JFES

Based on the jsmn project.

Json For Embedded Systems (JFES) is a minimalistic json engine written in plain C. It can be easily integrated into the code for embedded systems.

Features

• compatible with C99
• no dependencies (I'm serious!)
• highly portable
• you can use it as a json parser only
• incremental single-pass parsing

API

Initializing

Before use you need to initialize the jfes_config_t object.

/** JFES config structure. */
typedef struct jfes_config {
    jfes_malloc_t           jfes_malloc;        /**< Memory allocation function. */
    jfes_free_t             jfes_free;          /**< Memory deallocation function. */
} jfes_config_t;

Below you can see the prototypes of the memory management functions:

/** Memory allocator function type. */
typedef void *(__cdecl *jfes_malloc_t)(jfes_size_t);

/** Memory deallocator function type. */
typedef void (__cdecl *jfes_free_t)(void*);

As you can see, these functions have the same prototype as the C standard library functions.

So, you can initialize JFES configuration with the following code:

#include <stdlib.h>

/* ...some useful stuff... */

jfes_config_t config;

config.jfes_malloc = malloc;
config.jfes_free = free;

But, if you need to use your own memory management functions, you can use them.

Parser (optional)

If you just need to parse a *.json file without allocating any values (like jsmn), you can parse a json string and separate it into tokens. In this case, you only need to use two functions below:

/**
    JFES parser initialization.
    \param[out]     parser              Pointer to the jfes_parser_t object.
    \param[in]      config              JFES configuration.
    \return         jfes_success if everything is OK.
*/
jfes_status_t jfes_init_parser(jfes_parser_t *parser, jfes_config_t *config);

/******************************************************************/

/**
    Run JSON parser. It parses a JSON data string into and
    array of tokens, each describing a single JSON object.
    \param[in]      parser              Pointer to the jfes_parser_t object.
    \param[in]      json                JSON data string.
    \param[in]      length              JSON data length.
    \param[out]     tokens              Tokens array to fill.
    \param[in, out] max_tokens_count    Maximal count of tokens in tokens array.
                                        Will contain tokens count.
    \return         jfes_success if everything is OK.
*/
jfes_status_t jfes_parse_tokens(jfes_parser_t *parser, const char *json,
    jfes_size_t length, jfes_token_t *tokens, jfes_size_t *max_tokens_count);

You can see a parsing example below.

Loading *.json into value

You can load any json data into jfes_value_t.

/** JSON value structure. */
struct jfes_value {
    jfes_value_type_t       type;               /**< JSON value type. */
    jfes_value_data_t       data;               /**< Value data. */
};

Value type (jfes_value_type_t) can be one of the following:

• jfes_type_boolean
• jfes_type_integer
• jfes_type_double
• jfes_type_string
• jfes_type_array
• jfes_type_object

And jfes_value_data_t is:

/** JFES value data union. */
typedef union jfes_value_data {
    int                     bool_val;           /**< Boolean JSON value. */

    int                     int_val;            /**< Integer JSON value. */
    double                  double_val;         /**< Double JSON value. */
    jfes_string_t           string_val;         /**< String JSON value. */

    jfes_array_t            *array_val;         /**< Array JSON value. */
    jfes_object_t           *object_val;        /**< Object JSON value. */
} jfes_value_data_t;

You can easily load a json string into the value by using the following code:

jfes_config_t config;
config.jfes_malloc = malloc;
config.jfes_free = free;

jfes_value_t value;
jfes_parse_to_value(&config, json_data, json_size, &value);
/* Do something with value */
jfes_free_value(&config, &value);

That's all!

Value modification

You can modify or create jfes_value_t with any of these functions:

jfes_value_t *jfes_create_boolean_value(jfes_config_t *config, int value);
jfes_value_t *jfes_create_integer_value(jfes_config_t *config, int value);
jfes_value_t *jfes_create_double_value(jfes_config_t *config, double value);
jfes_value_t *jfes_create_string_value(jfes_config_t *config, const char *value, jfes_size_t length);
jfes_value_t *jfes_create_array_value(jfes_config_t *config);
jfes_value_t *jfes_create_object_value(jfes_config_t *config);

jfes_value_t *jfes_get_child(jfes_value_t *value, const char *key, jfes_size_t key_length);
jfes_object_map_t *jfes_get_mapped_child(jfes_value_t *value, const char *key, jfes_size_t key_length);

jfes_status_t jfes_place_to_array(jfes_config_t *config, jfes_value_t *value, jfes_value_t *item);
jfes_status_t jfes_place_to_array_at(jfes_config_t *config, jfes_value_t *value, jfes_value_t *item, jfes_size_t place_at);
jfes_status_t jfes_remove_from_array(jfes_config_t *config, jfes_value_t *value, jfes_size_t index);

jfes_status_t jfes_set_object_property(jfes_config_t *config, jfes_value_t *value, jfes_value_t *item, const char *key, jfes_size_t key_length);
jfes_status_t jfes_remove_object_property(jfes_config_t *config, jfes_value_t *value, const char *key, jfes_size_t key_length);

Serializing to json string

You can serialize any jfes_value_t to string with one line (actually, three lines, but two of them are for help):

char dump[1024];
jfes_size_t dump_size = 1024;
jfes_value_to_string(&value, beauty_dump, &dump_size, 1);
beauty_dump[dump_size] = '\0';  /* If you need null-terminated string. */

dump_size will store the dump size. If you pass the fourth argument as 1, the dump will be beautified. And if 0, the dump will be ugly.

Examples

You can find examples here.

Licence

The MIT License (MIT)
See full text.