sd_ble_gatts_rw_authorize_reply() return SUCCESS by long-length parameter

[loquat]

When create 128byte length's CHARACTERISTIC and read with NRFCONNECT on Android.
NRFCONNECT returns GATT_READ_NOT_PERMIT even though sd_ble_gatts_rw_authorize_reply() completes normally.

code is folowing,

Why sd_ble_gatts_rw_authorize_reply return SUCCESS?

#define	BUFFER_LENGTH				(128)

attr_md.vloc    = BLE_GATTS_VLOC_STACK;
attr_md.rd_auth = 1;
attr_md.wr_auth = 1;
attr_md.vlen    = 0;
memset(&attr_char_value, 0, sizeof(attr_char_value));
attr_char_value.p_uuid    = uuid;
attr_char_value.p_attr_md = &attr_md;
attr_char_value.init_offs = 0;
attr_char_value.init_len  = BUFFER_LENGTH;
attr_char_value.max_len   = BUFFER_LENGTH;
attr_char_value.p_value   = nullptr;
APP_ERROR_CHECK(sd_ble_gatts_characteristic_add(service_handle,
                          &char_md,
                          &attr_char_value,
                          char_param->p_handle));
...........
...........
case BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST:
if ( p_ble_evt->evt.gatts_evt.params.authorize_request.type == BLE_GATTS_AUTHORIZE_TYPE_READ ) {
    reply.params.read.len = BUFFER_LENGTH;
    reply.params.read.offset = 0;
    reply.params.read.p_data = buffer;
	reply.params.read.update = 1;
	reply.params.read.gatt_status = BLE_GATT_STATUS_SUCCESS;
    APP_ERROR_CHECK(sd_ble_gatts_rw_authorize_reply(m_conn_handle, &reply));
}

[Håkon]

Hi,

Have you tried  setting permissions using BLE_GAP_CONN_SEC_MODE_SET_OPEN()?

Read more in step 2.G in this blog post

https://devzone.nordicsemi.com/nordic/short-range-guides/b/bluetooth-low-energy/posts/ble-characteristics-a-beginners-tutorial

[loquat]

I do,
BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);
BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.write_perm);

When I set BUFFER_LENGTH to 20 for confirmation, NRFCONNECT on Android was able to read normally.

What I'm wander about is that sd_ble_gatts_rw_authorize_reply can set a len larger than ATT_MTU.

The ultimate goal is to send data longer than ATT_MTU from the GATT server.

Am I misled?
Is sd_ble_gatts_rw_authorize_reply len independent of ATT_MTU?

Problem is NRFCONNECT?

[Håkon]

Hi,

Have updated parameters NRF_SDH_BLE_GAP_DATA_LENGTH and NRF_SDH_BLE_GATT_MAX_MTU_SIZE in sdk_config.h?

[Håkon]

In example app_uart_ble is seems the BLE_GATT_ATT_MTU_DEFAULT is used instead of NRF_SDH_BLE_GAP_DATA_LENGTH from the sdk_config.h. Here the BLE_GATT_ATT_MTU_DEFAULT can be changed to a higher number.

[loquat]

Thank you.

I don't want to change ATT_MTU.
The GATT client plans to send multiple times using LongWrite to send 128 bytes of data.

The question is how many times the light is called on the server side (nrf52840)?
What happens if sd_ble_gatts_rw_authorize_reply returns a value greater than ATT_MTU?

[Håkon]

Hi,

Could I ask you to share an updated snippet or a stripped down version of your code?
Do you still have the GATT_READ_NOT_PERMIT permission issue?
Do you have some other errors now?

sd_ble_gatts_rw_authorize_reply does not return a length, it sets the permissions and returns status. 

[loquat]

My concern is that sd_ble_gatts_rw_authorize_reply returns success if you specify a read.len greater than ATT_MTU.
Is this correct behavior?