Avoid race condition in path check

File could be deleted between check and use

dissect/target/loaders/mqtt.py

@@ -547,13 +547,6 @@ def case(value: str) -> str:
     raise argparse.ArgumentTypeError(f"Invalid case name specified: '{value}'")
 
 
-def file_exists(file_path: str) -> str:
-    """Checks if the file exists."""
-    if not os.path.isfile(file_path):
-        raise argparse.ArgumentTypeError(f"File does not exist: '{file_path}'")
-    return file_path
-
-
 @arg("--mqtt-peers", type=strictly_positive, dest="peers", help="minimum number of peers to await for first alias")
 @arg(
     "--mqtt-case",
@@ -563,9 +556,9 @@ def file_exists(file_path: str) -> str:
 )
 @arg("--mqtt-port", type=port, dest="port", help="broker connection port")
 @arg("--mqtt-broker", type=host_name_or_ip_address, dest="broker", help="broker ip-address")
-@arg("--mqtt-key", type=file_exists, dest="key", help="private key file")
-@arg("--mqtt-crt", type=file_exists, dest="crt", help="client certificate file")
-@arg("--mqtt-ca", type=file_exists, dest="ca", help="certificate authority file")
+@arg("--mqtt-key", type=Path, dest="key", help="private key file")
+@arg("--mqtt-crt", type=Path, dest="crt", help="client certificate file")
+@arg("--mqtt-ca", type=Path, dest="ca", help="certificate authority file")
 @arg("--mqtt-command", dest="command", help="direct command to client(s)")
 @arg("--mqtt-diag", action="store_true", dest="diag", help="show MQTT diagnostic information")
 @arg("--mqtt-username", dest="username", help="Username for connection")

tests/loaders/test_mqtt.py

@@ -171,7 +171,8 @@ def generate_longest_valid_hostname():
         ("example-label.com", True),
         ("example..com", False),
         (generate_longest_valid_hostname(), True),
-    ], ids=[
+    ],
+    ids=[
         "valid_domain",
         "valid_domain_with_trailing_dot",
         "invalid_double_dot",
@@ -183,9 +184,8 @@ def generate_longest_valid_hostname():
         "invalid_end_hyphen",
         "valid_domain_with_hyphen",
         "invalid_empty_label",
-        "valid_max_length"
-    ]
+        "valid_max_length",
+    ],
 )
 def test_host_name_parser(hostname, is_valid_hostname) -> None:
     assert host_name(hostname) == is_valid_hostname
-