perf(apple): isolate lyrics from audio preparation

sidecars/apple-gateway/apple_gateway/app.py

@@ -366,11 +366,29 @@ def create_app(
     async def lyrics_song(song_id: str) -> dict[str, str]:
         try:
             song_url(config.storefront, song_id)
+            canonical_url = await catalog_client.song_url(song_id)
+            if canonical_url is None:
+                raise HTTPException(status_code=404, detail="song_not_found")
+            url, _ = safe_apple_url(canonical_url)
         except ValueError:
             raise HTTPException(status_code=400, detail="invalid_song_id") from None
+        except httpx.HTTPError:
+            raise HTTPException(status_code=502, detail="catalog_unavailable") from None
         cached = config.data_root / "lyrics" / f"{song_id}.lrc"
         if not cached.is_file():
-            await prepare_song(song_id, "alac-16-44")
+            root = config.data_root / "artifacts" / uuid.uuid4().hex
+            try:
+                lyrics = await process_runner.download_lyrics(
+                    url, root / "output", root / "temporary")
+                cached.parent.mkdir(exist_ok=True, mode=0o750)
+                partial = cached.with_suffix(".lrc.partial")
+                shutil.copyfile(lyrics[0], partial)
+                partial.replace(cached)
+            except ProcessFailure as exc:
+                status = 504 if exc.code == "process_timeout" else 404
+                raise HTTPException(status_code=status, detail=exc.code) from None
+            finally:
+                shutil.rmtree(root, ignore_errors=True)
         if not cached.is_file():
             raise HTTPException(status_code=404, detail="lyrics_not_found")
         try:

sidecars/apple-gateway/apple_gateway/runner.py

@@ -62,6 +62,19 @@ class BoundedProcessRunner:
         return retained.decode("utf-8", errors="replace")
 
     async def download(self, url: str, quality: str, output: Path, temporary: Path) -> list[Path]:
+        return await self._download(url, quality, output, temporary, lyrics_only=False)
+
+    async def download_lyrics(self, url: str, output: Path, temporary: Path) -> list[Path]:
+        return await self._download(url, "aac-he", output, temporary, lyrics_only=True)
+
+    async def _download(
+        self,
+        url: str,
+        quality: str,
+        output: Path,
+        temporary: Path,
+        lyrics_only: bool,
+    ) -> list[Path]:
         output.mkdir(parents=True, exist_ok=False, mode=0o750)
         temporary.mkdir(parents=True, exist_ok=False, mode=0o750)
         argv = [
@@ -79,11 +92,15 @@ class BoundedProcessRunner:
         ]
         if self._settings.cookies_path:
             argv.extend(["--cookies-path", str(self._settings.cookies_path)])
+        if lyrics_only:
+            argv.append("--synced-lyrics-only")
         argv.append(url)
         result = await self.execute(argv, temporary)
         if result.return_code != 0:
             raise ProcessFailure("gamdl_failed")
-        artifacts = safe_files(output, {".m4a", ".flac", ".mp4", ".m4v", ".lrc", ".srt", ".ttml", ".jpg", ".png"})
+        artifacts = safe_files(output, {".lrc"} if lyrics_only else {
+            ".m4a", ".flac", ".mp4", ".m4v", ".lrc", ".srt", ".ttml", ".jpg", ".png"
+        })
         if not artifacts:
             raise ProcessFailure("artifact_missing")
         return artifacts

sidecars/apple-gateway/tests/test_gateway.py

@@ -102,6 +102,14 @@ class FakeRunner:
         lyrics.write_text("[00:01.00]Fixture lyrics\n", encoding="utf-8")
         return [artifact, lyrics]
 
+    async def download_lyrics(self, url: str, output: Path, temporary: Path) -> list[Path]:
+        self.calls.append((url, "lyrics"))
+        output.mkdir(parents=True, exist_ok=False)
+        temporary.mkdir(parents=True, exist_ok=False)
+        lyrics = output / "fixture.lrc"
+        lyrics.write_text("[00:01.00]Fixture lyrics\n", encoding="utf-8")
+        return [lyrics]
+
     async def to_flac(self, source: Path, target: Path) -> Path:
         self.transcodes.append("file")
         target.write_bytes(b"fLaCfixture")
@@ -330,6 +338,7 @@ def test_song_lyrics_use_gamdl_artifact_and_cache(client):
     calls = len(client[2].calls)
     assert client[0].get("/api/lyrics/103").status_code == 200
     assert len(client[2].calls) == calls
+    assert client[2].calls == [("https://music.apple.com/us/album/fixture/1?i=103", "lyrics")]
 
 
 @pytest.mark.asyncio