refactor icon fetching

frontend/css/style.scss

@@ -3824,7 +3824,7 @@ html.picking-component * {
     // Theses durations are also referenced in code!
     transition:
         opacity 0.2s ease-in-out,
-        background-color 0.6s ease-in-out;
+        background-color 0.5s ease-in-out;
 
     & > * {
         transform: translateY(-2rem);

rio/app.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import functools
+import io
 import os
 import sys
 import threading
@@ -13,6 +14,7 @@ from pathlib import Path
 import fastapi
 import introspection
 import uvicorn
+from PIL import Image
 
 import __main__
 import rio
@@ -312,6 +314,63 @@ class App:
         else:
             self._ping_pong_interval = timedelta(seconds=ping_pong_interval)
 
+        # Initialized lazily, when the icon is first requested
+        #
+        # This starts out as `None`, then either becomes a `bytes` object if
+        # it's successfully fetched, or an error message if fetching failed.
+        self._icon_as_png_blob: bytes | str | None = None
+
+    async def fetch_icon_png_blob(self) -> bytes:
+        """
+        Fetches the app's icon as a PNG blob.
+
+        The result is cached. It will be loaded the first time you call this
+        method, and then returned immediately on subsequent calls. If fetching
+        the icon fails, the exception is also cached, and no further fetching
+        attempts will be made.
+
+        ## Raises
+
+        `IOError`: If the icon could not be fetched.
+        """
+
+        # Already cached?
+        if isinstance(self._icon_as_png_blob, bytes):
+            return self._icon_as_png_blob
+
+        # Already failed?
+        if isinstance(self._icon_as_png_blob, str):
+            raise IOError(self._icon_as_png_blob)
+
+        # Nope, get it
+        try:
+            icon_blob, _ = await self._icon.try_fetch_as_blob()
+
+            input_buffer = io.BytesIO(icon_blob)
+            output_buffer = io.BytesIO()
+
+            with Image.open(input_buffer) as image:
+                image.save(output_buffer, format="png")
+
+        except Exception as err:
+            if isinstance(self._icon, assets.PathAsset):
+                message = f"Could not fetch the app's icon from {self._icon.path.resolve()}"
+            elif isinstance(self._icon, assets.UrlAsset):
+                message = (
+                    f"Could not fetch the app's icon from {self._icon.url}"
+                )
+            else:
+                message = f"Could not fetch the app's icon from"
+
+            self._icon_as_png_blob = message
+            raise IOError(message) from err
+
+        # Cache it
+        self._icon_as_png_blob = output_buffer.getvalue()
+
+        # Done!
+        return self._icon_as_png_blob
+
     @functools.cached_property
     def _main_file_path(self) -> Path:
         if global_state.rio_run_app_module_path is not None:

rio/app_server/fastapi_server.py

@@ -4,12 +4,10 @@ import asyncio
 import contextlib
 import functools
 import html
-import io
 import json
 import logging
 import secrets
 import typing as t
-import warnings
 import weakref
 from datetime import timedelta
 from pathlib import Path
@@ -18,7 +16,6 @@ from xml.etree import ElementTree as ET
 import crawlerdetect
 import fastapi
 import timer_dict
-from PIL import Image
 from uniserde import Jsonable, JsonDoc
 
 import rio
@@ -234,9 +231,6 @@ class FastapiServer(fastapi.FastAPI, AbstractAppServer):
         self._can_create_new_sessions = asyncio.Event()
         self._can_create_new_sessions.set()
 
-        # Initialized lazily, when the favicon is first requested.
-        self._icon_as_png_blob: bytes | None = None
-
         # The session tokens and Request object for all clients that have made a
         # HTTP request, but haven't yet established a websocket connection. Once
         # the websocket connection is created, these will be turned into
@@ -617,43 +611,19 @@ Sitemap: {base_url / "/rio/sitemap"}
         """
         Handler for serving the favicon via fastapi, if one is set.
         """
-        # If an icon is set, make sure a cached version exists
-        if self._icon_as_png_blob is None and self.app._icon is not None:
-            try:
-                icon_blob, _ = await self.app._icon.try_fetch_as_blob()
+        # Fetch the favicon. This method is already caching, so it's fine to
+        # fetch every time.
+        try:
+            icon_png_blob = await self.app.fetch_icon_png_blob()
+        except IOError as err:
+            raise fastapi.HTTPException(
+                status_code=fastapi.status.HTTP_500_INTERNAL_SERVER_ERROR,
+                detail="Could not fetch the app's icon.",
+            ) from err
 
-                input_buffer = io.BytesIO(icon_blob)
-                output_buffer = io.BytesIO()
-
-                with Image.open(input_buffer) as image:
-                    image.save(output_buffer, format="png")
-
-            except Exception as err:
-                if isinstance(self.app._icon, assets.PathAsset):
-                    warnings.warn(
-                        f"Could not fetch the app's icon from {self.app._icon.path.resolve()}"
-                    )
-                elif isinstance(self.app._icon, assets.UrlAsset):
-                    warnings.warn(
-                        f"Could not fetch the app's icon from {self.app._icon.url}"
-                    )
-                else:
-                    warnings.warn(f"Could not fetch the app's icon from")
-
-                raise fastapi.HTTPException(
-                    status_code=fastapi.status.HTTP_500_INTERNAL_SERVER_ERROR,
-                    detail="Could not fetch the app's icon.",
-                ) from err
-
-            self._icon_as_png_blob = output_buffer.getvalue()
-
-        # No icon set or fetching failed
-        if self._icon_as_png_blob is None:
-            return fastapi.responses.Response(status_code=404)
-
-        # There is an icon, respond
+        # Respond
         return fastapi.responses.Response(
-            content=self._icon_as_png_blob,
+            content=icon_png_blob,
             media_type="image/png",
         )