decoder/OggUtil: add OggExpectFirstPage() and OggExpectPageIn()

src/decoder/OggUtil.cxx

@@ -51,3 +51,28 @@ OggExpectPage(ogg_sync_state &oy, ogg_page &page,
 			return false;
 	}
 }
+
+bool
+OggExpectFirstPage(ogg_sync_state &oy, ogg_stream_state &os,
+		   decoder *decoder, input_stream *is)
+{
+	ogg_page page;
+	if (!OggExpectPage(oy, page, decoder, is))
+		return false;
+
+	ogg_stream_init(&os, ogg_page_serialno(&page));
+	ogg_stream_pagein(&os, &page);
+	return true;
+}
+
+bool
+OggExpectPageIn(ogg_sync_state &oy, ogg_stream_state &os,
+		decoder *decoder, input_stream *is)
+{
+	ogg_page page;
+	if (!OggExpectPage(oy, page, decoder, is))
+		return false;
+
+	ogg_stream_pagein(&os, &page);
+	return true;
+}

src/decoder/OggUtil.hxx

@@ -48,4 +48,24 @@ bool
 OggExpectPage(ogg_sync_state &oy, ogg_page &page,
 	      decoder *decoder, input_stream *input_stream);
 
+/**
+ * Combines OggExpectPage(), ogg_stream_init() and
+ * ogg_stream_pagein().
+ *
+ * @return true if the stream was initialized and the first page was
+ * delivered to it
+ */
+bool
+OggExpectFirstPage(ogg_sync_state &oy, ogg_stream_state &os,
+		   decoder *decoder, input_stream *is);
+
+/**
+ * Combines OggExpectPage() and ogg_stream_pagein().
+ *
+ * @return true if a page was delivered to the stream
+ */
+bool
+OggExpectPageIn(ogg_sync_state &oy, ogg_stream_state &os,
+		decoder *decoder, input_stream *is);
+
 #endif

src/decoder/OpusDecoderPlugin.cxx

@@ -269,8 +269,8 @@ mpd_opus_scan_stream(struct input_stream *is,
 	ogg_sync_state oy;
 	ogg_sync_init(&oy);
 
-	ogg_page page;
-	if (!OggExpectPage(oy, page, nullptr, is)) {
+	ogg_stream_state os;
+	if (!OggExpectFirstPage(oy, os, nullptr, is)) {
 		ogg_sync_clear(&oy);
 		return false;
 	}
@@ -280,10 +280,6 @@ mpd_opus_scan_stream(struct input_stream *is,
 
 	bool result = false;
 
-	ogg_stream_state os;
-	ogg_stream_init(&os, ogg_page_serialno(&page));
-	ogg_stream_pagein(&os, &page);
-
 	ogg_packet packet;
 	while (true) {
 		int r = ogg_stream_packetout(&os, &packet);
@@ -296,12 +292,11 @@ mpd_opus_scan_stream(struct input_stream *is,
 			if (remaining_pages-- == 0)
 				break;
 
-			if (!OggExpectPage(oy, page, nullptr, is)) {
+			if (!OggExpectPageIn(oy, os, nullptr, is)) {
 				result = false;
 				break;
 			}
 
-			ogg_stream_pagein(&os, &page);
 			continue;
 		}