fix: add helpful error when symlink = false (#3747)

Add a better error message when follow-symlinks fail

marimo/_server/api/endpoints/assets.py

@@ -2,7 +2,6 @@
 from __future__ import annotations
 
 import mimetypes
-import os
 import re
 from pathlib import Path
 from typing import TYPE_CHECKING
@@ -33,20 +32,35 @@
 router = APIRouter()
 
 # Root directory for static assets
-root = os.path.realpath(str(import_files("marimo").joinpath("_static")))
+root = Path(import_files("marimo").joinpath("_static")).resolve()
 
 config = (
     get_default_config_manager(current_path=None)
     .get_config()
     .get("server", {})
 )
 
+assets_dir = root / "assets"
+follow_symlinks = config.get("follow_symlink", False)
+
+if not follow_symlinks and assets_dir.is_symlink():
+    LOGGER.error(
+        "Assets directory is a symlink but follow_symlink=false.\n"
+        "To fix this:\n"
+        "1. Run 'marimo config show' to see your current config\n"
+        "2. Add 'follow_symlink = true' under the [server] section in your config\n"
+        "3. Restart marimo\n\n"
+        "Example config:\n"
+        "[server]\n"
+        "follow_symlink = true"
+    )
+
 try:
     router.mount(
         "/assets",
         app=StaticFiles(
-            directory=os.path.join(root, "assets"),
-            follow_symlink=config.get("follow_symlink", False),
+            directory=assets_dir,
+            follow_symlink=follow_symlinks,
         ),
         name="assets",
     )
@@ -60,15 +74,14 @@
 @requires("read", redirect="auth:login_page")
 async def index(request: Request) -> HTMLResponse:
     app_state = AppState(request)
-    index_html = os.path.join(root, "index.html")
+    index_html = root / "index.html"
 
     file_key = (
         app_state.query_params(FILE_QUERY_PARAM_KEY)
         or app_state.session_manager.file_router.get_unique_file_key()
     )
 
-    with open(index_html, "r") as f:  # noqa: ASYNC101 ASYNC230
-        html = f.read()
+    html = index_html.read_text()
 
     if not file_key:
         # We don't know which file to use, so we need to render a homepage
@@ -215,7 +228,7 @@ async def public_files_service_worker(request: Request) -> Response:
 async def serve_public_file(request: Request) -> Response:
     """Serve files from the notebook's directory under /public/"""
     app_state = AppState(request)
-    filepath = request.path_params["filepath"]
+    filepath = str(request.path_params["filepath"])
     # Get notebook ID from header
     notebook_id = request.headers.get("X-Notebook-Id")
     if notebook_id:
@@ -233,7 +246,7 @@ async def serve_public_file(request: Request) -> Response:
         except ValueError:
             return Response(status_code=403, content="Access denied")
 
-        if file_path.is_file() and not os.path.islink(str(file_path)):
+        if file_path.is_file() and not file_path.is_symlink():
             return FileResponse(file_path)
 
     raise HTTPException(status_code=404, detail="File not found")
@@ -242,8 +255,8 @@ async def serve_public_file(request: Request) -> Response:
 # Catch all for serving static files
 @router.get("/{path:path}")
 async def serve_static(request: Request) -> FileResponse:
-    path = request.path_params["path"]
+    path = str(request.path_params["path"])
     if any(re.match(pattern, path) for pattern in STATIC_FILES):
-        return FileResponse(os.path.join(root, path))
+        return FileResponse(root / path)
 
     raise HTTPException(status_code=404, detail="Not Found")