// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Handles packets for connection_ids in time wait state by discarding the
// packet and sending the clients a public reset packet with exponential
// backoff.

#ifndef NET_QUIC_QUIC_TIME_WAIT_LIST_MANAGER_H_
#define NET_QUIC_QUIC_TIME_WAIT_LIST_MANAGER_H_

#include <deque>

#include "base/basictypes.h"
#include "base/containers/hash_tables.h"
#include "base/strings/string_piece.h"
#include "net/base/linked_hash_map.h"
#include "net/quic/quic_blocked_writer_interface.h"
#include "net/quic/quic_connection_helper.h"
#include "net/quic/quic_framer.h"
#include "net/quic/quic_packet_writer.h"
#include "net/quic/quic_protocol.h"

namespace net {

class ConnectionIdCleanUpAlarm;
class QuicServerSessionVisitor;

namespace test {
class QuicTimeWaitListManagerPeer;
}  // namespace test

// Maintains a list of all connection_ids that have been recently closed. A
// connection_id lives in this state for kTimeWaitPeriod. All packets received
// for connection_ids in this state are handed over to the
// QuicTimeWaitListManager by the QuicDispatcher.  Decides whether to send a
// public reset packet, a copy of the previously sent connection close packet,
// or nothing to the client which sent a packet with the connection_id in time
// wait state.  After the connection_id expires its time wait period, a new
// connection/session will be created if a packet is received for this
// connection_id.
class QuicTimeWaitListManager : public QuicBlockedWriterInterface {
 public:
  // writer - the entity that writes to the socket. (Owned by the dispatcher)
  // visitor - the entity that manages blocked writers. (The dispatcher)
  // helper - used to run clean up alarms. (Owned by the owner of the server)
  QuicTimeWaitListManager(QuicPacketWriter* writer,
                          QuicServerSessionVisitor* visitor,
                          QuicConnectionHelperInterface* helper,
                          const QuicVersionVector& supported_versions);
  ~QuicTimeWaitListManager() override;

  // Adds the given connection_id to time wait state for kTimeWaitPeriod.
  // Henceforth, any packet bearing this connection_id should not be processed
  // while the connection_id remains in this list. If a non-nullptr
  // |close_packet| is provided, it is sent again when packets are received for
  // added connection_ids. If nullptr, a public reset packet is sent with the
  // specified |version|. DCHECKs that connection_id is not already on the list.
  void AddConnectionIdToTimeWait(QuicConnectionId connection_id,
                                 QuicVersion version,
                                 QuicEncryptedPacket* close_packet);  // Owned.

  // Returns true if the connection_id is in time wait state, false otherwise.
  // Packets received for this connection_id should not lead to creation of new
  // QuicSessions.
  bool IsConnectionIdInTimeWait(QuicConnectionId connection_id) const;

  // Called when a packet is received for a connection_id that is in time wait
  // state. Sends a public reset packet to the client which sent this
  // connection_id. Sending of the public reset packet is throttled by using
  // exponential back off. DCHECKs for the connection_id to be in time wait
  // state. virtual to override in tests.
  virtual void ProcessPacket(const IPEndPoint& server_address,
                             const IPEndPoint& client_address,
                             QuicConnectionId connection_id,
                             QuicPacketSequenceNumber sequence_number,
                             const QuicEncryptedPacket& packet);

  // Called by the dispatcher when the underlying socket becomes writable again,
  // since we might need to send pending public reset packets which we didn't
  // send because the underlying socket was write blocked.
  void OnCanWrite() override;

  // Used to delete connection_id entries that have outlived their time wait
  // period.
  void CleanUpOldConnectionIds();

  // Given a ConnectionId that exists in the time wait list, returns the
  // QuicVersion associated with it.
  QuicVersion GetQuicVersionFromConnectionId(QuicConnectionId connection_id);

 protected:
  virtual QuicEncryptedPacket* BuildPublicReset(
      const QuicPublicResetPacket& packet);

 private:
  friend class test::QuicTimeWaitListManagerPeer;

  // Internal structure to store pending public reset packets.
  class QueuedPacket;

  // Decides if a packet should be sent for this connection_id based on the
  // number of received packets.
  bool ShouldSendResponse(int received_packet_count);

  // Creates a public reset packet and sends it or queues it to be sent later.
  void SendPublicReset(const IPEndPoint& server_address,
                       const IPEndPoint& client_address,
                       QuicConnectionId connection_id,
                       QuicPacketSequenceNumber rejected_sequence_number);

  // Either sends the packet and deletes it or makes pending_packets_queue_ the
  // owner of the packet.
  void SendOrQueuePacket(QueuedPacket* packet);

  // Sends the packet out. Returns true if the packet was successfully consumed.
  // If the writer got blocked and did not buffer the packet, we'll need to keep
  // the packet and retry sending. In case of all other errors we drop the
  // packet.
  bool WriteToWire(QueuedPacket* packet);

  // Register the alarm to wake up at appropriate time.
  void SetConnectionIdCleanUpAlarm();

  // A map from a recently closed connection_id to the number of packets
  // received after the termination of the connection bound to the
  // connection_id.
  struct ConnectionIdData {
    ConnectionIdData(int num_packets_,
                     QuicVersion version_,
                     QuicTime time_added_,
                     QuicEncryptedPacket* close_packet)
        : num_packets(num_packets_),
          version(version_),
          time_added(time_added_),
          close_packet(close_packet) {}
    int num_packets;
    QuicVersion version;
    QuicTime time_added;
    QuicEncryptedPacket* close_packet;
  };

  // linked_hash_map allows lookup by ConnectionId and traversal in add order.
  typedef linked_hash_map<QuicConnectionId, ConnectionIdData> ConnectionIdMap;
  ConnectionIdMap connection_id_map_;

  // Pending public reset packets that need to be sent out to the client
  // when we are given a chance to write by the dispatcher.
  std::deque<QueuedPacket*> pending_packets_queue_;

  // Used to schedule alarms to delete old connection_ids which have been in the
  // list for too long.
  QuicConnectionHelperInterface* helper_;

  // Time period for which connection_ids should remain in time wait state.
  const QuicTime::Delta kTimeWaitPeriod_;

  // Alarm registered with the connection helper to clean up connection_ids that
  // have
  // out lived their duration in time wait state.
  scoped_ptr<QuicAlarm> connection_id_clean_up_alarm_;

  // Interface that writes given buffer to the socket.
  QuicPacketWriter* writer_;

  // Interface that manages blocked writers.
  QuicServerSessionVisitor* visitor_;

  DISALLOW_COPY_AND_ASSIGN(QuicTimeWaitListManager);
};

}  // namespace net

#endif  // NET_QUIC_QUIC_TIME_WAIT_LIST_MANAGER_H_