/** @file
 *  @brief Generic Attribute Profile handling.
 */

/*
 * Copyright (c) 2015-2016 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */
#ifndef ZEPHYR_INCLUDE_BLUETOOTH_GATT_H_
#define ZEPHYR_INCLUDE_BLUETOOTH_GATT_H_

/**
 * @brief Generic Attribute Profile (GATT)
 * @defgroup bt_gatt Generic Attribute Profile (GATT)
 * @ingroup bluetooth
 * @{
 */

#include <stddef.h>
#include <sys/slist.h>
#include <sys/types.h>
#include <sys/util.h>
#include <bluetooth/conn.h>
#include <bluetooth/uuid.h>
#include <bluetooth/att.h>

#ifdef __cplusplus
extern "C" {
#endif

/** GATT attribute permission bit field values */
enum {
	/** No operations supported, e.g. for notify-only */
	BT_GATT_PERM_NONE = 0,

	/** Attribute read permission. */
	BT_GATT_PERM_READ = BIT(0),

	/** Attribute write permission. */
	BT_GATT_PERM_WRITE = BIT(1),

	/** @brief Attribute read permission with encryption.
	 *
	 *  If set, requires encryption for read access.
	 */
	BT_GATT_PERM_READ_ENCRYPT = BIT(2),

	/** @brief Attribute write permission with encryption.
	 *
	 *  If set, requires encryption for write access.
	 */
	BT_GATT_PERM_WRITE_ENCRYPT = BIT(3),

	/** @brief Attribute read permission with authentication.
	 *
	 *  If set, requires encryption using authenticated link-key for read
	 *  access.
	 */
	BT_GATT_PERM_READ_AUTHEN = BIT(4),

	/** @brief Attribute write permission with authentication.
	 *
	 *  If set, requires encryption using authenticated link-key for write
	 *  access.
	 */
	BT_GATT_PERM_WRITE_AUTHEN = BIT(5),

	/** @brief Attribute prepare write permission.
	 *
	 *  If set, allows prepare writes with use of BT_GATT_WRITE_FLAG_PREPARE
	 *  passed to write callback.
	 */
	BT_GATT_PERM_PREPARE_WRITE = BIT(6),
};

/** @def BT_GATT_ERR
 *  @brief Construct error return value for attribute read and write callbacks.
 *
 *  @param _att_err ATT error code
 *
 *  @return Appropriate error code for the attribute callbacks.
 */
#define BT_GATT_ERR(_att_err) (-(_att_err))

/** GATT attribute write flags */
enum {
	/** @brief Attribute prepare write flag
	 *
	 * If set, write callback should only check if the device is
	 * authorized but no data shall be written.
	 */
	BT_GATT_WRITE_FLAG_PREPARE = BIT(0),

	/** @brief Attribute write command flag
	 *
	 * If set, indicates that write operation is a command (Write without
	 * response) which doesn't generate any response.
	 */
	BT_GATT_WRITE_FLAG_CMD = BIT(1),

	/** @brief Attribute write execute flag
	 *
	 * If set, indicates that write operation is a execute, which indicates
	 * the end of a long write, and will come after 1 or more
	 * @ref BT_GATT_WRITE_FLAG_PREPARE.
	 */
	BT_GATT_WRITE_FLAG_EXECUTE = BIT(2),
};

/** @brief GATT Attribute structure. */
struct bt_gatt_attr {
	/** Attribute UUID */
	const struct bt_uuid *uuid;

	/** @brief Attribute read callback
	 *
	 *  The callback can also be used locally to read the contents of the
	 *  attribute in which case no connection will be set.
	 *
	 *  @param conn   The connection that is requesting to read
	 *  @param attr   The attribute that's being read
	 *  @param buf    Buffer to place the read result in
	 *  @param len    Length of data to read
	 *  @param offset Offset to start reading from
	 *
	 *  @return Number fo bytes read, or in case of an error
	 *          BT_GATT_ERR() with a specific ATT error code.
	 */
	ssize_t (*read)(struct bt_conn *conn, const struct bt_gatt_attr *attr,
			void *buf, uint16_t len, uint16_t offset);

	/** @brief Attribute write callback
	 *
	 *  @param conn   The connection that is requesting to write
	 *  @param attr   The attribute that's being written
	 *  @param buf    Buffer with the data to write
	 *  @param len    Number of bytes in the buffer
	 *  @param offset Offset to start writing from
	 *  @param flags  Flags (BT_GATT_WRITE_*)
	 *
	 *  @return Number of bytes written, or in case of an error
	 *          BT_GATT_ERR() with a specific ATT error code.
	 */
	ssize_t	(*write)(struct bt_conn *conn, const struct bt_gatt_attr *attr,
			 const void *buf, uint16_t len, uint16_t offset,
			 uint8_t flags);

	/** Attribute user data */
	void *user_data;
	/** Attribute handle */
	uint16_t handle;
	/** Attribute permissions */
	uint8_t perm;
};

/** @brief GATT Service structure */
struct bt_gatt_service_static {
	/** Service Attributes */
	const struct bt_gatt_attr *attrs;
	/** Service Attribute count */
	size_t attr_count;
};

/** @brief GATT Service structure */
struct bt_gatt_service {
	/** Service Attributes */
	struct bt_gatt_attr *attrs;
	/** Service Attribute count */
	size_t attr_count;

	sys_snode_t node;
};

/** @brief Service Attribute Value. */
struct bt_gatt_service_val {
	/** Service UUID. */
	const struct bt_uuid *uuid;
	/** Service end handle. */
	uint16_t end_handle;
};

/** @brief Include Attribute Value. */
struct bt_gatt_include {
	/** Service UUID. */
	const struct bt_uuid *uuid;
	/** Service start handle. */
	uint16_t start_handle;
	/** Service end handle. */
	uint16_t end_handle;
};

/** @brief GATT callback structure. */
struct bt_gatt_cb {
	/** @brief The maximum ATT MTU on a connection has changed.
	 *
	 *  This callback notifies the application that the maximum TX or RX
	 *  ATT MTU has increased.
	 *
	 *  @param conn Connection object.
	 *  @param tx Updated TX ATT MTU.
	 *  @param rx Updated RX ATT MTU.
	 */
	void (*att_mtu_updated)(struct bt_conn *conn, uint16_t tx, uint16_t rx);

	sys_snode_t node;
};

/** Characteristic Properties Bit field values */

/** @def BT_GATT_CHRC_BROADCAST
 *  @brief Characteristic broadcast property.
 *
 *  If set, permits broadcasts of the Characteristic Value using Server
 *  Characteristic Configuration Descriptor.
 */
#define BT_GATT_CHRC_BROADCAST			0x01
/** @def BT_GATT_CHRC_READ
 *  @brief Characteristic read property.
 *
 *  If set, permits reads of the Characteristic Value.
 */
#define BT_GATT_CHRC_READ			0x02
/** @def BT_GATT_CHRC_WRITE_WITHOUT_RESP
 *  @brief Characteristic write without response property.
 *
 *  If set, permits write of the Characteristic Value without response.
 */
#define BT_GATT_CHRC_WRITE_WITHOUT_RESP		0x04
/** @def BT_GATT_CHRC_WRITE
 *  @brief Characteristic write with response property.
 *
 *  If set, permits write of the Characteristic Value with response.
 */
#define BT_GATT_CHRC_WRITE			0x08
/** @def BT_GATT_CHRC_NOTIFY
 *  @brief Characteristic notify property.
 *
 *  If set, permits notifications of a Characteristic Value without
 *  acknowledgment.
 */
#define BT_GATT_CHRC_NOTIFY			0x10
/** @def BT_GATT_CHRC_INDICATE
 *  @brief Characteristic indicate property.
 *
 * If set, permits indications of a Characteristic Value with acknowledgment.
 */
#define BT_GATT_CHRC_INDICATE			0x20
/** @def BT_GATT_CHRC_AUTH
 *  @brief Characteristic Authenticated Signed Writes property.
 *
 *  If set, permits signed writes to the Characteristic Value.
 */
#define BT_GATT_CHRC_AUTH			0x40
/** @def BT_GATT_CHRC_EXT_PROP
 *  @brief Characteristic Extended Properties property.
 *
 * If set, additional characteristic properties are defined in the
 * Characteristic Extended Properties Descriptor.
 */
#define BT_GATT_CHRC_EXT_PROP			0x80

/** @brief Characteristic Attribute Value. */
struct bt_gatt_chrc {
	/** Characteristic UUID. */
	const struct bt_uuid *uuid;
	/** Characteristic Value handle. */
	uint16_t value_handle;
	/** Characteristic properties. */
	uint8_t	properties;
};

/** Characteristic Extended Properties Bit field values */
#define BT_GATT_CEP_RELIABLE_WRITE		0x0001
#define BT_GATT_CEP_WRITABLE_AUX		0x0002

/** @brief Characteristic Extended Properties Attribute Value. */
struct bt_gatt_cep {
	/** Characteristic Extended properties */
	uint16_t properties;
};

/** Client Characteristic Configuration Values */

/** @def BT_GATT_CCC_NOTIFY
 *  @brief Client Characteristic Configuration Notification.
 *
 *  If set, changes to Characteristic Value shall be notified.
 */
#define BT_GATT_CCC_NOTIFY			0x0001
/** @def BT_GATT_CCC_INDICATE
 *  @brief Client Characteristic Configuration Indication.
 *
 *  If set, changes to Characteristic Value shall be indicated.
 */
#define BT_GATT_CCC_INDICATE			0x0002

/** Client Characteristic Configuration Attribute Value */
struct bt_gatt_ccc {
	/** Client Characteristic Configuration flags */
	uint16_t flags;
};

/** Server Characteristic Configuration Values */

/** @def BT_GATT_SCC_BROADCAST
 *  @brief Server Characteristic Configuration Broadcast
 *
 *  If set, the characteristic value shall be broadcast in the advertising data
 *  when the server is advertising.
 */
#define BT_GATT_SCC_BROADCAST                   0x0001

/** Server Characteristic Configuration Attribute Value */
struct bt_gatt_scc {
	/** Server Characteristic Configuration flags */
	uint16_t flags;
};

/** @brief GATT Characteristic Presentation Format Attribute Value. */
struct bt_gatt_cpf {
	/** Format of the value of the characteristic */
	uint8_t format;
	/** Exponent field to determine how the value of this characteristic is
	 * further formatted
	 */
	int8_t exponent;
	/** Unit of the characteristic */
	uint16_t unit;
	/** Name space of the description */
	uint8_t name_space;
	/** Description of the characteristic as defined in a higher layer profile */
	uint16_t description;
};

/**
 * @defgroup bt_gatt_server GATT Server APIs
 * @ingroup bt_gatt
 * @{
 */

/** @brief Register GATT callbacks.
 *
 *  Register callbacks to monitor the state of GATT.
 *
 *  @param cb Callback struct.
 */
void bt_gatt_cb_register(struct bt_gatt_cb *cb);

/** @brief Register GATT service.
 *
 *  Register GATT service. Applications can make use of
 *  macros such as BT_GATT_PRIMARY_SERVICE, BT_GATT_CHARACTERISTIC,
 *  BT_GATT_DESCRIPTOR, etc.
 *
 *  When using @kconfig{CONFIG_BT_SETTINGS} then all services that should have
 *  bond configuration loaded, i.e. CCC values, must be registered before
 *  calling @ref settings_load.
 *
 *  When using @kconfig{CONFIG_BT_GATT_CACHING} and @kconfig{CONFIG_BT_SETTINGS}
 *  then all services that should be included in the GATT Database Hash
 *  calculation should be added before calling @ref settings_load.
 *  All services registered after settings_load will trigger a new database hash
 *  calculation and a new hash stored.
 *
 *  @param svc Service containing the available attributes
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_service_register(struct bt_gatt_service *svc);

/** @brief Unregister GATT service.
 *
 *  @param svc Service to be unregistered.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_service_unregister(struct bt_gatt_service *svc);

/** @brief Check if GATT service is registered.
 *
 *  @param svc Service to be checked.
 *
 *  @return true if registered or false if not register.
 */
bool bt_gatt_service_is_registered(const struct bt_gatt_service *svc);

enum {
	BT_GATT_ITER_STOP = 0,
	BT_GATT_ITER_CONTINUE,
};

/** @typedef bt_gatt_attr_func_t
 *  @brief Attribute iterator callback.
 *
 *  @param attr Attribute found.
 *  @param handle Attribute handle found.
 *  @param user_data Data given.
 *
 *  @return BT_GATT_ITER_CONTINUE if should continue to the next attribute.
 *  @return BT_GATT_ITER_STOP to stop.
 */
typedef uint8_t (*bt_gatt_attr_func_t)(const struct bt_gatt_attr *attr,
				       uint16_t handle,
				       void *user_data);

/** @brief Attribute iterator by type.
 *
 *  Iterate attributes in the given range matching given UUID and/or data.
 *
 *  @param start_handle Start handle.
 *  @param end_handle End handle.
 *  @param uuid UUID to match, passing NULL skips UUID matching.
 *  @param attr_data Attribute data to match, passing NULL skips data matching.
 *  @param num_matches Number matches, passing 0 makes it unlimited.
 *  @param func Callback function.
 *  @param user_data Data to pass to the callback.
 */
void bt_gatt_foreach_attr_type(uint16_t start_handle, uint16_t end_handle,
			       const struct bt_uuid *uuid,
			       const void *attr_data, uint16_t num_matches,
			       bt_gatt_attr_func_t func,
			       void *user_data);

/** @brief Attribute iterator.
 *
 *  Iterate attributes in the given range.
 *
 *  @param start_handle Start handle.
 *  @param end_handle End handle.
 *  @param func Callback function.
 *  @param user_data Data to pass to the callback.
 */
static inline void bt_gatt_foreach_attr(uint16_t start_handle, uint16_t end_handle,
					bt_gatt_attr_func_t func,
					void *user_data)
{
	bt_gatt_foreach_attr_type(start_handle, end_handle, NULL, NULL, 0, func,
				  user_data);
}

/** @brief Iterate to the next attribute
 *
 *  Iterate to the next attribute following a given attribute.
 *
 *  @param attr Current Attribute.
 *
 *  @return The next attribute or NULL if it cannot be found.
 */
struct bt_gatt_attr *bt_gatt_attr_next(const struct bt_gatt_attr *attr);

/** @brief Find Attribute by UUID.
 *
 *  Find the attribute with the matching UUID.
 *  To limit the search to a service set the attr to the service attributes and
 *  the attr_count to the service attribute count .
 *
 *  @param attr        Pointer to an attribute that serves as the starting point
 *                     for the search of a match for the UUID.
 *                     Passing NULL will search the entire range.
 *  @param attr_count  The number of attributes from the starting point to
 *                     search for a match for the UUID.
 *                     Set to 0 to search until the end.
 *  @param uuid        UUID to match.
 */
struct bt_gatt_attr *bt_gatt_find_by_uuid(const struct bt_gatt_attr *attr,
					  uint16_t attr_count,
					  const struct bt_uuid *uuid);

/** @brief Get Attribute handle.
 *
 *  @param attr Attribute object.
 *
 *  @return Handle of the corresponding attribute or zero if the attribute
 *          could not be found.
 */
uint16_t bt_gatt_attr_get_handle(const struct bt_gatt_attr *attr);

/** @brief Get the handle of the characteristic value descriptor.
 *
 * @param attr A Characteristic Attribute.
 *
 * @note The user_data of the attribute must of type @ref bt_gatt_chrc.
 *
 * @return the handle of the corresponding Characteristic Value. The value will
 *         be zero (the invalid handle) if @p attr was not a characteristic
 *         attribute.
 */
uint16_t bt_gatt_attr_value_handle(const struct bt_gatt_attr *attr);

/** @brief Generic Read Attribute value helper.
 *
 *  Read attribute value from local database storing the result into buffer.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value.
 *  @param buf_len Buffer length.
 *  @param offset Start offset.
 *  @param value Attribute value.
 *  @param value_len Length of the attribute value.
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read(struct bt_conn *conn, const struct bt_gatt_attr *attr,
			  void *buf, uint16_t buf_len, uint16_t offset,
			  const void *value, uint16_t value_len);

/** @brief Read Service Attribute helper.
 *
 *  Read service attribute value from local database storing the result into
 *  buffer after encoding it.
 *  @note Only use this with attributes which user_data is a bt_uuid.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read_service(struct bt_conn *conn,
				  const struct bt_gatt_attr *attr,
				  void *buf, uint16_t len, uint16_t offset);

/** @def BT_GATT_SERVICE_DEFINE
 *  @brief Statically define and register a service.
 *
 *  Helper macro to statically define and register a service.
 *
 *  @param _name Service name.
 */
#define BT_GATT_SERVICE_DEFINE(_name, ...)				\
	const struct bt_gatt_attr attr_##_name[] = { __VA_ARGS__ };	\
	const STRUCT_SECTION_ITERABLE(bt_gatt_service_static, _name) =	\
					BT_GATT_SERVICE(attr_##_name)

#define _BT_GATT_ATTRS_ARRAY_DEFINE(n, _instances, _attrs_def)	\
	static struct bt_gatt_attr attrs_##n[] = _attrs_def(_instances[n])

#define _BT_GATT_SERVICE_ARRAY_ITEM(_n, _) BT_GATT_SERVICE(attrs_##_n)

/** @def BT_GATT_SERVICE_INSTANCE_DEFINE
 *  @brief Statically define service structure array.
 *
 *  Helper macro to statically define service structure array. Each element
 *  of the array is linked to the service attribute array which is also
 *  defined in this scope using _attrs_def macro.
 *
 *  @param _name         Name of service structure array.
 *  @param _instances    Array of instances to pass as user context to the
 *                       attribute callbacks.
 *  @param _instance_num Number of elements in instance array.
 *  @param _attrs_def    Macro provided by the user that defines attribute
 *                       array for the service. This macro should accept single
 *                       parameter which is the instance context.
 */
#define BT_GATT_SERVICE_INSTANCE_DEFINE(				 \
	_name, _instances, _instance_num, _attrs_def)			 \
	BUILD_ASSERT(ARRAY_SIZE(_instances) == _instance_num,		 \
		"The number of array elements does not match its size"); \
	LISTIFY(_instance_num, _BT_GATT_ATTRS_ARRAY_DEFINE, (;),	 \
		_instances, _attrs_def);				 \
	static struct bt_gatt_service _name[] = {			 \
		LISTIFY(_instance_num, _BT_GATT_SERVICE_ARRAY_ITEM, (,)) \
	}

/** @def BT_GATT_SERVICE
 *  @brief Service Structure Declaration Macro.
 *
 *  Helper macro to declare a service structure.
 *
 *  @param _attrs Service attributes.
 */
#define BT_GATT_SERVICE(_attrs)						\
{									\
	.attrs = _attrs,						\
	.attr_count = ARRAY_SIZE(_attrs),				\
}

/** @def BT_GATT_PRIMARY_SERVICE
 *  @brief Primary Service Declaration Macro.
 *
 *  Helper macro to declare a primary service attribute.
 *
 *  @param _service Service attribute value.
 */
#define BT_GATT_PRIMARY_SERVICE(_service)				\
	BT_GATT_ATTRIBUTE(BT_UUID_GATT_PRIMARY, BT_GATT_PERM_READ,	\
			 bt_gatt_attr_read_service, NULL, _service)

/** @def BT_GATT_SECONDARY_SERVICE
 *  @brief Secondary Service Declaration Macro.
 *
 *  Helper macro to declare a secondary service attribute.
 *
 *  @param _service Service attribute value.
 */
#define BT_GATT_SECONDARY_SERVICE(_service)				\
	BT_GATT_ATTRIBUTE(BT_UUID_GATT_SECONDARY, BT_GATT_PERM_READ,	\
			 bt_gatt_attr_read_service, NULL, _service)

/** @brief Read Include Attribute helper.
 *
 *  Read include service attribute value from local database storing the result
 *  into buffer after encoding it.
 *  @note Only use this with attributes which user_data is a bt_gatt_include.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read_included(struct bt_conn *conn,
				   const struct bt_gatt_attr *attr,
				   void *buf, uint16_t len, uint16_t offset);

/** @def BT_GATT_INCLUDE_SERVICE
 *  @brief Include Service Declaration Macro.
 *
 *  Helper macro to declare database internal include service attribute.
 *
 *  @param _service_incl the first service attribute of service to include
 */
#define BT_GATT_INCLUDE_SERVICE(_service_incl)				\
	BT_GATT_ATTRIBUTE(BT_UUID_GATT_INCLUDE, BT_GATT_PERM_READ,	\
			  bt_gatt_attr_read_included, NULL, _service_incl)

/** @brief Read Characteristic Attribute helper.
 *
 *  Read characteristic attribute value from local database storing the result
 *  into buffer after encoding it.
 *  @note Only use this with attributes which user_data is a bt_gatt_chrc.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read_chrc(struct bt_conn *conn,
			       const struct bt_gatt_attr *attr, void *buf,
			       uint16_t len, uint16_t offset);

#define BT_GATT_CHRC_INIT(_uuid, _handle, _props) \
{                                                 \
	.uuid = _uuid,                            \
	.value_handle = _handle,                  \
	.properties = _props,                     \
}

/** @def BT_GATT_CHARACTERISTIC
 *  @brief Characteristic and Value Declaration Macro.
 *
 *  Helper macro to declare a characteristic attribute along with its
 *  attribute value.
 *
 *  @param _uuid Characteristic attribute uuid.
 *  @param _props Characteristic attribute properties.
 *  @param _perm Characteristic Attribute access permissions.
 *  @param _read Characteristic Attribute read callback.
 *  @param _write Characteristic Attribute write callback.
 *  @param _user_data Characteristic Attribute user data.
 */
#define BT_GATT_CHARACTERISTIC(_uuid, _props, _perm, _read, _write, _user_data) \
	BT_GATT_ATTRIBUTE(BT_UUID_GATT_CHRC, BT_GATT_PERM_READ,                 \
			  bt_gatt_attr_read_chrc, NULL,                         \
			  ((struct bt_gatt_chrc[]) {                            \
				BT_GATT_CHRC_INIT(_uuid, 0U, _props),           \
						   })),                         \
	BT_GATT_ATTRIBUTE(_uuid, _perm, _read, _write, _user_data)

#if defined(CONFIG_BT_SETTINGS_CCC_LAZY_LOADING)
	#define BT_GATT_CCC_MAX (CONFIG_BT_MAX_CONN)
#elif defined(CONFIG_BT_CONN)
	#define BT_GATT_CCC_MAX (CONFIG_BT_MAX_PAIRED + CONFIG_BT_MAX_CONN)
#else
	#define BT_GATT_CCC_MAX 0
#endif

/** @brief GATT CCC configuration entry. */
struct bt_gatt_ccc_cfg {
	/** Local identity, BT_ID_DEFAULT in most cases. */
	uint8_t id;
	/** Remote peer address. */
	bt_addr_le_t peer;
	/** Configuration value. */
	uint16_t value;
};

/** Internal representation of CCC value */
struct _bt_gatt_ccc {
	/** Configuration for each connection */
	struct bt_gatt_ccc_cfg cfg[BT_GATT_CCC_MAX];

	/** Highest value of all connected peer's subscriptions */
	uint16_t value;

	/** @brief CCC attribute changed callback
	 *
	 *  @param attr   The attribute that's changed value
	 *  @param value  New value
	 */
	void (*cfg_changed)(const struct bt_gatt_attr *attr, uint16_t value);

	/** @brief CCC attribute write validation callback
	 *
	 *  @param conn   The connection that is requesting to write
	 *  @param attr   The attribute that's being written
	 *  @param value  CCC value to write
	 *
	 *  @return Number of bytes to write, or in case of an error
	 *          BT_GATT_ERR() with a specific error code.
	 */
	ssize_t (*cfg_write)(struct bt_conn *conn,
			     const struct bt_gatt_attr *attr, uint16_t value);

	/** @brief CCC attribute match handler
	 *
	 *  Indicate if it is OK to send a notification or indication
	 *  to the subscriber.
	 *
	 *  @param conn   The connection that is being checked
	 *  @param attr   The attribute that's being checked
	 *
	 *  @return true  if application has approved notification/indication,
	 *          false if application does not approve.
	 */
	bool (*cfg_match)(struct bt_conn *conn,
			  const struct bt_gatt_attr *attr);
};

/** @brief Read Client Characteristic Configuration Attribute helper.
 *
 *  Read CCC attribute value from local database storing the result into buffer
 *  after encoding it.
 *
 *  @note Only use this with attributes which user_data is a _bt_gatt_ccc.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read_ccc(struct bt_conn *conn,
			      const struct bt_gatt_attr *attr, void *buf,
			      uint16_t len, uint16_t offset);

/** @brief Write Client Characteristic Configuration Attribute helper.
 *
 *  Write value in the buffer into CCC attribute.
 *
 *  @note Only use this with attributes which user_data is a _bt_gatt_ccc.
 *
 *  @param conn Connection object.
 *  @param attr Attribute to read.
 *  @param buf Buffer to store the value read.
 *  @param len Buffer length.
 *  @param offset Start offset.
 *  @param flags Write flags.
 *
 *  @return number of bytes written in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_write_ccc(struct bt_conn *conn,
			       const struct bt_gatt_attr *attr, const void *buf,
			       uint16_t len, uint16_t offset, uint8_t flags);


/** @def BT_GATT_CCC_INITIALIZER
 *  @brief Initialize Client Characteristic Configuration Declaration Macro.
 *
 *  Helper macro to initialize a Managed CCC attribute value.
 *
 *  @param _changed Configuration changed callback.
 *  @param _write Configuration write callback.
 *  @param _match Configuration match callback.
 */
#define BT_GATT_CCC_INITIALIZER(_changed, _write, _match) \
	{                                            \
		.cfg = {},                           \
		.cfg_changed = _changed,             \
		.cfg_write = _write,                 \
		.cfg_match = _match,                 \
	}

/** @def BT_GATT_CCC_MANAGED
 *  @brief Managed Client Characteristic Configuration Declaration Macro.
 *
 *  Helper macro to declare a Managed CCC attribute.
 *
 *  @param _ccc CCC attribute user data, shall point to a _bt_gatt_ccc.
 *  @param _perm CCC access permissions.
 */
#define BT_GATT_CCC_MANAGED(_ccc, _perm)				\
	BT_GATT_ATTRIBUTE(BT_UUID_GATT_CCC, _perm,			\
			bt_gatt_attr_read_ccc, bt_gatt_attr_write_ccc,  \
			_ccc)

/** @def BT_GATT_CCC
 *  @brief Client Characteristic Configuration Declaration Macro.
 *
 *  Helper macro to declare a CCC attribute.
 *
 *  @param _changed Configuration changed callback.
 *  @param _perm CCC access permissions.
 */
#define BT_GATT_CCC(_changed, _perm)				\
	BT_GATT_CCC_MANAGED(((struct _bt_gatt_ccc[])			\
		{BT_GATT_CCC_INITIALIZER(_changed, NULL, NULL)}), _perm)

/** @brief Read Characteristic Extended Properties Attribute helper
 *
 *  Read CEP attribute value from local database storing the result into buffer
 *  after encoding it.
 *
 *  @note Only use this with attributes which user_data is a bt_gatt_cep.
 *
 *  @param conn Connection object
 *  @param attr Attribute to read
 *  @param buf Buffer to store the value read
 *  @param len Buffer length
 *  @param offset Start offset
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read_cep(struct bt_conn *conn,
			      const struct bt_gatt_attr *attr, void *buf,
			      uint16_t len, uint16_t offset);

/** @def BT_GATT_CEP
 *  @brief Characteristic Extended Properties Declaration Macro.
 *
 *  Helper macro to declare a CEP attribute.
 *
 *  @param _value Pointer to a struct bt_gatt_cep.
 */
#define BT_GATT_CEP(_value)						\
	BT_GATT_DESCRIPTOR(BT_UUID_GATT_CEP, BT_GATT_PERM_READ,		\
			  bt_gatt_attr_read_cep, NULL, (void *)_value)

/** @brief Read Characteristic User Description Descriptor Attribute helper
 *
 *  Read CUD attribute value from local database storing the result into buffer
 *  after encoding it.
 *
 *  @note Only use this with attributes which user_data is a NULL-terminated C
 *        string.
 *
 *  @param conn Connection object
 *  @param attr Attribute to read
 *  @param buf Buffer to store the value read
 *  @param len Buffer length
 *  @param offset Start offset
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read_cud(struct bt_conn *conn,
			      const struct bt_gatt_attr *attr, void *buf,
			      uint16_t len, uint16_t offset);

/** @def BT_GATT_CUD
 *  @brief Characteristic User Format Descriptor Declaration Macro.
 *
 *  Helper macro to declare a CUD attribute.
 *
 *  @param _value User description NULL-terminated C string.
 *  @param _perm Descriptor attribute access permissions.
 */
#define BT_GATT_CUD(_value, _perm)					\
	BT_GATT_DESCRIPTOR(BT_UUID_GATT_CUD, _perm, bt_gatt_attr_read_cud, \
			   NULL, (void *)_value)

/** @brief Read Characteristic Presentation format Descriptor Attribute helper
 *
 *  Read CPF attribute value from local database storing the result into buffer
 *  after encoding it.
 *
 *  @note Only use this with attributes which user_data is a bt_gatt_pf.
 *
 *  @param conn Connection object
 *  @param attr Attribute to read
 *  @param buf Buffer to store the value read
 *  @param len Buffer length
 *  @param offset Start offset
 *
 *  @return number of bytes read in case of success or negative values in
 *          case of error.
 */
ssize_t bt_gatt_attr_read_cpf(struct bt_conn *conn,
			      const struct bt_gatt_attr *attr, void *buf,
			      uint16_t len, uint16_t offset);

/** @def BT_GATT_CPF
 *  @brief Characteristic Presentation Format Descriptor Declaration Macro.
 *
 *  Helper macro to declare a CPF attribute.
 *
 *  @param _value Pointer to a struct bt_gatt_cpf.
 */
#define BT_GATT_CPF(_value)						\
	BT_GATT_DESCRIPTOR(BT_UUID_GATT_CPF, BT_GATT_PERM_READ,		\
			  bt_gatt_attr_read_cpf, NULL, (void *)_value)

/** @def BT_GATT_DESCRIPTOR
 *  @brief Descriptor Declaration Macro.
 *
 *  Helper macro to declare a descriptor attribute.
 *
 *  @param _uuid Descriptor attribute uuid.
 *  @param _perm Descriptor attribute access permissions.
 *  @param _read Descriptor attribute read callback.
 *  @param _write Descriptor attribute write callback.
 *  @param _user_data Descriptor attribute user data.
 */
#define BT_GATT_DESCRIPTOR(_uuid, _perm, _read, _write, _user_data)	\
	BT_GATT_ATTRIBUTE(_uuid, _perm, _read, _write, _user_data)

/** @def BT_GATT_ATTRIBUTE
 *  @brief Attribute Declaration Macro.
 *
 *  Helper macro to declare an attribute.
 *
 *  @param _uuid Attribute uuid.
 *  @param _perm Attribute access permissions.
 *  @param _read Attribute read callback.
 *  @param _write Attribute write callback.
 *  @param _user_data Attribute user data.
 */
#define BT_GATT_ATTRIBUTE(_uuid, _perm, _read, _write, _user_data)	\
{									\
	.uuid = _uuid,							\
	.read = _read,							\
	.write = _write,						\
	.user_data = _user_data,					\
	.handle = 0,							\
	.perm = _perm,							\
}

/** @brief Notification complete result callback.
 *
 *  @param conn Connection object.
 *  @param user_data Data passed in by the user.
 */
typedef void (*bt_gatt_complete_func_t) (struct bt_conn *conn, void *user_data);

struct bt_gatt_notify_params {
	/** @brief Notification Attribute UUID type
	 *
	 *  Optional, use to search for an attribute with matching UUID when
	 *  the attribute object pointer is not known.
	 */
	const struct bt_uuid *uuid;
	/** @brief Notification Attribute object
	 *
	 *  Optional if uuid is provided, in this case it will be used as start
	 *  range to search for the attribute with the given UUID.
	 */
	const struct bt_gatt_attr *attr;
	/** Notification Value data */
	const void *data;
	/** Notification Value length */
	uint16_t len;
	/** Notification Value callback */
	bt_gatt_complete_func_t func;
	/** Notification Value callback user data */
	void *user_data;
};

/** @brief Notify attribute value change.
 *
 *  This function works in the same way as @ref bt_gatt_notify.
 *  With the addition that after sending the notification the
 *  callback function will be called.
 *
 *  The callback is run from System Workqueue context.
 *  When called from the System Workqueue context this API will not wait for
 *  resources for the callback but instead return an error.
 *  The number of pending callbacks can be increased with the
 *  @kconfig{CONFIG_BT_CONN_TX_MAX} option.
 *
 *  Alternatively it is possible to notify by UUID by setting it on the
 *  parameters, when using this method the attribute if provided is used as the
 *  start range when looking up for possible matches.
 *
 *  @param conn Connection object.
 *  @param params Notification parameters.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_notify_cb(struct bt_conn *conn,
		      struct bt_gatt_notify_params *params);

/** @brief Notify multiple attribute value change.
 *
 *  This function works in the same way as @ref bt_gatt_notify_cb.
 *
 *  @param conn Connection object.
 *  @param num_params Number of notification parameters.
 *  @param params Array of notification parameters.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_notify_multiple(struct bt_conn *conn, uint16_t num_params,
			    struct bt_gatt_notify_params *params);

/** @brief Notify attribute value change.
 *
 *  Send notification of attribute value change, if connection is NULL notify
 *  all peer that have notification enabled via CCC otherwise do a direct
 *  notification only the given connection.
 *
 *  The attribute object on the parameters can be the so called Characteristic
 *  Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed
 *  by BT_GATT_CCC, or the Characteristic Value Declaration which is
 *  automatically created after the Characteristic Declaration when using
 *  BT_GATT_CHARACTERISTIC.
 *
 *  @param conn Connection object.
 *  @param attr Characteristic or Characteristic Value attribute.
 *  @param data Pointer to Attribute data.
 *  @param len Attribute value length.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
static inline int bt_gatt_notify(struct bt_conn *conn,
				 const struct bt_gatt_attr *attr,
				 const void *data, uint16_t len)
{
	struct bt_gatt_notify_params params;

	memset(&params, 0, sizeof(params));

	params.attr = attr;
	params.data = data;
	params.len = len;

	return bt_gatt_notify_cb(conn, &params);
}

/** @brief Notify attribute value change by UUID.
 *
 *  Send notification of attribute value change, if connection is NULL notify
 *  all peer that have notification enabled via CCC otherwise do a direct
 *  notification only on the given connection.
 *
 *  The attribute object is the starting point for the search of the UUID.
 *
 *  @param conn Connection object.
 *  @param uuid The UUID. If the server contains multiple services with the same
 *              UUID, then the first occurrence, starting from the attr given,
 *              is used.
 *  @param attr Pointer to an attribute that serves as the starting point for
 *              the search of a match for the UUID.
 *  @param data Pointer to Attribute data.
 *  @param len  Attribute value length.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
static inline int bt_gatt_notify_uuid(struct bt_conn *conn,
				      const struct bt_uuid *uuid,
				      const struct bt_gatt_attr *attr,
				      const void *data, uint16_t len)
{
	struct bt_gatt_notify_params params;

	memset(&params, 0, sizeof(params));

	params.uuid = uuid;
	params.attr = attr;
	params.data = data;
	params.len = len;

	return bt_gatt_notify_cb(conn, &params);
}

/* Forward declaration of the bt_gatt_indicate_params structure */
struct bt_gatt_indicate_params;

/** @typedef bt_gatt_indicate_func_t
 *  @brief Indication complete result callback.
 *
 *  @param conn Connection object.
 *  @param params Indication params object.
 *  @param err ATT error code
 */
typedef void (*bt_gatt_indicate_func_t)(struct bt_conn *conn,
					struct bt_gatt_indicate_params *params,
					uint8_t err);

typedef void (*bt_gatt_indicate_params_destroy_t)(
		struct bt_gatt_indicate_params *params);

/** @brief GATT Indicate Value parameters */
struct bt_gatt_indicate_params {
	/** @brief Indicate Attribute UUID type
	 *
	 *  Optional, use to search for an attribute with matching UUID when
	 *  the attribute object pointer is not known.
	 */
	const struct bt_uuid *uuid;
	/** @brief Indicate Attribute object
	 *
	 *  Optional if uuid is provided, in this case it will be used as start
	 *  range to search for the attribute with the given UUID.
	 */
	const struct bt_gatt_attr *attr;
	/** Indicate Value callback */
	bt_gatt_indicate_func_t func;
	/** Indicate operation complete callback */
	bt_gatt_indicate_params_destroy_t destroy;
	/** Indicate Value data*/
	const void *data;
	/** Indicate Value length*/
	uint16_t len;
	/** Private reference counter */
	uint8_t _ref;
};

/** @brief Indicate attribute value change.
 *
 *  Send an indication of attribute value change. if connection is NULL
 *  indicate all peer that have notification enabled via CCC otherwise do a
 *  direct indication only the given connection.
 *
 *  The attribute object on the parameters can be the so called Characteristic
 *  Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed
 *  by BT_GATT_CCC, or the Characteristic Value Declaration which is
 *  automatically created after the Characteristic Declaration when using
 *  BT_GATT_CHARACTERISTIC.
 *
 *  Alternatively it is possible to indicate by UUID by setting it on the
 *  parameters, when using this method the attribute if provided is used as the
 *  start range when looking up for possible matches.
 *
 *  @note This procedure is asynchronous therefore the parameters need to
 *        remains valid while it is active. The procedure is active until
 *        the destroy callback is run.
 *
 *  @param conn Connection object.
 *  @param params Indicate parameters.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_indicate(struct bt_conn *conn,
		     struct bt_gatt_indicate_params *params);


/** @brief Check if connection have subscribed to attribute
 *
 *  Check if connection has subscribed to attribute value change.
 *
 *  The attribute object can be the so called Characteristic Declaration,
 *  which is usually declared with BT_GATT_CHARACTERISTIC followed
 *  by BT_GATT_CCC, or the Characteristic Value Declaration which is
 *  automatically created after the Characteristic Declaration when using
 *  BT_GATT_CHARACTERISTIC, or the Client Characteristic Configuration
 *  Descriptor (CCCD) which is created by BT_GATT_CCC.
 *
 *  @param conn Connection object.
 *  @param attr Attribute object.
 *  @param ccc_value The subscription type, either notifications or indications.
 *
 *  @return true if the attribute object has been subscribed.
 */
bool bt_gatt_is_subscribed(struct bt_conn *conn,
			   const struct bt_gatt_attr *attr, uint16_t ccc_value);

/** @brief Get ATT MTU for a connection
 *
 *  Get negotiated ATT connection MTU, note that this does not equal the largest
 *  amount of attribute data that can be transferred within a single packet.
 *
 *  @param conn Connection object.
 *
 *  @return MTU in bytes
 */
uint16_t bt_gatt_get_mtu(struct bt_conn *conn);

/** @} */

/**
 * @defgroup bt_gatt_client GATT Client APIs
 * @ingroup bt_gatt
 * @{
 */

/** @brief GATT Exchange MTU parameters */
struct bt_gatt_exchange_params {
	/** Response callback */
	void (*func)(struct bt_conn *conn, uint8_t err,
		     struct bt_gatt_exchange_params *params);
};

/** @brief Exchange MTU
 *
 *  This client procedure can be used to set the MTU to the maximum possible
 *  size the buffers can hold.
 *
 *  @note Shall only be used once per connection.
 *
 *  The Response comes in callback @p params->func. The callback is run from
 *  the BT RX thread. @p params must remain valid until start of callback.
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from the BT RX thread, as this would cause a deadlock.
 *
 *  @param conn Connection object.
 *  @param params Exchange MTU parameters.
 *
 *  @retval 0 Successfully queued request. Will call @p params->func on
 *  resolution.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside the BT RX thread to get blocking behavior. Queue size is controlled
 *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 *
 *  @retval -EALREADY The MTU exchange procedure has been already performed.
 */
int bt_gatt_exchange_mtu(struct bt_conn *conn,
			 struct bt_gatt_exchange_params *params);

struct bt_gatt_discover_params;

/** @typedef bt_gatt_discover_func_t
 *  @brief Discover attribute callback function.
 *
 *  @param conn Connection object.
 *  @param attr Attribute found, or NULL if not found.
 *  @param params Discovery parameters given.
 *
 *  If discovery procedure has completed this callback will be called with
 *  attr set to NULL. This will not happen if procedure was stopped by returning
 *  BT_GATT_ITER_STOP.
 *
 *  The attribute object as well as its UUID and value objects are temporary and
 *  must be copied to in order to cache its information.
 *  Only the following fields of the attribute contains valid information:
 *   - uuid      UUID representing the type of attribute.
 *   - handle    Handle in the remote database.
 *   - user_data The value of the attribute.
 *               Will be NULL when discovering descriptors
 *
 *  To be able to read the value of the discovered attribute the user_data
 *  must be cast to an appropriate type.
 *   - @ref bt_gatt_service_val when UUID is @ref BT_UUID_GATT_PRIMARY or
 *     @ref BT_UUID_GATT_SECONDARY.
 *   - @ref bt_gatt_include when UUID is @ref BT_UUID_GATT_INCLUDE.
 *   - @ref bt_gatt_chrc when UUID is @ref BT_UUID_GATT_CHRC.
 *
 *  @return BT_GATT_ITER_CONTINUE to continue discovery procedure.
 *  @return BT_GATT_ITER_STOP to stop discovery procedure.
 */
typedef uint8_t (*bt_gatt_discover_func_t)(struct bt_conn *conn,
					const struct bt_gatt_attr *attr,
					struct bt_gatt_discover_params *params);

/** GATT Discover types */
enum {
	/** Discover Primary Services. */
	BT_GATT_DISCOVER_PRIMARY,
	/** Discover Secondary Services. */
	BT_GATT_DISCOVER_SECONDARY,
	/** Discover Included Services. */
	BT_GATT_DISCOVER_INCLUDE,
	/** @brief Discover Characteristic Values.
	 *
	 *  Discover Characteristic Value and its properties.
	 */
	BT_GATT_DISCOVER_CHARACTERISTIC,
	/** @brief Discover Descriptors.
	 *
	 *  Discover Attributes which are not services or characteristics.
	 *
	 *  @note The use of this type of discover is not recommended for
	 *        discovering in ranges across multiple services/characteristics
	 *        as it may incur in extra round trips.
	 */
	BT_GATT_DISCOVER_DESCRIPTOR,
	/** @brief Discover Attributes.
	 *
	 *  Discover Attributes of any type.
	 *
	 *  @note The use of this type of discover is not recommended for
	 *        discovering in ranges across multiple services/characteristics
	 *        as it may incur in more round trips.
	 */
	BT_GATT_DISCOVER_ATTRIBUTE,
	/** @brief Discover standard characteristic descriptor values.
	 *
	 *  Discover standard characteristic descriptor values and their
	 *  properties.
	 *  Supported descriptors:
	 *   - Characteristic Extended Properties
	 *   - Client Characteristic Configuration
	 *   - Server Characteristic Configuration
	 *   - Characteristic Presentation Format
	 */
	BT_GATT_DISCOVER_STD_CHAR_DESC,
};

/** @brief GATT Discover Attributes parameters */
struct bt_gatt_discover_params {
	/** Discover UUID type */
	const struct bt_uuid *uuid;
	/** Discover attribute callback */
	bt_gatt_discover_func_t func;
	union {
		struct {
			/** Include service attribute declaration handle */
			uint16_t attr_handle;
			/** Included service start handle */
			uint16_t start_handle;
			/** Included service end handle */
			uint16_t end_handle;
		} _included;
		/** Discover start handle */
		uint16_t start_handle;
	};
	/** Discover end handle */
	uint16_t end_handle;
	/** Discover type */
	uint8_t type;
#if defined(CONFIG_BT_GATT_AUTO_DISCOVER_CCC)
	/** Only for stack-internal use, used for automatic discovery. */
	struct bt_gatt_subscribe_params *sub_params;
#endif /* defined(CONFIG_BT_GATT_AUTO_DISCOVER_CCC) */
};

/** @brief GATT Discover function
 *
 *  This procedure is used by a client to discover attributes on a server.
 *
 *  Primary Service Discovery: Procedure allows to discover specific Primary
 *                             Service based on UUID.
 *  Include Service Discovery: Procedure allows to discover all Include Services
 *                             within specified range.
 *  Characteristic Discovery:  Procedure allows to discover all characteristics
 *                             within specified handle range as well as
 *                             discover characteristics with specified UUID.
 *  Descriptors Discovery:     Procedure allows to discover all characteristic
 *                             descriptors within specified range.
 *
 *  For each attribute found the callback is called which can then decide
 *  whether to continue discovering or stop.
 *
 *  The Response comes in callback @p params->func. The callback is run from
 *  the BT RX thread. @p params must remain valid until start of callback where
 *  iter `attr` is `NULL` or callback will return `BT_GATT_ITER_STOP`.
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from the BT RX thread, as this would cause a deadlock.
 *
 *  @param conn Connection object.
 *  @param params Discover parameters.
 *
 *  @retval 0 Successfully queued request. Will call @p params->func on
 *  resolution.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside the BT RX thread to get blocking behavior. Queue size is controlled
 *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 */
int bt_gatt_discover(struct bt_conn *conn,
		     struct bt_gatt_discover_params *params);

struct bt_gatt_read_params;

/** @typedef bt_gatt_read_func_t
 *  @brief Read callback function
 *
 *  @param conn Connection object.
 *  @param err ATT error code.
 *  @param params Read parameters used.
 *  @param data Attribute value data. NULL means read has completed.
 *  @param length Attribute value length.
 *
 *  @return BT_GATT_ITER_CONTINUE if should continue to the next attribute.
 *  @return BT_GATT_ITER_STOP to stop.
 */
typedef uint8_t (*bt_gatt_read_func_t)(struct bt_conn *conn, uint8_t err,
				    struct bt_gatt_read_params *params,
				    const void *data, uint16_t length);

/** @brief GATT Read parameters */
struct bt_gatt_read_params {
	/** Read attribute callback. */
	bt_gatt_read_func_t func;
	/** If equals to 1 single.handle and single.offset are used.
	 *  If greater than 1 multiple.handles are used.
	 *  If equals to 0 by_uuid is used for Read Using Characteristic UUID.
	 */
	size_t handle_count;
	union {
		struct {
			/** Attribute handle. */
			uint16_t handle;
			/** Attribute data offset. */
			uint16_t offset;
		} single;
		struct {
			/** Attribute handles to read with Read Multiple
			 *  Characteristic Values.
			 */
			uint16_t *handles;
			/** If true use Read Multiple Variable Length
			 *  Characteristic Values procedure.
			 *  The values of the set of attributes may be of
			 *  variable or unknown length.
			 *  If false use Read Multiple Characteristic Values
			 *  procedure.
			 *  The values of the set of attributes must be of a
			 *  known fixed length, with the exception of the last
			 *  value that can have a variable length.
			 */
			bool variable;
		} multiple;
		struct {
			/** First requested handle number. */
			uint16_t start_handle;
			/** Last requested handle number. */
			uint16_t end_handle;
			/** 2 or 16 octet UUID. */
			const struct bt_uuid *uuid;
		} by_uuid;
	};
};

/** @brief Read Attribute Value by handle
 *
 *  This procedure read the attribute value and return it to the callback.
 *
 *  When reading attributes by UUID the callback can be called multiple times
 *  depending on how many instances of given the UUID exists with the
 *  start_handle being updated for each instance.
 *
 *  If an instance does contain a long value which cannot be read entirely the
 *  caller will need to read the remaining data separately using the handle and
 *  offset.
 *
 *  The Response comes in callback @p params->func. The callback is run from
 *  the BT RX thread. @p params must remain valid until start of callback.
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from the BT RX thread, as this would cause a deadlock.
 *
 *  @param conn Connection object.
 *  @param params Read parameters.
 *
 *  @retval 0 Successfully queued request. Will call @p params->func on
 *  resolution.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside the BT RX thread to get blocking behavior. Queue size is controlled
 *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 */
int bt_gatt_read(struct bt_conn *conn, struct bt_gatt_read_params *params);

struct bt_gatt_write_params;

/** @typedef bt_gatt_write_func_t
 *  @brief Write callback function
 *
 *  @param conn Connection object.
 *  @param err ATT error code.
 *  @param params Write parameters used.
 */
typedef void (*bt_gatt_write_func_t)(struct bt_conn *conn, uint8_t err,
				     struct bt_gatt_write_params *params);

/** @brief GATT Write parameters */
struct bt_gatt_write_params {
	/** Response callback */
	bt_gatt_write_func_t func;
	/** Attribute handle */
	uint16_t handle;
	/** Attribute data offset */
	uint16_t offset;
	/** Data to be written */
	const void *data;
	/** Length of the data */
	uint16_t length;
};

/** @brief Write Attribute Value by handle
 *
 *  The Response comes in callback @p params->func. The callback is run from
 *  the BT RX thread. @p params must remain valid until start of callback.
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from Bluetooth event context. When called from Bluetooth context,
 *  this function will instead instead return `-ENOMEM` if it would block to
 *  avoid a deadlock.
 *
 *  @param conn Connection object.
 *  @param params Write parameters.
 *
 *  @retval 0 Successfully queued request. Will call @p params->func on
 *  resolution.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside Bluetooth event context to get blocking behavior. Queue size is
 *  controlled by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 */
int bt_gatt_write(struct bt_conn *conn, struct bt_gatt_write_params *params);

/** @brief Write Attribute Value by handle without response with callback.
 *
 *  This function works in the same way as @ref bt_gatt_write_without_response.
 *  With the addition that after sending the write the callback function will be
 *  called.
 *
 *  The callback is run from System Workqueue context.
 *  When called from the System Workqueue context this API will not wait for
 *  resources for the callback but instead return an error.
 *  The number of pending callbacks can be increased with the
 *  @kconfig{CONFIG_BT_CONN_TX_MAX} option.
 *
 *  @note By using a callback it also disable the internal flow control
 *        which would prevent sending multiple commands without waiting for
 *        their transmissions to complete, so if that is required the caller
 *        shall not submit more data until the callback is called.
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from the BT RX thread, as this would cause a deadlock.
 *
 *  @param conn Connection object.
 *  @param handle Attribute handle.
 *  @param data Data to be written.
 *  @param length Data length.
 *  @param sign Whether to sign data
 *  @param func Transmission complete callback.
 *  @param user_data User data to be passed back to callback.
 *
 *  @retval 0 Successfully queued request.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside the BT RX thread to get blocking behavior. Queue size is controlled
 *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 */
int bt_gatt_write_without_response_cb(struct bt_conn *conn, uint16_t handle,
				      const void *data, uint16_t length,
				      bool sign, bt_gatt_complete_func_t func,
				      void *user_data);

/** @brief Write Attribute Value by handle without response
 *
 *  This procedure write the attribute value without requiring an
 *  acknowledgment that the write was successfully performed
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from the BT RX thread, as this would cause a deadlock.
 *
 *  @param conn Connection object.
 *  @param handle Attribute handle.
 *  @param data Data to be written.
 *  @param length Data length.
 *  @param sign Whether to sign data
 *
 *  @retval 0 Successfully queued request.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside the BT RX thread to get blocking behavior. Queue size is controlled
 *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 */
static inline int bt_gatt_write_without_response(struct bt_conn *conn,
						 uint16_t handle, const void *data,
						 uint16_t length, bool sign)
{
	return bt_gatt_write_without_response_cb(conn, handle, data, length,
						 sign, NULL, NULL);
}

struct bt_gatt_subscribe_params;

/** @typedef bt_gatt_notify_func_t
 *  @brief Notification callback function
 *
 *  In the case of an empty notification, the @p data pointer will be non-NULL
 *  while the @p length will be 0, which is due to the special case where
 *  a @p data NULL pointer means unsubscribed.
 *
 *  @param conn Connection object. May be NULL, indicating that the peer is
 *              being unpaired
 *  @param params Subscription parameters.
 *  @param data Attribute value data. If NULL then subscription was removed.
 *  @param length Attribute value length.
 *
 *  @return BT_GATT_ITER_CONTINUE to continue receiving value notifications.
 *          BT_GATT_ITER_STOP to unsubscribe from value notifications.
 */
typedef uint8_t (*bt_gatt_notify_func_t)(struct bt_conn *conn,
				      struct bt_gatt_subscribe_params *params,
				      const void *data, uint16_t length);

/** Subscription flags */
enum {
	/** @brief Persistence flag
	 *
	 *  If set, indicates that the subscription is not saved
	 *  on the GATT server side. Therefore, upon disconnection,
	 *  the subscription will be automatically removed
	 *  from the client's subscriptions list and
	 *  when the client reconnects, it will have to
	 *  issue a new subscription.
	 */
	BT_GATT_SUBSCRIBE_FLAG_VOLATILE,

	/** @brief No resubscribe flag
	 *
	 *  By default when BT_GATT_SUBSCRIBE_FLAG_VOLATILE is unset, the
	 *  subscription will be automatically renewed when the client
	 *  reconnects, as a workaround for GATT servers that do not persist
	 *  subscriptions.
	 *
	 *  This flag will disable the automatic resubscription. It is useful
	 *  if the application layer knows that the GATT server remembers
	 *  subscriptions from previous connections and wants to avoid renewing
	 *  the subscriptions.
	 */
	BT_GATT_SUBSCRIBE_FLAG_NO_RESUB,

	/** @brief Write pending flag
	 *
	 *  If set, indicates write operation is pending waiting remote end to
	 *  respond.
	 */
	BT_GATT_SUBSCRIBE_FLAG_WRITE_PENDING,

	BT_GATT_SUBSCRIBE_NUM_FLAGS
};

/** @brief GATT Subscribe parameters */
struct bt_gatt_subscribe_params {
	/** Notification value callback */
	bt_gatt_notify_func_t notify;
	/** Subscribe CCC write request response callback */
	bt_gatt_write_func_t write;
	/** Subscribe value handle */
	uint16_t value_handle;
	/** Subscribe CCC handle */
	uint16_t ccc_handle;
#if defined(CONFIG_BT_GATT_AUTO_DISCOVER_CCC)
	/** Subscribe End handle (for automatic discovery) */
	uint16_t end_handle;
	/** Discover parameters used when ccc_handle = 0 */
	struct bt_gatt_discover_params *disc_params;
#endif /* CONFIG_BT_GATT_AUTO_DISCOVER_CCC */
	/** Subscribe value */
	uint16_t value;
#if defined(CONFIG_BT_SMP)
	/** Minimum required security for received notification. Notifications
	 * and indications received over a connection with a lower security
	 * level are silently discarded.
	 */
	bt_security_t min_security;
#endif
	/** Subscription flags */
	ATOMIC_DEFINE(flags, BT_GATT_SUBSCRIBE_NUM_FLAGS);

	sys_snode_t node;
};

/** @brief Subscribe Attribute Value Notification
 *
 *  This procedure subscribe to value notification using the Client
 *  Characteristic Configuration handle.
 *  If notification received subscribe value callback is called to return
 *  notified value. One may then decide whether to unsubscribe directly from
 *  this callback. Notification callback with NULL data will not be called if
 *  subscription was removed by this method.
 *
 *  The Response comes in callback @p params->func. The callback is run from
 *  the BT RX thread. @p params must remain valid until start of callback.
 *  The Notification callback @p params->notify is also called from the BT RX
 *  thread.
 *
 *  @note Notifications are asynchronous therefore the parameters need to
 *        remain valid while subscribed.
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from the BT RX thread, as this would cause a deadlock.
 *
 *  @param conn Connection object.
 *  @param params Subscribe parameters.
 *
 *  @retval 0 Successfully queued request. Will call @p params->write on
 *  resolution.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside the BT RX thread to get blocking behavior. Queue size is controlled
 *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 */
int bt_gatt_subscribe(struct bt_conn *conn,
		      struct bt_gatt_subscribe_params *params);

/** @brief Resubscribe Attribute Value Notification subscription
 *
 *  Resubscribe to Attribute Value Notification when already subscribed from a
 *  previous connection. The GATT server will remember subscription from
 *  previous connections when bonded, so resubscribing can be done without
 *  performing a new subscribe procedure after a power cycle.
 *
 *  @note Notifications are asynchronous therefore the parameters need to
 *        remain valid while subscribed.
 *
 *  @param id     Local identity (in most cases BT_ID_DEFAULT).
 *  @param peer   Remote address.
 *  @param params Subscribe parameters.
 *
 *  @return 0 in case of success or negative value in case of error.
 */
int bt_gatt_resubscribe(uint8_t id, const bt_addr_le_t *peer,
			struct bt_gatt_subscribe_params *params);

/** @brief Unsubscribe Attribute Value Notification
 *
 *  This procedure unsubscribe to value notification using the Client
 *  Characteristic Configuration handle. Notification callback with NULL data
 *  will be called if subscription was removed by this call, until then the
 *  parameters cannot be reused.
 *
 *  The Response comes in callback @p params->func. The callback is run from
 *  the BT RX thread.
 *
 *  This function will block while the ATT request queue is full, except when
 *  called from the BT RX thread, as this would cause a deadlock.
 *
 *  @param conn Connection object.
 *  @param params Subscribe parameters.
 *
 *  @retval 0 Successfully queued request. Will call @p params->write on
 *  resolution.
 *
 *  @retval -ENOMEM ATT request queue is full and blocking would cause deadlock.
 *  Allow a pending request to resolve before retrying, or call this function
 *  outside the BT RX thread to get blocking behavior. Queue size is controlled
 *  by @kconfig{CONFIG_BT_L2CAP_TX_BUF_COUNT}.
 */
int bt_gatt_unsubscribe(struct bt_conn *conn,
			struct bt_gatt_subscribe_params *params);

/** @brief Try to cancel the first pending request identified by @p params.
 *
 *  This function does not release @p params for reuse. The usual callbacks
 *  for the request still apply. A successful cancel simulates a
 *  #BT_ATT_ERR_UNLIKELY response from the server.
 *
 *  This function can cancel the following request functions:
 *   - #bt_gatt_exchange_mtu
 *   - #bt_gatt_discover
 *   - #bt_gatt_read
 *   - #bt_gatt_write
 *   - #bt_gatt_subscribe
 *   - #bt_gatt_unsubscribe
 *
 *  @param conn The connection the request was issued on.
 *  @param params The address `params` used in the request function call.
 */
void bt_gatt_cancel(struct bt_conn *conn, void *params);

/** @} */

#ifdef __cplusplus
}
#endif

/**
 * @}
 */

#endif /* ZEPHYR_INCLUDE_BLUETOOTH_GATT_H_ */