add --config CLI parameter

src/capport/config.py

@@ -12,6 +12,7 @@ _cached_config: typing.Optional[Config] = None
 
 @dataclasses.dataclass
 class Config:
+    _source_filename: str
     controllers: typing.List[str]
     server_names: typing.List[str]
     comm_secret: str
@@ -21,10 +22,14 @@ class Config:
     debug: bool
 
     @staticmethod
-    def load_default_once() -> Config:
+    def load_default_once(filename: typing.Optional[str] = None) -> Config:
         global _cached_config
         if not _cached_config:
-            _cached_config = Config.load()
+            _cached_config = Config.load(filename)
+        elif not filename is None and filename != _cached_config._source_filename:
+            raise RuntimeError(
+                f"Already loaded different config from {_cached_config._source_filename!r} instead of {filename!r}",
+            )
         return _cached_config
 
     @staticmethod
@@ -38,6 +43,7 @@ class Config:
             data = yaml.safe_load(f)
         controllers = list(map(str, data['controllers']))
         return Config(
+            _source_filename=filename,
             controllers=controllers,
             server_names=data.get('server-names', []),
             comm_secret=str(data.get('comm-secret', None) or data['secret']),