decoder_plugin: scan tags with callback table

Makefile.am

@@ -335,6 +335,7 @@ src_mpd_SOURCES = \
 	src/tag_pool.c \
 	src/tag_print.c \
 	src/tag_save.c \
+	src/tag_handler.c src/tag_handler.h \
 	src/tokenizer.c \
 	src/text_file.c \
 	src/text_input_stream.c \
@@ -1006,6 +1007,7 @@ test_dump_playlist_SOURCES = test/dump_playlist.c \
 	src/conf.c src/tokenizer.c src/utils.c src/string_util.c\
 	src/uri.c \
 	src/song.c src/tag.c src/tag_pool.c src/tag_save.c \
+	src/tag_handler.c \
 	src/text_input_stream.c src/fifo_buffer.c \
 	src/cue/cue_parser.c src/cue/cue_parser.h \
 	src/fd_util.c
@@ -1027,7 +1029,7 @@ test_run_decoder_SOURCES = test/run_decoder.c \
 	test/stdbin.h \
 	src/io_thread.c src/io_thread.h \
 	src/conf.c src/tokenizer.c src/utils.c src/string_util.c src/log.c \
-	src/tag.c src/tag_pool.c \
+	src/tag.c src/tag_pool.c src/tag_handler.c \
 	src/replay_gain_info.c \
 	src/uri.c \
 	src/fd_util.c \
@@ -1049,7 +1051,7 @@ test_read_tags_LDADD = \
 test_read_tags_SOURCES = test/read_tags.c \
 	src/io_thread.c src/io_thread.h \
 	src/conf.c src/tokenizer.c src/utils.c src/string_util.c src/log.c \
-	src/tag.c src/tag_pool.c \
+	src/tag.c src/tag_pool.c src/tag_handler.c \
 	src/replay_gain_info.c \
 	src/uri.c \
 	src/fd_util.c \

src/decoder/audiofile_decoder_plugin.c

@@ -20,6 +20,7 @@
 #include "config.h"
 #include "decoder_api.h"
 #include "audio_check.h"
+#include "tag_handler.h"
 
 #include <audiofile.h>
 #include <af_vfs.h>
@@ -222,20 +223,20 @@ audiofile_stream_decode(struct decoder *decoder, struct input_stream *is)
 	afCloseFile(af_fp);
 }
 
-static struct tag *audiofile_tag_dup(const char *file)
+static bool
+audiofile_scan_file(const char *file,
+		    const struct tag_handler *handler, void *handler_ctx)
 {
-	struct tag *ret = NULL;
 	int total_time = audiofile_get_duration(file);
 
-	if (total_time >= 0) {
-		ret = tag_new();
-		ret->time = total_time;
-	} else {
+	if (total_time < 0) {
 		g_debug("Failed to get total song time from: %s\n",
 			file);
+		return false;
 	}
 
-	return ret;
+	tag_handler_invoke_duration(handler, handler_ctx, total_time);
+	return true;
 }
 
 static const char *const audiofile_suffixes[] = {
@@ -251,7 +252,7 @@ static const char *const audiofile_mime_types[] = {
 const struct decoder_plugin audiofile_decoder_plugin = {
 	.name = "audiofile",
 	.stream_decode = audiofile_stream_decode,
-	.tag_dup = audiofile_tag_dup,
+	.scan_file = audiofile_scan_file,
 	.suffixes = audiofile_suffixes,
 	.mime_types = audiofile_mime_types,
 };

src/decoder/dsdiff_decoder_plugin.c

@@ -433,8 +433,10 @@ dsdiff_stream_decode(struct decoder *decoder, struct input_stream *is)
 		dsd2pcm_destroy(dsd2pcm[i]);
 }
 
-static struct tag *
-dsdiff_stream_tag(struct input_stream *is)
+static bool
+dsdiff_scan_stream(struct input_stream *is,
+		   G_GNUC_UNUSED const struct tag_handler *handler,
+		   G_GNUC_UNUSED void *handler_ctx)
 {
 	struct dsdiff_metadata metadata = {
 		.sample_rate = 0,
@@ -443,17 +445,17 @@ dsdiff_stream_tag(struct input_stream *is)
 
 	struct dsdiff_chunk_header chunk_header;
 	if (!dsdiff_read_metadata(NULL, is, &metadata, &chunk_header))
-		return NULL;
+		return false;
 
 	struct audio_format audio_format;
 	if (!audio_format_init_checked(&audio_format, metadata.sample_rate / 8,
 				       SAMPLE_FORMAT_S24_P32,
 				       metadata.channels, NULL))
 		/* refuse to parse files which we cannot play anyway */
-		return NULL;
+		return false;
 
 	/* no total time estimate, no tags implemented yet */
-	return tag_new();
+	return true;
 }
 
 static const char *const dsdiff_suffixes[] = {
@@ -470,7 +472,7 @@ const struct decoder_plugin dsdiff_decoder_plugin = {
 	.name = "dsdiff",
 	.init = dsdiff_init,
 	.stream_decode = dsdiff_stream_decode,
-	.stream_tag = dsdiff_stream_tag,
+	.scan_stream = dsdiff_scan_stream,
 	.suffixes = dsdiff_suffixes,
 	.mime_types = dsdiff_mime_types,
 };

src/decoder/faad_decoder_plugin.c

@@ -21,6 +21,7 @@
 #include "decoder_api.h"
 #include "decoder_buffer.h"
 #include "audio_check.h"
+#include "tag_handler.h"
 
 #define AAC_MAX_CHANNELS	6
 
@@ -487,18 +488,17 @@ faad_stream_decode(struct decoder *mpd_decoder, struct input_stream *is)
 	faacDecClose(decoder);
 }
 
-static struct tag *
-faad_stream_tag(struct input_stream *is)
+static bool
+faad_scan_stream(struct input_stream *is,
+		 const struct tag_handler *handler, void *handler_ctx)
 {
 	int file_time = faad_get_file_time(is);
-	struct tag *tag;
 
 	if (file_time < 0)
-		return NULL;
+		return false;
 
-	tag = tag_new();
-	tag->time = file_time;
-	return tag;
+	tag_handler_invoke_duration(handler, handler_ctx, file_time);
+	return true;
 }
 
 static const char *const faad_suffixes[] = { "aac", NULL };
@@ -509,7 +509,7 @@ static const char *const faad_mime_types[] = {
 const struct decoder_plugin faad_decoder_plugin = {
 	.name = "faad",
 	.stream_decode = faad_stream_decode,
-	.stream_tag = faad_stream_tag,
+	.scan_stream = faad_scan_stream,
 	.suffixes = faad_suffixes,
 	.mime_types = faad_mime_types,
 };

src/decoder/ffmpeg_decoder_plugin.c

@@ -21,6 +21,7 @@
 #include "decoder_api.h"
 #include "audio_check.h"
 #include "ffmpeg_metadata.h"
+#include "tag_handler.h"
 
 #include <glib.h>
 
@@ -570,22 +571,23 @@ ffmpeg_decode(struct decoder *decoder, struct input_stream *input)
 }
 
 //no tag reading in ffmpeg, check if playable
-static struct tag *
-ffmpeg_stream_tag(struct input_stream *is)
+static bool
+ffmpeg_scan_stream(struct input_stream *is,
+		   const struct tag_handler *handler, void *handler_ctx)
 {
 	AVInputFormat *input_format = ffmpeg_probe(NULL, is);
 	if (input_format == NULL)
-		return NULL;
+		return false;
 
 	struct mpd_ffmpeg_stream *stream = mpd_ffmpeg_stream_open(NULL, is);
 	if (stream == NULL)
-		return NULL;
+		return false;
 
 	AVFormatContext *f = NULL;
 	if (mpd_ffmpeg_open_input(&f, stream->io, is->uri,
 				  input_format) != 0) {
 		mpd_ffmpeg_stream_close(stream);
-		return NULL;
+		return false;
 	}
 
 #if LIBAVFORMAT_VERSION_INT >= AV_VERSION_INT(53,6,0)
@@ -601,23 +603,22 @@ ffmpeg_stream_tag(struct input_stream *is)
 		av_close_input_stream(f);
 #endif
 		mpd_ffmpeg_stream_close(stream);
-		return NULL;
+		return false;
 	}
 
-	struct tag *tag = tag_new();
-
-	tag->time = f->duration != (int64_t)AV_NOPTS_VALUE
-		? f->duration / AV_TIME_BASE
-		: 0;
+	if (f->duration != (int64_t)AV_NOPTS_VALUE)
+		tag_handler_invoke_duration(handler, handler_ctx,
+					    f->duration / AV_TIME_BASE);
 
 #if LIBAVFORMAT_VERSION_INT < AV_VERSION_INT(52,101,0)
 	av_metadata_conv(f, NULL, f->iformat->metadata_conv);
 #endif
 
-	ffmpeg_copy_dictionary(tag, f->metadata);
+	ffmpeg_scan_dictionary(f->metadata, handler, handler_ctx);
 	int idx = ffmpeg_find_audio_stream(f);
 	if (idx >= 0)
-		ffmpeg_copy_dictionary(tag, f->streams[idx]->metadata);
+		ffmpeg_scan_dictionary(f->streams[idx]->metadata,
+				       handler, handler_ctx);
 
 #if LIBAVFORMAT_VERSION_INT >= AV_VERSION_INT(53,17,0)
 	avformat_close_input(&f);
@@ -626,7 +627,7 @@ ffmpeg_stream_tag(struct input_stream *is)
 #endif
 	mpd_ffmpeg_stream_close(stream);
 
-	return tag;
+	return true;
 }
 
 /**
@@ -745,7 +746,7 @@ const struct decoder_plugin ffmpeg_decoder_plugin = {
 	.name = "ffmpeg",
 	.init = ffmpeg_init,
 	.stream_decode = ffmpeg_decode,
-	.stream_tag = ffmpeg_stream_tag,
+	.scan_stream = ffmpeg_scan_stream,
 	.suffixes = ffmpeg_suffixes,
 	.mime_types = ffmpeg_mime_types
 };

src/decoder/ffmpeg_metadata.c

@@ -19,8 +19,8 @@
 
 #include "config.h"
 #include "ffmpeg_metadata.h"
-#include "tag.h"
 #include "tag_table.h"
+#include "tag_handler.h"
 
 #undef G_LOG_DOMAIN
 #define G_LOG_DOMAIN "ffmpeg"
@@ -39,23 +39,27 @@ static const struct tag_table ffmpeg_tags[] = {
 };
 
 static void
-ffmpeg_copy_metadata(struct tag *tag, enum tag_type type,
-		     AVDictionary *m, const char *name)
+ffmpeg_copy_metadata(enum tag_type type,
+		     AVDictionary *m, const char *name,
+		     const struct tag_handler *handler, void *handler_ctx)
 {
 	AVDictionaryEntry *mt = NULL;
 
 	while ((mt = av_dict_get(m, name, mt, 0)) != NULL)
-		tag_add_item(tag, type, mt->value);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       type, mt->value);
 }
 
 void
-ffmpeg_copy_dictionary(struct tag *tag, AVDictionary *dict)
+ffmpeg_scan_dictionary(AVDictionary *dict,
+		       const struct tag_handler *handler, void *handler_ctx)
 {
 	for (unsigned i = 0; i < TAG_NUM_OF_ITEM_TYPES; ++i)
-		ffmpeg_copy_metadata(tag, i,
-				     dict, tag_item_names[i]);
+		ffmpeg_copy_metadata(i, dict, tag_item_names[i],
+				     handler, handler_ctx);
 
 	for (const struct tag_table *i = ffmpeg_tags;
 	     i->name != NULL; ++i)
-		ffmpeg_copy_metadata(tag, i->type, dict, i->name);
+		ffmpeg_copy_metadata(i->type, dict, i->name,
+				     handler, handler_ctx);
 }

src/decoder/ffmpeg_metadata.h

@@ -32,9 +32,10 @@
 #define av_dict_get av_metadata_get
 #endif
 
-struct tag;
+struct tag_handler;
 
 void
-ffmpeg_copy_dictionary(struct tag *tag, AVDictionary *dict);
+ffmpeg_scan_dictionary(AVDictionary *dict,
+		       const struct tag_handler *handler, void *handler_ctx);
 
 #endif

src/decoder/flac_decoder_plugin.c

@@ -191,10 +191,11 @@ flac_write_cb(const FLAC__StreamDecoder *dec, const FLAC__Frame *frame,
 	return flac_common_write(data, frame, buf, nbytes);
 }
 
-static struct tag *
-flac_tag_dup(const char *file)
+static bool
+flac_scan_file(const char *file,
+	       const struct tag_handler *handler, void *handler_ctx)
 {
-	return flac_tag_load(file, NULL);
+	return flac_scan_file2(file, NULL, handler, handler_ctx);
 }
 
 /**
@@ -400,38 +401,33 @@ oggflac_init(G_GNUC_UNUSED const struct config_param *param)
 
 #if defined(FLAC_API_VERSION_CURRENT) && FLAC_API_VERSION_CURRENT > 7
 
-static struct tag *
-oggflac_tag_dup(const char *file)
+static bool
+oggflac_scan_file(const char *file,
+		  const struct tag_handler *handler, void *handler_ctx)
 {
-	struct tag *ret = NULL;
 	FLAC__Metadata_Iterator *it;
 	FLAC__StreamMetadata *block;
 	FLAC__Metadata_Chain *chain = FLAC__metadata_chain_new();
 
 	if (!(FLAC__metadata_chain_read_ogg(chain, file))) {
 		FLAC__metadata_chain_delete(chain);
-		return NULL;
+		return false;
 	}
 
 	it = FLAC__metadata_iterator_new();
 	FLAC__metadata_iterator_init(it, chain);
 
-	ret = tag_new();
 	do {
 		if (!(block = FLAC__metadata_iterator_get_block(it)))
 			break;
 
-		flac_tag_apply_metadata(ret, NULL, block);
+		flac_scan_metadata(NULL, block,
+				   handler, handler_ctx);
 	} while (FLAC__metadata_iterator_next(it));
 	FLAC__metadata_iterator_delete(it);
 
-	if (!tag_is_defined(ret)) {
-		tag_free(ret);
-		ret = NULL;
-	}
-
 	FLAC__metadata_chain_delete(chain);
-	return ret;
+	return true;
 }
 
 static void
@@ -464,7 +460,7 @@ const struct decoder_plugin oggflac_decoder_plugin = {
 	.init = oggflac_init,
 #if defined(FLAC_API_VERSION_CURRENT) && FLAC_API_VERSION_CURRENT > 7
 	.stream_decode = oggflac_decode,
-	.tag_dup = oggflac_tag_dup,
+	.scan_file = oggflac_scan_file,
 	.suffixes = oggflac_suffixes,
 	.mime_types = oggflac_mime_types
 #endif
@@ -484,7 +480,7 @@ static const char *const flac_mime_types[] = {
 const struct decoder_plugin flac_decoder_plugin = {
 	.name = "flac",
 	.stream_decode = flac_decode,
-	.tag_dup = flac_tag_dup,
+	.scan_file = flac_scan_file,
 	.suffixes = flac_suffixes,
 	.mime_types = flac_mime_types,
 };

src/decoder/flac_metadata.c

@@ -21,6 +21,7 @@
 #include "flac_metadata.h"
 #include "replay_gain_info.h"
 #include "tag.h"
+#include "tag_handler.h"
 #include "tag_table.h"
 
 #include <glib.h>
@@ -164,17 +165,19 @@ flac_comment_value(const FLAC__StreamMetadata_VorbisComment_Entry *entry,
  * the comment value into the tag.
  */
 static bool
-flac_copy_comment(struct tag *tag,
-		  const FLAC__StreamMetadata_VorbisComment_Entry *entry,
+flac_copy_comment(const FLAC__StreamMetadata_VorbisComment_Entry *entry,
 		  const char *name, enum tag_type tag_type,
-		  const char *char_tnum)
+		  const char *char_tnum,
+		  const struct tag_handler *handler, void *handler_ctx)
 {
 	const char *value;
 	size_t value_length;
 
 	value = flac_comment_value(entry, name, char_tnum, &value_length);
 	if (value != NULL) {
-		tag_add_item_n(tag, tag_type, value, value_length);
+		char *p = g_strndup(value, value_length);
+		tag_handler_invoke_tag(handler, handler_ctx, tag_type, p);
+		g_free(p);
 		return true;
 	}
 
@@ -189,42 +192,47 @@ static const struct tag_table flac_tags[] = {
 };
 
 static void
-flac_parse_comment(struct tag *tag, const char *char_tnum,
-		   const FLAC__StreamMetadata_VorbisComment_Entry *entry)
+flac_scan_comment(const char *char_tnum,
+		  const FLAC__StreamMetadata_VorbisComment_Entry *entry,
+		  const struct tag_handler *handler, void *handler_ctx)
 {
-	assert(tag != NULL);
-
 	for (const struct tag_table *i = flac_tags; i->name != NULL; ++i)
-		if (flac_copy_comment(tag, entry, i->name, i->type, char_tnum))
+		if (flac_copy_comment(entry, i->name, i->type, char_tnum,
+				      handler, handler_ctx))
 			return;
 
 	for (unsigned i = 0; i < TAG_NUM_OF_ITEM_TYPES; ++i)
-		if (flac_copy_comment(tag, entry,
-				      tag_item_names[i], i, char_tnum))
+		if (flac_copy_comment(entry,
+				      tag_item_names[i], i, char_tnum,
+				      handler, handler_ctx))
 			return;
 }
 
-void
-flac_vorbis_comments_to_tag(struct tag *tag, const char *char_tnum,
-			    const FLAC__StreamMetadata_VorbisComment *comment)
+static void
+flac_scan_comments(const char *char_tnum,
+		   const FLAC__StreamMetadata_VorbisComment *comment,
+		   const struct tag_handler *handler, void *handler_ctx)
 {
 	for (unsigned i = 0; i < comment->num_comments; ++i)
-		flac_parse_comment(tag, char_tnum, &comment->comments[i]);
+		flac_scan_comment(char_tnum, &comment->comments[i],
+				  handler, handler_ctx);
 }
 
 void
-flac_tag_apply_metadata(struct tag *tag, const char *track,
-			const FLAC__StreamMetadata *block)
+flac_scan_metadata(const char *track,
+		   const FLAC__StreamMetadata *block,
+		   const struct tag_handler *handler, void *handler_ctx)
 {
 	switch (block->type) {
 	case FLAC__METADATA_TYPE_VORBIS_COMMENT:
-		flac_vorbis_comments_to_tag(tag, track,
-					    &block->data.vorbis_comment);
+		flac_scan_comments(track, &block->data.vorbis_comment,
+				   handler, handler_ctx);
 		break;
 
 	case FLAC__METADATA_TYPE_STREAMINFO:
 		if (block->data.stream_info.sample_rate > 0)
-			tag->time = flac_duration(&block->data.stream_info);
+			tag_handler_invoke_duration(handler, handler_ctx,
+						    flac_duration(&block->data.stream_info));
 		break;
 
 	default:
@@ -232,10 +240,18 @@ flac_tag_apply_metadata(struct tag *tag, const char *track,
 	}
 }
 
-struct tag *
-flac_tag_load(const char *file, const char *char_tnum)
+void
+flac_vorbis_comments_to_tag(struct tag *tag, const char *char_tnum,
+			    const FLAC__StreamMetadata_VorbisComment *comment)
+{
+	flac_scan_comments(char_tnum, comment,
+			   &add_tag_handler, tag);
+}
+
+bool
+flac_scan_file2(const char *file, const char *char_tnum,
+		const struct tag_handler *handler, void *handler_ctx)
 {
-	struct tag *tag;
 	FLAC__Metadata_SimpleIterator *it;
 	FLAC__StreamMetadata *block = NULL;
 
@@ -262,22 +278,30 @@ flac_tag_load(const char *file, const char *char_tnum)
 		g_debug("Reading '%s' metadata gave the following error: %s\n",
 			file, err);
 		FLAC__metadata_simple_iterator_delete(it);
-		return NULL;
+		return false;
 	}
 
-	tag = tag_new();
 	do {
 		block = FLAC__metadata_simple_iterator_get_block(it);
 		if (!block)
 			break;
 
-		flac_tag_apply_metadata(tag, char_tnum, block);
+		flac_scan_metadata(char_tnum, block, handler, handler_ctx);
 		FLAC__metadata_object_delete(block);
 	} while (FLAC__metadata_simple_iterator_next(it));
 
 	FLAC__metadata_simple_iterator_delete(it);
 
-	if (!tag_is_defined(tag)) {
+	return true;
+}
+
+struct tag *
+flac_tag_load(const char *file, const char *char_tnum)
+{
+	struct tag *tag = tag_new();
+
+	if (!flac_scan_file2(file, char_tnum, &add_tag_handler, tag) ||
+	    tag_is_empty(tag)) {
 		tag_free(tag);
 		tag = NULL;
 	}

src/decoder/flac_metadata.h

@@ -24,6 +24,7 @@
 #include <stdbool.h>
 #include <FLAC/metadata.h>
 
+struct tag_handler;
 struct tag;
 struct replay_gain_info;
 
@@ -49,8 +50,13 @@ flac_vorbis_comments_to_tag(struct tag *tag, const char *char_tnum,
 			    const FLAC__StreamMetadata_VorbisComment *comment);
 
 void
-flac_tag_apply_metadata(struct tag *tag, const char *track,
-			const FLAC__StreamMetadata *block);
+flac_scan_metadata(const char *track,
+		   const FLAC__StreamMetadata *block,
+		   const struct tag_handler *handler, void *handler_ctx);
+
+bool
+flac_scan_file2(const char *file, const char *char_tnum,
+		const struct tag_handler *handler, void *handler_ctx);
 
 struct tag *
 flac_tag_load(const char *file, const char *char_tnum);

src/decoder/gme_decoder_plugin.c

@@ -2,6 +2,7 @@
 #include "../decoder_api.h"
 #include "audio_check.h"
 #include "uri.h"
+#include "tag_handler.h"
 
 #include <glib.h>
 #include <assert.h>
@@ -180,8 +181,9 @@ gme_file_decode(struct decoder *decoder, const char *path_fs)
 	gme_delete(emu);
 }
 
-static struct tag *
-gme_tag_dup(const char *path_fs)
+static bool
+gme_scan_file(const char *path_fs,
+	      const struct tag_handler *handler, void *handler_ctx)
 {
 	Music_Emu *emu;
 	gme_info_t *ti;
@@ -194,42 +196,49 @@ gme_tag_dup(const char *path_fs)
 	g_free(path_container);
 	if (gme_err != NULL) {
 		g_warning("%s", gme_err);
-		return NULL;
+		return false;
 	}
 	if((gme_err = gme_track_info(emu, &ti, song_num)) != NULL){
 		g_warning("%s", gme_err);
 		gme_delete(emu);
-		return NULL;
+		return false;
 	}
 
 	assert(ti != NULL);
 
-	struct tag *tag = tag_new();
-
 	if(ti->length > 0)
-		tag->time = ti->length / 1000;
+		tag_handler_invoke_duration(handler, handler_ctx,
+					    ti->length / 100);
+
 	if(ti->song != NULL){
 		if(gme_track_count(emu) > 1){
 			/* start numbering subtunes from 1 */
 			char *tag_title=g_strdup_printf("%s (%d/%d)",
 							ti->song, song_num+1, gme_track_count(emu));
-			tag_add_item(tag, TAG_TITLE, tag_title);
+			tag_handler_invoke_tag(handler, handler_ctx,
+					       TAG_TITLE, tag_title);
 			g_free(tag_title);
 		}else
-			tag_add_item(tag, TAG_TITLE, ti->song);
+			tag_handler_invoke_tag(handler, handler_ctx,
+					       TAG_TITLE, ti->song);
 	}
 	if(ti->author != NULL)
-		tag_add_item(tag, TAG_ARTIST, ti->author);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_ARTIST, ti->author);
 	if(ti->game != NULL)
-		tag_add_item(tag, TAG_ALBUM, ti->game);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_ALBUM, ti->game);
 	if(ti->comment != NULL)
-		tag_add_item(tag, TAG_COMMENT, ti->comment);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_COMMENT, ti->comment);
 	if(ti->copyright != NULL)
-		tag_add_item(tag, TAG_DATE, ti->copyright);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_DATE, ti->copyright);
 
 	gme_free_info(ti);
 	gme_delete(emu);
-	return tag;
+
+	return true;
 }
 
 static const char *const gme_suffixes[] = {
@@ -242,7 +251,7 @@ extern const struct decoder_plugin gme_decoder_plugin;
 const struct decoder_plugin gme_decoder_plugin = {
 	.name = "gme",
 	.file_decode = gme_file_decode,
-	.tag_dup = gme_tag_dup,
+	.scan_file = gme_scan_file,
 	.suffixes = gme_suffixes,
 	.container_scan = gme_container_scan,
 };

src/decoder/mad_decoder_plugin.c

@@ -22,6 +22,7 @@
 #include "conf.h"
 #include "tag_id3.h"
 #include "tag_rva2.h"
+#include "tag_handler.h"
 #include "audio_check.h"
 
 #include <assert.h>
@@ -1176,19 +1177,18 @@ mp3_decode(struct decoder *decoder, struct input_stream *input_stream)
 	mp3_data_finish(&data);
 }
 
-static struct tag *
-mad_decoder_stream_tag(struct input_stream *is)
+static bool
+mad_decoder_scan_stream(struct input_stream *is,
+			const struct tag_handler *handler, void *handler_ctx)
 {
-	struct tag *tag;
 	int total_time;
 
 	total_time = mad_decoder_total_file_time(is);
 	if (total_time < 0)
-		return NULL;
+		return false;
 
-	tag = tag_new();
-	tag->time = total_time;
-	return tag;
+	tag_handler_invoke_duration(handler, handler_ctx, total_time);
+	return true;
 }
 
 static const char *const mp3_suffixes[] = { "mp3", "mp2", NULL };
@@ -1198,7 +1198,7 @@ const struct decoder_plugin mad_decoder_plugin = {
 	.name = "mad",
 	.init = mp3_plugin_init,
 	.stream_decode = mp3_decode,
-	.stream_tag = mad_decoder_stream_tag,
+	.scan_stream = mad_decoder_scan_stream,
 	.suffixes = mp3_suffixes,
 	.mime_types = mp3_mime_types
 };

src/decoder/modplug_decoder_plugin.c

@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "decoder_api.h"
+#include "tag_handler.h"
 
 #include <glib.h>
 #include <modplug.h>
@@ -149,34 +150,33 @@ mod_decode(struct decoder *decoder, struct input_stream *is)
 	ModPlug_Unload(f);
 }
 
-static struct tag *
-modplug_stream_tag(struct input_stream *is)
+static bool
+modplug_scan_stream(struct input_stream *is,
+		    const struct tag_handler *handler, void *handler_ctx)
 {
 	ModPlugFile *f;
-	struct tag *ret = NULL;
 	GByteArray *bdatas;
-	char *title;
 
 	bdatas = mod_loadfile(NULL, is);
 	if (!bdatas)
-		return NULL;
+		return false;
 
 	f = ModPlug_Load(bdatas->data, bdatas->len);
 	g_byte_array_free(bdatas, TRUE);
 	if (f == NULL)
-		return NULL;
+		return false;
 
-	ret = tag_new();
-	ret->time = ModPlug_GetLength(f) / 1000;
+	tag_handler_invoke_duration(handler, handler_ctx,
+				    ModPlug_GetLength(f) / 1000);
 
-	title = g_strdup(ModPlug_GetName(f));
-	if (title)
-		tag_add_item(ret, TAG_TITLE, title);
-	g_free(title);
+	const char *title = ModPlug_GetName(f);
+	if (title != NULL)
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_TITLE, title);
 
 	ModPlug_Unload(f);
 
-	return ret;
+	return true;
 }
 
 static const char *const mod_suffixes[] = {
@@ -189,6 +189,6 @@ static const char *const mod_suffixes[] = {
 const struct decoder_plugin modplug_decoder_plugin = {
 	.name = "modplug",
 	.stream_decode = mod_decode,
-	.stream_tag = modplug_stream_tag,
+	.scan_stream = modplug_scan_stream,
 	.suffixes = mod_suffixes,
 };

src/decoder/mpcdec_decoder_plugin.c

@@ -20,6 +20,7 @@
 #include "config.h"
 #include "decoder_api.h"
 #include "audio_check.h"
+#include "tag_handler.h"
 
 #ifdef MPC_IS_OLD_API
 #include <mpcdec/mpcdec.h>
@@ -323,18 +324,17 @@ mpcdec_get_file_duration(struct input_stream *is)
 	return total_time;
 }
 
-static struct tag *
-mpcdec_stream_tag(struct input_stream *is)
+static bool
+mpcdec_scan_stream(struct input_stream *is,
+		   const struct tag_handler *handler, void *handler_ctx)
 {
 	float total_time = mpcdec_get_file_duration(is);
-	struct tag *tag;
 
 	if (total_time < 0)
-		return NULL;
+		return false;
 
-	tag = tag_new();
-	tag->time = total_time;
-	return tag;
+	tag_handler_invoke_duration(handler, handler_ctx, total_time);
+	return true;
 }
 
 static const char *const mpcdec_suffixes[] = { "mpc", NULL };
@@ -342,6 +342,6 @@ static const char *const mpcdec_suffixes[] = { "mpc", NULL };
 const struct decoder_plugin mpcdec_decoder_plugin = {
 	.name = "mpcdec",
 	.stream_decode = mpcdec_decode,
-	.stream_tag = mpcdec_stream_tag,
+	.scan_stream = mpcdec_scan_stream,
 	.suffixes = mpcdec_suffixes,
 };

src/decoder/mpg123_decoder_plugin.c

@@ -20,6 +20,7 @@
 #include "config.h" /* must be first for large file support */
 #include "decoder_api.h"
 #include "audio_check.h"
+#include "tag_handler.h"
 
 #include <glib.h>
 
@@ -192,41 +193,40 @@ mpd_mpg123_file_decode(struct decoder *decoder, const char *path_fs)
 	mpg123_delete(handle);
 }
 
-static struct tag *
-mpd_mpg123_tag_dup(const char *path_fs)
+static bool
+mpd_mpg123_scan_file(const char *path_fs,
+		     const struct tag_handler *handler, void *handler_ctx)
 {
 	struct audio_format audio_format;
 	mpg123_handle *handle;
 	int error;
 	off_t num_samples;
-	struct tag *tag;
 
 	handle = mpg123_new(NULL, &error);
 	if (handle == NULL) {
 		g_warning("mpg123_new() failed: %s",
 			  mpg123_plain_strerror(error));
-		return NULL;
+		return false;
 	}
 
 	if (!mpd_mpg123_open(handle, path_fs, &audio_format)) {
 		mpg123_delete(handle);
-		return NULL;
+		return false;
 	}
 
 	num_samples = mpg123_length(handle);
 	if (num_samples <= 0) {
 		mpg123_delete(handle);
-		return NULL;
+		return false;
 	}
 
-	tag = tag_new();
-
-	tag->time = num_samples / audio_format.sample_rate;
-
 	/* ID3 tag support not yet implemented */
 
 	mpg123_delete(handle);
-	return tag;
+
+	tag_handler_invoke_duration(handler, handler_ctx,
+				    num_samples / audio_format.sample_rate);
+	return true;
 }
 
 static const char *const mpg123_suffixes[] = {
@@ -240,6 +240,6 @@ const struct decoder_plugin mpg123_decoder_plugin = {
 	.finish = mpd_mpg123_finish,
 	.file_decode = mpd_mpg123_file_decode,
 	/* streaming not yet implemented */
-	.tag_dup = mpd_mpg123_tag_dup,
+	.scan_file = mpd_mpg123_scan_file,
 	.suffixes = mpg123_suffixes,
 };

src/decoder/sidplay_decoder_plugin.cxx

@@ -21,6 +21,7 @@
 
 extern "C" {
 #include "../decoder_api.h"
+#include "tag_handler.h"
 }
 
 #include <errno.h>
@@ -336,8 +337,9 @@ sidplay_file_decode(struct decoder *decoder, const char *path_fs)
 	} while (cmd != DECODE_COMMAND_STOP);
 }
 
-static struct tag *
-sidplay_tag_dup(const char *path_fs)
+static bool
+sidplay_scan_file(const char *path_fs,
+		  const struct tag_handler *handler, void *handler_ctx)
 {
 	int song_num=get_song_num(path_fs);
 	char *path_container=get_container_name(path_fs);
@@ -345,10 +347,9 @@ sidplay_tag_dup(const char *path_fs)
 	SidTune tune(path_container, NULL, true);
 	g_free(path_container);
 	if (!tune)
-		return NULL;
+		return false;
 
 	const SidTuneInfo &info = tune.getInfo();
-	struct tag *tag = tag_new();
 
 	/* title */
 	const char *title;
@@ -360,25 +361,28 @@ sidplay_tag_dup(const char *path_fs)
 	if(info.songs>1) {
 		char *tag_title=g_strdup_printf("%s (%d/%d)",
 			title, song_num, info.songs);
-		tag_add_item(tag, TAG_TITLE, tag_title);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_TITLE, tag_title);
 		g_free(tag_title);
 	} else
-		tag_add_item(tag, TAG_TITLE, title);
+		tag_handler_invoke_tag(handler, handler_ctx, TAG_TITLE, title);
 
 	/* artist */
 	if (info.numberOfInfoStrings > 1 && info.infoString[1] != NULL)
-		tag_add_item(tag, TAG_ARTIST, info.infoString[1]);
+		tag_handler_invoke_tag(handler, handler_ctx, TAG_ARTIST,
+				       info.infoString[1]);
 
 	/* track */
 	char *track=g_strdup_printf("%d", song_num);
-	tag_add_item(tag, TAG_TRACK, track);
+	tag_handler_invoke_tag(handler, handler_ctx, TAG_TRACK, track);
 	g_free(track);
 
 	/* time */
 	int song_len=get_song_length(path_fs);
-	if(song_len!=-1) tag->time=song_len;
+	if (song_len >= 0)
+		tag_handler_invoke_duration(handler, handler_ctx, song_len);
 
-	return tag;
+	return true;
 }
 
 static char *
@@ -421,7 +425,7 @@ const struct decoder_plugin sidplay_decoder_plugin = {
 	sidplay_finish,
 	NULL, /* stream_decode() */
 	sidplay_file_decode,
-	sidplay_tag_dup,
+	sidplay_scan_file,
 	NULL, /* stream_tag() */
 	sidplay_container_scan,
 	sidplay_suffixes,

src/decoder/sndfile_decoder_plugin.c

@@ -20,6 +20,7 @@
 #include "config.h"
 #include "decoder_api.h"
 #include "audio_check.h"
+#include "tag_handler.h"
 
 #include <sndfile.h>
 
@@ -172,44 +173,47 @@ sndfile_stream_decode(struct decoder *decoder, struct input_stream *is)
 	sf_close(sf);
 }
 
-static struct tag *
-sndfile_tag_dup(const char *path_fs)
+static bool
+sndfile_scan_file(const char *path_fs,
+		  const struct tag_handler *handler, void *handler_ctx)
 {
 	SNDFILE *sf;
 	SF_INFO info;
-	struct tag *tag;
 	const char *p;
 
 	info.format = 0;
 
 	sf = sf_open(path_fs, SFM_READ, &info);
 	if (sf == NULL)
-		return NULL;
+		return false;
 
 	if (!audio_valid_sample_rate(info.samplerate)) {
 		sf_close(sf);
 		g_warning("Invalid sample rate in %s\n", path_fs);
-		return NULL;
+		return false;
 	}
 
-	tag = tag_new();
-	tag->time = info.frames / info.samplerate;
+	tag_handler_invoke_duration(handler, handler_ctx,
+				    info.frames / info.samplerate);
 
 	p = sf_get_string(sf, SF_STR_TITLE);
 	if (p != NULL)
-		tag_add_item(tag, TAG_TITLE, p);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_TITLE, p);
 
 	p = sf_get_string(sf, SF_STR_ARTIST);
 	if (p != NULL)
-		tag_add_item(tag, TAG_ARTIST, p);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_ARTIST, p);
 
 	p = sf_get_string(sf, SF_STR_DATE);
 	if (p != NULL)
-		tag_add_item(tag, TAG_DATE, p);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_DATE, p);
 
 	sf_close(sf);
 
-	return tag;
+	return true;
 }
 
 static const char *const sndfile_suffixes[] = {
@@ -245,7 +249,7 @@ static const char *const sndfile_mime_types[] = {
 const struct decoder_plugin sndfile_decoder_plugin = {
 	.name = "sndfile",
 	.stream_decode = sndfile_stream_decode,
-	.tag_dup = sndfile_tag_dup,
+	.scan_file = sndfile_scan_file,
 	.suffixes = sndfile_suffixes,
 	.mime_types = sndfile_mime_types,
 };

src/decoder/vorbis_comments.c

@@ -21,6 +21,7 @@
 #include "vorbis_comments.h"
 #include "tag.h"
 #include "tag_table.h"
+#include "tag_handler.h"
 #include "replay_gain_info.h"
 
 #include <glib.h>
@@ -79,14 +80,15 @@ vorbis_comments_to_replay_gain(struct replay_gain_info *rgi, char **comments)
  * the comment value into the tag.
  */
 static bool
-vorbis_copy_comment(struct tag *tag, const char *comment,
-		    const char *name, enum tag_type tag_type)
+vorbis_copy_comment(const char *comment,
+		    const char *name, enum tag_type tag_type,
+		    const struct tag_handler *handler, void *handler_ctx)
 {
 	const char *value;
 
 	value = vorbis_comment_value(comment, name);
 	if (value != NULL) {
-		tag_add_item(tag, tag_type, value);
+		tag_handler_invoke_tag(handler, handler_ctx, tag_type, value);
 		return true;
 	}
 
@@ -101,27 +103,36 @@ static const struct tag_table vorbis_tags[] = {
 };
 
 static void
-vorbis_parse_comment(struct tag *tag, const char *comment)
+vorbis_scan_comment(const char *comment,
+		    const struct tag_handler *handler, void *handler_ctx)
 {
-	assert(tag != NULL);
-
 	for (const struct tag_table *i = vorbis_tags; i->name != NULL; ++i)
-		if (vorbis_copy_comment(tag, comment, i->name, i->type))
+		if (vorbis_copy_comment(comment, i->name, i->type,
+					handler, handler_ctx))
 			return;
 
 	for (unsigned i = 0; i < TAG_NUM_OF_ITEM_TYPES; ++i)
-		if (vorbis_copy_comment(tag, comment,
-					tag_item_names[i], i))
+		if (vorbis_copy_comment(comment,
+					tag_item_names[i], i,
+					handler, handler_ctx))
 			return;
 }
 
+void
+vorbis_comments_scan(char **comments,
+		     const struct tag_handler *handler, void *handler_ctx)
+{
+	while (*comments)
+		vorbis_scan_comment(*comments++,
+				    handler, handler_ctx);
+
+}
+
 struct tag *
 vorbis_comments_to_tag(char **comments)
 {
 	struct tag *tag = tag_new();
-
-	while (*comments)
-		vorbis_parse_comment(tag, *comments++);
+	vorbis_comments_scan(comments, &add_tag_handler, tag);
 
 	if (tag_is_empty(tag)) {
 		tag_free(tag);

src/decoder/vorbis_comments.h

@@ -25,10 +25,15 @@
 #include <stdbool.h>
 
 struct replay_gain_info;
+struct tag_handler;
 
 bool
 vorbis_comments_to_replay_gain(struct replay_gain_info *rgi, char **comments);
 
+void
+vorbis_comments_scan(char **comments,
+		     const struct tag_handler *handler, void *handler_ctx);
+
 struct tag *
 vorbis_comments_to_tag(char **comments);
 

src/decoder/vorbis_decoder_plugin.c

@@ -22,6 +22,7 @@
 #include "_ogg_common.h"
 #include "audio_check.h"
 #include "uri.h"
+#include "tag_handler.h"
 
 #ifndef HAVE_TREMOR
 #define OV_EXCLUDE_STATIC_CALLBACKS
@@ -268,24 +269,24 @@ vorbis_stream_decode(struct decoder *decoder,
 	ov_clear(&vf);
 }
 
-static struct tag *
-vorbis_stream_tag(struct input_stream *is)
+static bool
+vorbis_scan_stream(struct input_stream *is,
+		   const struct tag_handler *handler, void *handler_ctx)
 {
 	struct vorbis_input_stream vis;
 	OggVorbis_File vf;
 
 	if (!vorbis_is_open(&vis, &vf, NULL, is))
-		return NULL;
+		return false;
 
-	struct tag *tag = vorbis_comments_to_tag(ov_comment(&vf, -1)->user_comments);
+	tag_handler_invoke_duration(handler, handler_ctx,
+				    (int)(ov_time_total(&vf, -1) + 0.5));
 
-	if (tag == NULL)
-		tag = tag_new();
-	tag->time = (int)(ov_time_total(&vf, -1) + 0.5);
+	vorbis_comments_scan(ov_comment(&vf, -1)->user_comments,
+			     handler, handler_ctx);
 
 	ov_clear(&vf);
-
-	return tag;
+	return true;
 }
 
 static const char *const vorbis_suffixes[] = {
@@ -307,7 +308,7 @@ static const char *const vorbis_mime_types[] = {
 const struct decoder_plugin vorbis_decoder_plugin = {
 	.name = "vorbis",
 	.stream_decode = vorbis_stream_decode,
-	.stream_tag = vorbis_stream_tag,
+	.scan_stream = vorbis_scan_stream,
 	.suffixes = vorbis_suffixes,
 	.mime_types = vorbis_mime_types
 };

src/decoder/wavpack_decoder_plugin.c

@@ -22,6 +22,7 @@
 #include "audio_check.h"
 #include "path.h"
 #include "utils.h"
+#include "tag_handler.h"
 
 #include <wavpack/wavpack.h>
 #include <glib.h>
@@ -275,11 +276,11 @@ wavpack_replaygain(struct replay_gain_info *replay_gain_info,
 /*
  * Reads metainfo from the specified file.
  */
-static struct tag *
-wavpack_tagdup(const char *fname)
+static bool
+wavpack_scan_file(const char *fname,
+		  const struct tag_handler *handler, void *handler_ctx)
 {
 	WavpackContext *wpc;
-	struct tag *tag;
 	char error[ERRORLEN];
 	char *s;
 	int size, allocated_size;
@@ -290,12 +291,12 @@ wavpack_tagdup(const char *fname)
 			"failed to open WavPack file \"%s\": %s\n",
 			fname, error
 		);
-		return NULL;
+		return false;
 	}
 
-	tag = tag_new();
-	tag->time = WavpackGetNumSamples(wpc);
-	tag->time /= WavpackGetSampleRate(wpc);
+	tag_handler_invoke_duration(handler, handler_ctx,
+				    WavpackGetNumSamples(wpc) /
+				    WavpackGetSampleRate(wpc));
 
 	allocated_size = 0;
 	s = NULL;
@@ -315,7 +316,8 @@ wavpack_tagdup(const char *fname)
 			}
 
 			WavpackGetTagItem(wpc, tagtypes[i].name, s, size);
-			tag_add_item(tag, tagtypes[i].type, s);
+			tag_handler_invoke_tag(handler, handler_ctx,
+					       tagtypes[i].type, s);
 		}
 	}
 
@@ -323,7 +325,7 @@ wavpack_tagdup(const char *fname)
 
 	WavpackCloseFile(wpc);
 
-	return tag;
+	return true;
 }
 
 /*
@@ -576,7 +578,7 @@ const struct decoder_plugin wavpack_decoder_plugin = {
 	.name = "wavpack",
 	.stream_decode = wavpack_streamdecode,
 	.file_decode = wavpack_filedecode,
-	.tag_dup = wavpack_tagdup,
+	.scan_file = wavpack_scan_file,
 	.suffixes = wavpack_suffixes,
 	.mime_types = wavpack_mime_types
 };

src/decoder/wildmidi_decoder_plugin.c

@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "decoder_api.h"
+#include "tag_handler.h"
 
 #include <glib.h>
 
@@ -111,25 +112,26 @@ wildmidi_file_decode(struct decoder *decoder, const char *path_fs)
 	WildMidi_Close(wm);
 }
 
-static struct tag *
-wildmidi_tag_dup(const char *path_fs)
+static bool
+wildmidi_scan_file(const char *path_fs,
+		   const struct tag_handler *handler, void *handler_ctx)
 {
 	midi *wm = WildMidi_Open(path_fs);
 	if (wm == NULL)
-		return NULL;
+		return false;
 
 	const struct _WM_Info *info = WildMidi_GetInfo(wm);
 	if (info == NULL) {
 		WildMidi_Close(wm);
-		return NULL;
+		return false;
 	}
 
-	struct tag *tag = tag_new();
-	tag->time = info->approx_total_samples / WILDMIDI_SAMPLE_RATE;
+	int duration = info->approx_total_samples / WILDMIDI_SAMPLE_RATE;
+	tag_handler_invoke_duration(handler, handler_ctx, duration);
 
 	WildMidi_Close(wm);
 
-	return tag;
+	return true;
 }
 
 static const char *const wildmidi_suffixes[] = {
@@ -142,6 +144,6 @@ const struct decoder_plugin wildmidi_decoder_plugin = {
 	.init = wildmidi_init,
 	.finish = wildmidi_finish,
 	.file_decode = wildmidi_file_decode,
-	.tag_dup = wildmidi_tag_dup,
+	.scan_file = wildmidi_scan_file,
 	.suffixes = wildmidi_suffixes,
 };

src/decoder_plugin.h

@@ -26,6 +26,7 @@
 struct config_param;
 struct input_stream;
 struct tag;
+struct tag_handler;
 
 /**
  * Opaque handle which the decoder plugin passes to the functions in
@@ -70,18 +71,22 @@ struct decoder_plugin {
 	void (*file_decode)(struct decoder *decoder, const char *path_fs);
 
 	/**
-	 * Read the tags of a local file.
+	 * Scan metadata of a file.
 	 *
-	 * @return NULL if the operation has failed
+	 * @return false if the operation has failed
 	 */
-	struct tag *(*tag_dup)(const char *path_fs);
+	bool (*scan_file)(const char *path_fs,
+			  const struct tag_handler *handler,
+			  void *handler_ctx);
 
 	/**
-	 * Read the tags of a stream.
+	 * Scan metadata of a file.
 	 *
-	 * @return NULL if the operation has failed
+	 * @return false if the operation has failed
 	 */
-	struct tag *(*stream_tag)(struct input_stream *is);
+	bool (*scan_stream)(struct input_stream *is,
+			    const struct tag_handler *handler,
+			    void *handler_ctx);
 
 	/**
 	 * @brief Return a "virtual" filename for subtracks in
@@ -150,25 +155,28 @@ decoder_plugin_file_decode(const struct decoder_plugin *plugin,
 /**
  * Read the tag of a file.
  */
-static inline struct tag *
-decoder_plugin_tag_dup(const struct decoder_plugin *plugin,
-		       const char *path_fs)
+static inline bool
+decoder_plugin_scan_file(const struct decoder_plugin *plugin,
+			 const char *path_fs,
+			 const struct tag_handler *handler, void *handler_ctx)
 {
-	return plugin->tag_dup != NULL
-		? plugin->tag_dup(path_fs)
-		: NULL;
+	return plugin->scan_file != NULL
+		? plugin->scan_file(path_fs, handler, handler_ctx)
+		: false;
 }
 
 /**
  * Read the tag of a stream.
  */
-static inline struct tag *
-decoder_plugin_stream_tag(const struct decoder_plugin *plugin,
-			  struct input_stream *is)
+static inline bool
+decoder_plugin_scan_stream(const struct decoder_plugin *plugin,
+			   struct input_stream *is,
+			   const struct tag_handler *handler,
+			   void *handler_ctx)
 {
-	return plugin->stream_tag != NULL
-		? plugin->stream_tag(is)
-		: NULL;
+	return plugin->scan_stream != NULL
+		? plugin->scan_stream(is, handler, handler_ctx)
+		: false;
 }
 
 /**

src/song_update.c

@@ -27,6 +27,7 @@
 #include "tag_ape.h"
 #include "tag_id3.h"
 #include "tag.h"
+#include "tag_handler.h"
 #include "input_stream.h"
 
 #include <glib.h>
@@ -136,12 +137,16 @@ song_file_update(struct song *song)
 
 	do {
 		/* load file tag */
-		song->tag = decoder_plugin_tag_dup(plugin, path_fs);
-		if (song->tag != NULL)
+		song->tag = tag_new();
+		if (decoder_plugin_scan_file(plugin, path_fs,
+					     &add_tag_handler, song->tag))
 			break;
 
+		tag_free(song->tag);
+		song->tag = NULL;
+
 		/* fall back to stream tag */
-		if (plugin->stream_tag != NULL) {
+		if (plugin->scan_stream != NULL) {
 			/* open the input_stream (if not already
 			   open) */
 			if (is == NULL) {
@@ -153,11 +158,15 @@ song_file_update(struct song *song)
 
 			/* now try the stream_tag() method */
 			if (is != NULL) {
-				song->tag = decoder_plugin_stream_tag(plugin,
-								      is);
-				if (song->tag != NULL)
+				song->tag = tag_new();
+				if (decoder_plugin_scan_stream(plugin, is,
+							       &add_tag_handler,
+							       song->tag))
 					break;
 
+				tag_free(song->tag);
+				song->tag = NULL;
+
 				input_stream_lock_seek(is, 0, SEEK_SET, NULL);
 			}
 		}

src/tag_ape.c

@@ -21,6 +21,7 @@
 #include "tag_ape.h"
 #include "tag.h"
 #include "tag_table.h"
+#include "tag_handler.h"
 #include "ape.h"
 
 static const struct tag_table ape_tags[] = {
@@ -39,20 +40,18 @@ tag_ape_name_parse(const char *name)
 	return type;
 }
 
-static struct tag *
-tag_ape_import_item(struct tag *tag, unsigned long flags,
-		    const char *key, const char *value, size_t value_length)
+static void
+tag_ape_import_item(unsigned long flags,
+		    const char *key, const char *value, size_t value_length,
+		    const struct tag_handler *handler, void *handler_ctx)
 {
 	/* we only care about utf-8 text tags */
 	if ((flags & (0x3 << 1)) != 0)
-		return tag;
+		return;
 
 	enum tag_type type = tag_ape_name_parse(key);
 	if (type == TAG_NUM_OF_ITEM_TYPES)
-		return tag;
-
-	if (tag == NULL)
-		tag = tag_new();
+		return;
 
 	const char *end = value + value_length;
 	while (true) {
@@ -60,20 +59,22 @@ tag_ape_import_item(struct tag *tag, unsigned long flags,
 		const char *n = memchr(value, 0, end - value);
 		if (n != NULL) {
 			if (n > value)
-				tag_add_item_n(tag, type, value, n - value);
+				tag_handler_invoke_tag(handler, handler_ctx,
+						       type, value);
 			value = n + 1;
 		} else {
-			if (end > value)
-				tag_add_item_n(tag, type, value, end - value);
+			char *p = g_strndup(value, end - value);
+			tag_handler_invoke_tag(handler, handler_ctx,
+					       type, p);
+			g_free(p);
 			break;
 		}
 	}
-
-	return tag;
 }
 
 struct tag_ape_ctx {
-	struct tag *tag;
+	const struct tag_handler *handler;
+	void *handler_ctx;
 };
 
 static bool
@@ -82,16 +83,31 @@ tag_ape_callback(unsigned long flags, const char *key,
 {
 	struct tag_ape_ctx *ctx = _ctx;
 
-	ctx->tag = tag_ape_import_item(ctx->tag, flags, key,
-				       value, value_length);
+	tag_ape_import_item(flags, key, value, value_length,
+			    ctx->handler, ctx->handler_ctx);
 	return true;
 }
 
+bool
+tag_ape_scan2(const char *path_fs,
+	      const struct tag_handler *handler, void *handler_ctx)
+{
+	struct tag_ape_ctx ctx = {
+		.handler = handler,
+		.handler_ctx = handler_ctx,
+	};
+
+	return tag_ape_scan(path_fs, tag_ape_callback, &ctx);
+}
+
 struct tag *
-tag_ape_load(const char *file)
+tag_ape_load(const char *path_fs)
 {
-	struct tag_ape_ctx ctx = { .tag = NULL };
+	struct tag *tag = tag_new();
+	if (!tag_ape_scan2(path_fs, &add_tag_handler, tag)) {
+		tag_free(tag);
+		tag = NULL;
+	}
 
-	tag_ape_scan(file, tag_ape_callback, &ctx);
-	return ctx.tag;
+	return tag;
 }

src/tag_ape.h

@@ -20,6 +20,19 @@
 #ifndef MPD_TAG_APE_H
 #define MPD_TAG_APE_H
 
+#include <stdbool.h>
+
+struct tag_handler;
+
+/**
+ * Scan the APE tags of a file.
+ *
+ * @param path_fs the path of the file in filesystem encoding
+ */
+bool
+tag_ape_scan2(const char *path_fs,
+	      const struct tag_handler *handler, void *handler_ctx);
+
 /**
  * Loads the APE tag from a file.
  *

src/tag_handler.c

+/*
+ * Copyright (C) 2003-2011 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "tag_handler.h"
+
+static void
+add_tag_duration(unsigned seconds, void *ctx)
+{
+	struct tag *tag = ctx;
+
+	tag->time = seconds;
+}
+
+static void
+add_tag_tag(enum tag_type type, const char *value, void *ctx)
+{
+	struct tag *tag = ctx;
+
+	tag_add_item(tag, type, value);
+}
+
+const struct tag_handler add_tag_handler = {
+	.duration = add_tag_duration,
+	.tag = add_tag_tag,
+};
+

src/tag_handler.h

+/*
+ * Copyright (C) 2003-2011 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_TAG_HANDLER_H
+#define MPD_TAG_HANDLER_H
+
+#include "check.h"
+#include "tag.h"
+
+#include <assert.h>
+
+/**
+ * A callback table for receiving metadata of a song.
+ */
+struct tag_handler {
+	/**
+	 * Declare the duration of a song, in seconds.  Do not call
+	 * this when the duration could not be determined, because
+	 * there is no magic value for "unknown duration".
+	 */
+	void (*duration)(unsigned seconds, void *ctx);
+
+	/**
+	 * A tag has been read.
+	 *
+	 * @param the value of the tag; the pointer will become
+	 * invalid after returning
+	 */
+	void (*tag)(enum tag_type type, const char *value, void *ctx);
+};
+
+static inline void
+tag_handler_invoke_duration(const struct tag_handler *handler, void *ctx,
+			  unsigned seconds)
+{
+	assert(handler != NULL);
+
+	if (handler->duration != NULL)
+		handler->duration(seconds, ctx);
+}
+
+static inline void
+tag_handler_invoke_tag(const struct tag_handler *handler, void *ctx,
+		       enum tag_type type, const char *value)
+{
+	assert(handler != NULL);
+	assert((unsigned)type < TAG_NUM_OF_ITEM_TYPES);
+	assert(value != NULL);
+
+	if (handler->tag != NULL)
+		handler->tag(type, value, ctx);
+}
+
+/**
+ * This #tag_handler implementation adds tag values to a #tag object
+ * (casted from the context pointer).
+ */
+extern const struct tag_handler add_tag_handler;
+
+#endif

src/tag_id3.c

@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "tag_id3.h"
+#include "tag_handler.h"
 #include "tag_table.h"
 #include "tag.h"
 #include "riff.h"
@@ -127,9 +128,9 @@ import_id3_string(bool is_id3v1, const id3_ucs4_t *ucs4)
  * - string list
  */
 static void
-tag_id3_import_text_frame(struct tag *dest, struct id3_tag *tag,
-			  const struct id3_frame *frame,
-			  enum tag_type type)
+tag_id3_import_text_frame(struct id3_tag *tag, const struct id3_frame *frame,
+			  enum tag_type type,
+			  const struct tag_handler *handler, void *handler_ctx)
 {
 	id3_ucs4_t const *ucs4;
 	id3_utf8_t *utf8;
@@ -165,7 +166,8 @@ tag_id3_import_text_frame(struct tag *dest, struct id3_tag *tag,
 		if (utf8 == NULL)
 			continue;
 
-		tag_add_item(dest, type, (char *)utf8);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       type, (const char *)utf8);
 		g_free(utf8);
 	}
 }
@@ -175,13 +177,14 @@ tag_id3_import_text_frame(struct tag *dest, struct id3_tag *tag,
  * 4.2).  This is a wrapper for tag_id3_import_text_frame().
  */
 static void
-tag_id3_import_text(struct tag *dest, struct id3_tag *tag, const char *id,
-		    enum tag_type type)
+tag_id3_import_text(struct id3_tag *tag, const char *id, enum tag_type type,
+		    const struct tag_handler *handler, void *handler_ctx)
 {
 	const struct id3_frame *frame;
 	for (unsigned i = 0;
 	     (frame = id3_tag_findframe(tag, id, i)) != NULL; ++i)
-		tag_id3_import_text_frame(dest, tag, frame, type);
+		tag_id3_import_text_frame(tag, frame, type,
+					  handler, handler_ctx);
 }
 
 /**
@@ -194,9 +197,10 @@ tag_id3_import_text(struct tag *dest, struct id3_tag *tag, const char *id,
  * - full string (we use this one)
  */
 static void
-tag_id3_import_comment_frame(struct tag *dest, struct id3_tag *tag,
-			     const struct id3_frame *frame,
-			     enum tag_type type)
+tag_id3_import_comment_frame(struct id3_tag *tag,
+			     const struct id3_frame *frame, enum tag_type type,
+			     const struct tag_handler *handler,
+			     void *handler_ctx)
 {
 	id3_ucs4_t const *ucs4;
 	id3_utf8_t *utf8;
@@ -218,7 +222,7 @@ tag_id3_import_comment_frame(struct tag *dest, struct id3_tag *tag,
 	if (utf8 == NULL)
 		return;
 
-	tag_add_item(dest, type, (char *)utf8);
+	tag_handler_invoke_tag(handler, handler_ctx, type, (const char *)utf8);
 	g_free(utf8);
 }
 
@@ -227,13 +231,14 @@ tag_id3_import_comment_frame(struct tag *dest, struct id3_tag *tag,
  * wrapper for tag_id3_import_comment_frame().
  */
 static void
-tag_id3_import_comment(struct tag *dest, struct id3_tag *tag, const char *id,
-		       enum tag_type type)
+tag_id3_import_comment(struct id3_tag *tag, const char *id, enum tag_type type,
+		       const struct tag_handler *handler, void *handler_ctx)
 {
 	const struct id3_frame *frame;
 	for (unsigned i = 0;
 	     (frame = id3_tag_findframe(tag, id, i)) != NULL; ++i)
-		tag_id3_import_comment_frame(dest, tag, frame, type);
+		tag_id3_import_comment_frame(tag, frame, type,
+					     handler, handler_ctx);
 }
 
 /**
@@ -260,7 +265,9 @@ tag_id3_parse_txxx_name(const char *name)
  * Import all known MusicBrainz tags from TXXX frames.
  */
 static void
-tag_id3_import_musicbrainz(struct tag *mpd_tag, struct id3_tag *id3_tag)
+tag_id3_import_musicbrainz(struct id3_tag *id3_tag,
+			   const struct tag_handler *handler,
+			   void *handler_ctx)
 {
 	for (unsigned i = 0;; ++i) {
 		const struct id3_frame *frame;
@@ -285,7 +292,8 @@ tag_id3_import_musicbrainz(struct tag *mpd_tag, struct id3_tag *id3_tag)
 		if (value == NULL)
 			continue;
 
-		tag_add_item(mpd_tag, type, (const char*)value);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       type, (const char*)value);
 		free(value);
 	}
 }
@@ -294,7 +302,8 @@ tag_id3_import_musicbrainz(struct tag *mpd_tag, struct id3_tag *id3_tag)
  * Imports the MusicBrainz TrackId from the UFID tag.
  */
 static void
-tag_id3_import_ufid(struct tag *mpd_tag, struct id3_tag *id3_tag)
+tag_id3_import_ufid(struct id3_tag *id3_tag,
+		    const struct tag_handler *handler, void *handler_ctx)
 {
 	for (unsigned i = 0;; ++i) {
 		const struct id3_frame *frame;
@@ -324,35 +333,54 @@ tag_id3_import_ufid(struct tag *mpd_tag, struct id3_tag *id3_tag)
 		if (value == NULL || length == 0)
 			continue;
 
-		tag_add_item_n(mpd_tag, TAG_MUSICBRAINZ_TRACKID,
-			       (const char*)value, length);
+		char *p = g_strndup((const char *)value, length);
+		tag_handler_invoke_tag(handler, handler_ctx,
+				       TAG_MUSICBRAINZ_TRACKID, p);
+		g_free(p);
 	}
 }
 
+static void
+scan_id3_tag(struct id3_tag *tag,
+	     const struct tag_handler *handler, void *handler_ctx)
+{
+	tag_id3_import_text(tag, ID3_FRAME_ARTIST, TAG_ARTIST,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_ALBUM_ARTIST,
+			    TAG_ALBUM_ARTIST, handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_ARTIST_SORT,
+			    TAG_ARTIST_SORT, handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_ALBUM_ARTIST_SORT,
+			    TAG_ALBUM_ARTIST_SORT, handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_TITLE, TAG_TITLE,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_ALBUM, TAG_ALBUM,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_TRACK, TAG_TRACK,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_YEAR, TAG_DATE,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_GENRE, TAG_GENRE,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_COMPOSER, TAG_COMPOSER,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, "TPE3", TAG_PERFORMER,
+			    handler, handler_ctx);
+	tag_id3_import_text(tag, "TPE4", TAG_PERFORMER, handler, handler_ctx);
+	tag_id3_import_comment(tag, ID3_FRAME_COMMENT, TAG_COMMENT,
+			       handler, handler_ctx);
+	tag_id3_import_text(tag, ID3_FRAME_DISC, TAG_DISC,
+			    handler, handler_ctx);
+
+	tag_id3_import_musicbrainz(tag, handler, handler_ctx);
+	tag_id3_import_ufid(tag, handler, handler_ctx);
+}
+
 struct tag *tag_id3_import(struct id3_tag * tag)
 {
 	struct tag *ret = tag_new();
 
-	tag_id3_import_text(ret, tag, ID3_FRAME_ARTIST, TAG_ARTIST);
-	tag_id3_import_text(ret, tag, ID3_FRAME_ALBUM_ARTIST,
-			    TAG_ALBUM_ARTIST);
-	tag_id3_import_text(ret, tag, ID3_FRAME_ARTIST_SORT,
-			    TAG_ARTIST_SORT);
-	tag_id3_import_text(ret, tag, ID3_FRAME_ALBUM_ARTIST_SORT,
-			    TAG_ALBUM_ARTIST_SORT);
-	tag_id3_import_text(ret, tag, ID3_FRAME_TITLE, TAG_TITLE);
-	tag_id3_import_text(ret, tag, ID3_FRAME_ALBUM, TAG_ALBUM);
-	tag_id3_import_text(ret, tag, ID3_FRAME_TRACK, TAG_TRACK);
-	tag_id3_import_text(ret, tag, ID3_FRAME_YEAR, TAG_DATE);
-	tag_id3_import_text(ret, tag, ID3_FRAME_GENRE, TAG_GENRE);
-	tag_id3_import_text(ret, tag, ID3_FRAME_COMPOSER, TAG_COMPOSER);
-	tag_id3_import_text(ret, tag, "TPE3", TAG_PERFORMER);
-	tag_id3_import_text(ret, tag, "TPE4", TAG_PERFORMER);
-	tag_id3_import_comment(ret, tag, ID3_FRAME_COMMENT, TAG_COMMENT);
-	tag_id3_import_text(ret, tag, ID3_FRAME_DISC, TAG_DISC);
-
-	tag_id3_import_musicbrainz(ret, tag);
-	tag_id3_import_ufid(ret, tag);
+	scan_id3_tag(tag, &add_tag_handler, ret);
 
 	if (tag_is_empty(ret)) {
 		tag_free(ret);
@@ -510,6 +538,36 @@ tag_id3_riff_aiff_load(FILE *file)
 	return tag;
 }
 
+bool
+tag_id3_scan(const char *path_fs,
+	     const struct tag_handler *handler, void *handler_ctx)
+{
+	struct id3_tag *tag;
+	FILE *stream;
+
+	stream = fopen(path_fs, "rb");
+	if (!stream) {
+		g_debug("tag_id3_load: Failed to open file: '%s', %s",
+			path_fs, strerror(errno));
+		return false;
+	}
+
+	tag = tag_id3_find_from_beginning(stream);
+	if (tag == NULL)
+		tag = tag_id3_riff_aiff_load(stream);
+	if (!tag)
+		tag = tag_id3_find_from_end(stream);
+
+	fclose(stream);
+
+	if (!tag)
+		return false;
+
+	scan_id3_tag(tag, handler, handler_ctx);
+	id3_tag_delete(tag);
+	return true;
+}
+
 struct tag *tag_id3_load(const char *file)
 {
 	struct tag *ret;

src/tag_id3.h

@@ -22,9 +22,17 @@
 
 #include "check.h"
 
+#include <stdbool.h>
+
+struct tag_handler;
 struct tag;
 
 #ifdef HAVE_ID3TAG
+
+bool
+tag_id3_scan(const char *path_fs,
+	     const struct tag_handler *handler, void *handler_ctx);
+
 struct id3_tag;
 struct tag *tag_id3_import(struct id3_tag *);
 
@@ -34,6 +42,14 @@ struct tag *tag_id3_load(const char *file);
 
 #include <glib.h>
 
+static inline bool
+tag_id3_scan(G_GNUC_UNUSED const char *path_fs,
+	     G_GNUC_UNUSED const struct tag_handler *handler,
+	     G_GNUC_UNUSED void *handler_ctx)
+{
+	return false;
+}
+
 static inline struct tag *
 tag_id3_load(G_GNUC_UNUSED const char *file)
 {

src/update_walk.c

@@ -31,6 +31,8 @@
 #include "decoder_plugin.h"
 #include "playlist_list.h"
 #include "conf.h"
+#include "tag.h"
+#include "tag_handler.h"
 
 #ifdef ENABLE_ARCHIVE
 #include "archive_list.h"
@@ -511,7 +513,9 @@ update_container_file(	struct directory* directory,
 
 		child_path_fs = map_directory_child_fs(contdir, vtrack);
 
-		song->tag = plugin->tag_dup(child_path_fs);
+		song->tag = tag_new();
+		decoder_plugin_scan_file(plugin, child_path_fs,
+					 &add_tag_handler, song->tag);
 		g_free(child_path_fs);
 
 		directory_add_song(contdir, song);

test/read_tags.c

@@ -25,9 +25,9 @@
 #include "input_stream.h"
 #include "audio_format.h"
 #include "pcm_volume.h"
-#include "tag_pool.h"
 #include "tag_ape.h"
 #include "tag_id3.h"
+#include "tag_handler.h"
 #include "idle.h"
 
 #include <glib.h>
@@ -134,25 +134,31 @@ decoder_mixramp(G_GNUC_UNUSED struct decoder *decoder,
 	g_free(mixramp_end);
 }
 
+static bool empty = true;
+
 static void
-print_tag(const struct tag *tag)
+print_duration(unsigned seconds, G_GNUC_UNUSED void *ctx)
 {
-	if (tag->time >= 0)
-		g_print("time=%d\n", tag->time);
+	g_print("duration=%d\n", seconds);
+}
 
-	for (unsigned i = 0; i < tag->num_items; ++i)
-		g_print("%s=%s\n",
-			tag_item_names[tag->items[i]->type],
-			tag->items[i]->value);
+static void
+print_tag(enum tag_type type, const char *value, G_GNUC_UNUSED void *ctx)
+{
+	g_print("%s=%s\n", tag_item_names[type], value);
+	empty = false;
 }
 
+static const struct tag_handler print_handler = {
+	.duration = print_duration,
+	.tag = print_tag,
+};
+
 int main(int argc, char **argv)
 {
 	GError *error = NULL;
 	const char *decoder_name, *path;
 	const struct decoder_plugin *plugin;
-	struct tag *tag;
-	bool empty;
 
 #ifdef HAVE_LOCALE_H
 	/* initialize locale */
@@ -175,8 +181,6 @@ int main(int argc, char **argv)
 		return EXIT_FAILURE;
 	}
 
-	tag_pool_init();
-
 	if (!input_stream_global_init(&error)) {
 		g_warning("%s", error->message);
 		g_error_free(error);
@@ -191,8 +195,9 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	tag = decoder_plugin_tag_dup(plugin, path);
-	if (tag == NULL && plugin->stream_tag != NULL) {
+	bool success = decoder_plugin_scan_file(plugin, path,
+						&print_handler, NULL);
+	if (!success && plugin->scan_stream != NULL) {
 		GMutex *mutex = g_mutex_new();
 		GCond *cond = g_cond_new();
 
@@ -206,7 +211,8 @@ int main(int argc, char **argv)
 			return 1;
 		}
 
-		tag = decoder_plugin_stream_tag(plugin, is);
+		success = decoder_plugin_scan_stream(plugin, is,
+						     &print_handler, NULL);
 		input_stream_close(is);
 
 		g_cond_free(cond);
@@ -217,27 +223,16 @@ int main(int argc, char **argv)
 	input_stream_global_finish();
 	io_thread_deinit();
 
-	if (tag == NULL) {
+	if (!success) {
 		g_printerr("Failed to read tags\n");
 		return 1;
 	}
 
-	print_tag(tag);
-
-	empty = tag_is_empty(tag);
-	tag_free(tag);
-
 	if (empty) {
-		tag = tag_ape_load(path);
-		if (tag == NULL)
-			tag = tag_id3_load(path);
-		if (tag != NULL) {
-			print_tag(tag);
-			tag_free(tag);
-		}
+		tag_ape_scan2(path, &print_handler, NULL);
+		if (empty)
+			tag_id3_scan(path, &print_handler, NULL);
 	}
 
-	tag_pool_deinit();
-
 	return 0;
 }