dest_static.h

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/*
  Copyright (c) 2024, Oracle and/or its affiliates.
 
  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License, version 2.0,
  as published by the Free Software Foundation.
 
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  as designated in a particular file or component or in included license
  documentation.  The authors of MySQL hereby grant you an additional
  permission to link the program and your derivative works with the
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  This program is distributed in the hope that it will be useful,
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  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
 
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
 
#ifndef ROUTING_DEST_STATIC_INCLUDED
#define ROUTING_DEST_STATIC_INCLUDED
 
#include "destination.h"  // DestinationManager
 
/**
 * Base class for routing strategy handler.
 */
class StrategyHandler {
 public:
  virtual ~StrategyHandler() = default;
 
  virtual std::optional<std::uint32_t> get_destination_index(
      const bool last_connection_successful,
      const std::uint32_t dest_pool_size) = 0;
 
 protected:
  std::uint32_t index_pos_{0};
};
 
/**
 * First-available strategy. Move to next destination only if the last
 * connection was unsuccessful. After successful connection attempt always try
 * from the beginning.
 */
class First_available_strategy : public StrategyHandler {
 public:
  std::optional<std::uint32_t> get_destination_index(
      const bool last_connection_successful,
      const std::uint32_t dest_pool_size) override;
};
 
/**
 * First-available strategy. Move to the next destination if the last
 * connection was unsuccessful. Keep the current position if connection is
 * successful (not going back, might exhaust the destination list).
 */
class Next_available_strategy : public StrategyHandler {
 public:
  std::optional<std::uint32_t> get_destination_index(
      const bool last_connection_successful,
      const std::uint32_t dest_pool_size) override;
};
 
/**
 * Round-robin strategy. Move to next destination after each connection attempt.
 * If end of the destination candidates list is reached then loop around. If
 * destination candidates list is exhausted (after unsuccessful connection we
 * tried every destinaion from the list and eventually went back to the position
 * that failed at first) then fail the connection.
 */
class Round_robin_strategy : public StrategyHandler {
 public:
  std::optional<std::uint32_t> get_destination_index(
      const bool last_connection_successful,
      const std::uint32_t dest_pool_size) override;
 
 private:
  bool started_{false};
  std::optional<std::uint32_t> failed_instance_index_;
};
 
class StaticDestinationsManager final : public DestinationManager {
 public:
  StaticDestinationsManager(routing::RoutingStrategy strategy,
                            net::io_context &io_ctx,
                            MySQLRoutingContext &routing_ctx);
 
  /** @brief Adds a destination
   *
   * Adds a destination using the given address and port number.
   *
   * @param dest destination address
   */
  void add(const mysql_harness::Destination &dest);
 
  void start(const mysql_harness::PluginFuncEnv *) override;
 
  std::vector<mysql_harness::Destination> get_destination_candidates()
      const override {
    return destinations_;
  }
 
  bool refresh_destinations(const routing_guidelines::Session_info &) override {
    return false;
  }
 
  void handle_sockets_acceptors() override {}
 
  std::unique_ptr<Destination> get_next_destination(
      const routing_guidelines::Session_info &) override;
 
  std::unique_ptr<Destination> get_last_used_destination() const override {
    return std::make_unique<Destination>(last_destination_);
  }
 
  stdx::expected<void, std::error_code> init_destinations(
      const routing_guidelines::Session_info &) override {
    return {};
  }
 
  void connect_status(std::error_code ec) override;
 
  bool has_read_write() const override { return !destinations_.empty(); }
  bool has_read_only() const override { return !destinations_.empty(); }
 
 private:
  /** Get destination index based on routing strategy for static routes*/
  std::unique_ptr<StrategyHandler> strategy_handler_;
 
  /** @brief List of destinations */
  DestVector destinations_;
  Destination last_destination_;
 
  /** @brief Protocol for the endpoint */
  Protocol::Type protocol_;
};
 
#endif  // ROUTING_DEST_STATIC_INCLUDED