fetch index.html from --asset-url as a fallback (#7453)

mscolnick · web-flow · commit c6d0c5646a3f · 2025-12-11T16:04:34.000+08:00
This is not a public facing API, but helpful when running marimo from a branch (e.g.): ``` uvx --with git+https://github.com/marimo-team/marimo.git@BRANCH \ marimo edit nb.py --asset-url="https://cdn.jsdelivr.net/npm/@marimo-team/frontend@{version}/dist" ```
diff --git a/marimo/_server/api/endpoints/assets.py b/marimo/_server/api/endpoints/assets.py
@@ -72,6 +72,33 @@
 FILE_QUERY_PARAM_KEY = "file"
 
 
+async def _fetch_index_html_from_url(asset_url: str) -> str:
+    """Fetch index.html from the given asset URL."""
+    import marimo._utils.requests as requests
+    from marimo._version import __version__
+
+    # Replace {version} placeholder if present
+    if "{version}" in asset_url:
+        asset_url = asset_url.replace("{version}", __version__)
+
+    # Construct the full URL to index.html
+    # Remove trailing slash if present
+    asset_url = asset_url.rstrip("/")
+    index_url = f"{asset_url}/index.html"
+
+    try:
+        LOGGER.debug("Fetching index.html from: %s", index_url)
+        response = requests.get(index_url)
+        response.raise_for_status()
+        return response.text()
+    except Exception as e:
+        LOGGER.error("Failed to fetch index.html from %s: %s", index_url, e)
+        raise HTTPException(
+            status_code=500,
+            detail=f"Failed to fetch index.html from asset_url: {e}",
+        ) from e
+
+
 @router.get("/")
 @requires("read", redirect="auth:login_page")
 async def index(request: Request) -> HTMLResponse:
@@ -83,7 +110,20 @@ async def index(request: Request) -> HTMLResponse:
         or app_state.session_manager.file_router.get_unique_file_key()
     )
 
-    html = index_html.read_text()
+    # Try local index.html first, fallback to asset_url if local file doesn't exist
+    if index_html.exists():
+        html = index_html.read_text()
+    elif app_state.asset_url:
+        LOGGER.info(
+            "Local index.html not found, fetching from asset_url: %s",
+            app_state.asset_url,
+        )
+        html = await _fetch_index_html_from_url(app_state.asset_url)
+    else:
+        raise HTTPException(
+            status_code=500,
+            detail="index.html not found and no asset_url configured",
+        )
 
     if not file_key:
         # We don't know which file to use, so we need to render a homepage
diff --git a/tests/_server/api/endpoints/test_assets.py b/tests/_server/api/endpoints/test_assets.py
@@ -6,6 +6,7 @@
 from pathlib import Path
 from tempfile import TemporaryDirectory
 from typing import TYPE_CHECKING, Any, cast
+from unittest.mock import Mock, patch
 
 from marimo._server.api.deps import AppState
 from marimo._server.api.endpoints.assets import _inject_service_worker
@@ -217,3 +218,80 @@ def test_inject_service_worker() -> None:
         "const notebookId = 'c%3A%5Cpath%5Cto%5Cnotebook.py';"
         in _inject_service_worker("<body></body>", r"c:\path\to\notebook.py")
     )
+
+
+def test_index_with_missing_local_file_and_asset_url(
+    client: TestClient,
+) -> None:
+    """Test that index.html is fetched from asset_url when local file doesn't exist."""
+    app_state = AppState.from_app(cast(Any, client.app))
+
+    # Mock HTML content that would come from the CDN
+    mock_html = """<!DOCTYPE html>
+<html>
+<head><title>{{ title }}</title></head>
+<body>
+<marimo-filename hidden>{{ filename }}</marimo-filename>
+'{{ mount_config }}'
+</body>
+</html>"""
+
+    # Mock the requests.get to return our mock HTML
+    mock_response = Mock()
+    mock_response.text.return_value = mock_html
+    mock_response.raise_for_status.return_value = None
+
+    with (
+        patch("marimo._server.api.endpoints.assets.root") as mock_root,
+        patch("marimo._utils.requests.get", return_value=mock_response),
+    ):
+        # Make local index.html appear to not exist
+        mock_index_html = Mock()
+        mock_index_html.exists.return_value = False
+        mock_root.__truediv__.return_value = mock_index_html
+
+        # Set asset_url on the app state
+        client.app.state.asset_url = "https://cdn.example.com/assets/0.1.0"
+
+        response = client.get("/", headers=token_header())
+        assert response.status_code == 200, response.text
+        # The response should contain processed HTML
+        assert "<title>" in response.text
+
+
+def test_index_with_missing_local_file_no_asset_url(
+    client: TestClient,
+) -> None:
+    """Test that error is raised when local file doesn't exist and no asset_url."""
+    with patch("marimo._server.api.endpoints.assets.root") as mock_root:
+        # Make local index.html appear to not exist
+        mock_index_html = Mock()
+        mock_index_html.exists.return_value = False
+        mock_root.__truediv__.return_value = mock_index_html
+
+        # Ensure asset_url is None
+        client.app.state.asset_url = None
+
+        response = client.get("/", headers=token_header())
+        assert response.status_code == 500
+        assert "index.html not found" in response.json()["detail"]
+
+
+def test_index_prefers_local_file_over_asset_url(client: TestClient) -> None:
+    """Test that local index.html is preferred even when asset_url is set."""
+    # Set asset_url on the app state
+    client.app.state.asset_url = "https://cdn.example.com/assets/0.1.0"
+
+    # Mock requests.get to track if it's called
+    mock_response = Mock()
+    with patch(
+        "marimo._utils.requests.get", return_value=mock_response
+    ) as mock_get:
+        response = client.get("/", headers=token_header())
+        assert response.status_code == 200, response.text
+
+        # requests.get should NOT be called since local file exists
+        mock_get.assert_not_called()
+
+    # Reset asset_url
+    client.app.state.asset_url = None
