[Bug]: Fixes Issue #520, catches JSON parse error and displays error to user to fix (#521)

Fixes #520 a JSON parsing error that occurs when the AFC.var.unit file becomes corrupted, preventing the system from starting properly. The fix includes proper error handling and user-friendly error messages.

Author: jimmyjon711

CHANGELOG.md

@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2025-08-30]
+### Added
+- Catch for JSON decode error when trying to read and load AFC.var.unit file
+
 ## [2025-08-24]
 ### Added
 - You can now use the `install-afc.sh` script to delete the `AFC.var.unit` file if necessary. This option is located under

extras/AFC.py

@@ -27,7 +27,7 @@
 try: from extras.AFC_stats import AFCStats
 except: raise error(ERROR_STR.format(import_lib="AFC_stats", trace=traceback.format_exc()))
 
-AFC_VERSION="1.0.28"
+AFC_VERSION="1.0.29"
 
 # Class for holding different states so its clear what all valid states are
 class State:

extras/AFC_logger.py

@@ -33,6 +33,7 @@ def __init__(self, printer, afc_obj):
         self.afc     = afc_obj
         self.gcode   = printer.lookup_object('gcode')
         self.webhooks = printer.lookup_object('webhooks')
+        printer.register_event_handler( "gcode:request_restart", self._stop)
 
         log_path = printer.start_args['log_file']
         dirname = Path(log_path).parent
@@ -48,6 +49,9 @@ def __init__(self, printer, afc_obj):
         self.logger.setLevel(logging.DEBUG)
         self.print_debug_console = False
 
+    def _stop(self, eventtime):
+        self.afc_ql.stop()
+
     def _add_monotonic(self, message):
         return "{:10.3f} {}".format(self.reactor.monotonic(), message)
 

extras/AFC_prep.py

@@ -73,7 +73,17 @@ def PREP(self, gcmd):
         ## load Unit stored variables
         units={}
         if os.path.exists('{}.unit'.format(self.afc.VarFile)) and os.stat('{}.unit'.format(self.afc.VarFile)).st_size > 0:
-            units=json.load(open('{}.unit'.format(self.afc.VarFile)))
+            try:
+                units=json.load(open('{}.unit'.format(self.afc.VarFile)))
+            except json.JSONDecodeError as e:
+                # Displaying error for user to fix, do not want to continue just in case
+                # there is actual data in this file as we do not want to overwrite and put
+                # users boxturtles into a weird state if prep continues.
+                self.afc.error.AFC_error(f"Error when trying to open and decode {self.afc.VarFile}.unit file.\n" + \
+                                          "Please fix file or delete if file is empty, then restart klipper.", False)
+                self.logger.error("", traceback=f"{e}")
+                return
+
         else:
             error_string = 'Error: {}.unit file not found. Please check the path in the '.format(self.afc.VarFile)
             error_string += 'AFC.cfg file and make sure the file and path exists.'