client: Validate state transition on force update

Signed-off-by: Matthias Geihs <[email protected]>

channel/machine.go

@@ -475,15 +475,15 @@ func (m *machine) expect(tr PhaseTransition) error {
 	return nil
 }
 
-// validTransition checks that the transition from the current to the provided
+// ValidTransition checks that the transition from the current to the provided
 // state is valid. The following checks are run:
 // * matching channel ids
 // * no transition from final state
 // * version increase by 1
 // * preservation of balances
 // A StateMachine will additionally check the validity of the app-specific
 // transition whereas an ActionMachine checks each Action as being valid.
-func (m *machine) validTransition(to *State) error {
+func (m *machine) ValidTransition(to *State) error {
 	if to.ID != m.params.id {
 		return errors.New("new state's ID doesn't match")
 	}

channel/statemachine.go

@@ -134,7 +134,7 @@ func (m *StateMachine) validTransition(to *State, actor Index) (err error) {
 	if actor >= m.N() {
 		return errors.New("actor index is out of range")
 	}
-	if err := m.machine.validTransition(to); err != nil {
+	if err := m.machine.ValidTransition(to); err != nil {
 		return err
 	}
 

client/adjudicate.go

@@ -210,6 +210,11 @@ func (c *Channel) ForceUpdate(ctx context.Context, updater func(*channel.State))
 	updater(state)
 	state.Version++
 
+	// Check state transition.
+	if err := c.machine.ValidTransition(state); err != nil {
+		return errors.WithMessage(err, "validating state transition")
+	}
+
 	// Apply state in machine and generate signature
 	if err := c.machine.SetProgressing(ctx, state); err != nil {
 		return errors.WithMessage(err, "updating machine")