filter/chain: new library for creating a chain of filters

Makefile.am

@@ -45,6 +45,7 @@ mpd_headers = \
 	src/filter_internal.h \
 	src/filter_plugin.h \
 	src/filter_registry.h \
+	src/filter/chain_filter_plugin.h \
 	src/filter/volume_filter_plugin.h \
 	src/buffer2array.h \
 	src/command.h \
@@ -583,6 +584,7 @@ endif
 
 FILTER_SRC = \
 	src/filter/null_filter_plugin.c \
+	src/filter/chain_filter_plugin.c \
 	src/filter/volume_filter_plugin.c
 
 

src/filter/chain_filter_plugin.c

+/*
+ * 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/chain_filter_plugin.h"
+#include "filter_plugin.h"
+#include "filter_internal.h"
+#include "filter_registry.h"
+
+#include <assert.h>
+
+struct filter_chain {
+	/** the base class */
+	struct filter base;
+
+	GSList *children;
+};
+
+static struct filter *
+chain_filter_init(G_GNUC_UNUSED const struct config_param *param,
+		  G_GNUC_UNUSED GError **error_r)
+{
+	struct filter_chain *chain = g_new(struct filter_chain, 1);
+
+	filter_init(&chain->base, &chain_filter_plugin);
+	chain->children = NULL;
+
+	return &chain->base;
+}
+
+static void
+chain_free_child(gpointer data, G_GNUC_UNUSED gpointer user_data)
+{
+	struct filter *filter = data;
+
+	filter_free(filter);
+}
+
+static void
+chain_filter_finish(struct filter *_filter)
+{
+	struct filter_chain *chain = (struct filter_chain *)_filter;
+
+	g_slist_foreach(chain->children, chain_free_child, NULL);
+	g_slist_free(chain->children);
+
+	g_free(chain);
+}
+
+/**
+ * Close all filters in the chain until #until is reached.  #until
+ * itself is not closed.
+ */
+static void
+chain_close_until(struct filter_chain *chain, const struct filter *until)
+{
+	GSList *i = chain->children;
+	struct filter *filter;
+
+	while (true) {
+		/* this assertion fails if #until does not exist
+		   (anymore) */
+		assert(i != NULL);
+
+		if (i->data == until)
+			/* don't close this filter */
+			break;
+
+		/* close this filter */
+		filter = i->data;
+		filter_close(filter);
+
+		i = g_slist_next(i);
+	}
+}
+
+static const struct audio_format *
+chain_filter_open(struct filter *_filter,
+		  const struct audio_format *audio_format,
+		  GError **error_r)
+{
+	struct filter_chain *chain = (struct filter_chain *)_filter;
+
+	for (GSList *i = chain->children; i != NULL; i = g_slist_next(i)) {
+		struct filter *filter = i->data;
+
+		audio_format = filter_open(filter, audio_format, error_r);
+		if (audio_format == NULL) {
+			/* rollback, close all children */
+			chain_close_until(chain, filter);
+			return NULL;
+		}
+	}
+
+	/* return the output format of the last filter */
+	return audio_format;
+}
+
+static void
+chain_close_child(gpointer data, G_GNUC_UNUSED gpointer user_data)
+{
+	struct filter *filter = data;
+
+	filter_close(filter);
+}
+
+static void
+chain_filter_close(struct filter *_filter)
+{
+	struct filter_chain *chain = (struct filter_chain *)_filter;
+
+	g_slist_foreach(chain->children, chain_close_child, NULL);
+}
+
+static const void *
+chain_filter_filter(struct filter *_filter,
+		    const void *src, size_t src_size,
+		    size_t *dest_size_r, GError **error_r)
+{
+	struct filter_chain *chain = (struct filter_chain *)_filter;
+
+	for (GSList *i = chain->children; i != NULL; i = g_slist_next(i)) {
+		struct filter *filter = i->data;
+
+		/* feed the output of the previous filter as input
+		   into the current one */
+		src = filter_filter(filter, src, src_size, &src_size, error_r);
+		if (src == NULL)
+			chain_close_until(chain, filter);
+	}
+
+	/* return the output of the last filter */
+	*dest_size_r = src_size;
+	return src;
+}
+
+const struct filter_plugin chain_filter_plugin = {
+	.name = "chain",
+	.init = chain_filter_init,
+	.finish = chain_filter_finish,
+	.open = chain_filter_open,
+	.close = chain_filter_close,
+	.filter = chain_filter_filter,
+};
+
+struct filter *
+filter_chain_new(void)
+{
+	struct filter *filter = filter_new(&chain_filter_plugin, NULL, NULL);
+	/* chain_filter_init() never fails */
+	assert(filter != NULL);
+
+	return filter;
+}
+
+void
+filter_chain_append(struct filter *_chain, struct filter *filter)
+{
+	struct filter_chain *chain = (struct filter_chain *)_chain;
+
+	chain->children = g_slist_append(chain->children, filter);
+}

src/filter/chain_filter_plugin.h

+/*
+ * 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
+ *
+ * A filter chain is a container for several filters.  They are
+ * chained together, i.e. called in a row, one filter passing its
+ * output to the next one.
+ */
+
+#ifndef MPD_FILTER_CHAIN_H
+#define MPD_FILTER_CHAIN_H
+
+struct filter;
+
+/**
+ * Creates a new filter chain.
+ */
+struct filter *
+filter_chain_new(void);
+
+/**
+ * Appends a new filter at the end of the filter chain.  You must call
+ * this function before the first filter_open() call.
+ *
+ * @param chain the filter chain created with filter_chain_new()
+ * @param filter the filter to be appended to #chain
+ */
+void
+filter_chain_append(struct filter *chain, struct filter *filter);
+
+#endif

src/filter_registry.c

@@ -25,6 +25,7 @@
 
 const struct filter_plugin *const filter_plugins[] = {
 	&null_filter_plugin,
+	&chain_filter_plugin,
 	&volume_filter_plugin,
 	NULL,
 };

src/filter_registry.h

@@ -27,6 +27,7 @@
 #define MPD_FILTER_REGISTRY_H
 
 extern const struct filter_plugin null_filter_plugin;
+extern const struct filter_plugin chain_filter_plugin;
 extern const struct filter_plugin volume_filter_plugin;
 
 const struct filter_plugin *