Add exception handler for when pfctl operations fail

jail2ban/__init__.py

@@ -5,6 +5,7 @@ from ipaddress import ip_address
 import re
 from jail2ban.pfctl import pfctl_table_op, pfctl_cfg_read, pfctl_cfg_write
 from jail2ban.auth import get_users
+from subprocess import CalledProcessError
 
 
 auth = HTTPBasicAuth()
@@ -130,6 +131,14 @@ def create_app():
         app.logger.fatal(error)
         return jsonify({'error': str(error)}), 500
 
+    @app.errorhandler(CalledProcessError)
+    def subprocess_err(error):
+        '''
+        Show a json parsable error if the value is illegal
+        '''
+        app.logger.fatal(error)
+        return jsonify({'error': str(error)}), 500
+
     @auth.error_handler
     def auth_error():
         app.logger.error('Access Denied')