cppjson/cppjson/parse.cpp at main · StephenChips/cppjson · GitHub

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#include <array>

#include <cctype>

#include <stdexcept>

#include <string>

#include <utility>

#include <cstdlib>

#include <cmath>

#include <sstream>

#include <cstring>

#include <limits>

#include <cerrno>

#include "cppjson.hpp"

using std::isdigit;

using std::logic_error;

using std::pair;

using std::string;

pair<JSON, string::size_type> parseJSON(const string &input, string::size_type index);

pair<JSON, string::size_type> parseJSONObject(const string &input, string::size_type index);

pair<JSON, string::size_type> parseJSONArray(const string &input, string::size_type index);

pair<std::string, string::size_type> parseStringLiteral(const string &input, string::size_type index);

pair<JSON, string::size_type> parseJSONNumber(const string &input, string::size_type index);

string::size_type expectString(const string &input, string::size_type index, const string &keyword);

string::size_type skipWhitespaces(const string &input, string::size_type index);

inline bool isHexLiteral(const string &input, string::size_type index);

inline bool isOctalLiteral(const string &input, string::size_type index);

std::pair<char16_t, string::size_type> parseUTF16EscapedValue(const string &input, string::size_type index);

inline bool isLeadSurrogate(char16_t v);

inline bool isTrailSurrogate(char16_t v);

char32_t calculateCodepoint(char16_t leadSurroatge, char16_t trailSurrogate);

void writeAsUTF8CodeUnits(std::ostringstream &oss, char32_t codepoint);

void writeHexValueToBuffer(char buf[], const string &input, string::size_type index);

JSON parse(const string &str)

{

auto result = parseJSON(str, 0);

auto end = skipWhitespaces(str, result.second);

if (end != str.size())

throw SyntaxError();

return result.first;

}

pair<JSON, string::size_type> parseJSON(const string &input, string::size_type index)

{

index = skipWhitespaces(input, index);

auto ch = input[index];

if (ch == '{')

return parseJSONObject(input, index);

else if (ch == '[')

return parseJSONArray(input, index);

else if (ch == '"')

{

auto result = parseStringLiteral(input, index);

return std::make_pair(JSON(result.first), result.second);

}

else if (isdigit(ch) || ch == '-')

return parseJSONNumber(input, index);

else if (ch == 't')

{

index = expectString(input, index, "true");

return std::make_pair(JSON(true), index);

}

else if (ch == 'f')

{

index = expectString(input, index, "false");

return std::make_pair(JSON(false), index);

}

else if (ch == 'n')

{

index = expectString(input, index, "null");

return std::make_pair(JSON(nullptr), index);

}

else

throw SyntaxError();

}

// The program looked ahead the next character first, and confirmed the what

// JSON value would be next, before it actually calls the function to parse a

// value, so the initial `index` value must points to the first character of

// a JSON value, hence we can simply skip it without checking.

pair<JSON, string::size_type> parseJSONObject(const string &input, string::size_type index)

{

std::map<std::string, JSON> result;

index = skipWhitespaces(input, index + 1);

if (index == input.size())

throw SyntaxError();

if (input[index] == '}')

return std::make_pair(JSON(result), index + 1);

while (true)

{

index = skipWhitespaces(input, index);

auto objectKey = parseStringLiteral(input, index);

index = skipWhitespaces(input, objectKey.second);

index = expectString(input, index, ":");

index = skipWhitespaces(input, index);

auto objectValue = parseJSON(input, index);

index = skipWhitespaces(input, objectValue.second);

if (input[index] == '}')

{

result[objectKey.first] = objectValue.first;

return std::make_pair(JSON(result), index + 1);

}

else if (input[index] == ',')

{

result[objectKey.first] = objectValue.first;

index++;

}

else

throw SyntaxError();

}

throw SyntaxError();

}

pair<JSON, string::size_type> parseJSONArray(const string &input, string::size_type index)

{

std::vector<JSON> result;

index = skipWhitespaces(input, index + 1);

if (index == input.size())

throw SyntaxError();

if (input[index] == ']')

return std::make_pair(JSON(result), index + 1);

while (true)

{

auto jsonVal = parseJSON(input, index);

index = skipWhitespaces(input, jsonVal.second);

if (index == input.size())

throw SyntaxError();

else if (input[index] == ']')

{

result.push_back(jsonVal.first);

return std::make_pair(JSON(result), index + 1);

}

else if (input[index] == ',')

{

result.push_back(jsonVal.first);

index = skipWhitespaces(input, index + 1);

}

else

throw SyntaxError();

}

pair<std::string, string::size_type> parseStringLiteral(const string &input, string::size_type index)

{

// Skip the double-quote at the begining

index++;

string::size_type start = index;

std::ostringstream oss;

while (index != input.size())

{

if (input[index] == '\\')

{

if (index + 1 >= input.size())

throw SyntaxError();

oss << input.substr(start, index - start);

auto ch = input[index + 1];

if (ch == 'u')

{

auto v1 = parseUTF16EscapedValue(input, index);

if (isLeadSurrogate(v1.first))

{

// If the escaped value we just read is a lead surrogate, there must be a trail surrogate right after it.

// Together they indicate a single Unicode character.

// Since the value we have just parsed is a lead surrogate, we need to get its correspondent trail surrogate.

if (v1.second + 1 < input.size() && input[v1.second] == '\\' && input[v1.second + 1] == 'u')

{

auto v2 = parseUTF16EscapedValue(input, v1.second);

if (isTrailSurrogate(v2.first))

{

auto leadSurrogate = v1.first;

auto trailSurrogate = v2.first;

auto codePoint = calculateCodepoint(leadSurrogate, trailSurrogate);

writeAsUTF8CodeUnits(oss, codePoint);

}

else

{

// The trail surrogate isn't valid because it's value is out of range (which should be between 0xDC00 to 0xDFFF).

// In such case, two values are treated as two codepoints individually and will be written to the output together.

writeAsUTF8CodeUnits(oss, v1.first);

writeAsUTF8CodeUnits(oss, v2.first);

}

index = v2.second;

}

else

{

// There are no another UTF-16 escaped value after the lead surrogate, which is invalid. The program will write the

// lead surrogate to the output then continue.

writeAsUTF8CodeUnits(oss, v1.first);

index = v1.second;

}

else

{

// If the first escaped value isn't a lead surrogate, we will regard it as an Unicode codepoint and will write it to the

// output (It might be a trail surrogate but we need not to distinguish it).

writeAsUTF8CodeUnits(oss, v1.first);

index = v1.second;

}

else

{

if (ch == '\\')

oss << '\\';

else if (ch == '/')

oss << '/';

else if (ch == 'b')

oss << '\b';

else if (ch == 'f')

oss << '\f';

else if (ch == 'n')

oss << '\n';

else if (ch == 'r')

oss << '\r';

else if (ch == 't')

oss << '\t';

else

throw SyntaxError();

index += 2;

}

start = index;

}

else if (input[index] == '"')

{

if (start < index)

{

oss << input.substr(start, index - start);

}

return std::make_pair(oss.str(), index + 1);

}

else

{

index++;

}

throw SyntaxError();

}

pair<JSON, string::size_type> parseJSONNumber(const string &input, string::size_type index)

{

// correspondent regex:

// /^-?(0|([1-9][0-9]*))(\.[0-9]+)?((e|E)(-|\+)?[0-9]+)?$/

// We could parse a number with our own codes, but for now we will just use `std::strtod`

// instead.

// JSON doesn't supports hex literals and octal literals, but `strtod` can parse them,

// so we should exclude them before parsing.

// Hex literal is something like 0x3, 0XE2, a literal started with 0x or 0X, and Octal

// literals is somthing like 045, 022, a literal started with a leading zero.

// In JSON, if a number's interal part's first digit is zero, it must be followed by the

// decimal point (.), no other digits can be appeared behind it.

if (isHexLiteral(input, index) || isOctalLiteral(input, index))

throw SyntaxError();

const char *cStr = input.c_str();

char *endPtr = const_cast<char *>(cStr);

double result = std::strtod(cStr + index, &endPtr);

if (endPtr == cStr)

throw SyntaxError();

else if (result == HUGE_VAL)

result = std::numeric_limits<double>::infinity();

else if (errno == ERANGE)

// Underflow, like 1.0E-1000

result = result > 0 ? 0 : -0;

return std::make_pair(JSON(result), endPtr - cStr);

}

string::size_type expectString(const string &input, string::size_type index, const string &str)

{

auto i = index;

auto j = 0u;

while (i != input.size() && j != str.size())

{

if (input[i] != str[j])

break;

i++, j++;

}

if (j != str.size())

throw SyntaxError();

return i;

}

string::size_type skipWhitespaces(const string &input, string::size_type index)

{

while (index != input.size())

{

auto ch = input[index];

if (ch == ' ' || ch == '\n' || ch == '\r' || ch == '\t')

index++;

else

break;

}

return index;

}

inline bool isHexLiteral(const string &input, string::size_type index)

{

return index + 1 < input.size() && (input[index + 1] == 'x' || input[index + 1] == 'X');

}

inline bool isOctalLiteral(const string &input, string::size_type index)

{

return index + 1 < input.size() && input[index] == '0' && isdigit(input[index + 1]);

}

std::pair<char16_t, string::size_type> parseUTF16EscapedValue(const string &input, string::size_type index)

{

char digitBuffer[5];

writeHexValueToBuffer(digitBuffer, input, index + 2);

char16_t v = strtoul(digitBuffer, nullptr, 16);

return std::make_pair(v, index + 6);

}

inline bool isLeadSurrogate(char16_t v)

{

return v >= 0xD800u && v <= 0xDBFFu;

}

inline bool isTrailSurrogate(char16_t v)

{

return v >= 0xDC00u && v <= 0xDFFFu;

}

char32_t calculateCodepoint(char16_t leadSurroatge, char16_t trailSurrogate)

{

return (static_cast<char32_t>(leadSurroatge - 0xD800u) << 10) + (trailSurrogate - 0xDC00u) + 0x10000;

}

void writeAsUTF8CodeUnits(std::ostringstream &oss, char32_t codepoint)

{

if (codepoint <= 0x00007F)

{

oss << static_cast<char>(codepoint);

}

else if (codepoint <= 0x0007FF)

{

oss << static_cast<char>(0b11000000 | (codepoint >> 6));

oss << static_cast<char>(0b10000000 | (codepoint & 0b111111));

}

else if (codepoint <= 0x00FFFF)

{

// Strictly speaking, codepoints 0x00D800..0x00DFFF should only be used in UTF-16 text as

// surrogate pair. This is how JSON escapes unicode that takes more than two bytes.

// But in case we met an unpaired surrogate, instead throwing a syntax error, we will still

// translate it to correspondent UTF-8 codeunits as if it was a normal unicode character

// for this is how JSON.parse(...) behaves in browser.

oss << static_cast<char>(0b11100000 | (codepoint >> 12));

oss << static_cast<char>(0b10000000 | ((codepoint >> 6) & 0b111111));

oss << static_cast<char>(0b10000000 | (codepoint & 0b111111));

}

else if (codepoint <= 0x10FFFF)

{

oss << static_cast<char>(0b11110000 | (codepoint >> 18));

oss << static_cast<char>(0b10000000 | (codepoint >> 12) & 0b111111);

oss << static_cast<char>(0b10000000 | (codepoint >> 6) & 0b111111);

oss << static_cast<char>(0b10000000 | (codepoint & 0b111111));

}

else

{

throw std::range_error("The codepoint is out of range.");

}

void writeHexValueToBuffer(char xdigits[], const string &input, string::size_type index)

{

if (index + 4 >= input.size())

throw SyntaxError();

for (auto i = 0; i < 4; i++)

{

if (!std::isxdigit(input[index + i]))

throw SyntaxError();

}

for (auto i = 0; i < 4; i++)

{

xdigits[i] = input[index + i];

}

xdigits[4] = '\0';

}

cppjson/cppjson/parse.cpp at main · StephenChips/cppjson · GitHub

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