oggvorbis: disable seeking on remote songs

When libvorbis knows that a song is seekable, it seeks around like
crazy in the file before starting to decode it.  This is very
expensive on remote HTTP resources, and delays MPD for 10 or 20
seconds.

This patch disables seeking on remote songs, because the advantages of
quickly playing a song seem to weigh more than the theoretical ability
of seeking for most MPD users.  If users feel this feature is needed,
we will make a configuration option for that.

NEWS

@@ -19,6 +19,7 @@ MPD 0.14.1 - not yet released
   - mp4: support the writer/composer tag
   - id3: strip leading and trailing whitespace from ID3 tags
   - oggvorbis: fix tremor support
+  - oggvorbis: disable seeking on remote files
 * audio outputs:
   - jack: allocate default port names (fixes a crash)
 * update:

src/decoder/oggvorbis_plugin.c

@@ -20,6 +20,7 @@
 
 #include "_ogg_common.h"
 #include "config.h"
+#include "ls.h"
 
 #ifndef HAVE_TREMOR
 #include <vorbis/vorbisfile.h>
@@ -51,7 +52,9 @@
 
 typedef struct _OggCallbackData {
 	struct decoder *decoder;
+
 	struct input_stream *input_stream;
+	bool seekable;
 } OggCallbackData;
 
 static size_t ogg_read_cb(void *ptr, size_t size, size_t nmemb, void *vdata)
@@ -69,9 +72,11 @@ static size_t ogg_read_cb(void *ptr, size_t size, size_t nmemb, void *vdata)
 static int ogg_seek_cb(void *vdata, ogg_int64_t offset, int whence)
 {
 	const OggCallbackData *data = (const OggCallbackData *) vdata;
-	if(decoder_get_command(data->decoder) == DECODE_COMMAND_STOP)
+
-		return -1;
+	return data->seekable &&
-	return input_stream_seek(data->input_stream, offset, whence) ? 0 : -1;
+		decoder_get_command(data->decoder) != DECODE_COMMAND_STOP &&
+		input_stream_seek(data->input_stream, offset, whence)
+		? 0 : -1;
 }
 
 /* TODO: check Ogg libraries API and see if we can just not have this func */
@@ -209,6 +214,22 @@ vorbis_send_comments(struct decoder *decoder, struct input_stream *is,
 	tag_free(tag);
 }
 
+static bool
+oggvorbis_seekable(struct decoder *decoder)
+{
+	char *uri;
+	bool seekable;
+
+	uri = decoder_get_uri(decoder);
+	/* disable seeking on remote streams, because libvorbis seeks
+	   around like crazy, and due to being very expensive, this
+	   delays song playback my 10 or 20 seconds */
+	seekable = !uri_has_scheme(uri);
+	g_free(uri);
+
+	return seekable;
+}
+
 /* public */
 static void
 vorbis_stream_decode(struct decoder *decoder,
@@ -237,8 +258,9 @@ vorbis_stream_decode(struct decoder *decoder,
 	   moved it */
 	input_stream_seek(input_stream, 0, SEEK_SET);
 
-	data.input_stream = input_stream;
 	data.decoder = decoder;
+	data.input_stream = input_stream;
+	data.seekable = input_stream->seekable && oggvorbis_seekable(decoder);
 
 	callbacks.read_func = ogg_read_cb;
 	callbacks.seek_func = ogg_seek_cb;
@@ -314,7 +336,7 @@ vorbis_stream_decode(struct decoder *decoder,
 				if (total_time < 0)
 					total_time = 0;
 				decoder_initialized(decoder, &audio_format,
-						    input_stream->seekable,
+						    data.seekable,
 						    total_time);
 				initialized = true;
 			}