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zephyr/include/json.h

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/*
* Copyright (c) 2017 Intel Corporation
*
* SPDX-License-Identifier: Apache-2.0
*/
#ifndef ZEPHYR_INCLUDE_JSON_H_
#define ZEPHYR_INCLUDE_JSON_H_
/**
* @brief Structured Data
* @defgroup structured_data Structured Data
*/
/**
* @defgroup json JSON
* @ingroup structured_data
* @{
*/
#include <misc/util.h>
#include <stddef.h>
#include <zephyr/types.h>
#include <sys/types.h>
enum json_tokens {
/* Before changing this enum, ensure that its maximum
* value is still within 7 bits. See comment next to the
* declaration of `type` in struct json_obj_descr.
*/
JSON_TOK_NONE = '_',
JSON_TOK_OBJECT_START = '{',
JSON_TOK_OBJECT_END = '}',
JSON_TOK_LIST_START = '[',
JSON_TOK_LIST_END = ']',
JSON_TOK_STRING = '"',
JSON_TOK_COLON = ':',
JSON_TOK_COMMA = ',',
JSON_TOK_NUMBER = '0',
JSON_TOK_TRUE = 't',
JSON_TOK_FALSE = 'f',
JSON_TOK_NULL = 'n',
JSON_TOK_ERROR = '!',
JSON_TOK_EOF = '\0',
};
struct json_obj_descr {
const char *field_name;
/* Alignment can never be 0 or more than 4. The macros to create a
* struct json_obj_descr will subtract 1 from the result of
* __alignof__() calls in order to keep this value in the 0-3 range
* and thus use only 2 bits. 1 is added back when rounding it up to
* calculate the struct size while parsing an array or object.
*/
u32_t alignment : 2;
/* 127 characters is more than enough for a field name. */
u32_t field_name_len : 7;
/* Valid values here (enum json_tokens): JSON_TOK_STRING,
* JSON_TOK_NUMBER, JSON_TOK_TRUE, JSON_TOK_FALSE,
* JSON_TOK_OBJECT_START, JSON_TOK_LIST_START. (All others
* ignored.) Maximum value is '}' (125), so this has to be 7 bits
* long.
*/
u32_t type : 7;
/* 65535 bytes is more than enough for many JSON payloads. */
u32_t offset : 16;
union {
struct {
const struct json_obj_descr *sub_descr;
size_t sub_descr_len;
} object;
struct {
const struct json_obj_descr *element_descr;
size_t n_elements;
} array;
};
};
/**
* @brief Function pointer type to append bytes to a buffer while
* encoding JSON data.
*
* @param bytes Contents to write to the output
* @param len Number of bytes in @param bytes to append to output
* @param data User-provided pointer
*
* @return This callback function should return a negative number on
* error (which will be propagated to the return value of
* json_obj_encode()), or 0 on success.
*/
typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
void *data);
/**
* @brief Helper macro to declare a descriptor for supported primitive
* values.
*
* @param struct_ Struct packing the values
*
* @param field_name_ Field name in the struct
*
* @param type_ Token type for JSON value corresponding to a primitive
* type. Must be one of: JSON_TOK_STRING for strings, JSON_TOK_NUMBER
* for numbers, JSON_TOK_TRUE (or JSON_TOK_FALSE) for booleans.
*
* Here's an example of use:
*
* struct foo {
* int some_int;
* };
*
* struct json_obj_descr foo[] = {
* JSON_OBJ_DESCR_PRIM(struct foo, some_int, JSON_TOK_NUMBER),
* };
*/
#define JSON_OBJ_DESCR_PRIM(struct_, field_name_, type_) \
{ \
.field_name = (#field_name_), \
.field_name_len = sizeof(#field_name_) - 1, \
.offset = offsetof(struct_, field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = type_, \
}
/**
* @brief Helper macro to declare a descriptor for an object value
*
* @param struct_ Struct packing the values
*
* @param field_name_ Field name in the struct
*
* @param sub_descr_ Array of json_obj_descr describing the subobject
*
* Here's an example of use:
* struct nested {
* int foo;
* struct {
* int baz;
* } bar;
* };
*
* struct json_obj_descr nested_bar[] = {
* { ... declare bar.baz descriptor ... },
* };
* struct json_obj_descr nested[] = {
* { ... declare foo descriptor ... },
* JSON_OBJ_DESCR_OBJECT(struct nested, bar, nested_bar),
* };
*/
#define JSON_OBJ_DESCR_OBJECT(struct_, field_name_, sub_descr_) \
{ \
.field_name = (#field_name_), \
.field_name_len = (sizeof(#field_name_) - 1), \
.offset = offsetof(struct_, field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = JSON_TOK_OBJECT_START, \
.object = { \
.sub_descr = sub_descr_, \
.sub_descr_len = ARRAY_SIZE(sub_descr_), \
}, \
}
/**
* @brief Helper macro to declare a descriptor for an array of primitives
*
* @param struct_ Struct packing the values
*
* @param field_name_ Field name in the struct
*
* @param max_len_ Maximum number of elements in array
*
* @param len_field_ Field name in the struct for the number of elements
* in the array
*
* @param elem_type_ Element type, must be a primitive type
*
* Here's an example of use:
* struct example {
* int foo[10];
* size_t foo_len;
* };
*
* struct json_obj_descr array[] = {
* JSON_OBJ_DESCR_ARRAY(struct example, foo, 10, foo_len,
* JSON_TOK_NUMBER)
* };
*/
#define JSON_OBJ_DESCR_ARRAY(struct_, field_name_, max_len_, \
len_field_, elem_type_) \
{ \
.field_name = (#field_name_), \
.field_name_len = sizeof(#field_name_) - 1, \
.offset = offsetof(struct_, field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = JSON_TOK_LIST_START, \
.array = { \
.element_descr = &(struct json_obj_descr) { \
.type = elem_type_, \
.offset = offsetof(struct_, len_field_), \
.alignment = __alignof__(struct_) - 1, \
}, \
.n_elements = (max_len_), \
}, \
}
/**
* @brief Helper macro to declare a descriptor for an array of objects
*
* @param struct_ Struct packing the values
*
* @param field_name_ Field name in the struct containing the array
*
* @param max_len_ Maximum number of elements in the array
*
* @param len_field_ Field name in the struct for the number of elements
* in the array
*
* @param elem_descr_ Element descriptor, pointer to a descriptor array
*
* @param elem_descr_len_ Number of elements in elem_descr_
*
* Here's an example of use:
*
* struct person_height {
* const char *name;
* int height;
* };
*
* struct people_heights {
* struct person_height heights[10];
* size_t heights_len;
* };
*
* struct json_obj_descr person_height_descr[] = {
* JSON_OBJ_DESCR_PRIM(struct person_height, name, JSON_TOK_STRING),
* JSON_OBJ_DESCR_PRIM(struct person_height, height, JSON_TOK_NUMBER),
* };
*
* struct json_obj_descr array[] = {
* JSON_OBJ_DESCR_OBJ_ARRAY(struct people_heights, heights, 10,
* heights_len, person_height_descr,
* ARRAY_SIZE(person_height_descr)),
* };
*/
#define JSON_OBJ_DESCR_OBJ_ARRAY(struct_, field_name_, max_len_, \
len_field_, elem_descr_, elem_descr_len_) \
{ \
.field_name = (#field_name_), \
.field_name_len = sizeof(#field_name_) - 1, \
.offset = offsetof(struct_, field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = JSON_TOK_LIST_START, \
.array = { \
.element_descr = &(struct json_obj_descr) { \
.type = JSON_TOK_OBJECT_START, \
.object = { \
.sub_descr = elem_descr_, \
.sub_descr_len = elem_descr_len_, \
}, \
.offset = offsetof(struct_, len_field_), \
.alignment = __alignof__(struct_) - 1, \
}, \
.n_elements = (max_len_), \
}, \
}
/**
* @brief Helper macro to declare a descriptor for an array of array
*
* @param struct_ Struct packing the values
*
* @param field_name_ Field name in the struct containing the array
*
* @param max_len_ Maximum number of elements in the array
*
* @param len_field_ Field name in the struct for the number of elements
* in the array
*
* @param elem_descr_ Element descriptor, pointer to a descriptor array
*
* @param elem_descr_len_ Number of elements in elem_descr_
*
* Here's an example of use:
*
* struct person_height {
* const char *name;
* int height;
* };
*
* struct person_heigths_array {
* struct person_height heights;
* }
*
* struct people_heights {
* struct person_height_array heights[10];
* size_t heights_len;
* };
*
* struct json_obj_descr person_height_descr[] = {
* JSON_OBJ_DESCR_PRIM(struct person_height, name, JSON_TOK_STRING),
* JSON_OBJ_DESCR_PRIM(struct person_height, height, JSON_TOK_NUMBER),
* };
*
* struct json_obj_descr person_height_array_descr[] = {
* JSON_OBJ_DESCR_OBJECT(struct person_heigths_array,
* heights, person_heigth_descr),
* };
*
* struct json_obj_descr array_array[] = {
* JSON_OBJ_DESCR_ARRAY_ARRAY(struct people_heights, heights, 10,
* heights_len, person_height_array_descr,
* ARRAY_SIZE(person_height_array_descr)),
* };
*/
#define JSON_OBJ_DESCR_ARRAY_ARRAY(struct_, field_name_, max_len_, len_field_, \
elem_descr_, elem_descr_len_) \
{ \
.field_name = (#field_name_), \
.field_name_len = sizeof(#field_name_) - 1, \
.offset = offsetof(struct_, field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = JSON_TOK_LIST_START, \
.array = { \
.element_descr = &(struct json_obj_descr) { \
.type = JSON_TOK_LIST_START, \
.object = { \
.sub_descr = elem_descr_, \
.sub_descr_len = elem_descr_len_, \
}, \
.offset = offsetof(struct_, len_field_), \
.alignment = __alignof__(struct_) - 1, \
}, \
.n_elements = (max_len_), \
}, \
}
/**
* @brief Variant of JSON_OBJ_DESCR_PRIM that can be used when the
* structure and JSON field names differ.
*
* This is useful when the JSON field is not a valid C identifier.
*
* @param struct_ Struct packing the values.
*
* @param json_field_name_ String, field name in JSON strings
*
* @param struct_field_name_ Field name in the struct
*
* @param type_ Token type for JSON value corresponding to a primitive
* type.
*
* @see JSON_OBJ_DESCR_PRIM
*/
#define JSON_OBJ_DESCR_PRIM_NAMED(struct_, json_field_name_, \
struct_field_name_, type_) \
{ \
.field_name = (json_field_name_), \
.field_name_len = sizeof(json_field_name_) - 1, \
.offset = offsetof(struct_, struct_field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = type_, \
}
/**
* @brief Variant of JSON_OBJ_DESCR_OBJECT that can be used when the
* structure and JSON field names differ.
*
* This is useful when the JSON field is not a valid C identifier.
*
* @param struct_ Struct packing the values
*
* @param json_field_name_ String, field name in JSON strings
*
* @param struct_field_name_ Field name in the struct
*
* @param sub_descr_ Array of json_obj_descr describing the subobject
*
* @see JSON_OBJ_DESCR_OBJECT
*/
#define JSON_OBJ_DESCR_OBJECT_NAMED(struct_, json_field_name_, \
struct_field_name_, sub_descr_) \
{ \
.field_name = (json_field_name_), \
.field_name_len = (sizeof(json_field_name_) - 1), \
.offset = offsetof(struct_, struct_field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = JSON_TOK_OBJECT_START, \
.object = { \
.sub_descr = sub_descr_, \
.sub_descr_len = ARRAY_SIZE(sub_descr_), \
}, \
}
/**
* @brief Variant of JSON_OBJ_DESCR_ARRAY that can be used when the
* structure and JSON field names differ.
*
* This is useful when the JSON field is not a valid C identifier.
*
* @param struct_ Struct packing the values
*
* @param json_field_name_ String, field name in JSON strings
*
* @param struct_field_name_ Field name in the struct
*
* @param max_len_ Maximum number of elements in array
*
* @param len_field_ Field name in the struct for the number of elements
* in the array
*
* @param elem_type_ Element type, must be a primitive type
*
* @see JSON_OBJ_DESCR_ARRAY
*/
#define JSON_OBJ_DESCR_ARRAY_NAMED(struct_, json_field_name_,\
struct_field_name_, max_len_, len_field_, \
elem_type_) \
{ \
.field_name = (json_field_name_), \
.field_name_len = sizeof(json_field_name_) - 1, \
.offset = offsetof(struct_, struct_field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = JSON_TOK_LIST_START, \
.array = { \
.element_descr = &(struct json_obj_descr) { \
.type = elem_type_, \
.offset = offsetof(struct_, len_field_), \
.alignment = __alignof__(struct_) - 1, \
}, \
.n_elements = (max_len_), \
}, \
}
/**
* @brief Variant of JSON_OBJ_DESCR_OBJ_ARRAY that can be used when
* the structure and JSON field names differ.
*
* This is useful when the JSON field is not a valid C identifier.
*
* @param struct_ Struct packing the values
*
* @param json_field_name_ String, field name of the array in JSON strings
*
* @param struct_field_name_ Field name in the struct containing the array
*
* @param max_len_ Maximum number of elements in the array
*
* @param len_field_ Field name in the struct for the number of elements
* in the array
*
* @param elem_descr_ Element descriptor, pointer to a descriptor array
*
* @param elem_descr_len_ Number of elements in elem_descr_
*
* Here's an example of use:
*
* struct person_height {
* const char *name;
* int height;
* };
*
* struct people_heights {
* struct person_height heights[10];
* size_t heights_len;
* };
*
* struct json_obj_descr person_height_descr[] = {
* JSON_OBJ_DESCR_PRIM(struct person_height, name, JSON_TOK_STRING),
* JSON_OBJ_DESCR_PRIM(struct person_height, height, JSON_TOK_NUMBER),
* };
*
* struct json_obj_descr array[] = {
* JSON_OBJ_DESCR_OBJ_ARRAY_NAMED(struct people_heights,
* "people-heights", heights,
* 10, heights_len,
* person_height_descr,
* ARRAY_SIZE(person_height_descr)),
* };
*/
#define JSON_OBJ_DESCR_OBJ_ARRAY_NAMED(struct_, json_field_name_, \
struct_field_name_, max_len_, \
len_field_, elem_descr_, \
elem_descr_len_) \
{ \
.field_name = json_field_name_, \
.field_name_len = sizeof(json_field_name_) - 1, \
.offset = offsetof(struct_, struct_field_name_), \
.alignment = __alignof__(struct_) - 1, \
.type = JSON_TOK_LIST_START, \
.element_descr = &(struct json_obj_descr) { \
.type = JSON_TOK_OBJECT_START, \
.object = { \
.sub_descr = elem_descr_, \
.sub_descr_len = elem_descr_len_, \
}, \
.offset = offsetof(struct_, len_field_), \
.alignment = __alignof__(struct_) - 1, \
}, \
.n_elements = (max_len_), \
}
/**
* @brief Parses the JSON-encoded object pointer to by @a json, with
* size @a len, according to the descriptor pointed to by @a descr.
* Values are stored in a struct pointed to by @a val. Set up the
* descriptor like this:
*
* struct s { int foo; char *bar; }
* struct json_obj_descr descr[] = {
* JSON_OBJ_DESCR_PRIM(struct s, foo, JSON_TOK_NUMBER),
* JSON_OBJ_DESCR_PRIM(struct s, bar, JSON_TOK_STRING),
* };
*
* Since this parser is designed for machine-to-machine communications, some
* liberties were taken to simplify the design:
* (1) strings are not unescaped (but only valid escape sequences are
* accepted);
* (2) no UTF-8 validation is performed; and
* (3) only integer numbers are supported (no strtod() in the minimal libc).
*
* @param json Pointer to JSON-encoded value to be parsed
*
* @param len Length of JSON-encoded value
*
* @param descr Pointer to the descriptor array
*
* @param descr_len Number of elements in the descriptor array. Must be less
* than 31 due to implementation detail reasons (if more fields are
* necessary, use two descriptors)
*
* @param val Pointer to the struct to hold the decoded values
*
* @return < 0 if error, bitmap of decoded fields on success (bit 0
* is set if first field in the descriptor has been properly decoded, etc).
*/
int json_obj_parse(char *json, size_t len,
const struct json_obj_descr *descr, size_t descr_len,
void *val);
/**
* @brief Escapes the string so it can be used to encode JSON objects
*
* @param str The string to escape; the escape string is stored the
* buffer pointed to by this parameter
*
* @param len Points to a size_t containing the size before and after
* the escaping process
*
* @param buf_size The size of buffer str points to
*
* @return 0 if string has been escaped properly, or -ENOMEM if there
* was not enough space to escape the buffer
*/
ssize_t json_escape(char *str, size_t *len, size_t buf_size);
/**
* @brief Calculates the JSON-escaped string length
*
* @param str The string to analyze
*
* @param len String size
*
* @return The length str would have if it were escaped
*/
size_t json_calc_escaped_len(const char *str, size_t len);
/**
* @brief Calculates the string length to fully encode an object
*
* @param descr Pointer to the descriptor array
*
* @param descr_len Number of elements in the descriptor array
*
* @param val Struct holding the values
*
* @return Number of bytes necessary to encode the values if >0,
* an error code is returned.
*/
ssize_t json_calc_encoded_len(const struct json_obj_descr *descr,
size_t descr_len, const void *val);
/**
* @brief Encodes an object in a contiguous memory location
*
* @param descr Pointer to the descriptor array
*
* @param descr_len Number of elements in the descriptor array
*
* @param val Struct holding the values
*
* @param buffer Buffer to store the JSON data
*
* @param buf_size Size of buffer, in bytes, with space for the terminating
* NUL character
*
* @return 0 if object has been successfully encoded. A negative value
* indicates an error (as defined on errno.h).
*/
int json_obj_encode_buf(const struct json_obj_descr *descr, size_t descr_len,
const void *val, char *buffer, size_t buf_size);
/**
* @brief Encodes an object using an arbitrary writer function
*
* @param descr Pointer to the descriptor array
*
* @param descr_len Number of elements in the descriptor array
*
* @param val Struct holding the values
*
* @param append_bytes Function to append bytes to the output
*
* @param data Data pointer to be passed to the append_bytes callback
* function.
*
* @return 0 if object has been successfully encoded. A negative value
* indicates an error.
*/
int json_obj_encode(const struct json_obj_descr *descr, size_t descr_len,
const void *val, json_append_bytes_t append_bytes,
void *data);
/**
* @}
*/
#endif /* ZEPHYR_INCLUDE_JSON_H_ */
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