ATT Database Engine API

att_db.h

// map ATT ERROR CODES on to att_read_callback length
#define ATT_READ_ERROR_CODE_OFFSET       0xfe00

// custom BTstack ATT Response Pending for att_read_callback
#define ATT_READ_RESPONSE_PENDING                 0xffff

// internally used to signal write response pending
#define ATT_INTERNAL_WRITE_RESPONSE_PENDING       0xfffe

/**
 * @brief ATT Client Read Callback for Dynamic Data
 * - if buffer == NULL, don't copy data, just return size of value
 * - if buffer != NULL, copy data and return number bytes copied
 * If ENABLE_ATT_DELAYED_READ_RESPONSE is defined, you may return ATT_READ_RESPONSE_PENDING if data isn't available yet
 * @param con_handle of hci le connection
 * @param attribute_handle to be read
 * @param offset defines start of attribute value
 * @param buffer 
 * @param buffer_size
 * @return size of value if buffer is NULL, otherwise number of bytes copied
 */
typedef uint16_t (*att_read_callback_t)(hci_con_handle_t con_handle, uint16_t attribute_handle, uint16_t offset, uint8_t * buffer, uint16_t buffer_size);

/**
 * @brief ATT Client Write Callback for Dynamic Data
 * Each Prepared Write Request triggers a callback with transaction mode ATT_TRANSACTION_MODE_ACTIVE.
 * On Execute Write, the callback will be called with ATT_TRANSACTION_MODE_VALIDATE and allows to validate all queued writes and return an application error.
 * If none of the registered callbacks return an error for ATT_TRANSACTION_MODE_VALIDATE and the callback will be called with ATT_TRANSACTION_MODE_EXECUTE.
 * Otherwise, all callbacks will be called with ATT_TRANSACTION_MODE_CANCEL.
 *
 * If the additional validation step is not needed, just return 0 for all callbacks with transaction mode ATT_TRANSACTION_MODE_VALIDATE.
 *
 * @param con_handle of hci le connection
 * @param attribute_handle to be written
 * @param transaction - ATT_TRANSACTION_MODE_NONE for regular writes. For prepared writes: ATT_TRANSACTION_MODE_ACTIVE, ATT_TRANSACTION_MODE_VALIDATE, ATT_TRANSACTION_MODE_EXECUTE, ATT_TRANSACTION_MODE_CANCEL
 * @param offset into the value - used for queued writes and long attributes
 * @param buffer 
 * @param buffer_size
 * @param signature used for signed write commmands
 * @return 0 if write was ok, ATT_ERROR_PREPARE_QUEUE_FULL if no space in queue, ATT_ERROR_INVALID_OFFSET if offset is larger than max buffer
 */
typedef int (*att_write_callback_t)(hci_con_handle_t con_handle, uint16_t attribute_handle, uint16_t transaction_mode, uint16_t offset, uint8_t *buffer, uint16_t buffer_size);

// Read & Write Callbacks for handle range
typedef struct att_service_handler {
    btstack_linked_item_t * item;
    uint16_t start_handle;
    uint16_t end_handle;
    att_read_callback_t read_callback;
    att_write_callback_t write_callback;
    btstack_packet_handler_t packet_handler;
} att_service_handler_t;

// MARK: ATT Operations

/**
 * @brief setup ATT database
 * @param db
 */
void att_set_db(uint8_t const * db);

/*
 * @brief set callback for read of dynamic attributes
 * @param callback
 */
void att_set_read_callback(att_read_callback_t callback);

/**
 * @brief set callback for write of dynamic attributes
 * @param callback
 */
void att_set_write_callback(att_write_callback_t callback);

/**
 * @brief debug helper, dump ATT database to stdout using log_info
 */
void att_dump_attributes(void);

/**
 * @brief process ATT request against database and put response into response buffer
 * @param att_connection used for mtu and security properties
 * @param request_buffer, request_len: ATT request from clinet
 * @param response_buffer for result
 * @return len of data in response buffer. 0 = no response, 
 *          ATT_READ_RESPONSE_PENDING if it was returned at least once for dynamic data (requires ENABLE_ATT_DELAYED_READ_RESPONSE)
 */
uint16_t att_handle_request(att_connection_t * att_connection,
                            uint8_t * request_buffer,
                            uint16_t request_len,
                            uint8_t * response_buffer);

/**
 * @brief setup value notification in response buffer for a given handle and value
 * @param att_connection
 * @param attribute_handle
 * @param value
 * @param value_len
 * @param response_buffer for notification
 */
uint16_t att_prepare_handle_value_notification(att_connection_t * att_connection,
                                               uint16_t attribute_handle,
                                               const uint8_t *value,
                                               uint16_t value_len, 
                                               uint8_t * response_buffer);

/**
 * @brief setup value indication in response buffer for a given handle and value
 * @param att_connection
 * @param attribute_handle
 * @param value
 * @param value_len
 * @param response_buffer for indication
 */
uint16_t att_prepare_handle_value_indication(att_connection_t * att_connection,
                                             uint16_t attribute_handle,
                                             const uint8_t *value,
                                             uint16_t value_len, 
                                             uint8_t * response_buffer);

/**
 * @brief transcation queue of prepared writes, e.g., after disconnect
 * @return att_connection
 */
void att_clear_transaction_queue(att_connection_t * att_connection);

// att_read_callback helpers for a various data types

/**
 * @brief Handle read of blob like data for att_read_callback
 * @param blob of data
 * @param blob_size of blob
 * @param offset from att_read_callback
 * @param buffer from att_read_callback
 * @param buffer_size from att_read_callback
 * @return value size for buffer == 0 and num bytes copied otherwise
 */
uint16_t att_read_callback_handle_blob(const uint8_t * blob, uint16_t blob_size, uint16_t offset, uint8_t * buffer, uint16_t buffer_size);

/**
 * @brief Handle read of little endian unsigned 32 bit value for att_read_callback
 * @param value
 * @param offset from att_read_callback
 * @param buffer from att_read_callback
 * @param buffer_size from att_read_callback
 * @return value size for buffer == 0 and num bytes copied otherwise
 */
uint16_t att_read_callback_handle_little_endian_32(uint32_t value, uint16_t offset, uint8_t * buffer, uint16_t buffer_size);

/**
 * @brief Handle read of little endian unsigned 16 bit value for att_read_callback
 * @param value
 * @param offset from att_read_callback
 * @param buffer from att_read_callback
 * @param buffer_size from att_read_callback
 * @return value size for buffer == 0 and num bytes copied otherwise
 */
uint16_t att_read_callback_handle_little_endian_16(uint16_t value, uint16_t offset, uint8_t * buffer, uint16_t buffer_size);

/**
 * @brief Handle read of single byte for att_read_callback
 * @param blob of data
 * @param blob_size of blob
 * @param offset from att_read_callback
 * @param buffer from att_read_callback
 * @param buffer_size from att_read_callback
 * @return value size for buffer == 0 and num bytes copied otherwise
 */
uint16_t att_read_callback_handle_byte(uint8_t value, uint16_t offset, uint8_t * buffer, uint16_t buffer_size);


// experimental client API
/**
 * @brief Get UUID for handle
 * @param attribute_handle
 * @return 0 if not found
 */
uint16_t att_uuid_for_handle(uint16_t attribute_handle);

// experimental GATT Server API

/**
 * @brief Get handle range for primary service.
 * @param uuid16
 * @param start_handle
 * @param end_handle
 * @return false if not found
 */
bool gatt_server_get_handle_range_for_service_with_uuid16(uint16_t uuid16, uint16_t * start_handle, uint16_t * end_handle);

/**
 * @brief Get value handle for characteristic.
 * @param start_handle
 * @param end_handle
 * @param uuid16
 * @return 0 if not found
 */
uint16_t gatt_server_get_value_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t uuid16);

/**
 * @brief Get descriptor handle for characteristic.
 * @param start_handle
 * @param end_handle
 * @param characteristic_uuid16
 * @param descriptor_uuid16
 * @return 0 if not found
 */
uint16_t gatt_server_get_descriptor_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t characteristic_uuid16, uint16_t descriptor_uuid16);

/**
 * @brief Get client configuration handle for characteristic.
 * @param start_handle
 * @param end_handle
 * @param characteristic_uuid16
 * @return 0 if not found
 */
uint16_t gatt_server_get_client_configuration_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t characteristic_uuid16);

/**
 * @brief Get server configuration handle for characteristic.
 * @param start_handle
 * @param end_handle
 * @param characteristic_uuid16
 * @param descriptor_uuid16
 * @return 0 if not found
 */
uint16_t gatt_server_get_server_configuration_handle_for_characteristic_with_uuid16(uint16_t start_handle, uint16_t end_handle, uint16_t characteristic_uuid16);

/**
 * @brief Get handle range for primary service.
 * @param uuid128
 * @param start_handle
 * @param end_handle
 * @return 0 if not found
 */
int gatt_server_get_handle_range_for_service_with_uuid128(const uint8_t * uuid128, uint16_t * start_handle, uint16_t * end_handle);

/**
 * @brief Get value handle.
 * @param start_handle
 * @param end_handle
 * @param uuid128
 * @return 0 if not found
 */
uint16_t gatt_server_get_value_handle_for_characteristic_with_uuid128(uint16_t start_handle, uint16_t end_handle, const uint8_t * uuid128);

/**
 * @brief Get client configuration handle.
 * @param start_handle
 * @param end_handle
 * @param uuid128
 * @return 0 if not found
 */
uint16_t gatt_server_get_client_configuration_handle_for_characteristic_with_uuid128(uint16_t start_handle, uint16_t end_handle, const uint8_t * uuid128);