src/tree_data.h

/**
 * @file tree_data.h
 * @author Radek Krejci <rkrejci@cesnet.cz>
 * @brief libyang representation of data trees.
 *
 * Copyright (c) 2015 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_TREE_DATA_H_
#define LY_TREE_DATA_H_

#include <stddef.h>
#include <stdint.h>

#include "tree_schema.h"
#include "xml.h"

#ifdef __cplusplus
extern "C" {
#endif

/**
 * @defgroup datatree Data Tree
 * @{
 *
 * Data structures and functions to manipulate and access instance data tree.
 */

/**
 * @brief Data input/output formats supported by libyang [parser](@ref howtodataparsers) and
 * [printer](@ref howtodataprinters) functions.
 */
typedef enum {
    LYD_UNKNOWN,         /**< unknown format, used as return value in case of error */
    LYD_XML,             /**< XML format of the instance data */
    LYD_JSON,            /**< JSON format of the instance data */
} LYD_FORMAT;

/**
 * @brief List of possible value types stored in ::lyd_node_anydata.
 */
typedef enum {
    LYD_ANYDATA_CONSTSTRING = 0x00, /**< value is constant string (const char *) which is internally duplicated for
                                         storing in the anydata structure; XML sensitive characters (such as & or \>)
                                         are automatically escaped when the anydata is printed in XML format */
    LYD_ANYDATA_STRING = 0x01,      /**< value is dynamically allocated string (char*), so the data are used directly
                                         without duplication and caller is supposed to not manipulate with the data
                                         after a successful call (including calling free() on the provided data); XML
                                         sensitive characters (such as & or \>) are automatically escaped when the
                                         anydata is printed in XML format */
    LYD_ANYDATA_JSON = 0x02,        /**< value is string containing the data modeled by YANG and encoded as I-JSON. The
                                         string is handled as constant string. In case of using the value as input
                                         parameter, the #LYD_ANYDATA_JSOND can be used for dynamically allocated
                                         string. */
    LYD_ANYDATA_JSOND = 0x03,       /**< In case of using value as input parameter, this enumeration is supposed to be
                                         used for dynamically allocated strings (it is actually combination of
                                         #LYD_ANYDATA_JSON and #LYD_ANYDATA_STRING (and it can be also specified as
                                         ORed value of the mentioned values. */
    LYD_ANYDATA_SXML = 0x04,        /**< value is string containing the serialized XML data. The string is handled as
                                         constant string. In case of using the value as input parameter, the
                                         #LYD_ANYDATA_SXMLD can be used for dynamically allocated string. */
    LYD_ANYDATA_SXMLD = 0x05,       /**< In case of using serialized XML value as input parameter, this enumeration is
                                         supposed to be used for dynamically allocated strings (it is actually
                                         combination of #LYD_ANYDATA_SXML and #LYD_ANYDATA_STRING (and it can be also
                                         specified as ORed value of the mentioned values). */
    LYD_ANYDATA_XML = 0x08,         /**< value is struct lyxml_elem*, the structure is directly connected into the
                                         anydata node without duplication, caller is supposed to not manipulate with the
                                         data after a successful call (including calling lyxml_free() on the provided
                                         data) */
    LYD_ANYDATA_DATATREE = 0x10,    /**< value is struct lyd_node* (first sibling), the structure is directly connected
                                         into the anydata node without duplication, caller is supposed to not manipulate
                                         with the data after a successful call (including calling lyd_free() on the
                                         provided data) */
} LYD_ANYDATA_VALUETYPE;

/**
 * @brief Attribute structure.
 *
 * The structure provides information about attributes of a data element. Such attributes partially
 * maps to annotations from draft-ietf-netmod-yang-metadata. In XML, they are represented as standard
 * XML attrbutes. In JSON, they are represented as JSON elements starting with the '@' character
 * (for more information, see the yang metadata draft.
 *
 */
struct lyd_attr {
    struct lyd_attr *next;           /**< pointer to the next attribute of the same element */
    struct lys_module *module;       /**< pointer to the attribute's module.
                                          TODO when annotations will be supported, point to the annotation definition
                                          and validate that the attribute is really defined there. Currently, we just
                                          believe that it is defined in the module it says */
    const char *name;                /**< attribute name */
    const char *value;               /**< attribute value */
};

/**
 * @brief node's value representation
 */
typedef union lyd_value_u {
    const char *binary;          /**< base64 encoded, NULL terminated string */
    struct lys_type_bit **bit;   /**< bitmap of pointers to the schema definition of the bit value that are set,
                                      its size is always the number of defined bits in the schema */
    int8_t bln;                  /**< 0 as false, 1 as true */
    int64_t dec64;               /**< decimal64: value = dec64 / 10^fraction-digits  */
    struct lys_type_enum *enm;   /**< pointer to the schema definition of the enumeration value */
    struct lys_ident *ident;     /**< pointer to the schema definition of the identityref value */
    struct lyd_node *instance;   /**< pointer to the instance-identifier target, note that if the tree was modified,
                                      the target (address) can be invalid - the pointer is correctly checked and updated
                                      by lyd_validate() */
    int8_t int8;                 /**< 8-bit signed integer */
    int16_t int16;               /**< 16-bit signed integer */
    int32_t int32;               /**< 32-bit signed integer */
    int64_t int64;               /**< 64-bit signed integer */
    struct lyd_node *leafref;    /**< pointer to the referenced leaf/leaflist instance in data tree */
    const char *string;          /**< string */
    uint8_t uint8;               /**< 8-bit unsigned integer */
    uint16_t uint16;             /**< 16-bit signed integer */
    uint32_t uint32;             /**< 32-bit signed integer */
    uint64_t uint64;             /**< 64-bit signed integer */
} lyd_val;

/**
 * @defgroup validityflags Validity flags
 * @ingroup datatree
 *
 * Validity flags for data nodes.
 *
 * @{
 */
#define LYD_VAL_OK       0x00    /**< Node is successfully validated including whole subtree */
#define LYD_VAL_UNIQUE   0x01    /**< Unique value(s) changed, applicable only to ::lys_node_list data nodes */
#define LYD_VAL_MAND     0x02    /**< Some child added/removed and it is needed to perform check for mandatory
                                      node or min/max constraints of direct list/leaflist children, applicable only
                                      to ::lys_node_list and ::lys_node_container data nodes, but if on any other node
                                      except ::lys_node_leaflist, it means checking that data node for duplicities.
                                      Additionally, it can be set on truly any node type and then status references
                                      are checked for this node if flag #LYD_OPT_OBSOLETE is used. */
#define LYD_VAL_LEAFREF  0x04    /**< Node is a leafref, which needs to be resolved (it is invalid, new possible
                                      resolvent, or something similar) */
#define LYD_VAL_INUSE    0x80    /**< Internal flag for note about various processing on data, should be used only
                                      internally and removed before libyang returns the node to the caller */
/**
 * @}
 */

/**
 * @brief Generic structure for a data node, directly applicable to the data nodes defined as #LYS_CONTAINER, #LYS_LIST
 * and #LYS_CHOICE.
 *
 * Completely fits to containers and choices and is compatible (can be used interchangeably except the #child member)
 * with all other lyd_node_* structures. All data nodes are provides as ::lyd_node structure by default.
 * According to the schema's ::lys_node#nodetype member, the specific object is supposed to be cast to
 * ::lyd_node_leaf_list or ::lyd_node_anydata structures. This structure fits only to #LYS_CONTAINER, #LYS_LIST and
 * #LYS_CHOICE values.
 *
 * To traverse through all the child elements or attributes, use #LY_TREE_FOR or #LY_TREE_FOR_SAFE macro.
 */
struct lyd_node {
    struct lys_node *schema;         /**< pointer to the schema definition of this node */
    uint8_t validity;                /**< [validity flags](@ref validityflags) */
    uint8_t dflt:1;                  /**< flag for default node */
    uint8_t when_status:3;           /**< bit for checking if the when-stmt condition is resolved - internal use only,
                                          do not use this value! */

    struct lyd_attr *attr;           /**< pointer to the list of attributes of this node */
    struct lyd_node *next;           /**< pointer to the next sibling node (NULL if there is no one) */
    struct lyd_node *prev;           /**< pointer to the previous sibling node \note Note that this pointer is
                                          never NULL. If there is no sibling node, pointer points to the node
                                          itself. In case of the first node, this pointer points to the last
                                          node in the list. */
    struct lyd_node *parent;         /**< pointer to the parent node, NULL in case of root node */
    struct lyd_node *child;          /**< pointer to the first child node \note Since other lyd_node_*
                                          structures represent end nodes, this member
                                          is replaced in those structures. Therefore, be careful with accessing
                                          this member without having information about the node type from the schema's
                                          ::lys_node#nodetype member. */
};

/**
 * @brief Structure for data nodes defined as #LYS_LEAF or #LYS_LEAFLIST.
 *
 * Extension for ::lyd_node structure. It replaces the ::lyd_node#child member by
 * three new members (#value, #value_str and #value_type) to provide
 * information about the value. The first five members (#schema, #attr, #next,
 * #prev and #parent) are compatible with the ::lyd_node's members.
 *
 * To traverse through all the child elements or attributes, use #LY_TREE_FOR or #LY_TREE_FOR_SAFE macro.
 */
struct lyd_node_leaf_list {
    struct lys_node *schema;         /**< pointer to the schema definition of this node which is ::lys_node_leaflist
                                          structure */
    uint8_t validity;                /**< [validity flags](@ref validityflags) */
    uint8_t dflt:1;                  /**< flag for default node */
    uint8_t when_status:3;           /**< bit for checking if the when-stmt condition is resolved - internal use only,
                                          do not use this value! */

    struct lyd_attr *attr;           /**< pointer to the list of attributes of this node */
    struct lyd_node *next;           /**< pointer to the next sibling node (NULL if there is no one) */
    struct lyd_node *prev;           /**< pointer to the previous sibling node \note Note that this pointer is
                                          never NULL. If there is no sibling node, pointer points to the node
                                          itself. In case of the first node, this pointer points to the last
                                          node in the list. */
    struct lyd_node *parent;         /**< pointer to the parent node, NULL in case of root node */

    /* struct lyd_node *child; should be here, but is not */

    /* leaflist's specific members */
    const char *value_str;           /**< string representation of value (for comparison, printing,...), always corresponds to value_type */
    lyd_val value;                   /**< node's value representation, always corresponds to schema->type.base */
    LY_DATA_TYPE value_type;         /**< type of the value in the node, mainly for union to avoid repeating of type detection,
                                          if (schema->type.base == LY_TYPE_LEAFREF), then value_type may be
                                          (LY_TYPE_LEAFREF_UNRES | leafref target value_type) and (value.leafref == NULL) */
};

/**
 * @brief Structure for data nodes defined as #LYS_ANYDATA or #LYS_ANYXML.
 *
 * Extension for ::lyd_node structure - replaces the ::lyd_node#child member by new #value member. The first five
 * members (#schema, #attr, #next, #prev and #parent) are compatible with the ::lyd_node's members.
 *
 * To traverse through all the child elements or attributes, use #LY_TREE_FOR or #LY_TREE_FOR_SAFE macro.
 */
struct lyd_node_anydata {
    struct lys_node *schema;         /**< pointer to the schema definition of this node which is ::lys_node_anydata
                                          structure */
    uint8_t validity;                /**< [validity flags](@ref validityflags) */
    uint8_t dflt:1;                  /**< flag for default node */
    uint8_t when_status:3;           /**< bit for checking if the when-stmt condition is resolved - internal use only,
                                          do not use this value! */

    struct lyd_attr *attr;           /**< pointer to the list of attributes of this node */
    struct lyd_node *next;           /**< pointer to the next sibling node (NULL if there is no one) */
    struct lyd_node *prev;           /**< pointer to the previous sibling node \note Note that this pointer is
                                          never NULL. If there is no sibling node, pointer points to the node
                                          itself. In case of the first node, this pointer points to the last
                                          node in the list. */
    struct lyd_node *parent;         /**< pointer to the parent node, NULL in case of root node */

    /* struct lyd_node *child; should be here, but is not */

    /* anyxml's specific members */
    LYD_ANYDATA_VALUETYPE value_type;/**< type of the stored anydata value */
    union {
        const char *str;             /**< string value, in case of printing as XML, characters like '<' or '&' are escaped */
        struct lyxml_elem *xml;      /**< xml tree */
        struct lyd_node *tree;       /**< libyang data tree, does not change the root's parent, so it is not possible
                                          to get from the data tree into the anydata/anyxml */
    } value;
};

/**
 * @brief list of possible types of differencies in #lyd_difflist
 */
typedef enum {
    LYD_DIFF_END = 0,        /**< end of the differences list */
    LYD_DIFF_DELETED,        /**< deleted node
                                  - Node is present in the first tree, but not in the second tree.
                                  - To make both trees the same the node in lyd_difflist::first can be deleted from the
                                    first tree. The pointer at the same index in the lyd_difflist::second array is
                                    NULL */
    LYD_DIFF_CHANGED,        /**< value of a leaf or anyxml is changed, the lyd_difflist::first and lyd_difflist::second
                                  points to the leaf/anyxml instances in the first and the second tree respectively. */
    LYD_DIFF_MOVEDAFTER1,    /**< user-ordered (leaf-)list item was moved.
                                  - To make both trees the same, all #LYD_DIFF_MOVEDAFTER1 transactions must be applied
                                  to the first tree in the strict order they appear in the difflist. The
                                  lyd_difflist::first points to the first tree node being moved and the
                                  lyd_difflist::second points to the first tree node after which the first node is
                                  supposed to be moved. If the second pointer is NULL, the node is being moved into
                                  the beginning as the first node of the (leaf-)list instances. */
    LYD_DIFF_CREATED,        /**< newly created node
                                  - Node is present in the second tree, but not in the first tree.
                                  - To make both trees the same the node in lyd_difflist::second is supposed to be
                                    inserted (copied via lyd_dup()) into the node (as a child) at the same index in the
                                    lyd_difflist::first array (where is its parent). If the lyd_difflist::first at the
                                    index is NULL, the missing node is top-level. */
    LYD_DIFF_MOVEDAFTER2     /**< similar to LYD_DIFF_MOVEDAFTER1, but this time the moved item is in the second tree.
                                  This type is always used in combination with (as a successor of) #LYD_DIFF_CREATED
                                  as an instruction to move the newly created node to a specific position. Note, that
                                  due to applicability to the second tree, the meaning of lyd_difflist:first and
                                  lyd_difflist:second is inverse in comparison to #LYD_DIFF_MOVEDAFTER1. The
                                  lyd_difflist::second points to the (previously) created node in the second tree and
                                  the lyd_difflist::first points to the predecessor node in the second tree. If the
                                  predecessor is NULL, the node is supposed to bes the first sibling. */
} LYD_DIFFTYPE;

/**
 * @brief Structure for the result of lyd_diff(), describing differences between two data trees.
 */
struct lyd_difflist {
    LYD_DIFFTYPE *type;      /**< array of the differences types, terminated by #LYD_DIFF_END value. */
    struct lyd_node **first; /**< array of nodes in the first tree for the specific type of difference, see the
                                  description of #LYD_DIFFTYPE values for more information. */
    struct lyd_node **second;/**< array of nodes in the second tree for the specific type of difference, see the
                                  description of #LYD_DIFFTYPE values for more information. */
};

/**
 * @brief Free the result of lyd_diff(). It frees the structure of the lyd_diff() result, not the referenced nodes.
 *
 * @param[in] diff The lyd_diff() result to free.
 */
void lyd_free_diff(struct lyd_difflist *diff);

/**
 * @brief Compare two data trees and provide list of differences.
 *
 * Note, that the \p first and the \p second must have the same schema parent (or they must be top-level elements).
 * In case of using #LYD_OPT_NOSIBLINGS, they both must be instances of the same schema node.
 *
 * Order of the resulting set follows these rules:
 * - To change the first tree into the second tree, the resulting transactions are supposed to be applied in the order
 *   they appear in the result. First, the changed (#LYD_DIFF_CHANGED) nodes are described followed by the deleted
 *   (#LYD_DIFF_DELETED) nodes. Then, the moving of the user-ordered nodes present in both trees (#LYD_DIFF_MOVEDAFTER1)
 *   follows and the last transactions in the results are the newly created (#LYD_DIFF_CREATED) nodes. These nodes are
 *   supposed to be added as the last siblings, but in some case they can need additional move. In such a case, the
 *   #LYD_DIFF_MOVEDAFTER2 transactions can appear.
 * - The order of the changed (#LYD_DIFF_CHANGED) and created (#LYD_DIFF_CREATED) follows the nodes order in the
 *   second tree - the current siblings are processed first and then the children are processed. Note, that this is
 *   actually not the BFS:
 *
 *           1     2
 *          / \   / \
 *         3   4 7   8
 *        / \
 *       5   6
 *
 * - The order of the deleted (#LYD_DIFF_DELETED) nodes is the DFS:
 *
 *           1     6
 *          / \   / \
 *         2   5 7   8
 *        / \
 *       3   4
 *
 * To change the first tree into the second one, it is necessary to follow the order of transactions described in
 * the result. Note, that it is not possible just to use the transactions in the reverse order to transform the
 * second tree into the first one. The transactions can be generalized (to be used on a different instance of the
 * first tree) using lyd_path() to get identifiers for the nodes used in the transactions.
 *
 * @param[in] first The first (sub)tree to compare. Without #LYD_OPT_NOSIBLINGS option, all siblings are
 *            taken into comparison. If NULL, all the \p second nodes are supposed to be top level and they will
 *            be marked as #LYD_DIFF_CREATED.
 * @param[in] second The second (sub)tree to compare. Without #LYD_OPT_NOSIBLINGS option, all siblings are
 *            taken into comparison. If NULL, all the \p first nodes will be marked as #LYD_DIFF_DELETED.
 * @param[in] options The @ref diffoptions are accepted.
 * @return NULL on error, the list of differences on success. In case the trees are the same, the first item in the
 *         lyd_difflist::type array is #LYD_DIFF_END. The returned structure is supposed to be freed by lyd_free_diff().
 */
struct lyd_difflist *lyd_diff(struct lyd_node *first, struct lyd_node *second, int options);

/**
 * @defgroup diffoptions Diff options
 * @ingroup datatree
 *
 * @{
 */
/* LYD_DIFFOPT_NOSIBLINGS value is the same as LYD_OPT_NOSIBLINGS due to backward compatibility. The LYD_OPT_NOSIBLINGS
 * was used previously as an option for lyd_diff(). */
#define LYD_DIFFOPT_NOSIBLINGS   0x0800 /**< The both trees to diff have to instantiate the same schema node so only the
                                             single subtree is compared. */
#define LYD_DIFFOPT_WITHDEFAULTS 0x0001 /**< Take default nodes with their values into account and handle them as part
                                             of both trees. In this case, a node with defined default value cannot be
                                             deleted, because when it is removed from a tree, it is implicitly replaced
                                             by the default node, so the node is not #LYD_DIFF_DELETED, but
                                             #LYD_DIFF_CHANGED. Note that in this case, applying the resulting
                                             transactions on the first tree does not result to the exact second tree,
                                             because instead of having implicit default nodes you are going to have
                                             explicit default nodes. */
/**@} diffoptions */

/**
 * @brief Build path (usable as XPath) of the data node.
 * @param[in] node Data node to be processed. Note that the node should be from a complete data tree, having a subtree
 *            (after using lyd_unlink()) can cause generating invalid paths.
 * @return NULL on error, on success the buffer for the resulting path is allocated and caller is supposed to free it
 * with free().
 */
char *lyd_path(struct lyd_node *node);

/**
 * @defgroup parseroptions Data parser options
 * @ingroup datatree
 *
 * Various options to change the data tree parsers behavior.
 *
 * Default behavior:
 * - in case of XML, parser reads all data from its input (file, memory, XML tree) including the case of not well-formed
 * XML document (multiple top-level elements) and if there is an unknown element, it is skipped including its subtree
 * (see the next point). This can be changed by the #LYD_OPT_NOSIBLINGS option which make parser to read only a single
 * tree (with a single root element) from its input.
 * - parser silently ignores the data without a matching node in schema trees. If the caller want to stop
 * parsing in case of presence of unknown data, the #LYD_OPT_STRICT can be used. The strict mode is useful for
 * NETCONF servers, since NETCONF clients should always send data according to the capabilities announced by the server.
 * On the other hand, the default non-strict mode is useful for clients receiving data from NETCONF server since
 * clients are not required to understand everything the server does. Of course, the optimal strategy for clients is
 * to use filtering to get only the required data. Having an unknown element of the known namespace is always an error.
 * The behavior can be changed by #LYD_OPT_STRICT option.
 * - using obsolete statements (status set to obsolete) just generates a warning, but the processing continues. The
 * behavior can be changed by #LYD_OPT_OBSOLETE option.
 * - parser expects that the provided data provides complete datastore content (both the configuration and state data)
 * and performs data validation according to all YANG rules. This can be a problem in case of representing NETCONF's
 * subtree filter data, edit-config's data or other type of data set - such data do not represent a complete data set
 * and some of the validation rules can fail. Therefore there are other options (within lower 8 bits) to make parser
 * to accept such a data.
 * - when parser evaluates when-stmt condition to false, the constrained subtree is automatically removed. If the
 * #LYD_OPT_NOAUTODEL is used, error is raised instead of silent auto delete. The option (and also this default
 * behavior) takes effect only in case of #LYD_OPT_DATA or #LYD_OPT_CONFIG type of data.
 * @{
 */

#define LYD_OPT_DATA       0x00 /**< Default type of data - complete datastore content with configuration as well as
                                     state data. */
#define LYD_OPT_CONFIG     0x01 /**< A configuration datastore - complete datastore without state data.
                                     Validation modifications:
                                     - status data are not allowed */
#define LYD_OPT_GET        0x02 /**< Data content from a NETCONF reply message to the NETCONF \<get\> operation.
                                     Validation modifications:
                                     - mandatory nodes can be omitted
                                     - leafrefs and instance-identifier are not resolved
                                     - list's keys/unique nodes are not required (so duplication is not checked) */
#define LYD_OPT_GETCONFIG  0x04 /**< Data content from a NETCONF reply message to the NETCONF \<get-config\> operation
                                     Validation modifications:
                                     - mandatory nodes can be omitted
                                     - leafrefs and instance-identifier are not resolved
                                     - list's keys/unique nodes are not required (so duplication is not checked)
                                     - status data are not allowed */
#define LYD_OPT_EDIT       0x08 /**< Content of the NETCONF \<edit-config\>'s config element.
                                     Validation modifications:
                                     - mandatory nodes can be omitted
                                     - leafrefs and instance-identifier are not resolved
                                     - status data are not allowed */
#define LYD_OPT_RPC        0x10 /**< Data represents RPC's input parameters. */
#define LYD_OPT_RPCREPLY   0x20 /**< Data represents RPC's output parameters (maps to NETCONF <rpc-reply> data). */
#define LYD_OPT_NOTIF      0x40 /**< Data represents an event notification data. */
#define LYD_OPT_NOTIF_FILTER 0x80 /**< Data represents a filtered event notification data.
                                       Validation modification:
                                       - the only requirement is that the data tree matches the schema tree */
#define LYD_OPT_TYPEMASK   0xff /**< Mask to filter data type options. Always only a single data type option (only
                                     single bit from the lower 8 bits) can be set. */

/* 0x100 reserved, used internally */
#define LYD_OPT_STRICT     0x0200 /**< Instead of silent ignoring data without schema definition, raise an error. */
#define LYD_OPT_DESTRUCT   0x0400 /**< Free the provided XML tree during parsing the data. With this option, the
                                       provided XML tree is affected and all succesfully parsed data are freed.
                                       This option is applicable only to lyd_parse_xml() function. */
#define LYD_OPT_OBSOLETE   0x0800 /**< Raise an error when an obsolete statement (status set to obsolete) is used. */
#define LYD_OPT_NOSIBLINGS 0x1000 /**< Parse only a single XML tree from the input. This option applies only to
                                       XML input data. */
#define LYD_OPT_TRUSTED    0x2000 /**< Data comes from a trusted source and it is not needed to validate them. Data
                                       are connected with the schema, but the most validation checks (mandatory nodes,
                                       list instance uniqueness, etc.) are not performed. This option does not make
                                       sense for lyd_validate() so it is ignored by this function. */
#define LYD_OPT_NOAUTODEL  0x4000 /**< Avoid automatic delete of subtrees with false when-stmt condition. The flag is
                                       applicable only in combination with LYD_OPT_DATA and LYD_OPT_CONFIG flags.
                                       If used, libyang generates validation error instead of silently removing the
                                       constrained subtree. */

/**@} parseroptions */

/**
 * @brief Parse (and validate according to appropriate schema from the given context) data.
 *
 * In case of LY_XML format, the data string is parsed completely. It means that when it contains
 * a non well-formed XML with multiple root elements, all those sibling XML trees are parsed. The
 * returned data node is a root of the first tree with other trees connected via the next pointer.
 * This behavior can be changed by #LYD_OPT_NOSIBLINGS option.
 *
 * @param[in] ctx Context to connect with the data tree being built here.
 * @param[in] data Serialized data in the specified format.
 * @param[in] format Format of the input data to be parsed.
 * @param[in] options Parser options, see @ref parseroptions.
 * @param[in] ... Variable arguments depend on \p options. If they include:
 *                - #LYD_OPT_DATA:
 *                - #LYD_OPT_CONFIG:
 *                - #LYD_OPT_GET:
 *                - #LYD_OPT_GETCONFIG:
 *                - #LYD_OPT_EDIT:
 *                  - no variable arguments expected.
 *                - #LYD_OPT_RPC:
 *                - #LYD_OPT_NOTIF:
 *                  - struct lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 *                - #LYD_OPT_RPCREPLY:
 *                  - const struct ::lyd_node *rpc_act - pointer to the whole RPC or action operation data
 *                    tree (the request) of the reply.
 *                  - const struct ::lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 * @return Pointer to the built data tree or NULL in case of empty \p data. To free the returned structure,
 *         use lyd_free(). In these cases, the function sets #ly_errno to LY_SUCCESS. In case of error,
 *         #ly_errno contains appropriate error code (see #LY_ERR).
 */
struct lyd_node *lyd_parse_mem(struct ly_ctx *ctx, const char *data, LYD_FORMAT format, int options, ...);

/**
 * @brief Read data from the given file descriptor.
 *
 * \note Current implementation supports only reading data from standard (disk) file, not from sockets, pipes, etc.
 *
 * In case of LY_XML format, the file content is parsed completely. It means that when it contains
 * a non well-formed XML with multiple root elements, all those sibling XML trees are parsed. The
 * returned data node is a root of the first tree with other trees connected via the next pointer.
 * This behavior can be changed by #LYD_OPT_NOSIBLINGS option.
 *
 * @param[in] ctx Context to connect with the data tree being built here.
 * @param[in] fd The standard file descriptor of the file containing the data tree in the specified format.
 * @param[in] format Format of the input data to be parsed.
 * @param[in] options Parser options, see @ref parseroptions.
 * @param[in] ... Variable arguments depend on \p options. If they include:
 *                - #LYD_OPT_DATA:
 *                - #LYD_OPT_CONFIG:
 *                - #LYD_OPT_GET:
 *                - #LYD_OPT_GETCONFIG:
 *                - #LYD_OPT_EDIT:
 *                  - no variable arguments expected.
 *                - #LYD_OPT_RPC:
 *                - #LYD_OPT_NOTIF:
 *                  - struct lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 *                - #LYD_OPT_RPCREPLY:
 *                  - const struct ::lyd_node *rpc_act - pointer to the whole RPC or action operation data
 *                    tree (the request) of the reply.
 *                  - const struct ::lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 * @return Pointer to the built data tree or NULL in case of empty file. To free the returned structure,
 *         use lyd_free(). In these cases, the function sets #ly_errno to LY_SUCCESS. In case of error,
 *         #ly_errno contains appropriate error code (see #LY_ERR).
 */
struct lyd_node *lyd_parse_fd(struct ly_ctx *ctx, int fd, LYD_FORMAT format, int options, ...);

/**
 * @brief Read data from the given file path.
 *
 * In case of LY_XML format, the file content is parsed completely. It means that when it contains
 * a non well-formed XML with multiple root elements, all those sibling XML trees are parsed. The
 * returned data node is a root of the first tree with other trees connected via the next pointer.
 * This behavior can be changed by #LYD_OPT_NOSIBLINGS option.
 *
 * @param[in] ctx Context to connect with the data tree being built here.
 * @param[in] path Path to the file containing the data tree in the specified format.
 * @param[in] format Format of the input data to be parsed.
 * @param[in] options Parser options, see @ref parseroptions.
 * @param[in] ... Variable arguments depend on \p options. If they include:
 *                - #LYD_OPT_DATA:
 *                - #LYD_OPT_CONFIG:
 *                - #LYD_OPT_GET:
 *                - #LYD_OPT_GETCONFIG:
 *                - #LYD_OPT_EDIT:
 *                  - no variable arguments expected.
 *                - #LYD_OPT_RPC:
 *                - #LYD_OPT_NOTIF:
 *                  - struct lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 *                - #LYD_OPT_RPCREPLY:
 *                  - const struct ::lyd_node *rpc_act - pointer to the whole RPC or action operation data
 *                    tree (the request) of the reply.
 *                  - const struct ::lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 * @return Pointer to the built data tree or NULL in case of empty file. To free the returned structure,
 *         use lyd_free(). In these cases, the function sets #ly_errno to LY_SUCCESS. In case of error,
 *         #ly_errno contains appropriate error code (see #LY_ERR).
 */
struct lyd_node *lyd_parse_path(struct ly_ctx *ctx, const char *path, LYD_FORMAT format, int options, ...);

/**
 * @brief Parse (and validate according to appropriate schema from the given context) XML tree.
 *
 * The output data tree is parsed from the given XML tree previously parsed by one of the
 * lyxml_read* functions.
 *
 * If there are some sibling elements of the \p root (data were read with #LYXML_PARSE_MULTIROOT option
 * or the provided root is a root element of a subtree), all the sibling nodes (previous as well as
 * following) are processed as well. The returned data node is a root of the first tree with other
 * trees connected via the next pointer. This behavior can be changed by #LYD_OPT_NOSIBLINGS option.
 *
 * When the function is used with #LYD_OPT_DESTRUCT, all the successfully parsed data including the
 * XML \p root and all its siblings (if #LYD_OPT_NOSIBLINGS is not used) are freed. Only with
 * #LYD_OPT_DESTRUCT option the \p root pointer is changed - if all the data are parsed, it is set
 * to NULL, otherwise it will hold the XML tree without the successfully parsed elements.
 *
 * The context must be the same as the context used to parse XML tree by lyxml_read* function.
 *
 * @param[in] ctx Context to connect with the data tree being built here.
 * @param[in,out] root XML tree to parse (convert) to data tree. By default, parser do not change the XML tree. However,
 *            when #LYD_OPT_DESTRUCT is specified in \p options, parser frees all successfully parsed data.
 * @param[in] options Parser options, see @ref parseroptions.
 * @param[in] ... Variable arguments depend on \p options. If they include:
 *                - #LYD_OPT_DATA:
 *                - #LYD_OPT_CONFIG:
 *                - #LYD_OPT_GET:
 *                - #LYD_OPT_GETCONFIG:
 *                - #LYD_OPT_EDIT:
 *                  - no variable arguments expected.
 *                - #LYD_OPT_RPC:
 *                - #LYD_OPT_NOTIF:
 *                  - struct lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 *                - #LYD_OPT_RPCREPLY:
 *                  - const struct ::lyd_node *rpc_act - pointer to the whole RPC or action operation data
 *                    tree (the request) of the reply.
 *                  - const struct ::lyd_node *data_tree - additional data tree that will be used
 *                    when checking any "when" or "must" conditions in the parsed tree that require
 *                    some nodes outside their subtree. It must be a list of top-level elements!
 * @return Pointer to the built data tree or NULL in case of empty \p root. To free the returned structure,
 *         use lyd_free(). In these cases, the function sets #ly_errno to LY_SUCCESS. In case of error,
 *         #ly_errno contains appropriate error code (see #LY_ERR).
 */
struct lyd_node *lyd_parse_xml(struct ly_ctx *ctx, struct lyxml_elem **root, int options,...);

/**
 * @brief Create a new container node in a data tree.
 *
 * @param[in] parent Parent node for the node being created. NULL in case of creating top level element.
 * @param[in] module Module with the node being created.
 * @param[in] name Schema node name of the new data node. The node can be #LYS_CONTAINER, #LYS_LIST,
 * #LYS_NOTIF, #LYS_RPC, or #LYS_ACTION.
 * @return New node, NULL on error.
 */
struct lyd_node *lyd_new(struct lyd_node *parent, const struct lys_module *module, const char *name);

/**
 * @brief Create a new leaf or leaflist node in a data tree with a string value that is converted to
 * the actual value.
 *
 * @param[in] parent Parent node for the node being created. NULL in case of creating top level element.
 * @param[in] module Module with the node being created.
 * @param[in] name Schema node name of the new data node.
 * @param[in] val_str String form of the value of the node being created. In case the type is #LY_TYPE_INST
 * or #LY_TYPE_IDENT, JSON node-id format is expected (nodes are prefixed with module names, not XML namespaces).
 * @return New node, NULL on error.
 */
struct lyd_node *lyd_new_leaf(struct lyd_node *parent, const struct lys_module *module, const char *name,
                              const char *val_str);

/**
 * @brief Change value of a leaf node.
 *
 * Despite the prototype allows to provide a leaflist node as \p leaf parameter, only leafs are accepted.
 * Also, changing the value of a list key is prohibited.
 *
 * As for the other data tree manipulation functions, the change is not fully validated to allow multiple changes
 * in the data tree. Therefore, when all changes on the data tree are done, caller is supposed to call lyd_validate()
 * to check that the result is valid data tree. Specifically, if a leafref leaf is changed, it is not checked that
 * the (leafref) value is correct.
 *
 * @param[in] leaf A leaf node to change.
 * @param[in] val_str String form of the new value to be set to the \p leaf. In case the type is #LY_TYPE_INST
 * or #LY_TYPE_IDENT, JSON node-id format is expected (nodes are prefixed with module names, not XML namespaces).
 * @return 0 on success, non-zero on error.
 */
int lyd_change_leaf(struct lyd_node_leaf_list *leaf, const char *val_str);

/**
 * @brief Create a new anydata or anyxml node in a data tree.
 *
 * This function is supposed to be a replacement for the lyd_new_anyxml_str() and lyd_new_anyxml_xml().
 *
 * @param[in] parent Parent node for the node being created. NULL in case of creating top level element.
 * @param[in] module Module with the node being created.
 * @param[in] name Schema node name of the new data node. The schema node determines if the anydata or anyxml node
 *            is created.
 * @param[in] value Pointer to the value data to be stored in the anydata/anyxml node. The type of the data is
 *            determined according to the \p value_type parameter.
 * @param[in] value_type Type of the provided data \p value.
 * @return New node, NULL on error.
 */
struct lyd_node *lyd_new_anydata(struct lyd_node *parent, const struct lys_module *module, const char *name,
                                 void *value, LYD_ANYDATA_VALUETYPE value_type);

/**
 * @brief Create a new container node in a data tree. Ignore RPC/action input nodes and instead use RPC/action output ones.
 *
 * @param[in] parent Parent node for the node being created. NULL in case of creating top level element.
 * @param[in] module Module with the node being created.
 * @param[in] name Schema node name of the new data node. The node should only be #LYS_CONTAINER or #LYS_LIST,
 * but accepted are also #LYS_NOTIF, #LYS_RPC, or #LYS_ACTION.
 * @return New node, NULL on error.
 */
struct lyd_node *lyd_new_output(struct lyd_node *parent, const struct lys_module *module, const char *name);

/**
 * @brief Create a new leaf or leaflist node in a data tree with a string value that is converted to
 * the actual value. Ignore RPC/action input nodes and instead use RPC/action output ones.
 *
 * @param[in] parent Parent node for the node being created. NULL in case of creating top level element.
 * @param[in] module Module with the node being created.
 * @param[in] name Schema node name of the new data node.
 * @param[in] val_str String form of the value of the node being created. In case the type is #LY_TYPE_INST
 * or #LY_TYPE_IDENT, JSON node-id format is expected (nodes are prefixed with module names, not XML namespaces).
 * @return New node, NULL on error.
 */
struct lyd_node *lyd_new_output_leaf(struct lyd_node *parent, const struct lys_module *module, const char *name,
                                     const char *val_str);

/**
 * @brief Create a new anydata or anyxml node in a data tree. Ignore RPC/action input nodes and instead use
 * RPC/action output ones.
 *
 * @param[in] parent Parent node for the node being created. NULL in case of creating top level element.
 * @param[in] module Module with the node being created.
 * @param[in] name Schema node name of the new data node. The schema node determines if the anydata or anyxml node
 *            is created.
 * @param[in] value Pointer to the value data to be stored in the anydata/anyxml node. The type of the data is
 *            determined according to the \p value_type parameter. Data are supposed to be dynamically allocated.
 *            Since it is directly attached into the created data node, caller is supposed to not manipulate with
 *            the data after a successful call (including calling free() on the provided data).
 * @param[in] value_type Type of the provided data \p value.
 * @return New node, NULL on error.
 */
struct lyd_node *lyd_new_output_anydata(struct lyd_node *parent, const struct lys_module *module, const char *name,
                                        void *value, LYD_ANYDATA_VALUETYPE value_type);

/**
 * @defgroup pathoptions Data path creation options
 * @ingroup datatree
 *
 * Various options to change lyd_new_path() behavior.
 *
 * Default behavior:
 * - if the target node already exists, an error is returned.
 * - the whole path to the target node is created (with any missing parents) if necessary.
 * - RPC output schema children are completely ignored in all modules. Input is searched and nodes created normally.
 * @{
 */

#define LYD_PATH_OPT_UPDATE   0x01 /**< If the target node exists and is a leaf, it is updated with the new value and returned.
                                        If the target node exists and is not a leaf, NULL is returned and no error set. */
#define LYD_PATH_OPT_NOPARENT 0x02 /**< If any parents of the target node exist, return an error. */
#define LYD_PATH_OPT_OUTPUT   0x04 /**< Changes the behavior to ignoring RPC/action input schema nodes and using only output ones. */

/** @} pathoptions */

/**
 * @brief Create a new data node based on a simple XPath.
 *
 * The new node is normally inserted at the end, either as the last child of a parent or as the last sibling
 * if working with top-level elements. However, when manipulating RPC input or output, schema ordering is
 * required and always guaranteed.
 *
 * If \p path points to a list key and the list does not exist, the key value from the predicate is used
 * and \p value is ignored.
 *
 * @param[in] data_tree Existing data tree to add to/modify. If creating RPCs/actions, there should only be one
 * RPC/action and either input or output, not both. Can be NULL.
 * @param[in] ctx Context to use. Mandatory if \p data_tree is NULL.
 * @param[in] path Simple absolute data XPath of the new node. It can contain only simple node addressing with optional
 * module names as prefixes. List nodes must have predicates, one for each list key in the correct order and
 * with its value as well, leaves and leaf-lists can have predicates too that have preference over \p value,
 * see @ref howtoxpath.
 * @param[in] value Value of the new leaf/lealf-list (const char*). If creating anydata or anyxml, the following
 *            \p value_type parameter is required to be specified correctly. If creating nodes of other types, the
 *            parameter is ignored.
 * @param[in] value_type Type of the provided \p value parameter in case of creating anydata or anyxml node.
 * @param[in] options Bitmask of options flags, see @ref pathoptions.
 * @return First created (or updated with #LYD_PATH_OPT_UPDATE) node,
 * NULL if #LYD_PATH_OPT_UPDATE was used and the full path exists or the leaf original value matches \p value,
 * NULL and ly_errno is set on error.
 */
struct lyd_node *lyd_new_path(struct lyd_node *data_tree, struct ly_ctx *ctx, const char *path, void *value,
                              LYD_ANYDATA_VALUETYPE value_type, int options);

/**
 * @brief Create a copy of the specified data tree \p node. Namespaces are copied as needed,
 * schema references are kept the same.
 *
 * The duplicated tree (the result) is created non-validated. To guarantee safe operations
 * on it in the future, the recommended way of using it is after finishing all the partial data tree
 * modifications, validate all the trees where the copies from this function were placed (or the copies
 * themselves if they were kept separate).
 *
 * @param[in] node Data tree node to be duplicated.
 * @param[in] recursive 1 if all children are supposed to be also duplicated.
 * @return Created copy of the provided data \p node.
 */
struct lyd_node *lyd_dup(const struct lyd_node *node, int recursive);

/**
 * @brief Merge a (sub)tree into a data tree. Missing nodes are merged, leaf values updated.
 * If \p target and \p source do not share the top-level schema node, even if they
 * are from different modules, \p source parents up to top-level node will be created and
 * linked to the \p target (but only containers can be created this way, lists need keys,
 * so if lists are missing, an error will be returned).
 *
 * In short, this function will always try to return a fully valid data tree and will fail
 * if it is not possible. Also, in some less common cases, despite both trees \p target and
 * \p source are valid, the resulting tree may be invalid and this function will succeed.
 * If you know there are such possibilities in your data trees or you are not sure, always
 * validate the resulting merged \p target tree.
 *
 * @param[in] target Top-level (or an RPC output child) data tree to merge to. Must be valid.
 * @param[in] source Data tree to merge \p target with. Must be valid (at least as a subtree).
 * @param[in] options Bitmask of 2 option flags:
 * - #LYD_OPT_DESTRUCT - spend \p source in the function, otherwise \p source is left untouched,
 * - #LYD_OPT_NOSIBLINGS - merge only the \p source subtree (ignore siblings), otherwise merge
 * \p source and all its succeeding siblings (preceeding ones are still ignored!),
 * - #LYD_OPT_EXPLICIT - when merging an explicitly set node and a default node, always put
 * the explicit node into \p target, otherwise the node which is in \p source is used.
 * @return 0 on success, nonzero in case of an error.
 */
int lyd_merge(struct lyd_node *target, const struct lyd_node *source, int options);

#define LYD_OPT_EXPLICIT 0x0100

/**
 * @brief Insert the \p node element as child to the \p parent element. The \p node is inserted as a last child of the
 * \p parent.
 *
 * - if the node is part of some other tree, it is automatically unlinked.
 * - if the node is the first node of a node list (with no parent), all the subsequent nodes are also inserted.
 * - if the key of a list is being inserted, it is placed into a correct position instead of being placed as the last
 * element.
 * - if the target tree includes the default instance of the node being inserted, the default node is silently replaced
 * by the new node.
 * - if a default node is being inserted and the target tree already contains non-default instance, the existing
 * instance is silently replaced. If it contains the exact same default node, it is replaced as well.
 * - if a non-default node is being inserted and there is already its non-default instance in the target tree, the new
 * node is inserted and it is up to the caller to solve the presence of multiple instances afterwards.
 *
 * Note that this function differs from lyd_insert_before() and lyd_insert_after() because the position of the
 * node being inserted is determined automatically according to the rules described above. In contrast to
 * lyd_insert_parent(), lyd_insert() can not be used for top-level elements since the \p parent parameter must not be
 * NULL. If inserting something larger and not fitting the mentioned use-cases (or simply if unsure), you can always
 * use lyd_merge(), it should be able to handle any situation.
 *
 * @param[in] parent Parent node for the \p node being inserted.
 * @param[in] node The node being inserted.
 * @return 0 on success, nonzero in case of error, e.g. when the node is being inserted to an inappropriate place
 * in the data tree.
 */
int lyd_insert(struct lyd_node *parent, struct lyd_node *node);

/**
 * @brief Insert the \p node element as a last sibling of the specified \p sibling element.
 *
 * - if the node is part of some other tree, it is automatically unlinked.
 * - if the node is the first node of a node list (with no parent), all the subsequent nodes are also inserted.
 * - if the key of a list is being inserted, it is placed into a correct position instead of being placed as the last
 * element.
 * - if the target tree includes the default instance of the node being inserted, the default node is silently replaced
 * by the new node.
 * - if a default node is being inserted and the target tree already contains non-default instance, the existing
 * instance is silently replaced. If it contains the exact same default node, it is replaced as well.
 * - if a non-default node is being inserted and there is already its non-default instance in the target tree, the new
 * node is inserted and it is up to the caller to solve the presence of multiple instances afterwards.
 *
 * Note that this function differs from lyd_insert_before() and lyd_insert_after() because the position of the
 * node being inserted is determined automatically as in the case of lyd_insert(). In contrast to lyd_insert(),
 * lyd_insert_sibling() can be used to insert top-level elements. If inserting something larger and not fitting
 * the mentioned use-cases (or simply if unsure), you can always use lyd_merge(), it should be able to handle
 * any situation.
 *
 * @param[in,out] sibling Sibling node as a reference where to insert the \p node. When function succeeds, the sibling
 * is always set to point to the first sibling node. Note that in some cases described above, the provided sibling
 * node could be removed from the tree.
 * @param[in] node The node being inserted.
 * @return 0 on success, nonzero in case of error, e.g. when the node is being inserted to an inappropriate place
 * in the data tree.
 */
int lyd_insert_sibling(struct lyd_node **sibling, struct lyd_node *node);

/**
 * @brief Insert the \p node element after the \p sibling element. If \p node and \p siblings are already
 * siblings (just moving \p node position), skip validation.
 *
 * - if the target tree includes the default instance of the node being inserted, the default node is silently removed.
 * - if a default node is being inserted and the target tree already contains non-default instance, the existing
 * instance is removed. If it contains the exact same default node, it is removed as well.
 * - if a non-default node is being inserted and there is already its non-default instance in the target tree, the new
 * node is inserted and it is up to the caller to solve the presence of multiple instances afterwards.
 *
 * @param[in] sibling The data tree node before which the \p node will be inserted.
 * @param[in] node The data tree node to be inserted. If the node is connected somewhere, it is unlinked first.
 * @return 0 on success, nonzero in case of error, e.g. when the node is being inserted to an inappropriate place
 * in the data tree.
 */
int lyd_insert_before(struct lyd_node *sibling, struct lyd_node *node);

/**
 * @brief Insert the \p node element after the \p sibling element. If \p node and \p siblings are already
 * siblings (just moving \p node position), skip validation.
 *
 * - if the target tree includes the default instance of the node being inserted, the default node is silently removed.
 * - if a default node is being inserted and the target tree already contains non-default instance, the existing
 * instance is removed. If it contains the exact same default node, it is removed as well.
 * - if a non-default node is being inserted and there is already its non-default instance in the target tree, the new
 * node is inserted and it is up to the caller to solve the presence of multiple instances afterwards.
 *
 * @param[in] sibling The data tree node before which the \p node will be inserted. If \p node and \p siblings
 * are already siblings (just moving \p node position), skip validation.
 * @param[in] node The data tree node to be inserted. If the node is connected somewhere, it is unlinked first.
 * @return 0 on success, nonzero in case of error, e.g. when the node is being inserted to an inappropriate place
 * in the data tree.
 */
int lyd_insert_after(struct lyd_node *sibling, struct lyd_node *node);

/**
 * @brief Order siblings according to the schema node ordering.
 *
 * If the siblings include data nodes from other modules, they are
 * sorted based on the module order in the context.
 *
 * @param[in] sibling Node, whose siblings will be sorted.
 * @param[in] recursive Whether sort all siblings of siblings, recursively.
 * @return 0 on success, nonzero in case of an error.
 */
int lyd_schema_sort(struct lyd_node *sibling, int recursive);

/**
 * @brief Search in the given data for instances of nodes matching the provided XPath expression.
 *
 * The XPath expression is evaluated on data -> skip all non-data nodes (input, output, choice, case).
 *
 * Expr examples:
 *      "/ietf-yang-library:modules-state/module[name = 'ietf-yang-library']/namespace"
 *      "/ietf-netconf:get-config/source"
 *
 * @param[in] data Node in the data tree considered the context node if \p expr is relative,
 * otherwise any node.
 * @param[in] expr XPath expression filtering the matching nodes.
 * @return Set of found data nodes. If no nodes are matching \p expr or the result
 * would be a number, a string, or a boolean, the returned set is empty. In case of an error, NULL is returned.
 */
struct ly_set *lyd_find_xpath(const struct lyd_node *data, const char *expr);

/**
 * @brief Search in the given data for instances of the provided schema node.
 *
 * The \p data is used to find the data root and function then searches in the whole tree and all sibling trees.
 *
 * @param[in] data A node in the data tree to search.
 * @param[in] schema Schema node of the data nodes caller want to find.
 * @return Set of found data nodes. If no data node is found, the returned set is empty.
 * In case of error, NULL is returned.
 */
struct ly_set *lyd_find_instance(const struct lyd_node *data, const struct lys_node *schema);

/**
 * @brief Get the first sibling of the given node.
 *
 * @param[in] node Node which first sibling is going to be the result.
 * @return The first sibling of the given node or the node itself if it is the first child of the parent.
 */
struct lyd_node *lyd_first_sibling(struct lyd_node *node);

/**
 * @brief Validate \p node data subtree.
 *
 * @param[in,out] node Data tree to be validated. In case the \p options does not includes #LYD_OPT_NOAUTODEL, libyang
 *                     can modify the provided tree including the root \p node.
 * @param[in] options Options for the inserting data to the target data tree options, see @ref parseroptions.
 * @param[in] var_arg Variable argument depends on \p options. If they include:
 *                - #LYD_OPT_DATA:
 *                - #LYD_OPT_CONFIG:
 *                - #LYD_OPT_GET:
 *                - #LYD_OPT_GETCONFIG:
 *                - #LYD_OPT_EDIT:
 *                  - struct ly_ctx *ctx - context to use when \p node is NULL (for checking an empty tree),
 *                                         otherwise can be NULL.
 *                - #LYD_OPT_RPC:
 *                - #LYD_OPT_RPCREPLY:
 *                - #LYD_OPT_NOTIF:
 *                  - struct ::lyd_node *data_tree - additional data tree that will be used when checking
 *                                                   any "when" or "must" conditions in the \p node tree
 *                                                   that require some nodes outside their subtree. If set,
 *                                                   it must be a list of top-level elements!
 * @return 0 on success, nonzero in case of an error.
 */
int lyd_validate(struct lyd_node **node, int options, void *var_arg);

/**
 * @brief Get know if the node contain (despite implicit or explicit) default value.
 *
 * @param[in] node The leaf or leaf-list to check. Note, that leaf-list is marked as default only when the complete
 *                 and only the default set is present (node's siblings are also checked).
 * @return 1 if the node contains the default value, 0 otherwise.
 */
int lyd_wd_default(struct lyd_node_leaf_list *node);

/**
 * @brief Unlink the specified data subtree. All referenced namespaces are copied.
 *
 * Note, that the node's connection with the schema tree is kept. Therefore, in case of
 * reconnecting the node to a data tree using lyd_paste() it is necessary to paste it
 * to the appropriate place in the data tree following the schema.
 *
 * @param[in] node Data tree node to be unlinked (together with all children).
 * @return 0 for success, nonzero for error
 */
int lyd_unlink(struct lyd_node *node);

/**
 * @brief Free (and unlink) the specified data subtree. Use carefully, since libyang silently creates default nodes,
 * it is always better to use lyd_free_withsiblings() to free the complete data tree.
 *
 * @param[in] node Root of the (sub)tree to be freed.
 */
void lyd_free(struct lyd_node *node);

/**
 * @brief Free (and unlink) the specified data tree and all its siblings (preceding as well as following).
 *
 * @param[in] node One of the siblings root element of the (sub)trees to be freed.
 */
void lyd_free_withsiblings(struct lyd_node *node);

/**
 * @brief Insert attribute into the data node.
 *
 * @param[in] parent Data node where to place the attribute
 * @param[in] mod An alternative way to specify attribute's module (namespace) used in case the \p name does
 *            not include prefix. If neither prefix in the \p name nor mod is specified, the attribute's
 *            module is inherited from the \p parent node. It is not allowed to have attributes with no
 *            module (namespace).
 * @param[in] name Attribute name. The string can include the attribute's module (namespace) as the name's
 *            prefix (prefix:name). Prefix must be the name of one of the schema in the \p parent's context.
 *            If the prefix is not specified, the \p mod parameter is used. If neither of these parameters is
 *            usable, attribute inherits module (namespace) from the \p parent node. It is not allowed to
 *            have attributes with no module (namespace).
 * @param[in] value Attribute value
 * @return pointer to the created attribute (which is already connected in \p parent) or NULL on error.
 */
struct lyd_attr *lyd_insert_attr(struct lyd_node *parent, const struct lys_module *mod, const char *name,
                                 const char *value);

/**
 * @brief Destroy data attribute
 *
 * If the attribute to destroy is a member of a node attribute list, it is necessary to
 * provide the node itself as \p parent to keep the list consistent.
 *
 * @param[in] ctx Context where the attribute was created (usually it is the context of the \p parent)
 * @param[in] parent Parent node where the attribute is placed
 * @param[in] attr Attribute to destroy
 * @param[in] recursive Zero to destroy only the attribute, non-zero to destroy also all the subsequent attributes
 *            in the list.
 */
void lyd_free_attr(struct ly_ctx *ctx, struct lyd_node *parent, struct lyd_attr *attr, int recursive);

/**
 * @brief Return main module of the data tree node.
 *
 * In case of regular YANG module, it returns ::lys_node#module pointer,
 * but in case of submodule, it returns pointer to the main module.
 *
 * @param[in] node Data tree node to be examined
 * @return pointer to the main module (schema structure), NULL in case of error.
 */
struct lys_module *lyd_node_module(const struct lyd_node *node);

/**
 * @brief Get the type structure of a leaf. In case of union, the correct
 * specific type is found.
 *
 * @param[in] leaf Leaf to examine.
 * @return Type structure of \p leaf, NULL on error.
 */
const struct lys_type *lyd_leaf_type(const struct lyd_node_leaf_list *leaf);

/**
* @brief Print data tree in the specified format.
*
* Same as lyd_print(), but it allocates memory and store the data into it.
* It is up to caller to free the returned string by free().
*
* @param[out] strp Pointer to store the resulting dump.
* @param[in] root Root node of the data tree to print. It can be actually any (not only real root)
* node of the data tree to print the specific subtree.
* @param[in] format Data output format.
* @param[in] options [printer flags](@ref printerflags).
* @return 0 on success, 1 on failure (#ly_errno is set).
*/
int lyd_print_mem(char **strp, const struct lyd_node *root, LYD_FORMAT format, int options);

/**
 * @brief Print data tree in the specified format.
 *
 * Same as lyd_print(), but output is written into the specified file descriptor.
 *
 * @param[in] root Root node of the data tree to print. It can be actually any (not only real root)
 * node of the data tree to print the specific subtree.
 * @param[in] fd File descriptor where to print the data.
 * @param[in] format Data output format.
 * @param[in] options [printer flags](@ref printerflags).
 * @return 0 on success, 1 on failure (#ly_errno is set).
 */
int lyd_print_fd(int fd, const struct lyd_node *root, LYD_FORMAT format, int options);

/**
 * @brief Print data tree in the specified format.
 *
 * To write data into a file descriptor, use lyd_print_fd().
 *
 * @param[in] root Root node of the data tree to print. It can be actually any (not only real root)
 * node of the data tree to print the specific subtree.
 * @param[in] f File stream where to print the data.
 * @param[in] format Data output format.
 * @param[in] options [printer flags](@ref printerflags).
 * @return 0 on success, 1 on failure (#ly_errno is set).
 */
int lyd_print_file(FILE *f, const struct lyd_node *root, LYD_FORMAT format, int options);

/**
 * @brief Print data tree in the specified format.
 *
 * Same as lyd_print(), but output is written via provided callback.
 *
 * @param[in] root Root node of the data tree to print. It can be actually any (not only real root)
 * node of the data tree to print the specific subtree.
 * @param[in] writeclb Callback function to write the data (see write(1)).
 * @param[in] arg Optional caller-specific argument to be passed to the \p writeclb callback.
 * @param[in] format Data output format.
 * @param[in] options [printer flags](@ref printerflags).
 * @return 0 on success, 1 on failure (#ly_errno is set).
 */
int lyd_print_clb(ssize_t (*writeclb)(void *arg, const void *buf, size_t count), void *arg,
                  const struct lyd_node *root, LYD_FORMAT format, int options);

/**
 * @brief Get the double value of a decimal64 leaf/leaf-list.
 *
 * YANG decimal64 type enables higher precision numbers than IEEE 754 double-precision
 * format, so this conversion does not have to be lossless.
 *
 * @param[in] node Leaf/leaf-list of type decimal64.
 * @return Closest double equivalent to the decimal64 value.
 */
double lyd_dec64_to_double(const struct lyd_node *node);

/**@} */

#ifdef __cplusplus
}
#endif

#endif /* LY_TREE_DATA_H_ */