IPv4: Basic implementation of TCP socket shutdown

We can now participate in the TCP connection closing handshake. :^)
This implementation is definitely not complete and needs to handle a
bunch of other cases. But it's a huge improvement over not being able
to close connections at all.

Note that we hold on to pending-close sockets indefinitely, until they
are moved into the Closed state. This should also have a timeout but
that's still a FIXME. :^)

Fixes SerenityOS#428.

Kernel/Net/IPv4Socket.cpp

@@ -500,3 +500,8 @@ int IPv4Socket::ioctl(FileDescription&, unsigned request, unsigned arg)
 
  return -EINVAL;
 }
+
+void IPv4Socket::close()
+{
+ shutdown(SHUT_RDWR);
+}

Kernel/Net/IPv4Socket.h

@@ -46,6 +46,7 @@ class IPv4Socket : public Socket {
 
  static Lockable<HashTable<IPv4Socket*>>& all_sockets();
 
+ virtual void close() override;
  virtual KResult bind(const sockaddr*, socklen_t) override;
  virtual KResult connect(FileDescription&, const sockaddr*, socklen_t, ShouldBlock = ShouldBlock::Yes) override;
  virtual KResult listen(int) override;

Kernel/Net/NetworkTask.cpp

@@ -572,6 +572,9 @@ void handle_tcp(const IPv4Packet& ipv4_packet)
  socket->set_ack_number(tcp_packet.sequence_number() + payload_size + 1);
  socket->set_state(TCPSocket::State::TimeWait);
  return;
+ case TCPFlags::ACK | TCPFlags::RST:
+ socket->set_state(TCPSocket::State::Closed);
+ return;
  default:
  kprintf("handle_tcp: unexpected flags in FinWait2 state\n");
  socket->send_tcp_packet(TCPFlags::RST);
@@ -596,12 +599,8 @@ void handle_tcp(const IPv4Packet& ipv4_packet)
  socket->did_receive(ipv4_packet.source(), tcp_packet.source_port(), KBuffer::copy(&ipv4_packet, sizeof(IPv4Packet) + ipv4_packet.payload_size()));
 
  socket->set_ack_number(tcp_packet.sequence_number() + payload_size + 1);
- // TODO: We should only send a FIN packet out once we're shutting
- // down our side of the socket, so we should change this back to
- // just being an ACK and a transition to CloseWait once we have a
- // shutdown() implementation.
- socket->send_tcp_packet(TCPFlags::FIN | TCPFlags::ACK);
- socket->set_state(TCPSocket::State::Closing);
+ socket->send_tcp_packet(TCPFlags::ACK);
+ socket->set_state(TCPSocket::State::CloseWait);
  socket->set_connected(false);
  return;
  }

Kernel/Net/Socket.cpp

@@ -165,7 +165,13 @@ KResult Socket::shutdown(int how)
 {
  if (type() == SOCK_STREAM && !is_connected())
  return KResult(-ENOTCONN);
- m_shut_down_for_reading |= how & SHUT_RD;
- m_shut_down_for_writing |= how & SHUT_WR;
+ if (m_role == Role::Listener)
+ return KResult(-ENOTCONN);
+ if (!m_shut_down_for_writing && (how & SHUT_WR))
+ shut_down_for_writing();
+ if (!m_shut_down_for_reading && (how & SHUT_RD))
+ shut_down_for_reading();
+ m_shut_down_for_reading |= (how & SHUT_RD) != 0;
+ m_shut_down_for_writing |= (how & SHUT_WR) != 0;
  return KSuccess;
 }

Kernel/Net/Socket.h

@@ -141,6 +141,9 @@ class Socket : public File {
 
  virtual const char* class_name() const override { return "Socket"; }
 
+ virtual void shut_down_for_reading() {}
+ virtual void shut_down_for_writing() {}
+
  Role m_role { Role::None };
 
 protected:

Kernel/Net/TCPSocket.cpp

@@ -55,6 +55,19 @@ void TCPSocket::set_state(State new_state)
 
  if (new_state == State::Established && m_direction == Direction::Outgoing)
  m_role = Role::Connected;
+
+ if (new_state == State::Closed) {
+ LOCKER(closing_sockets().lock());
+ closing_sockets().resource().remove(tuple());
+ }
+}
+
+Lockable<HashMap<IPv4SocketTuple, RefPtr<TCPSocket>>>& TCPSocket::closing_sockets()
+{
+ static Lockable<HashMap<IPv4SocketTuple, RefPtr<TCPSocket>>>* s_map;
+ if (!s_map)
+ s_map = new Lockable<HashMap<IPv4SocketTuple, RefPtr<TCPSocket>>>;
+ return *s_map;
 }
 
 Lockable<HashMap<IPv4SocketTuple, TCPSocket*>>& TCPSocket::sockets_by_tuple()
@@ -137,6 +150,10 @@ TCPSocket::~TCPSocket()
 {
  LOCKER(sockets_by_tuple().lock());
  sockets_by_tuple().resource().remove(tuple());
+
+#ifdef TCP_SOCKET_DEBUG
+ dbg() << "~TCPSocket in state " << to_string(state());
+#endif
 }
 
 NonnullRefPtr<TCPSocket> TCPSocket::create(int protocol)
@@ -420,3 +437,27 @@ bool TCPSocket::protocol_is_disconnected() const
  return false;
  }
 }
+
+void TCPSocket::shut_down_for_writing()
+{
+ if (state() == State::Established) {
+ dbg() << " Sending FIN/ACK from Established and moving into FinWait1";
+ send_tcp_packet(TCPFlags::FIN | TCPFlags::ACK);
+ set_state(State::FinWait1);
+ } else {
+ dbg() << " Shutting down TCPSocket for writing but not moving to FinWait1 since state is " << to_string(state());
+ }
+}
+
+void TCPSocket::close()
+{
+ IPv4Socket::close();
+ if (state() == State::CloseWait) {
+ dbg() << " Sending FIN from CloseWait and moving into LastAck";
+ send_tcp_packet(TCPFlags::FIN | TCPFlags::ACK);
+ set_state(State::LastAck);
+ }
+
+ LOCKER(closing_sockets().lock());
+ closing_sockets().resource().set(tuple(), *this);
+}

Kernel/Net/TCPSocket.h

@@ -155,12 +155,16 @@ class TCPSocket final : public IPv4Socket
  static RefPtr<TCPSocket> from_tuple(const IPv4SocketTuple& tuple);
  static RefPtr<TCPSocket> from_endpoints(const IPv4Address& local_address, u16 local_port, const IPv4Address& peer_address, u16 peer_port);
 
+ static Lockable<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.make_weak_ptr(); }
  bool has_originator() { return !!m_originator; }
  void release_to_originator();
  void release_for_accept(RefPtr<TCPSocket>);
 
+ virtual void close() override;
+
 protected:
  void set_direction(Direction direction) { m_direction = direction; }
 
@@ -170,6 +174,8 @@ class TCPSocket final : public IPv4Socket
 
  static NetworkOrdered<u16> compute_tcp_checksum(const IPv4Address& source, const IPv4Address& destination, const TCPPacket&, u16 payload_size);
 
+ virtual void shut_down_for_writing() override;
+
  virtual int protocol_receive(const KBuffer&, void* buffer, size_t buffer_size, int flags) override;
  virtual int protocol_send(const void*, size_t) override;
  virtual KResult protocol_connect(FileDescription&, ShouldBlock) override;