fix incorrect SPECIAL_FOLDERS path check

remove trailing slash from SPECIAL_FOLDERS entry
create function to normalize paths before checking to make things easier for
caller
closes #8

processor.py

@@ -286,7 +286,20 @@ class DockerRunner(object):
         subprocess.run(cmd, check=True, stdout=subprocess.DEVNULL)
 
 
-SPECIAL_FOLDERS = ("dangerzone-processed", "dangerzone-processing/", "dangerzone-rejected/", "safe/")
+# NOTE: do *not* add a trailing or leading slash to a SPECIAL_FOLDERS entry
+# the `folder` param is stripped for a better check
+SPECIAL_FOLDERS = (
+    "dangerzone-processed",
+    "dangerzone-processing",
+    "dangerzone-rejected",
+    "safe"
+)
+
+
+def is_special_folder(folder: str) -> bool:
+    """Normalize `folder` and check if it's in `SPECIAL_FOLDERS`"""
+
+    return folder.strip('/') in SPECIAL_FOLDERS
 
 
 def main():