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 "json11.hpp"
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <cstdio>
#include <limits>

namespace json11 {

static const int max_depth = 200;

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

/* 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(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(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(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(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>(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>(move(values))) {}
Json::Json(const Json::object &values) : m_ptr(make_shared<JsonObject>(values)) {}
Json::Json(Json::object &&values) : m_ptr(make_shared<JsonObject>(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->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->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);
}

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

namespace {
/* JsonParser
 *
 * Object that tracks all state of an in-progress parse.
 */
struct JsonParser final {

 /* State
 */
 const string &str;
 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(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.size())
 return fail("unexpected end of input inside comment", false);
 if (str[i] == '/') { // inline comment
 i++;
 if (i == str.size())
 return fail("unexpected end of input inside inline comment", false);
 // advance until next line
 while (str[i] != '\n') {
 i++;
 if (i == str.size())
 return fail("unexpected end of input inside inline comment", false);
 }
 comment_found = true;
 }
 else if (str[i] == '*') { // multiline comment
 i++;
 if (i > str.size()-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.size()-2)
 return fail(
 "unexpected end of input inside multi-line comment", false);
 }
 i += 2;
 if (i == str.size())
 return fail(
 "unexpected end of input inside multi-line comment", false);
 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();
 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 (i == str.size())
 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(long 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;
 long last_escaped_codepoint = -1;
 while (true) {
 if (i == str.size())
 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(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.size())
 return fail("unexpected end of input in string", "");

 ch = str[i++];

 if (ch == 'u') {
 // Extract 4-byte escape sequence
 string esc = str.substr(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, "");
 }

 long codepoint = 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(last_escaped_codepoint, 0xD800, 0xDBFF)
 && in_range(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 std::atoi(str.c_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 std::strtod(str.c_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) {
 assert(i != 0);
 i--;
 if (str.compare(i, expected.length(), expected) == 0) {
 i += expected.length();
 return res;
 } else {
 return fail("parse error: expected " + expected + ", got " + str.substr(i, expected.length()));
 }
 }

 /* 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", true);

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

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

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

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

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

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

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

 // Check for any trailing garbage
 parser.consume_garbage();
 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, 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));
 // Check for another object
 parser.consume_garbage();
 if (!parser.failed)
 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