fix(lyrics): use normalized Genius response (#517)

go_backend/lyrics_paxsenix.go

@@ -151,7 +151,7 @@ func parsePaxsenixLyricsPayload(raw, provider string, multiPersonWordByWord bool
 	if err := json.Unmarshal([]byte(raw), &lrcPayload); err == nil {
 		lrcPayload = strings.TrimSpace(lrcPayload)
 		if lrcPayload == "" {
-			return nil, fmt.Errorf("%s returned empty lyrics", provider)
+			return nil, lyricsServiceUnavailableErrorf("%s returned empty lyrics", provider)
 		}
 		return lyricsResponseFromText(lrcPayload, provider), nil
 	}
@@ -191,7 +191,13 @@ func parsePaxsenixLyricsPayload(raw, provider string, multiPersonWordByWord bool
 	if trimmed != "" && !strings.HasPrefix(trimmed, "{") && !strings.HasPrefix(trimmed, "[") {
 		return lyricsResponseFromText(trimmed, provider), nil
 	}
-	return nil, fmt.Errorf("failed to decode %s lyrics response", provider)
+	if json.Valid([]byte(trimmed)) {
+		return nil, lyricsServiceUnavailableErrorf(
+			"%s returned a response without usable lyrics",
+			provider,
+		)
+	}
+	return nil, lyricsServiceUnavailableErrorf("failed to decode %s lyrics response", provider)
 }
 
 // lyricsResponseFromLRCText parses LRC-or-plain text into a response, or nil
@@ -541,6 +547,10 @@ func (c *GeniusLyricsClient) FetchLyrics(trackName, artistName string, durationS
 
 	params := url.Values{}
 	params.Set("url", geniusURL)
+	// The legacy v1 contract can report success with an empty lyrics string.
+	// v2 keeps the same string payload shape while using the maintained
+	// normalized Genius extractor.
+	params.Set("v", "2")
 	raw, err := fetchPaxsenixBody(c.httpClient, "https://lyrics.paxsenix.org/genius/lyrics", params)
 	if err != nil {
 		return nil, fmt.Errorf("genius lyrics fetch failed: %w", err)

go_backend/lyrics_supplement_test.go

@@ -165,6 +165,23 @@ func TestLyricsCacheParsingAndLRCLibClient(t *testing.T) {
 	}
 }
 
+func TestPaxsenixEmptyLyricsPayloadMarksProviderUnavailable(t *testing.T) {
+	lyrics, err := parsePaxsenixLyricsPayload(
+		`{"error":false,"lyrics":""}`,
+		"Genius",
+		false,
+	)
+	if lyrics != nil || err == nil {
+		t.Fatalf("empty PAX Senix payload = %#v/%v", lyrics, err)
+	}
+	if !isLyricsProviderUnavailableError(err) {
+		t.Fatalf("empty PAX Senix payload was not marked unavailable: %v", err)
+	}
+	if strings.Contains(strings.ToLower(err.Error()), "decode") {
+		t.Fatalf("empty JSON payload was misreported as a decode failure: %v", err)
+	}
+}
+
 func TestLyricsProviderHealthSkipsUnavailableProvider(t *testing.T) {
 	SetLyricsProviderOrder([]string{LyricsProviderLRCLIB})
 	defer SetLyricsProviderOrder(nil)
@@ -493,6 +510,9 @@ func TestExternalLyricsProvidersWithFakeHTTP(t *testing.T) {
 			}
 			return &http.Response{StatusCode: 200, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(`{"response":{"sections":[{"hits":[{"type":"song","result":{"title":"Song","primary_artist_names":"Artist","url":"https://genius.com/artist-song-lyrics"}}]}]}}`)), Request: req}, nil
 		case strings.Contains(req.URL.Path, "/genius/lyrics"):
+			if got := req.URL.Query().Get("v"); got != "2" {
+				t.Fatalf("genius API version = %q", got)
+			}
 			return &http.Response{StatusCode: 200, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(`{"error":false,"lyrics":"Genius line"}`)), Request: req}, nil
 		default:
 			return &http.Response{StatusCode: 404, Header: make(http.Header), Body: io.NopCloser(strings.NewReader(`{}`)), Request: req}, nil