YouTube-Kanäle: zufällige 404 abfangen; „Automatisch“ in der Android-App

- YouTube antwortet auf Kanal-Feeds derzeit bei etwa zwei von drei Abrufen
  grundlos mit 404 (Kanäle zeigten „lädt nicht: HTTP 404“): ein YouTube-Feed
  wird bis zu 12-mal im Abstand von 0,25 s gefragt. Tests dazu.
- Erscheinungsbild „Automatisch“: in der Android-App folgt die WebView nicht
  dem System, sondern dem (dunklen) App-Theme – die Seite fragt dort
  DioraNative.systemScheme() und hört __dioraSystemScheme bei einem Wechsel.
sw.js: diora-v129.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/theme.md

@@ -13,7 +13,10 @@ podcast-ui.css, feeds.js) and diora-desktop (desktop.css).
 * `window.__dioraTheme()` → the choice; `window.__dioraSetTheme(choice)` sets and applies it;
   `window.__dioraThemeChanged` (event `diora-theme` on `window`, `detail` = the scheme in
   effect) lets native code follow (Android status/navigation bars, Electron's window colour).
-* "auto" follows `prefers-color-scheme` live.
+* "auto" follows `prefers-color-scheme` live — except in the Android app, whose WebView
+  answers that query from the app's own (dark) theme, not the system's: there the page asks
+  `DioraNative.systemScheme()` ("dark" | "light") and the app calls
+  `window.__dioraSystemScheme(scheme)` when the system switches (uiMode change, or on return).
 * E-ink mode (`html.nui-eink`) keeps its own black-on-white rules and ignores this.
 * The reader has its own themes; its default is now "Wie die App" (`readerSettings.theme = 'app'`):
   dark → reader dark, light → reader bright. Sepia, Dunkel and Hell stay choosable.

docs/youtube.md

@@ -12,7 +12,10 @@ sound**: each app finds the audio stream itself.
   once (feed address, name, picture) and stores the feed
   `https://www.youtube.com/feeds/videos.xml?channel_id=UC…` (or `?playlist_id=…`).
   `GET /podcasts/search/?q=<YouTube address>` answers with that one channel.
-- From then on the feed is refreshed like any other. It carries the latest 15
+- From then on the feed is refreshed like any other — except that YouTube answers its
+  channel feeds with a 404 (or 5xx) now and then for no reason (October 2026: two
+  requests in three), so a YouTube feed is asked up to 12 times, 0.25 s apart, before
+  its refresh counts as failed (`YOUTUBE_FEED_TRIES` in `podcasts/views.py`). It carries the latest 15
   videos. **Shorts are left out.** There is no duration (`duration_seconds` 0)
   until a player knows it: `POST /podcasts/progress/save/` takes an optional
   `duration_seconds` (number, 1 s … 7 days), stored only while the episode has none.

podcasts/test_youtube.py

@@ -263,3 +263,46 @@ class MoveFeedTests(TestCase):
         bob = User.objects.create_user(username='bob', password='pw12345678')
         self.client.force_login(bob)
         self.assertEqual(self.move('https://www.youtube.com/@tagesschau').status_code, 404)
+
+
+class FlakyFeedTests(TestCase):
+    """YouTube's channel feeds answer 404 now and then; the next request gets them."""
+
+    FEED = 'https://www.youtube.com/feeds/videos.xml?channel_id=UCabcdefghijklmnopqrstuv'
+    BODY = (b'<?xml version="1.0"?><feed xmlns="http://www.w3.org/2005/Atom"><title>Kanal</title>'
+            b'<entry><id>yt:video:abcdefghijk</id><title>Folge</title></entry></feed>')
+
+    def _responses(self, codes):
+        from types import SimpleNamespace
+        calls = []
+
+        def get(url, **kw):
+            code = codes[min(len(calls), len(codes) - 1)]
+            calls.append(url)
+            return SimpleNamespace(status_code=code, content=self.BODY if code == 200 else b'',
+                                   headers={}, url=url, history=[])
+        return get, calls
+
+    def test_a_404_is_asked_again(self):
+        from .views import _fetch_feed
+        get, calls = self._responses([404, 404, 200])
+        with patch('podcasts.views.requests.get', get), patch('podcasts.views.time.sleep', lambda s: None):
+            fetched = _fetch_feed(self.FEED)
+        self.assertEqual(fetched.status, 200)
+        self.assertEqual(len(calls), 3)
+
+    def test_a_feed_that_stays_away_is_an_error(self):
+        from .views import _fetch_feed, FeedFetchError, YOUTUBE_FEED_TRIES
+        get, calls = self._responses([404])
+        with patch('podcasts.views.requests.get', get), patch('podcasts.views.time.sleep', lambda s: None):
+            with self.assertRaises(FeedFetchError):
+                _fetch_feed(self.FEED)
+        self.assertEqual(len(calls), YOUTUBE_FEED_TRIES)
+
+    def test_other_feeds_are_asked_once(self):
+        from .views import _fetch_feed, FeedFetchError
+        get, calls = self._responses([404, 200])
+        with patch('podcasts.views.requests.get', get), patch('podcasts.views.time.sleep', lambda s: None):
+            with self.assertRaises(FeedFetchError):
+                _fetch_feed('https://example.org/feed.xml')
+        self.assertEqual(len(calls), 1)

podcasts/views.py

@@ -332,6 +332,11 @@ def _body_hash(content):
 PERMANENT_REDIRECTS = (301, 308)
 
 
+YOUTUBE_FEED_TRIES = 12
+YOUTUBE_RETRY_STATUS = (404, 500, 502, 503)
+YOUTUBE_RETRY_PAUSE = 0.25   # seconds between tries
+
+
 def _fetch_feed(url, etag='', last_modified='', body_hash='', user_agent='diora podcast refresh'):
     """Download and parse a feed (with a timeout, unlike feedparser's own
     fetch). With etag/last_modified it is a conditional GET; with body_hash a
@@ -343,16 +348,24 @@ def _fetch_feed(url, etag='', last_modified='', body_hash='', user_agent='diora
         headers['If-None-Match'] = etag
     if last_modified:
         headers['If-Modified-Since'] = last_modified
-    try:
-        r = requests.get(url, timeout=FEED_TIMEOUT, headers=headers)
-    except requests.Timeout:
-        raise FeedFetchError('timeout')
-    except requests.TooManyRedirects:
-        raise FeedFetchError('too many redirects')
-    except requests.ConnectionError:
-        raise FeedFetchError('connection failed')
-    except requests.RequestException as e:
-        raise FeedFetchError(f'request failed ({type(e).__name__})')
+    # YouTube's channel feeds answer 404 (or a 5xx) now and then for no reason — in
+    # October 2026 about every other request — and the next request gets the feed: ask
+    # again a few times before calling it an error.
+    tries = YOUTUBE_FEED_TRIES if youtube_mod.is_feed(url) else 1
+    for attempt in range(tries):
+        try:
+            r = requests.get(url, timeout=FEED_TIMEOUT, headers=headers)
+        except requests.Timeout:
+            raise FeedFetchError('timeout')
+        except requests.TooManyRedirects:
+            raise FeedFetchError('too many redirects')
+        except requests.ConnectionError:
+            raise FeedFetchError('connection failed')
+        except requests.RequestException as e:
+            raise FeedFetchError(f'request failed ({type(e).__name__})')
+        if r.status_code not in YOUTUBE_RETRY_STATUS or attempt == tries - 1:
+            break
+        time.sleep(YOUTUBE_RETRY_PAUSE)
 
     # Each hop's target is the next hop's URL (the last one's is r.url).
     permanent_url = url

static/js/sw.js

@@ -2,7 +2,7 @@
  * diora service worker — caches the app shell for offline use.
  */
 
-const CACHE = 'diora-v128';
+const CACHE = 'diora-v129';
 const SHELL = [
   '/static/css/app.css',
   '/static/js/app/01-core.js',

templates/base.html

@@ -19,6 +19,15 @@
       var KEY = 'diora_theme';
       var LABELS = {dark: 'Dunkel', light: 'Hell', auto: 'Automatisch'};
       var mq = window.matchMedia ? window.matchMedia('(prefers-color-scheme: light)') : null;
+      // In the Android app the WebView's media query follows the app's own theme, not the
+      // system: the app tells what the system is set to (DioraNative.systemScheme, and
+      // __dioraSystemScheme when it switches).
+      var nat = window.DioraNative && typeof window.DioraNative.systemScheme === 'function' ? window.DioraNative : null;
+      var sys = null;
+      function systemLight() {
+        if (nat) { if (sys === null) { try { sys = nat.systemScheme(); } catch (e) { sys = 'dark'; } } return sys === 'light'; }
+        return !!(mq && mq.matches);
+      }
       function choice() {
         var v = null;
         try { v = localStorage.getItem(KEY); } catch (e) {}
@@ -26,7 +35,7 @@
       }
       function scheme() {
         var c = choice();
-        return c === 'light' || (c === 'auto' && mq && mq.matches) ? 'light' : 'dark';
+        return c === 'light' || (c === 'auto' && systemLight()) ? 'light' : 'dark';
       }
       function apply() {
         var s = scheme();
@@ -51,6 +60,7 @@
         window.__dioraSetTheme(order[(order.indexOf(choice()) + 1) % order.length]);
       };
       if (mq && mq.addEventListener) mq.addEventListener('change', function () { if (choice() === 'auto') apply(); });
+      window.__dioraSystemScheme = function (s) { sys = s; if (choice() === 'auto') apply(); };
       document.addEventListener('DOMContentLoaded', apply);
       document.documentElement.setAttribute('data-theme', scheme());
     })();