context: add metadata implementation

Add a simple metadata implementation to the core that clients can
use to manage metadata or export.

src/pipewire/context.c

@@ -230,6 +230,7 @@ struct pw_context *pw_context_new(struct pw_loop *main_loop,
 	spa_list_init(&this->client_list);
 	spa_list_init(&this->node_list);
 	spa_list_init(&this->factory_list);
+	spa_list_init(&this->metadata_list);
 	spa_list_init(&this->link_list);
 	spa_list_init(&this->control_list[0]);
 	spa_list_init(&this->control_list[1]);
@@ -411,6 +412,7 @@ void pw_context_destroy(struct pw_context *context)
 	struct pw_resource *resource;
 	struct pw_impl_node *node;
 	struct factory_entry *entry;
+	struct pw_impl_metadata *metadata;
 	struct pw_impl_core *core_impl;
 
 	pw_log_debug(NAME" %p: destroy", context);
@@ -437,6 +439,9 @@ void pw_context_destroy(struct pw_context *context)
 	spa_list_consume(global, &context->global_list, link)
 		pw_global_destroy(global);
 
+	spa_list_consume(metadata, &context->metadata_list, link)
+		pw_impl_metadata_destroy(metadata);
+
 	spa_list_consume(core_impl, &context->core_impl_list, link)
 		pw_impl_core_destroy(core_impl);
 

src/pipewire/impl-metadata.c

@@ -0,0 +1,572 @@
+/* PipeWire
+ *
+ * Copyright © 2021 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include <errno.h>
+
+#include <spa/debug/types.h>
+#include <spa/utils/string.h>
+
+#include "pipewire/impl.h"
+#include "pipewire/private.h"
+
+#include "extensions/metadata.h"
+
+#define NAME "metadata"
+
+#define pw_metadata_emit(hooks,method,version,...)			\
+	spa_hook_list_call_simple(hooks, struct pw_metadata_events,	\
+				method, version, ##__VA_ARGS__)
+
+#define pw_metadata_emit_property(hooks,...)	pw_metadata_emit(hooks,property, 0, ##__VA_ARGS__)
+
+struct metadata {
+	struct spa_interface iface;
+	struct pw_array storage;
+	struct spa_hook_list hooks;		/**< event listeners */
+};
+
+struct item {
+	uint32_t subject;
+	char *key;
+	char *type;
+	char *value;
+};
+
+static void clear_item(struct item *item)
+{
+	free(item->key);
+	free(item->type);
+	free(item->value);
+	spa_zero(*item);
+}
+
+static void set_item(struct item *item, uint32_t subject, const char *key, const char *type, const char *value)
+{
+	item->subject = subject;
+	item->key = strdup(key);
+	item->type = type ? strdup(type) : NULL;
+	item->value = strdup(value);
+}
+
+static int change_item(struct item *item, const char *type, const char *value)
+{
+	int changed = 0;
+	if (!spa_streq(item->type, type)) {
+		free((char*)item->type);
+		item->type = type ? strdup(type) : NULL;
+		changed++;
+	}
+	if (!spa_streq(item->value, value)) {
+		free((char*)item->value);
+		item->value = value ? strdup(value) : NULL;
+		changed++;
+	}
+	return changed;
+}
+
+static void emit_properties(struct metadata *this)
+{
+	struct item *item;
+	pw_array_for_each(item, &this->storage) {
+		pw_log_debug("metadata %p: %d %s %s %s",
+				this, item->subject, item->key, item->type, item->value);
+		pw_metadata_emit_property(&this->hooks,
+				item->subject,
+				item->key,
+				item->type,
+				item->value);
+	}
+}
+
+static int impl_add_listener(void *object,
+		struct spa_hook *listener,
+		const struct pw_metadata_events *events,
+		void *data)
+{
+	struct metadata *this = object;
+	struct spa_hook_list save;
+
+	spa_return_val_if_fail(this != NULL, -EINVAL);
+	spa_return_val_if_fail(events != NULL, -EINVAL);
+
+	pw_log_debug("metadata %p:", this);
+
+	spa_hook_list_isolate(&this->hooks, &save, listener, events, data);
+
+	emit_properties(this);
+
+	spa_hook_list_join(&this->hooks, &save);
+
+        return 0;
+}
+
+static struct item *find_item(struct metadata *this, uint32_t subject, const char *key)
+{
+	struct item *item;
+
+	pw_array_for_each(item, &this->storage) {
+		if (item->subject == subject && (key == NULL || spa_streq(item->key, key)))
+			return item;
+	}
+	return NULL;
+}
+
+static int clear_subjects(struct metadata *this, uint32_t subject)
+{
+	struct item *item;
+	uint32_t removed = 0;
+
+	while (true) {
+		item = find_item(this, subject, NULL);
+		if (item == NULL)
+			break;
+
+		pw_log_debug(NAME" %p: remove id:%d key:%s", this, subject, item->key);
+
+		clear_item(item);
+		pw_array_remove(&this->storage, item);
+		removed++;
+	}
+	if (removed > 0)
+		pw_metadata_emit_property(&this->hooks, subject, NULL, NULL, NULL);
+
+	return 0;
+}
+
+static void clear_items(struct metadata *this)
+{
+	struct item *item;
+	pw_array_consume(item, &this->storage)
+		clear_subjects(this, item->subject);
+	pw_array_reset(&this->storage);
+}
+
+static int impl_set_property(void *object,
+			uint32_t subject,
+			const char *key,
+			const char *type,
+			const char *value)
+{
+	struct metadata *this = object;
+	struct item *item = NULL;
+	int changed = 0;
+
+	pw_log_debug(NAME" %p: id:%d key:%s type:%s value:%s", this, subject, key, type, value);
+
+	if (key == NULL)
+		return clear_subjects(this, subject);
+
+	item = find_item(this, subject, key);
+	if (value == NULL) {
+		if (item != NULL) {
+			clear_item(item);
+			pw_array_remove(&this->storage, item);
+			type = NULL;
+			changed++;
+			pw_log_info(NAME" %p: remove id:%d key:%s", this,
+					subject, key);
+		}
+	} else if (item == NULL) {
+		item = pw_array_add(&this->storage, sizeof(*item));
+		if (item == NULL)
+			return -errno;
+		set_item(item, subject, key, type, value);
+		changed++;
+		pw_log_info(NAME" %p: add id:%d key:%s type:%s value:%s", this,
+				subject, key, type, value);
+	} else {
+		if (type == NULL)
+			type = item->type;
+		changed = change_item(item, type, value);
+		if (changed)
+			pw_log_info(NAME" %p: change id:%d key:%s type:%s value:%s", this,
+				subject, key, type, value);
+	}
+
+	if (changed) {
+		pw_metadata_emit_property(&this->hooks,
+					subject, key, type, value);
+	}
+	return 0;
+}
+
+static int impl_clear(void *object)
+{
+	struct metadata *this = object;
+	clear_items(this);
+	return 0;
+}
+
+static const struct pw_metadata_methods impl_metadata = {
+	PW_VERSION_METADATA_METHODS,
+	.add_listener = impl_add_listener,
+	.set_property = impl_set_property,
+	.clear = impl_clear,
+};
+
+static struct pw_metadata *metadata_init(struct metadata *this)
+{
+	this->iface = SPA_INTERFACE_INIT(
+			PW_TYPE_INTERFACE_Metadata,
+			PW_VERSION_METADATA,
+			&impl_metadata, this);
+	pw_array_init(&this->storage, 4096);
+        spa_hook_list_init(&this->hooks);
+	return (struct pw_metadata*)&this->iface;
+}
+
+static void metadata_reset(struct metadata *this)
+{
+	spa_hook_list_clean(&this->hooks);
+	clear_items(this);
+	pw_array_clear(&this->storage);
+}
+
+struct impl {
+	struct pw_impl_metadata this;
+
+	struct metadata def;
+};
+
+struct resource_data {
+	struct pw_impl_metadata *impl;
+
+	struct pw_resource *resource;
+	struct spa_hook resource_listener;
+	struct spa_hook object_listener;
+	struct spa_hook metadata_listener;
+};
+
+
+static int metadata_property(void *object, uint32_t subject, const char *key,
+		const char *type, const char *value)
+{
+	struct pw_impl_metadata *this = object;
+	pw_impl_metadata_emit_property(this, subject, key, type, value);
+	return 0;
+}
+
+static struct pw_metadata_events metadata_events = {
+	PW_VERSION_METADATA_EVENTS,
+	.property = metadata_property,
+};
+
+SPA_EXPORT
+struct pw_impl_metadata *pw_context_create_metadata(struct pw_context *context,
+		const char *name, struct pw_properties *properties,
+		size_t user_data_size)
+{
+	struct impl *impl;
+	struct pw_impl_metadata *this;
+	int res;
+
+	if (properties == NULL)
+		properties = pw_properties_new(NULL, NULL);
+	if (properties == NULL)
+		return NULL;
+
+	impl = calloc(1, sizeof(*impl) + user_data_size);
+	if (impl == NULL) {
+		res = -errno;
+		goto error_exit;
+	};
+	this = &impl->this;
+
+	this->context = context;
+	this->properties = properties;
+
+	if (name != NULL)
+		pw_properties_set(properties, PW_KEY_METADATA_NAME, name);
+
+	spa_hook_list_init(&this->listener_list);
+
+	pw_impl_metadata_set_implementation(this, metadata_init(&impl->def));
+
+	if (user_data_size > 0)
+		this->user_data = SPA_PTROFF(this, sizeof(*this), void);
+
+	pw_log_debug(NAME" %p: new", this);
+
+	return this;
+
+error_exit:
+	pw_properties_free(properties);
+	errno = -res;
+	return NULL;
+}
+
+SPA_EXPORT
+int pw_impl_metadata_set_implementation(struct pw_impl_metadata *metadata,
+		struct pw_metadata *meta)
+{
+	struct impl *impl = SPA_CONTAINER_OF(metadata, struct impl, this);
+
+	if (metadata->metadata == meta)
+		return 0;
+
+	if (metadata->metadata)
+		spa_hook_remove(&metadata->metadata_listener);
+	if (meta == NULL)
+		meta = (struct pw_metadata*)&impl->def.iface;
+
+	metadata->metadata = meta;
+	pw_metadata_add_listener(meta, &metadata->metadata_listener,
+			&metadata_events, metadata);
+
+	return 0;
+}
+SPA_EXPORT
+struct pw_metadata *pw_impl_metadata_get_implementation(struct pw_impl_metadata *metadata)
+{
+	return metadata->metadata;
+}
+
+SPA_EXPORT
+void pw_impl_metadata_destroy(struct pw_impl_metadata *metadata)
+{
+	struct impl *impl = SPA_CONTAINER_OF(metadata, struct impl, this);
+
+	pw_log_debug(NAME" %p: destroy", metadata);
+	pw_impl_metadata_emit_destroy(metadata);
+
+	if (metadata->registered)
+		spa_list_remove(&metadata->link);
+
+	if (metadata->global) {
+		spa_hook_remove(&metadata->global_listener);
+		pw_global_destroy(metadata->global);
+	}
+
+	pw_impl_metadata_emit_free(metadata);
+	pw_log_debug(NAME" %p: free", metadata);
+
+	metadata_reset(&impl->def);
+
+	spa_hook_list_clean(&metadata->listener_list);
+
+	pw_properties_free(metadata->properties);
+
+	free(metadata);
+}
+
+#define pw_metadata_resource(r,m,v,...)      \
+	pw_resource_call_res(r,struct pw_metadata_events,m,v,__VA_ARGS__)
+
+#define pw_metadata_resource_property(r,...)        \
+        pw_metadata_resource(r,property,0,__VA_ARGS__)
+
+static int metadata_resource_property(void *object,
+			uint32_t subject,
+			const char *key,
+			const char *type,
+			const char *value)
+{
+	struct resource_data *d = object;
+	struct pw_resource *resource = d->resource;
+	struct pw_impl_client *client = pw_resource_get_client(resource);
+
+	if (pw_impl_client_check_permissions(client, subject, PW_PERM_R) >= 0)
+		pw_metadata_resource_property(d->resource, subject, key, type, value);
+	return 0;
+}
+
+static const struct pw_metadata_events metadata_resource_events = {
+	PW_VERSION_METADATA_EVENTS,
+	.property = metadata_resource_property,
+};
+
+static int metadata_set_property(void *object,
+			uint32_t subject,
+			const char *key,
+			const char *type,
+			const char *value)
+{
+	struct resource_data *d = object;
+	struct pw_impl_metadata *impl = d->impl;
+	struct pw_resource *resource = d->resource;
+	struct pw_impl_client *client = pw_resource_get_client(resource);
+	int res;
+
+	if ((res = pw_impl_client_check_permissions(client, subject, PW_PERM_R)) < 0)
+		goto error;
+
+	pw_metadata_set_property(impl->metadata, subject, key, type, value);
+	return 0;
+
+error:
+	pw_resource_errorf(resource, res, "set property error for id %d: %s",
+		subject, spa_strerror(res));
+	return res;
+}
+
+static int metadata_clear(void *object)
+{
+	struct resource_data *d = object;
+	struct pw_impl_metadata *impl = d->impl;
+	pw_metadata_clear(impl->metadata);
+	return 0;
+}
+
+static const struct pw_metadata_methods metadata_methods = {
+	PW_VERSION_METADATA_METHODS,
+	.set_property = metadata_set_property,
+	.clear = metadata_clear,
+};
+
+static void global_unbind(void *data)
+{
+	struct resource_data *d = data;
+	if (d->resource) {
+	        spa_hook_remove(&d->resource_listener);
+	        spa_hook_remove(&d->object_listener);
+	        spa_hook_remove(&d->metadata_listener);
+	}
+}
+
+static const struct pw_resource_events resource_events = {
+	PW_VERSION_RESOURCE_EVENTS,
+	.destroy = global_unbind,
+};
+
+static int
+global_bind(void *_data, struct pw_impl_client *client, uint32_t permissions,
+		  uint32_t version, uint32_t id)
+{
+	struct pw_impl_metadata *this = _data;
+	struct pw_global *global = this->global;
+	struct pw_resource *resource;
+	struct resource_data *data;
+
+	resource = pw_resource_new(client, id, permissions, global->type, version, sizeof(*data));
+	if (resource == NULL)
+		goto error_resource;
+
+        data = pw_resource_get_user_data(resource);
+        data->impl = this;
+        data->resource = resource;
+
+	pw_log_debug(NAME" %p: bound to %d", this, resource->id);
+	pw_global_add_resource(global, resource);
+
+	/* listen for when the resource goes away */
+        pw_resource_add_listener(resource,
+                        &data->resource_listener,
+                        &resource_events, data);
+
+	/* resource methods -> implementation */
+	pw_resource_add_object_listener(resource,
+			&data->object_listener,
+                        &metadata_methods, data);
+
+	/* implementation events -> resource */
+	pw_metadata_add_listener(this->metadata,
+			&data->metadata_listener,
+			&metadata_resource_events, data);
+
+	return 0;
+
+error_resource:
+	pw_log_error(NAME" %p: can't create metadata resource: %m", this);
+	return -errno;
+}
+
+static void global_destroy(void *object)
+{
+	struct pw_impl_metadata *metadata = object;
+	spa_hook_remove(&metadata->global_listener);
+	metadata->global = NULL;
+	pw_impl_metadata_destroy(metadata);
+}
+
+static const struct pw_global_events global_events = {
+	PW_VERSION_GLOBAL_EVENTS,
+	.destroy = global_destroy,
+};
+
+SPA_EXPORT
+int pw_impl_metadata_register(struct pw_impl_metadata *metadata,
+			 struct pw_properties *properties)
+{
+	struct pw_context *context = metadata->context;
+	const char *keys[] = {
+		PW_KEY_MODULE_ID,
+		PW_KEY_METADATA_NAME,
+		NULL
+	};
+
+	if (metadata->registered)
+		goto error_existed;
+
+        metadata->global = pw_global_new(context,
+					PW_TYPE_INTERFACE_Metadata,
+					PW_VERSION_METADATA,
+					properties,
+					global_bind,
+					metadata);
+	if (metadata->global == NULL)
+		return -errno;
+
+	spa_list_append(&context->metadata_list, &metadata->link);
+	metadata->registered = true;
+
+	pw_global_update_keys(metadata->global, &metadata->properties->dict, keys);
+
+	pw_global_add_listener(metadata->global, &metadata->global_listener, &global_events, metadata);
+	pw_global_register(metadata->global);
+
+	return 0;
+
+error_existed:
+	pw_properties_free(properties);
+	return -EEXIST;
+}
+
+SPA_EXPORT
+void *pw_impl_metadata_get_user_data(struct pw_impl_metadata *metadata)
+{
+	return metadata->user_data;
+}
+
+SPA_EXPORT
+struct pw_global *pw_impl_metadata_get_global(struct pw_impl_metadata *metadata)
+{
+	return metadata->global;
+}
+
+SPA_EXPORT
+void pw_impl_metadata_add_listener(struct pw_impl_metadata *metadata,
+			     struct spa_hook *listener,
+			     const struct pw_impl_metadata_events *events,
+			     void *data)
+{
+	spa_hook_list_append(&metadata->listener_list, listener, events, data);
+}
+
+SPA_EXPORT
+int pw_impl_metadata_set_property(struct pw_impl_metadata *metadata,
+			uint32_t subject, const char *key, const char *type,
+			const char *value)
+{
+	return impl_set_property(metadata->metadata, subject, key, type, value);
+}

src/pipewire/impl-metadata.h

@@ -0,0 +1,110 @@
+/* PipeWire
+ *
+ * Copyright © 2021 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef PIPEWIRE_IMPL_METADATA_H
+#define PIPEWIRE_IMPL_METADATA_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** \defgroup pw_impl_metadata Pipewire Metadata Interface
+ *
+ * The metadata is used to store key/type/value pairs per object id.
+ */
+
+/**
+ * \addtogroup pw_impl_metadata
+ * \{
+ */
+struct pw_impl_metadata;
+
+#include <pipewire/context.h>
+#include <pipewire/impl-client.h>
+#include <pipewire/global.h>
+#include <pipewire/properties.h>
+#include <pipewire/resource.h>
+
+#include <extensions/metadata.h>
+
+/** Metadata events, listen to them with \ref pw_impl_metadata_add_listener */
+struct pw_impl_metadata_events {
+#define PW_VERSION_IMPL_METADATA_EVENTS	0
+	uint32_t version;
+
+	/** the metadata is destroyed */
+        void (*destroy) (void *data);
+	/** the metadata is freed */
+        void (*free) (void *data);
+
+	/** a property changed */
+	int (*property) (void *data,
+			uint32_t subject,
+			const char *key,
+			const char *type,
+			const char *value);
+};
+
+struct pw_impl_metadata *pw_context_create_metadata(struct pw_context *context,
+		const char *name, struct pw_properties *properties,
+		size_t user_data_size);
+
+/** Get the metadata properties */
+const struct pw_properties *pw_impl_metadata_get_properties(struct pw_impl_metadata *metadata);
+
+int pw_impl_metadata_register(struct pw_impl_metadata *metadata,
+			struct pw_properties *properties);
+
+void pw_impl_metadata_destroy(struct pw_impl_metadata *metadata);
+
+void *pw_impl_metadata_get_user_data(struct pw_impl_metadata *metadata);
+
+int pw_impl_metadata_set_implementation(struct pw_impl_metadata *metadata,
+		struct pw_metadata *impl);
+
+struct pw_metadata *pw_impl_metadata_get_implementation(struct pw_impl_metadata *metadata);
+
+/** Get the global of this metadata */
+struct pw_global *pw_impl_metadata_get_global(struct pw_impl_metadata *metadata);
+
+/** Add an event listener */
+void pw_impl_metadata_add_listener(struct pw_impl_metadata *metadata,
+			     struct spa_hook *listener,
+			     const struct pw_impl_metadata_events *events,
+			     void *data);
+
+/** Set a property */
+int pw_impl_metadata_set_property(struct pw_impl_metadata *metadata,
+			uint32_t subject, const char *key, const char *type,
+			const char *value);
+
+/**
+ * \}
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* PIPEWIRE_IMPL_METADATA_H */

src/pipewire/impl.h

@@ -39,6 +39,7 @@ extern "C" {
  * - \ref pw_impl_device
  * - \ref pw_impl_factory
  * - \ref pw_impl_link
+ * - \ref pw_impl_metadata
  * - \ref pw_impl_module
  * - \ref pw_impl_node
  * - \ref pw_impl_port
@@ -66,6 +67,7 @@ struct pw_resource;
 #include <pipewire/impl-factory.h>
 #include <pipewire/global.h>
 #include <pipewire/impl-link.h>
+#include <pipewire/impl-metadata.h>
 #include <pipewire/impl-module.h>
 #include <pipewire/impl-node.h>
 #include <pipewire/impl-port.h>

src/pipewire/meson.build

@@ -25,6 +25,7 @@ pipewire_headers = [
   'main-loop.h',
   'map.h',
   'mem.h',
+  'impl-metadata.h',
   'impl-module.h',
   'module.h',
   'impl-node.h',
@@ -65,6 +66,7 @@ pipewire_sources = [
   'impl-module.c',
   'impl-node.c',
   'impl-factory.c',
+  'impl-metadata.c',
   'pipewire.c',
   'impl-port.c',
   'properties.c',

src/pipewire/private.h

@@ -241,6 +241,29 @@ struct pw_impl_core {
 	unsigned int registered:1;
 };
 
+#define pw_impl_metadata_emit(s,m,v,...) spa_hook_list_call(&s->listener_list, struct pw_impl_metadata_events, m, v, ##__VA_ARGS__)
+
+#define pw_impl_metadata_emit_destroy(s)	pw_impl_metadata_emit(s, destroy, 0)
+#define pw_impl_metadata_emit_free(s)		pw_impl_metadata_emit(s, free, 0)
+#define pw_impl_metadata_emit_property(s, ...)	pw_impl_metadata_emit(s, property, 0, __VA_ARGS__)
+
+struct pw_impl_metadata {
+	struct pw_context *context;		/**< the context */
+	struct spa_list link;			/**< link in context metadata_list */
+	struct pw_global *global;		/**< global for this metadata */
+	struct spa_hook global_listener;
+
+	struct pw_properties *properties;	/**< properties of the metadata */
+
+	struct pw_metadata *metadata;
+	struct spa_hook metadata_listener;
+
+	struct spa_hook_list listener_list;	/**< event listeners */
+	void *user_data;
+
+	unsigned int registered:1;
+};
+
 struct pw_impl_client {
 	struct pw_impl_core *core;		/**< core object */
 	struct pw_context *context;		/**< context object */
@@ -401,6 +424,7 @@ struct pw_context {
 	struct spa_list client_list;		/**< list of clients */
 	struct spa_list node_list;		/**< list of nodes */
 	struct spa_list factory_list;		/**< list of factories */
+	struct spa_list metadata_list;		/**< list of metadata */
 	struct spa_list link_list;		/**< list of links */
 	struct spa_list control_list[2];	/**< list of controls, indexed by direction */
 	struct spa_list export_list;		/**< list of export types */