mad: skip ID3 frames when libid3tag is disabled

When libid3tag is disabled, the libmad decoder plugin is unable to
identify ID3 frames.  If the file starts with an (unidentified) ID3
frame, it assumes that the file is not a valid MP3 song.  This patch
solves this by adding minimal stubs for the ID3 functions.

1 files changed, 28 insertions, 6 deletions

diff --git a/src/decoder/mad_plugin.c b/src/decoder/mad_plugin.c
index c6b9d32d3..1ef7183fa 100644
--- a/src/decoder/mad_plugin.c
+++ b/src/decoder/mad_plugin.c
@@ -350,11 +350,11 @@ parse_id3_replay_gain_info(struct id3_tag *tag)
 }
 #endif
 
-#ifdef HAVE_ID3TAG
 static void mp3_parse_id3(struct mp3_data *data, size_t tagsize,
 			  struct tag **mpd_tag,
 			  struct replay_gain_info **replay_gain_info_r)
 {
+#ifdef HAVE_ID3TAG
 	struct id3_tag *id3_tag = NULL;
 	id3_length_t count;
 	id3_byte_t const *id3_data;
@@ -418,8 +418,34 @@ static void mp3_parse_id3(struct mp3_data *data, size_t tagsize,
 	id3_tag_delete(id3_tag);
 
 	g_free(allocated);
-}
+#else /* !HAVE_ID3TAG */
+	(void)mpd_tag;
+	(void)replay_gain_info_r;
+
+	/* This code is enabled when libid3tag is disabled.  Instead
+	   of parsing the ID3 frame, it just skips it. */
+
+	mad_stream_skip(&data->stream, tagsize);
 #endif
+}
+
+#ifndef HAVE_ID3TAG
+/**
+ * This function emulates libid3tag when it is disabled.  Instead of
+ * doing a real analyzation of the frame, it just checks whether the
+ * frame begins with the string "ID3".  If so, it returns the full
+ * length.
+ */
+static signed long
+id3_tag_query(const void *p0, size_t length)
+{
+	const char *p = p0;
+
+	return length > 3 && memcmp(p, "ID3", 3) == 0
+		? length
+		: 0;
+}
+#endif /* !HAVE_ID3TAG */
 
 static enum mp3_action
 decode_next_frame_header(struct mp3_data *data, G_GNUC_UNUSED struct tag **tag,
@@ -433,7 +459,6 @@ decode_next_frame_header(struct mp3_data *data, G_GNUC_UNUSED struct tag **tag,
 			return DECODE_BREAK;
 	}
 	if (mad_header_decode(&data->frame.header, &data->stream)) {
-#ifdef HAVE_ID3TAG
 		if ((data->stream).error == MAD_ERROR_LOSTSYNC &&
 		    (data->stream).this_frame) {
 			signed long tagsize = id3_tag_query((data->stream).
@@ -454,7 +479,6 @@ decode_next_frame_header(struct mp3_data *data, G_GNUC_UNUSED struct tag **tag,
 				return DECODE_CONT;
 			}
 		}
-#endif
 		if (MAD_RECOVERABLE((data->stream).error)) {
 			return DECODE_SKIP;
 		} else {
@@ -493,7 +517,6 @@ decodeNextFrame(struct mp3_data *data)
 			return DECODE_BREAK;
 	}
 	if (mad_frame_decode(&data->frame, &data->stream)) {
-#ifdef HAVE_ID3TAG
 		if ((data->stream).error == MAD_ERROR_LOSTSYNC) {
 			signed long tagsize = id3_tag_query((data->stream).
 							    this_frame,
@@ -506,7 +529,6 @@ decodeNextFrame(struct mp3_data *data)
 				return DECODE_CONT;
 			}
 		}
-#endif
 		if (MAD_RECOVERABLE((data->stream).error)) {
 			return DECODE_SKIP;
 		} else {