Lib JSON misbehaving

[ofirshe]

Hey,

I recently conducted a test and encountered an issue with the JSON encoding in my application, and I would appreciate your assistance. Below is a snippet of my code:

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdbool.h>
#include <zephyr/data/json.h>
 
#define REGULATOR_NUM_DEVICES 17
 
/* Regulator */
typedef struct regulator_stats
{
    /* Voltage, in millivolts */
    bool is_read_vout_supported;
    int32_t last_voltage_mv;
    int32_t max_voltage_mv;
    int32_t min_voltage_mv;
 
    /* Current, in milliamperes */
    bool is_read_iout_supported;
    int32_t last_current_ma;
    int32_t max_current_ma;
    int32_t min_current_ma;
 
    uint32_t last_measurement_from_uptime_ms;
} regulator_stats_t;
 
static const struct json_obj_descr regulator_stats_json_description[] =
{
    /* Voltage */
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, is_read_vout_supported, JSON_TOK_TRUE),
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, last_voltage_mv, JSON_TOK_NUMBER),
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, max_voltage_mv, JSON_TOK_NUMBER),
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, min_voltage_mv, JSON_TOK_NUMBER),
 
    /* Current */
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, is_read_iout_supported, JSON_TOK_TRUE),
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, last_current_ma, JSON_TOK_NUMBER),
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, max_current_ma, JSON_TOK_NUMBER),
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, min_current_ma, JSON_TOK_NUMBER),
 
    JSON_OBJ_DESCR_PRIM(struct regulator_stats, last_measurement_from_uptime_ms, JSON_TOK_NUMBER),
};
 
struct my_struct
{
    regulator_stats_t regulator_devices_stats_arr[REGULATOR_NUM_DEVICES];
    uint32_t regulator_devices_stats_arr_len;
};
 
static struct my_struct ms;
 
static const struct json_obj_descr ms_desc[] =
{
    /* Regulator Devices Stats */
    JSON_OBJ_DESCR_OBJ_ARRAY(struct my_struct, regulator_devices_stats_arr, REGULATOR_NUM_DEVICES,
                regulator_devices_stats_arr_len, regulator_stats_json_description,
                ARRAY_SIZE(regulator_stats_json_description)),
};
 
int main()
{
	int i;
	ssize_t encoded_len;
	char buffer[8192] = { 0 };
 
	for (i = 0; i < REGULATOR_NUM_DEVICES; i++)
	{
		ms.regulator_devices_stats_arr[i].is_read_vout_supported = ms.regulator_devices_stats_arr[i].is_read_iout_supported = false;
		ms.regulator_devices_stats_arr[i].max_voltage_mv = ms.regulator_devices_stats_arr[i].max_current_ma = INT32_MIN;
		ms.regulator_devices_stats_arr[i].min_voltage_mv = ms.regulator_devices_stats_arr[i].min_current_ma = INT32_MAX;
		ms.regulator_devices_stats_arr[i].last_voltage_mv = ms.regulator_devices_stats_arr[i].last_current_ma = 0;
		ms.regulator_devices_stats_arr[i].last_measurement_from_uptime_ms = 0;
	}
	ms.regulator_devices_stats_arr_len = REGULATOR_NUM_DEVICES;
	encoded_len = json_calc_encoded_len(ms_desc, ARRAY_SIZE(ms_desc), &ms);
	if (encoded_len < 0)
	{
		printf("failed to calculate the string length of the encoded json; rc = %d", encoded_len);
		return -1;
	}
	json_obj_encode_buf(ms_desc, ARRAY_SIZE(ms_desc), &ms, buffer, sizeof(buffer));
	printf("%s\n", buffer);
 
	return 0;
}

To run the application, I use the following configurations: CONFIG_MAIN_STACK_SIZE=131072 and CONFIG_JSON_LIBRARY=y.

I expected all 17 devices to be initialized with identical values like this:
{"is_read_vout_supported":false,"last_voltage_mv":0,"max_voltage_mv":-2147483648,"min_voltage_mv":2147483647,"is_read_iout_supported":false,"last_current_ma":0,"max_current_ma":-2147483648,"min_current_ma":2147483647,"last_measurement_from_uptime_ms":0}
However, the console output shows that after the first device, the values become corrupted and shift between fields:

{"regulator_devices_stats_arr":[{"is_read_vout_supported":false,"last_voltage_mv":0,"max_voltage_mv":-2147483648,"min_voltage_mv":2147483647,"is_read_iout_supported":false,"last_current_ma":0,"max_current_ma":-2147483648,"min_current_ma":2147483647,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":0,"max_voltage_mv":0,"min_voltage_mv":-2147483648,"is_read_iout_supported":true,"last_current_ma":0,"max_current_ma":0,"min_current_ma":-2147483648,"last_measurement_from_uptime_ms":2147483647},
								{"is_read_vout_supported":true,"last_voltage_mv":0,"max_voltage_mv":0,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":2147483647,"max_current_ma":0,"min_current_ma":0,"last_measurement_from_uptime_ms":-2147483648},
								{"is_read_vout_supported":false,"last_voltage_mv":2147483647,"max_voltage_mv":0,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":-2147483648,"max_current_ma":2147483647,"min_current_ma":0,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":-2147483648,"max_voltage_mv":2147483647,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":0,"max_current_ma":-2147483648,"min_current_ma":2147483647,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":0,"max_voltage_mv":-2147483648,"min_voltage_mv":2147483647,"is_read_iout_supported":false,"last_current_ma":0,"max_current_ma":0,"min_current_ma":-2147483648,"last_measurement_from_uptime_ms":2147483647},
								{"is_read_vout_supported":true,"last_voltage_mv":0,"max_voltage_mv":0,"min_voltage_mv":-2147483648,"is_read_iout_supported":true,"last_current_ma":0,"max_current_ma":0,"min_current_ma":0,"last_measurement_from_uptime_ms":-2147483648},
								{"is_read_vout_supported":false,"last_voltage_mv":2147483647,"max_voltage_mv":0,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":2147483647,"max_current_ma":0,"min_current_ma":0,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":-2147483648,"max_voltage_mv":2147483647,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":-2147483648,"max_current_ma":2147483647,"min_current_ma":0,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":0,"max_voltage_mv":-2147483648,"min_voltage_mv":2147483647,"is_read_iout_supported":false,"last_current_ma":0,"max_current_ma":-2147483648,"min_current_ma":2147483647,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":0,"max_voltage_mv":0,"min_voltage_mv":-2147483648,"is_read_iout_supported":true,"last_current_ma":0,"max_current_ma":0,"min_current_ma":-2147483648,"last_measurement_from_uptime_ms":2147483647},
								{"is_read_vout_supported":true,"last_voltage_mv":0,"max_voltage_mv":0,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":2147483647,"max_current_ma":0,"min_current_ma":0,"last_measurement_from_uptime_ms":-2147483648},
								{"is_read_vout_supported":false,"last_voltage_mv":2147483647,"max_voltage_mv":0,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":-2147483648,"max_current_ma":2147483647,"min_current_ma":0,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":-2147483648,"max_voltage_mv":2147483647,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":0,"max_current_ma":-2147483648,"min_current_ma":2147483647,"last_measurement_from_uptime_ms":0},
								{"is_read_vout_supported":false,"last_voltage_mv":0,"max_voltage_mv":-2147483648,"min_voltage_mv":2147483647,"is_read_iout_supported":false,"last_current_ma":0,"max_current_ma":0,"min_current_ma":-2147483648,"last_measurement_from_uptime_ms":2147483647},
								{"is_read_vout_supported":true,"last_voltage_mv":0,"max_voltage_mv":0,"min_voltage_mv":-2147483648,"is_read_iout_supported":true,"last_current_ma":0,"max_current_ma":0,"min_current_ma":0,"last_measurement_from_uptime_ms":-2147483648},
								{"is_read_vout_supported":false,"last_voltage_mv":2147483647,"max_voltage_mv":0,"min_voltage_mv":0,"is_read_iout_supported":false,"last_current_ma":2147483647,"max_current_ma":0,"min_current_ma":0,"last_measurement_from_uptime_ms":0}]}

I am unsure if this is an issue with my implementation or a potential problem with the library. I am currently using the latest changes in the JSON library 878640f.

Your help will be appreciated.

Best regards.

[ofirshe]

Hey,

When I add __attribute__((packed, aligned(1))) to the struct regulator_stats, the issue gets resolved. However, I don't see any indication in the library that requires all structs to be packed. I also checked the Zephyr json test source file, and none of the structs there are packed either.