sanei_usb: Allow backends to modify when USB recording is cleared

include/sane/sanei_usb.h

@@ -224,6 +224,19 @@ extern SANE_String sanei_usb_testing_get_backend();
  */
 extern SANE_Bool sanei_usb_is_replay_mode_enabled();
 
+/** Clears currently recorded data.
+
+    This is useful on certain backends to clear the currently recorded data if it relates to
+    other devices than the one that the scan will be performed on. On these backends all
+    devices that the backend supports are opened multiple times. Recording this interaction
+    to XML file makes it impossible to replay it, as the existence of these devices is not mocked
+    currently.
+
+    This function may only be called when no USB devices are open, otherwise the behavior is
+    unpredictable.
+ */
+extern void sanei_usb_testing_record_clear();
+
 /** Records a debug message in the captured USB data if testing mode is enabled. If testing mode
  * is not enabled, this function does nothing.
  *

sanei/sanei_usb.c

@@ -1124,6 +1124,19 @@ static void sanei_usb_replay_debug_msg(SANE_String_Const message)
     }
 }
 
+extern void sanei_usb_testing_record_clear()
+{
+  if (testing_mode != sanei_usb_testing_mode_record)
+    return;
+
+  // we only need to indicate that we never opened a device and sanei_usb_record_open() will
+  // reinitialize everything for us.
+  testing_already_opened = 0;
+  testing_known_commands_input_failed = 0;
+  testing_last_known_seq = 0;
+  testing_append_commands_node = NULL;
+}
+
 extern void sanei_usb_testing_record_message(SANE_String_Const message)
 {
   if (testing_mode == sanei_usb_testing_mode_record)
@@ -1356,6 +1369,10 @@ SANE_Bool sanei_usb_is_replay_mode_enabled()
   return SANE_FALSE;
 }
 
+void sanei_usb_testing_record_clear()
+{
+}
+
 void sanei_usb_testing_record_message(SANE_String_Const message)
 {
   (void) message;