/*
  This file is part of GNUnet.
  Copyright (C) 2013, 2016 GNUnet e.V.

  GNUnet is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published
  by the Free Software Foundation; either version 3, or (at your
  option) any later version.

  GNUnet 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
  General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with GNUnet; see the file COPYING.  If not, write to the
  Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  Boston, MA 02110-1301, USA.
*/
/**
 * @file conversation/gnunet-service-conversation.c
 * @brief conversation service implementation
 * @author Simon Dieterle
 * @author Andreas Fuchs
 * @author Christian Grothoff
 */
#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_protocols.h"
#include "gnunet_applications.h"
#include "gnunet_constants.h"
#include "gnunet_signatures.h"
#include "gnunet_cadet_service.h"
#include "gnunet_conversation_service.h"
#include "conversation.h"


/**
 * How long is our signature on a call valid?  Needs to be long enough for time zone
 * differences and network latency to not matter.  No strong need for it to be short,
 * but we simply like all signatures to eventually expire.
 */
#define RING_TIMEOUT GNUNET_TIME_UNIT_DAYS


/**
 * A line connects a local client with a cadet channel (or, if it is an
 * open line, is waiting for a cadet channel).
 */
struct Line;

/**
 * The possible connection status
 */
enum ChannelStatus
{
  /**
   * We just got the connection, but no introduction yet.
   */
  CS_CALLEE_INIT,

  /**
   * Our phone is ringing, waiting for the client to pick up.
   */
  CS_CALLEE_RINGING,

  /**
   * We are talking!
   */
  CS_CALLEE_CONNECTED,

  /**
   * We're in shutdown, sending hangup messages before cleaning up.
   */
  CS_CALLEE_SHUTDOWN,

  /**
   * We are waiting for the phone to be picked up.
   */
  CS_CALLER_CALLING,

  /**
   * We are talking!
   */
  CS_CALLER_CONNECTED,

  /**
   * We're in shutdown, sending hangup messages before cleaning up.
   */
  CS_CALLER_SHUTDOWN

};


/**
 * A `struct Channel` represents a cadet channel, which is a P2P
 * connection to another conversation service.  Multiple channels can
 * be attached the the same `struct Line`, which represents a local
 * client.  We keep them in a linked list.
 */
struct Channel
{

  /**
   * This is a DLL.
   */
  struct Channel *next;

  /**
   * This is a DLL.
   */
  struct Channel *prev;

  /**
   * Line associated with the channel.
   */
  struct Line *line;

  /**
   * Handle for the channel.
   */
  struct GNUNET_CADET_Channel *channel;

  /**
   * Message queue for control messages
   */
  struct GNUNET_MQ_Handle *mq;

  /**
   * Temporary buffer for audio data in the @e mq.
   */
  struct GNUNET_MQ_Envelope *env;

  /**
   * Channel identifier we use for this call with the client.
   */
  uint32_t cid;

  /**
   * Current status of this line.
   */
  enum ChannelStatus status;

  /**
   * #GNUNET_YES if the channel was suspended by the other peer.
   */
  int8_t suspended_remote;

  /**
   * #GNUNET_YES if the channel was suspended by the local client.
   */
  int8_t suspended_local;

};


/**
 * A `struct Line` connects a local client with cadet channels.
 */
struct Line
{
  /**
   * This is a DLL.
   */
  struct Channel *channel_head;

  /**
   * This is a DLL.
   */
  struct Channel *channel_tail;

  /**
   * Handle to the line client.
   */
  struct GNUNET_SERVER_Client *client;

  /**
   * Our open port.
   */
  struct GNUNET_CADET_Port *port;

  /**
   * Port number we are listening on (to verify signatures).
   * Only valid if @e port is non-NULL.
   */
  struct GNUNET_HashCode line_port;

  /**
   * Generator for channel IDs.
   */
  uint32_t cid_gen;

};


/**
 * Our configuration.
 */
static const struct GNUNET_CONFIGURATION_Handle *cfg;

/**
 * Notification context containing all connected clients.
 */
static struct GNUNET_SERVER_NotificationContext *nc;

/**
 * Handle for cadet
 */
static struct GNUNET_CADET_Handle *cadet;

/**
 * Identity of this peer.
 */
static struct GNUNET_PeerIdentity my_identity;


/**
 * Given a @a cid, find the corresponding channel given
 * a @a line.
 *
 * @param line a line to search
 * @param cid what to search for
 * @return NULL for not found
 */
static struct Channel *
find_channel_by_line (struct Line *line,
                      uint32_t cid)
{
  struct Channel *ch;

  for (ch = line->channel_head; NULL != ch; ch = ch->next)
    if (cid == ch->cid)
      return ch;
  return NULL;
}


/**
 * Function to handle a pickup request message from the client
 *
 * @param cls closure, NULL
 * @param client the client from which the message is
 * @param message the message from the client
 */
static void
handle_client_pickup_message (void *cls,
                              struct GNUNET_SERVER_Client *client,
                              const struct GNUNET_MessageHeader *message)
{
  const struct ClientPhonePickupMessage *msg;
  struct GNUNET_MQ_Envelope *e;
  struct CadetPhonePickupMessage *mppm;
  struct Line *line;
  struct Channel *ch;

  msg = (const struct ClientPhonePickupMessage *) message;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL == line)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    return;
  }
  for (ch = line->channel_head; NULL != ch; ch = ch->next)
    if (msg->cid == ch->cid)
      break;
  if (NULL == ch)
  {
    /* could have been destroyed asynchronously, ignore message */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Channel %u not found\n",
                msg->cid);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_YES);
    return;
  }
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_RINGING:
    ch->status = CS_CALLEE_CONNECTED;
    break;
  case CS_CALLEE_CONNECTED:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_SHUTDOWN:
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Ignoring client's PICKUP message, line is in SHUTDOWN\n");
    break;
  case CS_CALLER_CALLING:
  case CS_CALLER_CONNECTED:
  case CS_CALLER_SHUTDOWN:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    return;
  }
  GNUNET_break (CS_CALLEE_CONNECTED == ch->status);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending PICK_UP message to cadet\n");
  e = GNUNET_MQ_msg (mppm,
                     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_PICK_UP);
  GNUNET_MQ_send (ch->mq, e);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Destroy a channel.
 *
 * @param ch channel to destroy.
 */
static void
destroy_line_cadet_channels (struct Channel *ch)
{
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Destroying cadet channels\n");
  if (NULL != ch->mq)
  {
    GNUNET_MQ_destroy (ch->mq);
    ch->mq = NULL;
  }
  if (NULL != ch->channel)
    GNUNET_CADET_channel_destroy (ch->channel);
}


/**
 * We are done signalling shutdown to the other peer.  Close down
 * the channel.
 *
 * @param cls the `struct Channel` to reset/terminate
 */
static void
mq_done_finish_caller_shutdown (void *cls)
{
  struct Channel *ch = cls;

  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break (0);
    break;
  case CS_CALLEE_RINGING:
    GNUNET_break (0);
    break;
  case CS_CALLEE_CONNECTED:
    GNUNET_break (0);
    break;
  case CS_CALLEE_SHUTDOWN:
    destroy_line_cadet_channels (ch);
    break;
  case CS_CALLER_CALLING:
    GNUNET_break (0);
    break;
  case CS_CALLER_CONNECTED:
    GNUNET_break (0);
    break;
  case CS_CALLER_SHUTDOWN:
    destroy_line_cadet_channels (ch);
    break;
  }
}


/**
 * Function to handle a hangup request message from the client
 *
 * @param cls closure, NULL
 * @param client the client from which the message is
 * @param message the message from the client
 */
static void
handle_client_hangup_message (void *cls,
                              struct GNUNET_SERVER_Client *client,
                              const struct GNUNET_MessageHeader *message)
{
  const struct ClientPhoneHangupMessage *msg;
  struct GNUNET_MQ_Envelope *e;
  struct CadetPhoneHangupMessage *mhum;
  struct Line *line;
  struct Channel *ch;

  msg = (const struct ClientPhoneHangupMessage *) message;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL == line)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  for (ch = line->channel_head; NULL != ch; ch = ch->next)
    if (msg->cid == ch->cid)
      break;
  if (NULL == ch)
  {
    /* could have been destroyed asynchronously, ignore message */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Channel %u not found\n",
                msg->cid);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received HANGUP for channel %u which is in state %d\n",
              msg->cid,
              ch->status);
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_RINGING:
    ch->status = CS_CALLEE_SHUTDOWN;
    break;
  case CS_CALLEE_CONNECTED:
    ch->status = CS_CALLEE_SHUTDOWN;
    break;
  case CS_CALLEE_SHUTDOWN:
    /* maybe the other peer closed asynchronously... */
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  case CS_CALLER_CALLING:
    ch->status = CS_CALLER_SHUTDOWN;
    break;
  case CS_CALLER_CONNECTED:
    ch->status = CS_CALLER_SHUTDOWN;
    break;
  case CS_CALLER_SHUTDOWN:
    /* maybe the other peer closed asynchronously... */
    GNUNET_SERVER_receive_done (client, GNUNET_OK);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending HANG_UP message via cadet\n");
  e = GNUNET_MQ_msg (mhum,
                     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_HANG_UP);
  GNUNET_MQ_notify_sent (e,
                         &mq_done_finish_caller_shutdown,
                         ch);
  GNUNET_MQ_send (ch->mq,
                  e);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Function to handle a suspend request message from the client
 *
 * @param cls closure, NULL
 * @param client the client from which the message is
 * @param message the message from the client
 */
static void
handle_client_suspend_message (void *cls,
                               struct GNUNET_SERVER_Client *client,
                               const struct GNUNET_MessageHeader *message)
{
  const struct ClientPhoneSuspendMessage *msg;
  struct GNUNET_MQ_Envelope *e;
  struct CadetPhoneSuspendMessage *mhum;
  struct Line *line;
  struct Channel *ch;

  msg = (const struct ClientPhoneSuspendMessage *) message;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL == line)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  for (ch = line->channel_head; NULL != ch; ch = ch->next)
    if (msg->cid == ch->cid)
      break;
  if (NULL == ch)
  {
    /* could have been destroyed asynchronously, ignore message */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Channel %u not found\n",
                msg->cid);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  }
  if (GNUNET_YES == ch->suspended_local)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received SUSPEND for channel %u which is in state %d\n",
              msg->cid,
              ch->status);
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_RINGING:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_CONNECTED:
    ch->suspended_local = GNUNET_YES;
    break;
  case CS_CALLEE_SHUTDOWN:
    /* maybe the other peer closed asynchronously... */
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  case CS_CALLER_CALLING:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLER_CONNECTED:
    ch->suspended_local = GNUNET_YES;
    break;
  case CS_CALLER_SHUTDOWN:
    /* maybe the other peer closed asynchronously... */
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending SUSPEND message via cadet\n");
  e = GNUNET_MQ_msg (mhum,
                     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_SUSPEND);
  GNUNET_MQ_send (ch->mq,
                  e);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Function to handle a resume request message from the client
 *
 * @param cls closure, NULL
 * @param client the client from which the message is
 * @param message the message from the client
 */
static void
handle_client_resume_message (void *cls,
                              struct GNUNET_SERVER_Client *client,
                              const struct GNUNET_MessageHeader *message)
{
  const struct ClientPhoneResumeMessage *msg;
  struct GNUNET_MQ_Envelope *e;
  struct CadetPhoneResumeMessage *mhum;
  struct Line *line;
  struct Channel *ch;

  msg = (const struct ClientPhoneResumeMessage *) message;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL == line)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  for (ch = line->channel_head; NULL != ch; ch = ch->next)
    if (msg->cid == ch->cid)
      break;
  if (NULL == ch)
  {
    /* could have been destroyed asynchronously, ignore message */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Channel %u not found\n",
                msg->cid);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  }
  if (GNUNET_YES != ch->suspended_local)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received RESUME for channel %u which is in state %d\n",
              msg->cid,
              ch->status);
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_RINGING:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_CONNECTED:
    ch->suspended_local = GNUNET_NO;
    break;
  case CS_CALLEE_SHUTDOWN:
    /* maybe the other peer closed asynchronously... */
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  case CS_CALLER_CALLING:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLER_CONNECTED:
    ch->suspended_local = GNUNET_NO;
    break;
  case CS_CALLER_SHUTDOWN:
    /* maybe the other peer closed asynchronously... */
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending RESUME message via cadet\n");
  e = GNUNET_MQ_msg (mhum,
                     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_RESUME);
  GNUNET_MQ_send (ch->mq,
                  e);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Function to handle call request from the client
 *
 * @param cls closure, NULL
 * @param client the client from which the message is
 * @param message the message from the client
 */
static void
handle_client_call_message (void *cls,
                            struct GNUNET_SERVER_Client *client,
                            const struct GNUNET_MessageHeader *message)
{
  const struct ClientCallMessage *msg;
  struct Line *line;
  struct Channel *ch;
  struct GNUNET_MQ_Envelope *e;
  struct CadetPhoneRingMessage *ring;
  struct CadetPhoneRingInfoPS rs;

  msg = (const struct ClientCallMessage *) message;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL != line)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
    return;
  }
  line = GNUNET_new (struct Line);
  line->client = client;
  line->line_port = msg->line_port;
  GNUNET_SERVER_client_set_user_context (client,
                                         line);
  GNUNET_SERVER_notification_context_add (nc,
                                          client);
  rs.purpose.purpose = htonl (GNUNET_SIGNATURE_PURPOSE_CONVERSATION_RING);
  rs.purpose.size = htonl (sizeof (struct CadetPhoneRingInfoPS));
  rs.line_port = line->line_port;
  rs.target_peer = msg->target;
  rs.expiration_time
    = GNUNET_TIME_absolute_hton (GNUNET_TIME_relative_to_absolute (RING_TIMEOUT));

  ch = GNUNET_new (struct Channel);
  ch->line = line;
  GNUNET_CONTAINER_DLL_insert (line->channel_head,
                               line->channel_tail,
                               ch);
  ch->status = CS_CALLER_CALLING;
  ch->channel = GNUNET_CADET_channel_create (cadet,
                                             ch,
                                             &msg->target,
                                             &msg->line_port,
                                             GNUNET_CADET_OPTION_RELIABLE);
  ch->mq = GNUNET_CADET_mq_create (ch->channel);
  e = GNUNET_MQ_msg (ring,
                     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_RING);
  GNUNET_CRYPTO_ecdsa_key_get_public (&msg->caller_id,
                                      &ring->caller_id);
  ring->expiration_time = rs.expiration_time;
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CRYPTO_ecdsa_sign (&msg->caller_id,
                                           &rs.purpose,
                                           &ring->signature));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending RING message via CADET\n");
  GNUNET_MQ_send (ch->mq,
                  e);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Transmission of audio data via cadet channel finished.
 *
 * @param cls the `struct Channel` we are transmitting for
 */
static void
channel_audio_sent_notify (void *cls)
{
  struct Channel *ch = cls;

  ch->env = NULL;
}


/**
 * Function to handle audio data from the client
 *
 * @param cls closure, NULL
 * @param client the client from which the message is
 * @param message the message from the client
 */
static void
handle_client_audio_message (void *cls,
                             struct GNUNET_SERVER_Client *client,
                             const struct GNUNET_MessageHeader *message)
{
  const struct ClientAudioMessage *msg;
  struct ClientAudioMessage *mam;
  struct Line *line;
  struct Channel *ch;
  size_t size;

  size = ntohs (message->size) - sizeof (struct ClientAudioMessage);
  msg = (const struct ClientAudioMessage *) message;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL == line)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  ch = find_channel_by_line (line,
                             msg->cid);
  if (NULL == ch)
  {
    /* could have been destroyed asynchronously, ignore message */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Channel %u not found\n",
                msg->cid);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  }

  switch (ch->status)
  {
  case CS_CALLEE_INIT:
  case CS_CALLEE_RINGING:
  case CS_CALLER_CALLING:
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  case CS_CALLEE_CONNECTED:
  case CS_CALLER_CONNECTED:
    /* common case, handled below */
    break;
  case CS_CALLEE_SHUTDOWN:
  case CS_CALLER_SHUTDOWN:
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
                "Cadet audio channel in shutdown; audio data dropped\n");
    GNUNET_SERVER_receive_done (client,
                                GNUNET_OK);
    return;
  }
  if (GNUNET_YES == ch->suspended_local)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "This channel is suspended locally\n");
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  if (NULL != ch->env)
  {
    /* NOTE: we may want to not do this and instead combine the data */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Bandwidth insufficient; dropping previous audio data segment\n");
    GNUNET_MQ_send_cancel (ch->env);
    ch->env = NULL;
  }

  ch->env = GNUNET_MQ_msg_extra (mam,
                                 size,
                                 GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_AUDIO);
  GNUNET_memcpy (&mam[1],
                 &msg[1],
                 size);
  /* FIXME: set options for unreliable transmission */
  GNUNET_MQ_notify_sent (ch->env,
                         &channel_audio_sent_notify,
                         ch);
  GNUNET_MQ_send (ch->mq,
                  ch->env);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Function to handle a ring message incoming over cadet
 *
 * @param cls closure, NULL
 * @param channel the channel over which the message arrived
 * @param channel_ctx the channel context, can be NULL
 *                    or point to the `struct Channel`
 * @param message the incoming message
 * @return #GNUNET_OK
 */
static int
handle_cadet_ring_message (void *cls,
                           struct GNUNET_CADET_Channel *channel,
                           void **channel_ctx,
                           const struct GNUNET_MessageHeader *message)
{
  struct Channel *ch = *channel_ctx;
  struct Line *line = ch->line;
  const struct CadetPhoneRingMessage *msg;
  struct ClientPhoneRingMessage cring;
  struct CadetPhoneRingInfoPS rs;

  msg = (const struct CadetPhoneRingMessage *) message;
  rs.purpose.purpose = htonl (GNUNET_SIGNATURE_PURPOSE_CONVERSATION_RING);
  rs.purpose.size = htonl (sizeof (struct CadetPhoneRingInfoPS));
  rs.line_port = line->line_port;
  rs.target_peer = my_identity;
  rs.expiration_time = msg->expiration_time;

  if (GNUNET_OK !=
      GNUNET_CRYPTO_ecdsa_verify (GNUNET_SIGNATURE_PURPOSE_CONVERSATION_RING,
                                  &rs.purpose,
                                  &msg->signature,
                                  &msg->caller_id))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (0 == GNUNET_TIME_absolute_get_remaining (GNUNET_TIME_absolute_ntoh (msg->expiration_time)).rel_value_us)
  {
    /* ancient call, replay? */
    GNUNET_break_op (0);
    /* Note that our reliance on time here is awkward; better would be
       to use a more complex challenge-response protocol against
       replay attacks.  Left for future work ;-). */
    return GNUNET_SYSERR;
  }
  if (CS_CALLEE_INIT != ch->status)
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  GNUNET_CADET_receive_done (channel);
  ch->status = CS_CALLEE_RINGING;
  cring.header.type = htons (GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_RING);
  cring.header.size = htons (sizeof (cring));
  cring.cid = ch->cid;
  cring.caller_id = msg->caller_id;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending RING message to client. CID is %u\n",
              (unsigned int) ch->cid);
  GNUNET_SERVER_notification_context_unicast (nc,
                                              line->client,
                                              &cring.header,
                                              GNUNET_NO);
  return GNUNET_OK;
}


/**
 * Function to handle a hangup message incoming over cadet
 *
 * @param cls closure, NULL
 * @param channel the channel over which the message arrived
 * @param channel_ctx the channel context, can be NULL
 *                    or point to the `struct Channel`
 * @param message the incoming message
 * @return #GNUNET_OK
 */
static int
handle_cadet_hangup_message (void *cls,
                             struct GNUNET_CADET_Channel *channel,
                             void **channel_ctx,
                             const struct GNUNET_MessageHeader *message)
{
  struct Channel *ch = *channel_ctx;
  struct Line *line = ch->line;
  struct ClientPhoneHangupMessage hup;
  enum ChannelStatus status;

  GNUNET_CADET_receive_done (channel);
  hup.header.size = htons (sizeof (hup));
  hup.header.type = htons (GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_HANG_UP);
  hup.cid = ch->cid;
  status = ch->status;
  destroy_line_cadet_channels (ch);
  switch (status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break_op (0);
    return GNUNET_OK;
  case CS_CALLEE_RINGING:
  case CS_CALLEE_CONNECTED:
    break;
  case CS_CALLEE_SHUTDOWN:
    return GNUNET_OK;
  case CS_CALLER_CALLING:
  case CS_CALLER_CONNECTED:
    break;
  case CS_CALLER_SHUTDOWN:
    return GNUNET_OK;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending HANG UP message to client\n");
  GNUNET_SERVER_notification_context_unicast (nc,
                                              line->client,
                                              &hup.header,
                                              GNUNET_NO);
  return GNUNET_OK;
}


/**
 * Function to handle a pickup message incoming over cadet
 *
 * @param cls closure, NULL
 * @param channel the channel over which the message arrived
 * @param channel_ctx the channel context, can be NULL
 *                    or point to the `struct Channel`
 * @param message the incoming message
 * @return #GNUNET_OK if message was OK,
 *         #GNUNET_SYSERR if message violated the protocol
 */
static int
handle_cadet_pickup_message (void *cls,
                             struct GNUNET_CADET_Channel *channel,
                             void **channel_ctx,
                             const struct GNUNET_MessageHeader *message)
{
  struct Channel *ch = *channel_ctx;
  struct Line *line = ch->line;
  struct ClientPhonePickedupMessage pick;

  GNUNET_CADET_receive_done (channel);
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
  case CS_CALLEE_RINGING:
  case CS_CALLEE_CONNECTED:
    GNUNET_break_op (0);
    destroy_line_cadet_channels (ch);
    return GNUNET_SYSERR;
  case CS_CALLEE_SHUTDOWN:
    GNUNET_break_op (0);
    destroy_line_cadet_channels (ch);
    return GNUNET_SYSERR;
  case CS_CALLER_CALLING:
    ch->status = CS_CALLER_CONNECTED;
    break;
  case CS_CALLER_CONNECTED:
    GNUNET_break_op (0);
    return GNUNET_OK;
  case CS_CALLER_SHUTDOWN:
    GNUNET_break_op (0);
    mq_done_finish_caller_shutdown (ch);
    return GNUNET_SYSERR;
  }
  pick.header.size = htons (sizeof (pick));
  pick.header.type = htons (GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_PICKED_UP);
  pick.cid = ch->cid;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending PICKED UP message to client\n");
  GNUNET_SERVER_notification_context_unicast (nc,
                                              line->client,
                                              &pick.header,
                                              GNUNET_NO);
  return GNUNET_OK;
}


/**
 * Function to handle a suspend message incoming over cadet
 *
 * @param cls closure, NULL
 * @param channel the channel over which the message arrived
 * @param channel_ctx the channel context, can be NULL
 *                    or point to the `struct Channel`
 * @param message the incoming message
 * @return #GNUNET_OK
 */
static int
handle_cadet_suspend_message (void *cls,
                              struct GNUNET_CADET_Channel *channel,
                              void **channel_ctx,
                              const struct GNUNET_MessageHeader *message)
{
  struct Channel *ch = *channel_ctx;
  struct Line *line = ch->line;
  struct ClientPhoneSuspendMessage suspend;

  GNUNET_CADET_receive_done (channel);
  suspend.header.size = htons (sizeof (suspend));
  suspend.header.type = htons (GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_SUSPEND);
  suspend.cid = ch->cid;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Suspending channel CID: %u\n",
              ch->cid);
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break_op (0);
    break;
  case CS_CALLEE_RINGING:
    GNUNET_break_op (0);
    break;
  case CS_CALLEE_CONNECTED:
    ch->suspended_remote = GNUNET_YES;
    break;
  case CS_CALLEE_SHUTDOWN:
    return GNUNET_OK;
  case CS_CALLER_CALLING:
    GNUNET_break_op (0);
    break;
  case CS_CALLER_CONNECTED:
    ch->suspended_remote = GNUNET_YES;
    break;
  case CS_CALLER_SHUTDOWN:
    return GNUNET_OK;
  }
  GNUNET_SERVER_notification_context_unicast (nc,
                                              line->client,
                                              &suspend.header,
                                              GNUNET_NO);
  return GNUNET_OK;
}


/**
 * Function to handle a resume message incoming over cadet
 *
 * @param cls closure, NULL
 * @param channel the channel over which the message arrived
 * @param channel_ctx the channel context, can be NULL
 *                    or point to the `struct Channel`
 * @param message the incoming message
 * @return #GNUNET_OK
 */
static int
handle_cadet_resume_message (void *cls,
                             struct GNUNET_CADET_Channel *channel,
                             void **channel_ctx,
                             const struct GNUNET_MessageHeader *message)
{
  struct Channel *ch = *channel_ctx;
  struct Line *line;
  struct ClientPhoneResumeMessage resume;

  if (NULL == ch)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "RESUME message received for non-existing line, dropping channel.\n");
    return GNUNET_SYSERR;
  }
  line = ch->line;
  resume.header.size = htons (sizeof (resume));
  resume.header.type = htons (GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_RESUME);
  resume.cid = ch->cid;
  GNUNET_CADET_receive_done (channel);
  if (GNUNET_YES != ch->suspended_remote)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "RESUME message received for non-suspended channel, dropping channel.\n");
    return GNUNET_SYSERR;
  }
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    GNUNET_break (0);
    break;
  case CS_CALLEE_RINGING:
    GNUNET_break (0);
    break;
  case CS_CALLEE_CONNECTED:
    ch->suspended_remote = GNUNET_NO;
    break;
  case CS_CALLEE_SHUTDOWN:
    return GNUNET_OK;
  case CS_CALLER_CALLING:
    GNUNET_break (0);
    break;
  case CS_CALLER_CONNECTED:
    ch->suspended_remote = GNUNET_NO;
    break;
  case CS_CALLER_SHUTDOWN:
    return GNUNET_OK;
  }
  GNUNET_SERVER_notification_context_unicast (nc,
                                              line->client,
                                              &resume.header,
                                              GNUNET_NO);
  return GNUNET_OK;
}


/**
 * Function to handle an audio message incoming over cadet
 *
 * @param cls closure, NULL
 * @param channel the channel over which the message arrived
 * @param channel_ctx the channel context, can be NULL
 *                    or point to the `struct Channel`
 * @param message the incoming message
 * @return #GNUNET_OK
 */
static int
handle_cadet_audio_message (void *cls,
                            struct GNUNET_CADET_Channel *channel,
                            void **channel_ctx,
                            const struct GNUNET_MessageHeader *message)
{
  struct Channel *ch = *channel_ctx;
  const struct CadetAudioMessage *msg;
  size_t msize = ntohs (message->size) - sizeof (struct CadetAudioMessage);
  char buf[msize + sizeof (struct ClientAudioMessage)] GNUNET_ALIGN;
  struct ClientAudioMessage *cam;

  msg = (const struct CadetAudioMessage *) message;
  GNUNET_CADET_receive_done (channel);
  if ( (GNUNET_YES == ch->suspended_local) ||
       (GNUNET_YES == ch->suspended_remote) )
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Received %u bytes of AUDIO data on suspended channel CID %u; dropping\n",
                (unsigned int) msize,
                ch->cid);
    return GNUNET_OK;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Forwarding %u bytes of AUDIO data to client CID %u\n",
              (unsigned int) msize,
              ch->cid);
  cam = (struct ClientAudioMessage *) buf;
  cam->header.size = htons (sizeof (buf));
  cam->header.type = htons (GNUNET_MESSAGE_TYPE_CONVERSATION_CS_AUDIO);
  cam->cid = ch->cid;
  GNUNET_memcpy (&cam[1],
                 &msg[1],
                 msize);
  GNUNET_SERVER_notification_context_unicast (nc,
                                              ch->line->client,
                                              &cam->header,
                                              GNUNET_YES);
  return GNUNET_OK;
}


/**
 * Method called whenever another peer has added us to a channel
 * the other peer initiated.
 *
 * @param cls the `struct Line` receiving a connection
 * @param channel new handle to the channel
 * @param initiator peer that started the channel
 * @param port port
 * @param options channel option flags
 * @return initial channel context for the channel
 */
static void *
inbound_channel (void *cls,
                 struct GNUNET_CADET_Channel *channel,
                 const struct GNUNET_PeerIdentity *initiator,
                 const struct GNUNET_HashCode *port,
                 enum GNUNET_CADET_ChannelOption options)
{
  struct Line *line = cls;
  struct Channel *ch;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received incoming cadet channel on line %p\n",
              line);
  ch = GNUNET_new (struct Channel);
  ch->status = CS_CALLEE_INIT;
  ch->line = line;
  ch->channel = channel;
  ch->mq = GNUNET_CADET_mq_create (ch->channel);
  ch->cid = line->cid_gen++;
  GNUNET_CONTAINER_DLL_insert (line->channel_head,
                               line->channel_tail,
                               ch);
  return ch;
}


/**
 * Function called whenever an inbound channel is destroyed.  Should clean up
 * any associated state.
 *
 * @param cls closure (set from #GNUNET_CADET_connect)
 * @param channel connection to the other end (henceforth invalid)
 * @param channel_ctx place where local state associated
 *                   with the channel is stored;
 *                   may point to the `struct Channel`
 */
static void
inbound_end (void *cls,
             const struct GNUNET_CADET_Channel *channel,
	     void *channel_ctx)
{
  struct Channel *ch = channel_ctx;
  struct Line *line;
  struct ClientPhoneHangupMessage hup;

  if (NULL == ch)
  {
    GNUNET_break (0);
    return;
  }
  line = ch->line;
  GNUNET_assert (channel == ch->channel);
  ch->channel = NULL;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
	      "Channel destroyed by CADET in state %d\n",
              ch->status);
  hup.header.size = htons (sizeof (hup));
  hup.header.type = htons (GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_HANG_UP);
  hup.cid = ch->cid;
  switch (ch->status)
  {
  case CS_CALLEE_INIT:
    break;
  case CS_CALLEE_RINGING:
  case CS_CALLEE_CONNECTED:
    if (NULL != line)
      GNUNET_SERVER_notification_context_unicast (nc,
                                                  line->client,
                                                  &hup.header,
                                                  GNUNET_NO);
    break;
  case CS_CALLEE_SHUTDOWN:
    break;
  case CS_CALLER_CALLING:
  case CS_CALLER_CONNECTED:
    if (NULL != line)
      GNUNET_SERVER_notification_context_unicast (nc,
                                                  line->client,
                                                  &hup.header,
                                                  GNUNET_NO);
    break;
  case CS_CALLER_SHUTDOWN:
    break;
  }
  destroy_line_cadet_channels (ch);
  if (NULL != line)
    GNUNET_CONTAINER_DLL_remove (line->channel_head,
                                 line->channel_tail,
                                 ch);
  GNUNET_free (ch);
}


/**
 * A client disconnected.  Remove all of its data structure entries.
 *
 * @param cls closure, NULL
 * @param client identification of the client
 */
static void
handle_client_disconnect (void *cls,
                          struct GNUNET_SERVER_Client *client)
{
  struct Line *line;
  struct Channel *ch;
  struct Channel *chn;

  if (NULL == client)
    return;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL == line)
    return;
  GNUNET_SERVER_client_set_user_context (client,
                                         NULL);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client disconnected, closing line\n");
  if (NULL != line->port)
  {
    GNUNET_CADET_close_port (line->port);
    line->port = NULL;
  }
  for (ch = line->channel_head; NULL != ch; ch = chn)
  {
    chn = ch->next;
    ch->line = NULL;
    destroy_line_cadet_channels (ch);
  }
  GNUNET_free (line);
}


/**
 * Function to register a phone.
 *
 * @param cls closure, NULL
 * @param client the client from which the message is
 * @param message the message from the client
 */
static void
handle_client_register_message (void *cls,
                                struct GNUNET_SERVER_Client *client,
                                const struct GNUNET_MessageHeader *message)
{
  const struct ClientPhoneRegisterMessage *msg;
  struct Line *line;

  msg = (const struct ClientPhoneRegisterMessage *) message;
  line = GNUNET_SERVER_client_get_user_context (client,
                                                struct Line);
  if (NULL != line)
  {
    GNUNET_break (0);
    GNUNET_SERVER_receive_done (client,
                                GNUNET_SYSERR);
    return;
  }
  line = GNUNET_new (struct Line);
  line->client = client;
  GNUNET_SERVER_notification_context_add (nc,
                                          client);
  GNUNET_SERVER_client_set_user_context (client,
                                         line);
  line->line_port = msg->line_port;
  line->port = GNUNET_CADET_open_port (cadet,
                                       &msg->line_port,
                                       &inbound_channel,
                                       line);
  GNUNET_SERVER_receive_done (client,
                              GNUNET_OK);
}


/**
 * Shutdown nicely
 *
 * @param cls closure, NULL
 */
static void
do_shutdown (void *cls)
{
  if (NULL != cadet)
  {
    GNUNET_CADET_disconnect (cadet);
    cadet = NULL;
  }
  if (NULL != nc)
  {
    GNUNET_SERVER_notification_context_destroy (nc);
    nc = NULL;
  }
}


/**
 * Main function that will be run by the scheduler.
 *
 * @param cls closure
 * @param server server handle
 * @param c configuration
 */
static void
run (void *cls,
     struct GNUNET_SERVER_Handle *server,
     const struct GNUNET_CONFIGURATION_Handle *c)
{
  static const struct GNUNET_SERVER_MessageHandler server_handlers[] = {
    {&handle_client_register_message, NULL,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_REGISTER,
     sizeof (struct ClientPhoneRegisterMessage)},
    {&handle_client_pickup_message, NULL,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_PICK_UP,
     sizeof (struct ClientPhonePickupMessage) },
    {&handle_client_suspend_message, NULL,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_SUSPEND,
     sizeof (struct ClientPhoneSuspendMessage) },
    {&handle_client_resume_message, NULL,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_RESUME,
     sizeof (struct ClientPhoneResumeMessage) },
    {&handle_client_hangup_message, NULL,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_HANG_UP,
     sizeof (struct ClientPhoneHangupMessage) },
    {&handle_client_call_message, NULL,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CS_PHONE_CALL,
     sizeof (struct ClientCallMessage) },
    {&handle_client_audio_message, NULL,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CS_AUDIO,
     0},
    {NULL, NULL, 0, 0}
  };
  static struct GNUNET_CADET_MessageHandler cadet_handlers[] = {
    {&handle_cadet_ring_message,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_RING,
     sizeof (struct CadetPhoneRingMessage)},
    {&handle_cadet_hangup_message,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_HANG_UP,
     sizeof (struct CadetPhoneHangupMessage)},
    {&handle_cadet_pickup_message,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_PICK_UP,
     sizeof (struct CadetPhonePickupMessage)},
    {&handle_cadet_suspend_message,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_SUSPEND,
     sizeof (struct CadetPhoneSuspendMessage)},
    {&handle_cadet_resume_message,
     GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_PHONE_RESUME,
     sizeof (struct CadetPhoneResumeMessage)},
    {&handle_cadet_audio_message, GNUNET_MESSAGE_TYPE_CONVERSATION_CADET_AUDIO,
     0},
    {NULL, 0, 0}
  };

  cfg = c;
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CRYPTO_get_peer_identity (cfg,
                                                  &my_identity));
  cadet = GNUNET_CADET_connect (cfg,
                                NULL,
                                &inbound_end,
                                cadet_handlers);
  if (NULL == cadet)
  {
    GNUNET_break (0);
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  nc = GNUNET_SERVER_notification_context_create (server,
                                                  16);
  GNUNET_SERVER_add_handlers (server,
                              server_handlers);
  GNUNET_SERVER_disconnect_notify (server,
				   &handle_client_disconnect,
				   NULL);
  GNUNET_SCHEDULER_add_shutdown (&do_shutdown,
				 NULL);
}


/**
 * The main function for the conversation service.
 *
 * @param argc number of arguments from the command line
 * @param argv command line arguments
 * @return 0 ok, 1 on error
 */
int
main (int argc,
      char *const *argv)
{
  return (GNUNET_OK ==
	  GNUNET_SERVICE_run (argc, argv,
                              "conversation",
                              GNUNET_SERVICE_OPTION_NONE,
			      &run, NULL)) ? 0 : 1;
}

/* end of gnunet-service-conversation.c */