- verify_successor

[oweals/gnunet.git] / src / dht / gnunet-service-xdht_neighbours.c

/*
     This file is part of GNUnet.
     (C) 2009-2013 Christian Grothoff (and other contributing authors)

     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., 59 Temple Place - Suite 330,
     Boston, MA 02111-1307, USA.
*/

/**
 * @file dht/gnunet-service-xdht_neighbours.c
 * @brief GNUnet DHT service's finger and friend table management code
 * @author Supriti Singh
 */

#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_block_lib.h"
#include "gnunet_hello_lib.h"
#include "gnunet_constants.h"
#include "gnunet_protocols.h"
#include "gnunet_nse_service.h"
#include "gnunet_ats_service.h"
#include "gnunet_core_service.h"
#include "gnunet_datacache_lib.h"
#include "gnunet_transport_service.h"
#include "gnunet_hello_lib.h"
#include "gnunet_dht_service.h"
#include "gnunet_statistics_service.h"
#include "gnunet-service-xdht.h"
#include "gnunet-service-xdht_clients.h"
#include "gnunet-service-xdht_datacache.h"
#include "gnunet-service-xdht_hello.h"
#include "gnunet-service-xdht_neighbours.h"
#include "gnunet-service-xdht_nse.h"
#include "gnunet-service-xdht_routing.h"
#include <fenv.h>
#include "dht.h"


/* FIXME:
 * 1. do we need some mechanism to check if we already have found trail to 
 * our finger at a particular index. also real finger identifier that we
 * were looking for and successor it that we got. and whats the benefit of sending
 * 64 bit finger for searching? can we just send gnuent_peeridentity finger id
 * and only in find_successor we give 64 bit.
 * 2. Think of better names for variable especially for variables of type
 * uint64_t
 * 3. Add content and route replication later. 
 * 4. Algorithm to shorten the trail length - one possible solution could be
 * when we are in trail seutp result part. each peer in the trail check if any of
 * the corresponding peers is its friend list. Then it can shortcut the path.
 * 4. As we start looking for finger from i = 0, using this parameter to 
 * generate random value does not look smart in send_find_finger_trail_message. 
 * 6. Need to add a new task, fix fingers. For node join/leave, we need to 
 * upgrade our finger table periodically. So, we should call fix_fingers 
 * and change our finger table. 
 * 7. Should we look for fingers one by one in send_find_finger_trail_setup
 * 8. Change the message is gnunet_protocols.h 
 * 9. Can we just send the whole peer list as array for verify successor
 * and verify successor result instead of the way in which we send in peertrailmessage.
 * 10. I have added a new field trail length in finger info. so in finger_table_add
 * find this value to be added.
 */


/**
 * Maximum possible fingers of a peer.
 * FIXME: Should it be 64 as we are doing all the operation on 64 bit numbers now? 
 */
#define MAX_FINGERS 64

/**
 * Maximum allowed number of pending messages per friend peer.
 */
#define MAXIMUM_PENDING_PER_FRIEND 64

/**
 * How long at least to wait before sending another find finger trail request.
 */
#define DHT_MINIMUM_FIND_FINGER_TRAIL_INTERVAL GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 30)

/**
 * How long at most to wait before sending another find finger trail request.
 */
#define DHT_MAXIMUM_FIND_FINGER_TRAIL_INTERVAL GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MINUTES, 10)

/**
 * FIXME: Currently used in GDS_NEIGHBOURS_handle_trail_setup.
 * I have just copied it from gnunet-service-dht_neighbours. Will it work here? 
 * How long at most to wait for transmission of a GET request to another peer?
 */
#define GET_TIMEOUT GNUNET_TIME_relative_multiply(GNUNET_TIME_UNIT_MINUTES, 2)

GNUNET_NETWORK_STRUCT_BEGIN

/* FIXME:
 * 1) Bloomfilter is not required for X-Vine.
 * Keep the field now but remove it when implementing PUT/GET.
 * 2) also, check the field of put/get/result if all are required for
 * x-vine or not. */
  
/**
 * P2P PUT message
 */
struct PeerPutMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_P2P_PUT
   */
  struct GNUNET_MessageHeader header;

  /**
   * Processing options
   */
  uint32_t options GNUNET_PACKED;

  /**
   * Content type.
   */
  uint32_t type GNUNET_PACKED;

  /**
   * Hop count
   */
  uint32_t hop_count GNUNET_PACKED;

  /**
   * Replication level for this message
   */
  uint32_t desired_replication_level GNUNET_PACKED;

  /**
   * Length of the PUT path that follows (if tracked).
   */
  uint32_t put_path_length GNUNET_PACKED;

  /**
   * When does the content expire?
   */
  struct GNUNET_TIME_AbsoluteNBO expiration_time;

  /**
   * Bloomfilter (for peer identities) to stop circular routes
   */
  char bloomfilter[DHT_BLOOM_SIZE];

  /**
   * The key we are storing under.
   */
  struct GNUNET_HashCode key;

  /* put path (if tracked) */

  /* Payload */

};


/**
 * P2P Result message
 */
struct PeerResultMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_P2P_RESULT
   */
  struct GNUNET_MessageHeader header;

  /**
   * Content type.
   */
  uint32_t type GNUNET_PACKED;

  /**
   * Length of the PUT path that follows (if tracked).
   */
  uint32_t put_path_length GNUNET_PACKED;

  /**
   * Length of the GET path that follows (if tracked).
   */
  uint32_t get_path_length GNUNET_PACKED;

  /**
   * When does the content expire?
   */
  struct GNUNET_TIME_AbsoluteNBO expiration_time;

  /**
   * The key of the corresponding GET request.
   */
  struct GNUNET_HashCode key;

  /* put path (if tracked) */

  /* get path (if tracked) */

  /* Payload */

};


/**
 * P2P GET message
 */
struct PeerGetMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_P2P_GET
   */
  struct GNUNET_MessageHeader header;

  /**
   * Processing options
   */
  uint32_t options GNUNET_PACKED;

  /**
   * Desired content type.
   */
  uint32_t type GNUNET_PACKED;

  /**
   * Hop count
   */
  uint32_t hop_count GNUNET_PACKED;

  /**
   * Desired replication level for this request.
   */
  uint32_t desired_replication_level GNUNET_PACKED;

  /**
   * Size of the extended query.
   */
  uint32_t xquery_size;

  /**
   * Bloomfilter mutator.
   */
  uint32_t bf_mutator;

  /**
   * Bloomfilter (for peer identities) to stop circular routes
   */
  char bloomfilter[DHT_BLOOM_SIZE];

  /**
   * The key we are looking for.
   */
  struct GNUNET_HashCode key;

};


/**
 * A destination can be either a friend or finger.
 */
enum current_destination_type
{
  
  /* Friend */
  FRIEND ,
  
  /* Finger */
  FINGER ,

  /* My own identity */
  MY_ID        
};


/**
 * P2P Trail setup message
 * TODO: Take reference from put_path and get_path to understand how to use size of trail list.  
 */
struct PeerTrailSetupMessage
{
  
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP
   */
  struct GNUNET_MessageHeader header;

  /**
   * Source peer which wants to find trail to one of its finger. 
   */
  struct GNUNET_PeerIdentity source_peer;

  /**
   * FIXME: Do we need to store the real finger identifier we were searching
   * for in our finger table. Whats the use of storing it if any?
   * As we are not sending any hello messages to this destination
   * finger, we are only searching for it, we can just send 64 bit. 
   * Finger id to which we want to set up the trail to. 
   *
  struct GNUNET_PeerIdentity destination_finger; */

  /**
   * Finger id to which we want to set up the trail to. 
   */
  uint64_t destination_finger;
  
  /**
   * If set to 1, then we are looking for trail to our immediate successor. 
   */
  unsigned int successor_flag;
  
  /**
   * If set to 1, then we are looking for trail to our immediate predecessor. 
   */
  unsigned int predecessor_flag;
  
  /**
   * If the message is forwarded to finger or friend. 
   */
  enum current_destination_type current_destination_type;
  
  /**
   * This field contains the peer to which this packet is forwarded.
   */
  struct GNUNET_PeerIdentity current_destination;
 
  /**
   * Number of entries in trail list.
   * FIXME: Is this data type correct?
   * FIMXE: Is usage of GNUNET_PACKED correct?
   */
  uint32_t trail_length GNUNET_PACKED;
  
};


/**
 * P2P verify successor message. 
 */
struct PeerVerifySuccessorMessage
{
  
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR
   */
  struct GNUNET_MessageHeader header;
  
  /**
   * Source peer which wants to verify its successor. 
   */
  struct GNUNET_PeerIdentity source_peer;
  
  /**
   * Identity of our current successor.
   */
  struct GNUNET_PeerIdentity successor;
  
  /**
   * Total number of peers in trail. 
   */
  unsigned int trail_length;
  
  /**
   * The current index in trail for next destination to send this message to. 
   */
  unsigned int current_index;
  
};


/**
 *
 */
struct PeerVerifySuccessorResultMessage
{
  
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR_RESULT
   */
  struct GNUNET_MessageHeader header;
  
  /**
   * Destination peer which send the request to verify its successor. 
   */
  struct GNUNET_PeerIdentity destination_peer;
  
  /**
   * Identity of successor to which PeerVerifySuccessorMessage was sent.
   */
  struct GNUNET_PeerIdentity source_successor;
  
  /**
   * source_successor's predecessor
   */
  struct GNUNET_PeerIdentity my_predecessor;
  
  /**
   * Total number of peers in trail. 
   */
  unsigned int trail_length;
  
  /**
   * The current index in trail for next destination to send this message to. 
   */
  unsigned int current_index;
  
};

/**
 *
 */
struct PeerNotifyNewSuccessorMessage
{
  
};


/**FIXME: Here we can keep the whole list inside the message instead of attaching 
 * it all the time as the list remains constant all the time. 
 * P2P Trail setup Result message
 */
struct PeerTrailSetupResultMessage
{
  
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_RESULT_SETUP
   */
  struct GNUNET_MessageHeader header;
  
  /**
   * Finger to which we have found the path. 
   */
  struct GNUNET_PeerIdentity finger;

  /**
   * Peer which was looking for the trail to finger. 
   */
  struct GNUNET_PeerIdentity destination_peer;

  /**
   * This field contains the peer to which this packet is forwarded.
   */
  struct GNUNET_PeerIdentity current_destination;
  
  /**
   * FIXME: Temporary field used to remember at which index we should read
   * to get our next peer. 
   */
  unsigned int current_index;
  
  /**
   * If set to 1, then this trail is the trail to succcessor of our finger. 
   */
  unsigned int successor_flag;
  
  /**
   * If set to 1, then this trail is the trail to predecessor of our finger. 
   */
  unsigned int predecessor_flag;
  
  /**
   * Number of entries in trail list.
   * FIXME: Is this data type correct?
   * FIXME: Is usage of GNUNET_PACKED correct?
   */
  uint32_t trail_length GNUNET_PACKED;
  
};

GNUNET_NETWORK_STRUCT_END


/**
 * Linked list of messages to send to a particular other peer.
 */
struct P2PPendingMessage
{
  /**
   * Pointer to next item in the list
   */
  struct P2PPendingMessage *next;

  /**
   * Pointer to previous item in the list
   */
  struct P2PPendingMessage *prev;

  /**
   * When does this message time out?
   */
  struct GNUNET_TIME_Absolute timeout;

   /**
   * Message importance level.  FIXME: used? useful?
   */
  unsigned int importance;

  /**
   * Actual message to be sent, allocated at the end of the struct:
   * // msg = (cast) &pm[1];
   * // memcpy (&pm[1], data, len);
   */
  const struct GNUNET_MessageHeader *msg;

};


 /**
  * Linked List of peers which are part of trail to reach a particular Finger.
  */
struct TrailPeerList
{
   /**
   * Pointer to next item in the list
   */
   struct TrailPeerList *next;

   /**
   * Pointer to previous item in the list
   */
   struct TrailPeerList *prev;
   
   /**
    * An element in this trail list
    */
   struct GNUNET_PeerIdentity peer;
  
};


/** FIXME: 
 * 1.Previously I have added the field successor and predecessor of a friend.
 * But whats the use and is it even possible to have those values.
 *  Entry in friend_peermap.
 */
struct FriendInfo
{
  /**
   * What is the identity of the peer?
   */
  struct GNUNET_PeerIdentity id;

  /**
   * Count of outstanding messages for peer.
   */
  unsigned int pending_count;
  
  /**
   * Head of pending messages to be sent to this peer.
   */
 struct P2PPendingMessage *head;

 /**
  * Tail of pending messages to be sent to this peer.
  */
 struct P2PPendingMessage *tail;
 
 /**
  * Core handle for sending messages to this peer.
  */
 struct GNUNET_CORE_TransmitHandle *th;

};


/**
 * FIXME: We can also use an enum to say if its pred/suc/finger
 * FIXME: As in chord , where we store the actual finger identity we were looking
 * for and the real id which we got as successor. If we want to store like that 
 * then we will need to add a new field and search actual peer id. 
 * FIXME: Should we use another PeerIdentity which is smaller
 * than 256 bits while storing. 
 * Predcessor is needed in case of node join/fail. 
 * Entry in finger_peermap.
 */
struct FingerInfo
{
  /**
   * Finger identity.
   */
  struct GNUNET_PeerIdentity finger_identity;
  
  /**
   * If 1, then this finger entry is first finger /successor of the peer.
   */
  unsigned int successor;
  
  /**
   * If 1, then this finger entry is first predecessor of the peer.
   */
  unsigned int predecessor;
  
  /**
   * Total number of entries in trail. 
   */
  unsigned int trail_length;
  
  /**
   * List of peers in the trail to reach this finger.
   */
  struct GNUNET_PeerIdentity *trail_peer_list;
  
};


/**
 * Task that sends FIND FINGER TRAIL requests.
 */
static GNUNET_SCHEDULER_TaskIdentifier find_finger_trail_task;

/**
 * 
 * Task that periodically checks for the immediate successor. 
 */
static GNUNET_SCHEDULER_TaskIdentifier verify_successor;

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

/**
 * Hash map of all the friends of a peer
 */
static struct GNUNET_CONTAINER_MultiPeerMap *friend_peermap;

/**
 * Hash map of all the fingers of a peer
 */
static struct GNUNET_CONTAINER_MultiPeerMap *finger_peermap;

/**
 * TODO: Ask whats the use of ATS.
 * Handle to ATS.
 */
static struct GNUNET_ATS_PerformanceHandle *atsAPI;

/**
 * Handle to CORE.
 */
static struct GNUNET_CORE_Handle *core_api;

/**
 * FIXME: Is it safe to assume its initialized to 0 by default.
 * The current finger index that we have found trail to.
 */
static unsigned int current_finger_index;


/**
 * Called when core is ready to send a message we asked for
 * out to the destination.
 *
 * @param cls the 'struct PeerInfo' of the target peer
 * @param size number of bytes available in buf
 * @param buf where the callee should write the message
 * @return number of bytes written to buf
 */
static size_t
core_transmit_notify (void *cls, size_t size, void *buf)
{
  struct FriendInfo *peer = cls;
  char *cbuf = buf;
  struct P2PPendingMessage *pending;
  size_t off;
  size_t msize;
  
  peer->th = NULL;
  while ((NULL != (pending = peer->head)) &&
         (0 == GNUNET_TIME_absolute_get_remaining (pending->timeout).rel_value_us))
  {
    peer->pending_count--;
    GNUNET_CONTAINER_DLL_remove (peer->head, peer->tail, pending);  
    GNUNET_free (pending);
  }
  if (NULL == pending)
  {
    /* no messages pending */
    return 0;
  }
  if (NULL == buf)
  {
    peer->th =
        GNUNET_CORE_notify_transmit_ready (core_api, GNUNET_NO,
                                           GNUNET_CORE_PRIO_BEST_EFFORT,
                                           GNUNET_TIME_absolute_get_remaining
                                           (pending->timeout), &peer->id,
                                           ntohs (pending->msg->size),
                                           &core_transmit_notify, peer);
    GNUNET_break (NULL != peer->th);
    return 0;
  }
  off = 0;
  while ((NULL != (pending = peer->head)) &&
         (size - off >= (msize = ntohs (pending->msg->size))))
  {
    GNUNET_STATISTICS_update (GDS_stats,
                              gettext_noop
                              ("# Bytes transmitted to other peers"), msize,
                              GNUNET_NO);
    memcpy (&cbuf[off], pending->msg, msize);
    off += msize;
    peer->pending_count--;
    GNUNET_CONTAINER_DLL_remove (peer->head, peer->tail, pending);
    GNUNET_free (pending);
  }
  if (peer->head != NULL)
  {
    peer->th =
        GNUNET_CORE_notify_transmit_ready (core_api, GNUNET_NO,
                                           GNUNET_CORE_PRIO_BEST_EFFORT,
                                           GNUNET_TIME_absolute_get_remaining
                                           (pending->timeout), &peer->id, msize,
                                           &core_transmit_notify, peer);
    GNUNET_break (NULL != peer->th);
  }
  return off;
}


/**
 * Transmit all messages in the friend's message queue.
 *
 * @param peer message queue to process
 */
static void
process_friend_queue (struct FriendInfo *peer)
{
  struct P2PPendingMessage *pending;
  
  if (NULL == (pending = peer->head))
    return;
  if (NULL != peer->th)
    return;
  
  GNUNET_STATISTICS_update (GDS_stats,
                            gettext_noop
                            ("# Bytes of bandwidth requested from core"),
                            ntohs (pending->msg->size), GNUNET_NO);
  
  /* FIXME: Are we correctly initializing importance and pending. */
  peer->th =
      GNUNET_CORE_notify_transmit_ready (core_api, GNUNET_NO,
                                         pending->importance,
                                         GNUNET_TIME_absolute_get_remaining
                                         (pending->timeout), &peer->id,
                                         ntohs (pending->msg->size),
                                         &core_transmit_notify, peer);
  GNUNET_break (NULL != peer->th);
}


/**
 * SUPU:
 * We add the next destination i.e. friend to which we are sending the packet
 * to our peer list in the calling function and we also increment trail_length
 * in calling function i.e. send_find_finger_trail and handle_dht_p2p_trail_setup.
 * Here we only copy the whole trail into our peer_list. 
 * Setup the trail message and forward it to a friend. 
 * @param source_peer Peer which wants to set up the trail to one of its finger.
 * @param destination_finger Peer to which we want to set up the trail to.
 * @param current_destination Current peer to which this message should be forwarded.
 * @param trail_length Numbers of peers in the trail.
 * @param trail_peer_list peers this request has traversed so far
 * @param successor_flag If 1 then we are looking for trail to our successor. 
 */
void
GDS_NEIGHBOURS_handle_trail_setup(struct GNUNET_PeerIdentity *source_peer,
                                  uint64_t *destination_finger,
                                  struct FriendInfo *current_destination,
                                  unsigned int trail_length,
                                  struct GNUNET_PeerIdentity *trail_peer_list,
                                  unsigned int successor_flag,
                                  unsigned int predecessor_flag)
{
  struct P2PPendingMessage *pending;
  struct PeerTrailSetupMessage *tsm;
  struct GNUNET_PeerIdentity *peer_list;
  size_t msize;
  
  msize = sizeof (struct PeerTrailSetupMessage) + 
          (trail_length * sizeof (struct GNUNET_PeerIdentity));
  
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  if (current_destination->pending_count >= MAXIMUM_PENDING_PER_FRIEND)
  {  
    GNUNET_STATISTICS_update (GDS_stats, gettext_noop ("# P2P messages dropped due to full queue"),
                                1, GNUNET_NO);
  }
    
  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize); 
  pending->importance = 0;    /* FIXME */
  pending->timeout = GNUNET_TIME_relative_to_absolute (GET_TIMEOUT);
  tsm = (struct PeerTrailSetupMessage *) &pending[1]; 
  pending->msg = &tsm->header;
  tsm->header.size = htons (msize);
  tsm->header.type = htons (GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP);
  memcpy (&(tsm->destination_finger), destination_finger, sizeof (uint64_t)); 
  memcpy (&(tsm->source_peer), source_peer, sizeof (struct GNUNET_PeerIdentity));
  memcpy (&(tsm->current_destination),&(current_destination->id), 
          sizeof (struct GNUNET_PeerIdentity));
  tsm->current_destination_type = htonl(FRIEND); 
  tsm->trail_length = htonl(trail_length); 
  if(successor_flag == 1)
    tsm->successor_flag = 1;
  if(predecessor_flag == 1)
    tsm->predecessor_flag = 1;
  
  peer_list = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity) * trail_length); 
  peer_list = (struct GNUNET_PeerIdentity *) &tsm[1];
  memcpy (peer_list, trail_peer_list, trail_length * sizeof(struct GNUNET_PeerIdentity));
  
  GNUNET_CONTAINER_DLL_insert_tail (current_destination->head, current_destination->tail, pending);
  current_destination->pending_count++;
  process_friend_queue (current_destination);
  
}

/**FIXME: As we are having a fixed list of trail peer list we can just 
 * store inside the message instead of attaching it all the time. 
 * Handle a tail setup result message. 
 * @param destination_peer Peer which will get the trail to one of its finger.
 * @param source_finger Peer to which the trail has been setup to.
 * @param current_destination Current peer to which this message should be forwarded.
 * @param trail_length Numbers of peers in the trail.
 * @param trail_peer_list peers this request has traversed so far 
 * @param current_trail_index Index in trail_peer_list. 
 */
void
GDS_NEIGHBOURS_handle_trail_setup_result (struct GNUNET_PeerIdentity *destination_peer,
                                          struct GNUNET_PeerIdentity *source_finger,
                                          struct FriendInfo *current_destination,
                                          unsigned int trail_length,
                                          const struct GNUNET_PeerIdentity *trail_peer_list,
                                          unsigned int current_trail_index,
                                          unsigned int successor_flag,
                                          unsigned int predecessor_flag)
{
  struct P2PPendingMessage *pending;
  struct PeerTrailSetupResultMessage *tsrm;
  struct GNUNET_PeerIdentity *peer_list;
  size_t msize;
  
  msize = sizeof (struct PeerTrailSetupResultMessage) + 
          (trail_length * sizeof (struct GNUNET_PeerIdentity));
  
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  if (current_destination->pending_count >= MAXIMUM_PENDING_PER_FRIEND)
  {  
    GNUNET_STATISTICS_update (GDS_stats, gettext_noop ("# P2P messages dropped due to full queue"),
                                1, GNUNET_NO);
  }

  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize); 
  pending->importance = 0;    /* FIXME */
  pending->timeout = GNUNET_TIME_relative_to_absolute (GET_TIMEOUT);
  tsrm = (struct PeerTrailSetupResultMessage *) &pending[1]; 
  pending->msg = &tsrm->header;
  tsrm->header.size = htons (msize);
  tsrm->header.type = htons (GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP_RESULT);
  memcpy (&(tsrm->current_destination), &(current_destination->id), sizeof(struct GNUNET_PeerIdentity));
  memcpy (&(tsrm->destination_peer), destination_peer, sizeof(struct GNUNET_PeerIdentity));
  memcpy (&(tsrm->finger), source_finger, sizeof(struct GNUNET_PeerIdentity));
  tsrm->trail_length = htonl (trail_length);
  tsrm->current_index = htonl (current_trail_index);
  tsrm->successor_flag = htonl (successor_flag);
  tsrm->predecessor_flag = htonl (predecessor_flag);
  peer_list = (struct GNUNET_PeerIdentity *) &tsrm[1];
  memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
  
  /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (current_destination->head, current_destination->tail, pending);
  current_destination->pending_count++;
  process_friend_queue (current_destination);
}


/**FIXME: Calling function should provide the current destination
 * and also should compute the new current_trail_index. Also you should add
 * yourself to the list of peers and increment the length correctly. its 
 * responsibility of send_verify_successor_message and handle_verify_succesor_message. 
 * This function is called from send_verify_successor_message funciton
 * and handle_dht_p2p_verify_successor. 
 * Construct a PeerVerifySuccessor message and send it to friend.
 */
void GDS_NEIGUBOURS_handle_verify_successor(struct GNUNET_PeerIdentity *source_peer,
                                            struct GNUNET_PeerIdentity *successor,
                                            struct FriendInfo *current_destination,
                                            struct GNUNET_PeerIdentity *trail_peer_list,
                                            unsigned int trail_length,
                                            unsigned int current_trail_index)
{
  struct PeerVerifySuccessorMessage *vsm;
  struct P2PPendingMessage *pending;
  struct GNUNET_PeerIdentity *peer_list;
  size_t msize;
  
  msize = sizeof (struct PeerVerifySuccessorMessage) + 
          (trail_length * sizeof(struct GNUNET_PeerIdentity));
  
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  if (current_destination->pending_count >= MAXIMUM_PENDING_PER_FRIEND)
  {  
    GNUNET_STATISTICS_update (GDS_stats, gettext_noop ("# P2P messages dropped due to full queue"),
                                1, GNUNET_NO);
  }
  
  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize); 
  pending->importance = 0;    /* FIXME */
  pending->timeout = GNUNET_TIME_relative_to_absolute (GET_TIMEOUT);
  vsm = (struct PeerVerifySuccessorMessage *) &pending[1];
  pending->msg = &vsm->header;
  vsm->header.size = htons (msize);
  vsm->header.type = htons (GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR);
  memcpy (&(vsm->successor), successor, sizeof (struct GNUNET_PeerIdentity));
  memcpy (&(vsm->source_peer), source_peer, sizeof (struct GNUNET_PeerIdentity));
  vsm->trail_length = htonl (trail_length);
  vsm->current_index = htonl (current_trail_index);
  
  peer_list = (struct GNUNET_PeerIdentity *) &vsm[1];
  memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
  
  /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (current_destination->head, current_destination->tail, pending);
  current_destination->pending_count++;
  process_friend_queue (current_destination);
  
}


/**FIXME: 
 * 1. In this function we don't want the trail. so instead of maintaing the trail 
 * length and current_trail_index, we can just remove all the elements form trail list
 * and current_destination = last element of trail list. 
 * 1. Responsiblity of calling function to provide new current destination.
 * and correct current_trail_index. 
 * this function will be called by destination successor. and each peer 
 * which is in the trail to reach to the peer. as successor changed destination
 * peer may have replaced the entry in its finger table. so you have to use the
 * trial provided by source peer and so you should have source id in peerverifysuccessor 
 * Construct a PeerVerifySuccessorResult message and send it to friend.
 */
void GDS_NEIGHBOURS_handle_verify_successor_result(struct GNUNET_PeerIdentity *destination_peer,
                                                   struct GNUNET_PeerIdentity *source_successor,
                                                   struct GNUNET_PeerIdentity *my_predecessor,
                                                   struct FriendInfo *current_destination,
                                                   struct GNUNET_PeerIdentity *trail_peer_list,
                                                   unsigned int trail_length,
                                                   unsigned int current_trail_index)
{
  /* In this funciton, you receive 
   1. successor
   2. trial to reach that successor
   3. trail_length.
   4. current trail index --> this gives the next_hop on whose pending queue you should
   add the message. */
  struct PeerVerifySuccessorResultMessage *vsmr;
  struct P2PPendingMessage *pending;
  struct GNUNET_PeerIdentity *peer_list;
  size_t msize;
  
  msize = sizeof (struct PeerVerifySuccessorResultMessage) + 
          (trail_length * sizeof(struct GNUNET_PeerIdentity));
  
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  if (current_destination->pending_count >= MAXIMUM_PENDING_PER_FRIEND)
  {  
    GNUNET_STATISTICS_update (GDS_stats, gettext_noop ("# P2P messages dropped due to full queue"),
                                1, GNUNET_NO);
  }
  
  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize); 
  pending->importance = 0;    /* FIXME */
  pending->timeout = GNUNET_TIME_relative_to_absolute (GET_TIMEOUT);
  vsmr = (struct PeerVerifySuccessorResultMessage *) &pending[1];
  pending->msg = &vsmr->header;
  vsmr->header.size = htons (msize);
  vsmr->header.type = htons (GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR_RESULT);
  memcpy (&(vsmr->destination_peer), destination_peer, sizeof (struct GNUNET_PeerIdentity));
  memcpy (&(vsmr->source_successor), source_successor, sizeof (struct GNUNET_PeerIdentity));
  memcpy (&(vsmr->my_predecessor), my_predecessor, sizeof (struct GNUNET_PeerIdentity));
  vsmr->trail_length = htonl (trail_length);
  vsmr->current_index = htonl (current_trail_index);
  
  peer_list = (struct GNUNET_PeerIdentity *) &vsmr[1];
  memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
  
   /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (current_destination->head, current_destination->tail, pending);
  current_destination->pending_count++;
  process_friend_queue (current_destination);
}


/**
 * Construct a PeerNotifyNewSuccessor message and send it to friend.
 */
void GDS_NEIGHBOURS_handle_notify_new_successor()
{
  
}


/**FIXME: Old implementation just to remove error
 * TODO: Modify this function to handle our get request. 
 * Perform a GET operation.  Forwards the given request to other
 * peers.  Does not lookup the key locally.  May do nothing if this is
 * the only peer in the network (or if we are the closest peer in the
 * network).
 *
 * @param type type of the block
 * @param options routing options
 * @param desired_replication_level desired replication count
 * @param hop_count how many hops did this request traverse so far?
 * @param key key for the content
 * @param xquery extended query
 * @param xquery_size number of bytes in @a xquery
 * @param reply_bf bloomfilter to filter duplicates
 * @param reply_bf_mutator mutator for @a reply_bf
 * @param peer_bf filter for peers not to select (again)
 */
void
GDS_NEIGHBOURS_handle_get (enum GNUNET_BLOCK_Type type,
                           enum GNUNET_DHT_RouteOption options,
                           uint32_t desired_replication_level,
                           uint32_t hop_count, const struct GNUNET_HashCode * key,
                           const void *xquery, size_t xquery_size,
                           const struct GNUNET_CONTAINER_BloomFilter *reply_bf,
                           uint32_t reply_bf_mutator,
                           struct GNUNET_CONTAINER_BloomFilter *peer_bf)
{

  /*
   1. take the key, get the 64 bit value of the key.
   2. call find_successor to get the successor of the key.
   3. successor can be either a friend or finger.
   4. update the field in get message to reflect if its a friend or finger table
   5. add the put message to pending message and send it. 
   */
}

/**FIXME: Old implementation just to remove error.
 * TODO: Modify this function to handle our put request. 
 * Perform a PUT operation.   Forwards the given request to other
 * peers.   Does not store the data locally.  Does not give the
 * data to local clients.  May do nothing if this is the only
 * peer in the network (or if we are the closest peer in the
 * network).
 *
 * @param type type of the block
 * @param options routing options
 * @param desired_replication_level desired replication count
 * @param expiration_time when does the content expire
 * @param hop_count how many hops has this message traversed so far
 * @param bf Bloom filter of peers this PUT has already traversed
 * @param key key for the content
 * @param put_path_length number of entries in @a put_path
 * @param put_path peers this request has traversed so far (if tracked)
 * @param data payload to store
 * @param data_size number of bytes in @a data
 */
void
GDS_NEIGHBOURS_handle_put (enum GNUNET_BLOCK_Type type,
                           enum GNUNET_DHT_RouteOption options,
                           uint32_t desired_replication_level,
                           struct GNUNET_TIME_Absolute expiration_time,
                           uint32_t hop_count,
                           struct GNUNET_CONTAINER_BloomFilter *bf,
                           const struct GNUNET_HashCode *key,
                           unsigned int put_path_length,
                           struct GNUNET_PeerIdentity *put_path,
                           const void *data, size_t data_size)
{

   /*
   1. take the key, get the 64 bit value of the key.
   2. call find_successor to get the successor of the key.
   3. successor can be either a friend or finger.
   4. update the field in put message to reflect if its a friend or finger table
   5. add the put message to pending message and send it. 
   */
}


/**
 * FIXME: Check if this function actually iterates or not. 
 * Randomly choose one of your friends from the friends_peer map
 * @return Friend
 */
static struct FriendInfo *
select_random_friend()
{  
  unsigned int current_size;
  unsigned int *index; 
  unsigned int j = 0;
  struct GNUNET_CONTAINER_MultiPeerMapIterator *iter;
  struct GNUNET_PeerIdentity key_ret;
  struct FriendInfo *friend;
  
  current_size = GNUNET_CONTAINER_multipeermap_size (friend_peermap);
  
  /* Element stored at this index in friend_peermap should be selected friend. */
  index = GNUNET_CRYPTO_random_permute (GNUNET_CRYPTO_QUALITY_WEAK, current_size);
  
  /* Create an iterator for friend_peermap. */
  iter = GNUNET_CONTAINER_multipeermap_iterator_create (friend_peermap);
  
  /* Set the position of iterator to index. */
  while(j < (*index))
  {
    if(GNUNET_YES == GNUNET_CONTAINER_multipeermap_iterator_next (iter,NULL,NULL))
    {
      /* FIXME: I don't think we are actually incrementing iter. iter is always
       pointing to the same element. */
      j++;
    }
    else 
      return NULL;
  }  
  
  if(GNUNET_YES == GNUNET_CONTAINER_multipeermap_iterator_next (iter,&key_ret,(const void **)&friend))
  {
    return friend;
  }

  return NULL;
}


/**
 * Compute finger_identity to which we want to setup the trail
 * FIXME: If we maintain a index that is value of current_finger_index
 * to which a particular entry in finger map corresponds then should we first
 * check if there is already an entry for that index. If yes then don't
 * search for trail to that finger. 
 * @return finger_identity 
 */
static uint64_t *
compute_finger_identity()
{
  uint64_t *my_id64 ;
  uint64_t *finger_identity64;
  
  my_id64 = GNUNET_malloc (sizeof (uint64_t));
  finger_identity64 = GNUNET_malloc (sizeof (uint64_t));
  
  memcpy (my_id64, &(my_identity.public_key.q_y), sizeof (uint64_t));
  *finger_identity64 = fmod ((*my_id64 + pow (2,current_finger_index)),( (pow (2,MAX_FINGERS))));
  
  return finger_identity64;
}


/**
 * Find immediate predecessor in the network.
 * @param me my own identity
 * @return peer identity of immediate predecessor.
 */
static uint64_t *
find_predecessor()
{
  uint64_t *my_id ;
  uint64_t *predecessor;
  
  my_id = GNUNET_malloc (sizeof (uint64_t));
  predecessor = GNUNET_malloc (sizeof (uint64_t));
  
  memcpy (my_id, &(my_identity.public_key.q_y), sizeof (uint64_t));
  *predecessor = fmod ((*my_id -1), (pow (2,MAX_FINGERS)));
          
  return predecessor;
}


/**
 * Periodically ping your successor to ask its current predecessor
 * 
 * @param cls closure for this task
 * @param tc the context under which the task is running
 */
static void
send_verify_successor_message(void *cls,
          const struct GNUNET_SCHEDULER_TaskContext *tc )
{
  struct GNUNET_TIME_Relative next_send_time;
  struct GNUNET_CONTAINER_MultiPeerMapIterator *finger_iter;
  struct GNUNET_PeerIdentity key_ret;
  struct FriendInfo *current_destination;
  struct GNUNET_PeerIdentity *finger_trail;
  unsigned int finger_trail_length;
  unsigned int finger_trail_current_index;
  struct FingerInfo *finger;
  unsigned int finger_index;
  
  /* Iterate over your finger peermap to find the element with successor field set.
     That field is your successor. */
  /* FIXME: Again if the iteration is correct or not? */
  finger_iter = GNUNET_CONTAINER_multipeermap_iterator_create (finger_peermap);  
  for (finger_index = 0; finger_index < GNUNET_CONTAINER_multipeermap_size (finger_peermap); finger_index++)
  {
    /* FIXME: I don't think we are actually iterating.
     Read about how to iterate over the multi peer map. */
    if(GNUNET_YES == GNUNET_CONTAINER_multipeermap_iterator_next(finger_iter,&key_ret,(const void **)&finger)) 
    {
      if(1 == finger->successor)
        break; /* FIXME: Do I come out of inner if or outer for */
    }
  }
  
  /* FIXME: Is this copy correct? */
  finger_trail = GNUNET_malloc ((finger->trail_length * 
                                 sizeof (struct GNUNET_PeerIdentity)));
  current_destination = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity));
  
  /* FIXME: Should we add ourself to peer list . When we get the result back
   then we should have to be in the list so that message reaches to us. */
  memcpy (finger_trail, finger->trail_peer_list, 
         (finger->trail_length * sizeof (struct GNUNET_PeerIdentity)));
  finger_trail_length = finger->trail_length; 
  finger_trail_current_index = 1;
  memcpy (current_destination, &finger_trail[1], 
          sizeof (struct GNUNET_PeerIdentity));
  
  /* FIXME: current_destination should be friend not gnunet_peeridentity.
   Search over your friend_peermap to find the friend corresponding to
   current_destination. */
  GDS_NEIGUBOURS_handle_verify_successor (&my_identity,
                                         &(finger->finger_identity),
                                         current_destination,
                                         finger_trail,
                                         finger_trail_length,
                                         finger_trail_current_index);
  
  
  /* FIXME: Use a random value so that this message is send not at the same
   interval as send_find_finger_trail_message. */
  next_send_time.rel_value_us =
      DHT_MINIMUM_FIND_FINGER_TRAIL_INTERVAL.rel_value_us +
      GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK,
                                DHT_MAXIMUM_FIND_FINGER_TRAIL_INTERVAL.rel_value_us /
                                (current_finger_index + 1));
 
  verify_successor =
      GNUNET_SCHEDULER_add_delayed (next_send_time, &send_verify_successor_message,
                                    NULL);
}


/**
 * Task to send a find finger trail message. We attempt to find trail
 * to our finger and successor in the network.
 *
 * @param cls closure for this task
 * @param tc the context under which the task is running
 */
static void
send_find_finger_trail_message (void *cls,
                        const struct GNUNET_SCHEDULER_TaskContext *tc)
{
  struct FriendInfo *friend;
  struct GNUNET_TIME_Relative next_send_time;
  struct GNUNET_PeerIdentity *peer_list;
  unsigned int successor_flag;
  unsigned int predecessor_flag;
  uint64_t *finger_identity;
  
  if (1 == current_finger_index)
  {
    /* We have started the process to find the successor. We should search 
     for our predecessor. */
    finger_identity = find_predecessor();  
    
    /* FIXME: There is no case in find_predecessor which returns NULL. It can
     return NULL, only if we already have found a trial to predecessor. is it
     required or not need to check.*/
    if(NULL == finger_identity)
    {
      /* We already have a trail to reach to immediate predecessor. */
      goto new_find_finger_trail_request;
    }
    predecessor_flag = 1; 
    goto choose_friend;
  }
  else
  {
    finger_identity = compute_finger_identity();
    
    if(finger_identity == NULL)
    {
      goto new_find_finger_trail_request;
    }
  }
  
  if(0 == current_finger_index)
  {
    /* We are searching for our successor in the network. */
    successor_flag = 1;
  }
  
  choose_friend:
  current_finger_index = current_finger_index + 1;
  friend = GNUNET_malloc (sizeof (struct FriendInfo));
  friend = select_random_friend();
 
  /* We found a friend.*/
  if(NULL != friend)
  { 
    /*SUPU: Here you are adding yourself to peer list so that trail result
     reaches back to you. */
    unsigned int trail_length = 2;
    peer_list = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity) * trail_length);
    memcpy (&peer_list[0], &(my_identity), sizeof (struct GNUNET_PeerIdentity)); 
    memcpy (&peer_list[1], &(friend->id), sizeof (struct GNUNET_PeerIdentity)); 
    
    GDS_NEIGHBOURS_handle_trail_setup (&my_identity, finger_identity, 
                                      friend, trail_length, peer_list,
                                      successor_flag, predecessor_flag);
  }
  
  /* FIXME: Should we be using current_finger_index to generate random interval.*/
  new_find_finger_trail_request:
  next_send_time.rel_value_us =
      DHT_MINIMUM_FIND_FINGER_TRAIL_INTERVAL.rel_value_us +
      GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK,
                                DHT_MAXIMUM_FIND_FINGER_TRAIL_INTERVAL.rel_value_us /
                                (current_finger_index + 1));
 
  find_finger_trail_task =
      GNUNET_SCHEDULER_add_delayed (next_send_time, &send_find_finger_trail_message,
                                    NULL);
}


/**
 * Method called whenever a peer connects.
 *
 * @param cls closure
 * @param peer peer identity this notification is about
 */
static void
handle_core_connect (void *cls, const struct GNUNET_PeerIdentity *peer)
{
  struct FriendInfo *ret;
  
  /* Check for connect to self message */
  if (0 == memcmp (&my_identity, peer, sizeof (struct GNUNET_PeerIdentity)))
    return;
  
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Connected to %s\n",
              GNUNET_i2s (peer));
  
  /* If peer already exists in our friend_peermap, then exit. */
  if (GNUNET_YES ==
      GNUNET_CONTAINER_multipeermap_contains (friend_peermap,
                                              peer))
  {
    GNUNET_break (0);
    return;
  }

  GNUNET_STATISTICS_update (GDS_stats, gettext_noop ("# peers connected"), 1,
                            GNUNET_NO);

  
  ret = GNUNET_new (struct FriendInfo);
  ret->id = *peer;
  
  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CONTAINER_multipeermap_put (friend_peermap,
                                                    peer, ret,
                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));

  
  /* got a first connection, good time to start with FIND FINGER TRAIL requests... */
  if (1 == GNUNET_CONTAINER_multipeermap_size (friend_peermap))
    find_finger_trail_task = GNUNET_SCHEDULER_add_now (&send_find_finger_trail_message, NULL);
}


/**
 * FIXME: Implement after testing finger/friend table setup.
 * Method called whenever a peer disconnects.
 *
 * @param cls closure
 * @param peer peer identity this notification is about
 */
static void
handle_core_disconnect (void *cls,
                        const struct GNUNET_PeerIdentity *peer)
{
  /**
   * 1. remove the friend from the friend map.
   * 2. remove the trail for the fingers for which this peer was the first hop.
   * 3. start send_find_finger_trail for these fingers to find a new trail 
   * in the network.
   * 4. Also when a node gets disconnected, how should we update pointers of its
   * immediate successor and predecessor in the network ?
   * 5. Also how do we distribute the keys in the network?
   * 6. Here is case where we started put operation but a peer got disconnected and 
      we removed the entry from the table. How to handle such a case. 
   */
}


/**
 * To be called on core init/fail.
 *
 * @param cls service closure
 * @param identity the public identity of this peer
 */
static void
core_init (void *cls,
           const struct GNUNET_PeerIdentity *identity)
{
  my_identity = *identity;
}


/**
 * Core handler for p2p put requests.
 *
 * @param cls closure
 * @param peer sender of the request
 * @param message message
 * @param peer peer identity this notification is about
 * @return #GNUNET_OK to keep the connection open,
 *         #GNUNET_SYSERR to close it (signal serious error)
 */
static int
handle_dht_p2p_put (void *cls,
                    const struct GNUNET_PeerIdentity *peer,
                    const struct GNUNET_MessageHeader *message)
{
    /**
    1. Check if destination is friend or finger.
    2. If finger then get the next hop from routing table and 
     * call GDS_NEGIHBOURS_handle_get.
    3. If friend then call find_successor to get the next hop and again
     * call GDS_NEIGHBOURS_handle_get to send to chosen hop.
     4. If you are the destination then do datacache_store.
     */
  return 0;
}


/**
 * Core handler for p2p get requests.
 *
 * @param cls closure
 * @param peer sender of the request
 * @param message message
 * @return #GNUNET_OK to keep the connection open,
 *         #GNUNET_SYSERR to close it (signal serious error)
 */
static int
handle_dht_p2p_get (void *cls, const struct GNUNET_PeerIdentity *peer,
                    const struct GNUNET_MessageHeader *message)
{
  /**
    1. Check if destination is friend or finger.
    2. If finger then get the next hop from routing table and 
     * call GDS_NEGIHBOURS_handle_get.
    3. If friend then call find_successor to get the next hop and again
     * call GDS_NEIGHBOURS_handle_get to send to chosen hop.
     4. If you are the destination then send the data back to source peer
   * Assuming we have trail setup we can
   * either store the whole trail or again do the search process..
     */
  return 0;
}


/**
 * Compare two peer identities.
 * @param p1 Peer identity
 * @param p2 Peer identity
 * @return 1 if p1 > p2, -1 if p1 < p2 and 0 if p1 == p2. 
 */
static int
compare_peer_id (const void *p1, const void *p2)
{
  return memcmp (p1, p2, sizeof (uint64_t));
}


/**
 * Returns the previous element of value in all_known_peers.
 * @param all_known_peers list of all the peers
 * @param value value we have to search in the all_known_peers.
 * @return 
 */
static struct GNUNET_PeerIdentity *
binary_search(struct GNUNET_PeerIdentity *all_known_peers, uint64_t *value,
              unsigned int size)
{
  unsigned int first;
  unsigned int last;
  unsigned int middle;
  struct GNUNET_PeerIdentity *successor;
  successor = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity));
  
  first = 0;
  last = size - 1;
  middle = (first + last)/2;
  
  while(first <= last)
  {
    /* all_known_peers[middle] > value*/
    if(0 > compare_peer_id(&all_known_peers[middle], &value))
    {
      first = middle + 1; 
    }
    else if(0 == compare_peer_id(&all_known_peers[middle], &value))
    {
      if(middle == 0)
      {
        successor = &(all_known_peers[size - 1]);
      }
      else
        successor = &(all_known_peers[middle-1]);
    }
    else
    {
       last = middle - 1;
    }
  
    middle = (first + last)/2;  
  }
  return successor;
}


/**
 * Find closest successor for the value.
 * @param value Value for which we are looking for successor
 * @param current_destination NULL if my_identity is successor else finger/friend 
 * identity 
 * @param type Next destination type
 * @return Peer identity of next destination i.e. successor of value. 
 */
static struct GNUNET_PeerIdentity *
find_successor(uint64_t *value, struct GNUNET_PeerIdentity *current_destination,
               enum current_destination_type *type)
{
  struct GNUNET_CONTAINER_MultiPeerMapIterator *friend_iter;
  struct GNUNET_CONTAINER_MultiPeerMapIterator *finger_iter;
  struct GNUNET_PeerIdentity key_ret;
  struct FriendInfo *friend;
  struct FingerInfo *finger;
  unsigned int finger_index;
  unsigned int friend_index;
  struct GNUNET_PeerIdentity *all_known_peers;
  struct GNUNET_PeerIdentity *successor;
  unsigned int size;
  unsigned int j;
  /* SUPU: 2 is added for my_identity and value. */
  size = GNUNET_CONTAINER_multipeermap_size (friend_peermap)+
         GNUNET_CONTAINER_multipeermap_size (finger_peermap)+
         2;
  
  all_known_peers = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity) * size);
  
  j = 0;
  memcpy (&all_known_peers[j], &(my_identity), sizeof (struct GNUNET_PeerIdentity));
  j++;
  memcpy (&all_known_peers[j], value, sizeof(struct GNUNET_PeerIdentity));
  
  /* Iterate over friend peermap and copy all the elements into array. */
  friend_iter = GNUNET_CONTAINER_multipeermap_iterator_create (friend_peermap); 
  for (friend_index = 0; friend_index < GNUNET_CONTAINER_multipeermap_size (friend_peermap); friend_index++)
  {
    /* FIXME: I don't think we are actually iterating.
     Read about how to iterate over the multipeermap. */
    if(GNUNET_YES == GNUNET_CONTAINER_multipeermap_iterator_next(friend_iter,&key_ret,(const void **)&friend)) 
    {
      memcpy (&all_known_peers[j], &(friend->id), sizeof (struct GNUNET_PeerIdentity));
      j++;
    }
  }
  
  /* Iterate over finger map and copy all the entries into all_known_peers array. */
  finger_iter = GNUNET_CONTAINER_multipeermap_iterator_create (finger_peermap);  
  for (finger_index = 0; finger_index < GNUNET_CONTAINER_multipeermap_size (finger_peermap); finger_index++)
  {
    /* FIXME: I don't think we are actually iterating.
     Read about how to iterate over the multi peer map. */
    if(GNUNET_YES == GNUNET_CONTAINER_multipeermap_iterator_next(finger_iter,&key_ret,(const void **)&finger)) 
    {
      memcpy (&all_known_peers[j], &(finger->finger_identity), sizeof (struct GNUNET_PeerIdentity));
      j++;
    }
  }
  
  qsort (all_known_peers, size, sizeof (struct GNUNET_PeerIdentity), &compare_peer_id);
  
  /* search value in all_known_peers array. */
  successor = binary_search (all_known_peers, value, size);
  
  /* compare successor with my_identity, finger and friend */
  if(0 == GNUNET_CRYPTO_cmp_peer_identity(&(my_identity), successor))
  {
    *type = MY_ID;
    return NULL;
  }
  else if (GNUNET_YES == GNUNET_CONTAINER_multipeermap_contains (friend_peermap,
                                              successor))
  {
    *type = FRIEND;
    memcpy (current_destination, successor, sizeof (struct GNUNET_PeerIdentity));
    return successor;
  }
  else if (GNUNET_YES == GNUNET_CONTAINER_multipeermap_contains (finger_peermap,
                                              successor))
  {
    *type = FINGER;
    memcpy (current_destination, successor, sizeof (struct GNUNET_PeerIdentity));
    /* get the corresponding finger for succcesor and read the first element from
     the trail list and return that element. */
    struct FingerInfo *successor_finger;
    struct GNUNET_PeerIdentity *next_hop;
    next_hop = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity));
    successor_finger = GNUNET_malloc (sizeof (struct FingerInfo));
    successor_finger = GNUNET_CONTAINER_multipeermap_get (finger_peermap, successor);
    memcpy (next_hop, &(successor_finger->trail_peer_list[0]), sizeof (struct GNUNET_PeerIdentity));
    return next_hop;
  }
  return NULL;
}


/**
 * Handle a PeerTrailSetupMessage. 
 * @param cls closure
 * @param message message
 * @param peer peer identity this notification is about
 * @return GNUNET_OK on success, GNUNET_SYSERR on error
 */
static int
handle_dht_p2p_trail_setup(void *cls, const struct GNUNET_PeerIdentity *peer,
                    const struct GNUNET_MessageHeader *message)
{
  struct PeerTrailSetupMessage *trail_setup; 
  struct GNUNET_PeerIdentity *next_hop; 
  struct FriendInfo *target_friend;
  size_t msize;
  uint32_t trail_length;
  enum current_destination_type peer_type;
  struct GNUNET_PeerIdentity *trail_peer_list; 
  uint32_t current_trail_index;
  struct GNUNET_PeerIdentity *next_peer;

  
  /* parse and validate message. */
  msize = ntohs (message->size);
  if (msize < sizeof (struct PeerTrailSetupMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
  
  trail_setup = (struct PeerTrailSetupMessage *) message; 
  trail_length = ntohl (trail_setup->trail_length); 
  peer_type = ntohl (trail_setup->current_destination_type);
  trail_peer_list = (struct GNUNET_PeerIdentity *) &trail_setup[1];
  
  if ((msize <
       sizeof (struct PeerTrailSetupMessage) +
       trail_length * sizeof (struct GNUNET_PeerIdentity)) ||
      (trail_length >
       GNUNET_SERVER_MAX_MESSAGE_SIZE / sizeof (struct GNUNET_PeerIdentity)))
  {
    GNUNET_break_op (0);
    return GNUNET_YES; /*TODO: Why do we send GNUNET_YES here? */
  }
 
  
  GNUNET_STATISTICS_update (GDS_stats,
                            gettext_noop ("# TRAIL SETUP requests received"), 1,
                            GNUNET_NO);
  GNUNET_STATISTICS_update (GDS_stats,
                            gettext_noop ("# TRAIL SETUP bytes received"), msize,
                            GNUNET_NO);
  
  if(peer_type == FRIEND)
  {
    if(0 == (GNUNET_CRYPTO_cmp_peer_identity (&(trail_setup->current_destination),
                                              &my_identity)))
    {
      next_hop = find_successor (&(trail_setup->destination_finger),
                                 &(trail_setup->current_destination),
                                 &(peer_type));
    }
    else
      return GNUNET_SYSERR; /*TODO: Should we handle this case differently? */
  }
  else if(peer_type == FINGER)
  {
    if(0 != (GNUNET_CRYPTO_cmp_peer_identity (&(trail_setup->current_destination),
                                              &my_identity)))
    {
      /* I am part of trail. 
       SUPU: So, I should ask for next hop to reach the current_destination which is the finger
       for which this packet has been sent. */
      next_hop = GDS_ROUTING_search (&(trail_setup->source_peer),
                                     &(trail_setup->current_destination));
      
      /*TODO: 
       call find_successor and compare the two peer ids 
       and choose whichever is closest to the destination finger. */
    } 
    else
    {
      /* I am the current_destination finger
       FIXME: Why are we sending current_destination to find_successor. 
       In this case, is it safe to assume current_Destination = my_identity.
       I guess we are sending current_destination so that we update it with new
       current_destination, if could either me, friend or finger.*/
      next_hop = find_successor (&(trail_setup->destination_finger),
                                 &(trail_setup->current_destination),&(peer_type));
    }
  }
   
  /* If you are the next hop */
  if(peer_type == MY_ID)
  {
    /* FIXME: Verify if its allowed here to definer peer_list and define it
       again in the next block below? */
      struct GNUNET_PeerIdentity *peer_list;
      peer_list = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity) * (trail_length));
      memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
      current_trail_index = trail_length - 2;
      next_peer = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity)); //FIXME: Do we need to allocate the memory?
      memcpy (next_peer, &peer_list[current_trail_index], sizeof (struct GNUNET_PeerIdentity));
      
      target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_peer);
     
      /* FIXME: It does not find a friend. Could be possible error in find_successor 
       function. Change the logic in find_successor and change it again. */
   
      /* FIXME: Here as destination_finger is 64 bit instead of struct
       GNUNET_PeerIdentity, but you need destination_peer id. If you calling the 
       function handle_Trail_setup_result from here, it means you are the
       destination. So, you can send your own identity. */
      GDS_NEIGHBOURS_handle_trail_setup_result (&(trail_setup->source_peer),
                                                &(my_identity),
                                                target_friend, trail_length,
                                                peer_list,current_trail_index,
                                                trail_setup->successor_flag, 
                                                trail_setup->predecessor_flag);
  
    return GNUNET_YES;
  }
  
  /* Add next_hop to list of peers that trail setup message have traversed so far
   and increment trail length. */
  struct GNUNET_PeerIdentity *peer_list;
  peer_list = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity) * (trail_length + 1));
  memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
  memcpy (&peer_list[trail_length], next_hop, sizeof (struct GNUNET_PeerIdentity));
  trail_length++;
  
  target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop);
  
  if(peer_type == FINGER)
  {
    GDS_ROUTING_add (&(trail_setup->source_peer), 
                     &(trail_setup->current_destination),
                     next_hop);
  }
  
  GDS_NEIGHBOURS_handle_trail_setup (&(trail_setup->source_peer),
                                     &(trail_setup->destination_finger),
                                     target_friend,
                                     trail_setup->trail_length,
                                     peer_list,trail_setup->successor_flag,
                                     trail_setup->predecessor_flag);
return GNUNET_YES;
}


/**
 * Add an entry in finger table. 
 * @param finger Finger to be added to finger table
 * @param peer_list peers this request has traversed so far
 * @param trail_length Numbers of peers in the trail.
 */
static 
void finger_table_add(struct GNUNET_PeerIdentity *finger,
                      const struct GNUNET_PeerIdentity *peer_list,
                      unsigned int trail_length,
                      unsigned int successor_flag,
                      unsigned int predecessor_flag)
{
  /*FIXME: okay so there are two fields. one we should remember what finger 
   identity we were looking for and what successor id we got. */
  struct FingerInfo *finger_entry;
  finger_entry = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity));
  memcpy (&(finger_entry->finger_identity), finger, sizeof (struct GNUNET_PeerIdentity));
  memcpy (&(finger_entry->trail_peer_list), peer_list, 
          sizeof (struct GNUNET_PeerIdentity)* trail_length);
  finger_entry->successor = successor_flag;
  finger_entry->predecessor = predecessor_flag;
  
  /*FIXME: Is it really a good time to call verify successor message. */
  if (1 == GNUNET_CONTAINER_multipeermap_size (finger_peermap))
    verify_successor = GNUNET_SCHEDULER_add_now (&send_verify_successor_message, NULL);
}


/**
 * Core handle for p2p trail construction result messages.
 * @param cls closure
 * @param message message
 * @param peer peer identity this notification is about
 * @return GNUNET_OK on success, GNUNET_SYSERR on error
 */
static int
handle_dht_p2p_trail_setup_result(void *cls, const struct GNUNET_PeerIdentity *peer,
                    const struct GNUNET_MessageHeader *message)
{
  struct PeerTrailSetupResultMessage *trail_result;
  size_t msize;
  uint32_t trail_length;
  const struct GNUNET_PeerIdentity *trail_peer_list;
  uint32_t current_trail_index;
  struct GNUNET_PeerIdentity *next_peer;
  struct FriendInfo *target_friend;
  
  msize = ntohs (message->size);
  if (msize < sizeof (struct PeerTrailSetupMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
  
  trail_result = (struct PeerTrailSetupResultMessage *) message; 
  trail_length = ntohl (trail_result->trail_length); 
  current_trail_index = ntohl (trail_result->current_index);
  trail_peer_list = (struct GNUNET_PeerIdentity *) &trail_result[1];
  
  if ((msize <
       sizeof (struct PeerTrailSetupResultMessage) +
       trail_length * sizeof (struct GNUNET_PeerIdentity)) ||
      (trail_length >
       GNUNET_SERVER_MAX_MESSAGE_SIZE / sizeof (struct GNUNET_PeerIdentity)))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
 
  if(0 == (GNUNET_CRYPTO_cmp_peer_identity (&(trail_result->current_destination),
                                            &my_identity)))
  {
    /* Am I the destination? */
    if( 0 == (GNUNET_CRYPTO_cmp_peer_identity (&(trail_result->destination_peer),
                                               &my_identity)))
    {
      finger_table_add (&(trail_result->finger), trail_peer_list,trail_length, 
                       trail_result->successor_flag, trail_result->predecessor_flag);
      
      return GNUNET_YES;
    }
    else
    {
      next_peer = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity));
      current_trail_index = current_trail_index - 1;
      memcpy (next_peer, &(trail_peer_list[trail_length-1]), 
              sizeof (struct GNUNET_PeerIdentity));
      
      target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_peer);
    
      GDS_NEIGHBOURS_handle_trail_setup_result(&(trail_result->destination_peer),
                                               &(trail_result->finger),
                                               target_friend, trail_length,
                                               trail_peer_list,current_trail_index,
                                               trail_result->successor_flag,
                                               trail_result->predecessor_flag);
      return GNUNET_YES;
    }
  }
  else
    return GNUNET_SYSERR;
}


/**
 * Core handle for p2p trail construction result messages.
 * @param cls closure
 * @param message message
 * @param peer peer identity this notification is about
 * @return GNUNET_OK on success, GNUNET_SYSERR on error
 */
static int
handle_dht_p2p_verify_successor(void *cls, const struct GNUNET_PeerIdentity *peer,
                                const struct GNUNET_MessageHeader *message)
{
  /*
   * In this function you have received the message verify successor,
   * Now, either you are the destination or just part of the trail.
   * As we already know the whole path find out the next destination
   * and pass the packet forward.
   * If you are the final destination, check who is your predecessor.  
   * and send your predecessor back to calling function. call GDS_NEIGHBOURS_handle_verify_successor
   * FIXME: Should we have a different handler function for it. 
   */
  struct PeerVerifySuccessorMessage *vsm;
  size_t msize;
  unsigned int trail_length;
  
  /* Uncomment after initialization
  struct GNUNET_PeerIdentity *trail_peer_list;
  unsigned int current_trail_index;
  struct GNUNET_PeerIdentity *next_peer;
  struct FriendInfo *target_friend;
  */  
   msize = ntohs (message->size);
  if (msize < sizeof (struct PeerVerifySuccessorMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
  
  vsm = (struct PeerVerifySuccessorMessage *) message;
  trail_length = ntohl (vsm->trail_length);
  //current_trail_index = ntohl (vsm->current_index);
          
  //trail_peer_list = (struct GNUNET_PeerIdentity *) &vsm[1];
  if ((msize <
       sizeof (struct PeerVerifySuccessorMessage) +
       trail_length * sizeof (struct GNUNET_PeerIdentity)) ||
       (trail_length >
       GNUNET_SERVER_MAX_MESSAGE_SIZE / sizeof (struct GNUNET_PeerIdentity)))
       {
         GNUNET_break_op (0);
         return GNUNET_YES;
       }
  
  if(0 == (GNUNET_CRYPTO_cmp_peer_identity (&(vsm->successor),
                                            &my_identity)))
  {
    /* You are the successor for which this message has been sent. */
    /* Search over your finger peer map to find the predecessor and then call
     GDS_NEIGHBOURS_handle_verify_successor_result with correct parameters. */
    struct GNUNET_CONTAINER_MultiPeerMapIterator *finger_iter;
    struct GNUNET_PeerIdentity key_ret;
    unsigned int finger_index;
    struct FingerInfo *finger;
    struct GNUNET_PeerIdentity *destination_peer;
    
    finger_iter = GNUNET_CONTAINER_multipeermap_iterator_create (finger_peermap);  
    for (finger_index = 0; finger_index < GNUNET_CONTAINER_multipeermap_size (finger_peermap); finger_index++)
    {
      /* FIXME: I don't think we are actually iterating.
      Read about how to iterate over the multi peer map. */
      if(GNUNET_YES == GNUNET_CONTAINER_multipeermap_iterator_next(finger_iter,&key_ret,(const void **)&finger)) 
      {
       if(1 == finger->predecessor)
        break; /* FIXME: Do I come out of inner if or outer for */
      }
    }
    
    destination_peer = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity));
    memcpy (destination_peer, &(vsm->source_peer), sizeof (struct GNUNET_PeerIdentity));
    
    /*SUPU: Initialize all the fields. */
    /* FIXME: Initialize all the parameters of this function.
     Also, target_friend in this case is the peer id which is last in the trail.
     check if destination peer is in peer list or not. To check you will have to
     check the trail_setup and how we are adding the peer in there. */
    /* FIXME: Uncomment after initializing the fields
     * GDS_NEIGHBOURS_handle_verify_successor_result (destination_peer,
                                                   &(my_identity),
                                                   &(finger->finger_identity),
                                                   target_friend,
                                                   trail_peer_list,
                                                   trail_length,
                                                   current_trail_index); */
  }
  else
  {
    /* FIXME: Initialize all the parameters to 
     * this function. Read the element at current_trail_index + 1
     and call GDS_NEIGHBOURS_handle_verify_successor with correct parameters. */
    /* FIXME: Uncomment after initializing the fields. 
     * GDS_NEIGUBOURS_handle_verify_successor(&(vsm->source_peer),
                                           &(vsm->successor),
                                           target_friend,
                                           trail_peer_list,
                                           trail_length,
                                           current_trail_index); */
  }
  return GNUNET_YES;
}


/**
 * Core handle for p2p trail construction result messages.
 * @param cls closure
 * @param message message
 * @param peer peer identity this notification is about
 * @return GNUNET_OK on success, GNUNET_SYSERR on error
 */
static int
handle_dht_p2p_notify_new_successor(void *cls, const struct GNUNET_PeerIdentity *peer,
                                    const struct GNUNET_MessageHeader *message)
{
  /*
   * So, if you are the destination you should update your
   * predecessor field with peer id of source peer of this message.
   * If you are not the destination peer, then just check your routing
   * table and pass on the message. 
   */
  return GNUNET_YES;
}


/**
 * Core handle for p2p trail construction result messages.
 * @param cls closure
 * @param message message
 * @param peer peer identity this notification is about
 * @return GNUNET_OK on success, GNUNET_SYSERR on error
 */
static int
handle_dht_p2p_verify_successor_result(void *cls, const struct GNUNET_PeerIdentity *peer,
                                       const struct GNUNET_MessageHeader *message)
{
  /*
   * In this function you have received the message verify successor result,
   If you are not the destination, just pass this message forward
   * if you are destination,
   * then check if immediate predecessor of this peer is you or someone else.
   * If its you, then don't do anything.
   * If its some one else, then call notify method to let your new successor
   * know that you are its predecessor. 
   */
  return GNUNET_YES;
}


/**
 * Initialize neighbours subsystem.
 * @return GNUNET_OK on success, GNUNET_SYSERR on error
 */
int
GDS_NEIGHBOURS_init()
{
  static struct GNUNET_CORE_MessageHandler core_handlers[] = {
    {&handle_dht_p2p_get, GNUNET_MESSAGE_TYPE_DHT_P2P_GET, 0},
    {&handle_dht_p2p_put, GNUNET_MESSAGE_TYPE_DHT_P2P_PUT, 0},
    {&handle_dht_p2p_trail_setup, GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP, 0},
    {&handle_dht_p2p_trail_setup_result, GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP_RESULT, 0},
    {&handle_dht_p2p_verify_successor, GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR, 0},
    {&handle_dht_p2p_notify_new_successor, GNUNET_MESSAGE_TYPE_DHT_P2P_NOTIFY_NEW_SUCCESSOR, 0},
    {&handle_dht_p2p_verify_successor_result, GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR_RESULT, 0},
    {NULL, 0, 0}
  };

  /*TODO: What is ATS? Why do we need it? */
  atsAPI = GNUNET_ATS_performance_init (GDS_cfg, NULL, NULL);
  core_api =
    GNUNET_CORE_connect (GDS_cfg, NULL, &core_init, &handle_core_connect,
                           &handle_core_disconnect, NULL, GNUNET_NO, NULL,
                           GNUNET_NO, core_handlers);
  if (core_api == NULL)
    return GNUNET_SYSERR;

  friend_peermap = GNUNET_CONTAINER_multipeermap_create (256, GNUNET_NO);
  finger_peermap = GNUNET_CONTAINER_multipeermap_create (MAX_FINGERS, GNUNET_NO); 
 
  return GNUNET_OK;
}


/**
 * Shutdown neighbours subsystem.
 */
void
GDS_NEIGHBOURS_done ()
{
  if (NULL == core_api)
    return;
  
  GNUNET_CORE_disconnect (core_api);
  core_api = NULL;
  GNUNET_ATS_performance_done (atsAPI);
  atsAPI = NULL;

  /* FIXME: Once handle_core_disconnect is implemented, both below assertion should not
   fail. */
  GNUNET_assert (0 == GNUNET_CONTAINER_multipeermap_size (friend_peermap));
  GNUNET_CONTAINER_multipeermap_destroy (friend_peermap);
  friend_peermap = NULL;

  GNUNET_assert (0 == GNUNET_CONTAINER_multipeermap_size (finger_peermap));
  GNUNET_CONTAINER_multipeermap_destroy (finger_peermap);
  finger_peermap = NULL;

  if (GNUNET_SCHEDULER_NO_TASK != find_finger_trail_task)
  {
    GNUNET_SCHEDULER_cancel (find_finger_trail_task);
    find_finger_trail_task = GNUNET_SCHEDULER_NO_TASK;
  }
  
  /* FIXME: fix_fingers will also be a task like this.
     Add it later. */
  if (GNUNET_SCHEDULER_NO_TASK != verify_successor)
  {
    GNUNET_SCHEDULER_cancel (verify_successor);
    verify_successor = GNUNET_SCHEDULER_NO_TASK;
  }
  
}


/**
 * Get the ID of the local node.
 *
 * @return identity of the local node
 */
struct GNUNET_PeerIdentity *
GDS_NEIGHBOURS_get_id ()
{
  return &my_identity;
}


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