OpenVPNAdapter/openvpn/client/cliproto.hpp

//    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) 2012-2017 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/>.

#ifndef OPENVPN_CLIENT_CLIPROTO_H
#define OPENVPN_CLIENT_CLIPROTO_H

// This is a middle-layer object in the OpenVPN client protocol stack.
// It is above the general OpenVPN protocol implementation in
// class ProtoContext but below the top
// level object in a client connect (ClientConnect).  See ClientConnect for
// a fuller description of the full client stack.
//
// This layer deals with setting up an OpenVPN client connection:
//
// 1. handles creation of transport-layer handler via TransportClientFactory
// 2. handles creation of tun-layer handler via TunClientFactory
// 3. handles sending PUSH_REQUEST to server and processing reply of server-pushed options
// 4. manages the underlying OpenVPN protocol object (class ProtoContext)
// 5. handles timers on behalf of the underlying OpenVPN protocol object
// 6. acts as an exception dispatcher for errors occuring in any of the underlying layers

#include <string>
#include <vector>
#include <memory>
#include <algorithm>         // for std::min
#include <cstdint>           // for std::uint...

#include <openvpn/io/io.hpp>

#include <openvpn/common/rc.hpp>
#include <openvpn/common/count.hpp>
#include <openvpn/common/string.hpp>
#include <openvpn/common/base64.hpp>
#include <openvpn/ip/ptb.hpp>
#include <openvpn/tun/client/tunbase.hpp>
#include <openvpn/transport/client/transbase.hpp>
#include <openvpn/transport/client/relay.hpp>
#include <openvpn/options/continuation.hpp>
#include <openvpn/options/sanitize.hpp>
#include <openvpn/client/clievent.hpp>
#include <openvpn/client/clicreds.hpp>
#include <openvpn/client/cliconstants.hpp>
#include <openvpn/client/clihalt.hpp>
#include <openvpn/time/asiotimer.hpp>
#include <openvpn/time/coarsetime.hpp>
#include <openvpn/time/durhelper.hpp>
#include <openvpn/error/excode.hpp>

#include <openvpn/ssl/proto.hpp>

#ifdef OPENVPN_DEBUG_CLIPROTO
#define OPENVPN_LOG_CLIPROTO(x) OPENVPN_LOG(x)
#else
#define OPENVPN_LOG_CLIPROTO(x)
#endif

namespace openvpn {
  namespace ClientProto {

    struct NotifyCallback {
      virtual void client_proto_terminate() = 0;
      virtual void client_proto_connected() {}
    };

    class Session : ProtoContext,
                    TransportClientParent,
                    TunClientParent,
		    public RC<thread_unsafe_refcount>
    {
      typedef ProtoContext Base;
      typedef Base::PacketType PacketType;

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

    public:
      typedef RCPtr<Session> Ptr;
      typedef Base::Config ProtoConfig;

      OPENVPN_EXCEPTION(client_exception);
      OPENVPN_EXCEPTION(client_halt_restart);
      OPENVPN_EXCEPTION(tun_exception);
      OPENVPN_EXCEPTION(transport_exception);
      OPENVPN_EXCEPTION(max_pushed_options_exceeded);
      OPENVPN_SIMPLE_EXCEPTION(session_invalidated);
      OPENVPN_SIMPLE_EXCEPTION(authentication_failed);
      OPENVPN_SIMPLE_EXCEPTION(inactive_timer_expired);
      OPENVPN_SIMPLE_EXCEPTION(relay_event);

      OPENVPN_EXCEPTION(proxy_exception);

      struct Config : public RC<thread_unsafe_refcount>
      {
	typedef RCPtr<Config> Ptr;

	Config()
	  : pushed_options_limit("server-pushed options data too large",
				 ProfileParseLimits::MAX_PUSH_SIZE,
				 ProfileParseLimits::OPT_OVERHEAD,
				 ProfileParseLimits::TERM_OVERHEAD,
				 0,
				 ProfileParseLimits::MAX_DIRECTIVE_SIZE)
	{}

	ProtoConfig::Ptr proto_context_config;
	ProtoContextOptions::Ptr proto_context_options;
	PushOptionsBase::Ptr push_base;
	TransportClientFactory::Ptr transport_factory;
	TunClientFactory::Ptr tun_factory;
	SessionStats::Ptr cli_stats;
	ClientEvent::Queue::Ptr cli_events;
	ClientCreds::Ptr creds;
	OptionList::Limits pushed_options_limit;
	OptionList::FilterBase::Ptr pushed_options_filter;
	unsigned int tcp_queue_limit = 0;
	bool echo = false;
	bool info = false;
	bool autologin_sessions = false;
      };

      Session(openvpn_io::io_context& io_context_arg,
	      const Config& config,
	      NotifyCallback* notify_callback_arg)
	: Base(config.proto_context_config, config.cli_stats),
	  io_context(io_context_arg),
	  transport_factory(config.transport_factory),
	  tun_factory(config.tun_factory),
	  tcp_queue_limit(config.tcp_queue_limit),
	  notify_callback(notify_callback_arg),
	  housekeeping_timer(io_context_arg),
	  push_request_timer(io_context_arg),
	  received_options(config.push_base),
	  creds(config.creds),
	  proto_context_options(config.proto_context_options),
	  cli_stats(config.cli_stats),
	  cli_events(config.cli_events),
	  echo(config.echo),
	  info(config.info),
	  autologin_sessions(config.autologin_sessions),
	  pushed_options_limit(config.pushed_options_limit),
	  pushed_options_filter(config.pushed_options_filter),
	  inactive_timer(io_context_arg),
	  info_hold_timer(io_context_arg)
      {
#ifdef OPENVPN_PACKET_LOG
	packet_log.open(OPENVPN_PACKET_LOG, std::ios::binary);
	if (!packet_log)
	  OPENVPN_THROW(open_file_error, "cannot open packet log for output: " << OPENVPN_PACKET_LOG);
#endif
	Base::update_now();
	Base::reset();
	//Base::enable_strict_openvpn_2x();

	info_hold.reset(new std::vector<ClientEvent::Base::Ptr>());
      }

      bool first_packet_received() const { return first_packet_received_; }

      void start()
      {
	if (!halt)
	  {
	    Base::update_now();

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

	    // initialize transport-layer packet handler
	    transport = transport_factory->new_transport_client_obj(io_context, this);
	    transport_has_send_queue = transport->transport_has_send_queue();
	    if (transport_factory->is_relay())
	      transport_connecting();
	    else
	      transport->transport_start();
	  }
      }

      TransportClientFactory::Ptr transport_factory_relay()
      {
	TransportClient::Ptr tc(new TransportRelayFactory::TransportClientNull(transport.get()));
	tc.swap(transport);
	return new TransportRelayFactory(io_context, std::move(tc), this);
      }

      void transport_factory_override(TransportClientFactory::Ptr factory)
      {
	transport_factory = std::move(factory);
      }

      void send_explicit_exit_notify()
      {
	if (!halt)
	  Base::send_explicit_exit_notify();
      }

      void tun_set_disconnect()
      {
	if (tun)
	  tun->set_disconnect();
      }

      void post_cc_msg(const std::string& msg)
      {
	Base::update_now();
	Base::write_control_string(msg);
	Base::flush(true);
	set_housekeeping_timer();
      }

      void stop(const bool call_terminate_callback)
      {
	if (!halt)
	  {
	    halt = true;
	    housekeeping_timer.cancel();
	    push_request_timer.cancel();
	    inactive_timer.cancel();
	    info_hold_timer.cancel();
	    if (notify_callback && call_terminate_callback)
	      notify_callback->client_proto_terminate();
	    if (tun)
	      tun->stop(); // call after client_proto_terminate() so it can call back to tun_set_disconnect
	    if (transport)
	      transport->stop();
	  }
      }

      void stop_on_signal(const openvpn_io::error_code& error, int signal_number)
      {
	stop(true);
      }

      bool reached_connected_state() const { return bool(connected_); }

      // If fatal() returns something other than Error::UNDEF, it
      // is intended to flag the higher levels (cliconnect.hpp)
      // that special handling is required.  This handling might include
      // considering the error to be fatal and stopping future connect
      // retries, or emitting a special event.  See cliconnect.hpp
      // for actual implementation.
      Error::Type fatal() const { return fatal_; }
      const std::string& fatal_reason() const { return fatal_reason_; }

      virtual ~Session()
      {
	stop(false);
      }

    private:
      virtual bool transport_is_openvpn_protocol()
      {
	return true;
      }

      // transport obj calls here with incoming packets
      virtual void transport_recv(BufferAllocated& buf)
      {
	try {
	  OPENVPN_LOG_CLIPROTO("Transport RECV " << server_endpoint_render() << ' ' << Base::dump_packet(buf));

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

	  // update last packet received
	  stat().update_last_packet_received(now());

	  // log connecting event (only on first packet received)
	  if (!first_packet_received_)
	    {
	      ClientEvent::Base::Ptr ev = new ClientEvent::Connecting();
	      cli_events->add_event(std::move(ev));
	      first_packet_received_ = true;
	    }

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

	  // process packet
	  if (pt.is_data())
	    {
	      // data packet
	      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 (tun)
		    {
		      OPENVPN_LOG_CLIPROTO("TUN send, size=" << buf.size());
		      tun->tun_send(buf);
		    }
		}

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

	      // do a full flush
	      Base::flush(true);
	    }
	  else
	    cli_stats->error(Error::KEY_STATE_ERROR);

	  // schedule housekeeping wakeup
	  set_housekeeping_timer();
	}
	catch (const ExceptionCode& e)
	  {
	    if (e.code_defined())
	      {
		if (e.fatal())
		  transport_error((Error::Type)e.code(), e.what());
		else
		  cli_stats->error((Error::Type)e.code());
	      }
	    else
	      process_exception(e, "transport_recv_excode");
	  }
	catch (const std::exception& e)
	  {
	    process_exception(e, "transport_recv");
	  }
      }

      virtual void transport_needs_send()
      {
      }

      // tun i/o driver calls here with incoming packets
      virtual void tun_recv(BufferAllocated& buf)
      {
	try {
	  OPENVPN_LOG_CLIPROTO("TUN recv, size=" << buf.size());

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

	  // log packet
#ifdef OPENVPN_PACKET_LOG
	  log_packet(buf, true);
#endif

	  // if transport layer has an output queue, check if it's full
	  if (transport_has_send_queue)
	    {
	      if (transport->transport_send_queue_size() > tcp_queue_limit)
		{
		  buf.reset_size(); // queue full, drop packet
		  cli_stats->error(Error::TCP_OVERFLOW);
		}
	    }

	  // encrypt packet
	  if (buf.size())
	    {
	      const ProtoContext::Config& c = Base::conf();
	      if (c.mss_inter > 0 && buf.size() > c.mss_inter)
		{
		  Ptb::generate_icmp_ptb(buf, c.mss_inter);
		  tun->tun_send(buf);
		}
	      else
		{
		  Base::data_encrypt(buf);
		  if (buf.size())
		  {
		    // send packet via transport to destination
		    OPENVPN_LOG_CLIPROTO("Transport SEND " << server_endpoint_render() << ' ' << Base::dump_packet(buf));
		    if (transport->transport_send(buf))
		      Base::update_last_sent();
		    else if (halt)
		      return;
		  }
		}
	    }

	  // do a lightweight flush
	  Base::flush(false);

	  // schedule housekeeping wakeup
	  set_housekeeping_timer();
	}
	catch (const std::exception& e)
	  {
	    process_exception(e, "tun_recv");
	  }
      }

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

      // Disable keepalive for rest of session, but fetch
      // the keepalive parameters (in seconds).
      virtual void disable_keepalive(unsigned int& keepalive_ping,
				     unsigned int& keepalive_timeout)
      {
	Base::disable_keepalive(keepalive_ping, keepalive_timeout);
      }

      virtual void transport_pre_resolve()
      {
	ClientEvent::Base::Ptr ev = new ClientEvent::Resolve();
	cli_events->add_event(std::move(ev));
      }

      std::string server_endpoint_render()
      {
	std::string server_host, server_port, server_proto, server_ip;
	transport->server_endpoint_info(server_host, server_port, server_proto, server_ip);
	std::ostringstream out;
	out << '[' << server_host << "]:" << server_port << " (" << server_ip << ") via " << server_proto;
	return out.str();
      }

      virtual void transport_wait_proxy()
      {
	ClientEvent::Base::Ptr ev = new ClientEvent::WaitProxy();
	cli_events->add_event(std::move(ev));
      }

      virtual void transport_wait()
      {
	ClientEvent::Base::Ptr ev = new ClientEvent::Wait();
	cli_events->add_event(std::move(ev));
      }

      virtual void transport_connecting()
      {
	try {
	  OPENVPN_LOG("Connecting to " << server_endpoint_render());
	  Base::set_protocol(transport->transport_protocol());
	  Base::start();
	  Base::flush(true);
	  set_housekeeping_timer();
	}
	catch (const std::exception& e)
	  {
	    process_exception(e, "transport_connecting");
	  }
      }

      virtual void transport_error(const Error::Type fatal_err, const std::string& err_text)
      {
	if (fatal_err != Error::UNDEF)
	  {
	    fatal_ = fatal_err;
	    fatal_reason_ = err_text;
	  }
	if (notify_callback)
	  {
	    OPENVPN_LOG("Transport Error: " << err_text);
	    stop(true);
	  }
	else
	  throw transport_exception(err_text);
      }

      virtual void proxy_error(const Error::Type fatal_err, const std::string& err_text)
      {
	if (fatal_err != Error::UNDEF)
	  {
	    fatal_ = fatal_err;
	    fatal_reason_ = err_text;
	  }
	if (notify_callback)
	  {
	    OPENVPN_LOG("Proxy Error: " << err_text);
	    stop(true);
	  }
	else
	  throw proxy_exception(err_text);
      }

      void extract_auth_token(const OptionList& opt)
      {
	std::string username;

	// auth-token-user
	{
	  const Option* o = opt.get_ptr("auth-token-user");
	  if (o)
	    username = base64->decode(o->get(1, 340)); // 255 chars after base64 decode
	}

	// auth-token
	{
	  // if auth-token is present, use it as the password for future renegotiations
	  const Option* o = opt.get_ptr("auth-token");
	  if (o)
	    {
	      const std::string& sess_id = o->get(1, 256);
	      if (creds)
		{
		  if (!username.empty())
		    OPENVPN_LOG("Session user: " << username);
#ifdef OPENVPN_SHOW_SESSION_TOKEN
		  OPENVPN_LOG("Session token: " << sess_id);
#else
		  OPENVPN_LOG("Session token: [redacted]");
#endif
		  creds->set_session_id(username, sess_id);
		}
	    }
	}
      }

      // proto base class calls here for control channel network sends
      virtual void control_net_send(const Buffer& net_buf)
      {
	OPENVPN_LOG_CLIPROTO("Transport SEND " << server_endpoint_render() << ' ' << Base::dump_packet(net_buf));
	if (transport->transport_send_const(net_buf))
	  Base::update_last_sent();
      }

      // proto base class calls here for app-level control-channel messages received
      virtual void control_recv(BufferPtr&& app_bp)
      {
	const std::string msg = Unicode::utf8_printable(Base::template read_control_string<std::string>(*app_bp),
							Unicode::UTF8_FILTER|Unicode::UTF8_PASS_FMT);

	//OPENVPN_LOG("SERVER: " << sanitize_control_message(msg));

	if (!received_options.complete() && string::starts_with(msg, "PUSH_REPLY,"))
	  {
	    // parse the received options
	    received_options.add(OptionList::parse_from_csv_static(msg.substr(11), &pushed_options_limit),
				 pushed_options_filter.get());
	    if (received_options.complete())
	      {
		// show options
		OPENVPN_LOG("OPTIONS:" << std::endl << render_options_sanitized(received_options, Option::RENDER_PASS_FMT|Option::RENDER_NUMBER|Option::RENDER_BRACKET));

		// relay servers are not allowed to establish a tunnel with us
		if (Base::conf().relay_mode)
		  {
		    tun_error(Error::RELAY_ERROR, "tunnel not permitted to relay server");
		    return;
		  }

		// process "echo" directives
		if (echo)
		  process_echo(received_options);

		// process auth-token
		extract_auth_token(received_options);

		// modify proto config (cipher, auth, and compression methods)
		Base::process_push(received_options, *proto_context_options);

		// initialize tun/routing
		tun = tun_factory->new_tun_client_obj(io_context, *this, transport.get());
		tun->tun_start(received_options, *transport, Base::dc_settings());

		// we should be connected at this point
		if (!connected_)
		  throw tun_exception("not connected");

		// initialize data channel after pushed options have been processed
		Base::init_data_channel();

		// Allow ProtoContext to suggest an alignment adjustment
		// hint for transport layer.
		transport->reset_align_adjust(Base::align_adjust_hint());

		// process "inactive" directive
		process_inactive(received_options);

		// tell parent that we are connected
		if (notify_callback)
		  notify_callback->client_proto_connected();

		// start info-hold timer
		schedule_info_hold_callback();

		// send the Connected event
		cli_events->add_event(connected_);

		// Issue an event if compression is enabled
		CompressContext::Type comp_type = Base::conf().comp_ctx.type();
		if (comp_type != CompressContext::NONE
		    && !CompressContext::is_any_stub(comp_type))
		{
		  std::ostringstream msg;
		  msg << (proto_context_options->is_comp_asym()
			  ? "Asymmetric compression enabled.  Server may send compressed data."
			  : "Compression enabled.");
		  msg << "  This may be a potential security issue.";
		  ClientEvent::Base::Ptr ev = new ClientEvent::CompressionEnabled(msg.str());
		  cli_events->add_event(std::move(ev));
		}
	      }
	    else
	      OPENVPN_LOG("Options continuation...");
	  }
	else if (received_options.complete() && string::starts_with(msg, "PUSH_REPLY,"))
	{
	  // We got a PUSH REPLY in the middle of a session. Ignore it apart from
	  // updating the auth-token if included in the push reply
	  auto opts = OptionList::parse_from_csv_static(msg.substr(11), nullptr);
	  extract_auth_token(opts);
	}
	else if (string::starts_with(msg, "AUTH_FAILED"))
	  {
	    std::string reason;
	    std::string log_reason;

	    // get reason (if it exists) for authentication failure
	    if (msg.length() >= 13)
	      reason = string::trim_left_copy(std::string(msg, 12));

	    // If session token problem (such as expiration), and we have a cached
	    // password, retry with it.  Otherwise, fail without retry.
	    if (string::starts_with(reason, "SESSION:")
		&& (autologin_sessions
		    || (creds && creds->can_retry_auth_with_cached_password())))
	      {
		log_reason = "SESSION_AUTH_FAILED";
	      }
	    else
	      {
		fatal_ = Error::AUTH_FAILED;
		fatal_reason_ = reason;
		log_reason = "AUTH_FAILED";
	      }
	    if (notify_callback)
	      {
		OPENVPN_LOG(log_reason);
		stop(true);
	      }
	    else
	      throw authentication_failed();
	  }
	else if (ClientHalt::match(msg))
	  {
	    const ClientHalt ch(msg, true);
	    process_halt_restart(ch);
	  }
	else if (info && string::starts_with(msg, "INFO,"))
	  {
	    // Buffer INFO messages received near Connected event to fire
	    // one second after Connected event, to reduce the chance of
	    // race conditions in the client app, if the INFO event
	    // triggers the client app to perform an operation that
	    // requires the VPN tunnel to be ready.
	    ClientEvent::Base::Ptr ev = new ClientEvent::Info(msg.substr(5));
	    if (info_hold)
	      info_hold->push_back(std::move(ev));
	    else
	      cli_events->add_event(std::move(ev));
	  }
	else if (info && string::starts_with(msg, "INFO_PRE,"))
	  {
	    // INFO_PRE is like INFO but it is never buffered
	    ClientEvent::Base::Ptr ev = new ClientEvent::Info(msg.substr(9));
	    cli_events->add_event(std::move(ev));
	  }
	else if (msg == "AUTH_PENDING")
	  {
	    // AUTH_PENDING indicates an out-of-band authentication step must
	    // be performed before the server will send the PUSH_REPLY message.
	    if (!auth_pending)
	      {
		auth_pending = true;
		ClientEvent::Base::Ptr ev = new ClientEvent::AuthPending();
		cli_events->add_event(std::move(ev));
	      }
	  }
	else if (msg == "RELAY")
	  {
	    if (Base::conf().relay_mode)
	      {
		fatal_ = Error::RELAY;
		fatal_reason_ = "";
	      }
	    else
	      {
		fatal_ = Error::RELAY_ERROR;
		fatal_reason_ = "not in relay mode";
	      }
	    if (notify_callback)
	      {
		OPENVPN_LOG(Error::name(fatal_) << ' ' << fatal_reason_);
		stop(true);
	      }
	    else
	      throw relay_event();
	  }
      }

      virtual void tun_pre_tun_config()
      {
	ClientEvent::Base::Ptr ev = new ClientEvent::AssignIP();
	cli_events->add_event(std::move(ev));
      }

      virtual void tun_pre_route_config()
      {
	ClientEvent::Base::Ptr ev = new ClientEvent::AddRoutes();
	cli_events->add_event(std::move(ev));
      }

      virtual void tun_connected()
      {
	OPENVPN_LOG("Connected via " + tun->tun_name());

	ClientEvent::Connected::Ptr ev = new ClientEvent::Connected();
	if (creds)
	  ev->user = creds->get_username();
	transport->server_endpoint_info(ev->server_host, ev->server_port, ev->server_proto, ev->server_ip);
	ev->vpn_ip4 = tun->vpn_ip4();
	ev->vpn_ip6 = tun->vpn_ip6();
	ev->vpn_gw4 = tun->vpn_gw4();
	ev->vpn_gw6 = tun->vpn_gw6();
	try {
	  std::string client_ip = received_options.get_optional("client-ip", 1, 256);
	  if (!client_ip.empty())
	    ev->client_ip = IP::Addr::validate(client_ip, "client-ip");
	}
	catch (const std::exception& e)
	  {
	    OPENVPN_LOG("exception parsing client-ip: " << e.what());
	  }
	ev->tun_name = tun->tun_name();
	connected_ = std::move(ev);
      }

      virtual void tun_error(const Error::Type fatal_err, const std::string& err_text)
      {
	if (fatal_err == Error::TUN_HALT)
	  send_explicit_exit_notify();
	if (fatal_err != Error::UNDEF)
	  {
	    fatal_ = fatal_err;
	    fatal_reason_ = err_text;
	  }
	if (notify_callback)
	  {
	    OPENVPN_LOG("TUN Error: " << err_text);
	    stop(true);
	  }
	else
	  throw tun_exception(err_text);
      }

      // proto base class calls here to get auth credentials
      virtual void client_auth(Buffer& buf)
      {
	// we never send creds to a relay server
	if (creds && !Base::conf().relay_mode)
	  {
	    OPENVPN_LOG("Creds: " << creds->auth_info());
	    Base::write_auth_string(creds->get_username(), buf);
	    Base::write_auth_string(creds->get_password(), buf);
	  }
	else
	  {
	    OPENVPN_LOG("Creds: None");
	    Base::write_empty_string(buf); // username
	    Base::write_empty_string(buf); // password
	  }
      }

      void send_push_request_callback(const Time::Duration& dur,
				      const openvpn_io::error_code& e)
      {
	try {
	  if (!e && !halt && !received_options.partial())
	    {
	      Base::update_now();
	      if (!sent_push_request)
		{
		  ClientEvent::Base::Ptr ev = new ClientEvent::GetConfig();
		  cli_events->add_event(std::move(ev));
		  sent_push_request = true;
		}
	      OPENVPN_LOG("Sending PUSH_REQUEST to server...");
	      Base::write_control_string(std::string("PUSH_REQUEST"));
	      Base::flush(true);
	      set_housekeeping_timer();

	      {
		if (auth_pending)
		  {
		    // With auth_pending, we can dial back the PUSH_REQUEST
		    // frequency, but we still need back-and-forth network
		    // activity to avoid an inactivity timeout, since the crypto
		    // layer (and hence keepalive ping) is not initialized until
		    // we receive the PUSH_REPLY from the server.
		    schedule_push_request_callback(Time::Duration::seconds(8));
		  }
		else
		  {
		    // step function with ceiling: 1 sec, 2 secs, 3 secs, 3, 3, ...
		    const Time::Duration newdur = std::min(dur + Time::Duration::seconds(1),
							   Time::Duration::seconds(3));
		    schedule_push_request_callback(newdur);
		  }
	      }
	    }
	}
	catch (const std::exception& e)
	  {
	    process_exception(e, "send_push_request_callback");
	  }
      }

      void schedule_push_request_callback(const Time::Duration& dur)
      {
	if (!received_options.partial())
	  {
	    push_request_timer.expires_after(dur);
	    push_request_timer.async_wait([self=Ptr(this), dur](const openvpn_io::error_code& error)
                                          {
                                            OPENVPN_ASYNC_HANDLER;
                                            self->send_push_request_callback(dur, error);
                                          });
	  }
      }

      // react to any tls warning triggered during the tls-handshake
      virtual void check_tls_warnings()
      {
	uint32_t tls_warnings = get_tls_warnings();

	if (tls_warnings & SSLAPI::TLS_WARN_SIG_MD5)
	  {
	    ClientEvent::Base::Ptr ev = new ClientEvent::Warn("TLS: received certificate signed with MD5. Please inform your admin to upgrade to a stronger algorithm. Support for MD5 will be dropped at end of Apr 2018");
	    cli_events->add_event(std::move(ev));
	  }

	if (tls_warnings & SSLAPI::TLS_WARN_NAME_CONSTRAINTS)
	  {
	    ClientEvent::Base::Ptr ev = new ClientEvent::Warn("TLS: Your CA contains a 'x509v3 Name Constraints' extension, but its validation is not supported. This might be a security breach, please contact your administrator.");
	    cli_events->add_event(std::move(ev));
	  }
      }

      // base class calls here when primary session transitions to ACTIVE state
      virtual void active()
      {
	OPENVPN_LOG("Session is ACTIVE");
	check_tls_warnings();
	schedule_push_request_callback(Time::Duration::seconds(0));
      }

      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())
		{
		  if (notify_callback)
		    {
		      OPENVPN_LOG("Session invalidated: " << Error::name(Base::invalidation_reason()));
		      stop(true);
		    }
		  else
		    throw session_invalidated();
		}
	      set_housekeeping_timer();
	    }
	}
	catch (const std::exception& e)
	  {
	    process_exception(e, "housekeeping_callback");
	  }
      }

      void set_housekeeping_timer()
      {
	if (halt)
	  return;

	Time next = Base::next_housekeeping();
	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)
                                              {
                                                OPENVPN_ASYNC_HANDLER;
                                                self->housekeeping_callback(error);
                                              });
	      }
	    else
	      {
		housekeeping_timer.cancel();
		housekeeping_schedule.reset();
	      }
	  }
      }

      void process_inactive(const OptionList& opt)
      {
	try {
	  const Option *o = load_duration_parm(inactive_duration, "inactive", opt, 1, false, false);
	  if (o)
	    {
	      if (o->size() >= 3)
		inactive_bytes = parse_number_throw<unsigned int>(o->get(2, 16), "inactive bytes");
	      schedule_inactive_timer();
	    }
	}
	catch (const std::exception& e)
	  {
	    OPENVPN_LOG("exception parsing inactive: " << e.what());
	  }
      }

      void schedule_inactive_timer()
      {
	inactive_timer.expires_after(inactive_duration);
	inactive_timer.async_wait([self=Ptr(this)](const openvpn_io::error_code& error)
                                  {
                                    OPENVPN_ASYNC_HANDLER;
                                    self->inactive_callback(error);
                                  });
      }

      void inactive_callback(const openvpn_io::error_code& e) // fixme for DCO
      {
	try {
	  if (!e && !halt)
	    {
	      // update current time
	      Base::update_now();
	      const count_t sample = cli_stats->get_stat(SessionStats::TUN_BYTES_IN) + cli_stats->get_stat(SessionStats::TUN_BYTES_OUT);
	      const count_t delta = sample - inactive_last_sample;
	      //OPENVPN_LOG("*** INACTIVE SAMPLE " << delta << ' ' << inactive_bytes);
	      if (delta <= count_t(inactive_bytes))
		{
		  fatal_ = Error::INACTIVE_TIMEOUT;
		  send_explicit_exit_notify();
		  if (notify_callback)
		    {
		      OPENVPN_LOG("inactive timer expired");
		      stop(true);
		    }
		  else
		    throw inactive_timer_expired();
		}
	      else
		{
		  inactive_last_sample = sample;
		  schedule_inactive_timer();
		}
	    }
	}
	catch (const std::exception& e)
	  {
	    process_exception(e, "inactive_callback");
	  }
      }

      void process_echo(const OptionList& opt)
      {
	OptionList::IndexMap::const_iterator echo_opt = opt.map().find("echo");
	if (echo_opt != opt.map().end())
	  {
	    for (OptionList::IndexList::const_iterator i = echo_opt->second.begin(); i != echo_opt->second.end(); ++i)
	      {
		const Option& o = opt[*i];
		o.touch();
		const std::string& value = o.get(1, 512);
		ClientEvent::Base::Ptr ev = new ClientEvent::Echo(value);
		cli_events->add_event(std::move(ev));
	      }
	  }
      }

      void process_exception(const std::exception& e, const char *method_name)
      {
	if (notify_callback)
	  {
	    OPENVPN_LOG("Client exception in " << method_name << ": " << e.what());
	    stop(true);
	  }
	else
	  throw client_exception(e.what());
      }

      void process_halt_restart(const ClientHalt& ch)
      {
	if (!ch.psid() && creds)
	  creds->purge_session_id();
	if (ch.restart())
	  fatal_ = Error::CLIENT_RESTART;
	else
	  fatal_ = Error::CLIENT_HALT;
	fatal_reason_ = ch.reason();
	if (notify_callback)
	  {
	    OPENVPN_LOG("Client halt/restart: " << ch.render());
	    stop(true);
	  }
	else
	  throw client_halt_restart(ch.render());
      }

      void schedule_info_hold_callback()
      {
	Base::update_now();
	info_hold_timer.expires_after(Time::Duration::seconds(1));
	info_hold_timer.async_wait([self=Ptr(this)](const openvpn_io::error_code& error)
                                  {
                                    OPENVPN_ASYNC_HANDLER;
                                    self->info_hold_callback(error);
                                  });
      }

      void info_hold_callback(const openvpn_io::error_code& e)
      {
	try {
	  if (!e && !halt)
	    {
	      Base::update_now();
	      if (info_hold)
		{
		  for (auto &ev : *info_hold)
		    cli_events->add_event(std::move(ev));
		  info_hold.reset();
		}
	    }
	}
	catch (const std::exception& e)
	  {
	    process_exception(e, "info_hold_callback");
	  }
      }

#ifdef OPENVPN_PACKET_LOG
      void log_packet(const Buffer& buf, const bool out)
      {
	if (buf.size())
	  {
	    std::uint16_t len = buf.size() & 0x7FFF;
	    if (out)
	      len |= 0x8000;
	    packet_log.write((const char *)&len, sizeof(len));
	    packet_log.write((const char *)buf.c_data(), buf.size());
	  }
      }
#endif

      openvpn_io::io_context& io_context;

      TransportClientFactory::Ptr transport_factory;
      TransportClient::Ptr transport;

      TunClientFactory::Ptr tun_factory;
      TunClient::Ptr tun;

      unsigned int tcp_queue_limit;
      bool transport_has_send_queue = false;

      NotifyCallback* notify_callback;

      CoarseTime housekeeping_schedule;
      AsioTimer housekeeping_timer;
      AsioTimer push_request_timer;
      bool halt = false;

      OptionListContinuation received_options;

      ClientCreds::Ptr creds;

      ProtoContextOptions::Ptr proto_context_options;

      bool first_packet_received_ = false;
      bool sent_push_request = false;
      bool auth_pending = false;

      SessionStats::Ptr cli_stats;
      ClientEvent::Queue::Ptr cli_events;

      ClientEvent::Connected::Ptr connected_;

      bool echo;
      bool info;
      bool autologin_sessions;

      Error::Type fatal_ = Error::UNDEF;
      std::string fatal_reason_;

      OptionList::Limits pushed_options_limit;
      OptionList::FilterBase::Ptr pushed_options_filter;

      AsioTimer inactive_timer;
      Time::Duration inactive_duration;
      unsigned int inactive_bytes = 0;
      count_t inactive_last_sample = 0;

      std::unique_ptr<std::vector<ClientEvent::Base::Ptr>> info_hold;
      AsioTimer info_hold_timer;

#ifdef OPENVPN_PACKET_LOG
      std::ofstream packet_log;
#endif
    };
  }
}

#endif