// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SHILL_ROUTING_TABLE_H_
#define SHILL_ROUTING_TABLE_H_

#include <deque>
#include <memory>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>

#include <base/callback.h>
#include <base/lazy_instance.h>
#include <base/memory/ref_counted.h>

#include "shill/net/ip_address.h"
#include "shill/net/rtnl_message.h"
#include "shill/refptr_types.h"
#include "shill/routing_policy_entry.h"
#include "shill/routing_table_entry.h"

namespace shill {

class RTNLHandler;
class RTNLListener;

// This singleton maintains an in-process copy of the routing table on
// a per-interface basis.  It offers the ability for other modules to
// make modifications to the routing table, centered around setting the
// default route for an interface or modifying its metric (priority).
class RoutingTable {
 public:
  // Callback for RequestRouteToHost completion.
  using QueryCallback =
      base::Callback<void(int interface_index, const RoutingTableEntry& entry)>;

  // Priority of the rule sending all traffic to the local routing table.
  static const uint32_t kRulePriorityLocal;
  // Priority of the rule sending all traffic to the main routing table.
  static const uint32_t kRulePriorityMain;

  // Used to detect default route added by kernel when receiving RA.
  // Note that since 5.18 kernel this value will become configurable through
  // net.ipv6.conf.all.ra_defrtr_metric and we need to be sure this value
  // remains identical with kernel configuration.
  static constexpr int kKernelSlaacRouteMetric = 1024;

  // The metric shill will install its IPv4 default route. Does not have real
  // impact to the routing decision since there will only be one default route
  // in each routing table.
  static constexpr int kShillDefaultRouteMetric = 65536;

  virtual ~RoutingTable();

  static RoutingTable* GetInstance();

  virtual void Start();
  virtual void Stop();

  // Informs RoutingTable that a new Device has come up. While RoutingTable
  // could find out about a new Device by seeing a new interface index in a
  // kernel-added route, having this allows for any required setup to occur
  // prior to routes being created for the Device in question.
  void RegisterDevice(int interface_index, const std::string& link_name);

  // Causes RoutingTable to stop managing a particular interface index. This
  // method does not perform clean up that would allow corresponding interface
  // to be used as an unmanaged Device *unless* routes for that interface are
  // re-added. For example, changing accept_ra_rt_table for an interface from -N
  // to 0 will not cause the routes to move back to the main routing table, and
  // in many cases (like a regular link down event for a managed interface), we
  // would not want shill to manually move those routes back.
  void DeregisterDevice(int interface_index, const std::string& link_name);

  // Add an entry to the routing table.
  virtual bool AddRoute(int interface_index, const RoutingTableEntry& entry);
  // Remove an entry from the routing table.
  virtual bool RemoveRoute(int interface_index, const RoutingTableEntry& entry);

  // Add an entry to the routing rule table.
  virtual bool AddRule(int interface_index, const RoutingPolicyEntry& entry);

  // Get the default route associated with an interface of a given addr family.
  // The route is copied into |*entry|.
  virtual bool GetDefaultRoute(int interface_index,
                               IPAddress::Family family,
                               RoutingTableEntry* entry);

  // Get the default IPv6 route associated with an interface which was created
  // by the kernel. The route is copied into |*entry|.
  virtual bool GetDefaultRouteFromKernel(int interface_index,
                                         RoutingTableEntry* entry);

  // Set the default route for an interface with index |interface_index|,
  // given the IPAddress of the gateway |gateway_address| and priority
  // |metric|.
  virtual bool SetDefaultRoute(int interface_index,
                               const IPAddress& gateway_address,
                               uint32_t table_id);

  // Create a blackhole route for a given IP family.  Returns true
  // on successfully sending the route request, false otherwise.
  virtual bool CreateBlackholeRoute(int interface_index,
                                    IPAddress::Family family,
                                    uint32_t metric,
                                    uint32_t table_id);

  // Create a route to a link-attached remote host.  |remote_address|
  // must be directly reachable from |local_address|.  Returns true
  // on successfully sending the route request, false otherwise.
  virtual bool CreateLinkRoute(int interface_index,
                               const IPAddress& local_address,
                               const IPAddress& remote_address,
                               uint32_t table_id);

  // Remove routes associated with interface.
  // Route entries are immediately purged from our copy of the routing table.
  virtual void FlushRoutes(int interface_index);

  // Iterate over all routing tables removing routes tagged with |tag|.
  // Route entries are immediately purged from our copy of the routing table.
  virtual void FlushRoutesWithTag(int tag);

  // Flush the routing cache for all interfaces.
  virtual bool FlushCache();

  // Flush all routing rules for |interface_index|.
  virtual void FlushRules(int interface_index);

  // Reset local state for this interface.
  virtual void ResetTable(int interface_index);

  // Get the route to |destination| through |interface_index|.  If |callback|
  // is not null, it will be invoked when the request-route response is
  // received.
  virtual bool RequestRouteToHost(const IPAddress& destination,
                                  int interface_index,
                                  const QueryCallback& callback);

  static uint32_t GetInterfaceTableId(int interface_index);

  // Allocates a routing table, and returns the ID.  If no IDs are available,
  // returns RT_TABLE_UNSPEC. This should *not* be used to allocate a per-Device
  // table, which is not explicitly allocated and freed, but is instead
  // retrieved using GetInterfaceTableId.
  virtual uint32_t RequestAdditionalTableId();
  // Frees routing table |id| that was obtained from RequestAdditionalTableId().
  virtual void FreeAdditionalTableId(uint32_t id);

 protected:
  RoutingTable();
  RoutingTable(const RoutingTable&) = delete;
  RoutingTable& operator=(const RoutingTable&) = delete;

 private:
  friend base::LazyInstanceTraitsBase<RoutingTable>;
  friend class RoutingTableTest;

  using RouteTableEntryVector = std::vector<RoutingTableEntry>;
  using RouteTables = std::unordered_map<int, RouteTableEntryVector>;
  using PolicyTableEntryVector = std::vector<RoutingPolicyEntry>;
  using PolicyTables = std::unordered_map<int, PolicyTableEntryVector>;

  struct Query {
    Query() : sequence(0) {}
    Query(uint32_t sequence_in, QueryCallback callback_in)
        : sequence(sequence_in), callback(callback_in) {}

    uint32_t sequence;
    QueryCallback callback;
  };

  // Add an entry to the kernel routing table without modifying the internal
  // routing-table bookkeeping.
  bool AddRouteToKernelTable(int interface_index,
                             const RoutingTableEntry& entry);
  // Remove an entry to the kernel routing table without modifying the internal
  // routing-table bookkeeping.
  bool RemoveRouteFromKernelTable(int interface_index,
                                  const RoutingTableEntry& entry);

  void RouteMsgHandler(const RTNLMessage& msg);
  bool ApplyRoute(uint32_t interface_index,
                  const RoutingTableEntry& entry,
                  RTNLMessage::Mode mode,
                  unsigned int flags);
  // Get the default route associated with an interface of a given addr family.
  // A pointer to the route is placed in |*entry|.
  virtual bool GetDefaultRouteInternal(int interface_index,
                                       IPAddress::Family family,
                                       RoutingTableEntry** entry);

  bool ApplyRule(uint32_t interface_index,
                 const RoutingPolicyEntry& entry,
                 RTNLMessage::Mode mode,
                 unsigned int flags);
  bool ParseRoutingPolicyMessage(const RTNLMessage& message,
                                 RoutingPolicyEntry* entry);
  bool HandleRoutingPolicyMessage(const RTNLMessage& message);

  RouteTables tables_;
  PolicyTables policy_tables_;
  std::set<int> managed_interfaces_;

  std::unique_ptr<RTNLListener> route_listener_;
  std::deque<Query> route_queries_;

  // A list of unused routing table IDs.
  std::vector<uint32_t> available_table_ids_;

  // Cache singleton pointer for performance and test purposes.
  RTNLHandler* rtnl_handler_;
};

}  // namespace shill

#endif  // SHILL_ROUTING_TABLE_H_