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

1 files changed, 177 insertions, 0 deletions

diff --git a/src/filter/chain_filter_plugin.c b/src/filter/chain_filter_plugin.c
new file mode 100644
index 00000000..ec8bef5c
--- /dev/null
+++ b/src/filter/chain_filter_plugin.c
@@ -0,0 +1,177 @@
+/*
+ * 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);
+}