feat(previews): serve dynamic library previews

tests/routes/test_preview_routes.py

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+import urllib.parse
+from pathlib import Path
+
+import pytest
+from aiohttp import web
+from aiohttp.test_utils import make_mocked_request
+
+from py.config import Config
+from py.routes.handlers.preview_handlers import PreviewHandler
+
+
+async def test_preview_handler_serves_preview_from_active_library(tmp_path):
+    library_root = tmp_path / "library"
+    library_root.mkdir()
+    preview_file = library_root / "model.webp"
+    preview_file.write_bytes(b"preview")
+
+    config = Config()
+    config.apply_library_settings(
+        {
+            "folder_paths": {
+                "loras": [str(library_root)],
+                "checkpoints": [],
+                "unet": [],
+                "embeddings": [],
+            }
+        }
+    )
+
+    handler = PreviewHandler(config=config)
+    encoded_path = urllib.parse.quote(str(preview_file), safe="")
+    request = make_mocked_request("GET", f"/api/lm/previews?path={encoded_path}")
+
+    response = await handler.serve_preview(request)
+
+    assert isinstance(response, web.FileResponse)
+    assert response.status == 200
+    assert Path(response._path) == preview_file
+
+
+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": [],
+            }
+        }
+    )
+
+    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)
+
+
+async def test_config_updates_preview_roots_after_switch(tmp_path):
+    first_root = tmp_path / "first"
+    first_root.mkdir()
+    second_root = tmp_path / "second"
+    second_root.mkdir()
+
+    first_preview = first_root / "model.webp"
+    first_preview.write_bytes(b"a")
+    second_preview = second_root / "model.webp"
+    second_preview.write_bytes(b"b")
+
+    config = Config()
+    config.apply_library_settings(
+        {
+            "folder_paths": {
+                "loras": [str(first_root)],
+                "checkpoints": [],
+                "unet": [],
+                "embeddings": [],
+            }
+        }
+    )
+
+    assert config.is_preview_path_allowed(str(first_preview))
+    assert not config.is_preview_path_allowed(str(second_preview))
+
+    config.apply_library_settings(
+        {
+            "folder_paths": {
+                "loras": [str(second_root)],
+                "checkpoints": [],
+                "unet": [],
+                "embeddings": [],
+            }
+        }
+    )
+
+    assert config.is_preview_path_allowed(str(second_preview))
+    assert not config.is_preview_path_allowed(str(first_preview))
+
+    preview_url = config.get_preview_static_url(str(second_preview))
+    assert preview_url.startswith("/api/lm/previews?path=")
+    decoded = urllib.parse.unquote(preview_url.split("path=", 1)[1])
+    assert decoded.replace("\\", "/").endswith("model.webp")