json11.cpp

/* Copyright (c) 2013 Dropbox, Inc.
 *
 * 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 <LightGBM/utils/json11.h>

#include <LightGBM/utils/log.h>

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <limits>

namespace json11 {

static const int max_depth = 200;

using std::initializer_list;
using std::make_shared;
using std::map;
using std::string;
using std::vector;

using LightGBM::Log;

/* Helper for representing null - just a do-nothing struct, plus comparison
 * operators so the helpers in JsonValue work. We can't use nullptr_t because
 * it may not be orderable.
 */
struct NullStruct {
  bool operator==(NullStruct) const { return true; }
  bool operator<(NullStruct) const { return false; }
};

/* * * * * * * * * * * * * * * * * * * *
 * Serialization
 */

static void dump(NullStruct, string *out) { *out += "null"; }

static void dump(double value, string *out) {
  if (std::isfinite(value)) {
    char buf[32];
    snprintf(buf, sizeof buf, "%.17g", value);
    *out += buf;
  } else {
    *out += "null";
  }
}

static void dump(int value, string *out) {
  char buf[32];
  snprintf(buf, sizeof buf, "%d", value);
  *out += buf;
}

static void dump(bool value, string *out) { *out += value ? "true" : "false"; }

static void dump(const string &value, string *out) {
  *out += '"';
  for (size_t i = 0; i < value.length(); i++) {
    const char ch = value[i];
    if (ch == '\\') {
      *out += "\\\\";
    } else if (ch == '"') {
      *out += "\\\"";
    } else if (ch == '\b') {
      *out += "\\b";
    } else if (ch == '\f') {
      *out += "\\f";
    } else if (ch == '\n') {
      *out += "\\n";
    } else if (ch == '\r') {
      *out += "\\r";
    } else if (ch == '\t') {
      *out += "\\t";
    } else if (static_cast<uint8_t>(ch) <= 0x1f) {
      char buf[8];
      snprintf(buf, sizeof buf, "\\u%04x", ch);
      *out += buf;
    } else if (static_cast<uint8_t>(ch) == 0xe2 &&
               static_cast<uint8_t>(value[i + 1]) == 0x80 &&
               static_cast<uint8_t>(value[i + 2]) == 0xa8) {
      *out += "\\u2028";
      i += 2;
    } else if (static_cast<uint8_t>(ch) == 0xe2 &&
               static_cast<uint8_t>(value[i + 1]) == 0x80 &&
               static_cast<uint8_t>(value[i + 2]) == 0xa9) {
      *out += "\\u2029";
      i += 2;
    } else {
      *out += ch;
    }
  }
  *out += '"';
}

static void dump(const Json::array &values, string *out) {
  bool first = true;
  *out += "[";
  for (const auto &value : values) {
    if (!first) *out += ", ";
    value.dump(out);
    first = false;
  }
  *out += "]";
}

static void dump(const Json::object &values, string *out) {
  bool first = true;
  *out += "{";
  for (const auto &kv : values) {
    if (!first) *out += ", ";
    dump(kv.first, out);
    *out += ": ";
    kv.second.dump(out);
    first = false;
  }
  *out += "}";
}

void Json::dump(string *out) const { m_ptr->dump(out); }

/* * * * * * * * * * * * * * * * * * * *
 * Value wrappers
 */

template <Json::Type tag, typename T>
class Value : public JsonValue {
 protected:
  // Constructors
  explicit Value(const T &value) : m_value(value) {}
  explicit Value(T &&value) : m_value(std::move(value)) {}

  // Get type tag
  Json::Type type() const override { return tag; }

  // Comparisons
  bool equals(const JsonValue *other) const override {
    return m_value == static_cast<const Value<tag, T> *>(other)->m_value;
  }
  bool less(const JsonValue *other) const override {
    return m_value < (static_cast<const Value<tag, T> *>(other)->m_value);
  }

  const T m_value;
  void dump(string *out) const override { json11::dump(m_value, out); }
};

class JsonDouble final : public Value<Json::NUMBER, double> {
  double number_value() const override { return m_value; }
  int int_value() const override { return static_cast<int>(m_value); }
  bool equals(const JsonValue *other) const override {
    return m_value == other->number_value();
  }
  bool less(const JsonValue *other) const override {
    return m_value < other->number_value();
  }

 public:
  explicit JsonDouble(double value) : Value(value) {}
};

class JsonInt final : public Value<Json::NUMBER, int> {
  double number_value() const override { return m_value; }
  int int_value() const override { return m_value; }
  bool equals(const JsonValue *other) const override {
    return m_value == other->number_value();
  }
  bool less(const JsonValue *other) const override {
    return m_value < other->number_value();
  }

 public:
  explicit JsonInt(int value) : Value(value) {}
};

class JsonBoolean final : public Value<Json::BOOL, bool> {
  bool bool_value() const override { return m_value; }

 public:
  explicit JsonBoolean(bool value) : Value(value) {}
};

class JsonString final : public Value<Json::STRING, string> {
  const string &string_value() const override { return m_value; }

 public:
  explicit JsonString(const string &value) : Value(value) {}
  explicit JsonString(string &&value) : Value(std::move(value)) {}
};

class JsonArray final : public Value<Json::ARRAY, Json::array> {
  const Json::array &array_items() const override { return m_value; }
  const Json &operator[](size_t i) const override;

 public:
  explicit JsonArray(const Json::array &value) : Value(value) {}
  explicit JsonArray(Json::array &&value) : Value(std::move(value)) {}
};

class JsonObject final : public Value<Json::OBJECT, Json::object> {
  const Json::object &object_items() const override { return m_value; }
  const Json &operator[](const string &key) const override;

 public:
  explicit JsonObject(const Json::object &value) : Value(value) {}
  explicit JsonObject(Json::object &&value) : Value(std::move(value)) {}
};

class JsonNull final : public Value<Json::NUL, NullStruct> {
 public:
  JsonNull() : Value({}) {}
};

/* * * * * * * * * * * * * * * * * * * *
 * Static globals - static-init-safe
 */
struct Statics {
  const std::shared_ptr<JsonValue> null = make_shared<JsonNull>();
  const std::shared_ptr<JsonValue> t = make_shared<JsonBoolean>(true);
  const std::shared_ptr<JsonValue> f = make_shared<JsonBoolean>(false);
  const string empty_string;
  const vector<Json> empty_vector;
  const map<string, Json> empty_map;
  Statics() {}
};

static const Statics &statics() {
  static const Statics s{};
  return s;
}

static const Json &static_null() {
  // This has to be separate, not in Statics, because Json() accesses
  // statics().null.
  static const Json json_null;
  return json_null;
}

/* * * * * * * * * * * * * * * * * * * *
 * Constructors
 */

Json::Json() noexcept : m_ptr(statics().null) {}
Json::Json(std::nullptr_t) noexcept : m_ptr(statics().null) {}
Json::Json(double value) : m_ptr(make_shared<JsonDouble>(value)) {}
Json::Json(int value) : m_ptr(make_shared<JsonInt>(value)) {}
Json::Json(bool value) : m_ptr(value ? statics().t : statics().f) {}
Json::Json(const string &value) : m_ptr(make_shared<JsonString>(value)) {}
Json::Json(string &&value) : m_ptr(make_shared<JsonString>(std::move(value))) {}
Json::Json(const char *value) : m_ptr(make_shared<JsonString>(value)) {}
Json::Json(const Json::array &values) : m_ptr(make_shared<JsonArray>(values)) {}
Json::Json(Json::array &&values)
    : m_ptr(make_shared<JsonArray>(std::move(values))) {}
Json::Json(const Json::object &values)
    : m_ptr(make_shared<JsonObject>(values)) {}
Json::Json(Json::object &&values)
    : m_ptr(make_shared<JsonObject>(std::move(values))) {}

/* * * * * * * * * * * * * * * * * * * *
 * Accessors
 */

Json::Type Json::type() const { return m_ptr->type(); }
double Json::number_value() const { return m_ptr->number_value(); }
int Json::int_value() const { return m_ptr->int_value(); }
bool Json::bool_value() const { return m_ptr->bool_value(); }
const string &Json::string_value() const { return m_ptr->string_value(); }
const vector<Json> &Json::array_items() const { return m_ptr->array_items(); }
const map<string, Json> &Json::object_items() const {
  return m_ptr->object_items();
}
const Json &Json::operator[](size_t i) const { return (*m_ptr)[i]; }
const Json &Json::operator[](const string &key) const { return (*m_ptr)[key]; }

double JsonValue::number_value() const { return 0; }
int JsonValue::int_value() const { return 0; }
bool JsonValue::bool_value() const { return false; }
const string &JsonValue::string_value() const { return statics().empty_string; }
const vector<Json> &JsonValue::array_items() const {
  return statics().empty_vector;
}
const map<string, Json> &JsonValue::object_items() const {
  return statics().empty_map;
}
const Json &JsonValue::operator[](size_t) const { return static_null(); }
const Json &JsonValue::operator[](const string &) const {
  return static_null();
}

const Json &JsonObject::operator[](const string &key) const {
  auto iter = m_value.find(key);
  return (iter == m_value.end()) ? static_null() : iter->second;
}
const Json &JsonArray::operator[](size_t i) const {
  if (i >= m_value.size())
    return static_null();
  else
    return m_value[i];
}

/* * * * * * * * * * * * * * * * * * * *
 * Comparison
 */

bool Json::operator==(const Json &other) const {
  if (m_ptr == other.m_ptr) return true;
  if (m_ptr->type() != other.m_ptr->type()) return false;

  return m_ptr->equals(other.m_ptr.get());
}

bool Json::operator<(const Json &other) const {
  if (m_ptr == other.m_ptr) return false;
  if (m_ptr->type() != other.m_ptr->type())
    return m_ptr->type() < other.m_ptr->type();

  return m_ptr->less(other.m_ptr.get());
}

/* * * * * * * * * * * * * * * * * * * *
 * Parsing
 */

/* esc(c)
 *
 * Format char c suitable for printing in an error message.
 */
static inline string esc(char c) {
  char buf[12];
  if (static_cast<uint8_t>(c) >= 0x20 && static_cast<uint8_t>(c) <= 0x7f) {
    snprintf(buf, sizeof buf, "'%c' (%d)", c, c);
  } else {
    snprintf(buf, sizeof buf, "(%d)", c);
  }
  return string(buf);
}

template <typename T>
static inline bool in_range(T x, T lower, T upper) {
  return (x >= lower && x <= upper);
}

namespace {
/* JsonParser
 *
 * Object that tracks all state of an in-progress parse.
 */
struct JsonParser final {
  /* State
   */
  const char *str;
  const size_t str_len;
  size_t i;
  string *err;
  bool failed;
  const JsonParse strategy;

  /* fail(msg, err_ret = Json())
   *
   * Mark this parse as failed.
   */
  Json fail(string &&msg) { return fail(std::move(msg), Json()); }

  template <typename T>
  T fail(string &&msg, const T err_ret) {
    if (!failed) *err = std::move(msg);
    failed = true;
    return err_ret;
  }

  /* consume_whitespace()
   *
   * Advance until the current character is non-whitespace.
   */
  void consume_whitespace() {
    while (str[i] == ' ' || str[i] == '\r' || str[i] == '\n' || str[i] == '\t')
      i++;
  }

  /* consume_comment()
   *
   * Advance comments (c-style inline and multiline).
   */
  bool consume_comment() {
    bool comment_found = false;
    if (str[i] == '/') {
      i++;
      if (i == str_len)
        return fail("Unexpected end of input after start of comment", false);
      if (str[i] == '/') {  // inline comment
        i++;
        // advance until next line, or end of input
        while (i < str_len && str[i] != '\n') {
          i++;
        }
        comment_found = true;
      } else if (str[i] == '*') {  // multiline comment
        i++;
        if (i > str_len - 2)
          return fail("Unexpected end of input inside multi-line comment",
                      false);
        // advance until closing tokens
        while (!(str[i] == '*' && str[i + 1] == '/')) {
          i++;
          if (i > str_len - 2)
            return fail("Unexpected end of input inside multi-line comment",
                        false);
        }
        i += 2;
        comment_found = true;
      } else {
        return fail("Malformed comment", false);
      }
    }
    return comment_found;
  }

  /* consume_garbage()
   *
   * Advance until the current character is non-whitespace and non-comment.
   */
  void consume_garbage() {
    consume_whitespace();
    if (strategy == JsonParse::COMMENTS) {
      bool comment_found = false;
      do {
        comment_found = consume_comment();
        if (failed) return;
        consume_whitespace();
      } while (comment_found);
    }
  }

  /* get_next_token()
   *
   * Return the next non-whitespace character. If the end of the input is
   * reached, flag an error and return 0.
   */
  char get_next_token() {
    consume_garbage();
    if (failed) return char{0};
    if (i == str_len) return fail("Unexpected end of input", char{0});

    return str[i++];
  }

  /* encode_utf8(pt, out)
   *
   * Encode pt as UTF-8 and add it to out.
   */
  void encode_utf8(int64_t pt, string* out) {
    if (pt < 0) return;

    if (pt < 0x80) {
      *out += static_cast<char>(pt);
    } else if (pt < 0x800) {
      *out += static_cast<char>((pt >> 6) | 0xC0);
      *out += static_cast<char>((pt & 0x3F) | 0x80);
    } else if (pt < 0x10000) {
      *out += static_cast<char>((pt >> 12) | 0xE0);
      *out += static_cast<char>(((pt >> 6) & 0x3F) | 0x80);
      *out += static_cast<char>((pt & 0x3F) | 0x80);
    } else {
      *out += static_cast<char>((pt >> 18) | 0xF0);
      *out += static_cast<char>(((pt >> 12) & 0x3F) | 0x80);
      *out += static_cast<char>(((pt >> 6) & 0x3F) | 0x80);
      *out += static_cast<char>((pt & 0x3F) | 0x80);
    }
  }

  /* parse_string()
   *
   * Parse a string, starting at the current position.
   */
  string parse_string() {
    string out;
    int64_t last_escaped_codepoint = -1;
    while (true) {
      if (i == str_len) return fail("Unexpected end of input in string", "");

      char ch = str[i++];

      if (ch == '"') {
        encode_utf8(last_escaped_codepoint, &out);
        return out;
      }

      if (in_range<int64_t>(ch, 0, 0x1f))
        return fail("Unescaped " + esc(ch) + " in string", "");

      // The usual case: non-escaped characters
      if (ch != '\\') {
        encode_utf8(last_escaped_codepoint, &out);
        last_escaped_codepoint = -1;
        out += ch;
        continue;
      }

      // Handle escapes
      if (i == str_len) return fail("Unexpected end of input in string", "");

      ch = str[i++];

      if (ch == 'u') {
        // Extract 4-byte escape sequence
        string esc = string(str + i, 4);
        // Explicitly check length of the substring. The following loop
        // relies on std::string returning the terminating NUL when
        // accessing str[length]. Checking here reduces brittleness.
        if (esc.length() < 4) {
          return fail("Bad \\u escape: " + esc, "");
        }
        for (size_t j = 0; j < 4; j++) {
          if (!in_range(esc[j], 'a', 'f') && !in_range(esc[j], 'A', 'F') &&
              !in_range(esc[j], '0', '9'))
            return fail("Bad \\u escape: " + esc, "");
        }

        int64_t codepoint =
            static_cast<int64_t>(strtol(esc.data(), nullptr, 16));

        // JSON specifies that characters outside the BMP shall be encoded as a
        // pair of 4-hex-digit \u escapes encoding their surrogate pair
        // components. Check whether we're in the middle of such a beast: the
        // previous codepoint was an escaped lead (high) surrogate, and this is
        // a trail (low) surrogate.
        if (in_range<int64_t>(last_escaped_codepoint, 0xD800, 0xDBFF) &&
            in_range<int64_t>(codepoint, 0xDC00, 0xDFFF)) {
          // Reassemble the two surrogate pairs into one astral-plane character,
          // per the UTF-16 algorithm.
          encode_utf8((((last_escaped_codepoint - 0xD800) << 10) |
                       (codepoint - 0xDC00)) +
                          0x10000,
                      &out);
          last_escaped_codepoint = -1;
        } else {
          encode_utf8(last_escaped_codepoint, &out);
          last_escaped_codepoint = codepoint;
        }

        i += 4;
        continue;
      }

      encode_utf8(last_escaped_codepoint, &out);
      last_escaped_codepoint = -1;

      if (ch == 'b') {
        out += '\b';
      } else if (ch == 'f') {
        out += '\f';
      } else if (ch == 'n') {
        out += '\n';
      } else if (ch == 'r') {
        out += '\r';
      } else if (ch == 't') {
        out += '\t';
      } else if (ch == '"' || ch == '\\' || ch == '/') {
        out += ch;
      } else {
        return fail("Invalid escape character " + esc(ch), "");
      }
    }
  }

  /* parse_number()
   *
   * Parse a double.
   */
  Json parse_number() {
    size_t start_pos = i;

    if (str[i] == '-') i++;

    // Integer part
    if (str[i] == '0') {
      i++;
      if (in_range(str[i], '0', '9'))
        return fail("Leading 0s not permitted in numbers");
    } else if (in_range(str[i], '1', '9')) {
      i++;
      while (in_range(str[i], '0', '9')) i++;
    } else {
      return fail("Invalid " + esc(str[i]) + " in number");
    }

    if (str[i] != '.' && str[i] != 'e' && str[i] != 'E' &&
        (i - start_pos) <=
            static_cast<size_t>(std::numeric_limits<int>::digits10)) {
      return Json(std::atoi(str + start_pos));
    }

    // Decimal part
    if (str[i] == '.') {
      i++;
      if (!in_range(str[i], '0', '9'))
        return fail("At least one digit required in fractional part");

      while (in_range(str[i], '0', '9')) i++;
    }

    // Exponent part
    if (str[i] == 'e' || str[i] == 'E') {
      i++;

      if (str[i] == '+' || str[i] == '-') i++;

      if (!in_range(str[i], '0', '9'))
        return fail("At least one digit required in exponent");

      while (in_range(str[i], '0', '9')) i++;
    }

    return Json(std::strtod(str + start_pos, nullptr));
  }

  /* expect(str, res)
   *
   * Expect that 'str' starts at the character that was just read. If it does,
   * advance the input and return res. If not, flag an error.
   */
  Json expect(const string &expected, Json res) {
    CHECK_NE(i, 0)
    i--;
    auto substr = string(str + i, expected.length());
    if (substr == expected) {
      i += expected.length();
      return res;
    } else {
      return fail("Parse error: expected " + expected + ", got " + substr);
    }
  }

  /* parse_json()
   *
   * Parse a JSON object.
   */
  Json parse_json(int depth) {
    if (depth > max_depth) {
      return fail("Exceeded maximum nesting depth");
    }

    char ch = get_next_token();
    if (failed) return Json();

    if (ch == '-' || (ch >= '0' && ch <= '9')) {
      i--;
      return parse_number();
    }

    if (ch == 't') return expect("true", Json(true));

    if (ch == 'f') return expect("false", Json(false));

    if (ch == 'n') return expect("null", Json());

    if (ch == '"') return Json(parse_string());

    if (ch == '{') {
      map<string, Json> data;
      ch = get_next_token();
      if (ch == '}') return Json(data);

      while (1) {
        if (ch != '"') return fail("Expected '\"' in object, got " + esc(ch));

        string key = parse_string();
        if (failed) return Json();

        ch = get_next_token();
        if (ch != ':') return fail("Expected ':' in object, got " + esc(ch));

        data[std::move(key)] = parse_json(depth + 1);
        if (failed) return Json();

        ch = get_next_token();
        if (ch == '}') break;
        if (ch != ',') return fail("Expected ',' in object, got " + esc(ch));

        ch = get_next_token();
      }
      return Json(data);
    }

    if (ch == '[') {
      vector<Json> data;
      ch = get_next_token();
      if (ch == ']') return Json(data);

      while (1) {
        i--;
        data.push_back(parse_json(depth + 1));
        if (failed) return Json();

        ch = get_next_token();
        if (ch == ']') break;
        if (ch != ',') return fail("Expected ',' in list, got " + esc(ch));

        ch = get_next_token();
        (void)ch;
      }
      return Json(data);
    }

    return fail("Expected value, got " + esc(ch));
  }
};
}  // namespace

Json Json::parse(const string &in, string *err, JsonParse strategy) {
  JsonParser parser{in.c_str(), in.size(), 0, err, false, strategy};
  Json result = parser.parse_json(0);

  // Check for any trailing garbage
  parser.consume_garbage();
  if (parser.failed) return Json();
  if (parser.i != in.size())
    return parser.fail("Unexpected trailing " + esc(in[parser.i]));

  return result;
}

// Documented in json11.hpp
vector<Json> Json::parse_multi(const string &in,
                               std::string::size_type *parser_stop_pos,
                               string *err, JsonParse strategy) {
  JsonParser parser{in.c_str(), in.size(), 0, err, false, strategy};
  *parser_stop_pos = 0;
  vector<Json> json_vec;
  while (parser.i != in.size() && !parser.failed) {
    json_vec.push_back(parser.parse_json(0));
    if (parser.failed) break;

    // Check for another object
    parser.consume_garbage();
    if (parser.failed) break;
    *parser_stop_pos = parser.i;
  }
  return json_vec;
}

/* * * * * * * * * * * * * * * * * * * *
 * Shape-checking
 */

bool Json::has_shape(const shape &types, string *err) const {
  if (!is_object()) {
    *err = "Expected JSON object, got " + dump();
    return false;
  }

  for (auto &item : types) {
    if ((*this)[item.first].type() != item.second) {
      *err = "Bad type for " + item.first + " in " + dump();
      return false;
    }
  }

  return true;
}

}  // namespace json11