write only characteristic?

[victor]

Hi, how to create a write only characteristic?

I have tried: ble_char_md.char_props.read = 0;

This does not work.

[Alex]

typedef struct
{
  /* Standard properties */
  uint8_t broadcast       :1; /**< Broadcasting of the value permitted. */
  uint8_t read            :1; /**< Reading the value permitted. */
  uint8_t write_wo_resp   :1; /**< Writing the value with Write Command permitted. */
  uint8_t write           :1; /**< Writing the value with Write Request permitted. */
  uint8_t notify          :1; /**< Notications of the value permitted. */
  uint8_t indicate        :1; /**< Indications of the value permitted. */
  uint8_t auth_signed_wr  :1; /**< Writing the value with Signed Write Command permitted. */
} ble_gatt_char_props_t;

You need to add ble_char_md.char_props.write = 1;

[victor]

My complete code for creating the characteristic:

	{
	/* ATT metadata */
	ble_gatts_attr_md_t ble_attr_md;

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

	/* No security is required whatsoever, needs to be changed when encryption
		        is added */
	ble_attr_md.read_perm.lv = 1;
	ble_attr_md.read_perm.sm = 1;
	ble_attr_md.write_perm.lv = 1;
	ble_attr_md.write_perm.sm = 1;

	ble_attr_md.vloc = BLE_GATTS_VLOC_STACK;
	ble_attr_md.rd_auth = 0;
	ble_attr_md.wr_auth = 0;
	ble_attr_md.vlen = 0;

	/* BLE GATT metadata */
	ble_gatts_char_md_t ble_char_md;

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

	ble_char_md.p_char_pf = NULL;
	ble_char_md.char_props.read = 0;
	ble_char_md.char_props.write = 1;
	ble_char_md.char_props.write_wo_resp = 1;
	ble_char_md.char_props.notify = 0;

	ble_char_md.p_cccd_md = NULL;
	ble_char_md.p_sccd_md = NULL;
	ble_char_md.p_char_user_desc = NULL;
	ble_char_md.p_user_desc_md = NULL;
	uint8_t name[]="Crypto key";
	ble_char_md.p_char_user_desc = name;
	ble_char_md.char_user_desc_size=strlen((const char*)name);
	ble_char_md.char_user_desc_max_size=strlen((const char*)name);

	/* ble characteristic UUID */
	ble_uuid_t ble_uuid;

	ble_uuid.type = mesh_base_uuid_type;
	ble_uuid.uuid = MESH_AES_KEY_UUID;

	/* ble attribute */
	ble_gatts_attr_t ble_attr;

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

	uint8_t key[16]={0};

	ble_attr.init_offs = 0;
	ble_attr.init_len = 16;
	ble_attr.max_len = 16;
	ble_attr.p_attr_md = &ble_attr_md;
	ble_attr.p_uuid = &ble_uuid;
	ble_attr.p_value = (uint8_t*)&key;

	/* add to service */
	ble_gatts_char_handles_t ble_value_char_handles;

	error_code = sd_ble_gatts_characteristic_add(
			g_mesh_service.service_handle,
			&ble_char_md,
			&ble_attr,
			&ble_value_char_handles);

}

When connecting with master control I can write some data and then read the data. I do not want to be able to read the data.

[Hung Bui]

@victor: Next time, please edit your question to add more information instead of posting it as an answer :)

There are 2 sets of a characteristic attribute: permissions and properties. set char_props.read = 0 only set the property of the characteristic. You should also set the permission : read_perm.lv and read_perm.sm to zero. Please have a look at the macro BLE_GAP_CONN_SEC_MODE_SET_NO_ACCESS() in ble_gap.h