Fix forwarded media from private channels showing broken placeholder (#126)

* Fix forwarded media from private channels producing broken records

When a message is forwarded from a private channel and contains a
document, media.document is None. The _get_media_type() method
incorrectly returned "document" for this case because the fallback
return was outside the `if media.document` block, causing
telegram_file_id to become the string "None" and downloads to fail
permanently.

Move `return "document"` inside the truthy branch and return None
when the document reference is inaccessible. Add a safety guard in
_process_media to catch any remaining str("None") file IDs.

Fixes #125

* Update tests to match new _get_media_type behavior for null documents

Tests now assert None instead of "document" when media.document is None,
matching the fix for forwarded media from private channels.

Author: GeiserX

src/listener.py

@@ -516,7 +516,8 @@ def _get_media_type(self, media) -> str | None:
                         return "sticker"
                 if is_animated:
                     return "animation"
-            return "document"
+                return "document"
+            return None  # document reference unavailable (e.g., forwarded from private channel)
         elif isinstance(media, MessageMediaContact):
             return "contact"
         elif isinstance(media, MessageMediaGeo):
@@ -572,6 +573,10 @@ async def _download_media(self, message, chat_id: int) -> str | None:
             elif hasattr(media, "document"):
                 telegram_file_id = str(getattr(media.document, "id", None))
 
+            # Guard against inaccessible media producing "None" string IDs
+            if telegram_file_id == "None":
+                telegram_file_id = None
+
             # Check file size
             file_size = 0
             if hasattr(media, "document") and media.document:

src/telegram_backup.py

@@ -1313,6 +1313,10 @@ async def _process_media(self, message: Message, chat_id: int) -> dict | None:
         elif hasattr(media, "document"):
             telegram_file_id = str(getattr(media.document, "id", None))
 
+        # Guard against inaccessible media producing "None" string IDs
+        if telegram_file_id == "None":
+            telegram_file_id = None
+
         # Check file size (estimated)
         file_size = self._get_media_size(media)
         max_size = self.config.get_max_media_size_bytes()
@@ -1483,7 +1487,8 @@ def _get_media_type(self, media) -> str | None:
                 # If animated but no video attribute, still an animation
                 if is_animated:
                     return "animation"
-            return "document"
+                return "document"
+            return None  # document reference unavailable (e.g., forwarded from private channel)
         elif isinstance(media, MessageMediaContact):
             return "contact"
         elif isinstance(media, MessageMediaGeo):

tests/test_listener_extended.py

@@ -433,13 +433,13 @@ def test_document_media_sticker(self):
         assert listener._get_media_type(media) == "sticker"
 
     def test_document_media_no_document_body(self):
-        """MessageMediaDocument with document=None returns 'document'."""
+        """MessageMediaDocument with document=None returns None (inaccessible)."""
         from telethon.tl.types import MessageMediaDocument
 
         listener = self._listener()
         media = MagicMock(spec=MessageMediaDocument)
         media.document = None
-        assert listener._get_media_type(media) == "document"
+        assert listener._get_media_type(media) is None
 
     def test_contact_media(self):
         """MessageMediaContact returns 'contact'."""

tests/test_telegram_backup.py

@@ -917,11 +917,11 @@ def test_unknown_media_returns_none(self):
         media = MagicMock()
         self.assertIsNone(self.backup._get_media_type(media))
 
-    def test_document_without_document_attr_returns_document(self):
-        """MessageMediaDocument with no .document returns document."""
+    def test_document_without_document_attr_returns_none(self):
+        """MessageMediaDocument with no .document returns None (inaccessible)."""
         media = MagicMock(spec=MessageMediaDocument)
         media.document = None
-        self.assertEqual(self.backup._get_media_type(media), "document")
+        self.assertIsNone(self.backup._get_media_type(media))
 
 
 class TestGetMediaExtension(unittest.TestCase):