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.

Makefile.am

@@ -42,6 +42,9 @@ mpd_headers = \
 	src/output_state.h \
 	src/output_print.h \
 	src/output_command.h \
+	src/filter_internal.h \
+	src/filter_plugin.h \
+	src/filter_registry.h \
 	src/buffer2array.h \
 	src/command.h \
 	src/idle.h \
@@ -188,6 +191,9 @@ src_mpd_SOURCES = \
 	src/database.c \
 	src/dirvec.c \
 	src/fifo_buffer.c \
+	src/filter_plugin.c \
+	src/filter_registry.c \
+	src/filter/null_filter_plugin.c \
 	src/update.c \
 	src/client.c \
 	src/listen.c \

src/filter/null_filter_plugin.c

@@ -0,0 +1,93 @@
+/*
+ * 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.
+ */
+
+/** \file
+ *
+ * This filter plugin does nothing.  That is not quite useful, except
+ * for testing the filter core, or as a template for new filter
+ * plugins.
+ */
+
+#include "filter_plugin.h"
+#include "filter_internal.h"
+#include "filter_registry.h"
+
+#include <assert.h>
+
+struct null_filter {
+	struct filter filter;
+};
+
+static struct filter *
+null_filter_init(G_GNUC_UNUSED const struct config_param *param,
+		 G_GNUC_UNUSED GError **error_r)
+{
+	struct null_filter *filter = g_new(struct null_filter, 1);
+
+	filter_init(&filter->filter, &null_filter_plugin);
+	return &filter->filter;
+}
+
+static void
+null_filter_finish(struct filter *_filter)
+{
+	struct null_filter *filter = (struct null_filter *)_filter;
+
+	g_free(filter);
+}
+
+static const struct audio_format *
+null_filter_open(struct filter *_filter,
+		 const struct audio_format *audio_format,
+		 G_GNUC_UNUSED GError **error_r)
+{
+	struct null_filter *filter = (struct null_filter *)_filter;
+	(void)filter;
+
+	return audio_format;
+}
+
+static void
+null_filter_close(struct filter *_filter)
+{
+	struct null_filter *filter = (struct null_filter *)_filter;
+	(void)filter;
+}
+
+static const void *
+null_filter_filter(struct filter *_filter,
+		   const void *src, size_t src_size,
+		   size_t *dest_size_r, G_GNUC_UNUSED GError **error_r)
+{
+	struct null_filter *filter = (struct null_filter *)_filter;
+	(void)filter;
+
+	/* return the unmodified source buffer */
+	*dest_size_r = src_size;
+	return src;
+}
+
+const struct filter_plugin null_filter_plugin = {
+	.name = "null",
+	.init = null_filter_init,
+	.finish = null_filter_finish,
+	.open = null_filter_open,
+	.close = null_filter_close,
+	.filter = null_filter_filter,
+};

src/filter_internal.h

@@ -0,0 +1,38 @@
+/*
+ * 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.
+ */
+
+/** \file
+ *
+ * Internal stuff for the filter core and filter plugins.
+ */
+
+#ifndef MPD_FILTER_INTERNAL_H
+#define MPD_FILTER_INTERNAL_H
+
+struct filter {
+	const struct filter_plugin *plugin;
+};
+
+static inline void
+filter_init(struct filter *filter, const struct filter_plugin *plugin)
+{
+	filter->plugin = plugin;
+}
+
+#endif

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);
+}

src/filter_plugin.h

@@ -0,0 +1,145 @@
+/*
+ * 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.
+ */
+
+/** \file
+ *
+ * This header declares the filter_plugin class.  It describes a
+ * plugin API for objects which filter raw PCM data.
+ */
+
+#ifndef MPD_FILTER_PLUGIN_H
+#define MPD_FILTER_PLUGIN_H
+
+#include <glib.h>
+
+#include <stdbool.h>
+#include <stddef.h>
+
+struct config_param;
+struct filter;
+
+struct filter_plugin {
+	const char *name;
+
+	/**
+         * Allocates and configures a filter.
+	 */
+	struct filter *(*init)(const struct config_param *param,
+			       GError **error_r);
+
+	/**
+	 * Free instance data.
+         */
+	void (*finish)(struct filter *filter);
+
+	/**
+	 * Opens a filter.
+	 */
+	const struct audio_format *
+	(*open)(struct filter *filter,
+		const struct audio_format *audio_format,
+		GError **error_r);
+
+	/**
+	 * Closes a filter.
+	 */
+	void (*close)(struct filter *filter);
+
+	/**
+	 * Filters a block of PCM data.
+	 */
+	const void *(*filter)(struct filter *filter,
+			      const void *src, size_t src_size,
+			      size_t *dest_buffer_r,
+			      GError **error_r);
+};
+
+/**
+ * Creates a new instance of the specified filter plugin.
+ *
+ * @param plugin the filter plugin
+ * @param param optional configuration section
+ * @param error location to store the error occuring, or NULL to
+ * ignore errors.
+ * @return a new filter object, or NULL on error
+ */
+struct filter *
+filter_new(const struct filter_plugin *plugin,
+	   const struct config_param *param, GError **error_r);
+
+/**
+ * Creates a new filter, loads configuration and the plugin name from
+ * the specified configuration section.
+ *
+ * @param param the configuration section
+ * @param error location to store the error occuring, or NULL to
+ * ignore errors.
+ * @return a new filter object, or NULL on error
+ */
+struct filter *
+filter_configured_new(const struct config_param *param, GError **error_r);
+
+/**
+ * Deletes a filter.  It must be closed prior to calling this
+ * function, see filter_close().
+ *
+ * @param filter the filter object
+ */
+void
+filter_free(struct filter *filter);
+
+/**
+ * Opens the filter, preparing it for filter_filter().
+ *
+ * @param filter the filter object
+ * @param audio_format the audio format of incoming and outgoing data
+ * @param error location to store the error occuring, or NULL to
+ * ignore errors.
+ * @return true on success, false on error
+ */
+const struct audio_format *
+filter_open(struct filter *filter, const struct audio_format *audio_format,
+	    GError **error_r);
+
+/**
+ * Closes the filter.  After that, you may call filter_open() again.
+ *
+ * @param filter the filter object
+ */
+void
+filter_close(struct filter *filter);
+
+/**
+ * Filters a block of PCM data.
+ *
+ * @param filter the filter object
+ * @param src the input buffer
+ * @param src_size the size of #src_buffer in bytes
+ * @param dest_size_r the size of the returned buffer
+ * @param error location to store the error occuring, or NULL to
+ * ignore errors.
+ * @return the destination buffer on success (will be invalidated by
+ * filter_close() or filter_filter()), NULL on error
+ */
+const void *
+filter_filter(struct filter *filter, const void *src, size_t src_size,
+	      size_t *dest_size_r,
+	      GError **error_r);
+
+#endif

src/filter_registry.c

@@ -0,0 +1,39 @@
+/*
+ * 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_registry.h"
+#include "filter_plugin.h"
+
+#include <stddef.h>
+#include <string.h>
+
+const struct filter_plugin *const filter_plugins[] = {
+	&null_filter_plugin,
+	NULL,
+};
+
+const struct filter_plugin *
+filter_plugin_by_name(const char *name)
+{
+	for (unsigned i = 0; filter_plugins[i] != NULL; ++i)
+		if (strcmp(filter_plugins[i]->name, name) == 0)
+			return filter_plugins[i];
+
+	return NULL;
+}

src/filter_registry.h

@@ -0,0 +1,34 @@
+/*
+ * 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.
+ */
+
+/** \file
+ *
+ * This library manages all filter plugins which are enabled at
+ * compile time.
+ */
+
+#ifndef MPD_FILTER_REGISTRY_H
+#define MPD_FILTER_REGISTRY_H
+
+extern const struct filter_plugin null_filter_plugin;
+
+const struct filter_plugin *
+filter_plugin_by_name(const char *name);
+
+#endif