json.c

/*
\file   json.c

\brief  A simple JSON string parser

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*/
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include "mcc_generated_files/cryptoauthlib/lib/basic/atca_helpers.h"

uint8_t * JSON_findQuote(uint8_t *p) {
    while(*p) {
        if (*p == '"') return p;    // return pointer AFTER \"
        if (*p == '\\') {
            p++;
            if (*p == '\0') break;// '\' was last char in string
        }
        p++;
    }
    return p;    // encountered end of string
}

// advance pointer skipping white spaces
//
uint8_t * next(uint8_t *p) {
    while (*p && isWhiteSpace(*p)) p++;
    return p;
}

// search for a "key" inside a JSON object
//      return a pointer to value string (open quote or first alphanum)
//      return NULL if not found
uint8_t * JSON_getValue(uint8_t *json, char* key){
    uint8_t *p = json;    // point immediately to first "

    while( *p != '\0') { // loop over json object key pairs
        p = JSON_findQuote(p);
        if (strncmp((char*)p+1, key, strlen(key)) == 0) {
            p += 1+ strlen(key);
            if (*p == '"') { // key must be in quotes -> it is a match
                p = next(p+1);            // skip whitespace
                if (*p != ':') break;   // key must be followed by ':' -> bad json
                p = next(p+1);            // skip whitespace
                if ((*p == '\0')||(*p == '}')) break; // value missing
                return p;   // return pointing to the value
            }
        }
        // not a match, find the next key pair
        p = JSON_findQuote(p+1); // skip past the key
        if (*p == '\0') break;  // key must be in quotes -> bad json
        p = next(p+1);            // skip whitespace
        if (*p != ':') break;   // key must be followed by ':' -> bad json
        p = next(p+1);            // skip whitespace
        if ((*p == '\0')||(*p == '}')) break; // value missing
        if (*p == '"') {        // skip past string value
            p = JSON_findQuote(p+1);
            if (*p == '\0') break;
            p = next(p+1);            // skip white spaces
            }
        else {
            while(isDigit(*p)) p++;
        }
        p = next(p);            // skip white spaces
        if (*p != ',') break;     // expecting a ',' -> not found or bad json
    }
    return NULL;
}

inline static uint8_t hex_digit_to_num(char c)
{
    if (c >= '0' && c <= '9') {
        return (uint8_t)(c - '0');
    }
    if (c >= 'a' && c <= 'f') {
        return (uint8_t)(c - 'a') + 10;
    }
    if (c >= 'A' && c <= 'F') {
        return (uint8_t)(c - 'A') + 10;
    }
    return 16;
}

bool get_number(uint8_t *p, int *value){
    int sign = 1;
    *value = 0;

    if ((p[0] == '"') &&  (p[1] != '\0'))    // if inside a string, (i.e. slider)
        p++;

    if (*p == '-') {
        p++;
        sign = -1;
    }
    if ((p[0] == '0') && (p[1] == 'x')) {    // if hexadecimal (i.e. RGB value)
        p += 2;
        while (*p && isHexDigit(*p)) {
            *value <<= 4;
            *value += hex_digit_to_num(*p);
            p++;
            }
        *value *= sign;
        return true;
    } else {
        while (*p && isDigit(*p)) {
            *value *= 10;
            *value += (*p - '0');
            p++;
        }
        *value *= sign;
        return true;
    }

    return false;
}

bool JSON_getInt(uint8_t *p, char * key, int* value) {
    uint8_t *pV = JSON_getValue(p, key);
    if (pV != NULL) {
        bool r = get_number(pV, value);
//        printf("%s : %d\n", key, *value);
        return r;
    }
    return false;
}