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+/**
+ * @file plugins.h
+ * @author Radek Krejci <rkrejci@cesnet.cz>
+ * @brief Plugins manipulation.
+ *
+ * Copyright (c) 2021 CESNET, z.s.p.o.
+ *
+ * This source code is licensed under BSD 3-Clause License (the "License").
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://opensource.org/licenses/BSD-3-Clause
+ */
+
+#ifndef LY_PLUGINS_H_
+#define LY_PLUGINS_H_
+
+#include "log.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @page howtoPlugins Plugins
+ *
+ * libyang supports two types of plugins to better support generic features of YANG that need some specific code for
+ * their specific instances in YANG modules. This is the case of YANG types, which are derived from YANG built-in types.
+ * The description of a derived type can specify some additional requirements or restriction that cannot be implemented
+ * generically and some special code is needed. The second case for libyang plugins are YANG extensions. For YANG extensions,
+ * most of the specification is hidden in their description (e.g. allowed substatements or place of the extension
+ * instantiation) and libyang is not able to process such a text in a generic way.
+ *
+ * In both cases, libyang provides API to get functionality implementing the specifics of each type or extension.
+ * Furthermore, there are several internal plugins, implementing built-in data types and selected derived types and YANG
+ * extensions. These internal plugins uses the same API and can be taken as examples for implementing user plugins. Internal
+ * plugins are always loaded with the first created [context](@ref howtoContext) and unloaded with destroying the last one.
+ * The external plugins are in the same phase loaded from the default directories specified at compile time via cmake
+ * variables `PLUGINS_DIR` (where the `extensions` and `types` subdirectories are added for each plugin type) or separately
+ * via `PLUGINS_DIR_EXTENSIONS` and `PLUGINS_DIR_TYPES` for each plugin type. The default directories can be replaced runtime
+ * using environment variables `LIBYANG_TYPES_PLUGINS_DIR` and `LIBYANG_EXTENSIONS_PLUGINS_DIR`.
+ *
+ * Order of the plugins determines their priority. libyang searches for the first match with the extension and type, so the
+ * firstly loaded plugin for the specific item is used. Since the internal plugins are loaded always before the external
+ * plugins, the internal plugins cannot be replaced.
+ *
+ * There is also a separate function ::lyplg_add() to add a plugin anytime later. Note, that such a plugin is being used
+ * after it is added with the lowest priority among other already loaded plugins. Also note that since all the plugins are
+ * unloaded with the destruction of the last context, creating a new context after that starts the standard plugins
+ * initiation and the manually added plugins are not loaded automatically.
+ *
+ * The following pages contain description of the API for creating user plugins.
+ *
+ * - @subpage howtoPluginsTypes
+ * - @subpage howtoPluginsExtensions
+ */
+
+/**
+ * @defgroup plugins Plugins
+ * @{
+ *
+ */
+
+/**
+ * @brief Identifiers of the plugin type.
+ */
+enum LYPLG {
+    LYPLG_TYPE,      /**< Specific type (typedef) */
+    LYPLG_EXTENSION  /**< YANG extension */
+};
+
+/**
+ * @brief Manually load a plugin file.
+ *
+ * Note, that a plugin can be loaded only if there is at least one context. The loaded plugins are connected with the
+ * existence of a context. When all the contexts are destroyed, all the plugins are unloaded.
+ *
+ * @param[in] pathname Path to the plugin file. It can contain types or extensions plugins, both are accepted and correctly
+ * loaded.
+ *
+ * @return LY_SUCCESS if the file contains valid plugin compatible with the library version.
+ * @return LY_EDENIED in case there is no context and the plugin cannot be loaded.
+ * @return LY_EINVAL when pathname is NULL or the plugin contains invalid content for this libyang version.
+ * @return LY_ESYS when the plugin file cannot be loaded.
+ */
+LIBYANG_API_DECL LY_ERR lyplg_add(const char *pathname);
+
+/** @} plugins */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* LY_PLUGINS_H_ */