libs: import json11.

This commit imports the code from upstream commit
dropbox/json11@8ccf1f0c5ecab6151a65f216e7eeccd8588e5457.

1 files changed, 788 insertions, 0 deletions

diff --git a/libs/json11/json11.cpp b/libs/json11/json11.cpp
new file mode 100644
index 000000000..549463d71
--- /dev/null
+++ b/libs/json11/json11.cpp
@@ -0,0 +1,788 @@
+/* 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 == 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);
+}
+
+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 after start of comment", false);
+        if (str[i] == '/') { // inline comment
+          i++;
+          // advance until next line, or end of input
+          while (i < str.size() && str[i] != '\n') {
+            i++;
+          }
+          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;
+          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 static_cast<char>(0);
+        if (i == str.size())
+            return fail("unexpected end of input", static_cast<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.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, 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