ArduinoJson/src/Internals/EscapedString.cpp

/*
 * Arduino JSON library
 * Benoit Blanchon 2014 - MIT License
 */

#include "ArduinoJson/Internals/QuotedString.h"

using namespace ArduinoJson::Internals;

static inline char getSpecialChar(char c)
{
    // Optimized for code size on a 8-bit AVR

    const char* p = "\"\"\\\\\bb\ff\nn\rr\tt\0";

    while (p[0] && p[0] != c)
    {
        p += 2;
    }

    return p[1];
}

static inline size_t printCharTo(char c, Print* p)
{
    char specialChar = getSpecialChar(c);

    return specialChar != 0
        ? p->write('\\') + p->write(specialChar)
        : p->write(c);
}

size_t QuotedString::printTo(const char* s, Print* p)
{
    if (!s) return p->print("null");
    
    size_t n = p->write('\"');

    while (*s)
    {
        n += printCharTo(*s++, p);
    }

    return n + p->write('\"');
}

static char unescapeChar(char c)
{
    // Optimized for code size on a 8-bit AVR

    const char* p = "b\bf\fn\nr\rt\t";

    while (true)
    {
        if (p[0] == 0) return c;
        if (p[0] == c) return p[1];
        p += 2;
    }
}

static inline bool isQuote(char c)
{
    return c == '\"' || c == '\'';
}

char* QuotedString::extractFrom(char* input, char** endPtr)
{
    char firstChar = *input;
    char stopChar;
    char* startPtr;

    if (isQuote(firstChar))
    {
        stopChar = firstChar; // closing quote is the same as opening quote
        startPtr = input + 1; // skip the quote
    }
    else
    {
        stopChar = ':'; // assume we're parsing a key in an object
        startPtr = input; // no quote to skip
    }

    char* readPtr = startPtr;
    char* writePtr = startPtr;
    char c;

    for (;;)
    {
        c = *readPtr++;

        if (c == 0)
        {
            // premature ending
            *endPtr = 0; 
            return 0;
        }

        if (c == stopChar)
        {
            // closing quote
            break;
        }

        if (c == '\\')
        {
            // replace char
            c = unescapeChar(*readPtr++);
        }

        *writePtr++ = c;
    } 

    // end the string here
    *writePtr = 0;

    // update end ptr
    *endPtr = readPtr;

    return startPtr;
}