fix(wecom): fallback to default filename when sanitize strips to empty

nanobot/channels/wecom/runtime.py

@@ -30,12 +30,12 @@ WECOM_UPLOAD_MAX_BYTES = 1024 * 1024 * 200  # 200MB
 _SAFE_NAME_RE = re.compile(r"[^\w.\-()\[\]（）【】\u4e00-\u9fff]+", re.UNICODE)
 
 
-def _sanitize_filename(name: str) -> str:
+def _sanitize_filename(name: str, fallback: str = "unnamed") -> str:
     """Sanitize filename to avoid traversal and problematic chars."""
     name = (name or "").strip()
     name = Path(name).name
     name = _SAFE_NAME_RE.sub("_", name).strip("._ ")
-    return name
+    return name or fallback
 
 
 _IMAGE_EXTS = {".jpg", ".jpeg", ".png", ".gif", ".webp", ".bmp"}
@@ -399,9 +399,8 @@ class WecomChannel(BaseChannel):
                 return None
 
             media_dir = get_media_dir("wecom")
-            if not filename:
-                filename = fname or f"{media_type}_{hash(file_url) % 100000}"
-            filename = _sanitize_filename(cast(str, filename))
+            fallback_name = fname or f"{media_type}_{hash(file_url) % 100000}"
+            filename = _sanitize_filename(cast(str, filename or fallback_name), fallback=fallback_name)
 
             file_path = media_dir / filename
             await asyncio.to_thread(file_path.write_bytes, data)

nanobot/channels/wecom/tests/test_wecom_channel.py

@@ -93,9 +93,14 @@ def test_sanitize_filename_keeps_chinese_chars() -> None:
 
 
 def test_sanitize_filename_empty_input() -> None:
-    assert _sanitize_filename("") == ""
+    assert _sanitize_filename("") == "unnamed"
 
 
+def test_sanitize_filename_empty_or_dots_fallback() -> None:
+    assert _sanitize_filename("...") == "unnamed"
+    assert _sanitize_filename("..", fallback="fallback.txt") == "fallback.txt"
+    assert _sanitize_filename("") == "unnamed"
+
 def test_guess_wecom_media_type_image() -> None:
     for ext in (".jpg", ".jpeg", ".png", ".gif", ".webp", ".bmp"):
         assert _guess_wecom_media_type(f"photo{ext}") == "image"