yaml_config.hpp

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#pragma once
 
/// @file userver/yaml_config/yaml_config.hpp
/// @brief @copybrief yaml_config::YamlConfig
 
#include <chrono>
#include <cstdint>
#include <optional>
#include <string>
#include <string_view>
 
#include <userver/formats/json_fwd.hpp>
#include <userver/formats/parse/common.hpp>
#include <userver/formats/parse/common_containers.hpp>
#include <userver/formats/yaml/value.hpp>
 
#include <userver/yaml_config/iterator.hpp>
 
USERVER_NAMESPACE_BEGIN
 
/// Utilities to work with static YAML config
namespace yaml_config {
 
using Exception = formats::yaml::Exception;
using ParseException = formats::yaml::ParseException;
 
/// @ingroup userver_formats userver_universal
///
/// @brief Datatype that represents YAML with substituted variables
///
/// If YAML has value that starts with an `$`, then such value is treated as
/// a variable from `config_vars`. For example if `config_vars` contains
/// `variable: 42` and the YAML is following:
/// @snippet universal/src/yaml_config/yaml_config_test.cpp  sample vars
/// Then the result of `yaml["some_element"]["some"].As<int>()` is `42`.
///
/// If YAML key ends on '#env' and the mode is YamlConfig::Mode::kEnvAllowed
/// or YamlConfig::Mode::kEnvAndFileAllowed,
/// then the value of the key is searched in
/// environment variables of the process and returned as a value. For example:
/// @snippet universal/src/yaml_config/yaml_config_test.cpp  sample env
///
/// If YAML key ends on '#file' and the mode is
/// YamlConfig::Mode::kEnvAndFileAllowed, then the value of the key is the
/// content of specified YAML parsed file. For example:
/// @snippet universal/src/yaml_config/yaml_config_test.cpp  sample read_file
///
/// If YAML key ends on '#fallback', then the value of the key is used as a
/// fallback for environment, file and `$` variables. For example for the
/// following YAML with YamlConfig::Mode::kEnvAndFileAllowed:
/// @snippet universal/src/yaml_config/yaml_config_test.cpp  sample multiple
/// The result of `yaml["some_element"]["some"].As<int>()` is the value of
/// `variable` from `config_vars` if it exists; otherwise the value is the
/// contents of the environment variable `SOME_ENV_VARIABLE` if it exists;
/// otherwise the value is the content of the file with name `file.yaml`;
/// otherwise the value is `100500`, from the fallback.
///
/// Another example:
/// @snippet universal/src/yaml_config/yaml_config_test.cpp  sample env fallback
/// With YamlConfig::Mode::kEnvAllowed the result of
/// `yaml["some_element"]["value"].As<int>()` is the value of `ENV_NAME`
/// environment variable if it exists; otherwise it is `5`.
///
/// @note `#env`, `#file` and `#fallback` also work for keys inside
/// `config_vars`.
///
/// @warning YamlConfig::Mode::kEnvAllowed or
/// YamlConfig::Mode::kEnvAndFileAllowed should be used only on configs that
/// come from trusted environments. Otherwise, an attacker could create a
/// config and read any of your environment variables of files, including
/// variables that contain passwords and other sensitive data.
class YamlConfig {
public:
    struct IterTraits {
        using value_type = YamlConfig;
        using reference = const YamlConfig&;
        using pointer = const YamlConfig*;
    };
    struct DefaultConstructed {};
 
    enum class Mode {
        kSecure,             /// < secure mode, without reading environment variables or files
        kEnvAllowed,         /// < allows reading of environment variables
        kEnvAndFileAllowed,  /// < allows reading of environment variables and
                             /// files
    };
 
    using const_iterator = Iterator<IterTraits>;
    using Exception = yaml_config::Exception;
    using ParseException = yaml_config::ParseException;
 
    YamlConfig() = default;
 
    /// YamlConfig = config + config_vars
    YamlConfig(formats::yaml::Value yaml, formats::yaml::Value config_vars, Mode mode = Mode::kSecure);
 
    /// Get the plain Yaml without substitutions. It may contain raw references.
    const formats::yaml::Value& Yaml() const;
 
    /// @brief Access member by key for read.
    /// @throw TypeMismatchException if value is not missing and is not object.
    YamlConfig operator[](std::string_view key) const;
 
    /// @brief Access member by index for read.
    /// @throw TypeMismatchException if value is not missing and is not array.
    YamlConfig operator[](size_t index) const;
 
    /// @brief Returns array size or object members count.
    /// @throw TypeMismatchException if not array or object value.
    std::size_t GetSize() const;
 
    /// @brief Returns true if *this holds nothing. When `IsMissing()` returns
    /// `true` any attempt to get the actual value or iterate over *this will
    /// throw MemberMissingException.
    bool IsMissing() const noexcept;
 
    /// @brief Returns true if *this holds 'null'.
    bool IsNull() const noexcept;
 
    /// @brief Returns true if *this is convertible to bool.
    bool IsBool() const noexcept;
 
    /// @brief Returns true if *this is convertible to int.
    bool IsInt() const noexcept;
 
    /// @brief Returns true if *this is convertible to int64_t.
    bool IsInt64() const noexcept;
 
    /// @brief Returns true if *this is convertible to uint64_t.
    bool IsUInt64() const noexcept;
 
    /// @brief Returns true if *this is convertible to double.
    bool IsDouble() const noexcept;
 
    /// @brief Returns true if *this is convertible to std::string.
    bool IsString() const noexcept;
 
    /// @brief Returns true if *this is an array (Type::kArray).
    bool IsArray() const noexcept;
 
    /// @brief Returns true if *this is a map (Type::kObject).
    bool IsObject() const noexcept;
 
    /// @throw MemberMissingException if `this->IsMissing()`.
    void CheckNotMissing() const;
 
    /// @throw MemberMissingException if `*this` is not an array.
    void CheckArray() const;
 
    /// @throw MemberMissingException 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 a map.
    void CheckObject() const;
 
    /// @throw TypeMismatchException if `*this` is not convertible to std::string.
    void CheckString() const;
 
    /// @throw TypeMismatchException if `*this` is not a map, array or Null.
    void CheckObjectOrArrayOrNull() const;
 
    /// @brief Returns value of *this converted to T.
    /// @throw Anything derived from std::exception.
    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 Returns true if *this holds a `key`.
    /// @throw Nothing.
    bool HasMember(std::string_view key) const;
 
    /// @brief Returns full path to this value.
    std::string GetPath() const;
 
    /// @brief Returns an iterator to the beginning of the held array or map.
    /// @throw TypeMismatchException is the value of *this is not a map, array
    /// or Null.
    const_iterator begin() const;
 
    /// @brief Returns an iterator to the end of the held array or map.
    /// @throw TypeMismatchException is the value of *this is not a map, array
    /// or Null.
    const_iterator end() const;
 
private:
    formats::yaml::Value yaml_;
    formats::yaml::Value config_vars_;
    Mode mode_{Mode::kSecure};
 
    friend bool Parse(const YamlConfig& value, formats::parse::To<bool>);
    friend int64_t Parse(const YamlConfig& value, formats::parse::To<int64_t>);
    friend uint64_t Parse(const YamlConfig& value, formats::parse::To<uint64_t>);
    friend double Parse(const YamlConfig& value, formats::parse::To<double>);
    friend std::string Parse(const YamlConfig& value, formats::parse::To<std::string>);
};
 
using Value = YamlConfig;
 
template <typename T>
auto YamlConfig::As() const {
    static_assert(
        formats::common::impl::kHasParse<YamlConfig, T>,
        "There is no `Parse(const yaml_config::YamlConfig&, "
        "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 YamlConfig& value, formats::parse::To<bool>);
 
int64_t Parse(const YamlConfig& value, formats::parse::To<int64_t>);
 
uint64_t Parse(const YamlConfig& value, formats::parse::To<uint64_t>);
 
double Parse(const YamlConfig& value, formats::parse::To<double>);
 
std::string Parse(const YamlConfig& value, formats::parse::To<std::string>);
 
template <typename T, typename First, typename... Rest>
auto YamlConfig::As(First&& default_arg, Rest&&... more_default_args) const {
    if (IsMissing()) {
        // 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 YamlConfig::As(YamlConfig::DefaultConstructed) const {
    return IsMissing() ? decltype(As<T>())() : As<T>();
}
 
/// @brief Wrapper for handy python-like iteration over a map
///
/// @code
///   for (const auto& [name, value]: Items(map)) ...
/// @endcode
using formats::common::Items;
 
/// @brief Parses duration from string, understands suffixes: ms, s, m, h, d
/// @throws On invalid type, invalid string format, and if the duration is not a
/// whole amount of seconds
std::chrono::seconds Parse(const YamlConfig& value, formats::parse::To<std::chrono::seconds>);
 
/// @brief Parses duration from string, understands suffixes: ms, s, m, h, d
/// @throws On invalid type and invalid string format
std::chrono::milliseconds Parse(const YamlConfig& value, formats::parse::To<std::chrono::milliseconds>);
 
/// @brief Converts YAML to JSON
/// @throws formats::json::Value::Exception if `value.IsMissing()`
formats::json::Value Parse(const YamlConfig& value, formats::parse::To<formats::json::Value>);
 
}  // namespace yaml_config
 
USERVER_NAMESPACE_END