Unable to properly copy values out of BLE buffer

[scath999]

I've been working with two nrf52840s to create observations and transmit over BLE.

This works fine - I can send and receive the data.

What I'm not seeing is a clear way to copy data OUT of the provided data buffer void *data once transmission is complete.

For example:

int on_read_observations_notify(struct bt_conn *conn, struct bt_gatt_subscribe_params *params, const void *data, uint16_t length)
{
    int err;
    
    printk("\n[on_read_observations_notify] data = %p", data);
    printk("\n[on_read_observations_notify] len = %d", length);
    printk("\n[on_read_observations_notify] err = %2x", err);
    printk("\n[on_read_observations_notify] value = %d\n", params->value);

    LOG_HEXDUMP_ERR(data, length, "OBSERVATION DATA: ");
    
    ...

This code shows me EXACTLY what I want:

[on_read_observations_notify] data = 0x2001ce34
[on_read_observations_notify] len = 32
[on_read_observations_notify] err =  0
[on_read_observations_notify] value = 1

[00:00:26.929,565] <err> ble: on_read_observations_notify: OBSERVATION DATA:
                                     30 2f 56 42 41 54 2f 28  38 32 2e 31 32 29       |0/VBAT/( 82.12)

In this case I'm sending a placeholder timestamp ("0"), a data descriptor ("VBAT": battery voltage as a percentage) and the actual value generated by the sensor (in this case 82.12).

My issue is that I can't copy that string out into a variable so I can reliably parse it.

I've jumped through multiple hoops to copy the buffer contents one character at a time. I then tokenize the resulting string into the values I want.

This works in every case EXCEPT one, where one of my sensors transmits a rather larger value. In that case, the string length gets calculated incorrectly (which is a mystery to me since I'm using strlen()), and nonsense data is being included in the final string because my method reads past the end of the actual buffer (using the value returned by strlen()).

...
 if (length > 0){
            char observation[length];
            char * data_ptr = data;
            int i = 0;
            for (; i < length; i++){
                // only include characters with ascii values between 33 and 122
                if (data_ptr[i] > 32 || data_ptr < 123){
                    if (data_ptr[i] == 41){
                        //If this is a right bracket, add it to the observation string and break
                        observation[i] = data_ptr[i];
                        break;
                    }
                    else{
                        observation[i] = data_ptr[i];
                    }

                }
                else{
                    LOG_ERR("Found unwanted char : %c", data_ptr[i]);
                    observation[i] = ""; 
                }
            }
            // Append str termination char
            observation[length] = '\0';

            /** tokenize the observation string **/
            char *token = NULL;
            char *saveptr;
            char *tokens[3];
            for (int i = 0; i < 3; i++)
                tokens[i] = NULL;
            
            //get first token - time
            token = strtok_r(observation, "/", &saveptr);
            int count = 0;
            // process the rest
            while (token != NULL){
                LOG_WRN("TOKEN[%d] = %s | STRLEN = %d", count, token, strlen(token));
                tokens[count] = (char *) malloc(strlen(token));
                sprintf(tokens[count], "%s", token);
                token = strtok_r(NULL, "/", &saveptr);
                count++;
            }

This results in the following:

[00:12:28.408,142] <wrn> ble: on_read_observations_notify: TOKEN[0] = 0 | STRLEN = 1
[00:12:28.418,914] <wrn> ble: on_read_observations_notify: TOKEN[1] = RGBW | STRLEN = 4
[00:12:28.430,206] <wrn> ble: on_read_observations_notify: TOKEN[2] = (13027,18608,10595,23059)▒' ▒ | STRLEN = 31

As previously mentioned, there's noise in token[2]. Worse, the calculated strlen is 31, which is both incorrect (it should be 25) and impossible since the total strlen reported by the system to the callback function is 32.

There has to be an easier way to do this.

Can anyone shed light on this?