filter: added new plugin API for filters

The filter API allows us to implement software volume as a pluggable
filter, and we will be able to integrate libraries like SoX.

src/filter_plugin.c

@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 2003-2009 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 "filter_plugin.h"
+#include "filter_internal.h"
+#include "filter_registry.h"
+#include "conf.h"
+
+#ifndef NDEBUG
+#include "audio_format.h"
+#endif
+
+#include <assert.h>
+
+struct filter *
+filter_new(const struct filter_plugin *plugin,
+	   const struct config_param *param, GError **error_r)
+{
+	assert(plugin != NULL);
+	assert(error_r == NULL || *error_r == NULL);
+
+	return plugin->init(param, error_r);
+}
+
+struct filter *
+filter_configured_new(const struct config_param *param, GError **error_r)
+{
+	const char *plugin_name;
+	const struct filter_plugin *plugin;
+
+	assert(param != NULL);
+	assert(error_r == NULL || *error_r == NULL);
+
+	plugin_name = config_get_block_string(param, "plugin", NULL);
+	if (plugin_name == NULL)
+		g_set_error(error_r, config_quark(), 0,
+			    "No filter plugin specified");
+
+	plugin = filter_plugin_by_name(plugin_name);
+	if (plugin == NULL)
+		g_set_error(error_r, config_quark(), 0,
+			    "No such filter plugin: %s", plugin_name);
+
+	return filter_new(plugin, param, error_r);
+}
+
+void
+filter_free(struct filter *filter)
+{
+	assert(filter != NULL);
+
+	filter->plugin->finish(filter);
+}
+
+const struct audio_format *
+filter_open(struct filter *filter, const struct audio_format *audio_format,
+	    GError **error_r)
+{
+	assert(filter != NULL);
+	assert(audio_format != NULL);
+	assert(audio_format_valid(audio_format));
+	assert(error_r == NULL || *error_r == NULL);
+
+	audio_format = filter->plugin->open(filter, audio_format, error_r);
+	assert(audio_format == NULL || audio_format_valid(audio_format));
+
+	return audio_format;
+}
+
+void
+filter_close(struct filter *filter)
+{
+	assert(filter != NULL);
+
+	filter->plugin->close(filter);
+}
+
+const void *
+filter_filter(struct filter *filter, const void *src, size_t src_size,
+	      size_t *dest_size_r,
+	      GError **error_r)
+{
+	assert(filter != NULL);
+	assert(src != NULL);
+	assert(src_size > 0);
+	assert(dest_size_r != NULL);
+	assert(error_r == NULL || *error_r == NULL);
+
+	return filter->plugin->filter(filter, src, src_size, dest_size_r, error_r);
+}