value.hpp

Go to the documentation of this file.

#pragma once
 
/// @file userver/formats/json/value.hpp
/// @brief @copybrief formats::json::Value
 
#include <chrono>
#include <iosfwd>
#include <string_view>
#include <type_traits>
 
#include <userver/formats/common/items.hpp>
#include <userver/formats/common/meta.hpp>
#include <userver/formats/json/exception.hpp>
#include <userver/formats/json/impl/types.hpp>
#include <userver/formats/json/iterator.hpp>
#include <userver/formats/json/string_builder_fwd.hpp>
#include <userver/formats/parse/common.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace logging {
class LogHelper;
}  // namespace logging
 
namespace formats::json {
namespace impl {
class InlineObjectBuilder;
class InlineArrayBuilder;
class MutableValueWrapper;
class StringBuffer;
 
// do not make a copy of string
impl::Value MakeJsonStringViewValue(std::string_view view);
 
}  // namespace impl
 
class ValueBuilder;
struct PrettyFormat;
class Schema;
 
namespace parser {
class JsonValueParser;
}  // namespace parser
 
/// @ingroup userver_universal userver_containers userver_formats
///
/// @brief Non-mutable JSON value representation.
///
/// Class provides non mutable access JSON value. For modification and
/// construction of new JSON values use formats::json::ValueBuilder.
///
/// ## Example usage:
///
/// @snippet formats/json/value_test.cpp  Sample formats::json::Value usage
///
/// @see @ref scripts/docs/en/userver/formats.md
///
/// To iterate over `Value` as object use formats::common::Items.
class Value {
public:
    struct IterTraits {
        using ValueType = formats::json::Value;
        using Reference = const formats::json::Value&;
        using Pointer = const formats::json::Value*;
        using ContainerType = Value;
    };
    struct DefaultConstructed {};
 
    using const_iterator = Iterator<IterTraits, common::IteratorDirection::kForward>;
    using const_reverse_iterator = Iterator<IterTraits, common::IteratorDirection::kReverse>;
    using Exception = formats::json::Exception;
    using ParseException = formats::json::ParseException;
    using ExceptionWithPath = formats::json::ExceptionWithPath;
    using Builder = ValueBuilder;
 
    /// @brief Constructs a Value that holds a null.
    Value();
 
    Value(const Value&) = default;
    Value(Value&&) noexcept;
 
    Value& operator=(const Value&) & = default;
    Value& operator=(Value&&) noexcept;
 
    template <class T>
    Value& operator=(T&&) && {
        static_assert(
            !sizeof(T),
            "You're assigning to a temporary formats::json::Value! Use "
            "formats::json::ValueBuilder for data modifications."
        );
        return *this;
    }
 
    /// @brief Access member by key for read.
    /// @throw TypeMismatchException if not a missing value, an object or null.
    Value operator[](std::string_view key) const;
    /// @brief Access array member by index for read.
    /// @throw TypeMismatchException if not an array value.
    /// @throw OutOfBoundsException if index is greater or equal
    /// than size.
    Value operator[](std::size_t index) const;
 
    /// @brief Returns an iterator to the beginning of the held array or map.
    /// @throw TypeMismatchException if not an array, object, or null.
    ///
    /// To iterate over `Value` as object use formats::common::Items.
    const_iterator begin() const;
 
    /// @brief Returns an iterator to the end of the held array or map.
    /// @throw TypeMismatchException if not an array, object, or null.
    const_iterator end() const;
 
    /// @brief Returns an iterator to the reversed begin of the held array.
    /// @throw TypeMismatchException if not an array or null.
    const_reverse_iterator rbegin() const;
 
    /// @brief Returns an iterator to the reversed end of the held array.
    /// @throw TypeMismatchException if not an array or null.
    const_reverse_iterator rend() const;
 
    /// @brief Returns whether the array or object is empty.
    /// Returns true for null.
    /// @throw TypeMismatchException if not an array, object, or null.
    bool IsEmpty() const;
 
    /// @brief Returns array size, object members count, or 0 for null.
    /// @throw TypeMismatchException if not an array, object, or null.
    std::size_t GetSize() const;
 
    /// @brief Compares values.
    /// @throw MemberMissingException if `*this` or `other` is missing.
    bool operator==(const Value& other) const;
    bool operator!=(const Value& other) const;
 
    /// @brief Returns true if *this holds nothing. When `IsMissing()` returns
    /// `true` any attempt to get the actual value or iterate over *this will
    bool IsMissing() const noexcept;
 
    /// @brief Returns true if *this holds a null (Type::kNull).
    bool IsNull() const noexcept;
 
    /// @brief Returns true if *this holds a bool.
    bool IsBool() const noexcept;
 
    /// @brief Returns true if *this holds an int.
    bool IsInt() const noexcept;
 
    /// @brief Returns true if *this holds an int64_t.
    bool IsInt64() const noexcept;
 
    /// @brief Returns true if *this holds an uint.
    bool IsUInt() const noexcept;
 
    /// @brief Returns true if *this holds an uint64_t.
    bool IsUInt64() const noexcept;
 
    /// @brief Returns true if *this holds a double.
    bool IsDouble() const noexcept;
 
    /// @brief Returns true if *this is holds a std::string.
    bool IsString() const noexcept;
 
    /// @brief Returns true if *this is holds an array (Type::kArray).
    bool IsArray() const noexcept;
 
    /// @brief Returns true if *this holds a map (Type::kObject).
    bool IsObject() const noexcept;
 
    // clang-format off
 
  /// @brief Returns value of *this converted to the result type of
  ///        Parse(const Value&, parse::To<T>). Almost always it is T.
  /// @throw Anything derived from std::exception.
  ///
  /// ## Example usage:
  ///
  /// @snippet formats/json/value_test.cpp  Sample formats::json::Value::As<T>() usage
  ///
  /// @see @ref scripts/docs/en/userver/formats.md
 
    // clang-format on
 
    template <typename T>
    auto As() const;
 
    /// @brief Returns value of *this converted to T or T(args) if
    /// this->IsMissing().
    /// @throw Anything derived from std::exception.
    template <typename T, typename First, typename... Rest>
    auto As(First&& default_arg, Rest&&... more_default_args) const;
 
    /// @brief Returns value of *this converted to T or T() if this->IsMissing().
    /// @throw Anything derived from std::exception.
    /// @note Use as `value.As<T>({})`
    template <typename T>
    auto As(DefaultConstructed) const;
 
    /// @brief Extracts the specified type with relaxed type checks.
    /// For example, `true` may be converted to 1.0.
    template <typename T>
    T ConvertTo() const;
 
    /// Extracts the specified type with strict type checks, or constructs the
    /// default value when the field is not present
    template <typename T, typename First, typename... Rest>
    T ConvertTo(First&& default_arg, Rest&&... more_default_args) const;
 
    /// @brief Returns true if *this holds a `key`.
    /// @throw TypeMismatchException if `*this` is not a map or null.
    bool HasMember(std::string_view key) const;
 
    /// @brief Returns full path to this value.
    std::string GetPath() const;
 
    /// @cond
    void DropRootPath();
    /// @endcond
 
    /// @brief Returns new value that is an exact copy of the existing one
    /// but references different memory (a deep copy of a *this). The returned
    /// value is a root value with path '/'.
    /// @throws MemberMissingException if `this->IsMissing()`.
    Value Clone() const;
 
    /// @throw MemberMissingException if `this->IsMissing()`.
    void CheckNotMissing() const;
 
    /// @throw TypeMismatchException if `*this` is not an array or null.
    void CheckArrayOrNull() const;
 
    /// @throw TypeMismatchException if `*this` is not a map or null.
    void CheckObjectOrNull() const;
 
    /// @throw TypeMismatchException if `*this` is not an array.
    void CheckArray() const;
 
    /// @throw TypeMismatchException if `*this` is not a map.
    void CheckObject() const;
 
    /// @throw TypeMismatchException if `*this` is not a map, array or null.
    void CheckObjectOrArrayOrNull() const;
 
    /// @throw TypeMismatchException if `*this` is not an array or null;
    /// `OutOfBoundsException` if `index >= this->GetSize()`.
    void CheckInBounds(std::size_t index) const;
 
    /// @brief Returns true if *this is a first (root) value.
    bool IsRoot() const noexcept;
 
    /// @brief Returns true if `*this` and `other` reference the value by the same
    /// pointer.
    bool DebugIsReferencingSameMemory(const Value& other) const { return value_ptr_ == other.value_ptr_; }
 
private:
    struct EmplaceEnabler {
        explicit EmplaceEnabler() = default;
    };
 
    class LazyDetachedPath;
 
public:
    /// @cond
    Value(
        EmplaceEnabler,
        const impl::VersionedValuePtr& root,
        const impl::Value* root_ptr_for_path,
        const impl::Value* value_ptr,
        int depth
    );
 
    Value(
        EmplaceEnabler,
        const impl::VersionedValuePtr& root,
        impl::Value* root_ptr_for_path,
        LazyDetachedPath&& lazy_detached_path
    );
    /// @endcond
 
private:
    explicit Value(impl::VersionedValuePtr root) noexcept;
 
    bool IsUniqueReference() const;
    void EnsureNotMissing() const;
    const impl::Value& GetNative() const;
    impl::Value& GetNative();
    void SetNative(impl::Value&);  // does not copy
    int GetExtendedType() const;
 
    impl::VersionedValuePtr holder_{};
    impl::Value* root_ptr_for_path_{nullptr};
    impl::Value* value_ptr_{nullptr};
    /// Depth of the node to ease recursive traversal in GetPath()
    int depth_{0};
 
    // We don't want to calculate the path for missing node before it is
    // explicitly requested, because GetPath() call is very costly.
    // This helps with patterns like 'json["missing"].As<T>({})':
    // path is not needed here (note default arg), and if we have a lot of missing
    // keys during parsing we save a lot of expensive calculations.
    class LazyDetachedPath final {
    public:
        LazyDetachedPath() noexcept;
        LazyDetachedPath(impl::Value* parent_value_ptr, int parent_depth, std::string_view key);
 
        LazyDetachedPath(const LazyDetachedPath&);
        LazyDetachedPath(LazyDetachedPath&&) noexcept;
        LazyDetachedPath& operator=(const LazyDetachedPath&);
        LazyDetachedPath& operator=(LazyDetachedPath&&) noexcept;
 
        std::string Get(const impl::Value* root) const;
        LazyDetachedPath Chain(std::string_view key) const;
 
    private:
        impl::Value* parent_value_ptr_{nullptr};
        int parent_depth_{0};
        std::string virtual_path_{};
    };
 
    LazyDetachedPath lazy_detached_path_;
 
    template <typename, common::IteratorDirection>
    friend class Iterator;
    friend class ValueBuilder;
    friend class StringBuilder;
    friend class Schema;
    friend class impl::InlineObjectBuilder;
    friend class impl::InlineArrayBuilder;
    friend class impl::MutableValueWrapper;
    friend class parser::JsonValueParser;
    friend class impl::StringBuffer;
 
    friend bool Parse(const Value& value, parse::To<bool>);
    friend std::int64_t Parse(const Value& value, parse::To<std::int64_t>);
    friend std::uint64_t Parse(const Value& value, parse::To<std::uint64_t>);
    friend double Parse(const Value& value, parse::To<double>);
    friend std::string Parse(const Value& value, parse::To<std::string>);
 
    friend formats::json::Value FromString(std::string_view);
    friend formats::json::Value FromStream(std::istream&);
    friend void Serialize(const formats::json::Value&, std::ostream&);
    friend std::string ToString(const formats::json::Value&);
    friend std::string ToStableString(const formats::json::Value&);
    friend std::string ToStableString(formats::json::Value&&);
    friend std::string ToPrettyString(const formats::json::Value& doc, PrettyFormat format);
    friend logging::LogHelper& operator<<(logging::LogHelper&, const Value&);
};
 
template <typename T>
auto Value::As() const {
    static_assert(
        formats::common::impl::kHasParse<Value, T>,
        "There is no `Parse(const Value&, formats::parse::To<T>)` "
        "in namespace of `T` or `formats::parse`. "
        "Probably you forgot to include the "
        "<userver/formats/parse/common_containers.hpp> or you "
        "have not provided a `Parse` function overload."
    );
 
    return Parse(*this, formats::parse::To<T>{});
}
 
bool Parse(const Value& value, parse::To<bool>);
 
std::int64_t Parse(const Value& value, parse::To<std::int64_t>);
 
std::uint64_t Parse(const Value& value, parse::To<std::uint64_t>);
 
double Parse(const Value& value, parse::To<double>);
 
std::string Parse(const Value& value, parse::To<std::string>);
 
template <>
bool Value::ConvertTo<bool>() const;
 
template <>
int64_t Value::ConvertTo<int64_t>() const;
 
template <>
uint64_t Value::ConvertTo<uint64_t>() const;
 
template <>
double Value::ConvertTo<double>() const;
 
template <>
std::string Value::ConvertTo<std::string>() const;
 
template <typename T, typename First, typename... Rest>
auto Value::As(First&& default_arg, Rest&&... more_default_args) const {
    if (IsMissing() || IsNull()) {
        // intended raw ctor call, sometimes casts
        // NOLINTNEXTLINE(google-readability-casting)
        return decltype(As<T>())(std::forward<First>(default_arg), std::forward<Rest>(more_default_args)...);
    }
    return As<T>();
}
 
template <typename T>
auto Value::As(Value::DefaultConstructed) const {
    return (IsMissing() || IsNull()) ? decltype(As<T>())() : As<T>();
}
 
template <typename T>
T Value::ConvertTo() const {
    if constexpr (formats::common::impl::kHasConvert<Value, T>) {
        return Convert(*this, formats::parse::To<T>{});
    } else if constexpr (formats::common::impl::kHasParse<Value, T>) {
        return Parse(*this, formats::parse::To<T>{});
    } else {
        static_assert(
            !sizeof(T),
            "There is no `Convert(const Value&, formats::parse::To<T>)` or"
            "`Parse(const Value&, formats::parse::To<T>)`"
            "in namespace of `T` or `formats::parse`. "
            "Probably you have not provided a `Convert` function overload."
        );
    }
}
 
template <typename T, typename First, typename... Rest>
T Value::ConvertTo(First&& default_arg, Rest&&... more_default_args) const {
    if (IsMissing() || IsNull()) {
        // NOLINTNEXTLINE(google-readability-casting)
        return T(std::forward<First>(default_arg), std::forward<Rest>(more_default_args)...);
    }
    return ConvertTo<T>();
}
 
inline Value Parse(const Value& value, parse::To<Value>) { return value; }
 
std::chrono::microseconds Parse(const Value& value, parse::To<std::chrono::microseconds>);
 
std::chrono::milliseconds Parse(const Value& value, parse::To<std::chrono::milliseconds>);
 
std::chrono::minutes Parse(const Value& value, parse::To<std::chrono::minutes>);
 
std::chrono::hours Parse(const Value& value, parse::To<std::chrono::hours>);
 
/// @brief Wrapper for handy python-like iteration over a map
///
/// @code
///   for (const auto& [name, value]: Items(map)) ...
/// @endcode
using formats::common::Items;
 
/// gtest formatter for formats::json::Value
void PrintTo(const Value&, std::ostream*);
 
}  // namespace formats::json
 
/// Although we provide user defined literals, please beware that
/// 'using namespace ABC' may contradict code style of your company.
namespace formats::literals {
 
json::Value operator""_json(const char* str, std::size_t len);
 
}  // namespace formats::literals
 
USERVER_NAMESPACE_END