fix empty PUBLIC_HOST_AUDIO_URL handling (closes #1010)

app/main.py

@@ -112,6 +112,13 @@ class Config:
         if not self.URL_PREFIX.endswith('/'):
             self.URL_PREFIX += '/'
 
+        # A blank PUBLIC_HOST_AUDIO_URL (e.g. set empty in a compose file) bypasses the
+        # default via os.environ.get, which would leave audio links root-relative and 404.
+        # Fall back to the 'audio_download/' route that serves AUDIO_DOWNLOAD_DIR. When
+        # PUBLIC_HOST_URL is also blank we leave it blank to preserve serving from web root.
+        if not self.PUBLIC_HOST_AUDIO_URL and self.PUBLIC_HOST_URL:
+            self.PUBLIC_HOST_AUDIO_URL = self._DEFAULTS['PUBLIC_HOST_AUDIO_URL']
+
         for attr in ('PUBLIC_HOST_URL', 'PUBLIC_HOST_AUDIO_URL'):
             val = getattr(self, attr)
             if val and not val.endswith('/'):

app/tests/test_config.py

@@ -51,6 +51,19 @@ class ConfigTests(unittest.TestCase):
         self.assertEqual(c.PUBLIC_HOST_URL, "")
         self.assertEqual(c.PUBLIC_HOST_AUDIO_URL, "")
 
+    def test_blank_audio_host_falls_back_to_audio_download_route(self):
+        # Regression: a present-but-blank PUBLIC_HOST_AUDIO_URL must not stay empty
+        # (which produced root-relative, 404ing audio links). It falls back to the
+        # 'audio_download/' route that serves AUDIO_DOWNLOAD_DIR.
+        with patch.dict(
+            os.environ,
+            _base_env(PUBLIC_HOST_URL="https://ytdl.example.com", PUBLIC_HOST_AUDIO_URL=""),
+            clear=False,
+        ):
+            c = Config()
+        self.assertEqual(c.PUBLIC_HOST_URL, "https://ytdl.example.com/")
+        self.assertEqual(c.PUBLIC_HOST_AUDIO_URL, "audio_download/")
+
     def test_public_host_url_already_slashed_unchanged(self):
         with patch.dict(
             os.environ,