moonraker: backup the most recent working config

Attempt to take a backup of the configuration file if Moonraker
loads successfully and has not seen a config change.

If Moonraker fails to load due to a config error, attempt to fallback
to the backup configuration.  If that fails, exit the server.

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

moonraker/moonraker.py

@@ -122,9 +122,12 @@ class Server:
         self.register_upload_handler = app.register_upload_handler
         self.register_api_transport = app.register_api_transport
 
-        log_warn: Optional[str] = args.get('log_warning')
-        if log_warn is not None:
+        log_warn = args.get('log_warning', "")
+        if log_warn:
             self.add_warning(log_warn)
+        cfg_warn = args.get("config_warning", "")
+        if cfg_warn:
+            self.add_warning(cfg_warn)
 
         self.register_endpoint(
             "/server/info", ['GET'], self._handle_info_request)
@@ -188,6 +191,10 @@ class Server:
         if optional_comps:
             await asyncio.gather(*optional_comps)
 
+        if not self.warnings:
+            cfg_file = self.app_args['config_file']
+            await self.event_loop.run_in_thread(utils.backup_config, cfg_file)
+
         # Start HTTP Server
         logging.info(
             f"Starting Moonraker on ({self.host}, {self.port}), "
@@ -859,7 +866,8 @@ def main() -> None:
             os.path.expanduser(cmd_line_args.logfile))
     app_args['software_version'] = version
     ql, file_logger, warning = utils.setup_logging(app_args)
-    app_args['log_warning'] = warning
+    if warning is not None:
+        app_args['log_warning'] = warning
 
     if sys.version_info < (3, 7):
         msg = f"Moonraker requires Python 3.7 or above.  " \
@@ -871,10 +879,27 @@ def main() -> None:
 
     # Start asyncio event loop and server
     event_loop = EventLoop()
+    alt_config_loaded = False
     estatus = 0
     while True:
         try:
             server = Server(app_args, file_logger, event_loop)
+        except confighelper.ConfigError as e:
+            backup_cfg = utils.find_config_backup(app_args['config_file'])
+            if alt_config_loaded or backup_cfg is None:
+                logging.exception("Server Config Error")
+                estatus = 1
+                break
+            app_args['config_file'] = backup_cfg
+            app_args['config_warning'] = (
+                f"Server configuration error: {e}\n"
+                f"Loaded server from most recent working configuration:"
+                f" '{app_args['config_file']}'\n"
+                f"Please fix the issue in moonraker.conf and restart "
+                f"the server."
+            )
+            alt_config_loaded = True
+            continue
         except Exception:
             logging.exception("Moonraker Error")
             estatus = 1
@@ -887,6 +912,12 @@ def main() -> None:
             break
         if server.exit_reason == "terminate":
             break
+        # Restore the original config and clear the warning
+        # before the server restarts
+        if alt_config_loaded:
+            app_args['config_file'] = cmd_line_args.configfile
+            app_args.pop('config_warning', None)
+            alt_config_loaded = False
         event_loop.close()
         # Since we are running outside of the the server
         # it is ok to use a blocking sleep here

moonraker/utils.py

@@ -18,6 +18,8 @@ import hashlib
 import json
 import shlex
 import re
+import shutil
+import filecmp
 from queue import SimpleQueue as Queue
 
 # Annotation imports
@@ -230,3 +232,22 @@ def load_system_module(name: str) -> ModuleType:
     else:
         raise ServerError(f"Unable to import module {name}")
     return module
+
+def backup_config(cfg_path: str) -> None:
+    cfg = pathlib.Path(cfg_path).expanduser().resolve()
+    backup = cfg.parent.joinpath(f".{cfg.name}.bkp")
+    try:
+        if backup.exists() and filecmp.cmp(cfg, backup):
+            # Backup already exists and is current
+            return
+        shutil.copy2(cfg, backup)
+        logging.info(f"Backing up last working configuration to '{backup}'")
+    except Exception:
+        logging.exception("Failed to create a backup")
+
+def find_config_backup(cfg_path: str) -> Optional[str]:
+    cfg = pathlib.Path(cfg_path).expanduser().resolve()
+    backup = cfg.parent.joinpath(f".{cfg.name}.bkp")
+    if backup.is_file():
+        return str(backup)
+    return None