secdist.hpp

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#pragma once
 
/// @file userver/storages/secdist/secdist.hpp
/// @brief @copybrief storages::secdist::SecdistConfig
 
#include <any>
#include <chrono>
#include <cstdint>
#include <functional>
#include <optional>
#include <stdexcept>
#include <string>
#include <string_view>
#include <typeindex>
#include <vector>
 
#include <userver/concurrent/async_event_source.hpp>
#include <userver/engine/task/task_processor_fwd.hpp>
#include <userver/formats/json/value.hpp>
#include <userver/rcu/rcu.hpp>
#include <userver/storages/secdist/provider.hpp>
#include <userver/utils/fast_pimpl.hpp>
 
USERVER_NAMESPACE_BEGIN
 
/// Credentials storage
namespace storages::secdist {
 
class SecdistConfig;
 
namespace detail {
 
template <typename T>
class SecdistModule final {
 public:
  static const T& Get(const SecdistConfig& config);
  static std::any Factory(const formats::json::Value& data) { return T(data); }
 
 private:
  static std::size_t index_;
};
 
}  // namespace detail
 
/// Secdist file format
enum class SecdistFormat {
  kJson,
  kYaml,
};
 
// clang-format off
 
/// @ingroup userver_clients
///
/// @brief Client to retrieve credentials from the components::Secdist.
///
/// ## Example usage:
///
/// Declare a type that would work with the credentials:
///
/// @snippet storages/secdist/secdist_test.cpp UserPasswords
///
/// Fill the components::Secdist `config` from file with the secure data:
///
/// @snippet storages/secdist/secdist_test.cpp Secdist Usage Sample - json
///
/// Retrieve SecdistConfig from components::Secdist and get the type from it:
///
/// @snippet storages/secdist/secdist_test.cpp Secdist Usage Sample - SecdistConfig
///
/// Json with secure data can also be loaded from environment variable with name defined in `environment_secrets_key`.
/// Sample variable value: `{"user-passwords":{"username":"password","another username":"another password"}}`.
/// It has the same format as data from file.
/// If both sources are presented, data from environment variable will be merged with data from file
/// (json objects will be merged, duplicate fields of other types will be overridden by data from environment variable).
 
// clang-format on
class SecdistConfig final {
 public:
  struct Settings {
    SecdistProvider* provider{nullptr};
    std::chrono::milliseconds update_period{std::chrono::milliseconds::zero()};
  };
 
  SecdistConfig();
  explicit SecdistConfig(const Settings& settings);
 
  template <typename T>
  static std::size_t Register(
      std::function<std::any(const formats::json::Value&)>&& factory) {
    return Register(std::move(factory));
  }
 
  template <typename T>
  const T& Get() const {
    return detail::SecdistModule<T>::Get(*this);
  }
 
 private:
  void Init(const formats::json::Value& doc);
 
  static std::size_t Register(
      std::function<std::any(const formats::json::Value&)>&& factory);
  const std::any& Get(const std::type_index& type, std::size_t index) const;
 
  template <typename T>
  friend class detail::SecdistModule;
 
  std::vector<std::any> configs_;
};
 
/// @ingroup userver_clients
///
/// @brief Client to retrieve credentials from the components::Secdist and to
/// subscribe to their updates.
class Secdist final {
 public:
  explicit Secdist(SecdistConfig::Settings settings);
  ~Secdist();
 
  /// Returns secdist data loaded on service start.
  /// Does not support secdist updating during service work.
  const storages::secdist::SecdistConfig& Get() const;
 
  /// Returns fresh secdist data (from last update).
  /// Supports secdist updating during service work.
  rcu::ReadablePtr<storages::secdist::SecdistConfig> GetSnapshot() const;
 
  /// Subscribes to secdist updates using a member function, named
  /// `OnSecdistUpdate` by convention. Also immediately invokes the function
  /// with the current secdist data.
  template <typename Class>
  concurrent::AsyncEventSubscriberScope UpdateAndListen(
      Class* obj, std::string_view name,
      void (Class::*func)(const storages::secdist::SecdistConfig& secdist));
 
  bool IsPeriodicUpdateEnabled() const;
 
 private:
  using EventSource = concurrent::AsyncEventSource<const SecdistConfig&>;
 
  concurrent::AsyncEventSubscriberScope DoUpdateAndListen(
      concurrent::FunctionId id, std::string_view name,
      EventSource::Function&& func);
 
  class Impl;
  utils::FastPimpl<Impl, 1280, 16> impl_;
};
 
template <typename Class>
concurrent::AsyncEventSubscriberScope Secdist::UpdateAndListen(
    Class* obj, std::string_view name,
    void (Class::*func)(const storages::secdist::SecdistConfig& secdist)) {
  return DoUpdateAndListen(
      concurrent::FunctionId(obj), name,
      [obj, func](const SecdistConfig& config) { (obj->*func)(config); });
}
 
namespace detail {
 
template <typename T>
const T& SecdistModule<T>::Get(const SecdistConfig& config) {
  return std::any_cast<const T&>(config.Get(typeid(T), index_));
}
 
template <typename T>
std::size_t SecdistModule<T>::index_ =
    SecdistConfig::Register<T>(&SecdistModule<T>::Factory);
 
}  // namespace detail
 
}  // namespace storages::secdist
 
USERVER_NAMESPACE_END