JSON¶

JSON is a data interchange format. The description of this format can be found from IETF RFC 4627.

Description
Data structures
- Encoding
- Decoding
API

Description ¶

This package helps in converting between C data types and JSON data objects. It supports both encoding and decoding.

Data structures ¶

Encoding ¶

/* Encoding functions */
typedef int (*json_write_func_t)(void *buf, char *data,
        int len);

struct json_encoder {
    json_write_func_t je_write;
    void *je_arg;
    int je_wr_commas:1;
    char je_encode_buf[64];
};

Here’s the data structure encoder funtions use, and it must be initialized by the caller. The key element is je_write, which is a function pointer which gets called whenever encoding routine is ready with encoded data. The element je_arg is passed to je_write as the first argument. The rest of the structure contents are for internal state management. This function should collect all the data encoder function generates. It can collect this data to a flat buffer, chain of mbufs or even stream through.

/**
 * For encode.  The contents of a JSON value to encode.
 */
struct json_value {
    uint8_t jv_pad1;
    uint8_t jv_type;
    uint16_t jv_len;

    union {
        uint64_t u;
        float fl;
        char *str;
        struct {
            char **keys;
            struct json_value **values;
        } composite;
    } jv_val;
};

This data structure is filled with data to be encoded. It is best to fill this using the macros JSON_VALUE_STRING() or JSON_VALUE_STRINGN() when value is string, JSON_VALUE_INT() when value is an integer, and so forth.

Decoding ¶

/* when you implement a json buffer, you must implement these functions */

/* returns the next character in the buffer or '\0'*/
typedef char (*json_buffer_read_next_byte_t)(struct json_buffer *);
/* returns the previous character in the buffer or '\0' */
typedef char (*json_buffer_read_prev_byte_t)(struct json_buffer *);
/* returns the number of characters read or zero */
typedef int (*json_buffer_readn_t)(struct json_buffer *, char *buf, int n);

struct json_buffer {
    json_buffer_readn_t jb_readn;
    json_buffer_read_next_byte_t jb_read_next;
    json_buffer_read_prev_byte_t jb_read_prev;
};

Function pointers within this structure are used by decoder when it is reading in more data to decode.

struct json_attr_t {
    char *attribute;
    json_type type;
    union {
        int *integer;
        unsigned int *uinteger;
        double *real;
        char *string;
        bool *boolean;
        char *character;
        struct json_array_t array;
        size_t offset;
    } addr;
    union {
        int integer;
        unsigned int uinteger;
        double real;
        bool boolean;
        char character;
        char *check;
    } dflt;
    size_t len;
    const struct json_enum_t *map;
    bool nodefault;
};

This structure tells the decoder about a particular name/value pair. Structure must be filled in before calling the decoder routine json_read_object().

Element	Description
attribute	Name of the value
type	The type of the variable; see enum json_type
addr	Contains the address where value should be stored
dflt	Default value to fill in, if this name is not found
len	Max number of bytes to read in for value
nodefault	If set, default value is not copied name

API ¶

Defines

JSON_VALUE_TYPE_BOOL¶

JSON_VALUE_TYPE_UINT64¶

JSON_VALUE_TYPE_INT64¶

JSON_VALUE_TYPE_STRING¶

JSON_VALUE_TYPE_ARRAY¶

JSON_VALUE_TYPE_OBJECT¶

JSON_VALUE_STRING(__jv, __str)¶

JSON_VALUE_STRINGN(__jv, __str, __len)¶

JSON_VALUE_BOOL(__jv, __v)¶

JSON_VALUE_INT(__jv, __v)¶

JSON_VALUE_UINT(__jv, __v)¶

JSON_NITEMS(x)¶

JSON_ATTR_MAX¶

JSON_VAL_MAX¶

JSON_ERR_OBSTART¶

JSON_ERR_ATTRSTART¶

JSON_ERR_BADATTR¶

JSON_ERR_ATTRLEN¶

JSON_ERR_NOARRAY¶

JSON_ERR_NOBRAK¶

JSON_ERR_STRLONG¶

JSON_ERR_TOKLONG¶

JSON_ERR_BADTRAIL¶

JSON_ERR_ARRAYSTART¶

JSON_ERR_OBJARR¶

JSON_ERR_SUBTOOLONG¶

JSON_ERR_BADSUBTRAIL¶

JSON_ERR_SUBTYPE¶

JSON_ERR_BADSTRING¶

JSON_ERR_CHECKFAIL¶

JSON_ERR_NOPARSTR¶

JSON_ERR_BADENUM¶

JSON_ERR_QNONSTRING¶

JSON_ERR_NONQSTRING¶

JSON_ERR_MISC¶

JSON_ERR_BADNUM¶

JSON_ERR_NULLPTR¶

JSON_STRUCT_OBJECT(s, f)¶

JSON_STRUCT_ARRAY(a, e, n)¶

Typedefs

typedef int (*json_write_func_t)(void *buf, char *data, int len)¶

typedef char (*json_buffer_read_next_byte_t)(struct json_buffer*)¶

typedef char (*json_buffer_read_prev_byte_t)(struct json_buffer*)¶

typedef int (*json_buffer_readn_t)(struct json_buffer*, char *buf, int n)¶

Enums

enum json_type¶

Values:

enumerator t_integer¶

enumerator t_uinteger¶

enumerator t_real¶

enumerator t_string¶

enumerator t_boolean¶

enumerator t_character¶

enumerator t_object¶

enumerator t_structobject¶

enumerator t_array¶

enumerator t_check¶

enumerator t_ignore¶

Functions

int json_encode_object_start(struct json_encoder*)¶

int json_encode_object_key(struct json_encoder *encoder, char *key)¶

int json_encode_object_entry(struct json_encoder*, char*, struct json_value*)¶

int json_encode_object_finish(struct json_encoder*)¶

int json_encode_array_name(struct json_encoder *encoder, char *name)¶

int json_encode_array_start(struct json_encoder *encoder)¶

int json_encode_array_value(struct json_encoder *encoder, struct json_value *val)¶

int json_encode_array_finish(struct json_encoder *encoder)¶

int json_read_object(struct json_buffer*, const struct json_attr_t*)¶

int json_read_array(struct json_buffer*, const struct json_array_t*)¶

struct json_value¶

#include <json.h>

Public Members

uint8_t jv_pad1¶

uint8_t jv_type¶

uint16_t jv_len¶

union json_value.[anonymous] jv_val¶

struct json_encoder¶

#include <json.h>

Public Members

json_write_func_t je_write¶

void *je_arg¶

unsigned int je_wr_commas¶

char je_encode_buf[64]¶

struct json_enum_t¶

#include <json.h>

Public Members

char *name¶

long long int value¶

struct json_array_t¶

#include <json.h>

Public Members

json_type element_type¶

union json_array_t.[anonymous] arr¶

int *count¶

int maxlen¶

struct json_attr_t¶

#include <json.h>

Public Members

char *attribute¶

json_type type¶

union json_attr_t.[anonymous] addr¶

union json_attr_t.[anonymous] dflt¶

size_t len¶

const struct json_enum_t *map¶

bool nodefault¶

struct json_buffer¶

#include <json.h>

Public Members

json_buffer_readn_t jb_readn¶

json_buffer_read_next_byte_t jb_read_next¶

json_buffer_read_prev_byte_t jb_read_prev¶

union json_value.jv_val

Public Members

uint64_t u¶

float fl¶

char *str¶

struct json_value.[anonymous].[anonymous] composite¶

struct json_value.jv_val.composite

Public Members

char **keys¶

struct json_value **values¶

union json_array_t.arr

Public Members

struct json_array_t.[anonymous].[anonymous] objects¶

struct json_array_t.[anonymous].[anonymous] strings¶

struct json_array_t.[anonymous].[anonymous] integers¶

struct json_array_t.[anonymous].[anonymous] uintegers¶

struct json_array_t.[anonymous].[anonymous] reals¶

struct json_array_t.[anonymous].[anonymous] booleans¶

struct json_array_t.arr.objects

Public Members

const struct json_attr_t *subtype¶

char *base¶

size_t stride¶

struct json_array_t.arr.strings

Public Members

char **ptrs¶

char *store¶

int storelen¶

struct json_array_t.arr.integers

Public Members

long long int *store¶

struct json_array_t.arr.uintegers

Public Members

long long unsigned int * store

struct json_array_t.arr.reals

Public Members

double *store¶

struct json_array_t.arr.booleans

Public Members

bool *store¶

union json_attr_t.addr

Public Members

long long int *integer¶

long long unsigned int * uinteger

double *real¶

char *string¶

bool *boolean¶

char *character¶

struct json_array_t array¶

size_t offset¶

union json_attr_t.dflt

Public Members

long long int integer¶

long long unsigned int uinteger

double real¶

bool boolean¶

char character¶

char *check¶

An OS to build, deploy and securely manage billions of devices

Latest News:

JSON¶

Description ¶

Data structures ¶

Encoding ¶

Decoding ¶

API ¶

An OS to build, deploy and securely manage billions of devices

Latest News:

JSON¶

Description¶

Data structures¶

Encoding¶

Decoding¶

API¶

Description ¶

Data structures ¶

Encoding ¶

Decoding ¶

API ¶