
 	"github.com/admin-else/strom/mc/proto_generated/v1_21_9"
+	"github.com/admin-else/strom/mc/proto_generated/v26_2"
 )
 
 func TestCanSmartConvert(t *testing.T) {
@@ -66,3 +67,15 @@ func TestSmartConvert(t *testing.T) {
 		}
 	}
 }
+
+func TestLoginSuccessNotConvertibleAcross26_2(t *testing.T) {
+	// login_success gained an extra SessionId field in 26.2, so it is not
+	// smart-convertible in either direction. This is why the login server has
+	// version-gated send code and the login client has a dedicated 26.2 handler.
+	if proto2.SmartConvertibleTo(reflect.TypeFor[*v1_21_8.LoginToClientPacketSuccess](), reflect.TypeFor[*v26_2.LoginToClientPacketSuccess]()) {
+		t.Fatal("expected v1_21_8 login_success NOT to be convertible to v26_2")
+	}
+	if proto2.SmartConvertibleTo(reflect.TypeFor[*v26_2.LoginToClientPacketSuccess](), reflect.TypeFor[*v1_21_8.LoginToClientPacketSuccess]()) {
+		t.Fatal("expected v26_2 login_success NOT to be convertible to v1_21_8")
+	}
+}

mc/server/login_server.go

@@ -12,10 +12,12 @@ import (
 
 	api2 "github.com/admin-else/strom/mc/api"
 	"github.com/admin-else/strom/mc/crypto"
+	"github.com/admin-else/strom/mc/data"
 	"github.com/admin-else/strom/mc/event"
 	"github.com/admin-else/strom/mc/proto"
 	"github.com/admin-else/strom/mc/proto_base"
 	"github.com/admin-else/strom/mc/proto_generated/v1_21_8"
+	"github.com/admin-else/strom/mc/proto_generated/v26_2"
 	"github.com/google/uuid"
 )
 
@@ -183,11 +185,20 @@ func (l *LoginServer) FinishLogin() (err error) {
 	if l.Given == nil {
 		l.Given = &l.Requested
 	}
+	if l.ProtocolVersion >= data.MustLookupProtocolVersion("26.2") {
+		err = l.Send(&v26_2.LoginToClientPacketSuccess{
+			Uuid:       l.Given.UUID,
+			Username:   l.Given.Name,
+			Properties: nil,
+			SessionId:  uuid.New(),
+		})
+	} else {
 		err = l.Send(&v1_21_8.LoginToClientPacketSuccess{
 			Uuid:       l.Given.UUID,
 			Username:   l.Given.Name,
 			Properties: nil,
 		})
+	}
 	return
 }
 
@@ -195,9 +206,6 @@ type LoginServerSetting func(*LoginServer)
 
 func WithOtherAccount(a *api2.Account) LoginServerSetting {
 	return func(s *LoginServer) {
-		if s.Given == nil {
-			return
-		}
 		s.Given = &NameAndUUID{
 			Name: a.Name,
 			UUID: a.Uuid,

mc/server/login_server_test.go

@@ -0,0 +1,60 @@
+package server_test
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/admin-else/strom/mc/data"
+	"github.com/admin-else/strom/mc/proto"
+	"github.com/admin-else/strom/mc/proto_base"
+	"github.com/admin-else/strom/mc/proto_generated/v1_21_8"
+)
+
+func assertSendConvertible(t *testing.T, srcType reflect.Type, name string, state proto_base.State, direction proto_base.Direction, targetVersion int32) {
+	t.Helper()
+	targetInfo, ok := proto.LookupPacketInfoByNameProtocolVersionStateAndDirection(name, targetVersion, state, direction)
+	if !ok {
+		t.Fatalf("packet %s not found for version %d", name, targetVersion)
+	}
+	targetType := reflect.TypeOf(targetInfo.Type)
+	if !proto.SmartConvertibleTo(srcType, targetType) {
+		t.Fatalf("%s is not smart-convertible from v1_21_8 to version %d", name, targetVersion)
+	}
+}
+
+func assertReceiveConvertible(t *testing.T, dstType reflect.Type, name string, state proto_base.State, direction proto_base.Direction, targetVersion int32) {
+	t.Helper()
+	targetInfo, ok := proto.LookupPacketInfoByNameProtocolVersionStateAndDirection(name, targetVersion, state, direction)
+	if !ok {
+		t.Fatalf("packet %s not found for version %d", name, targetVersion)
+	}
+	targetType := reflect.TypeOf(targetInfo.Type)
+	if !proto.SmartConvertibleTo(targetType, dstType) {
+		t.Fatalf("%s is not smart-convertible from version %d to v1_21_8", name, targetVersion)
+	}
+}
+
+func TestLoginServerSendAssumptions(t *testing.T) {
+	v26_1Version := data.MustLookupProtocolVersion("26.1")
+
+	// Packets sent by LoginServer as v1_21_8 must be convertible to every version
+	// they are actually sent to. login_success is excluded because it is not
+	// convertible across the 26.2 boundary; it has dedicated version-gated send code.
+	assertSendConvertible(t, reflect.TypeFor[*v1_21_8.StatusToClientPacketServerInfo](), "server_info", proto_base.Status, proto_base.ToClient, v26_1Version)
+	assertSendConvertible(t, reflect.TypeFor[*v1_21_8.StatusToClientPacketPing](), "ping", proto_base.Status, proto_base.ToClient, v26_1Version)
+	assertSendConvertible(t, reflect.TypeFor[*v1_21_8.LoginToClientPacketCompress](), "compress", proto_base.Login, proto_base.ToClient, v26_1Version)
+	assertSendConvertible(t, reflect.TypeFor[*v1_21_8.LoginToClientPacketEncryptionBegin](), "encryption_begin", proto_base.Login, proto_base.ToClient, v26_1Version)
+}
+
+func TestLoginServerReceiveAssumptions(t *testing.T) {
+	v26_1Version := data.MustLookupProtocolVersion("26.1")
+
+	// Packets received by LoginServer via RegisterCriticalUntilLatest must be
+	// convertible from each later version back to v1_21_8.
+	assertReceiveConvertible(t, reflect.TypeFor[*v1_21_8.HandshakingToServerPacketSetProtocol](), "set_protocol", proto_base.Handshaking, proto_base.ToServer, v26_1Version)
+	assertReceiveConvertible(t, reflect.TypeFor[*v1_21_8.StatusToServerPacketPingStart](), "ping_start", proto_base.Status, proto_base.ToServer, v26_1Version)
+	assertReceiveConvertible(t, reflect.TypeFor[*v1_21_8.StatusToServerPacketPing](), "ping", proto_base.Status, proto_base.ToServer, v26_1Version)
+	assertReceiveConvertible(t, reflect.TypeFor[*v1_21_8.LoginToServerPacketLoginStart](), "login_start", proto_base.Login, proto_base.ToServer, v26_1Version)
+	assertReceiveConvertible(t, reflect.TypeFor[*v1_21_8.LoginToServerPacketEncryptionBegin](), "encryption_begin", proto_base.Login, proto_base.ToServer, v26_1Version)
+	assertReceiveConvertible(t, reflect.TypeFor[*v1_21_8.LoginToServerPacketLoginAcknowledged](), "login_acknowledged", proto_base.Login, proto_base.ToServer, v26_1Version)
+}