xref: /btstack/src/ble/gatt_client.c (revision 6c124bc24f267d5ae707c5d5137367237eff4d16)

/*
 * Copyright (C) 2014 BlueKitchen GmbH
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 * 4. Any redistribution, use, or modification is done solely for
 *    personal benefit and not for any commercial purpose or for
 *    monetary gain.
 *
 * THIS SOFTWARE IS PROVIDED BY BLUEKITCHEN GMBH AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MATTHIAS
 * RINGWALD OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
 * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Please inquire about commercial licensing options at
 * [email protected]
 *
 */

#define BTSTACK_FILE__ "gatt_client.c"

#include <stdint.h>
#include <string.h>

#include "btstack_config.h"

#include "att_dispatch.h"
#include "ad_parser.h"
#include "ble/att_db.h"
#include "ble/core.h"
#include "ble/gatt_client.h"
#include "ble/le_device_db.h"
#include "ble/sm.h"
#include "btstack_debug.h"
#include "btstack_event.h"
#include "btstack_memory.h"
#include "btstack_run_loop.h"
#include "btstack_util.h"
#include "classic/sdp_util.h"
#include "hci.h"
#include "hci_cmd.h"
#include "hci_dump.h"
#include "l2cap.h"

static btstack_linked_list_t gatt_client_connections;
static btstack_linked_list_t gatt_client_value_listeners;
static btstack_packet_callback_registration_t hci_event_callback_registration;

#if defined(ENABLE_GATT_CLIENT_PAIRING) || defined (ENABLE_LE_SIGNED_WRITE) || defined (ENABLE_LE_PROACTIVE_AUTHENTICATION)
static btstack_packet_callback_registration_t sm_event_callback_registration;
#endif

static uint8_t mtu_exchange_enabled;

static void gatt_client_att_packet_handler(uint8_t packet_type, uint16_t handle, uint8_t *packet, uint16_t size);
static void gatt_client_event_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size);
static void gatt_client_report_error_if_pending(gatt_client_t *gatt_client, uint8_t att_error_code);

#ifdef ENABLE_LE_SIGNED_WRITE
static void att_signed_write_handle_cmac_result(uint8_t hash[8]);
#endif

void gatt_client_init(void){
    gatt_client_connections = NULL;
    mtu_exchange_enabled = 1;

    // regsister for HCI Events
    hci_event_callback_registration.callback = &gatt_client_event_packet_handler;
    hci_add_event_handler(&hci_event_callback_registration);

#if defined(ENABLE_GATT_CLIENT_PAIRING) || defined (ENABLE_LE_SIGNED_WRITE) || defined (ENABLE_LE_PROACTIVE_AUTHENTICATION)
    // register for SM Events
    sm_event_callback_registration.callback = &gatt_client_event_packet_handler;
    sm_add_event_handler(&sm_event_callback_registration);
#endif

    // and ATT Client PDUs
    att_dispatch_register_client(gatt_client_att_packet_handler);
}

static gatt_client_t * gatt_client_for_timer(btstack_timer_source_t * ts){
    btstack_linked_list_iterator_t it;
    btstack_linked_list_iterator_init(&it, &gatt_client_connections);
    while (btstack_linked_list_iterator_has_next(&it)){
        gatt_client_t * gatt_client = (gatt_client_t *) btstack_linked_list_iterator_next(&it);
        if (&gatt_client->gc_timeout == ts) {
            return gatt_client;
        }
    }
    return NULL;
}

static void gatt_client_timeout_handler(btstack_timer_source_t * timer){
    gatt_client_t * gatt_client = gatt_client_for_timer(timer);
    if (gatt_client == NULL) return;
    log_info("GATT client timeout handle, handle 0x%02x", gatt_client->con_handle);
    gatt_client_report_error_if_pending(gatt_client, ATT_ERROR_TIMEOUT);
}

static void gatt_client_timeout_start(gatt_client_t * gatt_client){
    log_info("GATT client timeout start, handle 0x%02x", gatt_client->con_handle);
    btstack_run_loop_remove_timer(&gatt_client->gc_timeout);
    btstack_run_loop_set_timer_handler(&gatt_client->gc_timeout, gatt_client_timeout_handler);
    btstack_run_loop_set_timer(&gatt_client->gc_timeout, 30000); // 30 seconds sm timeout
    btstack_run_loop_add_timer(&gatt_client->gc_timeout);
}

static void gatt_client_timeout_stop(gatt_client_t * gatt_client){
    log_info("GATT client timeout stop, handle 0x%02x", gatt_client->con_handle);
    btstack_run_loop_remove_timer(&gatt_client->gc_timeout);
}

static gatt_client_t * gatt_client_get_context_for_handle(uint16_t handle){
    btstack_linked_item_t *it;
    for (it = (btstack_linked_item_t *) gatt_client_connections; it != NULL; it = it->next){
        gatt_client_t * gatt_client = (gatt_client_t *) it;
        if (gatt_client->con_handle == handle){
            return gatt_client;
        }
    }
    return NULL;
}


// @returns gatt_client context
// returns existing one, or tries to setup new one
static gatt_client_t * gatt_client_provide_context_for_handle(hci_con_handle_t con_handle){
    gatt_client_t * gatt_client = gatt_client_get_context_for_handle(con_handle);
    if (gatt_client) return gatt_client;

    // bail if no such hci connection
    if (!hci_connection_for_handle(con_handle)){
        log_error("No connection for handle 0x%04x", con_handle);
        return NULL;
    }
    gatt_client = btstack_memory_gatt_client_get();
    if (!gatt_client) return NULL;
    // init state
    gatt_client->con_handle = con_handle;
    gatt_client->mtu = ATT_DEFAULT_MTU;
    if (mtu_exchange_enabled){
        gatt_client->mtu_state = SEND_MTU_EXCHANGE;
    } else {
        gatt_client->mtu_state = MTU_AUTO_EXCHANGE_DISABLED;
    }
    gatt_client->gatt_client_state = P_READY;
    btstack_linked_list_add(&gatt_client_connections, (btstack_linked_item_t*)gatt_client);
    return gatt_client;
}

static gatt_client_t * gatt_client_provide_context_for_handle_and_start_timer(hci_con_handle_t con_handle){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle(con_handle);
    if (gatt_client == NULL) return NULL;
    gatt_client_timeout_start(gatt_client);
    return gatt_client;
}

static int is_ready(gatt_client_t * gatt_client){
    return gatt_client->gatt_client_state == P_READY;
}

int gatt_client_is_ready(hci_con_handle_t con_handle){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle(con_handle);
    if (gatt_client == NULL) return 0;
    return is_ready(gatt_client);
}

void gatt_client_mtu_enable_auto_negotiation(uint8_t enabled){
    mtu_exchange_enabled = enabled;
}

uint8_t gatt_client_get_mtu(hci_con_handle_t con_handle, uint16_t * mtu){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;

    if ((gatt_client->mtu_state == MTU_EXCHANGED) || (gatt_client->mtu_state == MTU_AUTO_EXCHANGE_DISABLED)){
        *mtu = gatt_client->mtu;
        return ERROR_CODE_SUCCESS;
    }
    *mtu = ATT_DEFAULT_MTU;
    return GATT_CLIENT_IN_WRONG_STATE;
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_confirmation(uint16_t con_handle){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = ATT_HANDLE_VALUE_CONFIRMATION;

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 1);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_find_information_request(uint16_t request_type, uint16_t con_handle, uint16_t start_handle, uint16_t end_handle){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, start_handle);
    little_endian_store_16(request, 3, end_handle);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 5);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_find_by_type_value_request(uint16_t request_type, uint16_t attribute_group_type, uint16_t con_handle, uint16_t start_handle, uint16_t end_handle, uint8_t * value, uint16_t value_size){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();

    request[0] = request_type;
    little_endian_store_16(request, 1, start_handle);
    little_endian_store_16(request, 3, end_handle);
    little_endian_store_16(request, 5, attribute_group_type);
    (void)memcpy(&request[7], value, value_size);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 7u + value_size);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_read_by_type_or_group_request_for_uuid16(uint16_t request_type, uint16_t uuid16, uint16_t con_handle, uint16_t start_handle, uint16_t end_handle){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, start_handle);
    little_endian_store_16(request, 3, end_handle);
    little_endian_store_16(request, 5, uuid16);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 7);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_read_by_type_or_group_request_for_uuid128(uint16_t request_type, uint8_t * uuid128, uint16_t con_handle, uint16_t start_handle, uint16_t end_handle){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, start_handle);
    little_endian_store_16(request, 3, end_handle);
    reverse_128(uuid128, &request[5]);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 21);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_read_request(uint16_t request_type, uint16_t con_handle, uint16_t attribute_handle){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, attribute_handle);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 3);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_read_blob_request(uint16_t request_type, uint16_t con_handle, uint16_t attribute_handle, uint16_t value_offset){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, attribute_handle);
    little_endian_store_16(request, 3, value_offset);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 5);
}

static uint8_t att_read_multiple_request(uint16_t con_handle, uint16_t num_value_handles, uint16_t * value_handles){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = ATT_READ_MULTIPLE_REQUEST;
    int i;
    int offset = 1;
    for (i=0;i<num_value_handles;i++){
        little_endian_store_16(request, offset, value_handles[i]);
        offset += 2;
    }

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, offset);
}

#ifdef ENABLE_LE_SIGNED_WRITE
// precondition: can_send_packet_now == TRUE
static uint8_t att_signed_write_request(uint16_t request_type, uint16_t con_handle, uint16_t attribute_handle, uint16_t value_length, uint8_t * value, uint32_t sign_counter, uint8_t sgn[8]){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, attribute_handle);
    (void)memcpy(&request[3], value, value_length);
    little_endian_store_32(request, 3 + value_length, sign_counter);
    reverse_64(sgn, &request[3 + value_length + 4]);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 3 + value_length + 12);
}
#endif

// precondition: can_send_packet_now == TRUE
static uint8_t att_write_request(uint16_t request_type, uint16_t con_handle, uint16_t attribute_handle, uint16_t value_length, uint8_t * value){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, attribute_handle);
    (void)memcpy(&request[3], value, value_length);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 3u + value_length);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_execute_write_request(uint16_t request_type, uint16_t con_handle, uint8_t execute_write){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    request[1] = execute_write;

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 2);
}

// precondition: can_send_packet_now == TRUE
static uint8_t att_prepare_write_request(uint16_t request_type, uint16_t con_handle, uint16_t attribute_handle, uint16_t value_offset, uint16_t blob_length, uint8_t * value){
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = request_type;
    little_endian_store_16(request, 1, attribute_handle);
    little_endian_store_16(request, 3, value_offset);
    (void)memcpy(&request[5], &value[value_offset], blob_length);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 5u + blob_length);
}

static uint8_t att_exchange_mtu_request(uint16_t con_handle){
    uint16_t mtu = l2cap_max_le_mtu();
    l2cap_reserve_packet_buffer();
    uint8_t * request = l2cap_get_outgoing_buffer();
    request[0] = ATT_EXCHANGE_MTU_REQUEST;
    little_endian_store_16(request, 1, mtu);

    return l2cap_send_prepared_connectionless(con_handle, L2CAP_CID_ATTRIBUTE_PROTOCOL, 3);
}

static uint16_t write_blob_length(gatt_client_t * gatt_client){
    uint16_t max_blob_length = gatt_client->mtu - 5u;
    if (gatt_client->attribute_offset >= gatt_client->attribute_length) {
        return 0;
    }
    uint16_t rest_length = gatt_client->attribute_length - gatt_client->attribute_offset;
    if (max_blob_length > rest_length){
        return rest_length;
    }
    return max_blob_length;
}

static void send_gatt_services_request(gatt_client_t *gatt_client){
    att_read_by_type_or_group_request_for_uuid16(ATT_READ_BY_GROUP_TYPE_REQUEST, GATT_PRIMARY_SERVICE_UUID, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle);
}

static void send_gatt_by_uuid_request(gatt_client_t *gatt_client, uint16_t attribute_group_type){
    if (gatt_client->uuid16){
        uint8_t uuid16[2];
        little_endian_store_16(uuid16, 0, gatt_client->uuid16);
        att_find_by_type_value_request(ATT_FIND_BY_TYPE_VALUE_REQUEST, attribute_group_type, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle, uuid16, 2);
        return;
    }
    uint8_t uuid128[16];
    reverse_128(gatt_client->uuid128, uuid128);
    att_find_by_type_value_request(ATT_FIND_BY_TYPE_VALUE_REQUEST, attribute_group_type, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle, uuid128, 16);
}

static void send_gatt_services_by_uuid_request(gatt_client_t *gatt_client){
    send_gatt_by_uuid_request(gatt_client, GATT_PRIMARY_SERVICE_UUID);
}

static void send_gatt_included_service_uuid_request(gatt_client_t *gatt_client){
    att_read_request(ATT_READ_REQUEST, gatt_client->con_handle, gatt_client->query_start_handle);
}

static void send_gatt_included_service_request(gatt_client_t *gatt_client){
    att_read_by_type_or_group_request_for_uuid16(ATT_READ_BY_TYPE_REQUEST, GATT_INCLUDE_SERVICE_UUID, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle);
}

static void send_gatt_characteristic_request(gatt_client_t *gatt_client){
    att_read_by_type_or_group_request_for_uuid16(ATT_READ_BY_TYPE_REQUEST, GATT_CHARACTERISTICS_UUID, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle);
}

static void send_gatt_characteristic_descriptor_request(gatt_client_t *gatt_client){
    att_find_information_request(ATT_FIND_INFORMATION_REQUEST, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle);
}

static void send_gatt_read_characteristic_value_request(gatt_client_t *gatt_client){
    att_read_request(ATT_READ_REQUEST, gatt_client->con_handle, gatt_client->attribute_handle);
}

static void send_gatt_read_by_type_request(gatt_client_t * gatt_client){
    if (gatt_client->uuid16){
        att_read_by_type_or_group_request_for_uuid16(ATT_READ_BY_TYPE_REQUEST, gatt_client->uuid16, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle);
    } else {
        att_read_by_type_or_group_request_for_uuid128(ATT_READ_BY_TYPE_REQUEST, gatt_client->uuid128, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle);
    }
}

static void send_gatt_read_blob_request(gatt_client_t *gatt_client){
    att_read_blob_request(ATT_READ_BLOB_REQUEST, gatt_client->con_handle, gatt_client->attribute_handle, gatt_client->attribute_offset);
}

static void send_gatt_read_multiple_request(gatt_client_t * gatt_client){
    att_read_multiple_request(gatt_client->con_handle, gatt_client->read_multiple_handle_count, gatt_client->read_multiple_handles);
}

static void send_gatt_write_attribute_value_request(gatt_client_t * gatt_client){
    att_write_request(ATT_WRITE_REQUEST, gatt_client->con_handle, gatt_client->attribute_handle, gatt_client->attribute_length, gatt_client->attribute_value);
}

static void send_gatt_write_client_characteristic_configuration_request(gatt_client_t * gatt_client){
    att_write_request(ATT_WRITE_REQUEST, gatt_client->con_handle, gatt_client->client_characteristic_configuration_handle, 2, gatt_client->client_characteristic_configuration_value);
}

static void send_gatt_prepare_write_request(gatt_client_t * gatt_client){
    att_prepare_write_request(ATT_PREPARE_WRITE_REQUEST, gatt_client->con_handle, gatt_client->attribute_handle, gatt_client->attribute_offset, write_blob_length(gatt_client), gatt_client->attribute_value);
}

static void send_gatt_execute_write_request(gatt_client_t * gatt_client){
    att_execute_write_request(ATT_EXECUTE_WRITE_REQUEST, gatt_client->con_handle, 1);
}

static void send_gatt_cancel_prepared_write_request(gatt_client_t * gatt_client){
    att_execute_write_request(ATT_EXECUTE_WRITE_REQUEST, gatt_client->con_handle, 0);
}

#ifndef ENABLE_GATT_FIND_INFORMATION_FOR_CCC_DISCOVERY
static void send_gatt_read_client_characteristic_configuration_request(gatt_client_t * gatt_client){
    att_read_by_type_or_group_request_for_uuid16(ATT_READ_BY_TYPE_REQUEST, GATT_CLIENT_CHARACTERISTICS_CONFIGURATION, gatt_client->con_handle, gatt_client->start_group_handle, gatt_client->end_group_handle);
}
#endif

static void send_gatt_read_characteristic_descriptor_request(gatt_client_t * gatt_client){
    att_read_request(ATT_READ_REQUEST, gatt_client->con_handle, gatt_client->attribute_handle);
}

#ifdef ENABLE_LE_SIGNED_WRITE
static void send_gatt_signed_write_request(gatt_client_t * gatt_client, uint32_t sign_counter){
    att_signed_write_request(ATT_SIGNED_WRITE_COMMAND, gatt_client->con_handle, gatt_client->attribute_handle, gatt_client->attribute_length, gatt_client->attribute_value, sign_counter, gatt_client->cmac);
}
#endif

static uint16_t get_last_result_handle_from_service_list(uint8_t * packet, uint16_t size){
    uint8_t attr_length = packet[1];
    return little_endian_read_16(packet, size - attr_length + 2u);
}

static uint16_t get_last_result_handle_from_characteristics_list(uint8_t * packet, uint16_t size){
    uint8_t attr_length = packet[1];
    return little_endian_read_16(packet, size - attr_length + 3u);
}

static uint16_t get_last_result_handle_from_included_services_list(uint8_t * packet, uint16_t size){
    uint8_t attr_length = packet[1];
    return little_endian_read_16(packet, size - attr_length);
}

static void gatt_client_handle_transaction_complete(gatt_client_t * gatt_client){
    gatt_client->gatt_client_state = P_READY;
    gatt_client_timeout_stop(gatt_client);
}

static void emit_event_new(btstack_packet_handler_t callback, uint8_t * packet, uint16_t size){
    if (!callback) return;
    hci_dump_packet(HCI_EVENT_PACKET, 0, packet, size);
    (*callback)(HCI_EVENT_PACKET, 0, packet, size);
}

void gatt_client_listen_for_characteristic_value_updates(gatt_client_notification_t * notification, btstack_packet_handler_t packet_handler, hci_con_handle_t con_handle, gatt_client_characteristic_t * characteristic){
    notification->callback = packet_handler;
    notification->con_handle = con_handle;
    if (characteristic == NULL){
        notification->attribute_handle = GATT_CLIENT_ANY_VALUE_HANDLE;
    } else {
        notification->attribute_handle = characteristic->value_handle;
    }
    btstack_linked_list_add(&gatt_client_value_listeners, (btstack_linked_item_t*) notification);
}

void gatt_client_stop_listening_for_characteristic_value_updates(gatt_client_notification_t * notification){
    btstack_linked_list_remove(&gatt_client_value_listeners, (btstack_linked_item_t*) notification);
}

static void emit_event_to_registered_listeners(hci_con_handle_t con_handle, uint16_t attribute_handle, uint8_t * packet, uint16_t size){
    btstack_linked_list_iterator_t it;
    btstack_linked_list_iterator_init(&it, &gatt_client_value_listeners);
    while (btstack_linked_list_iterator_has_next(&it)){
        gatt_client_notification_t * notification = (gatt_client_notification_t*) btstack_linked_list_iterator_next(&it);
        if ((notification->con_handle       != GATT_CLIENT_ANY_CONNECTION)   && (notification->con_handle       != con_handle)) continue;
        if ((notification->attribute_handle != GATT_CLIENT_ANY_VALUE_HANDLE) && (notification->attribute_handle != attribute_handle)) continue;
        (*notification->callback)(HCI_EVENT_PACKET, 0, packet, size);
    }
}

static void emit_gatt_complete_event(gatt_client_t * gatt_client, uint8_t att_status){
    // @format H1
    uint8_t packet[5];
    packet[0] = GATT_EVENT_QUERY_COMPLETE;
    packet[1] = 3;
    little_endian_store_16(packet, 2, gatt_client->con_handle);
    packet[4] = att_status;
    emit_event_new(gatt_client->callback, packet, sizeof(packet));
}

static void emit_gatt_service_query_result_event(gatt_client_t * gatt_client, uint16_t start_group_handle, uint16_t end_group_handle, uint8_t * uuid128){
    // @format HX
    uint8_t packet[24];
    packet[0] = GATT_EVENT_SERVICE_QUERY_RESULT;
    packet[1] = sizeof(packet) - 2u;
    little_endian_store_16(packet, 2, gatt_client->con_handle);
    ///
    little_endian_store_16(packet, 4, start_group_handle);
    little_endian_store_16(packet, 6, end_group_handle);
    reverse_128(uuid128, &packet[8]);
    emit_event_new(gatt_client->callback, packet, sizeof(packet));
}

static void emit_gatt_included_service_query_result_event(gatt_client_t * gatt_client, uint16_t include_handle, uint16_t start_group_handle, uint16_t end_group_handle, uint8_t * uuid128){
    // @format HX
    uint8_t packet[26];
    packet[0] = GATT_EVENT_INCLUDED_SERVICE_QUERY_RESULT;
    packet[1] = sizeof(packet) - 2u;
    little_endian_store_16(packet, 2, gatt_client->con_handle);
    ///
    little_endian_store_16(packet, 4, include_handle);
    //
    little_endian_store_16(packet, 6, start_group_handle);
    little_endian_store_16(packet, 8, end_group_handle);
    reverse_128(uuid128, &packet[10]);
    emit_event_new(gatt_client->callback, packet, sizeof(packet));
}

static void emit_gatt_characteristic_query_result_event(gatt_client_t * gatt_client, uint16_t start_handle, uint16_t value_handle, uint16_t end_handle,
                                                        uint16_t properties, uint8_t * uuid128){
    // @format HY
    uint8_t packet[28];
    packet[0] = GATT_EVENT_CHARACTERISTIC_QUERY_RESULT;
    packet[1] = sizeof(packet) - 2u;
    little_endian_store_16(packet, 2, gatt_client->con_handle);
    ///
    little_endian_store_16(packet, 4,  start_handle);
    little_endian_store_16(packet, 6,  value_handle);
    little_endian_store_16(packet, 8,  end_handle);
    little_endian_store_16(packet, 10, properties);
    reverse_128(uuid128, &packet[12]);
    emit_event_new(gatt_client->callback, packet, sizeof(packet));
}

static void emit_gatt_all_characteristic_descriptors_result_event(
        gatt_client_t * gatt_client, uint16_t descriptor_handle, uint8_t * uuid128){
    // @format HZ
    uint8_t packet[22];
    packet[0] = GATT_EVENT_ALL_CHARACTERISTIC_DESCRIPTORS_QUERY_RESULT;
    packet[1] = sizeof(packet) - 2u;
    little_endian_store_16(packet, 2, gatt_client->con_handle);
    ///
    little_endian_store_16(packet, 4,  descriptor_handle);
    reverse_128(uuid128, &packet[6]);
    emit_event_new(gatt_client->callback, packet, sizeof(packet));
}

static void emit_gatt_mtu_exchanged_result_event(gatt_client_t * gatt_client, uint16_t new_mtu){
    // @format H2
    uint8_t packet[6];
    packet[0] = GATT_EVENT_MTU;
    packet[1] = sizeof(packet) - 2u;
    little_endian_store_16(packet, 2, gatt_client->con_handle);
    little_endian_store_16(packet, 4, new_mtu);
    att_dispatch_client_mtu_exchanged(gatt_client->con_handle, new_mtu);
    emit_event_new(gatt_client->callback, packet, sizeof(packet));
}
///
static void report_gatt_services(gatt_client_t * gatt_client, uint8_t * packet, uint16_t size){
    uint8_t attr_length = packet[1];
    uint8_t uuid_length = attr_length - 4u;

    int i;
    for (i = 2; i < size; i += attr_length){
        uint16_t start_group_handle = little_endian_read_16(packet,i);
        uint16_t end_group_handle   = little_endian_read_16(packet,i+2);
        uint8_t  uuid128[16];
        uint16_t uuid16 = 0;

        if (uuid_length == 2u){
            uuid16 = little_endian_read_16(packet, i+4);
            uuid_add_bluetooth_prefix((uint8_t*) &uuid128, uuid16);
        } else {
            reverse_128(&packet[i+4], uuid128);
        }
        emit_gatt_service_query_result_event(gatt_client, start_group_handle, end_group_handle, uuid128);
    }
}

// helper
static void characteristic_start_found(gatt_client_t * gatt_client, uint16_t start_handle, uint8_t properties, uint16_t value_handle, uint8_t * uuid, uint16_t uuid_length){
    uint8_t uuid128[16];
    uint16_t uuid16 = 0;
    if (uuid_length == 2u){
        uuid16 = little_endian_read_16(uuid, 0);
        uuid_add_bluetooth_prefix((uint8_t*) uuid128, uuid16);
    } else if (uuid_length == 16u){
        reverse_128(uuid, uuid128);
    } else {
        return;
    }

    if (gatt_client->filter_with_uuid && (memcmp(gatt_client->uuid128, uuid128, 16) != 0)) return;

    gatt_client->characteristic_properties = properties;
    gatt_client->characteristic_start_handle = start_handle;
    gatt_client->attribute_handle = value_handle;

    if (gatt_client->filter_with_uuid) return;

    gatt_client->uuid16 = uuid16;
    (void)memcpy(gatt_client->uuid128, uuid128, 16);
}

static void characteristic_end_found(gatt_client_t * gatt_client, uint16_t end_handle){
    // TODO: stop searching if filter and uuid found

    if (!gatt_client->characteristic_start_handle) return;

    emit_gatt_characteristic_query_result_event(gatt_client, gatt_client->characteristic_start_handle, gatt_client->attribute_handle,
                                                end_handle, gatt_client->characteristic_properties, gatt_client->uuid128);

    gatt_client->characteristic_start_handle = 0;
}

static void report_gatt_characteristics(gatt_client_t * gatt_client, uint8_t * packet, uint16_t size){
    if (size < 2u) return;
    uint8_t attr_length = packet[1];
    if ((attr_length != 7u) && (attr_length != 21u)) return;
    uint8_t uuid_length = attr_length - 5u;
    int i;
    for (i = 2u; (i + attr_length) <= size; i += attr_length){
        uint16_t start_handle = little_endian_read_16(packet, i);
        uint8_t  properties = packet[i+2];
        uint16_t value_handle = little_endian_read_16(packet, i+3);
        characteristic_end_found(gatt_client, start_handle - 1u);
        characteristic_start_found(gatt_client, start_handle, properties, value_handle, &packet[i + 5], uuid_length);
    }
}

static void report_gatt_included_service_uuid16(gatt_client_t * gatt_client, uint16_t include_handle, uint16_t uuid16){
    uint8_t normalized_uuid128[16];
    uuid_add_bluetooth_prefix(normalized_uuid128, uuid16);
    emit_gatt_included_service_query_result_event(gatt_client, include_handle, gatt_client->query_start_handle,
                                                  gatt_client->query_end_handle, normalized_uuid128);
}

static void report_gatt_included_service_uuid128(gatt_client_t * gatt_client, uint16_t include_handle, uint8_t *uuid128){
    emit_gatt_included_service_query_result_event(gatt_client, include_handle, gatt_client->query_start_handle,
                                                  gatt_client->query_end_handle, uuid128);
}

// @returns packet pointer
// @note assume that value is part of an l2cap buffer - overwrite HCI + L2CAP packet headers
static const int characteristic_value_event_header_size = 8;
static uint8_t * setup_characteristic_value_packet(uint8_t type, hci_con_handle_t con_handle, uint16_t attribute_handle, uint8_t * value, uint16_t length){
#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
    // avoid using pre ATT headers.
    return NULL;
#endif
    // before the value inside the ATT PDU
    uint8_t * packet = value - characteristic_value_event_header_size;
    packet[0] = type;
    packet[1] = characteristic_value_event_header_size - 2 + length;
    little_endian_store_16(packet, 2, con_handle);
    little_endian_store_16(packet, 4, attribute_handle);
    little_endian_store_16(packet, 6, length);
    return packet;
}

// @returns packet pointer
// @note assume that value is part of an l2cap buffer - overwrite parts of the HCI/L2CAP/ATT packet (4/4/3) bytes
static const int long_characteristic_value_event_header_size = 10;
static uint8_t * setup_long_characteristic_value_packet(uint8_t type, hci_con_handle_t con_handle, uint16_t attribute_handle, uint16_t offset, uint8_t * value, uint16_t length){
#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
    // avoid using pre ATT headers.
    return NULL;
#endif
#if defined(HCI_INCOMING_PRE_BUFFER_SIZE) && (HCI_INCOMING_PRE_BUFFER_SIZE >= 10 - 8) // L2CAP Header (4) - ACL Header (4)
    // before the value inside the ATT PDU
    uint8_t * packet = value - long_characteristic_value_event_header_size;
    packet[0] = type;
    packet[1] = long_characteristic_value_event_header_size - 2 + length;
    little_endian_store_16(packet, 2, con_handle);
    little_endian_store_16(packet, 4, attribute_handle);
    little_endian_store_16(packet, 6, offset);
    little_endian_store_16(packet, 8, length);
    return packet;
#else
    log_error("HCI_INCOMING_PRE_BUFFER_SIZE >= 2 required for long characteristic reads");
    return NULL;
#endif
}

// test if notification/indication should be delivered to application (BLESA)
static bool gatt_client_accept_server_message(hci_con_handle_t con_handle){
#ifdef ENABLE_LE_PROACTIVE_AUTHENTICATION
	// ignore messages until re-encryption is complete
    if (gap_reconnect_security_setup_active(con_handle)) return false;

	// after that ignore if bonded but not encrypted
	return !gap_bonded(con_handle) || (gap_encryption_key_size(con_handle) > 0);
#else
	return true;
#endif
}


// @note assume that value is part of an l2cap buffer - overwrite parts of the HCI/L2CAP/ATT packet (4/4/3) bytes
static void report_gatt_notification(hci_con_handle_t con_handle, uint16_t value_handle, uint8_t * value, int length){
	if (!gatt_client_accept_server_message(con_handle)) return;
    uint8_t * packet = setup_characteristic_value_packet(GATT_EVENT_NOTIFICATION, con_handle, value_handle, value, length);
    emit_event_to_registered_listeners(con_handle, value_handle, packet, characteristic_value_event_header_size + length);
}

// @note assume that value is part of an l2cap buffer - overwrite parts of the HCI/L2CAP/ATT packet (4/4/3) bytes
static void report_gatt_indication(hci_con_handle_t con_handle, uint16_t value_handle, uint8_t * value, int length){
	if (!gatt_client_accept_server_message(con_handle)) return;
    uint8_t * packet = setup_characteristic_value_packet(GATT_EVENT_INDICATION, con_handle, value_handle, value, length);
    emit_event_to_registered_listeners(con_handle, value_handle, packet, characteristic_value_event_header_size + length);
}

// @note assume that value is part of an l2cap buffer - overwrite parts of the HCI/L2CAP/ATT packet (4/4/3) bytes
static void report_gatt_characteristic_value(gatt_client_t * gatt_client, uint16_t attribute_handle, uint8_t * value, uint16_t length){
    uint8_t * packet = setup_characteristic_value_packet(GATT_EVENT_CHARACTERISTIC_VALUE_QUERY_RESULT, gatt_client->con_handle, attribute_handle, value, length);
    emit_event_new(gatt_client->callback, packet, characteristic_value_event_header_size + length);
}

// @note assume that value is part of an l2cap buffer - overwrite parts of the HCI/L2CAP/ATT packet (4/4/3) bytes
static void report_gatt_long_characteristic_value_blob(gatt_client_t * gatt_client, uint16_t attribute_handle, uint8_t * blob, uint16_t blob_length, int value_offset){
    uint8_t * packet = setup_long_characteristic_value_packet(GATT_EVENT_LONG_CHARACTERISTIC_VALUE_QUERY_RESULT, gatt_client->con_handle, attribute_handle, value_offset, blob, blob_length);
    if (!packet) return;
    emit_event_new(gatt_client->callback, packet, blob_length + long_characteristic_value_event_header_size);
}

static void report_gatt_characteristic_descriptor(gatt_client_t * gatt_client, uint16_t descriptor_handle, uint8_t *value, uint16_t value_length, uint16_t value_offset){
    UNUSED(value_offset);
    uint8_t * packet = setup_characteristic_value_packet(GATT_EVENT_CHARACTERISTIC_DESCRIPTOR_QUERY_RESULT, gatt_client->con_handle, descriptor_handle, value, value_length);
    emit_event_new(gatt_client->callback, packet, value_length + 8u);
}

static void report_gatt_long_characteristic_descriptor(gatt_client_t * gatt_client, uint16_t descriptor_handle, uint8_t *blob, uint16_t blob_length, uint16_t value_offset){
    uint8_t * packet = setup_long_characteristic_value_packet(GATT_EVENT_LONG_CHARACTERISTIC_DESCRIPTOR_QUERY_RESULT, gatt_client->con_handle, descriptor_handle, value_offset, blob, blob_length);
    if (!packet) return;
    emit_event_new(gatt_client->callback, packet, blob_length + long_characteristic_value_event_header_size);
}

static void report_gatt_all_characteristic_descriptors(gatt_client_t * gatt_client, uint8_t * packet, uint16_t size, uint16_t pair_size){
    int i;
    for (i = 0u; (i + pair_size) <= size; i += pair_size){
        uint16_t descriptor_handle = little_endian_read_16(packet,i);
        uint8_t uuid128[16];
        uint16_t uuid16 = 0;
        if (pair_size == 4u){
            uuid16 = little_endian_read_16(packet,i+2);
            uuid_add_bluetooth_prefix(uuid128, uuid16);
        } else {
            reverse_128(&packet[i+2], uuid128);
        }
        emit_gatt_all_characteristic_descriptors_result_event(gatt_client, descriptor_handle, uuid128);
    }

}

static int is_query_done(gatt_client_t * gatt_client, uint16_t last_result_handle){
    return last_result_handle >= gatt_client->end_group_handle;
}

static void trigger_next_query(gatt_client_t * gatt_client, uint16_t last_result_handle, gatt_client_state_t next_query_state){
    if (is_query_done(gatt_client, last_result_handle)){
        gatt_client_handle_transaction_complete(gatt_client);
        emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
        return;
    }
    // next
    gatt_client->start_group_handle = last_result_handle + 1u;
    gatt_client->gatt_client_state = next_query_state;
}

static void trigger_next_included_service_query(gatt_client_t * gatt_client, uint16_t last_result_handle){
    trigger_next_query(gatt_client, last_result_handle, P_W2_SEND_INCLUDED_SERVICE_QUERY);
}

static void trigger_next_service_query(gatt_client_t * gatt_client, uint16_t last_result_handle){
    trigger_next_query(gatt_client, last_result_handle, P_W2_SEND_SERVICE_QUERY);
}

static void trigger_next_service_by_uuid_query(gatt_client_t * gatt_client, uint16_t last_result_handle){
    trigger_next_query(gatt_client, last_result_handle, P_W2_SEND_SERVICE_WITH_UUID_QUERY);
}

static void trigger_next_characteristic_query(gatt_client_t * gatt_client, uint16_t last_result_handle){
    if (is_query_done(gatt_client, last_result_handle)){
        // report last characteristic
        characteristic_end_found(gatt_client, gatt_client->end_group_handle);
    }
    trigger_next_query(gatt_client, last_result_handle, P_W2_SEND_ALL_CHARACTERISTICS_OF_SERVICE_QUERY);
}

static void trigger_next_characteristic_descriptor_query(gatt_client_t * gatt_client, uint16_t last_result_handle){
    trigger_next_query(gatt_client, last_result_handle, P_W2_SEND_ALL_CHARACTERISTIC_DESCRIPTORS_QUERY);
}

static void trigger_next_read_by_type_query(gatt_client_t * gatt_client, uint16_t last_result_handle){
    trigger_next_query(gatt_client, last_result_handle, P_W2_SEND_READ_BY_TYPE_REQUEST);
}

static void trigger_next_prepare_write_query(gatt_client_t * gatt_client, gatt_client_state_t next_query_state, gatt_client_state_t done_state){
    gatt_client->attribute_offset += write_blob_length(gatt_client);
    uint16_t next_blob_length =  write_blob_length(gatt_client);

    if (next_blob_length == 0u){
        gatt_client->gatt_client_state = done_state;
        return;
    }
    gatt_client->gatt_client_state = next_query_state;
}

static void trigger_next_blob_query(gatt_client_t * gatt_client, gatt_client_state_t next_query_state, uint16_t received_blob_length){

    uint16_t max_blob_length = gatt_client->mtu - 1u;
    if (received_blob_length < max_blob_length){
        gatt_client_handle_transaction_complete(gatt_client);
        emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
        return;
    }

    gatt_client->attribute_offset += received_blob_length;
    gatt_client->gatt_client_state = next_query_state;
}


static int is_value_valid(gatt_client_t *gatt_client, uint8_t *packet, uint16_t size){
    uint16_t attribute_handle = little_endian_read_16(packet, 1);
    uint16_t value_offset = little_endian_read_16(packet, 3);

    if (gatt_client->attribute_handle != attribute_handle) return 0;
    if (gatt_client->attribute_offset != value_offset) return 0;
    return memcmp(&gatt_client->attribute_value[gatt_client->attribute_offset], &packet[5], size - 5u) == 0u;
}

// returns 1 if packet was sent
static int gatt_client_run_for_gatt_client(gatt_client_t * gatt_client){

    // wait until re-encryption as central is complete
    if (gap_reconnect_security_setup_active(gatt_client->con_handle)) return 0;

#ifdef ENABLE_LE_PROACTIVE_AUTHENTICATION
    // wait until re-encryption complete
    if (gatt_client->reencryption_active) return 0;

    // report bonding information missing, if re-encryption failed
    if ((gatt_client->reencryption_result != ERROR_CODE_SUCCESS) && (gatt_client->gatt_client_state != P_READY)){
        gatt_client_handle_transaction_complete(gatt_client);
        emit_gatt_complete_event(gatt_client, ATT_ERROR_BONDING_INFORMATION_MISSING);
        return 0;
    }
#endif

#ifdef ENABLE_GATT_CLIENT_PAIRING
    // wait until pairing complete
    if (gatt_client->wait_for_pairing_complete) return 0;
#endif

    switch (gatt_client->mtu_state) {
        case SEND_MTU_EXCHANGE:
            gatt_client->mtu_state = SENT_MTU_EXCHANGE;
            att_exchange_mtu_request(gatt_client->con_handle);
            return 1;
        case SENT_MTU_EXCHANGE:
            return 0;
        default:
            break;
    }

    if (gatt_client->send_confirmation){
        gatt_client->send_confirmation = 0;
        att_confirmation(gatt_client->con_handle);
        return 1;
    }

    // check MTU for writes
    switch (gatt_client->gatt_client_state){
        case P_W2_SEND_WRITE_CHARACTERISTIC_VALUE:
        case P_W2_SEND_WRITE_CHARACTERISTIC_DESCRIPTOR:
            if (gatt_client->attribute_length <= (gatt_client->mtu - 3u)) break;
            log_error("gatt_client_run: value len %u > MTU %u - 3\n", gatt_client->attribute_length,gatt_client->mtu);
            gatt_client_handle_transaction_complete(gatt_client);
            emit_gatt_complete_event(gatt_client, ATT_ERROR_INVALID_ATTRIBUTE_VALUE_LENGTH);
            return 0;
        default:
            break;
    }

    switch (gatt_client->gatt_client_state){
        case P_W2_SEND_SERVICE_QUERY:
            gatt_client->gatt_client_state = P_W4_SERVICE_QUERY_RESULT;
            send_gatt_services_request(gatt_client);
            return 1;

        case P_W2_SEND_SERVICE_WITH_UUID_QUERY:
            gatt_client->gatt_client_state = P_W4_SERVICE_WITH_UUID_RESULT;
            send_gatt_services_by_uuid_request(gatt_client);
            return 1;

        case P_W2_SEND_ALL_CHARACTERISTICS_OF_SERVICE_QUERY:
            gatt_client->gatt_client_state = P_W4_ALL_CHARACTERISTICS_OF_SERVICE_QUERY_RESULT;
            send_gatt_characteristic_request(gatt_client);
            return 1;

        case P_W2_SEND_CHARACTERISTIC_WITH_UUID_QUERY:
            gatt_client->gatt_client_state = P_W4_CHARACTERISTIC_WITH_UUID_QUERY_RESULT;
            send_gatt_characteristic_request(gatt_client);
            return 1;

        case P_W2_SEND_ALL_CHARACTERISTIC_DESCRIPTORS_QUERY:
            gatt_client->gatt_client_state = P_W4_CHARACTERISTIC_WITH_UUID_QUERY_RESULT;
            send_gatt_characteristic_descriptor_request(gatt_client);
            return 1;

        case P_W2_SEND_INCLUDED_SERVICE_QUERY:
            gatt_client->gatt_client_state = P_W4_INCLUDED_SERVICE_QUERY_RESULT;
            send_gatt_included_service_request(gatt_client);
            return 1;

        case P_W2_SEND_INCLUDED_SERVICE_WITH_UUID_QUERY:
            gatt_client->gatt_client_state = P_W4_INCLUDED_SERVICE_UUID_WITH_QUERY_RESULT;
            send_gatt_included_service_uuid_request(gatt_client);
            return 1;

        case P_W2_SEND_READ_CHARACTERISTIC_VALUE_QUERY:
            gatt_client->gatt_client_state = P_W4_READ_CHARACTERISTIC_VALUE_RESULT;
            send_gatt_read_characteristic_value_request(gatt_client);
            return 1;

        case P_W2_SEND_READ_BLOB_QUERY:
            gatt_client->gatt_client_state = P_W4_READ_BLOB_RESULT;
            send_gatt_read_blob_request(gatt_client);
            return 1;

        case P_W2_SEND_READ_BY_TYPE_REQUEST:
            gatt_client->gatt_client_state = P_W4_READ_BY_TYPE_RESPONSE;
            send_gatt_read_by_type_request(gatt_client);
            return 1;

        case P_W2_SEND_READ_MULTIPLE_REQUEST:
            gatt_client->gatt_client_state = P_W4_READ_MULTIPLE_RESPONSE;
            send_gatt_read_multiple_request(gatt_client);
            return 1;

        case P_W2_SEND_WRITE_CHARACTERISTIC_VALUE:
            gatt_client->gatt_client_state = P_W4_WRITE_CHARACTERISTIC_VALUE_RESULT;
            send_gatt_write_attribute_value_request(gatt_client);
            return 1;

        case P_W2_PREPARE_WRITE:
            gatt_client->gatt_client_state = P_W4_PREPARE_WRITE_RESULT;
            send_gatt_prepare_write_request(gatt_client);
            return 1;

        case P_W2_PREPARE_WRITE_SINGLE:
            gatt_client->gatt_client_state = P_W4_PREPARE_WRITE_SINGLE_RESULT;
            send_gatt_prepare_write_request(gatt_client);
            return 1;

        case P_W2_PREPARE_RELIABLE_WRITE:
            gatt_client->gatt_client_state = P_W4_PREPARE_RELIABLE_WRITE_RESULT;
            send_gatt_prepare_write_request(gatt_client);
            return 1;

        case P_W2_EXECUTE_PREPARED_WRITE:
            gatt_client->gatt_client_state = P_W4_EXECUTE_PREPARED_WRITE_RESULT;
            send_gatt_execute_write_request(gatt_client);
            return 1;

        case P_W2_CANCEL_PREPARED_WRITE:
            gatt_client->gatt_client_state = P_W4_CANCEL_PREPARED_WRITE_RESULT;
            send_gatt_cancel_prepared_write_request(gatt_client);
            return 1;

        case P_W2_CANCEL_PREPARED_WRITE_DATA_MISMATCH:
            gatt_client->gatt_client_state = P_W4_CANCEL_PREPARED_WRITE_DATA_MISMATCH_RESULT;
            send_gatt_cancel_prepared_write_request(gatt_client);
            return 1;

#ifdef ENABLE_GATT_FIND_INFORMATION_FOR_CCC_DISCOVERY
        case P_W2_SEND_FIND_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY:
            // use Find Information
            gatt_client->gatt_client_state = P_W4_FIND_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY_RESULT;
            send_gatt_characteristic_descriptor_request(gatt_client);
#else
        case P_W2_SEND_READ_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY:
            // Use Read By Type
            gatt_client->gatt_client_state = P_W4_READ_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY_RESULT;
            send_gatt_read_client_characteristic_configuration_request(gatt_client);
#endif
            return 1;

        case P_W2_SEND_READ_CHARACTERISTIC_DESCRIPTOR_QUERY:
            gatt_client->gatt_client_state = P_W4_READ_CHARACTERISTIC_DESCRIPTOR_RESULT;
            send_gatt_read_characteristic_descriptor_request(gatt_client);
            return 1;

        case P_W2_SEND_READ_BLOB_CHARACTERISTIC_DESCRIPTOR_QUERY:
            gatt_client->gatt_client_state = P_W4_READ_BLOB_CHARACTERISTIC_DESCRIPTOR_RESULT;
            send_gatt_read_blob_request(gatt_client);
            return 1;

        case P_W2_SEND_WRITE_CHARACTERISTIC_DESCRIPTOR:
            gatt_client->gatt_client_state = P_W4_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT;
            send_gatt_write_attribute_value_request(gatt_client);
            return 1;

        case P_W2_WRITE_CLIENT_CHARACTERISTIC_CONFIGURATION:
            gatt_client->gatt_client_state = P_W4_CLIENT_CHARACTERISTIC_CONFIGURATION_RESULT;
            send_gatt_write_client_characteristic_configuration_request(gatt_client);
            return 1;

        case P_W2_PREPARE_WRITE_CHARACTERISTIC_DESCRIPTOR:
            gatt_client->gatt_client_state = P_W4_PREPARE_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT;
            send_gatt_prepare_write_request(gatt_client);
            return 1;

        case P_W2_EXECUTE_PREPARED_WRITE_CHARACTERISTIC_DESCRIPTOR:
            gatt_client->gatt_client_state = P_W4_EXECUTE_PREPARED_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT;
            send_gatt_execute_write_request(gatt_client);
            return 1;

#ifdef ENABLE_LE_SIGNED_WRITE
        case P_W4_IDENTITY_RESOLVING:
            log_info("P_W4_IDENTITY_RESOLVING - state %x", sm_identity_resolving_state(gatt_client->con_handle));
            switch (sm_identity_resolving_state(gatt_client->con_handle)){
                case IRK_LOOKUP_SUCCEEDED:
                    gatt_client->le_device_index = sm_le_device_index(gatt_client->con_handle);
                    gatt_client->gatt_client_state = P_W4_CMAC_READY;
                    break;
                case IRK_LOOKUP_FAILED:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_BONDING_INFORMATION_MISSING);
                    return 0;
                default:
                    return 0;
            }

            /* Fall through */

        case P_W4_CMAC_READY:
            if (sm_cmac_ready()){
                sm_key_t csrk;
                le_device_db_local_csrk_get(gatt_client->le_device_index, csrk);
                uint32_t sign_counter = le_device_db_local_counter_get(gatt_client->le_device_index);
                gatt_client->gatt_client_state = P_W4_CMAC_RESULT;
                sm_cmac_signed_write_start(csrk, ATT_SIGNED_WRITE_COMMAND, gatt_client->attribute_handle, gatt_client->attribute_length, gatt_client->attribute_value, sign_counter, att_signed_write_handle_cmac_result);
            }
            return 0;

        case P_W2_SEND_SIGNED_WRITE: {
            gatt_client->gatt_client_state = P_W4_SEND_SINGED_WRITE_DONE;
            // bump local signing counter
            uint32_t sign_counter = le_device_db_local_counter_get(gatt_client->le_device_index);
            le_device_db_local_counter_set(gatt_client->le_device_index, sign_counter + 1);
            // send signed write command
            send_gatt_signed_write_request(gatt_client, sign_counter);
            // finally, notifiy client that write is complete
            gatt_client_handle_transaction_complete(gatt_client);
            emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
            return 1;
        }
#endif
        default:
            break;
    }

    // requested can send snow?
    if (gatt_client->write_without_response_callback){
        btstack_packet_handler_t packet_handler = gatt_client->write_without_response_callback;
        gatt_client->write_without_response_callback = NULL;
        uint8_t event[4];
        event[0] = GATT_EVENT_CAN_WRITE_WITHOUT_RESPONSE;
        event[1] = sizeof(event) - 2u;
        little_endian_store_16(event, 2, gatt_client->con_handle);
        packet_handler(HCI_EVENT_PACKET, gatt_client->con_handle, event, sizeof(event));
        return 1; // to trigger requeueing (even if higher layer didn't sent)
    }

    return 0;
}

static void gatt_client_run(void){
    btstack_linked_item_t *it;
    for (it = (btstack_linked_item_t *) gatt_client_connections; it != NULL; it = it->next){
        gatt_client_t * gatt_client = (gatt_client_t *) it;
        if (!att_dispatch_client_can_send_now(gatt_client->con_handle)) {
            att_dispatch_client_request_can_send_now_event(gatt_client->con_handle);
            return;
        }
        int packet_sent = gatt_client_run_for_gatt_client(gatt_client);
        if (packet_sent){
            // request new permission
            att_dispatch_client_request_can_send_now_event(gatt_client->con_handle);
            // requeue client for fairness and exit
            // note: iterator has become invalid
            btstack_linked_list_remove(&gatt_client_connections, (btstack_linked_item_t *) gatt_client);
            btstack_linked_list_add_tail(&gatt_client_connections, (btstack_linked_item_t *) gatt_client);
            return;
        }
    }
}

static void gatt_client_report_error_if_pending(gatt_client_t *gatt_client, uint8_t att_error_code) {
    if (is_ready(gatt_client) == 1) return;
    gatt_client_handle_transaction_complete(gatt_client);
    emit_gatt_complete_event(gatt_client, att_error_code);
}

static void gatt_client_event_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
    UNUSED(channel);    // ok: handling own l2cap events
    UNUSED(size);       // ok: there is no channel

    if (packet_type != HCI_EVENT_PACKET) return;

    hci_con_handle_t con_handle;
    gatt_client_t * gatt_client;
    switch (hci_event_packet_get_type(packet)) {
        case HCI_EVENT_DISCONNECTION_COMPLETE:
            log_info("GATT Client: HCI_EVENT_DISCONNECTION_COMPLETE");
            con_handle = little_endian_read_16(packet,3);
            gatt_client = gatt_client_get_context_for_handle(con_handle);
            if (gatt_client == NULL) break;

            gatt_client_report_error_if_pending(gatt_client, ATT_ERROR_HCI_DISCONNECT_RECEIVED);
            gatt_client_timeout_stop(gatt_client);
            btstack_linked_list_remove(&gatt_client_connections, (btstack_linked_item_t *) gatt_client);
            btstack_memory_gatt_client_free(gatt_client);
            break;

#ifdef ENABLE_GATT_CLIENT_PAIRING
        // Pairing complete (with/without bonding=storing of pairing information)
        case SM_EVENT_PAIRING_COMPLETE:
            con_handle = sm_event_pairing_complete_get_handle(packet);
            gatt_client = gatt_client_get_context_for_handle(con_handle);
            if (gatt_client == NULL) break;

            if (gatt_client->wait_for_pairing_complete){
                gatt_client->wait_for_pairing_complete = 0;
                if (sm_event_pairing_complete_get_status(packet)){
                    log_info("pairing failed, report previous error 0x%x", gatt_client->pending_error_code);
                    gatt_client_report_error_if_pending(gatt_client, gatt_client->pending_error_code);
                } else {
                    log_info("pairing success, retry operation");
                }
            }
            break;
#endif
#ifdef ENABLE_LE_SIGNED_WRITE
        // Identity Resolving completed (no code, gatt_client_run will continue)
        case SM_EVENT_IDENTITY_RESOLVING_SUCCEEDED:
        case SM_EVENT_IDENTITY_RESOLVING_FAILED:
            break;
#endif
#ifdef ENABLE_LE_PROACTIVE_AUTHENTICATION
        // re-encryption started
        case SM_EVENT_REENCRYPTION_STARTED:
            con_handle = sm_event_reencryption_complete_get_handle(packet);
            gatt_client = gatt_client_get_context_for_handle(con_handle);
            if (gatt_client == NULL) break;

            gatt_client->reencryption_active = true;
            gatt_client->reencryption_result = ERROR_CODE_SUCCESS;
            break;

        // re-encryption complete
        case SM_EVENT_REENCRYPTION_COMPLETE:
            con_handle = sm_event_reencryption_complete_get_handle(packet);
            gatt_client = gatt_client_get_context_for_handle(con_handle);
            if (gatt_client == NULL) break;

            gatt_client->reencryption_result = sm_event_reencryption_complete_get_status(packet);
            gatt_client->reencryption_active = false;
            break;
#endif
        default:
            break;
    }

    gatt_client_run();
}

static void gatt_client_att_packet_handler(uint8_t packet_type, uint16_t handle, uint8_t *packet, uint16_t size){
    gatt_client_t * gatt_client;
    if (size < 1u) return;

    if (packet_type == HCI_EVENT_PACKET) {
        switch (packet[0]){
            case L2CAP_EVENT_CAN_SEND_NOW:
                gatt_client_run();
                break;
            // att_server has negotiated the mtu for this connection, cache if context exists
            case ATT_EVENT_MTU_EXCHANGE_COMPLETE:
                if (size < 6u) break;
                gatt_client = gatt_client_get_context_for_handle(handle);
                if (gatt_client == NULL) break;
                gatt_client->mtu = little_endian_read_16(packet, 4);
                break;
            default:
                break;
        }
        return;
    }

    if (packet_type != ATT_DATA_PACKET) return;

    // special cases: notifications don't need a context while indications motivate creating one
    switch (packet[0]){
        case ATT_HANDLE_VALUE_NOTIFICATION:
            if (size < 3u) return;
            report_gatt_notification(handle, little_endian_read_16(packet,1u), &packet[3], size-3u);
            return;
        case ATT_HANDLE_VALUE_INDICATION:
            gatt_client = gatt_client_provide_context_for_handle(handle);
            break;
        default:
            gatt_client = gatt_client_get_context_for_handle(handle);
            break;
    }

    if (gatt_client == NULL) return;

    uint8_t error_code;
    switch (packet[0]){
        case ATT_EXCHANGE_MTU_RESPONSE:
        {
            if (size < 3u) break;
            uint16_t remote_rx_mtu = little_endian_read_16(packet, 1);
            uint16_t local_rx_mtu = l2cap_max_le_mtu();
            gatt_client->mtu = (remote_rx_mtu < local_rx_mtu) ? remote_rx_mtu : local_rx_mtu;
            gatt_client->mtu_state = MTU_EXCHANGED;
            emit_gatt_mtu_exchanged_result_event(gatt_client, gatt_client->mtu);
            break;
        }
        case ATT_READ_BY_GROUP_TYPE_RESPONSE:
            switch(gatt_client->gatt_client_state){
                case P_W4_SERVICE_QUERY_RESULT:
                    report_gatt_services(gatt_client, packet, size);
                    trigger_next_service_query(gatt_client, get_last_result_handle_from_service_list(packet, size));
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                    break;
                default:
                    break;
            }
            break;
        case ATT_HANDLE_VALUE_INDICATION:
            if (size < 3u) break;
            report_gatt_indication(handle, little_endian_read_16(packet,1u), &packet[3], size-3u);
            gatt_client->send_confirmation = 1;
            break;

        case ATT_READ_BY_TYPE_RESPONSE:
            switch (gatt_client->gatt_client_state){
                case P_W4_ALL_CHARACTERISTICS_OF_SERVICE_QUERY_RESULT:
                    report_gatt_characteristics(gatt_client, packet, size);
                    trigger_next_characteristic_query(gatt_client, get_last_result_handle_from_characteristics_list(packet, size));
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done, or by ATT_ERROR
                    break;
                case P_W4_CHARACTERISTIC_WITH_UUID_QUERY_RESULT:
                    report_gatt_characteristics(gatt_client, packet, size);
                    trigger_next_characteristic_query(gatt_client, get_last_result_handle_from_characteristics_list(packet, size));
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done, or by ATT_ERROR
                    break;
                case P_W4_INCLUDED_SERVICE_QUERY_RESULT:
                {
                    if (size < 2u) break;
                    uint16_t uuid16 = 0;
                    uint16_t pair_size = packet[1];

                    if (pair_size == 6u){
                        if (size < 8u) break;
                        // UUIDs not available, query first included service
                        gatt_client->start_group_handle = little_endian_read_16(packet, 2); // ready for next query
                        gatt_client->query_start_handle = little_endian_read_16(packet, 4);
                        gatt_client->query_end_handle = little_endian_read_16(packet, 6);
                        gatt_client->gatt_client_state = P_W2_SEND_INCLUDED_SERVICE_WITH_UUID_QUERY;
                        break;
                    }

                    if (pair_size != 8u) break;

                    // UUIDs included, report all of them
                    uint16_t offset;
                    for (offset = 2u; (offset + 8u) <= size; offset += pair_size){
                        uint16_t include_handle = little_endian_read_16(packet, offset);
                        gatt_client->query_start_handle = little_endian_read_16(packet, offset + 2u);
                        gatt_client->query_end_handle = little_endian_read_16(packet, offset + 4u);
                        uuid16 = little_endian_read_16(packet, offset+6u);
                        report_gatt_included_service_uuid16(gatt_client, include_handle, uuid16);
                    }

                    trigger_next_included_service_query(gatt_client, get_last_result_handle_from_included_services_list(packet, size));
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                    break;
                }
#ifndef ENABLE_GATT_FIND_INFORMATION_FOR_CCC_DISCOVERY
                case P_W4_READ_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY_RESULT:
                    gatt_client->client_characteristic_configuration_handle = little_endian_read_16(packet, 2);
                    gatt_client->gatt_client_state = P_W2_WRITE_CLIENT_CHARACTERISTIC_CONFIGURATION;
                    break;
#endif
                case P_W4_READ_BY_TYPE_RESPONSE: {
                    uint16_t pair_size = packet[1];
                    uint16_t offset;
                    uint16_t last_result_handle = 0;
                    for (offset = 2; offset < size ; offset += pair_size){
                        uint16_t value_handle = little_endian_read_16(packet, offset);
                        report_gatt_characteristic_value(gatt_client, value_handle, &packet[offset + 2u], pair_size - 2u);
                        last_result_handle = value_handle;
                    }
                    trigger_next_read_by_type_query(gatt_client, last_result_handle);
                    break;
                }
                default:
                    break;
            }
            break;
        case ATT_READ_RESPONSE:
            switch (gatt_client->gatt_client_state){
                case P_W4_INCLUDED_SERVICE_UUID_WITH_QUERY_RESULT: {
                    uint8_t uuid128[16];
                    reverse_128(&packet[1], uuid128);
                    report_gatt_included_service_uuid128(gatt_client, gatt_client->start_group_handle, uuid128);
                    trigger_next_included_service_query(gatt_client, gatt_client->start_group_handle);
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                    break;
                }
                case P_W4_READ_CHARACTERISTIC_VALUE_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    report_gatt_characteristic_value(gatt_client, gatt_client->attribute_handle, &packet[1], size - 1u);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;

                case P_W4_READ_CHARACTERISTIC_DESCRIPTOR_RESULT:{
                    gatt_client_handle_transaction_complete(gatt_client);
                    report_gatt_characteristic_descriptor(gatt_client, gatt_client->attribute_handle, &packet[1], size - 1u, 0u);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                }
                default:
                    break;
            }
            break;

        case ATT_FIND_BY_TYPE_VALUE_RESPONSE:
        {
            uint8_t pair_size = 4;
            int i;
            uint16_t start_group_handle;
            uint16_t   end_group_handle= 0xffff; // asserts GATT_EVENT_QUERY_COMPLETE is emitted if no results
            for (i = 1u; (i + pair_size) <= size; i += pair_size){
                start_group_handle = little_endian_read_16(packet,i);
                end_group_handle = little_endian_read_16(packet,i+2);
                emit_gatt_service_query_result_event(gatt_client, start_group_handle, end_group_handle, gatt_client->uuid128);
            }
            trigger_next_service_by_uuid_query(gatt_client, end_group_handle);
            // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
            break;
        }
        case ATT_FIND_INFORMATION_REPLY:
        {
            if (size < 2u) break;

            uint8_t pair_size = 4;
            if (packet[1u] == 2u){
                pair_size = 18;
            }
            uint16_t offset = 2;

            if (size < (pair_size + offset)) break;
            uint16_t last_descriptor_handle = little_endian_read_16(packet, size - pair_size);

#ifdef ENABLE_GATT_FIND_INFORMATION_FOR_CCC_DISCOVERY
            log_info("ENABLE_GATT_FIND_INFORMATION_FOR_CCC_DISCOVERY, state %x", gatt_client->gatt_client_state);
            if (gatt_client->gatt_client_state == P_W4_FIND_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY_RESULT){
                // iterate over descriptors looking for CCC
                if (pair_size == 4){
                    while ((offset + 4) <= size){
                        uint16_t uuid16 = little_endian_read_16(packet, offset + 2);
                        if (uuid16 == GATT_CLIENT_CHARACTERISTICS_CONFIGURATION){
                            gatt_client->client_characteristic_configuration_handle = little_endian_read_16(packet, offset);
                            gatt_client->gatt_client_state = P_W2_WRITE_CLIENT_CHARACTERISTIC_CONFIGURATION;
                            log_info("CCC found %x", gatt_client->client_characteristic_configuration_handle);
                            break;
                        }
                        offset += pair_size;
                    }
                }
                if (is_query_done(gatt_client, last_descriptor_handle)){

                } else {
                    // next
                    gatt_client->start_group_handle = last_descriptor_handle + 1;
                    gatt_client->gatt_client_state = P_W2_SEND_FIND_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY;
                }
                break;
            }
#endif
            report_gatt_all_characteristic_descriptors(gatt_client, &packet[2], size - 2u, pair_size);
            trigger_next_characteristic_descriptor_query(gatt_client, last_descriptor_handle);
            // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
            break;
        }

        case ATT_WRITE_RESPONSE:
            switch (gatt_client->gatt_client_state){
                case P_W4_WRITE_CHARACTERISTIC_VALUE_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                case P_W4_CLIENT_CHARACTERISTIC_CONFIGURATION_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                case P_W4_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                default:
                    break;
            }
            break;

        case ATT_READ_BLOB_RESPONSE:{
            uint16_t received_blob_length = size-1u;
            switch(gatt_client->gatt_client_state){
                case P_W4_READ_BLOB_RESULT:
                    report_gatt_long_characteristic_value_blob(gatt_client, gatt_client->attribute_handle, &packet[1], received_blob_length, gatt_client->attribute_offset);
                    trigger_next_blob_query(gatt_client, P_W2_SEND_READ_BLOB_QUERY, received_blob_length);
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                    break;
                case P_W4_READ_BLOB_CHARACTERISTIC_DESCRIPTOR_RESULT:
                    report_gatt_long_characteristic_descriptor(gatt_client, gatt_client->attribute_handle,
                                                               &packet[1], received_blob_length,
                                                               gatt_client->attribute_offset);
                    trigger_next_blob_query(gatt_client, P_W2_SEND_READ_BLOB_CHARACTERISTIC_DESCRIPTOR_QUERY, received_blob_length);
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                    break;
                default:
                    break;
            }
            break;
        }
        case ATT_PREPARE_WRITE_RESPONSE:
            switch (gatt_client->gatt_client_state){
                case P_W4_PREPARE_WRITE_SINGLE_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    if (is_value_valid(gatt_client, packet, size)){
                        emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    } else {
                        emit_gatt_complete_event(gatt_client, ATT_ERROR_DATA_MISMATCH);
                    }
                    break;

                case P_W4_PREPARE_WRITE_RESULT:{
                    gatt_client->attribute_offset = little_endian_read_16(packet, 3);
                    trigger_next_prepare_write_query(gatt_client, P_W2_PREPARE_WRITE, P_W2_EXECUTE_PREPARED_WRITE);
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                    break;
                }
                case P_W4_PREPARE_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT:{
                    gatt_client->attribute_offset = little_endian_read_16(packet, 3);
                    trigger_next_prepare_write_query(gatt_client, P_W2_PREPARE_WRITE_CHARACTERISTIC_DESCRIPTOR, P_W2_EXECUTE_PREPARED_WRITE_CHARACTERISTIC_DESCRIPTOR);
                    // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                    break;
                }
                case P_W4_PREPARE_RELIABLE_WRITE_RESULT:{
                    if (is_value_valid(gatt_client, packet, size)){
                        gatt_client->attribute_offset = little_endian_read_16(packet, 3);
                        trigger_next_prepare_write_query(gatt_client, P_W2_PREPARE_RELIABLE_WRITE, P_W2_EXECUTE_PREPARED_WRITE);
                        // GATT_EVENT_QUERY_COMPLETE is emitted by trigger_next_xxx when done
                        break;
                    }
                    gatt_client->gatt_client_state = P_W2_CANCEL_PREPARED_WRITE_DATA_MISMATCH;
                    break;
                }
                default:
                    break;
            }
            break;

        case ATT_EXECUTE_WRITE_RESPONSE:
            switch (gatt_client->gatt_client_state){
                case P_W4_EXECUTE_PREPARED_WRITE_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                case P_W4_CANCEL_PREPARED_WRITE_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                case P_W4_CANCEL_PREPARED_WRITE_DATA_MISMATCH_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_DATA_MISMATCH);
                    break;
                case P_W4_EXECUTE_PREPARED_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT:
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                default:
                    break;

            }
            break;

        case ATT_READ_MULTIPLE_RESPONSE:
            switch(gatt_client->gatt_client_state){
                case P_W4_READ_MULTIPLE_RESPONSE:
                    report_gatt_characteristic_value(gatt_client, 0u, &packet[1], size - 1u);
                    gatt_client_handle_transaction_complete(gatt_client);
                    emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                    break;
                default:
                    break;
            }
            break;

        case ATT_ERROR_RESPONSE:
            if (size < 5u) return;
            error_code = packet[4];
            switch (error_code){
                case ATT_ERROR_ATTRIBUTE_NOT_FOUND: {
                    switch(gatt_client->gatt_client_state){
                        case P_W4_SERVICE_QUERY_RESULT:
                        case P_W4_SERVICE_WITH_UUID_RESULT:
                        case P_W4_INCLUDED_SERVICE_QUERY_RESULT:
                        case P_W4_ALL_CHARACTERISTIC_DESCRIPTORS_QUERY_RESULT:
                            gatt_client_handle_transaction_complete(gatt_client);
                            emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                            break;
                        case P_W4_ALL_CHARACTERISTICS_OF_SERVICE_QUERY_RESULT:
                        case P_W4_CHARACTERISTIC_WITH_UUID_QUERY_RESULT:
                            characteristic_end_found(gatt_client, gatt_client->end_group_handle);
                            gatt_client_handle_transaction_complete(gatt_client);
                            emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                            break;
                        case P_W4_READ_BY_TYPE_RESPONSE:
                            gatt_client_handle_transaction_complete(gatt_client);
                            if (gatt_client->start_group_handle == gatt_client->query_start_handle){
                                emit_gatt_complete_event(gatt_client, ATT_ERROR_ATTRIBUTE_NOT_FOUND);
                            } else {
                                emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
                            }
                            break;
                        default:
                            gatt_client_report_error_if_pending(gatt_client, error_code);
                            break;
                    }
                    break;
                }

#ifdef ENABLE_GATT_CLIENT_PAIRING

                case ATT_ERROR_INSUFFICIENT_AUTHENTICATION:
                case ATT_ERROR_INSUFFICIENT_ENCRYPTION_KEY_SIZE:
                case ATT_ERROR_INSUFFICIENT_ENCRYPTION: {

                    // security too low
                    if (gatt_client->security_counter > 0) {
                        gatt_client_report_error_if_pending(gatt_client, error_code);
                        break;
                    }
                    // start security
                    gatt_client->security_counter++;

                    // setup action
                    int retry = 1;
                    switch (gatt_client->gatt_client_state){
                        case P_W4_READ_CHARACTERISTIC_VALUE_RESULT:
                            gatt_client->gatt_client_state = P_W2_SEND_READ_CHARACTERISTIC_VALUE_QUERY ;
                            break;
                        case P_W4_READ_BLOB_RESULT:
                            gatt_client->gatt_client_state = P_W2_SEND_READ_BLOB_QUERY;
                            break;
                        case P_W4_READ_BY_TYPE_RESPONSE:
                            gatt_client->gatt_client_state = P_W2_SEND_READ_BY_TYPE_REQUEST;
                            break;
                        case P_W4_READ_MULTIPLE_RESPONSE:
                            gatt_client->gatt_client_state = P_W2_SEND_READ_MULTIPLE_REQUEST;
                            break;
                        case P_W4_WRITE_CHARACTERISTIC_VALUE_RESULT:
                            gatt_client->gatt_client_state = P_W2_SEND_WRITE_CHARACTERISTIC_VALUE;
                            break;
                        case P_W4_PREPARE_WRITE_RESULT:
                            gatt_client->gatt_client_state = P_W2_PREPARE_WRITE;
                            break;
                        case P_W4_PREPARE_WRITE_SINGLE_RESULT:
                            gatt_client->gatt_client_state = P_W2_PREPARE_WRITE_SINGLE;
                            break;
                        case P_W4_PREPARE_RELIABLE_WRITE_RESULT:
                            gatt_client->gatt_client_state = P_W2_PREPARE_RELIABLE_WRITE;
                            break;
                        case P_W4_EXECUTE_PREPARED_WRITE_RESULT:
                            gatt_client->gatt_client_state = P_W2_EXECUTE_PREPARED_WRITE;
                            break;
                        case P_W4_CANCEL_PREPARED_WRITE_RESULT:
                            gatt_client->gatt_client_state = P_W2_CANCEL_PREPARED_WRITE;
                            break;
                        case P_W4_CANCEL_PREPARED_WRITE_DATA_MISMATCH_RESULT:
                            gatt_client->gatt_client_state = P_W2_CANCEL_PREPARED_WRITE_DATA_MISMATCH;
                            break;
                        case P_W4_READ_CHARACTERISTIC_DESCRIPTOR_RESULT:
                            gatt_client->gatt_client_state = P_W2_SEND_READ_CHARACTERISTIC_DESCRIPTOR_QUERY;
                            break;
                        case P_W4_READ_BLOB_CHARACTERISTIC_DESCRIPTOR_RESULT:
                            gatt_client->gatt_client_state = P_W2_SEND_READ_BLOB_CHARACTERISTIC_DESCRIPTOR_QUERY;
                            break;
                        case P_W4_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT:
                            gatt_client->gatt_client_state = P_W2_SEND_WRITE_CHARACTERISTIC_DESCRIPTOR;
                            break;
                        case P_W4_CLIENT_CHARACTERISTIC_CONFIGURATION_RESULT:
                            gatt_client->gatt_client_state = P_W2_WRITE_CLIENT_CHARACTERISTIC_CONFIGURATION;
                            break;
                        case P_W4_PREPARE_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT:
                            gatt_client->gatt_client_state = P_W2_PREPARE_WRITE_CHARACTERISTIC_DESCRIPTOR;
                            break;
                        case P_W4_EXECUTE_PREPARED_WRITE_CHARACTERISTIC_DESCRIPTOR_RESULT:
                            gatt_client->gatt_client_state = P_W2_EXECUTE_PREPARED_WRITE_CHARACTERISTIC_DESCRIPTOR;
                            break;
#ifdef ENABLE_LE_SIGNED_WRITE
                        case P_W4_SEND_SINGED_WRITE_DONE:
                            gatt_client->gatt_client_state = P_W2_SEND_SIGNED_WRITE;
                            break;
#endif
                        default:
                            log_info("retry not supported for state %x", gatt_client->gatt_client_state);
                            retry = 0;
                            break;
                    }

                    if (!retry) {
                        gatt_client_report_error_if_pending(gatt_client, error_code);
                        break;
                    }

                    log_info("security error, start pairing");

                    // start pairing for higher security level
                    gatt_client->wait_for_pairing_complete = 1;
                    gatt_client->pending_error_code = error_code;
                    sm_request_pairing(gatt_client->con_handle);
                    break;
                }
#endif

                // nothing we can do about that
                case ATT_ERROR_INSUFFICIENT_AUTHORIZATION:
                default:
                    gatt_client_report_error_if_pending(gatt_client, error_code);
                    break;
            }
            break;

        default:
            log_info("ATT Handler, unhandled response type 0x%02x", packet[0]);
            break;
    }
    gatt_client_run();
}

#ifdef ENABLE_LE_SIGNED_WRITE
static void att_signed_write_handle_cmac_result(uint8_t hash[8]){
    btstack_linked_list_iterator_t it;
    btstack_linked_list_iterator_init(&it, &gatt_client_connections);
    while (btstack_linked_list_iterator_has_next(&it)){
        gatt_client_t * gatt_client = (gatt_client_t *) btstack_linked_list_iterator_next(&it);
        if (gatt_client->gatt_client_state == P_W4_CMAC_RESULT){
            // store result
            (void)memcpy(gatt_client->cmac, hash, 8);
            // reverse_64(hash, gatt_client->cmac);
            gatt_client->gatt_client_state = P_W2_SEND_SIGNED_WRITE;
            gatt_client_run();
            return;
        }
    }
}

uint8_t gatt_client_signed_write_without_response(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t handle, uint16_t message_len, uint8_t * message){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = handle;
    gatt_client->attribute_length = message_len;
    gatt_client->attribute_value = message;
    gatt_client->gatt_client_state = P_W4_IDENTITY_RESOLVING;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}
#endif

uint8_t gatt_client_discover_primary_services(btstack_packet_handler_t callback, hci_con_handle_t con_handle){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = 0x0001;
    gatt_client->end_group_handle   = 0xffff;
    gatt_client->gatt_client_state = P_W2_SEND_SERVICE_QUERY;
    gatt_client->uuid16 = 0;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}


uint8_t gatt_client_discover_primary_services_by_uuid16(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t uuid16){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = 0x0001;
    gatt_client->end_group_handle   = 0xffff;
    gatt_client->gatt_client_state = P_W2_SEND_SERVICE_WITH_UUID_QUERY;
    gatt_client->uuid16 = uuid16;
    uuid_add_bluetooth_prefix((uint8_t*) &(gatt_client->uuid128), gatt_client->uuid16);
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_discover_primary_services_by_uuid128(btstack_packet_handler_t callback, hci_con_handle_t con_handle, const uint8_t * uuid128){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = 0x0001;
    gatt_client->end_group_handle   = 0xffff;
    gatt_client->uuid16 = 0;
    (void)memcpy(gatt_client->uuid128, uuid128, 16);
    gatt_client->gatt_client_state = P_W2_SEND_SERVICE_WITH_UUID_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_discover_characteristics_for_service(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_service_t *service){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = service->start_group_handle;
    gatt_client->end_group_handle   = service->end_group_handle;
    gatt_client->filter_with_uuid = 0;
    gatt_client->characteristic_start_handle = 0;
    gatt_client->gatt_client_state = P_W2_SEND_ALL_CHARACTERISTICS_OF_SERVICE_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_find_included_services_for_service(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_service_t *service){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;
    gatt_client->callback = callback;
    gatt_client->start_group_handle = service->start_group_handle;
    gatt_client->end_group_handle   = service->end_group_handle;
    gatt_client->gatt_client_state = P_W2_SEND_INCLUDED_SERVICE_QUERY;

    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_discover_characteristics_for_handle_range_by_uuid16(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t start_handle, uint16_t end_handle, uint16_t uuid16){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = start_handle;
    gatt_client->end_group_handle   = end_handle;
    gatt_client->filter_with_uuid = 1;
    gatt_client->uuid16 = uuid16;
    uuid_add_bluetooth_prefix((uint8_t*) &(gatt_client->uuid128), uuid16);
    gatt_client->characteristic_start_handle = 0;
    gatt_client->gatt_client_state = P_W2_SEND_CHARACTERISTIC_WITH_UUID_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_discover_characteristics_for_handle_range_by_uuid128(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t start_handle, uint16_t end_handle, uint8_t * uuid128){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = start_handle;
    gatt_client->end_group_handle   = end_handle;
    gatt_client->filter_with_uuid = 1;
    gatt_client->uuid16 = 0;
    (void)memcpy(gatt_client->uuid128, uuid128, 16);
    gatt_client->characteristic_start_handle = 0;
    gatt_client->gatt_client_state = P_W2_SEND_CHARACTERISTIC_WITH_UUID_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}


uint8_t gatt_client_discover_characteristics_for_service_by_uuid16(btstack_packet_handler_t callback, uint16_t handle, gatt_client_service_t *service, uint16_t  uuid16){
    return gatt_client_discover_characteristics_for_handle_range_by_uuid16(callback, handle, service->start_group_handle, service->end_group_handle, uuid16);
}

uint8_t gatt_client_discover_characteristics_for_service_by_uuid128(btstack_packet_handler_t callback, uint16_t handle, gatt_client_service_t *service, uint8_t * uuid128){
    return gatt_client_discover_characteristics_for_handle_range_by_uuid128(callback, handle, service->start_group_handle, service->end_group_handle, uuid128);
}

uint8_t gatt_client_discover_characteristic_descriptors(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_characteristic_t *characteristic){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    if (characteristic->value_handle == characteristic->end_handle){
        emit_gatt_complete_event(gatt_client, ATT_ERROR_SUCCESS);
        return ERROR_CODE_SUCCESS;
    }
    gatt_client->callback = callback;
    gatt_client->start_group_handle = characteristic->value_handle + 1u;
    gatt_client->end_group_handle   = characteristic->end_handle;
    gatt_client->gatt_client_state = P_W2_SEND_ALL_CHARACTERISTIC_DESCRIPTORS_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_read_value_of_characteristic_using_value_handle(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t value_handle){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = value_handle;
    gatt_client->attribute_offset = 0;
    gatt_client->gatt_client_state = P_W2_SEND_READ_CHARACTERISTIC_VALUE_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_read_value_of_characteristics_by_uuid16(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t start_handle, uint16_t end_handle, uint16_t uuid16){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = start_handle;
    gatt_client->end_group_handle = end_handle;
    gatt_client->query_start_handle = start_handle;
    gatt_client->query_end_handle = end_handle;
    gatt_client->uuid16 = uuid16;
    uuid_add_bluetooth_prefix((uint8_t*) &(gatt_client->uuid128), uuid16);
    gatt_client->gatt_client_state = P_W2_SEND_READ_BY_TYPE_REQUEST;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_read_value_of_characteristics_by_uuid128(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t start_handle, uint16_t end_handle, uint8_t * uuid128){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->start_group_handle = start_handle;
    gatt_client->end_group_handle = end_handle;
    gatt_client->query_start_handle = start_handle;
    gatt_client->query_end_handle = end_handle;
    gatt_client->uuid16 = 0;
    (void)memcpy(gatt_client->uuid128, uuid128, 16);
    gatt_client->gatt_client_state = P_W2_SEND_READ_BY_TYPE_REQUEST;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}


uint8_t gatt_client_read_value_of_characteristic(btstack_packet_handler_t callback, uint16_t handle, gatt_client_characteristic_t *characteristic){
    return gatt_client_read_value_of_characteristic_using_value_handle(callback, handle, characteristic->value_handle);
}

uint8_t gatt_client_read_long_value_of_characteristic_using_value_handle_with_offset(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t characteristic_value_handle, uint16_t offset){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = characteristic_value_handle;
    gatt_client->attribute_offset = offset;
    gatt_client->gatt_client_state = P_W2_SEND_READ_BLOB_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_read_long_value_of_characteristic_using_value_handle(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t characteristic_value_handle){
    return gatt_client_read_long_value_of_characteristic_using_value_handle_with_offset(callback, con_handle, characteristic_value_handle, 0);
}

uint8_t gatt_client_read_long_value_of_characteristic(btstack_packet_handler_t callback, uint16_t handle, gatt_client_characteristic_t *characteristic){
    return gatt_client_read_long_value_of_characteristic_using_value_handle(callback, handle, characteristic->value_handle);
}

uint8_t gatt_client_read_multiple_characteristic_values(btstack_packet_handler_t callback, hci_con_handle_t con_handle, int num_value_handles, uint16_t * value_handles){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->read_multiple_handle_count = num_value_handles;
    gatt_client->read_multiple_handles = value_handles;
    gatt_client->gatt_client_state = P_W2_SEND_READ_MULTIPLE_REQUEST;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_write_value_of_characteristic_without_response(hci_con_handle_t con_handle, uint16_t value_handle, uint16_t value_length, uint8_t * value){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;

    if (value_length > (gatt_client->mtu - 3u)) return GATT_CLIENT_VALUE_TOO_LONG;
    if (!att_dispatch_client_can_send_now(gatt_client->con_handle)) return GATT_CLIENT_BUSY;

    return att_write_request(ATT_WRITE_COMMAND, gatt_client->con_handle, value_handle, value_length, value);
}

uint8_t gatt_client_write_value_of_characteristic(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t value_handle, uint16_t value_length, uint8_t * data){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = value_handle;
    gatt_client->attribute_length = value_length;
    gatt_client->attribute_value = data;
    gatt_client->gatt_client_state = P_W2_SEND_WRITE_CHARACTERISTIC_VALUE;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_write_long_value_of_characteristic_with_offset(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t value_handle, uint16_t offset, uint16_t value_length, uint8_t  * data){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = value_handle;
    gatt_client->attribute_length = value_length;
    gatt_client->attribute_offset = offset;
    gatt_client->attribute_value = data;
    gatt_client->gatt_client_state = P_W2_PREPARE_WRITE;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_write_long_value_of_characteristic(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t value_handle, uint16_t value_length, uint8_t * value){
    return gatt_client_write_long_value_of_characteristic_with_offset(callback, con_handle, value_handle, 0, value_length, value);
}

uint8_t gatt_client_reliable_write_long_value_of_characteristic(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t value_handle, uint16_t value_length, uint8_t * value){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = value_handle;
    gatt_client->attribute_length = value_length;
    gatt_client->attribute_offset = 0;
    gatt_client->attribute_value = value;
    gatt_client->gatt_client_state = P_W2_PREPARE_RELIABLE_WRITE;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_write_client_characteristic_configuration(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_characteristic_t * characteristic, uint16_t configuration){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    if ( (configuration & GATT_CLIENT_CHARACTERISTICS_CONFIGURATION_NOTIFICATION) &&
        ((characteristic->properties & ATT_PROPERTY_NOTIFY) == 0u)) {
        log_info("gatt_client_write_client_characteristic_configuration: GATT_CLIENT_CHARACTERISTIC_NOTIFICATION_NOT_SUPPORTED");
        return GATT_CLIENT_CHARACTERISTIC_NOTIFICATION_NOT_SUPPORTED;
    } else if ( (configuration & GATT_CLIENT_CHARACTERISTICS_CONFIGURATION_INDICATION) &&
               ((characteristic->properties & ATT_PROPERTY_INDICATE) == 0u)){
        log_info("gatt_client_write_client_characteristic_configuration: GATT_CLIENT_CHARACTERISTIC_INDICATION_NOT_SUPPORTED");
        return GATT_CLIENT_CHARACTERISTIC_INDICATION_NOT_SUPPORTED;
    }

    gatt_client->callback = callback;
    gatt_client->start_group_handle = characteristic->value_handle;
    gatt_client->end_group_handle = characteristic->end_handle;
    little_endian_store_16(gatt_client->client_characteristic_configuration_value, 0, configuration);

#ifdef ENABLE_GATT_FIND_INFORMATION_FOR_CCC_DISCOVERY
    gatt_client->gatt_client_state = P_W2_SEND_FIND_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY;
#else
    gatt_client->gatt_client_state = P_W2_SEND_READ_CLIENT_CHARACTERISTIC_CONFIGURATION_QUERY;
#endif
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_read_characteristic_descriptor_using_descriptor_handle(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t descriptor_handle){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = descriptor_handle;

    gatt_client->gatt_client_state = P_W2_SEND_READ_CHARACTERISTIC_DESCRIPTOR_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_read_characteristic_descriptor(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_characteristic_descriptor_t * descriptor){
    return gatt_client_read_characteristic_descriptor_using_descriptor_handle(callback, con_handle, descriptor->handle);
}

uint8_t gatt_client_read_long_characteristic_descriptor_using_descriptor_handle_with_offset(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t descriptor_handle, uint16_t offset){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = descriptor_handle;
    gatt_client->attribute_offset = offset;
    gatt_client->gatt_client_state = P_W2_SEND_READ_BLOB_CHARACTERISTIC_DESCRIPTOR_QUERY;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_read_long_characteristic_descriptor_using_descriptor_handle(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t descriptor_handle){
    return gatt_client_read_long_characteristic_descriptor_using_descriptor_handle_with_offset(callback, con_handle, descriptor_handle, 0);
}

uint8_t gatt_client_read_long_characteristic_descriptor(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_characteristic_descriptor_t * descriptor){
    return gatt_client_read_long_characteristic_descriptor_using_descriptor_handle(callback, con_handle, descriptor->handle);
}

uint8_t gatt_client_write_characteristic_descriptor_using_descriptor_handle(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t descriptor_handle, uint16_t length, uint8_t  * data){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = descriptor_handle;
    gatt_client->attribute_length = length;
    gatt_client->attribute_offset = 0;
    gatt_client->attribute_value = data;
    gatt_client->gatt_client_state = P_W2_SEND_WRITE_CHARACTERISTIC_DESCRIPTOR;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_write_characteristic_descriptor(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_characteristic_descriptor_t * descriptor, uint16_t length, uint8_t * value){
    return gatt_client_write_characteristic_descriptor_using_descriptor_handle(callback, con_handle, descriptor->handle, length, value);
}

uint8_t gatt_client_write_long_characteristic_descriptor_using_descriptor_handle_with_offset(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t descriptor_handle, uint16_t offset, uint16_t length, uint8_t  * data){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = descriptor_handle;
    gatt_client->attribute_length = length;
    gatt_client->attribute_offset = offset;
    gatt_client->attribute_value = data;
    gatt_client->gatt_client_state = P_W2_PREPARE_WRITE_CHARACTERISTIC_DESCRIPTOR;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

uint8_t gatt_client_write_long_characteristic_descriptor_using_descriptor_handle(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t descriptor_handle, uint16_t length, uint8_t * data){
    return gatt_client_write_long_characteristic_descriptor_using_descriptor_handle_with_offset(callback, con_handle, descriptor_handle, 0, length, data );
}

uint8_t gatt_client_write_long_characteristic_descriptor(btstack_packet_handler_t callback, hci_con_handle_t con_handle, gatt_client_characteristic_descriptor_t * descriptor, uint16_t length, uint8_t * value){
    return gatt_client_write_long_characteristic_descriptor_using_descriptor_handle(callback, con_handle, descriptor->handle, length, value);
}

/**
 * @brief -> gatt complete event
 */
uint8_t gatt_client_prepare_write(btstack_packet_handler_t callback, hci_con_handle_t con_handle, uint16_t attribute_handle, uint16_t offset, uint16_t length, uint8_t * data){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->attribute_handle = attribute_handle;
    gatt_client->attribute_length = length;
    gatt_client->attribute_offset = offset;
    gatt_client->attribute_value = data;
    gatt_client->gatt_client_state = P_W2_PREPARE_WRITE_SINGLE;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

/**
 * @brief -> gatt complete event
 */
uint8_t gatt_client_execute_write(btstack_packet_handler_t callback, hci_con_handle_t con_handle){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);

    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->gatt_client_state = P_W2_EXECUTE_PREPARED_WRITE;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

/**
 * @brief -> gatt complete event
 */
uint8_t gatt_client_cancel_write(btstack_packet_handler_t callback, hci_con_handle_t con_handle){
    gatt_client_t * gatt_client = gatt_client_provide_context_for_handle_and_start_timer(con_handle);
    if (gatt_client == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (is_ready(gatt_client) == 0) return GATT_CLIENT_IN_WRONG_STATE;

    gatt_client->callback = callback;
    gatt_client->gatt_client_state = P_W2_CANCEL_PREPARED_WRITE;
    gatt_client_run();
    return ERROR_CODE_SUCCESS;
}

void gatt_client_deserialize_service(const uint8_t *packet, int offset, gatt_client_service_t *service){
    service->start_group_handle = little_endian_read_16(packet, offset);
    service->end_group_handle = little_endian_read_16(packet, offset + 2);
    reverse_128(&packet[offset + 4], service->uuid128);
    if (uuid_has_bluetooth_prefix(service->uuid128)){
        service->uuid16 = big_endian_read_32(service->uuid128, 0);
    } else {
        service->uuid16 = 0;
    }
}

void gatt_client_deserialize_characteristic(const uint8_t * packet, int offset, gatt_client_characteristic_t * characteristic){
    characteristic->start_handle = little_endian_read_16(packet, offset);
    characteristic->value_handle = little_endian_read_16(packet, offset + 2);
    characteristic->end_handle = little_endian_read_16(packet, offset + 4);
    characteristic->properties = little_endian_read_16(packet, offset + 6);
    reverse_128(&packet[offset+8], characteristic->uuid128);
    if (uuid_has_bluetooth_prefix(characteristic->uuid128)){
        characteristic->uuid16 = big_endian_read_32(characteristic->uuid128, 0);
    } else {
        characteristic->uuid16 = 0;
    }
}

void gatt_client_deserialize_characteristic_descriptor(const uint8_t * packet, int offset, gatt_client_characteristic_descriptor_t * descriptor){
    descriptor->handle = little_endian_read_16(packet, offset);
    reverse_128(&packet[offset+2], descriptor->uuid128);
    if (uuid_has_bluetooth_prefix(descriptor->uuid128)){
        descriptor->uuid16 = big_endian_read_32(descriptor->uuid128, 0);
    } else {
        descriptor->uuid16 = 0;
    }
}

void gatt_client_send_mtu_negotiation(btstack_packet_handler_t callback, hci_con_handle_t con_handle){
    gatt_client_t * context = gatt_client_provide_context_for_handle(con_handle);
    if (context == NULL) return;
    if (context->mtu_state == MTU_AUTO_EXCHANGE_DISABLED){
        context->callback = callback;
        context->mtu_state = SEND_MTU_EXCHANGE;
        gatt_client_run();
    }
}

uint8_t gatt_client_request_can_write_without_response_event(btstack_packet_handler_t callback, hci_con_handle_t con_handle){
    gatt_client_t * context = gatt_client_provide_context_for_handle(con_handle);
    if (context == NULL) return BTSTACK_MEMORY_ALLOC_FAILED;
    if (context->write_without_response_callback != NULL) return GATT_CLIENT_IN_WRONG_STATE;
    context->write_without_response_callback = callback;
    att_dispatch_client_request_can_send_now_event(context->con_handle);
    return ERROR_CODE_SUCCESS;
}

#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
void gatt_client_att_packet_handler_fuzz(uint8_t packet_type, uint16_t handle, uint8_t *packet, uint16_t size){
    gatt_client_att_packet_handler(packet_type, handle, packet, size);
}
#endif