meshtastic-firmware/src/mqtt/JSON.cpp

/*
 * File JSON.cpp part of the SimpleJSON Library - http://mjpa.in/json
 *
 * Copyright (C) 2010 Mike Anchor
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "JSON.h"

/**
 * Blocks off the public constructor
 *
 * @access private
 *
 */
JSON::JSON() {}

/**
 * Parses a complete JSON encoded string
 *
 * @access public
 *
 * @param char* data The JSON text
 *
 * @return JSONValue* Returns a JSON Value representing the root, or NULL on error
 */
JSONValue *JSON::Parse(const char *data)
{
    // Skip any preceding whitespace, end of data = no JSON = fail
    if (!SkipWhitespace(&data))
        return NULL;

    // We need the start of a value here now...
    JSONValue *value = JSONValue::Parse(&data);
    if (value == NULL)
        return NULL;

    // Can be white space now and should be at the end of the string then...
    if (SkipWhitespace(&data)) {
        delete value;
        return NULL;
    }

    // We're now at the end of the string
    return value;
}

/**
 * Turns the passed in JSONValue into a JSON encode string
 *
 * @access public
 *
 * @param JSONValue* value The root value
 *
 * @return std::string Returns a JSON encoded string representation of the given value
 */
std::string JSON::Stringify(const JSONValue *value)
{
    if (value != NULL)
        return value->Stringify();
    else
        return "";
}

/**
 * Skips over any whitespace characters (space, tab, \r or \n) defined by the JSON spec
 *
 * @access protected
 *
 * @param char** data Pointer to a char* that contains the JSON text
 *
 * @return bool Returns true if there is more data, or false if the end of the text was reached
 */
bool JSON::SkipWhitespace(const char **data)
{
    while (**data != 0 && (**data == ' ' || **data == '\t' || **data == '\r' || **data == '\n'))
        (*data)++;

    return **data != 0;
}

/**
 * Extracts a JSON String as defined by the spec - "<some chars>"
 * Any escaped characters are swapped out for their unescaped values
 *
 * @access protected
 *
 * @param char** data Pointer to a char* that contains the JSON text
 * @param std::string& str Reference to a std::string to receive the extracted string
 *
 * @return bool Returns true on success, false on failure
 */
bool JSON::ExtractString(const char **data, std::string &str)
{
    str = "";

    while (**data != 0) {
        // Save the char so we can change it if need be
        char next_char = **data;

        // Escaping something?
        if (next_char == '\\') {
            // Move over the escape char
            (*data)++;

            // Deal with the escaped char
            switch (**data) {
            case '"':
                next_char = '"';
                break;
            case '\\':
                next_char = '\\';
                break;
            case '/':
                next_char = '/';
                break;
            case 'b':
                next_char = '\b';
                break;
            case 'f':
                next_char = '\f';
                break;
            case 'n':
                next_char = '\n';
                break;
            case 'r':
                next_char = '\r';
                break;
            case 't':
                next_char = '\t';
                break;
            case 'u': {
                // We need 5 chars (4 hex + the 'u') or its not valid
                if (!simplejson_csnlen(*data, 5))
                    return false;

                // Deal with the chars
                next_char = 0;
                for (int i = 0; i < 4; i++) {
                    // Do it first to move off the 'u' and leave us on the
                    // final hex digit as we move on by one later on
                    (*data)++;

                    next_char <<= 4;

                    // Parse the hex digit
                    if (**data >= '0' && **data <= '9')
                        next_char |= (**data - '0');
                    else if (**data >= 'A' && **data <= 'F')
                        next_char |= (10 + (**data - 'A'));
                    else if (**data >= 'a' && **data <= 'f')
                        next_char |= (10 + (**data - 'a'));
                    else {
                        // Invalid hex digit = invalid JSON
                        return false;
                    }
                }
                break;
            }

            // By the spec, only the above cases are allowed
            default:
                return false;
            }
        }

        // End of the string?
        else if (next_char == '"') {
            (*data)++;
            str.reserve(); // Remove unused capacity
            return true;
        }

        // Disallowed char?
        else if (next_char < ' ' && next_char != '\t') {
            // SPEC Violation: Allow tabs due to real world cases
            return false;
        }

        // Add the next char
        str += next_char;

        // Move on
        (*data)++;
    }

    // If we're here, the string ended incorrectly
    return false;
}

/**
 * Parses some text as though it is an integer
 *
 * @access protected
 *
 * @param char** data Pointer to a char* that contains the JSON text
 *
 * @return double Returns the double value of the number found
 */
double JSON::ParseInt(const char **data)
{
    double integer = 0;
    while (**data != 0 && **data >= '0' && **data <= '9')
        integer = integer * 10 + (*(*data)++ - '0');

    return integer;
}

/**
 * Parses some text as though it is a decimal
 *
 * @access protected
 *
 * @param char** data Pointer to a char* that contains the JSON text
 *
 * @return double Returns the double value of the decimal found
 */
double JSON::ParseDecimal(const char **data)
{
    double decimal = 0.0;
    double factor = 0.1;
    while (**data != 0 && **data >= '0' && **data <= '9') {
        int digit = (*(*data)++ - '0');
        decimal = decimal + digit * factor;
        factor *= 0.1;
    }
    return decimal;
}