decoder_plugin: scan tags with callback table

Pass a callback table to scan_file() and scan_stream(), instead of
returning a tag object.

1 files changed, 76 insertions, 0 deletions

diff --git a/src/tag_handler.h b/src/tag_handler.h
new file mode 100644
index 00000000..13e40f38
--- /dev/null
+++ b/src/tag_handler.h
@@ -0,0 +1,76 @@
+/*
+ * 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