Apple Notification Center Service - hard coded max attribute length of 32?

RE: Apple Notification Center Service - hard coded max attribute length of 32?

denis — Sun, 21 Mar 2021 15:18:14 GMT

I'm not using the SDK version any longer. Moving to the NCS version now. So closing this issue...

RE: Apple Notification Center Service - hard coded max attribute length of 32?

ThierryC — Fri, 05 Mar 2021 08:33:09 GMT

No, but I did't tried on latest SDK.

RE: Apple Notification Center Service - hard coded max attribute length of 32?

thomas oggier — Tue, 02 Mar 2021 11:07:29 GMT

Has this problem found a solution?

RE: Apple Notification Center Service - hard coded max attribute length of 32?

thomas oggier — Tue, 02 Mar 2021 11:07:02 GMT

Has this problem found a solution?

RE: Apple Notification Center Service - hard coded max attribute length of 32?

Håvard — Fri, 09 Aug 2019 19:30:43 GMT

You are correct, it would be safer to explicitly set values to 0 first. Here the example assumes that the variables are initialized to 0 by the compiler, and then replaced by the nrf_ble_ancs_c_attr_add() funcitons.

RE: Apple Notification Center Service - hard coded max attribute length of 32?

Håvard — Fri, 09 Aug 2019 19:26:45 GMT

Looking at this snippet and the code around it in the c file, I think it terminates after the attribute if there is enough buffer to do so.

If the allocated buffer is 32 bytes, and a 20 byte attribute is received, a nul-terminator is placed on byte 21. If the allocated buffer is 10 bytes, and the message received is 10 bytes, the nul-terminator is placed on byte 10, thereby truncating the data, but at least turning it into a printable string. (replacing the last character to fit into the buffer with a '\0' and then ignoring the rest of the attribute because there is no buffer to store it in.)

RE: Apple Notification Center Service - hard coded max attribute length of 32?

denis — Fri, 09 Aug 2019 16:25:35 GMT

My point is that nrf_ble_ancs_c_app_attr_add should not check the length against BLE_ANCS_ATTR_DATA_MAX, since there doesn't appear to be such a limitation and the buffer passed in can be of any size.

RE: Apple Notification Center Service - hard coded max attribute length of 32?

Håvard — Fri, 09 Aug 2019 16:19:17 GMT

Hello,

#define BLE_ANCS_ATTR_DATA_MAX              32  //!< Maximum data length of an iOS notification attribute.

1. The comment for the definition could be more clear. The define is also used for application attributes in addition to notification attributes. The App ID is an attribute, so I think the naming of the definition itself is ok. But that is subjective of course.

2. This define is safe to increase so that you can receive more of the attribute. It should have been placed in sdk_config.h.

nrf_ble_ancs_c_app_attr_add() will return NRF_ERROR_INVALID_LENGTH if you supply a "len" param larger than BLE_ANCS_ATTR_DATA_MAX. This could have been mentioned directly in the API documentation.

RE: Apple Notification Center Service - hard coded max attribute length of 32?

denis — Thu, 08 Aug 2019 13:12:20 GMT

One other note: It looks like in the example nrf_ble_ancs_c_attr_add is called before ble_ancs_c_init. Seems like it would be safer for ble_ancs_c_init to initialize all the ancs_notif_attr_list values to get = false and then call nrf_ble_ancs_c_attr_add only on the attributes that you want to retrieve. (As it is now if you comment out any of the nrf_ble_ancs_c_attr_add then you have undefined values, which leads to undefined behavior.)

RE: Apple Notification Center Service - hard coded max attribute length of 32?

denis — Wed, 07 Aug 2019 20:22:19 GMT

It also looks like the null termination on an attribute writes 1 past the buffer end in ancs_attr_parser.c:

    // We have reached the end of the attribute, or our max allocated internal size.
    // Stop copying data over to our buffer. NUL-terminate at the current index.
    if ( (p_ancs->parse_info.current_attr_index == p_ancs->evt.attr.attr_len) ||
         (p_ancs->parse_info.current_attr_index == p_ancs->parse_info.p_attr_list[p_ancs->evt.attr.attr_id].attr_len - 1))
    {
        if (attr_is_requested(p_ancs, p_ancs->evt.attr))
        {
            p_ancs->evt.attr.p_attr_data[p_ancs->parse_info.current_attr_index] = '\0';
        }