characteristic user description is always shown as writable

RE: characteristic user description is always shown as writable

paul — Wed, 29 May 2019 22:22:17 GMT

Thanks Hung,

essentially set_security_req applies the security setting macros to the two permission variables in the user_description metadata. I am already doing the equivalent:

BLE_GAP_CONN_SEC_MODE_SET_ENC_NO_MITM(&desc_md.read_perm);
BLE_GAP_CONN_SEC_MODE_SET_NO_ACCESS(&desc_md.write_perm);

So I guess you are right in saying that nrfConnect probably has a bug.

Cheers Paul

RE: characteristic user description is always shown as writable

Hung Bui — Wed, 29 May 2019 12:31:52 GMT

To change the permission, you set this value: user_descr_attr_md.read_perm. Have a look inside characteristic_add() in ble_srv_common.c , we set the value of that in:

set_security_req(p_char_props->p_user_descr->read_access, &user_descr_attr_md.read_perm);

RE: characteristic user description is always shown as writable

paul — Tue, 28 May 2019 22:29:40 GMT

Hi Hung,

thanks for this. I am seeing the behavior on the Android version of nrfConnect. I haven't seen how to get the same functionality on the PC version on Linux.

char_md.char_ext_props.wr_aux is documented as: "Writing the Characteristic User Description descriptor permitted." hence my setting of it. I also set the metadata for the description - pointed to in the same struct to no access.

How are you supposed to set the permission?

Cheers Paul

RE: characteristic user description is always shown as writable

Hung Bui — Tue, 28 May 2019 11:34:31 GMT

Hi Paul,

It could be a bug inside our nRFConnect code. Which nRFConnect were you testing with ? If you were testing with the nRFConnect on PC, could you try the same with nRFConnect on Android/iOS.

Please be aware that setting char_md.char_ext_props.wr_aux is only control the properties of the characteristic. What more important is the permission of the characteristic/user description of the characteristic. The permission decides if the attribute can be written or not. The property is only providing information, as a reference.