feat: enhance symlink detection and cache invalidation

- Add `_entry_is_symlink` method to detect symlinks and Windows junctions
- Include first-level symlinks in fingerprint for better cache invalidation
- Re-enable preview path validation for security
- Update tests to verify retargeted symlinks trigger rescan

py/config.py

@@ -223,6 +223,20 @@ class Config:
             logger.error(f"Error checking link status for {path}: {e}")
             return False
 
+    def _entry_is_symlink(self, entry: os.DirEntry) -> bool:
+        """Check if a directory entry is a symlink, including Windows junctions."""
+        if entry.is_symlink():
+            return True
+        if platform.system() == 'Windows':
+            try:
+                import ctypes
+                FILE_ATTRIBUTE_REPARSE_POINT = 0x400
+                attrs = ctypes.windll.kernel32.GetFileAttributesW(entry.path)
+                return attrs != -1 and (attrs & FILE_ATTRIBUTE_REPARSE_POINT)
+            except Exception:
+                pass
+        return False
+
     def _normalize_path(self, path: str) -> str:
         return os.path.normpath(path).replace(os.sep, '/')
 
@@ -241,8 +255,32 @@ class Config:
     def _build_symlink_fingerprint(self) -> Dict[str, object]:
         roots = [self._normalize_path(path) for path in self._symlink_roots() if path]
         unique_roots = sorted(set(roots))
-        # Fingerprint now only contains the root paths to avoid sensitivity to folder content changes.
-        return {"roots": unique_roots}
+
+        # Include first-level symlinks in fingerprint for change detection.
+        # This ensures new symlinks under roots trigger a cache invalidation.
+        # Use lists (not tuples) for JSON serialization compatibility.
+        direct_symlinks: List[List[str]] = []
+        for root in unique_roots:
+            try:
+                if os.path.isdir(root):
+                    with os.scandir(root) as it:
+                        for entry in it:
+                            if self._entry_is_symlink(entry):
+                                try:
+                                    target = os.path.realpath(entry.path)
+                                    direct_symlinks.append([
+                                        self._normalize_path(entry.path),
+                                        self._normalize_path(target)
+                                    ])
+                                except OSError:
+                                    pass
+            except (OSError, PermissionError):
+                pass
+
+        return {
+            "roots": unique_roots,
+            "direct_symlinks": sorted(direct_symlinks)
+        }
 
     def _initialize_symlink_mappings(self) -> None:
         start = time.perf_counter()
@@ -362,10 +400,9 @@ class Config:
                 with os.scandir(current_display) as it:
                     for entry in it:
                         try:
-                            # 1. High speed detection using dirent data (is_symlink)
-                            is_link = entry.is_symlink()
-                            
-                            # On Windows, is_symlink handles reparse points
+                            # 1. Detect symlinks including Windows junctions
+                            is_link = self._entry_is_symlink(entry)
+
                             if is_link:
                                 # Only resolve realpath when we actually find a link
                                 target_path = os.path.realpath(entry.path)

py/routes/handlers/preview_handlers.py

@@ -41,10 +41,8 @@ class PreviewHandler:
             raise web.HTTPBadRequest(text="Unable to resolve preview path") from exc
 
         resolved_str = str(resolved)
-        # TODO: Temporarily disabled path validation due to issues #772 and #774
-        # Re-enable after fixing preview root path handling
-        # if not self._config.is_preview_path_allowed(resolved_str):
-        #     raise web.HTTPForbidden(text="Preview path is not within an allowed directory")
+        if not self._config.is_preview_path_allowed(resolved_str):
+            raise web.HTTPForbidden(text="Preview path is not within an allowed directory")
 
         if not resolved.is_file():
             logger.debug("Preview file not found at %s", resolved_str)

tests/config/test_symlink_cache.py

@@ -112,7 +112,8 @@ def test_symlink_cache_survives_noise_mtime(monkeypatch: pytest.MonkeyPatch, tmp
     assert second_cfg.map_path_to_link(str(target_dir)) == _normalize(str(dir_link))
 
 
-def test_manual_rescan_refreshes_cache(monkeypatch: pytest.MonkeyPatch, tmp_path):
+def test_retargeted_symlink_triggers_rescan(monkeypatch: pytest.MonkeyPatch, tmp_path):
+    """Changing a symlink's target should trigger automatic cache invalidation."""
     loras_dir, _ = _setup_paths(monkeypatch, tmp_path)
 
     target_dir = loras_dir / "target"
@@ -122,22 +123,16 @@ def test_manual_rescan_refreshes_cache(monkeypatch: pytest.MonkeyPatch, tmp_path
 
     # Build initial cache pointing at the first target
     first_cfg = config_module.Config()
-    old_real = _normalize(os.path.realpath(target_dir))
     assert first_cfg.map_path_to_link(str(target_dir)) == _normalize(str(dir_link))
 
-    # Retarget the symlink to a new directory without touching the cache file
+    # Retarget the symlink to a new directory
     new_target = loras_dir / "target_v2"
     new_target.mkdir()
     dir_link.unlink()
     dir_link.symlink_to(new_target, target_is_directory=True)
 
+    # Second config should automatically detect the change and rescan
     second_cfg = config_module.Config()
-
-    # Cache still point at the old real path immediately after load
-    assert second_cfg.map_path_to_link(str(new_target)) == _normalize(str(new_target))
-
-    # Manual rescan should refresh the mapping to the new target
-    second_cfg.rebuild_symlink_cache()
     new_real = _normalize(os.path.realpath(new_target))
     assert second_cfg._path_mappings.get(new_real) == _normalize(str(dir_link))
     assert second_cfg.map_path_to_link(str(new_target)) == _normalize(str(dir_link))
@@ -177,3 +172,48 @@ def test_symlink_roots_are_preserved(monkeypatch: pytest.MonkeyPatch, tmp_path):
     cache_path = settings_dir / "cache" / "symlink_map.json"
     payload = json.loads(cache_path.read_text(encoding="utf-8"))
     assert payload["path_mappings"][normalized_real] == normalized_link
+
+
+def test_symlink_subfolder_to_external_location(monkeypatch: pytest.MonkeyPatch, tmp_path):
+    """Symlink under root pointing outside root should be detected and allowed."""
+    loras_dir, settings_dir = _setup_paths(monkeypatch, tmp_path)
+
+    # Create external directory (outside loras_dir)
+    external_dir = tmp_path / "external_models"
+    external_dir.mkdir()
+    preview_file = external_dir / "model.preview.png"
+    preview_file.write_bytes(b"preview")
+
+    # Create symlink under loras_dir pointing to external location
+    symlink = loras_dir / "characters"
+    symlink.symlink_to(external_dir, target_is_directory=True)
+
+    cfg = config_module.Config()
+
+    # Verify symlink was detected
+    normalized_external = _normalize(str(external_dir))
+    normalized_link = _normalize(str(symlink))
+    assert cfg._path_mappings[normalized_external] == normalized_link
+
+    # Verify preview path is allowed
+    assert cfg.is_preview_path_allowed(str(preview_file))
+
+
+def test_new_symlink_triggers_rescan(monkeypatch: pytest.MonkeyPatch, tmp_path):
+    """Adding a new symlink should trigger cache invalidation."""
+    loras_dir, settings_dir = _setup_paths(monkeypatch, tmp_path)
+
+    # Initial scan with no symlinks
+    first_cfg = config_module.Config()
+    assert len(first_cfg._path_mappings) == 0
+
+    # Create a symlink after initial cache
+    external_dir = tmp_path / "external"
+    external_dir.mkdir()
+    symlink = loras_dir / "new_link"
+    symlink.symlink_to(external_dir, target_is_directory=True)
+
+    # Second config should detect the change and rescan
+    second_cfg = config_module.Config()
+    normalized_external = _normalize(str(external_dir))
+    assert normalized_external in second_cfg._path_mappings

tests/routes/test_preview_routes.py

@@ -39,33 +39,32 @@ async def test_preview_handler_serves_preview_from_active_library(tmp_path):
     assert response.status == 200
     assert Path(response._path) == preview_file
 
-# TODO: disable temporarily. Enable this once the symlink scan bug fixed
-# async def test_preview_handler_forbids_paths_outside_active_library(tmp_path):
-#     allowed_root = tmp_path / "allowed"
-#     allowed_root.mkdir()
-#     forbidden_root = tmp_path / "forbidden"
-#     forbidden_root.mkdir()
-#     forbidden_file = forbidden_root / "sneaky.webp"
-#     forbidden_file.write_bytes(b"x")
+async def test_preview_handler_forbids_paths_outside_active_library(tmp_path):
+    allowed_root = tmp_path / "allowed"
+    allowed_root.mkdir()
+    forbidden_root = tmp_path / "forbidden"
+    forbidden_root.mkdir()
+    forbidden_file = forbidden_root / "sneaky.webp"
+    forbidden_file.write_bytes(b"x")
 
-#     config = Config()
-#     config.apply_library_settings(
-#         {
-#             "folder_paths": {
-#                 "loras": [str(allowed_root)],
-#                 "checkpoints": [],
-#                 "unet": [],
-#                 "embeddings": [],
-#             }
-#         }
-#     )
+    config = Config()
+    config.apply_library_settings(
+        {
+            "folder_paths": {
+                "loras": [str(allowed_root)],
+                "checkpoints": [],
+                "unet": [],
+                "embeddings": [],
+            }
+        }
+    )
 
-#     handler = PreviewHandler(config=config)
-#     encoded_path = urllib.parse.quote(str(forbidden_file), safe="")
-#     request = make_mocked_request("GET", f"/api/lm/previews?path={encoded_path}")
+    handler = PreviewHandler(config=config)
+    encoded_path = urllib.parse.quote(str(forbidden_file), safe="")
+    request = make_mocked_request("GET", f"/api/lm/previews?path={encoded_path}")
 
-#     with pytest.raises(web.HTTPForbidden):
-#         await handler.serve_preview(request)
+    with pytest.raises(web.HTTPForbidden):
+        await handler.serve_preview(request)
 
 
 async def test_config_updates_preview_roots_after_switch(tmp_path):