//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2020 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// OpenVPN protocol implementation for client-instance object on server

#ifndef OPENVPN_SERVER_SERVPROTO_H
#define OPENVPN_SERVER_SERVPROTO_H

#include <memory>
#include <utility> // for std::move

#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/common/rc.hpp>
#include <openvpn/common/unicode.hpp>
#include <openvpn/common/abort.hpp>
#include <openvpn/common/link.hpp>
#include <openvpn/common/string.hpp>
#include <openvpn/buffer/bufstream.hpp>
#include <openvpn/time/asiotimer.hpp>
#include <openvpn/time/coarsetime.hpp>
#include <openvpn/crypto/cryptodc.hpp>
#include <openvpn/ssl/proto.hpp>
#include <openvpn/transport/server/transbase.hpp>
#include <openvpn/tun/server/tunbase.hpp>
#include <openvpn/server/manage.hpp>

#ifdef OPENVPN_DEBUG_SERVPROTO
#define OPENVPN_LOG_SERVPROTO(x) OPENVPN_LOG(x)
#else
#define OPENVPN_LOG_SERVPROTO(x)
#endif

namespace openvpn {

  class ServerProto
  {
    typedef ProtoContext Base;
    typedef Link<TransportClientInstance::Send, TransportClientInstance::Recv> TransportLink;
    typedef Link<TunClientInstance::Send, TunClientInstance::Recv> TunLink;
    typedef Link<ManClientInstance::Send, ManClientInstance::Recv> ManLink;

  public:
    class Session;

    class Factory : public TransportClientInstance::Factory
    {
    public:
      typedef RCPtr<Factory> Ptr;
      typedef Base::Config ProtoConfig;

      Factory(openvpn_io::io_context& io_context_arg,
	      const Base::Config& c)
	: io_context(io_context_arg)
      {
	if (c.tls_crypt_enabled())
	  preval.reset(new Base::TLSCryptPreValidate(c, true));
	else if (c.tls_auth_enabled())
	  preval.reset(new Base::TLSAuthPreValidate(c, true));
      }

      virtual TransportClientInstance::Recv::Ptr new_client_instance() override;

      virtual bool validate_initial_packet(const BufferAllocated& net_buf) override
      {
	if (preval)
	  {
	    const bool ret = preval->validate(net_buf);
	    if (!ret)
	      stats->error(Error::TLS_AUTH_FAIL);
	    return ret;
	  }
	else
	  return true;
      }

      ProtoConfig::Ptr clone_proto_config() const
      {
	return new ProtoConfig(*proto_context_config);
      }

      openvpn_io::io_context& io_context;
      ProtoConfig::Ptr proto_context_config;

      ManClientInstance::Factory::Ptr man_factory;
      TunClientInstance::Factory::Ptr tun_factory;

      SessionStats::Ptr stats;

    private:
      Base::TLSWrapPreValidate::Ptr preval;
    };

    // This is the main server-side client instance object
    class Session : Base,                  // OpenVPN protocol implementation
		    public TransportLink,  // Transport layer
		    public TunLink,        // Tun/routing layer
		    public ManLink         // Management layer
    {
      friend class Factory; // calls constructor

      typedef Base::PacketType PacketType;

      using Base::now;
      using Base::stat;

    public:
      typedef RCPtr<Session> Ptr;

      virtual bool defined() const override
      {
	return defined_();
      }

      virtual TunClientInstance::Recv* override_tun(TunClientInstance::Send* tun) override
      {
	TunLink::send.reset(tun);
	return this;
      }

      virtual void start(const TransportClientInstance::Send::Ptr& parent,
			 const PeerAddr::Ptr& addr,
			 const int local_peer_id) override
      {
	TransportLink::send = parent;
	peer_addr = addr;

	// init OpenVPN protocol handshake
	Base::update_now();
	Base::reset();
	Base::set_local_peer_id(local_peer_id);
	Base::start();
	Base::flush(true);

	// coarse wakeup range
	housekeeping_schedule.init(Time::Duration::binary_ms(512), Time::Duration::binary_ms(1024));
      }

      virtual PeerStats stats_poll() override
      {
	if (TransportLink::send)
	  return TransportLink::send->stats_poll();
	else
	  return PeerStats();
      }

      virtual bool should_preserve_session_id() override
      {
	return preserve_session_id;
      }

      virtual void stop() override
      {
	if (!halt)
	  {
	    halt = true;
	    housekeeping_timer.cancel();

	    if (ManLink::send)
	      ManLink::send->pre_stop();

	    // deliver final peer stats to management layer
	    if (TransportLink::send && ManLink::send)
	      {
		if (TransportLink::send->stats_pending())
		  ManLink::send->stats_notify(TransportLink::send->stats_poll(), true);
	      }

	    Base::pre_destroy();
	    Base::reset_dc_factory();
	    if (TransportLink::send)
	      {
		TransportLink::send->stop();
		TransportLink::send.reset();
	      }
	    if (TunLink::send)
	      {
		TunLink::send->stop();
		TunLink::send.reset();
	      }
	    if (ManLink::send)
	      {
		ManLink::send->stop();
		ManLink::send.reset();
	      }
	  }
      }

      // called with OpenVPN-encapsulated packets from transport layer
      virtual bool transport_recv(BufferAllocated& buf) override
      {
	bool ret = false;
	if (!Base::primary_defined())
	  return false;
	try {
	  OPENVPN_LOG_SERVPROTO("Transport RECV[" << buf.size() << "] " << client_endpoint_render() << ' ' << Base::dump_packet(buf));

	  // update current time
	  Base::update_now();

	  // get packet type
	  Base::PacketType pt = Base::packet_type(buf);

	  // process packet
	  if (pt.is_data())
	    {
	      // data packet
	      ret = Base::data_decrypt(pt, buf);
	      if (buf.size())
		{
#ifdef OPENVPN_PACKET_LOG
		  log_packet(buf, false);
#endif
		  // make packet appear as incoming on tun interface
		  if (true) // fixme: was tun
		    {
		      OPENVPN_LOG_SERVPROTO("TUN SEND[" << buf.size() << ']');
		      // fixme -- code me
		    }
		}

	      // do a lightweight flush
	      Base::flush(false);
	    }
	  else if (pt.is_control())
	    {
	      // control packet
	      ret = Base::control_net_recv(pt, std::move(buf));

	      // do a full flush
	      Base::flush(true);
	    }

	  // schedule housekeeping wakeup
	  set_housekeeping_timer();
	}
	catch (const std::exception& e)
	  {
	    error(e);
	    ret = false;
	  }

	return ret;
      }

      // called with cleartext IP packets from routing layer
      virtual void tun_recv(BufferAllocated& buf) override
      {
	// fixme -- code me
      }

      // Return true if keepalive parameter(s) are enabled.
      virtual bool is_keepalive_enabled() const override
      {
	return Base::is_keepalive_enabled();
      }

      // Disable keepalive for rest of session, but fetch
      // the keepalive parameters (in seconds).
      // Also, allow the management layer to override parameters.
      virtual void disable_keepalive(unsigned int& keepalive_ping,
				     unsigned int& keepalive_timeout) override
      {
	Base::disable_keepalive(keepalive_ping, keepalive_timeout);
	if (ManLink::send)
	  ManLink::send->keepalive_override(keepalive_ping, keepalive_timeout);
      }

      // override the data channel factory
      virtual void override_dc_factory(const CryptoDCFactory::Ptr& dc_factory) override
      {
	Base::dc_settings().set_factory(dc_factory);
      }

      virtual ~Session()
      {
	// fatal error if destructor called while Session is active
	if (defined_())
	  std::abort();
      }

    private:
      Session(openvpn_io::io_context& io_context_arg,
	      const Factory& factory,
	      ManClientInstance::Factory::Ptr man_factory_arg,
	      TunClientInstance::Factory::Ptr tun_factory_arg)
	: Base(factory.clone_proto_config(), factory.stats),
	  housekeeping_timer(io_context_arg),
	  disconnect_at(Time::infinite()),
	  stats(factory.stats),
	  man_factory(man_factory_arg),
	  tun_factory(tun_factory_arg)
      {}

      bool defined_() const
      {
	return !halt && TransportLink::send;
      }

      // proto base class calls here for control channel network sends
      virtual void control_net_send(const Buffer& net_buf) override
      {
	OPENVPN_LOG_SERVPROTO("Transport SEND[" << net_buf.size() << "] " << client_endpoint_render() << ' ' << Base::dump_packet(net_buf));
	if (TransportLink::send)
	  {
	    if (TransportLink::send->transport_send_const(net_buf))
	      Base::update_last_sent();
	  }
      }

      // Called on server with credentials and peer info provided by client.
      // Should be overriden by derived class if credentials are required.
      virtual void server_auth(const std::string& username,
			       const SafeString& password,
			       const std::string& peer_info,
			       const AuthCert::Ptr& auth_cert) override
      {
	constexpr size_t MAX_USERNAME_SIZE = 256;
	constexpr size_t MAX_PASSWORD_SIZE = 16384;

	if (get_management())
	  {
	    AuthCreds::Ptr auth_creds(new AuthCreds(Unicode::utf8_printable(username, MAX_USERNAME_SIZE|Unicode::UTF8_FILTER),
						    Unicode::utf8_printable(password, MAX_PASSWORD_SIZE|Unicode::UTF8_FILTER|Unicode::UTF8_PASS_FMT),
						    Unicode::utf8_printable(peer_info, Unicode::UTF8_FILTER|Unicode::UTF8_PASS_FMT)));
	    ManLink::send->auth_request(auth_creds, auth_cert, peer_addr);
	  }
      }

      // proto base class calls here for app-level control-channel messages received
      virtual void control_recv(BufferPtr&& app_bp) override
      {
	const std::string msg = Unicode::utf8_printable(Base::template read_control_string<std::string>(*app_bp),
							Unicode::UTF8_FILTER);
	if (msg == "PUSH_REQUEST")
	  {
	    if (get_management())
	      ManLink::send->push_request(Base::conf_ptr());
	    else
	      auth_failed("no management provider", false);
	  }
	else if (string::starts_with(msg, "INFO,"))
	  {
	    if (get_management())
	      ManLink::send->info_request(msg.substr(5));
	  }
	else
	  {
	    OPENVPN_LOG("Unrecognized client request: " << msg);
	  }
      }

      virtual void auth_failed(const std::string& reason,
			       const bool tell_client) override
      {
	push_halt_restart_msg(HaltRestart::AUTH_FAILED, reason, tell_client);
      }

      virtual void relay(const IP::Addr& target, const int port) override
      {
	if (halt || disconnect_type == DT_HALT_RESTART)
	  return;

	Base::update_now();

	if (TunLink::send && (disconnect_type < DT_RELAY_TRANSITION))
	  {
	    disconnect_type = DT_RELAY_TRANSITION;
	    TunLink::send->relay(target, port);
	    disconnect_in(Time::Duration::seconds(10)); // not a real disconnect, just complete transition to relay
	  }

	if (Base::primary_defined())
	  {
	    BufferPtr buf(new BufferAllocated(64, 0));
	    buf_append_string(*buf, "RELAY");
	    buf->null_terminate();
	    Base::control_send(std::move(buf));
	    Base::flush(true);
	  }

	set_housekeeping_timer();
      }

      virtual void push_reply(std::vector<BufferPtr>&& push_msgs) override
      {
	if (halt || (disconnect_type >= DT_RELAY_TRANSITION) || !Base::primary_defined())
	  return;

	if (disconnect_type == DT_AUTH_PENDING)
	  {
	    disconnect_type = DT_NONE;
	    cancel_disconnect();
	  }

	Base::update_now();

	if (get_tun())
	  {
	    Base::init_data_channel();
	    for (auto &msg : push_msgs)
	      {
		msg->null_terminate();
		Base::control_send(std::move(msg));
	      }
	    Base::flush(true);
	    set_housekeeping_timer();
	  }
	else
	  {
	    auth_failed("no tun provider", false);
	  }
      }

      virtual TunClientInstance::NativeHandle tun_native_handle() override
      {
	if (get_tun())
	  return TunLink::send->tun_native_handle();
	else
	  return TunClientInstance::NativeHandle();
      }

      virtual void push_halt_restart_msg(const HaltRestart::Type type,
					 const std::string& reason,
					 const bool tell_client) override
      {
	if (halt || disconnect_type == DT_HALT_RESTART)
	  return;

	Base::update_now();

	BufferPtr buf(new BufferAllocated(128, BufferAllocated::GROW));
	BufferStreamOut os(*buf);

	std::string ts;

	switch (type)
	  {
	  case HaltRestart::HALT:
	    ts = "HALT";
	    os << "HALT,";
	    if (tell_client && !reason.empty())
	      os << reason;
	    else
	      os << "client was disconnected from server";
	    disconnect_type = DT_HALT_RESTART;
	    disconnect_in(Time::Duration::seconds(1));
	    preserve_session_id = false;
	    break;
	  case HaltRestart::RESTART:
	    ts = "RESTART";
	    os << "RESTART,";
	    if (tell_client && !reason.empty())
	      os << reason;
	    else
	      os << "server requested a client reconnect";
	    disconnect_type = DT_HALT_RESTART;
	    disconnect_in(Time::Duration::seconds(1));
	    preserve_session_id = false;
	    break;
	  case HaltRestart::RESTART_PASSIVE:
	    ts = "RESTART_PASSIVE";
	    os << "RESTART,[P]:";
	    if (tell_client && !reason.empty())
	      os << reason;
	    else
	      os << "server requested a client reconnect";
	    break;
	  case HaltRestart::RESTART_PSID:
	    ts = "RESTART_PSID";
	    os << "RESTART,[P]:";
	    if (tell_client && !reason.empty())
	      os << reason;
	    else
	      os << "server requested a client reconnect";
	    disconnect_type = DT_HALT_RESTART;
	    disconnect_in(Time::Duration::seconds(1));
	    break;
	  case HaltRestart::AUTH_FAILED:
	    ts = "AUTH_FAILED";
	    os << ts;
	    if (tell_client && !reason.empty())
	      os << ',' << reason;
	    disconnect_type = DT_HALT_RESTART;
	    disconnect_in(Time::Duration::seconds(1));
	    preserve_session_id = false;
	    break;
	  case HaltRestart::RAW:
	    {
	      const size_t pos = reason.find_first_of(',');
	      if (pos != std::string::npos)
		ts = reason.substr(0, pos);
	      else
		ts = reason;
	      os << reason;
	      disconnect_type = DT_HALT_RESTART;
	      disconnect_in(Time::Duration::seconds(1));
	      preserve_session_id = false;
	      break;
	    }
	  }

	OPENVPN_LOG("Disconnect: " << ts << ' ' << reason);

	if (Base::primary_defined())
	  {
	    buf->null_terminate();
	    Base::control_send(std::move(buf));
	    Base::flush(true);
	  }

	set_housekeeping_timer();
      }

      virtual void schedule_disconnect(const unsigned int seconds) override
      {
	if (halt || disconnect_type == DT_HALT_RESTART)
	  return;
	Base::update_now();
	disconnect_in(Time::Duration::seconds(seconds));
	set_housekeeping_timer();
      }

      virtual void schedule_auth_pending_timeout(const unsigned int seconds) override
      {
	if (halt || (disconnect_type >= DT_RELAY_TRANSITION) || !seconds)
	  return;
	Base::update_now();
	disconnect_type = DT_AUTH_PENDING;
	disconnect_in(Time::Duration::seconds(seconds));
	set_housekeeping_timer();
      }

      virtual void post_cc_msg(BufferPtr&& msg) override
      {
	if (halt || !Base::primary_defined())
	  return;

	Base::update_now();
	msg->null_terminate();
	Base::control_send(std::move(msg));
	Base::flush(true);
	set_housekeeping_timer();
      }

      virtual void stats_notify(const PeerStats& ps, const bool final) override
      {
	if (ManLink::send)
	  ManLink::send->stats_notify(ps, final);
      }

      virtual void float_notify(const PeerAddr::Ptr& addr) override
      {
	if (ManLink::send)
	  ManLink::send->float_notify(addr);
      }

      virtual void data_limit_notify(const int key_id,
				     const DataLimit::Mode cdl_mode,
				     const DataLimit::State cdl_status) override
      {
	Base::update_now();
	Base::data_limit_notify(key_id, cdl_mode, cdl_status);
	Base::flush(true);
	set_housekeeping_timer();
      }

      bool get_management()
      {
	if (!ManLink::send)
	  {
	    if (man_factory)
	      ManLink::send = man_factory->new_obj(this);
	  }
	return bool(ManLink::send);
      }

      bool get_tun()
      {
	if (!TunLink::send)
	  {
	    if (tun_factory)
	      TunLink::send = tun_factory->new_obj(this);
	  }
	return bool(TunLink::send);
      }

      // caller must ensure that update_now() was called before
      // and set_housekeeping_timer() called after this method
      void disconnect_in(const Time::Duration& dur)
      {
	disconnect_at = now() + dur;
      }

      void cancel_disconnect()
      {
	disconnect_at = Time::infinite();
      }

      void housekeeping_callback(const openvpn_io::error_code& e)
      {
	try {
	  if (!e && !halt)
	    {
	      // update current time
	      Base::update_now();

	      housekeeping_schedule.reset();
	      Base::housekeeping();
	      if (Base::invalidated())
		invalidation_error(Base::invalidation_reason());
	      else if (now() >= disconnect_at)
		{
		  switch (disconnect_type)
		    {
		    case DT_HALT_RESTART:
		      error("disconnect triggered");
		      break;
		    case DT_RELAY_TRANSITION:
		      Base::pre_destroy();
		      break;
		    case DT_AUTH_PENDING:
		      auth_failed("Auth Pending Timeout", true);
		      break;
		    default:
		      error("unknown disconnect");
		      break;
		    }
		}
	      else
		set_housekeeping_timer();
	    }
	}
	catch (const std::exception& e)
	  {
	    error(e);
	  }
      }

      void set_housekeeping_timer()
      {
	Time next = Base::next_housekeeping();
	next.min(disconnect_at);
	if (!housekeeping_schedule.similar(next))
	  {
	    if (!next.is_infinite())
	      {
		next.max(now());
		housekeeping_schedule.reset(next);
		housekeeping_timer.expires_at(next);
		housekeeping_timer.async_wait([self=Ptr(this)](const openvpn_io::error_code& error)
                                              {
                                                self->housekeeping_callback(error);
                                              });
	      }
	    else
	      {
		housekeeping_timer.cancel();
		housekeeping_schedule.reset();
	      }
	  }
      }

      std::string client_endpoint_render()
      {
	if (TransportLink::send)
	  return TransportLink::send->transport_info();
	else
	  return "";
      }

      void error(const std::string& error)
      {
	OPENVPN_LOG("ServerProto: " << error);
	stop();
      }

      void error(const std::exception& e)
      {
	error(e.what());
      }

      void error()
      {
	stop();
      }

      void invalidation_error(const Error::Type err)
      {
	switch (err)
	  {
	  case Error::KEV_NEGOTIATE_ERROR:
	  case Error::KEEPALIVE_TIMEOUT:
	    error();
	    break;
	  default:
	    error(std::string("Session invalidated: ") + Error::name(err));
	    break;
	  }
      }

      // higher values are higher priority
      enum DisconnectType {
	DT_NONE=0,
	DT_AUTH_PENDING,
	DT_RELAY_TRANSITION,
	DT_HALT_RESTART,
      };
      int disconnect_type = DT_NONE;
      bool preserve_session_id = true;

      bool halt = false;

      PeerAddr::Ptr peer_addr;

      CoarseTime housekeeping_schedule;
      AsioTimer housekeeping_timer;

      Time disconnect_at;

      SessionStats::Ptr stats;

      ManClientInstance::Factory::Ptr man_factory;
      TunClientInstance::Factory::Ptr tun_factory;
    };
  };

  inline TransportClientInstance::Recv::Ptr ServerProto::Factory::new_client_instance()
  {
    return new Session(io_context, *this, man_factory, tun_factory);
  }
}

#endif