text: /*
   * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #pragma once
  
  #include <AK/Function.h>
  #include <AK/HashMap.h>
  #include <AK/SinglyLinkedList.h>
  #include <AK/WeakPtr.h>
  #include <Kernel/KResult.h>
  #include <Kernel/Locking/MutexProtected.h>
  #include <Kernel/Net/IPv4Socket.h>
  
  namespace Kernel {
  
  class TCPSocket final : public IPv4Socket {
  public:
      static void for_each(Function<void(const TCPSocket&)>);
      static KResultOr<NonnullRefPtr<TCPSocket>> create(int protocol, NonnullOwnPtr<DoubleBuffer> receive_buffer);
      virtual ~TCPSocket() override;
  
      enum class Direction {
          Unspecified,
          Outgoing,
          Incoming,
          Passive,
      };
  
      static StringView to_string(Direction direction)
      {
          switch (direction) {
          case Direction::Unspecified:
              return "Unspecified"sv;
          case Direction::Outgoing:
              return "Outgoing"sv;
          case Direction::Incoming:
              return "Incoming"sv;
          case Direction::Passive:
              return "Passive"sv;
          default:
              return "None"sv;
          }
      }
  
      enum class State {
          Closed,
          Listen,
          SynSent,
          SynReceived,
          Established,
          CloseWait,
          LastAck,
          FinWait1,
          FinWait2,
          Closing,
          TimeWait,
      };
  
      static StringView to_string(State state)
      {
          switch (state) {
          case State::Closed:
              return "Closed"sv;
          case State::Listen:
              return "Listen"sv;
          case State::SynSent:
              return "SynSent"sv;
          case State::SynReceived:
              return "SynReceived"sv;
          case State::Established:
              return "Established"sv;
          case State::CloseWait:
              return "CloseWait"sv;
          case State::LastAck:
              return "LastAck"sv;
          case State::FinWait1:
              return "FinWait1"sv;
          case State::FinWait2:
              return "FinWait2"sv;
          case State::Closing:
              return "Closing"sv;
          case State::TimeWait:
              return "TimeWait"sv;
          default:
              return "None";
          }
      }
  
      enum class Error {
          None,
          FINDuringConnect,
          RSTDuringConnect,
          UnexpectedFlagsDuringConnect,
          RetransmitTimeout,
      };
  
      static StringView to_string(Error error)
      {
          switch (error) {
          case Error::None:
              return "None"sv;
          case Error::FINDuringConnect:
              return "FINDuringConnect"sv;
          case Error::RSTDuringConnect:
              return "RSTDuringConnect"sv;
          case Error::UnexpectedFlagsDuringConnect:
              return "UnexpectedFlagsDuringConnect"sv;
          default:
              return "Invalid"sv;
          }
      }
  
      State state() const { return m_state; }
      void set_state(State state);
  
      Direction direction() const { return m_direction; }
  
      bool has_error() const { return m_error != Error::None; }
      Error error() const { return m_error; }
      void set_error(Error error) { m_error = error; }
  
      void set_ack_number(u32 n) { m_ack_number = n; }
      void set_sequence_number(u32 n) { m_sequence_number = n; }
      u32 ack_number() const { return m_ack_number; }
      u32 sequence_number() const { return m_sequence_number; }
      u32 packets_in() const { return m_packets_in; }
      u32 bytes_in() const { return m_bytes_in; }
      u32 packets_out() const { return m_packets_out; }
      u32 bytes_out() const { return m_bytes_out; }
  
      // FIXME: Make this configurable?
      static constexpr u32 maximum_duplicate_acks = 5;
      void set_duplicate_acks(u32 acks) { m_duplicate_acks = acks; }
      u32 duplicate_acks() const { return m_duplicate_acks; }
  
      KResult send_ack(bool allow_duplicate = false);
      KResult send_tcp_packet(u16 flags, const UserOrKernelBuffer* = nullptr, size_t = 0, RoutingDecision* = nullptr);
      void receive_tcp_packet(const TCPPacket&, u16 size);
  
      bool should_delay_next_ack() const;
  
      static MutexProtected<HashMap<IPv4SocketTuple, TCPSocket*>>& sockets_by_tuple();
      static RefPtr<TCPSocket> from_tuple(const IPv4SocketTuple& tuple);
  
      static MutexProtected<HashMap<IPv4SocketTuple, RefPtr<TCPSocket>>>& closing_sockets();
  
      RefPtr<TCPSocket> create_client(const IPv4Address& local_address, u16 local_port, const IPv4Address& peer_address, u16 peer_port);
      void set_originator(TCPSocket& originator) { m_originator = originator; }
      bool has_originator() { return !!m_originator; }
      void release_to_originator();
      void release_for_accept(RefPtr<TCPSocket>);
  
      void retransmit_packets();
  
      virtual KResult close() override;
  
      virtual bool can_write(const FileDescription&, size_t) const override;
  
      static NetworkOrdered<u16> compute_tcp_checksum(IPv4Address const& source, IPv4Address const& destination, TCPPacket const&, u16 payload_size);
  
  protected:
      void set_direction(Direction direction) { m_direction = direction; }
  
  private:
      explicit TCPSocket(int protocol, NonnullOwnPtr<DoubleBuffer> receive_buffer, OwnPtr<KBuffer> scratch_buffer);
      virtual StringView class_name() const override { return "TCPSocket"; }
  
      virtual void shut_down_for_writing() override;
  
      virtual KResultOr<size_t> protocol_receive(ReadonlyBytes raw_ipv4_packet, UserOrKernelBuffer& buffer, size_t buffer_size, int flags) override;
      virtual KResultOr<size_t> protocol_send(const UserOrKernelBuffer&, size_t) override;
      virtual KResult protocol_connect(FileDescription&, ShouldBlock) override;
      virtual KResultOr<u16> protocol_allocate_local_port() override;
      virtual bool protocol_is_disconnected() const override;
      virtual KResult protocol_bind() override;
      virtual KResult protocol_listen(bool did_allocate_port) override;
  
      void enqueue_for_retransmit();
      void dequeue_for_retransmit();
  
      WeakPtr<TCPSocket> m_originator;
      HashMap<IPv4SocketTuple, NonnullRefPtr<TCPSocket>> m_pending_release_for_accept;
      Direction m_direction { Direction::Unspecified };
      Error m_error { Error::None };
      RefPtr<NetworkAdapter> m_adapter;
      u32 m_sequence_number { 0 };
      u32 m_ack_number { 0 };
      State m_state { State::Closed };
      u32 m_packets_in { 0 };
      u32 m_bytes_in { 0 };
      u32 m_packets_out { 0 };
      u32 m_bytes_out { 0 };
  
      struct OutgoingPacket {
          u32 ack_number { 0 };
          RefPtr<PacketWithTimestamp> buffer;
          size_t ipv4_payload_offset;
          WeakPtr<NetworkAdapter> adapter;
          int tx_counter { 0 };
      };
  
      struct UnackedPackets {
          SinglyLinkedList<OutgoingPacket> packets;
          size_t size { 0 };
      };
  
      MutexProtected<UnackedPackets> m_unacked_packets;
  
      u32 m_duplicate_acks { 0 };
  
      u32 m_last_ack_number_sent { 0 };
      Time m_last_ack_sent_time;
  
      // FIXME: Make this configurable (sysctl)
      static constexpr u32 maximum_retransmits = 5;
      Time m_last_retransmit_time;
      u32 m_retransmit_attempts { 0 };
  
      // FIXME: Parse window size TCP option from the peer
      u32 m_send_window_size { 64 * KiB };
  
      IntrusiveListNode<TCPSocket> m_retransmit_list_node;
  
  public:
      using RetransmitList = IntrusiveList<TCPSocket, RawPtr<TCPSocket>, &TCPSocket::m_retransmit_list_node>;
      static MutexProtected<TCPSocket::RetransmitList>& sockets_for_retransmit();
  };
  
  }
  