fix(voice): bound header slice when seeking truncated audio

internal/voice/player.go

@@ -125,7 +125,7 @@ func (p *Player) seek(position time.Duration) error {
 		offset += size
 	}
 
-	decoder, err := oggopus.NewDecoder(io.MultiReader(bytes.NewReader(p.audio[:headers]), bytes.NewReader(p.audio[min(start, len(p.audio)):])))
+	decoder, err := oggopus.NewDecoder(io.MultiReader(bytes.NewReader(p.audio[:min(headers, len(p.audio))]), bytes.NewReader(p.audio[min(start, len(p.audio)):])))
 	if err != nil {
 		return err
 	}

internal/voice/player_test.go

@@ -12,6 +12,7 @@ import (
 )
 
 func TestPlayerSeek(t *testing.T) {
+	t.Run("valid", func(t *testing.T) {
 		const seconds = 10
 
 		var audio bytes.Buffer
@@ -36,4 +37,18 @@ func TestPlayerSeek(t *testing.T) {
 				t.Errorf("seek to %v: %v is left, want %v", position, got, want)
 			}
 		}
+	})
+
+	// A page whose segment table claims far more bytes than the file holds must not make seek read out of bounds.
+	t.Run("truncated page", func(t *testing.T) {
+		page := make([]byte, oggHeaderSize+255)
+		copy(page, "OggS")
+		page[oggSegmentsOffset] = 255
+		for i := range page[oggHeaderSize:] {
+			page[oggHeaderSize+i] = 255
+		}
+
+		p := Player{audio: page}
+		_ = p.seek(0)
+	})
 }