x-vine:fixes

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

/*
     This file is part of GNUnet.
     (C) 2009-2014 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_ats_service.h"
#include "gnunet_core_service.h"
#include "gnunet_datacache_lib.h"
#include "gnunet_transport_service.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_neighbours.h"
#include "gnunet-service-xdht_routing.h"
#include <fenv.h>
#include "dht.h"

/**
 * TODO: 
 * 1. In X-Vine paper, there is no policy defined for replicating the data to
 * recover in case of peer failure. We can do it in Chord way. In R5N, the key
 * is hashed and then data is stored according to the key value generated after
 * hashing.
 */


/**
 * Maximum possible fingers (including predecessor) of a peer 
 */
#define MAX_FINGERS 65

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

/**
 * How long to wait before sending another find finger trail request
 */
#define DHT_FIND_FINGER_TRAIL_INTERVAL GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 2)

/**
 * How long to wait before sending another verify successor message. 
 */
#define DHT_SEND_VERIFY_SUCCESSOR_INTERVAL GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 1)

/**
 * How long at most to wait for transmission of a request to a friend ?
 */
#define GET_TIMEOUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MINUTES, 2)

/**
 * Duration for which I may remain congested. 
 * Note: Its a static value. In future, a peer may do some analysis and calculate 
 * congestion_timeout based on 'some' parameters. 
 */
#define CONGESTION_TIMEOUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MINUTES, 2)

/**
 * Maximum number of trails allowed to go through a friend.
 */
#define TRAILS_THROUGH_FRIEND_THRESHOLD 64

/**
 * Maximum number of trails stored per finger.
 */
#define MAXIMUM_TRAILS_PER_FINGER 1

/**
 * Finger map index for predecessor entry in finger table.
 */
#define PREDECESSOR_FINGER_ID 64

/**
 * Wrap around in peer identity circle. 
 */
#define PEER_IDENTITES_WRAP_AROUND pow(2, 64) - 1

/**
 * FIXME: Its use only at 3 places check if you can remove it.
 * To check if a finger is predecessor or not. 
 */
enum GDS_NEIGHBOURS_finger_type
{
  GDS_FINGER_TYPE_PREDECESSOR = 1,
  GDS_FINGER_TYPE_NON_PREDECESSOR = 0
};

GNUNET_NETWORK_STRUCT_BEGIN

/**
 * P2P PUT message
 */
struct PeerPutMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_PUT
   */
  struct GNUNET_MessageHeader header;

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

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

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

  /**
   * Replication level for this message
   * In the current implementation, this value is not used. 
   */
  uint32_t desired_replication_level GNUNET_PACKED;

  /**
   * Length of the PUT path that follows (if tracked).
   */
  uint32_t put_path_length GNUNET_PACKED;
  
  /** 
   * Best known destination (could be my friend or finger) which should
   * get this message next. 
   */
  struct GNUNET_PeerIdentity best_known_destination;
  
  /**
   * In case best_known_destination is a finger, then trail to reach
   * to that finger. Else its default value is 0. 
   */
  struct GNUNET_HashCode intermediate_trail_id;
  
  /**
   * When does the content expire?
   */
  struct GNUNET_TIME_AbsoluteNBO expiration_time;
  
  /**
   * The key to store the value under.
   */
  struct GNUNET_HashCode key GNUNET_PACKED;

  /* put path (if tracked) */

  /* Payload */
 
};

/**
 * P2P GET message
 */
struct PeerGetMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_GET
   */
  struct GNUNET_MessageHeader header;
  
  /**
   * Processing options
   */
  uint32_t options GNUNET_PACKED;

  /**
   * Desired content type.
   */
  uint32_t block_type GNUNET_PACKED;
  
  /**
   * Hop count
   */
  uint32_t hop_count GNUNET_PACKED;
 
  /**
   * Desired replication level for this request.
   * In the current implementation, this value is not used. 
   */
  uint32_t desired_replication_level GNUNET_PACKED;
  
  /**
   * Total number of peers in get path. 
   */
  unsigned int get_path_length;
  
  /**
   * Best known destination (could be my friend or finger) which should
   * get this message next. 
   */
  struct GNUNET_PeerIdentity best_known_destination;
  
  /**
   * In case best_known_destination is a finger, then trail to reach
   * to that finger. Else its default value is 0. 
   */
  struct GNUNET_HashCode intermediate_trail_id;
 
  /**
   * The key we are looking for.
   */
  struct GNUNET_HashCode key;
  
  /* Get path. */
  /* struct GNUNET_PeerIdentity[]*/
};

/**
 * P2P Result message
 */
struct PeerGetResultMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_GET_RESULT
   */
  struct GNUNET_MessageHeader header;

  /**
   * The type for the data.
   */
  uint32_t type GNUNET_PACKED;
  
  /**
   * Number of peers recorded in the outgoing path from source to the
   * stored location of this message.
   */
  uint32_t put_path_length GNUNET_PACKED;
  
  /**
   * Length of the GET path that follows (if tracked).
   */
  uint32_t get_path_length GNUNET_PACKED;
  
  /**
   * Peer which queried for get and should get the result. 
   */
  struct GNUNET_PeerIdentity querying_peer;
  
  /**
   * When does the content expire?
   */
  struct GNUNET_TIME_Absolute expiration_time;

  /**
   * The key of the corresponding GET request.
   */
  struct GNUNET_HashCode key;
 
  /* put path (if tracked) */

  /* get path (if tracked) */

  /* Payload */

};

/**
 * P2P Trail setup message
 */
struct PeerTrailSetupMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_SETUP
   */
  struct GNUNET_MessageHeader header;
  
  /**
   * Is source_peer trying to setup the trail to a predecessor or any finger.
   */
  uint32_t is_predecessor; 
  
  /**
   * Peer closest to this value will be our finger.
   */
  uint64_t final_destination_finger_value;

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

  /**
   * Best known destination (could be my friend or finger) which should
   * get this message next. 
   */
  struct GNUNET_PeerIdentity best_known_destination; 

  /**
   * In case best_known_destination is a finger, then trail id of trail to
   * reach to this finger.
   */
  struct GNUNET_HashCode intermediate_trail_id;
  
  /**
   * Trail id for trail which we are trying to setup.
   */
  struct GNUNET_HashCode trail_id; 

  /* List of peers which are part of trail setup so far.
   * Trail does NOT include source_peer and peer which will be closest to
   * ultimate_destination_finger_value.
   * struct GNUNET_PeerIdentity trail[]
   */
};

/**
  * P2P Trail Setup Result message
 */
struct PeerTrailSetupResultMessage
{

  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_SETUP_RESULT
   */
  struct GNUNET_MessageHeader header;

  /**
   * Finger to which we have found the path.
   */
  struct GNUNET_PeerIdentity finger_identity;

  /**
   * Peer which started trail_setup to find trail to finger_identity
   */
  struct GNUNET_PeerIdentity querying_peer; 

  /**
   * Is the trail setup to querying_peer's predecessor or finger?
   */
  uint32_t is_predecessor; 

  /**
   * Value to which finger_identity is the closest peer. 
   */
  uint64_t ulitmate_destination_finger_value;
  
  /**
   * Identifier of the trail from querying peer to finger_identity, NOT
   * including both endpoints. 
   */
  struct GNUNET_HashCode trail_id;

  /* List of peers which are part of the trail from querying peer to 
   * finger_identity, NOT including both endpoints.
   * struct GNUNET_PeerIdentity trail[] 
   */
};

/**
 * P2P Verify Successor Message.
 */
struct PeerVerifySuccessorMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_VERIFY_SUCCESSOR
   */
  struct GNUNET_MessageHeader header;

  /**
   * Peer which wants to verify its successor.
   */
  struct GNUNET_PeerIdentity source_peer;

  /**
   * Source Peer's current successor.
   */
  struct GNUNET_PeerIdentity successor;

  /**
   * Identifier of trail to reach from source_peer to successor.
   */
  struct GNUNET_HashCode trail_id;

  /* List of the peers which are part of trail to reach  from source_peer 
   * to successor, NOT including them
   * struct GNUNET_PeerIdentity trail[] 
   */
};

/**
 * P2P Verify Successor Result Message
 */
struct PeerVerifySuccessorResultMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_VERIFY_SUCCESSOR_RESULT
   */
  struct GNUNET_MessageHeader header;

  /**
   * Peer which sent the request to verify its successor.
   */
  struct GNUNET_PeerIdentity querying_peer;

  /**
   * Successor to which PeerVerifySuccessorMessage was sent.
   */
  struct GNUNET_PeerIdentity current_successor;

  /**
   * Current Predecessor of source_successor. It can be same as querying peer
   * or different. In case it is different then it can be querying_peer's
   * probable successor. 
   */
  struct GNUNET_PeerIdentity probable_successor;

  /**
   * Trail identifier of trail from querying_peer to current_successor.
   */
  struct GNUNET_HashCode trail_id;

  /**
   * Direction in which we are looking at the trail.
   */
  uint32_t trail_direction;

  /* In case probable_successor != querying_peer, then trail to reach from
   * querying_peer to probable_successor, NOT including end points.
   * struct GNUNET_PeerIdentity trail[]
   */
};

/**
 * P2P Notify New Successor Message.
 */
struct PeerNotifyNewSuccessorMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_NOTIFY_NEW_SUCCESSOR
   */
  struct GNUNET_MessageHeader header;

  /**
   * Peer which wants to notify its new successor.
   */
  struct GNUNET_PeerIdentity source_peer;

  /**
   * New successor of source_peer.
   */
  struct GNUNET_PeerIdentity new_successor;

  /**
   * Unique identifier of the trail from source_peer to new_successor,
   * NOT including the endpoints.
   */
  struct GNUNET_HashCode trail_id;

  /* List of peers in trail from source_peer to new_successor, 
   * NOT including the endpoints. 
   * struct GNUNET_PeerIdentity trail[]
   */
};

/**
 * P2P Trail Compression Message.
 */
struct PeerTrailCompressionMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_COMPRESSION
   */
  struct GNUNET_MessageHeader header;

  /**
   * Source peer of this trail.
   */
  struct GNUNET_PeerIdentity source_peer;

  /**
   * Trail from source_peer to destination_peer compressed such that
   * new_first_friend is the first hop in the trail from source to
   * destination.
   */
  struct GNUNET_PeerIdentity new_first_friend;

  /**
   * Unique identifier of trail.
   */
  struct GNUNET_HashCode trail_id;
};


/**
 * P2P Trail Tear Down message.
 */
struct PeerTrailTearDownMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_TEARDOWN
   */
  struct GNUNET_MessageHeader header;

  /**
   * Unique identifier of the trail.
   */
  struct GNUNET_HashCode trail_id;

  /**
   * Direction of trail.
   */
  uint32_t trail_direction;
};


/**
 * P2P Trail Rejection Message.
 */
struct PeerTrailRejectionMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_SETUP_REJECTION
   */
  struct GNUNET_MessageHeader header;

  /**
   * Peer which wants to set up the trail.
   */
  struct GNUNET_PeerIdentity source_peer;

  /**
   * Peer which sent trail rejection message as it it congested. 
   */
  struct GNUNET_PeerIdentity congested_peer;

  /**
   * Peer identity closest to this value will be finger of
   * source_peer.
   */
  uint64_t ultimate_destination_finger_value;

  /**
   * Is source_peer trying to setup the trail to its predecessor or finger.
   */
  uint32_t is_predecessor;

  /**
   * Identifier for the trail that source peer is trying to setup.
   */
  struct GNUNET_HashCode trail_id;
  
  /**
   * Relative time for which congested_peer will remain congested.
   */
  struct GNUNET_TIME_Relative congestion_time;

  /* Trail_list from source_peer to peer which sent the message for trail setup
   * to congested peer. This trail does NOT include source_peer.
   struct GNUNET_PeerIdnetity trail[]*/
};

/**
 * P2P Add Trail Message.
 */
struct PeerAddTrailMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_XDHT_P2P_ADD_TRAIL
   */
  struct GNUNET_MessageHeader header;

  /**
   * Source of the routing trail.
   */
  struct GNUNET_PeerIdentity source_peer;

  /**
   * Destination of the routing trail.
   */
  struct GNUNET_PeerIdentity destination_peer;

  /**
   * Unique identifier of the trail from source_peer to destination_peer,
   * NOT including the endpoints.
   */
  struct GNUNET_HashCode trail_id;

  /* Trail from source peer to destination peer, NOT including them.
   * struct GNUNET_PeerIdentity trail[]
   */
};

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;

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

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

  /**
   * 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;

};

/**
 *  Entry in friend_peermap.
 */
struct FriendInfo
{
  /**
   * Friend Identity
   */
  struct GNUNET_PeerIdentity id;

  /**
   * Number of trails for which this friend is the first hop or if the friend
   * is finger. 
   */
  unsigned int trails_count;

  /**
   * Count of outstanding messages for this friend.
   */
  unsigned int pending_count;

  /**
   * In case not 0, then amount of time for which this friend is congested.
   */
  struct GNUNET_TIME_Absolute congestion_timestamp;

  /**
   * Head of pending messages to be sent to this friend.
   */
  struct P2PPendingMessage *head;

  /**
   * Tail of pending messages to be sent to this friend.
   */
  struct P2PPendingMessage *tail;

  /**
   * Core handle for sending messages to this friend.
   */
  struct GNUNET_CORE_TransmitHandle *th;

};

/**
 * An individual element of the trail to reach to a finger.
 */
struct Trail_Element 
{
  /**
    * Pointer to next item in the list
    */
  struct Trail_Element *next;

  /**
    * Pointer to prev item in the list
    */
  struct Trail_Element *prev;

  /**
   * An element in this trail.
   */
  struct GNUNET_PeerIdentity peer;
};

/**
 * Information about an individual trail. 
 */
struct Trail 
{
  /**
   * Head of trail.
   */
  struct Trail_Element *trail_head;

  /**
   * Tail of trail.
   */
  struct Trail_Element *trail_tail;

  /**
   * Unique identifier of this trail.
   */
  struct GNUNET_HashCode trail_id;

  /**
   * Length of trail pointed
   */
  unsigned int trail_length;
  
  /**
   * Is there a valid trail entry. 
   */
  unsigned int is_present;
};

/**
 * An entry in finger_table
 */
struct FingerInfo
{
  /**
   * Finger identity.
   */
  struct GNUNET_PeerIdentity finger_identity;

  /**
   * Is any finger stored at this finger index. 
   */
  unsigned int is_present;
  
  /**
   * Index in finger peer map
   */
  uint32_t finger_table_index;

  /**
   * Number of trails setup so far for this finger.
   * Should not cross MAXIMUM_TRAILS_PER_FINGER.
   */
  uint32_t trails_count;

  /**
   * Array of trails to reach to this finger.
   */
  struct Trail trail_list[MAXIMUM_TRAILS_PER_FINGER]; 
};


/**
 * Stores information about the peer which is closest to destination_finger_value.
 * 'closest' can be either successor or predecessor depending on is_predecessor
 * flag.
 */
struct Closest_Peer
{
  /**
   * Destination finger value. 
   */
  uint64_t destination_finger_value;
  
  /**
   * Is finger_value a predecessor or any other finger. 
   */
  unsigned int is_predecessor;
  
  /**
   * Trail id to reach to peer.
   * In case peer is my identity or friend, it is set to 0.
   */
  struct GNUNET_HashCode trail_id;

  /**
   * Next destination. In case of friend and my_identity , it is same as next_hop
   * In case of finger it is finger identity.
   */
  struct GNUNET_PeerIdentity best_known_destination;
  
  /**
   * In case best_known_destination is a finger, then first friend in the trail
   * to reach to it. In other case, same as best_known_destination.
   */
  struct GNUNET_PeerIdentity next_hop;
};


/**
 * Data structure to store the trail chosen to reach to finger.
 */
struct Selected_Finger_Trail
{
  /**
   * First friend in the trail to reach finger.
   */
  struct FriendInfo friend;

  /**
   * Identifier of this trail.
   */
  struct GNUNET_HashCode trail_id;

  /**
   * Total number of peers in this trail.
   */
  unsigned int trail_length;
};

/**
 * Task that sends FIND FINGER TRAIL requests. This task is started when we have
 * get our first friend.
 */
static GNUNET_SCHEDULER_TaskIdentifier find_finger_trail_task;

/**
 * Task that sends verify successor message. This task is started when we get 
 * our successor for the first time. 
 */
static GNUNET_SCHEDULER_TaskIdentifier send_verify_successor_task;

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

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

/**
 * Array of all the fingers. 
 */
static struct FingerInfo finger_table [MAX_FINGERS];

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

/**
 * Handle for the statistics service.
 */
extern struct GNUNET_STATISTICS_Handle *GDS_stats;

/**
 * The current finger index that we have want to find trail to. We start the
 * search with value = 0, i.e. successor  and then go to PREDCESSOR_FINGER_ID
 * and decrement it. For any index 63 <= index < 0, if finger is same as successor,
 * we reset this index to 0.
 */
static unsigned int current_search_finger_index;

/**
 * Should we store our topology predecessor and successor IDs into statistics?
 */
unsigned int track_topology;

/**
 * Called when core is ready to send a message we asked for
 * out to the destination.
 *
 * @param cls the 'struct FriendInfo' of the target friend
 * @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);

  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);
}


/**
 * Construct a trail setup message and forward it to target_friend
 * @param source_peer Peer which wants to setup the trail
 * @param ultimate_destination_finger_value Peer identity closest to this value 
 *                                          will be finger to @a source_peer
 * @param best_known_destination Best known destination (could be finger or friend)
 *                               which should get this message. In case it is 
 *                               friend, then it is same as target_friend
 * @param target_friend Friend to which message is forwarded now.
 * @param trail_length Total number of peers in trail setup so far.
 * @param trail_peer_list Trail setup so far
 * @param is_predecessor Is @a source_peer looking for trail to a predecessor or not.
 * @param trail_id Unique identifier for the trail we are trying to setup.
 * @param intermediate_trail_id Trail id of intermediate trail to reach to 
 *                              best_known_destination when its a finger. If not 
 *                              used then set to 0.
 */
void
GDS_NEIGHBOURS_send_trail_setup (struct GNUNET_PeerIdentity source_peer,
                                 uint64_t ultimate_destination_finger_value,
                                 struct GNUNET_PeerIdentity best_known_destination,
                                 struct FriendInfo *target_friend,
                                 unsigned int trail_length,
                                 const struct GNUNET_PeerIdentity *trail_peer_list,
                                 unsigned int is_predecessor,
                                 struct GNUNET_HashCode trail_id,
                                 struct GNUNET_HashCode intermediate_trail_id)
{
  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 (target_friend->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->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_XDHT_P2P_TRAIL_SETUP);
  tsm->final_destination_finger_value = GNUNET_htonll (ultimate_destination_finger_value);
  tsm->source_peer = source_peer;
  tsm->best_known_destination = best_known_destination;
  tsm->is_predecessor = htonl (is_predecessor);
  tsm->trail_id = trail_id;
  tsm->intermediate_trail_id = intermediate_trail_id;

  if (trail_length > 0)
  {
    peer_list = (struct GNUNET_PeerIdentity *) &tsm[1];
    memcpy (peer_list, trail_peer_list, trail_length * sizeof(struct GNUNET_PeerIdentity));
  }
 
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Construct a trail setup result message and forward it to target friend.
 * @param querying_peer Peer which sent the trail setup request and should get
 *                      the result back. 
 * @param Finger Peer to which the trail has been setup to.
 * @param target_friend Friend to which this message should be forwarded.
 * @param trail_length Numbers of peers in the trail.
 * @param trail_peer_list Peers which are part of the trail from 
 *                        querying_peer to Finger, NOT including them. 
 * @param is_predecessor Is @a Finger predecessor to @a querying_peer ?
 * @param ultimate_destination_finger_value Value to which @a finger is the closest
 *                                          peer. 
 * @param trail_id Unique identifier of the trail.
 */
void
GDS_NEIGHBOURS_send_trail_setup_result (struct GNUNET_PeerIdentity querying_peer,
                                        struct GNUNET_PeerIdentity finger,
                                        struct FriendInfo *target_friend,
                                        unsigned int trail_length,
                                        const struct GNUNET_PeerIdentity *trail_peer_list,
                                        unsigned int is_predecessor,
                                        uint64_t ultimate_destination_finger_value,
                                        struct GNUNET_HashCode trail_id)
{
  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 (target_friend->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;
  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_XDHT_P2P_TRAIL_SETUP_RESULT);
  tsrm->querying_peer = querying_peer;
  tsrm->finger_identity = finger;
  tsrm->is_predecessor = htonl (is_predecessor);
  tsrm->trail_id = trail_id;
  tsrm->ulitmate_destination_finger_value = 
          GNUNET_htonll (ultimate_destination_finger_value);
  peer_list = (struct GNUNET_PeerIdentity *) &tsrm[1];

  if (trail_length > 0)
  {
    memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
  }
  /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Send trail rejection message to target friend
 * @param source_peer Peer which is trying to setup the trail.
 * @param ultimate_destination_finger_value Peer closest to this value will be 
 *                                          @a source_peer's finger
 * @param congested_peer Peer which sent this message as it is congested.
 * @param is_predecessor Is source_peer looking for trail to a predecessor or not.
 * @param trail_peer_list Trails seen so far in trail setup before getting rejected
 *                        by congested_peer. This does NOT include @a source_peer
 *                        and congested_peer.
 * @param trail_length Total number of peers in trail_peer_list, NOT including
 *                     @a source_peer and @a congested_peer
 * @param trail_id Unique identifier of this trail.
 * @param congestion_timeout Duration given by congested peer as an estimate of
 *                           how long it may remain congested.
 */
void
GDS_NEIGHBOURS_send_trail_rejection (struct GNUNET_PeerIdentity source_peer,
                                     uint64_t ultimate_destination_finger_value,
                                     struct GNUNET_PeerIdentity congested_peer,
                                     unsigned int is_predecessor,
                                     const struct GNUNET_PeerIdentity *trail_peer_list,
                                     unsigned int trail_length,
                                     struct GNUNET_HashCode trail_id,
                                     struct FriendInfo *target_friend,
                                     const struct GNUNET_TIME_Relative congestion_timeout)
{
  struct PeerTrailRejectionMessage *trm;
  struct P2PPendingMessage *pending;
  struct GNUNET_PeerIdentity *peer_list;
  size_t msize;
  
  msize = sizeof (struct PeerTrailRejectionMessage) +
          (trail_length * sizeof (struct GNUNET_PeerIdentity));

  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }

  if (target_friend->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;
  pending->timeout = GNUNET_TIME_relative_to_absolute (GET_TIMEOUT);
  trm = (struct PeerTrailRejectionMessage *)&pending[1];
  pending->msg = &trm->header;
  trm->header.size = htons (msize);
  trm->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_SETUP_REJECTION);
  trm->source_peer = source_peer;
  trm->congested_peer = congested_peer;
  trm->congestion_time = congestion_timeout;
  trm->is_predecessor = htonl (is_predecessor);
  trm->trail_id = trail_id;
  trm->ultimate_destination_finger_value = 
          GNUNET_htonll (ultimate_destination_finger_value);

  peer_list = (struct GNUNET_PeerIdentity *) &trm[1];
  if (trail_length > 0)
  {
    memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
  }
  
  /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Construct a verify successor message and forward it to target_friend.
 * @param source_peer Peer which wants to verify its successor.
 * @param successor Peer which is @a source_peer's current successor.
 * @param trail_id Unique Identifier of trail from @a source_peer to @a successor,
 *                 NOT including them. 
 * @param trail List of peers which are part of trail to reach from @a source_peer
 *              to @a successor, NOT including them. 
 * @param trail_length Total number of peers in @a trail.
 * @param target_friend Next friend to get this message. 
 */
void
GDS_NEIGHBOURS_send_verify_successor_message (struct GNUNET_PeerIdentity source_peer,
                                              struct GNUNET_PeerIdentity successor,
                                              struct GNUNET_HashCode trail_id,
                                              struct GNUNET_PeerIdentity *trail,
                                              unsigned int trail_length,
                                              struct FriendInfo *target_friend)
{
  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 (target_friend->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_XDHT_P2P_VERIFY_SUCCESSOR);
  vsm->source_peer = source_peer;
  vsm->successor = successor;
  vsm->trail_id = trail_id;
  
  if (trail_length != 0)
  {
    peer_list = (struct GNUNET_PeerIdentity *) &vsm[1];
    memcpy (peer_list, trail, trail_length * sizeof (struct GNUNET_PeerIdentity));
  }

  /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * FIXME: In every function we pass target friend except for this one.
 * so, either change everything or this one. also, should se just store
 * the pointer to friend in routing table rather than gnunet_peeridentity.
 * if yes then we should keep friend info in.h  andmake lot of changes. 
 * Construct a trail teardown message and forward it to target friend. 
 * @param trail_id Unique identifier of the trail.
 * @param trail_direction Direction of trail.
 * @param target_friend Friend to get this message.
 */
void
GDS_NEIGHBOURS_send_trail_teardown (struct GNUNET_HashCode trail_id,
                                    unsigned int trail_direction,
                                    struct GNUNET_PeerIdentity peer)
{
  struct PeerTrailTearDownMessage *ttdm;
  struct P2PPendingMessage *pending;
  struct FriendInfo *target_friend;
  size_t msize;

  msize = sizeof (struct PeerTrailTearDownMessage);

  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  /*FIXME:In what case friend can be null. ?*/
  if (NULL == (target_friend = 
                 GNUNET_CONTAINER_multipeermap_get (friend_peermap, &peer)));
  return;
  
  if (target_friend->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);
  ttdm = (struct PeerTrailTearDownMessage *) &pending[1];
  pending->msg = &ttdm->header;
  ttdm->header.size = htons (msize);
  ttdm->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_TEARDOWN);
  ttdm->trail_id = trail_id;
  ttdm->trail_direction = htonl (trail_direction);

  /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Construct a verify successor result message and send it to target_friend
 * @param querying_peer Peer which sent the verify successor message. 
 * @param source_successor Current_successor of @a querying_peer. 
 * @param current_predecessor Current predecessor of @a successor. Could be same
 *                            or different from @a querying_peer.
 * @param trail_id Unique identifier of the trail from @a querying_peer to 
 *                 @a successor, NOT including them.
 * @param trail List of peers which are part of trail from @a querying_peer to 
 *                 @a successor, NOT including them.
 * @param trail_length Total number of peers in @a trail
 * @param trail_direction Direction in which we are sending the message. In this
 *                        case we are sending result from @a successor to @a querying_peer.
 * @param target_friend Next friend to get this message. 
 */
void
GDS_NEIGHBOURS_send_verify_successor_result (struct GNUNET_PeerIdentity querying_peer,
                                             struct GNUNET_PeerIdentity current_successor,
                                             struct GNUNET_PeerIdentity probable_successor,
                                             struct GNUNET_HashCode trail_id,
                                             const struct GNUNET_PeerIdentity *trail,
                                             unsigned int trail_length,
                                             enum GDS_ROUTING_trail_direction trail_direction,
                                             struct FriendInfo *target_friend)
{
  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 (target_friend->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_XDHT_P2P_VERIFY_SUCCESSOR_RESULT);
  vsmr->querying_peer = querying_peer;
  vsmr->current_successor = current_successor;
  vsmr->probable_successor = probable_successor;
  vsmr->trail_direction = htonl (trail_direction);
  vsmr->trail_id = trail_id;
  
  if (trail_length > 0)
  {
    peer_list = (struct GNUNET_PeerIdentity *) &vsmr[1];
    memcpy (peer_list, trail, trail_length * sizeof (struct GNUNET_PeerIdentity));
  }

   /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Construct a notify new successor message and send it to target_friend
 * @param source_peer Peer which wants to notify to its new successor that it
 *                    could be its predecessor. 
 * @param successor New successor of @a source_peer
 * @param successor_trail List of peers in Trail to reach from 
 *                            @a source_peer to @a new_successor, NOT including 
 *                            the endpoints. 
 * @param successor_trail_length Total number of peers in @a new_successor_trail.
 * @param successor_trail_id Unique identifier of @a new_successor_trail. 
 * @param target_friend Next friend to get this message. 
 */
void
GDS_NEIGHBOURS_send_notify_new_successor (struct GNUNET_PeerIdentity source_peer,
                                          struct GNUNET_PeerIdentity successor,
                                          const struct GNUNET_PeerIdentity *successor_trail,
                                          unsigned int successor_trail_length,
                                          struct GNUNET_HashCode succesor_trail_id,
                                          struct FriendInfo *target_friend)
{
  struct PeerNotifyNewSuccessorMessage *nsm;
  struct P2PPendingMessage *pending;
  struct GNUNET_PeerIdentity *peer_list;
  size_t msize;

  msize = sizeof (struct PeerNotifyNewSuccessorMessage) +
          (successor_trail_length * sizeof(struct GNUNET_PeerIdentity));

  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }

  if (target_friend->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);
  nsm = (struct PeerNotifyNewSuccessorMessage *) &pending[1];
  pending->msg = &nsm->header;
  nsm->header.size = htons (msize);
  nsm->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_NOTIFY_NEW_SUCCESSOR);
  nsm->new_successor = successor;
  nsm->source_peer = source_peer;
  nsm->trail_id = succesor_trail_id;
  
  if (successor_trail_length > 0)
  {
    peer_list = (struct GNUNET_PeerIdentity *) &nsm[1];
    memcpy (peer_list, successor_trail,
            successor_trail_length * sizeof (struct GNUNET_PeerIdentity));
  }

   /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Construct an add_trail message and send it to target_friend
 * @param source_peer Source of the trail.
 * @param destination_peer Destination of the trail.
 * @param trail_id Unique identifier of the trail from 
 *                 @a source_peer to @a destination_peer, NOT including the endpoints.
 * @param trail List of peers in Trail from @a source_peer to @a destination_peer,
 *              NOT including the endpoints. 
 * @param trail_length Total number of peers in @a trail.
 * @param target_friend Next friend to get this message.
 */
void
GDS_NEIGHBOURS_send_add_trail (struct GNUNET_PeerIdentity source_peer,
                               struct GNUNET_PeerIdentity destination_peer,
                               struct GNUNET_HashCode trail_id,
                               const struct GNUNET_PeerIdentity *trail,
                               unsigned int trail_length,
                               struct FriendInfo *target_friend)
{
  struct PeerAddTrailMessage *adm;
  struct GNUNET_PeerIdentity *peer_list;
  struct P2PPendingMessage *pending;
  size_t msize;

  msize = sizeof (struct PeerAddTrailMessage) +
          (trail_length * sizeof(struct GNUNET_PeerIdentity));

  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }

  if (target_friend->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);
  adm = (struct PeerAddTrailMessage *) &pending[1];
  pending->msg = &adm->header;
  adm->header.size = htons (msize);
  adm->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_ADD_TRAIL);
  adm->source_peer = source_peer;
  adm->destination_peer = destination_peer;
  adm->trail_id = trail_id;
  
  if (trail_length > 0)
  {
    peer_list = (struct GNUNET_PeerIdentity *)&adm[1];
    memcpy (peer_list, trail, sizeof (struct GNUNET_PeerIdentity) * trail_length);
  }
  /* Send the message to chosen friend. */
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);

}


/**
 * Construct a trail compression message and send it to target_friend.
 * @param source_peer Source of the trail.
 * @param trail_id Unique identifier of trail.
 * @param first_friend First hop in compressed trail to reach from source to finger
 * @param target_friend Next friend to get this message.
 */
void
GDS_NEIGHBOURS_send_trail_compression (struct GNUNET_PeerIdentity source_peer,
                                       struct GNUNET_HashCode trail_id,
                                       struct GNUNET_PeerIdentity first_friend,
                                       struct FriendInfo *target_friend)
{
  struct P2PPendingMessage *pending;
  struct PeerTrailCompressionMessage *tcm;
  size_t msize;

  msize = sizeof (struct PeerTrailCompressionMessage);

  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }

  if (target_friend->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);
  tcm = (struct PeerTrailCompressionMessage *) &pending[1];
  pending->msg = &tcm->header;
  tcm->header.size = htons (msize);
  tcm->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_COMPRESSION);
  tcm->source_peer = source_peer;
  tcm->new_first_friend = first_friend;
  tcm->trail_id = trail_id;

  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);

}


/**
 * Search my location in trail. In case I am present more than once in the
 * trail (can happen during trail setup), then return my lowest index.
 * @param trail List of peers
 * @return my_index if found
 *         -1 if no entry found.
 */
static int
search_my_index (const struct GNUNET_PeerIdentity *trail,
                 int trail_length)
{
  int i;
  int lowest_index = -1;
  
  for (i = 0; i < trail_length; i++)
  {
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &trail[i]))
      //lowest_index = i;
      return i;
  }

  return lowest_index;
}


/**
 * Check if the friend is congested or have reached maximum number of trails
 * it can be part of of. 
 * @param friend Friend to be checked.
 * @return #GNUNET_NO if friend is not congested or have not crossed threshold.
 *         #GNUNET_YES if friend is either congested or have crossed threshold 
 */
static int
is_friend_congested (struct FriendInfo *friend)
{
  if ((TRAILS_THROUGH_FRIEND_THRESHOLD > friend->trails_count) && 
      ((0 == GNUNET_TIME_absolute_get_remaining
             (friend->congestion_timestamp).rel_value_us)))
    return GNUNET_NO;
  else
    return GNUNET_YES;
}


/**
 * FIXME; not handling the wrap around logic correctly. 
 * Select closest finger to value.
 * @param peer1 First peer
 * @param peer2 Second peer
 * @param value Value to be compare
 * @return Closest peer
 */
static struct GNUNET_PeerIdentity *
select_closest_finger (struct GNUNET_PeerIdentity *peer1,
                       struct GNUNET_PeerIdentity *peer2,
                       uint64_t value)
{
  uint64_t peer1_value;
  uint64_t peer2_value;
  
  memcpy (&peer1_value, peer1, sizeof (uint64_t));
  memcpy (&peer2_value, peer2, sizeof (uint64_t));
  peer1_value = GNUNET_ntohll (peer1_value);
  peer2_value = GNUNET_ntohll (peer2_value);
  
  if (peer1_value == value)
  {
    return peer1;
  }
  
  if (peer2_value == value)
  {
    return peer2;
  }
   
  if (peer2_value < peer1_value)
  {
    if ((peer2_value < value) && (value < peer1_value))
    {
      return peer1;
    }
    else if (((peer1_value < value) && (value < PEER_IDENTITES_WRAP_AROUND)) ||
             ((0 < value) && (value < peer2_value)))
    {
      return peer2;
    }
  }  
   
  if (peer1_value < peer2_value)
  {
    if ((peer1_value < value) && (value < peer2_value))
    {
      return peer2;
    }
    else if (((peer2_value < value) && (value < PEER_IDENTITES_WRAP_AROUND)) ||
             ((0 < value) && (value < peer1_value)))
    {
      return peer1;
    }
  }
  return NULL;
}


/**
 * Select closest predecessor to value.
 * @param peer1 First peer
 * @param peer2 Second peer
 * @param value Value to be compare
 * @return Peer which precedes value in the network.
 */
static struct GNUNET_PeerIdentity *
select_closest_predecessor (struct GNUNET_PeerIdentity *peer1,
                            struct GNUNET_PeerIdentity *peer2,
                            uint64_t value)
{
  uint64_t peer1_value;
  uint64_t peer2_value;
  
  memcpy (&peer1_value, peer1, sizeof (uint64_t));
  memcpy (&peer2_value, peer2, sizeof (uint64_t));
  peer1_value = GNUNET_ntohll (peer1_value);
  peer2_value = GNUNET_ntohll (peer2_value);
  
  if (peer1_value == value)
    return peer1;
  
  if (peer2_value == value)
    return peer2;
  
  if (peer1_value < peer2_value)
  {
    if ((peer1_value < value) && (value < peer2_value))
    {
      return peer1;
    }
    else if (((peer2_value < value) && (value < PEER_IDENTITES_WRAP_AROUND)) ||
             ((PEER_IDENTITES_WRAP_AROUND > value) && (value < peer1_value)))
    {
      return peer2;
    }
  }
  
  if (peer2_value < peer1_value)
  {
    if ((peer2_value < value) && (value < peer1_value))
    {
      return peer2;
    }
    else if (((peer1_value < value) && (value < PEER_IDENTITES_WRAP_AROUND)) ||
             ((PEER_IDENTITES_WRAP_AROUND > value) && (value < peer2_value)))
    {
      return peer1;
    }
  }
  return NULL;
}

#if 0
/**
 * This is a test function to print all the entries of friend table.
 */
static void
test_friend_peermap_print ()
{
  struct FriendInfo *friend;
  struct GNUNET_CONTAINER_MultiPeerMapIterator *friend_iter;
  struct GNUNET_PeerIdentity print_peer;
  struct GNUNET_PeerIdentity key_ret;
  int i;
  
  print_peer = my_identity;
  FPRINTF (stderr,_("\nSUPU************  FRIEND_PEERMAP of %s"),GNUNET_i2s(&print_peer));
  friend_iter = GNUNET_CONTAINER_multipeermap_iterator_create (friend_peermap);
  
  for (i = 0; i < GNUNET_CONTAINER_multipeermap_size (friend_peermap); i++)
  {
    if(GNUNET_YES == GNUNET_CONTAINER_multipeermap_iterator_next (friend_iter,
                                                                  &key_ret,
                                                                  (const void **)&friend))
    {
      memcpy (&print_peer, &key_ret, sizeof (struct GNUNET_PeerIdentity));
      FPRINTF (stderr,_("\nSUPU %s, %s, %d, friend = %s, friend->trails_count = %d"),
              __FILE__, __func__,__LINE__, GNUNET_i2s(&print_peer), friend->trails_count);
    }
  }
}

/**
 * This is a test function, to print all the entries of finger table.
 */
static void
test_finger_table_print()
{
  struct FingerInfo *finger;
  struct GNUNET_PeerIdentity print_peer;
  //struct Trail *trail;
  int i;
  //int j;
  //int k;
  print_peer = my_identity;
  FPRINTF (stderr,_("\nSUPU************  FINGER_TABLE of %s"),GNUNET_i2s(&print_peer));
  for (i = 0; i < MAX_FINGERS; i++)
  {
    finger = &finger_table[i];
    
    if (GNUNET_NO == finger->is_present)
      continue;
    
    print_peer = finger->finger_identity;
    FPRINTF (stderr,_("\nSUPU %s, %s, %d, finger_table[%d] = %s, trails_count = %d"),
            __FILE__, __func__,__LINE__,i,GNUNET_i2s (&print_peer), finger->trails_count);
    
#if 0
    for (j = 0; j < finger->trails_count; j++)
    {
      trail = &finger->trail_list[j];
      FPRINTF (stderr,_("\nSUPU %s, %s, %d, trail_id[%d]=%s"),__FILE__, __func__,__LINE__,j, GNUNET_h2s(&trail->trail_id));
      struct Trail_Element *element;
      element = trail->trail_head;
      for (k = 0; k < trail->trail_length; k++)
      {  
        print_peer = element->peer;
        FPRINTF (stderr,_("\nSUPU %s, %s, %d,trail[%d] = %s "),__FILE__, __func__,__LINE__,k, GNUNET_i2s(&print_peer));
        element = element->next;
      }
    }
    #endif
  }
}
#endif

/**
 * Select the closest peer among two peers (which should not be same)
 * with respect to value and finger_table_index
 * NOTE: peer1 != peer2
 * @param peer1 First peer
 * @param peer2 Second peer
 * @param value Value relative to which we find the closest
 * @param is_predecessor Is value a predecessor or any other finger. 
 * @return Closest peer among two peers.
 */
static struct GNUNET_PeerIdentity *
select_closest_peer (struct GNUNET_PeerIdentity *peer1,
                     struct GNUNET_PeerIdentity *peer2,
                     uint64_t value,
                     unsigned int is_predecessor)
{
  struct GNUNET_PeerIdentity *closest_peer;
  
  if (1 == is_predecessor)
  {
    closest_peer = select_closest_predecessor (peer1, peer2, value);
    
  }
  else
  {
    closest_peer = select_closest_finger (peer1, peer2, value);
  }
  return closest_peer;
}


/**
 * Iterate over the list of all the trails of a finger. In case the first
 * friend to reach the finger has reached trail threshold or is congested,
 * then don't select it. In case there multiple available good trails to reach
 * to Finger, choose the one with shortest trail length.
 * Note: We use length as parameter. But we can use any other suitable parameter
 * also. 
 * @param finger Finger
 * @return struct Selected_Finger_Trail which contains the first friend , trail id
 * and trail length. NULL in case none of the trails are free.
 */
static struct Selected_Finger_Trail *
select_finger_trail (struct FingerInfo *finger)
{
  struct FriendInfo *friend;
  struct Trail *iterator;
  struct Selected_Finger_Trail *finger_trail;
  unsigned int i;
  unsigned int flag = 0;
  unsigned int j = 0;
 
  finger_trail = GNUNET_new (struct Selected_Finger_Trail);
  GNUNET_assert (finger->trails_count > 0);
  
  for (i = 0; i < finger->trails_count; i++)
  {
    iterator = &finger->trail_list[i];
    
    /* No trail stored at this index. */
    if (GNUNET_NO == iterator->is_present)
      continue;

    GNUNET_assert (NULL != 
                  (friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                      &iterator->trail_head->peer)));
    
    /* First friend to reach trail is not free. */
    if (GNUNET_YES == is_friend_congested (friend))
    {
      j++;
      continue;
    }
    
    if (!flag)
    {
      flag = 1;
      finger_trail->trail_length = iterator->trail_length;
      finger_trail->friend = *friend;
      finger_trail->trail_id = iterator->trail_id;   
    }
    else if (finger_trail->trail_length > iterator->trail_length)
    {
      finger_trail->friend = *friend;
      finger_trail->trail_id = iterator->trail_id;
      finger_trail->trail_length = iterator->trail_length;
    }
  }

  /* All the first friend in all the trails to reach to finger are either 
   congested or have crossed trail threshold. */
  if (j == finger->trails_count)
    return NULL;
  
  return finger_trail;
}


/**
 * Compare FINGER entry with current successor. If finger's first friend of all
 * its trail is not congested and  has not crossed trail threshold, then check 
 * if finger peer identity is closer to final_destination_finger_value than
 * current_successor. If yes then update current_successor. 
 * @param current_successor[in/out]
 * @return 
 */
static void
compare_finger_and_current_successor (struct Closest_Peer *current_closest_peer)
{
  struct FingerInfo *finger;
  struct GNUNET_PeerIdentity *closest_peer;
  struct Selected_Finger_Trail *finger_trail;
  int i;
  
  /* Iterate over finger table. */
  for (i = 0; i < MAX_FINGERS; i++)
  {
    finger = &finger_table[i];
    
    if (GNUNET_NO == finger->is_present)
      continue;

    /* If my identity is same as current closest peer then don't consider me*/
    if (0 == 
            GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                             &current_closest_peer->best_known_destination))
      continue;
    
    /* If I am my own finger, then ignore this finger. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                              &my_identity))
      continue;
    
    /* If finger is a friend, then do nothing. As we have already checked
     * for each friend in compare_friend_and_current_successor(). */
    if (NULL != (GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                    &finger->finger_identity)))
    {
      continue;
    }
    
    /* Choose one of the trail to reach to finger. */
    finger_trail = select_finger_trail (finger);
    
    /* In case no trail found, ignore this finger. */
    if (NULL == finger_trail)
      continue;

    closest_peer = select_closest_peer (&finger->finger_identity, 
                                        &current_closest_peer->best_known_destination,
                                        current_closest_peer->destination_finger_value,
                                        current_closest_peer->is_predecessor);
    
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                              closest_peer))
    {
      current_closest_peer->best_known_destination = finger->finger_identity;
      current_closest_peer->next_hop = finger_trail->friend.id;
      current_closest_peer->trail_id = finger_trail->trail_id;
      //GNUNET_free(finger_trail);//FIXME: where should we free the finger trail.
    }
    continue;
  }
}


/**
 * Compare friend entry with current successor.
 * If friend identity and current_successor is same, then do nothing. 
 * If friend is not congested and has not crossed trail threshold, then check 
 * if friend peer identity is closer to final_destination_finger_value than 
 * current_successor. If yes then update current_successor. 
 * @param cls closure
 * @param key current public key
 * @param value struct Closest_Peer
 * @return #GNUNET_YES if we should continue to iterate,
 *         #GNUNET_NO if not.
 */
static int
compare_friend_and_current_closest_peer (void *cls,
                                         const struct GNUNET_PeerIdentity *key,
                                         void *value)
{
  struct FriendInfo *friend = value;
  struct Closest_Peer *current_closest_peer = cls;
  struct GNUNET_PeerIdentity *closest_peer;
  
  /* Friend is either congested or has crossed threshold. */
  if (GNUNET_YES == is_friend_congested (friend))
    return GNUNET_YES;
 
  /* If current_closest_peer and friend identity are same, then do nothing.*/
  if (0 == 
        GNUNET_CRYPTO_cmp_peer_identity (&friend->id,
                                         &current_closest_peer->best_known_destination))
    return GNUNET_YES;

  closest_peer = select_closest_peer (&friend->id, 
                                      &current_closest_peer->best_known_destination,
                                      current_closest_peer->destination_finger_value,
                                      current_closest_peer->is_predecessor);

  /* Is friend the closest successor? */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&friend->id, closest_peer))
  {
    current_closest_peer->best_known_destination = friend->id;
    current_closest_peer->next_hop = friend->id;
  }
  
  return GNUNET_YES;
}


/**
 * Initialize current_successor to my_identity.
 * @param my_identity My peer identity
 * @return Updated closest_peer
 */
static struct Closest_Peer 
init_current_successor (struct GNUNET_PeerIdentity my_identity,
                        uint64_t destination_finger_value,
                        unsigned int is_predecessor)
{
  struct Closest_Peer current_closest_peer;
  
  memset (&current_closest_peer.trail_id, 0, sizeof(struct GNUNET_HashCode));
  current_closest_peer.destination_finger_value = destination_finger_value;
  current_closest_peer.is_predecessor = is_predecessor;
  current_closest_peer.next_hop = my_identity;
  current_closest_peer.best_known_destination = my_identity;
  
  return current_closest_peer;
}


/**
 * FIXME: at the moment, there is not 100% get and put in case of non-malicious
 * peer. It could be because of the logic we wrote here. Verify if its correct.
 * If not then return immediate_successor. 
 * 
 * Find the successor for destination_finger_value among my_identity, my
 * friends and my fingers. Don't consider friends or fingers which are either
 * congested or have crossed the threshold.
 * NOTE: In case a friend is also a finger, then it is always chosen as friend
 * not a finger. 
 * @param destination_finger_value Peer closest to this value will be the next successor.
 * @param is_predecessor Are we looking for predecessor or finger?
 * @return Successor It is never NULL, in case none of friend or finger is closest,
 *                   then we return my_identity.
 */
static struct Closest_Peer
find_successor (uint64_t destination_finger_value,
                unsigned int is_predecessor)
{
  struct Closest_Peer current_closest_peer;
  
   /* Initialize current_successor to my_identity. */
  current_closest_peer = init_current_successor (my_identity,
                                                 destination_finger_value,
                                                 is_predecessor);
 
  /* Compare each friend entry with current_successor and update current_successor
   * with friend if its closest. */
  GNUNET_assert 
          (GNUNET_SYSERR != 
           GNUNET_CONTAINER_multipeermap_iterate (friend_peermap, 
                                                  &compare_friend_and_current_closest_peer,
                                                  &current_closest_peer));
   
  /* Compare each finger entry with current_successor and update current_successor
   * with finger if its closest. */
  compare_finger_and_current_successor (&current_closest_peer);
 
  return current_closest_peer;
}


/**
 * Construct a Put message and send it to target_peer.
 * @param key Key for the content
 * @param block_type Type of the block
 * @param options Routing options
 * @param desired_replication_level Desired replication count
 * @param best_known_dest Peer to which this message should reach eventually,
 *                        as it is best known destination to me. 
 * @param intermediate_trail_id Trail id in case 
 * @param target_peer Peer to which this message will be forwarded.
 * @param hop_count Number of hops traversed so far.
 * @param put_path_length Total number of peers in @a put_path
 * @param put_path Number of peers traversed so far
 * @param expiration_time When does the content expire
 * @param data Content to store
 * @param data_size Size of content @a data in bytes
 */
void
GDS_NEIGHBOURS_send_put (const struct GNUNET_HashCode *key,
                         enum GNUNET_BLOCK_Type block_type,
                                           enum GNUNET_DHT_RouteOption options,
                                           uint32_t desired_replication_level,
                                           struct GNUNET_PeerIdentity best_known_dest,
                                           struct GNUNET_HashCode intermediate_trail_id,
                                           struct GNUNET_PeerIdentity *target_peer,
                         uint32_t hop_count,
                         uint32_t put_path_length,
                         struct GNUNET_PeerIdentity *put_path,
                         struct GNUNET_TIME_Absolute expiration_time,
                         const void *data, size_t data_size)
{
  struct PeerPutMessage *ppm;
  struct P2PPendingMessage *pending;
  struct FriendInfo *target_friend;
  struct GNUNET_PeerIdentity *pp;
  struct GNUNET_PeerIdentity next_hop;

  size_t msize;
  
  msize = put_path_length * sizeof (struct GNUNET_PeerIdentity) + data_size +
          sizeof (struct PeerPutMessage);
  
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    put_path_length = 0;
    msize = data_size + sizeof (struct PeerPutMessage);
  }

  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  /* This is the first call made from clients file. So, we should search for the
     target_friend. */
  if (NULL == target_peer)
  {
    uint64_t key_value;
    struct Closest_Peer successor;

    memcpy (&key_value, key, sizeof (uint64_t));  
    key_value = GNUNET_ntohll (key_value);
    
    successor = find_successor (key_value, GDS_FINGER_TYPE_NON_PREDECESSOR);
    best_known_dest = successor.best_known_destination;
    next_hop = successor.next_hop;
    intermediate_trail_id = successor.trail_id;

    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&best_known_dest, &my_identity)) 
    {
      /* I am the destination. */
      GDS_DATACACHE_handle_put (expiration_time, key, 0, NULL, 
                                ntohl (block_type),data_size,data);
      return;
    }
    else
      GNUNET_assert (NULL != 
                    (target_friend = 
                     GNUNET_CONTAINER_multipeermap_get (friend_peermap, &next_hop)));  
  }
  else
  {
    GNUNET_assert (NULL !=
                   (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, target_peer))); 
  }
  
  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize);
  pending->timeout = expiration_time;
  ppm = (struct PeerPutMessage *) &pending[1];
  pending->msg = &ppm->header;
  ppm->header.size = htons (msize);
  ppm->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_PUT);
  ppm->options = htonl (options);
  ppm->block_type = htonl (block_type);
  ppm->hop_count = htonl (hop_count + 1);
  ppm->desired_replication_level = htonl (desired_replication_level);
  ppm->put_path_length = htonl (put_path_length);
  ppm->expiration_time = GNUNET_TIME_absolute_hton (expiration_time);
  ppm->best_known_destination = best_known_dest;
  ppm->key = *key;
  
  pp = (struct GNUNET_PeerIdentity *) &ppm[1];
  if (put_path_length != 0)
  {
    memcpy (pp, put_path,
            sizeof (struct GNUNET_PeerIdentity) * put_path_length);
  }
  memcpy (&pp[put_path_length], data, data_size);
  
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Construct a Get message and send it to target_peer.
 * @param key Key for the content
 * @param block_type Type of the block
 * @param options Routing options
 * @param desired_replication_level Desired replication count
 * @param best_known_dest Peer which should get this message. Same as target peer
 *                        if best_known_dest is a friend else its a finger.
 * @param intermediate_trail_id  Trail id to reach to @a best_known_dest
 *                              in case it is a finger else set to 0.
 * @param target_peer Peer to which this message will be forwarded.
 * @param hop_count Number of hops traversed so far.
 * @param data Content to store
 * @param data_size Size of content @a data in bytes
 * @param get_path_length Total number of peers in @a get_path
 * @param get_path Number of peers traversed so far
 */
void
GDS_NEIGHBOURS_send_get (const struct GNUNET_HashCode *key,
                         enum GNUNET_BLOCK_Type block_type,
                         enum GNUNET_DHT_RouteOption options,
                         uint32_t desired_replication_level,
                         struct GNUNET_PeerIdentity best_known_dest,
                         struct GNUNET_HashCode intermediate_trail_id,
                         struct GNUNET_PeerIdentity *target_peer,
                         uint32_t hop_count,
                         uint32_t get_path_length,
                         struct GNUNET_PeerIdentity *get_path)
{
  struct PeerGetMessage *pgm;
  struct P2PPendingMessage *pending;
  struct FriendInfo *target_friend;
  struct GNUNET_PeerIdentity *gp;
  size_t msize;
  
  msize = sizeof (struct PeerGetMessage) + 
          (get_path_length * sizeof (struct GNUNET_PeerIdentity));
  
  /* In this case we don't make get_path_length = 0, as we need get path to
   * return the message back to querying client. */
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  /* This is the first time we got request from our own client file. */
  if (NULL == target_peer)
  {
    uint64_t key_value;
    struct Closest_Peer successor;
    
    memcpy (&key_value, key, sizeof (uint64_t)); 
    key_value = GNUNET_ntohll (key_value);
    successor = find_successor (key_value, GDS_FINGER_TYPE_NON_PREDECESSOR);
    
    best_known_dest = successor.best_known_destination;
    intermediate_trail_id = successor.trail_id;
    
    /* I am the destination. I have the data. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity,
                                              &best_known_dest)) 
    {
      GDS_DATACACHE_handle_get (key,block_type, NULL, 0, 
                                NULL, 0, 1, &my_identity, NULL,&my_identity);
      
      return;
    }
    else
    {
      GNUNET_assert (NULL != 
                    (target_friend = 
                     GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                        &successor.next_hop)));
    }
    
  }
  else
  {
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, target_peer))); //FIXME: assertion fails.
  }
  
  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize);
  pending->timeout = GNUNET_TIME_relative_to_absolute (GET_TIMEOUT);
  pending->importance = 0;    /* FIXME */
  pgm = (struct PeerGetMessage *) &pending[1];
  pending->msg = &pgm->header;
  pgm->header.size = htons (msize);
  pgm->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_GET);
  pgm->get_path_length = htonl (get_path_length);
  pgm->best_known_destination = best_known_dest;
  pgm->key = *key;
  pgm->intermediate_trail_id = intermediate_trail_id;
  pgm->hop_count = htonl (hop_count + 1);
  gp = (struct GNUNET_PeerIdentity *) &pgm[1];
  
  if (get_path_length != 0)
  {
    memcpy (gp, get_path, get_path_length * sizeof (struct GNUNET_PeerIdentity));
  }
  
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Send the get result to requesting client.
 * @param key Key of the requested data.
 * @param type Block type
 * @param target_peer Next peer to forward the message to.
 * @param source_peer Peer which has the data for the key.
 * @param put_path_length Number of peers in @a put_path
 * @param put_path Path taken to put the data at its stored location.
 * @param get_path_length Number of peers in @a get_path
 * @param get_path Path taken to reach to the location of the key.
 * @param expiration When will this result expire?
 * @param data Payload to store
 * @param data_size Size of the @a data
 */
void
GDS_NEIGHBOURS_send_get_result (const struct GNUNET_HashCode *key,
                                enum GNUNET_BLOCK_Type type,
                                const struct GNUNET_PeerIdentity *target_peer,
                                const struct GNUNET_PeerIdentity *source_peer,
                                unsigned int put_path_length,
                                const struct GNUNET_PeerIdentity *put_path,
                                unsigned int get_path_length,
                                const struct GNUNET_PeerIdentity *get_path,
                                struct GNUNET_TIME_Absolute expiration,
                                const void *data, size_t data_size)
{
  struct PeerGetResultMessage *get_result;
  struct GNUNET_PeerIdentity *paths;
  struct P2PPendingMessage *pending;
  struct FriendInfo *target_friend;
  int current_path_index;
  size_t msize;

  msize = (put_path_length + get_path_length )* sizeof (struct GNUNET_PeerIdentity) + 
          data_size +
          sizeof (struct PeerGetResultMessage);

  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  current_path_index = 0;
  if(get_path_length > 0)
  {
    current_path_index = search_my_index(get_path, get_path_length);
    if (-1 == current_path_index)
    {
      GNUNET_break (0);
      return;
    }
  }
  if (0 == current_path_index)
  {
    GDS_CLIENTS_handle_reply (expiration, key, get_path_length, 
                              get_path, put_path_length,
                              put_path, type, data_size, data);
    return;
  }

  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize);
  pending->timeout = GNUNET_TIME_relative_to_absolute (GET_TIMEOUT);
  pending->importance = 0;   
  get_result = (struct PeerGetResultMessage *)&pending[1];
  pending->msg = &get_result->header;
  get_result->header.size = htons (msize);
  get_result->header.type = htons (GNUNET_MESSAGE_TYPE_XDHT_P2P_GET_RESULT);
  get_result->key = *key;
  get_result->querying_peer = *source_peer;
  get_result->expiration_time = expiration;
  get_result->get_path_length = htonl (get_path_length);
  get_result->put_path_length = htonl (put_path_length);
  paths = (struct GNUNET_PeerIdentity *)&get_result[1];
  memcpy (paths, put_path,
          put_path_length * sizeof (struct GNUNET_PeerIdentity));
  memcpy (&paths[put_path_length], get_path,
          get_path_length * sizeof (struct GNUNET_PeerIdentity));
  memcpy (&paths[put_path_length + get_path_length], data, data_size);
  
  GNUNET_assert (NULL != 
                (target_friend = 
                 GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                    &get_path[current_path_index - 1])));
  GNUNET_CONTAINER_DLL_insert_tail (target_friend->head, target_friend->tail, pending);
  target_friend->pending_count++;
  process_friend_queue (target_friend);
}


/**
 * Randomly choose one of your friends (which is not congested and have not crossed
 * trail threshold) from the friend_peermap
 * @return Friend Randomly chosen friend.
 *         NULL in case friend peermap is empty, or all the friends are either
 *              congested or have crossed trail threshold.
 */
static struct FriendInfo *
select_random_friend ()
{
  unsigned int current_size;
  uint32_t 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);
  
  /* No friends.*/
  if (0 == current_size)
    return NULL;

  index = GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK, current_size);
  iter = GNUNET_CONTAINER_multipeermap_iterator_create (friend_peermap);

  /* Iterate till you don't reach to index. */
  for (j = 0; j < index ; j++)
    GNUNET_assert (GNUNET_YES ==
                   GNUNET_CONTAINER_multipeermap_iterator_next (iter, NULL, NULL));
  do
  {
    /* Reset the index in friend peermap to 0 as we reached to the end. */
    if (j == current_size)
    {
      j = 0;
      GNUNET_CONTAINER_multipeermap_iterator_destroy (iter);
      iter = GNUNET_CONTAINER_multipeermap_iterator_create (friend_peermap);

    }
    
    /* Get the friend stored at the index, j*/
    GNUNET_assert (GNUNET_YES ==
                   GNUNET_CONTAINER_multipeermap_iterator_next (iter,
                                                                &key_ret,
                                                                (const void **)&friend));

    /* This friend is not congested and has not crossed trail threshold. */
    if ((TRAILS_THROUGH_FRIEND_THRESHOLD > friend->trails_count) &&
        (0 == GNUNET_TIME_absolute_get_remaining (friend->congestion_timestamp).rel_value_us))
    {
      break;
    }
    friend = NULL;
    j++;
  } while (j != index);

  GNUNET_CONTAINER_multipeermap_iterator_destroy (iter);
  return friend;
}


/**
 * Compute 64 bit value of finger_identity corresponding to a finger index using 
 * chord formula. 
 * For all fingers, n.finger[i] = n + pow (2,i),
 * For predecessor, n.finger[PREDECESSOR_FINGER_ID] = n - 1, where
 * n = my_identity, i = finger_index, n.finger[i] = 64 bit finger value
 * @param finger_index Index corresponding to which we calculate 64 bit value.
 * @return 64 bit value.
 */
static uint64_t
compute_finger_identity_value (unsigned int finger_index)
{
  uint64_t my_id64;

  memcpy (&my_id64, &my_identity, sizeof (uint64_t));
  my_id64 = GNUNET_ntohll (my_id64);
  
  /* Are we looking for immediate predecessor? */
  if (PREDECESSOR_FINGER_ID == finger_index)
    return (my_id64 - 1);
  else
  {
    uint64_t add = (uint64_t)1 << finger_index;  
    return (my_id64 + add);
  }
}


/*
 * Choose a random friend. Calculate the next finger identity to search,from 
 * current_search_finger_index. Start looking for the trail to reach to
 * finger identity through this random friend.
 *
 * @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 *target_friend;
  struct GNUNET_TIME_Relative next_send_time;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_HashCode intermediate_trail_id;
  unsigned int is_predecessor;
  uint64_t finger_id_value;

  /* Schedule another send_find_finger_trail_message task. */
  next_send_time.rel_value_us =
      DHT_FIND_FINGER_TRAIL_INTERVAL.rel_value_us +
      GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK,
                                DHT_FIND_FINGER_TRAIL_INTERVAL.rel_value_us);
  find_finger_trail_task =
      GNUNET_SCHEDULER_add_delayed (next_send_time, &send_find_finger_trail_message,
                                    NULL);

   /* No space in my routing table. (Source and destination peers also store entries
   * in their routing table).  */
  if (GNUNET_YES == GDS_ROUTING_threshold_reached())
    return;
  
    
  target_friend = select_random_friend ();
  if (NULL == target_friend)
  {
    return;
  }
  
  finger_id_value = compute_finger_identity_value (current_search_finger_index);
  
  if (PREDECESSOR_FINGER_ID == current_search_finger_index)
    is_predecessor = 1;
  else
    is_predecessor = 0;
  
  /* Generate a unique trail id for trail we are trying to setup. */
  GNUNET_CRYPTO_random_block (GNUNET_CRYPTO_QUALITY_STRONG,
                              &trail_id, sizeof (trail_id));
  memset(&intermediate_trail_id, 0, sizeof (struct GNUNET_HashCode));
  
  GDS_NEIGHBOURS_send_trail_setup (my_identity, finger_id_value,
                                   target_friend->id, target_friend, 0, NULL,
                                   is_predecessor, trail_id, 
                                   intermediate_trail_id);
}


/**
 * In case there are already maximum number of possible trails to reach to a
 * finger, then check if the new trail's length is lesser than any of the
 * existing trails.
 * If yes then replace that old trail by new trail.
 *
 * Note: Here we are taking length as a parameter to choose the best possible
 * trail, but there could be other parameters also like:
 * 1. duration of existence of a trail - older the better.
 * 2. if the new trail is completely disjoint than the
 *    other trails, then may be choosing it is better.
 *
 * @param existing_finger
 * @param new_finger_trail
 * @param new_finger_trail_length
 * @param new_finger_trail_id
 */
static void
select_and_replace_trail (struct FingerInfo *existing_finger,
                          const struct GNUNET_PeerIdentity *new_trail,
                          unsigned int new_trail_length,
                          struct GNUNET_HashCode new_trail_id)
{
  struct Trail *trail_list_iterator;
  unsigned int largest_trail_length;
  unsigned int largest_trail_index;
  struct Trail_Element *trail_element;
  unsigned int i;

  largest_trail_length = new_trail_length;
  largest_trail_index = MAXIMUM_TRAILS_PER_FINGER + 1;

  GNUNET_assert (MAXIMUM_TRAILS_PER_FINGER == existing_finger->trails_count);

  for (i = 0; i < existing_finger->trails_count; i++)
  {
    trail_list_iterator = &existing_finger->trail_list[i];
    if (trail_list_iterator->trail_length > largest_trail_length)
    {
      largest_trail_length = trail_list_iterator->trail_length;
      largest_trail_index = i;
    }
  }

  /* New trail is not better than existing ones. Send trail teardown. */
  if (largest_trail_index == (MAXIMUM_TRAILS_PER_FINGER + 1))
  {
    struct GNUNET_PeerIdentity next_hop;
    
    memcpy (&next_hop, &new_trail[0], sizeof(struct GNUNET_PeerIdentity));
    GDS_ROUTING_remove_trail (new_trail_id);
    GDS_NEIGHBOURS_send_trail_teardown (new_trail_id, 
                                        GDS_ROUTING_SRC_TO_DEST,
                                        next_hop);
    return;
  }

  /* Send trail teardown message across the replaced trail. */
  struct Trail *replace_trail = &existing_finger->trail_list[largest_trail_index];
  existing_finger->trail_list[largest_trail_index].is_present = GNUNET_NO;
  GNUNET_assert (GNUNET_YES == GDS_ROUTING_remove_trail (replace_trail->trail_id));
  GDS_NEIGHBOURS_send_trail_teardown (replace_trail->trail_id,
                                      GDS_ROUTING_SRC_TO_DEST,
                                      replace_trail->trail_head->peer);
  /* Free the trail. */
  while (NULL != (trail_element = replace_trail->trail_head))
  {
    GNUNET_CONTAINER_DLL_remove (replace_trail->trail_head,
                                 replace_trail->trail_tail, trail_element);
    GNUNET_free_non_null (trail_element);
  }

  /* Add new trial at that location. */
  replace_trail->is_present = GNUNET_YES;
  replace_trail->trail_length = new_trail_length;
  replace_trail->trail_id = new_trail_id;
  //FIXME: Do we need to add pointers for head and tail. 
  i = 0;
  while (i < new_trail_length)
  {
    struct Trail_Element *element = GNUNET_new (struct Trail_Element);
    element->peer = new_trail[i];

    GNUNET_CONTAINER_DLL_insert_tail (replace_trail->trail_head,
                                      replace_trail->trail_tail,
                                      element);
  }
}


/**
 * Check if the new trail to reach to finger is unique or do we already have
 * such a trail present for finger.
 * @param existing_finger Finger identity
 * @param new_trail New trail to reach @a existing_finger
 * @param trail_length Total number of peers in new_trail.
 * @return #GNUNET_YES if the new trail is unique
 *         #GNUNET_NO if same trail is already present.
 */
static int
is_new_trail_unique (struct FingerInfo *existing_finger,
                     const struct GNUNET_PeerIdentity *new_trail,
                     unsigned int trail_length)
{
  struct Trail *trail_list_iterator;
  struct Trail_Element *trail_element;
  int i;
  int j;
  int trail_unique = GNUNET_NO;

  GNUNET_assert (existing_finger->trails_count > 0);
  
  /* Iterate over list of trails. */
  for (i = 0; i < existing_finger->trails_count; i++)
  {
    trail_list_iterator = &existing_finger->trail_list[i];
    GNUNET_assert (GNUNET_YES == trail_list_iterator->is_present);
    
    /* New trail and existing trail length are not same. */
    if (trail_list_iterator->trail_length != trail_length)
    {
      trail_unique = GNUNET_YES;
      continue;
    }
    
    trail_element = trail_list_iterator->trail_head;
    for (j = 0; j < trail_list_iterator->trail_length; j++)
    {
      if (0 != GNUNET_CRYPTO_cmp_peer_identity (&new_trail[j],
                                                &trail_element->peer))
      {
        trail_unique = GNUNET_YES;
        continue;
      }
      trail_element = trail_element->next;
    }
    
    trail_unique = GNUNET_NO;
  }
  
  return trail_unique;
}


/**
 * Add a new trail to existing finger. This function is called only when finger 
 * is not my own identity or a friend.
 * @param existing_finger Finger 
 * @param new_finger_trail New trail from me to finger, NOT including endpoints
 * @param new_finger_trail_length Total number of peers in @a new_finger_trail
 * @param new_finger_trail_id Unique identifier of the trail.
 */
static void
add_new_trail (struct FingerInfo *existing_finger,
               const struct GNUNET_PeerIdentity *new_trail,
               unsigned int new_trail_length,
               struct GNUNET_HashCode new_trail_id)
{
  struct Trail *trail_list_iterator;
  struct FriendInfo *first_friend;
  int i;

  if (GNUNET_NO == is_new_trail_unique (existing_finger, new_trail,
                                        new_trail_length))
  {
    return;
  }
  
  trail_list_iterator = &existing_finger->trail_list[existing_finger->trails_count];
  GNUNET_assert (GNUNET_NO == trail_list_iterator->is_present);
  trail_list_iterator->trail_id = new_trail_id;
  trail_list_iterator->trail_length = new_trail_length;
  existing_finger->trails_count++;
  trail_list_iterator->is_present = GNUNET_YES;
  
  GNUNET_assert (NULL == (GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                             &existing_finger->finger_identity)));
  /* If finger is a friend then we never call this function. */
  GNUNET_assert (new_trail_length > 0);
  
  first_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                    &new_trail[0]);
  first_friend->trails_count++;
  
  for (i = 0; i < new_trail_length; i++)
  {
    struct Trail_Element *element;
    
    element = GNUNET_new (struct Trail_Element);
    element->peer = new_trail[i];
    GNUNET_CONTAINER_DLL_insert_tail (trail_list_iterator->trail_head,
                                      trail_list_iterator->trail_tail,
                                      element);
  }
  /* Do we need to add trail head and trail tail in the trail list itearator.*/
  
}


/**
 * FIXME Check if this function is called for opposite direction if yes then 
 * take it as parameter. 
 * Get the next hop to send trail teardown message from routing table and
 * then delete the entry from routing table. Send trail teardown message for a 
 * specific trail of a finger. 
 * @param finger Finger whose trail is to be removed. 
 * @param trail List of peers in trail from me to a finger, NOT including 
 *              endpoints. 
 */
static void
send_trail_teardown (struct FingerInfo *finger,
                     struct Trail *trail)
{
  struct FriendInfo *friend;
  struct GNUNET_PeerIdentity *next_hop;
  
  GNUNET_assert (NULL != 
                (next_hop = GDS_ROUTING_get_next_hop (trail->trail_id, 
                                                      GDS_ROUTING_SRC_TO_DEST)));
  
  GNUNET_assert (0 != GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                                       &my_identity));

  GNUNET_assert (trail->is_present == GNUNET_YES);
  
  /* Finger is not a friend. */
  if (trail->trail_length > 0)
  {
    GNUNET_assert (NULL != (friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                      &trail->trail_head->peer)));
  }
  else
  {
    GNUNET_assert (NULL != (friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                      &finger->finger_identity)));
  }
    
  GNUNET_assert (0 == GNUNET_CRYPTO_cmp_peer_identity (next_hop, &friend->id)); //Fixme: assertion fails. 
  GNUNET_assert (GNUNET_YES == GDS_ROUTING_remove_trail (trail->trail_id));
  friend->trails_count--;
  GDS_NEIGHBOURS_send_trail_teardown (trail->trail_id,
                                      GDS_ROUTING_SRC_TO_DEST,
                                      friend->id);
}


/**
 * Send trail teardown message across all the trails to reach to finger. 
 * @param finger Finger whose all the trail should be freed. 
 */
static void
send_all_finger_trails_teardown (struct FingerInfo *finger)
{
  unsigned int i;
  
  for (i = 0; i < finger->trails_count; i++)
  {
    struct Trail *trail;
    
    trail = &finger->trail_list[i];
    GNUNET_assert (trail->is_present == GNUNET_YES);
    send_trail_teardown (finger, trail);
    trail->is_present = GNUNET_NO;
   }
}


/**
 * Free a specific trail
 * @param trail List of peers to be freed. 
 */
static void
free_trail (struct Trail *trail)
{
  struct Trail_Element *trail_element;

  while (NULL != (trail_element = trail->trail_head))
  {
    GNUNET_CONTAINER_DLL_remove (trail->trail_head, 
                                 trail->trail_tail,
                                 trail_element);
    GNUNET_free_non_null (trail_element);
  }  
  trail->trail_head = NULL;
  trail->trail_tail = NULL;
}


/**
 * Free finger and its trail.
 * @param finger Finger to be freed.
 */
static void
free_finger (struct FingerInfo *finger, unsigned int finger_table_index)
{
  struct Trail *trail;
  unsigned int i;

  /* Free all the trails to reach to finger */
  for (i = 0; i < finger->trails_count; i++)
  {
    trail = &finger->trail_list[i];
    //FIXME: Check if there are any missing entry in this list because of 
    // how we insert. If not then no need of this check.
    if (GNUNET_NO == trail->is_present)
      continue;
    
    if (trail->trail_length > 0)
    {
      free_trail (trail);
    }
    trail->is_present = GNUNET_NO;
  }
  
  finger->is_present = GNUNET_NO;
  memset ((void *)&finger_table[finger_table_index], 0, sizeof (finger_table[finger_table_index]));
}


/**
 * FIXME: ensure that you are not adding any trail to reach to a friend which
 * is a finger. Also decide on should you increment trails count of a friend
 * which is also a finger. 
 * Add a new entry in finger table at finger_table_index. 
 * In case finger identity is me or a friend, then don't add a trail. NOTE
 * trail length to reach to a finger can be 0 only if the finger is a friend
 * or my identity.
 * In case a finger is a friend, then increment the trails count of the friend.
 * @param finger_identity Peer Identity of new finger
 * @param finger_trail Trail to reach from me to finger (excluding both end points).
 * @param finger_trail_length Total number of peers in @a finger_trail.
 * @param trail_id Unique identifier of the trail.
 * @param finger_table_index Index in finger table.
 */
static void
add_new_finger (struct GNUNET_PeerIdentity finger_identity,
                const struct GNUNET_PeerIdentity *finger_trail,
                unsigned int finger_trail_length,
                struct GNUNET_HashCode trail_id,
                unsigned int finger_table_index)
{
  struct FingerInfo *new_entry;
  struct FriendInfo *first_trail_hop;
  struct Trail *trail;
  int i = 0;
  
  new_entry = GNUNET_new (struct FingerInfo);
  new_entry->finger_identity = finger_identity;
  new_entry->finger_table_index = finger_table_index;
  new_entry->is_present = GNUNET_YES;
  
  /* If the new entry is my own identity. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &finger_identity))
  {
    new_entry->trails_count = 0;
    finger_table[finger_table_index] = *new_entry;
    GNUNET_free (new_entry);
    return;
  }
  
  /* If finger is a friend, then we don't actually have a trail.
   *  Just a trail id */
  if (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                 &finger_identity))
  {
    new_entry->trail_list[0].trail_id = trail_id;
    new_entry->trails_count = 1;
    new_entry->trail_list[0].is_present = GNUNET_YES;
    new_entry->trail_list[0].trail_length = 0;
    new_entry->trail_list[0].trail_head = NULL;
    new_entry->trail_list[0].trail_tail = NULL;
    finger_table[finger_table_index] = *new_entry;
    GNUNET_assert (NULL != 
                (first_trail_hop = 
                       GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                          &finger_identity)));

    first_trail_hop->trails_count++;
    GNUNET_free (new_entry);
    return;
  }
  
  /* finger trail length can be 0 only in case if finger is my identity or
   finger is friend. We should never reach here. */
  GNUNET_assert (finger_trail_length > 0);
  
  GNUNET_assert (NULL != 
                (first_trail_hop = 
                       GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                          &finger_trail[0])));
  new_entry->trails_count = 1;
  first_trail_hop->trails_count++;
   
  /* Copy the finger trail into trail. */
  trail = GNUNET_new (struct Trail);
  while (i < finger_trail_length)
  {
    struct Trail_Element *element = GNUNET_new (struct Trail_Element);

    element->next = NULL;
    element->prev = NULL;
    element->peer = finger_trail[i];
    GNUNET_CONTAINER_DLL_insert_tail (trail->trail_head,
                                      trail->trail_tail,
                                      element);
    i++;
  }
  
  /* Add trail to trail list. */
  new_entry->trail_list[0].trail_head = trail->trail_head;
  new_entry->trail_list[0].trail_tail = trail->trail_tail;
  new_entry->trail_list[0].trail_length = finger_trail_length;
  new_entry->trail_list[0].trail_id = trail_id;
  new_entry->trail_list[0].is_present = GNUNET_YES;
  finger_table[finger_table_index] = *new_entry;
  //GNUNET_free (new_entry);
  //GNUNET_free (trail);
  return;
}


/**
 * Scan the trail to check if there is any other friend in the trail other than
 * first hop. If yes then shortcut the trail, send trail compression message to
 * peers which are no longer part of trail and send back the updated trail
 * and trail_length to calling function.
 * @param finger_identity Finger whose trail we will scan.
 * @param finger_trail [in, out] Trail to reach from source to finger,
 * @param finger_trail_length  Total number of peers in original finger_trail.
 * @param finger_trail_id Unique identifier of the finger trail.
 * @return updated trail length in case we shortcut the trail, else original
 *         trail length.
 */
static struct GNUNET_PeerIdentity *
scan_and_compress_trail (struct GNUNET_PeerIdentity finger_identity,
                         const struct GNUNET_PeerIdentity *trail,
                         unsigned int trail_length,
                         struct GNUNET_HashCode trail_id,
                         int *new_trail_length)
{
  struct FriendInfo *target_friend;
  struct GNUNET_PeerIdentity *new_trail;
  unsigned int i;
  
  /* I am my own finger. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &finger_identity))
  {
    *new_trail_length = 0;
    return NULL;
  }

  if (0 == trail_length)
  {
    *new_trail_length = 0;
    return NULL;
  }
  
  /* If finger identity is a friend. */
  if (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap, &finger_identity))
  {
    *new_trail_length = 0;
    
    /* If there is trail to reach this finger/friend */
    if (trail_length > 0)
    {
      /* Finger is your first friend. */
      GDS_ROUTING_update_trail_next_hop (trail_id, finger_identity);
      GNUNET_assert (NULL != 
                    (target_friend = 
                     GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                        &trail[0])));
      

      GDS_NEIGHBOURS_send_trail_compression (my_identity, 
                                             trail_id, finger_identity,
                                             target_friend);
    }
    return NULL;
  }

  /*  For other cases, when its neither a friend nor my own identity.*/
  for (i = trail_length - 1; i > 0; i--)
  {
    /* If the element at this index in trail is a friend. */
    if (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap, &trail[i]))
    {
      struct FriendInfo *target_friend;
      int j = 0;

      GNUNET_assert (NULL != 
                    (target_friend = 
                     GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                        &trail[0])));
      GDS_ROUTING_update_trail_next_hop (trail_id, trail[i]);
      GDS_NEIGHBOURS_send_trail_compression (my_identity, 
                                             trail_id, trail[i],
                                             target_friend);

    
      /* Copy the trail from index i to index (trail_length -1) into a new trail
       *  and update new trail length */
      new_trail = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity) * (trail_length - i));
      while (i < trail_length)
      {
        memcpy (&new_trail[j], &trail[i], sizeof(struct GNUNET_PeerIdentity));
        j++;
        i++;
      }
      *new_trail_length = j+1;
      GNUNET_assert((j+1) == (trail_length - 1)); //FIXME: remove it afterwards.
      return new_trail;
    }
  }
  
  /* If we did not compress the trail, return the original trail back.*/
  new_trail = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity) * trail_length); 
  *new_trail_length = trail_length;
  memcpy (new_trail, trail, trail_length * sizeof (struct GNUNET_PeerIdentity));
  return new_trail;
}


/**
 * Periodic task to verify current successor. There can be multiple trails to reach
 * to successor, choose the shortest one and send verify successor message
 * across that trail. 
 * @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 FriendInfo *target_friend;
  struct GNUNET_HashCode trail_id;
  int i;
  struct GNUNET_TIME_Relative next_send_time;
  struct Trail *trail;
  struct Trail_Element *element;
  unsigned int trail_length;
  unsigned int j = 0;
  struct FingerInfo *successor;
   
  /* Schedule another send_find_finger_trail_message task. */
  next_send_time.rel_value_us =
      DHT_FIND_FINGER_TRAIL_INTERVAL.rel_value_us +
      GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK,
                                DHT_FIND_FINGER_TRAIL_INTERVAL.rel_value_us);
  send_verify_successor_task =
      GNUNET_SCHEDULER_add_delayed (next_send_time, &send_verify_successor_message,
                                    NULL);
  
  successor = &finger_table[0];
  i = 0;
  trail = &successor->trail_list[i];
  
  /* Store the successor for path tracking */
  if (track_topology &&  (NULL != GDS_stats))
  {
    char *my_id_str;
    char *succ_id_str;
    char *key;

    my_id_str = GNUNET_strdup (GNUNET_i2s (&my_identity));
    succ_id_str = GNUNET_strdup (GNUNET_i2s
                                 (&successor->finger_identity));
    GNUNET_asprintf (&key, "XDHT:0:%.4s:%.4s", my_id_str, succ_id_str);
    GNUNET_free (my_id_str);
    GNUNET_free (succ_id_str);
    GNUNET_STATISTICS_update (GDS_stats, "key", 1, 0);
    GNUNET_free (key);
  }
  
  GNUNET_assert(0 != GNUNET_CRYPTO_cmp_peer_identity (&my_identity, 
                                                      &successor->finger_identity));
  
  /* Trail stored at this index. */
  GNUNET_assert (GNUNET_YES == trail->is_present);
    
  trail_id = trail->trail_id;
  trail_length = trail->trail_length;
       
  if (trail_length > 0)
  {
     /* Copy the trail into peer list. */
    struct GNUNET_PeerIdentity peer_list[trail_length];
    
    element = trail->trail_head;
    while (j < trail_length)
    {
      peer_list[j] = element->peer;
      element = element->next;
      j++;
    }
      
    GNUNET_assert (NULL != (target_friend = 
                            GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                               &peer_list[0])));
    GDS_NEIGHBOURS_send_verify_successor_message (my_identity,
                                                  successor->finger_identity,
                                                  trail_id, peer_list, trail_length,
                                                  target_friend);
    return;
  }
  else
  {
    GNUNET_assert (NULL != (target_friend = 
                            GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                               &successor->finger_identity)));
    GDS_NEIGHBOURS_send_verify_successor_message (my_identity,
                                                  successor->finger_identity,
                                                  trail_id, NULL, 0,
                                                  target_friend);
    return;
  }
}


/**
 * Update the current search finger index. 
 */
static void
update_current_search_finger_index (struct GNUNET_PeerIdentity finger_identity,
                                    unsigned int finger_table_index)
{
  struct FingerInfo *successor;
  
  if (finger_table_index != current_search_finger_index)
    return;
  
  successor = &finger_table[0];
  GNUNET_assert (GNUNET_YES == successor->is_present);
 
  /* We were looking for immediate successor.  */
  if (0 == current_search_finger_index)
  {
    /* Start looking for immediate predecessor. */
    current_search_finger_index = PREDECESSOR_FINGER_ID;
  
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &finger_identity))
    {
      if (GNUNET_SCHEDULER_NO_TASK == send_verify_successor_task) 
        send_verify_successor_task = GNUNET_SCHEDULER_add_now (&send_verify_successor_message, NULL);
    }
    
    return;
  }
  
  current_search_finger_index = current_search_finger_index - 1;
  return;
}


/**
 * Get the first set bit in val. 
 * @param val Value
 * @return Position of first bit set.
 */
static unsigned int
find_set_bit(uint64_t val)
{
  uint64_t i;
  unsigned int pos;
  
  i = 1;
  pos = 0;
  
  while(!(i && val))
  {
    i = i << val;
    pos++;
  }
  return pos;
}

/**
 * Calculate finger_table_index from initial 64 bit finger identity value that 
 * we send in trail setup message. 
 * @param ultimate_destination_finger_value Value that we calculated from our
 *                                          identity and finger_table_index.
 * @param is_predecessor Is the entry for predecessor or not?
 * @return finger_table_index Value between 0 <= finger_table_index <= 64
 *                            finger_table_index > PREDECESSOR_FINGER_ID , 
 *                            if no valid finger_table_index is found. 
 */
static unsigned int
get_finger_table_index (uint64_t ultimate_destination_finger_value,
                        unsigned int is_predecessor)
{
  uint64_t my_id64;
  uint64_t diff;
  unsigned int finger_table_index;

  memcpy (&my_id64, &my_identity, sizeof (uint64_t));
  my_id64 = GNUNET_ntohll (my_id64);
  
  /* Is this a predecessor finger? */
  if (1 == is_predecessor)
  {
    diff =  my_id64 - ultimate_destination_finger_value;
    if (1 == diff)
      finger_table_index = PREDECESSOR_FINGER_ID;
    else
      finger_table_index = PREDECESSOR_FINGER_ID + 1; //error value
    
  }
  else 
  {
    diff = ultimate_destination_finger_value - my_id64;
    finger_table_index = find_set_bit(diff);
  }
  
  return finger_table_index;
}


/**
 * Remove finger and its associated data structures from finger table. 
 * @param finger Finger to be removed.
 */
static void
remove_existing_finger (struct FingerInfo *existing_finger, 
                        unsigned int finger_table_index)
{
  struct FingerInfo *finger;

  finger = &finger_table[finger_table_index];
  GNUNET_assert (GNUNET_YES == finger->is_present);
  
  /* If I am my own finger, then we have no trails. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                            &my_identity))
  {
    finger->is_present = GNUNET_NO;
    memset ((void *)&finger_table[finger_table_index], 0,
            sizeof (finger_table[finger_table_index]));
    return;
  }
  
  /* For all other fingers, send trail teardown across all the trails to reach
   finger, and free the finger. */
  send_all_finger_trails_teardown (finger);
  free_finger (finger, finger_table_index);
  return;
}


/**
 * Check if there is already an entry in finger_table at finger_table_index.
 * We get the finger_table_index from 64bit finger value we got from the network.
 * -- If yes, then select the closest finger.
 *   -- If new and existing finger are same, then check if you can store more 
 *      trails. 
 *      -- If yes then add trail, else keep the best trails to reach to the 
 *         finger. 
 *   -- If the new finger is closest, remove the existing entry, send trail
 *      teardown message across all the trails to reach the existing entry.
 *      Add the new finger.
 *  -- If new and existing finger are different, and existing finger is closest
 *     then do nothing.  
 * -- Update current_search_finger_index.
 * @param finger_identity Peer Identity of new finger
 * @param finger_trail Trail to reach the new finger
 * @param finger_trail_length Total number of peers in @a new_finger_trail.
 * @param is_predecessor Is this entry for predecessor in finger_table?
 * @param finger_value 64 bit value of finger identity that we got from network.
 * @param finger_trail_id Unique identifier of @finger_trail.
 */
static void
finger_table_add (struct GNUNET_PeerIdentity finger_identity, 
                  const struct GNUNET_PeerIdentity *finger_trail, 
                  unsigned int finger_trail_length,
                  unsigned int is_predecessor,
                  uint64_t finger_value,
                  struct GNUNET_HashCode finger_trail_id)
{
  struct FingerInfo *existing_finger;
  struct GNUNET_PeerIdentity *closest_peer;
  struct FingerInfo *successor;
  int updated_finger_trail_length; 
  unsigned int finger_table_index;
  
  /* Get the finger_table_index corresponding to finger_value we got from network.*/
  finger_table_index = get_finger_table_index (finger_value, is_predecessor);
   
  /* Invalid finger_table_index. */
  if ((finger_table_index > PREDECESSOR_FINGER_ID))
  {
    GNUNET_break_op (0);
    return;
  }

  /* New entry same as successor. */
  if ((0 != finger_table_index) && 
      (PREDECESSOR_FINGER_ID != finger_table_index)) 
  {
    successor = &finger_table[0];
    GNUNET_assert (GNUNET_YES == successor->is_present);
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger_identity,
                                              &successor->finger_identity))
    {
      current_search_finger_index = 0;
      return;
    }
  }
  
  existing_finger = &finger_table[finger_table_index];
 
  /* No entry present in finger_table for given finger map index. */
  if (GNUNET_NO == existing_finger->is_present)
  {
    struct GNUNET_PeerIdentity *updated_trail;
     
    /* Shorten the trail if possible. */
    updated_finger_trail_length = finger_trail_length;
    updated_trail =
         scan_and_compress_trail (finger_identity, finger_trail,
                                  finger_trail_length, finger_trail_id, 
                                  &updated_finger_trail_length);

    add_new_finger (finger_identity, updated_trail, 
                    updated_finger_trail_length,
                    finger_trail_id, finger_table_index);
    update_current_search_finger_index (finger_identity, 
                                        finger_table_index);
    return;
  }
  
  
  /* If existing entry and finger identity are not same. */
  if (0 != GNUNET_CRYPTO_cmp_peer_identity (&(existing_finger->finger_identity),
                                            &finger_identity))
  {
    closest_peer = select_closest_peer (&existing_finger->finger_identity,
                                        &finger_identity,
                                        finger_value, 
                                        is_predecessor);
    
    /* If the new finger is the closest peer. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger_identity, closest_peer))
    {
      struct GNUNET_PeerIdentity *updated_trail;
      /* Shorten the trail if possible. */
      updated_finger_trail_length = finger_trail_length;
      updated_trail =
        scan_and_compress_trail (finger_identity, finger_trail,
                                 finger_trail_length, finger_trail_id, 
                                 &updated_finger_trail_length);
      remove_existing_finger (existing_finger, finger_table_index);
      add_new_finger (finger_identity, updated_trail, updated_finger_trail_length,
                      finger_trail_id, finger_table_index);
      
    }
    else
    {
      /* Existing finger is the closest one. We need to send trail teardown  
         across the trail setup in routing table of all the peers. */
      if (0 != GNUNET_CRYPTO_cmp_peer_identity (&finger_identity, &my_identity))
      {
        if (finger_trail_length > 0)
          GDS_NEIGHBOURS_send_trail_teardown (finger_trail_id, 
                                              GDS_ROUTING_SRC_TO_DEST,
                                              finger_trail[0]);
        else
          GDS_NEIGHBOURS_send_trail_teardown (finger_trail_id, 
                                              GDS_ROUTING_SRC_TO_DEST,
                                              finger_identity);
      }
    }
  }
  else
  {
    /* If both new and existing entry are same as my_identity, then do nothing. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&(existing_finger->finger_identity),
                                              &my_identity))
    {
      return;
    }
    /* If the existing finger is not a friend. */
    if (NULL ==
        GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                           &existing_finger->finger_identity))
    {
      struct GNUNET_PeerIdentity *updated_trail;
      
      /* Shorten the trail if possible. */
      updated_finger_trail_length = finger_trail_length;
      updated_trail =
         scan_and_compress_trail (finger_identity, finger_trail,
                                  finger_trail_length, finger_trail_id, 
                                  &updated_finger_trail_length);
      /* If there is space to store more trails. */
      if (existing_finger->trails_count < MAXIMUM_TRAILS_PER_FINGER)
        add_new_trail (existing_finger, updated_trail,
                       updated_finger_trail_length, finger_trail_id);
      else
        select_and_replace_trail (existing_finger, updated_trail,
                                  updated_finger_trail_length, finger_trail_id);
       
    }
  }
  update_current_search_finger_index (finger_identity, finger_table_index);
  return;
}

/**
 * Core handler for P2P put messages.
 * @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_put (void *cls, const struct GNUNET_PeerIdentity *peer,
                    const struct GNUNET_MessageHeader *message)
{
  struct PeerPutMessage *put;
  struct GNUNET_PeerIdentity *put_path;
  struct GNUNET_PeerIdentity best_known_dest;
  struct GNUNET_HashCode intermediate_trail_id;
  struct GNUNET_PeerIdentity *next_hop;
  enum GNUNET_DHT_RouteOption options;
  struct GNUNET_HashCode test_key;
  void *payload;
  size_t msize;
  uint32_t putlen;
  size_t payload_size;
  uint64_t key_value;
  
  msize = ntohs (message->size);
  if (msize < sizeof (struct PeerPutMessage))
  { 
    GNUNET_break_op (0);
    return GNUNET_OK;
  }
  
  put = (struct PeerPutMessage *) message;
  putlen = ntohl (put->put_path_length);
  
  
  if ((msize <
       sizeof (struct PeerPutMessage) +
       putlen * sizeof (struct GNUNET_PeerIdentity)) ||
      (putlen >
       GNUNET_SERVER_MAX_MESSAGE_SIZE / sizeof (struct GNUNET_PeerIdentity)))
  {
    GNUNET_break_op (0);
    return GNUNET_OK;
  }

  best_known_dest = put->best_known_destination;
  put_path = (struct GNUNET_PeerIdentity *) &put[1];
  payload = &put_path[putlen];
  options = ntohl (put->options);
  intermediate_trail_id = put->intermediate_trail_id;
  
  payload_size = msize - (sizeof (struct PeerPutMessage) + 
                          putlen * sizeof (struct GNUNET_PeerIdentity));
  
  switch (GNUNET_BLOCK_get_key (GDS_block_context, ntohl (put->block_type),
                                payload, payload_size, &test_key))
  {
    case GNUNET_YES:
      if (0 != memcmp (&test_key, &put->key, sizeof (struct GNUNET_HashCode)))
      {
        char *put_s = GNUNET_strdup (GNUNET_h2s_full (&put->key));
        GNUNET_break_op (0);
        GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                    "PUT with key `%s' for block with key %s\n",
                     put_s, GNUNET_h2s_full (&test_key));
        GNUNET_free (put_s);
        return GNUNET_OK;
      }
    break;
    case GNUNET_NO:
      GNUNET_break_op (0);
      return GNUNET_OK;
    case GNUNET_SYSERR:
      /* cannot verify, good luck */
      break;
  }
  
   if (ntohl (put->block_type) == GNUNET_BLOCK_TYPE_REGEX) /* FIXME: do for all tpyes */
  {
    switch (GNUNET_BLOCK_evaluate (GDS_block_context,
                                   ntohl (put->block_type),
                                   NULL,    /* query */
                                   NULL, 0, /* bloom filer */
                                   NULL, 0, /* xquery */
                                   payload, payload_size))
    {
    case GNUNET_BLOCK_EVALUATION_OK_MORE:
    case GNUNET_BLOCK_EVALUATION_OK_LAST:
      break;

    case GNUNET_BLOCK_EVALUATION_OK_DUPLICATE:
    case GNUNET_BLOCK_EVALUATION_RESULT_INVALID:
    case GNUNET_BLOCK_EVALUATION_RESULT_IRRELEVANT:
    case GNUNET_BLOCK_EVALUATION_REQUEST_VALID:
    case GNUNET_BLOCK_EVALUATION_REQUEST_INVALID:
    case GNUNET_BLOCK_EVALUATION_TYPE_NOT_SUPPORTED:
    default:
      GNUNET_break_op (0);
      return GNUNET_OK;
    }
  }
  
  /* extend 'put path' by sender */
  struct GNUNET_PeerIdentity pp[putlen + 1];
  if (0 != (options & GNUNET_DHT_RO_RECORD_ROUTE))
  {
    memcpy (pp, put_path, putlen * sizeof (struct GNUNET_PeerIdentity));
    pp[putlen] = *peer;
    putlen++;
  }
  else
    putlen = 0;
  
  memcpy (&key_value, &(put->key), sizeof (uint64_t));
  if (0 != (GNUNET_CRYPTO_cmp_peer_identity (&best_known_dest, &my_identity)))
  {
    next_hop = GDS_ROUTING_get_next_hop (intermediate_trail_id, 
                                         GDS_ROUTING_SRC_TO_DEST);
    if (NULL == next_hop)
    {
      GNUNET_STATISTICS_update (GDS_stats,
                                gettext_noop ("# Next hop to forward the packet not found "
                                "trail setup request, packet dropped."),
                                1, GNUNET_NO);
      return GNUNET_SYSERR;
    }
  }
  else
  {
    struct Closest_Peer successor;
    key_value = GNUNET_ntohll (key_value);
    successor = find_successor (key_value, GDS_FINGER_TYPE_NON_PREDECESSOR);
    
    next_hop = GNUNET_new (struct GNUNET_PeerIdentity);
    *next_hop = successor.next_hop;
    intermediate_trail_id = successor.trail_id;
    best_known_dest = successor.best_known_destination;
  }
  
  GDS_CLIENTS_process_put (options,
                           ntohl (put->block_type),
                           ntohl (put->hop_count),
                           ntohl (put->desired_replication_level),
                           putlen, pp,
                           GNUNET_TIME_absolute_ntoh (put->expiration_time),
                           &put->key,
                           payload,
                           payload_size);
  
  /* I am the final destination */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &best_known_dest)) 
  {
    GDS_DATACACHE_handle_put (GNUNET_TIME_absolute_ntoh (put->expiration_time),
                              &(put->key),putlen, pp, ntohl (put->block_type), 
                              payload_size, payload);
  }
  else
  {
    GDS_NEIGHBOURS_send_put (&put->key,  
                             ntohl (put->block_type),ntohl (put->options),
                             ntohl (put->desired_replication_level),
                             best_known_dest, intermediate_trail_id, next_hop,
                             ntohl (put->hop_count), putlen, pp,
                             GNUNET_TIME_absolute_ntoh (put->expiration_time),
                             payload, payload_size);
  }
  return GNUNET_OK;
}


/**
 * 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)
{
  const struct PeerGetMessage *get;
  const struct GNUNET_PeerIdentity *get_path;
  struct GNUNET_PeerIdentity best_known_dest;
  struct GNUNET_HashCode intermediate_trail_id;
  struct GNUNET_PeerIdentity *next_hop;
  uint32_t get_length;
  uint64_t key_value;
  size_t msize;
  
  msize = ntohs (message->size);
  if (msize < sizeof (struct PeerGetMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }

  get = (const struct PeerGetMessage *)message;
  get_length = ntohl (get->get_path_length);
  best_known_dest = get->best_known_destination;
  intermediate_trail_id = get->intermediate_trail_id;
  get_path = (const struct GNUNET_PeerIdentity *)&get[1];
  
  if ((msize <
       sizeof (struct PeerGetMessage) +
       get_length * sizeof (struct GNUNET_PeerIdentity)) ||
       (get_length >
        GNUNET_SERVER_MAX_MESSAGE_SIZE / sizeof (struct GNUNET_PeerIdentity)))
  {
    GNUNET_break_op (0);
    return GNUNET_YES; 
  }
   
  /* Add sender to get path */
  struct GNUNET_PeerIdentity gp[get_length + 1];
  if (get_length > 0)
    memcpy (gp, get_path, get_length * sizeof (struct GNUNET_PeerIdentity));
  gp[get_length] = *peer;
  get_length = get_length + 1;
  
  memcpy (&key_value, &(get->key), sizeof (uint64_t));
  key_value = GNUNET_ntohll (key_value);

  /* I am not the final destination. I am part of trail to reach final dest. */
  if (0 != (GNUNET_CRYPTO_cmp_peer_identity (&best_known_dest, &my_identity)))
  {
    next_hop = GDS_ROUTING_get_next_hop (intermediate_trail_id, 
                                         GDS_ROUTING_SRC_TO_DEST);
    if (NULL == next_hop)
    {
      GNUNET_STATISTICS_update (GDS_stats,
                                gettext_noop ("# Next hop to forward the packet not found "
                                "GET request, packet dropped."),
                                1, GNUNET_NO);
      return GNUNET_SYSERR;
    }
  }
  else
  {
    struct Closest_Peer successor;

    successor = find_successor (key_value, GDS_FINGER_TYPE_NON_PREDECESSOR);
    next_hop = GNUNET_new (struct GNUNET_PeerIdentity);
    *next_hop = successor.next_hop;
    best_known_dest = successor.best_known_destination;
    intermediate_trail_id = successor.trail_id;
  }
  
  GDS_CLIENTS_process_get (get->options, get->block_type,get->hop_count,
                           get->desired_replication_level, get->get_path_length,
                           gp, &get->key);
  /* I am the final destination. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity(&my_identity, &best_known_dest))
  {
    struct GNUNET_PeerIdentity final_get_path[get_length+1];

    memcpy (final_get_path, gp, get_length * sizeof (struct GNUNET_PeerIdentity));
    memcpy (&final_get_path[get_length], &my_identity, sizeof (struct GNUNET_PeerIdentity));
    get_length = get_length + 1;
    
    GDS_DATACACHE_handle_get (&(get->key),(get->block_type), NULL, 0, NULL, 0,
                              get_length, final_get_path, 
                              &final_get_path[get_length-2], &my_identity);
  }
  else
  {
    GDS_NEIGHBOURS_send_get (&(get->key), get->block_type, get->options, 
                             get->desired_replication_level, best_known_dest,
                             intermediate_trail_id, next_hop, 0,
                             get_length, gp); 
  }
  return GNUNET_YES;
}


/**
 * Core handler for get result
 * @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_result (void *cls, const struct GNUNET_PeerIdentity *peer,
                           const struct GNUNET_MessageHeader *message)
{
  const struct PeerGetResultMessage *get_result;
  const struct GNUNET_PeerIdentity *get_path;
  const struct GNUNET_PeerIdentity *put_path;
  const void *payload;
  size_t payload_size;
  size_t msize;
  unsigned int getlen;
  unsigned int putlen;
  int current_path_index;
  
  msize = ntohs (message->size);
  if (msize < sizeof (struct PeerGetResultMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }

  get_result = (const struct PeerGetResultMessage *)message;
  getlen = ntohl (get_result->get_path_length);
  putlen = ntohl (get_result->put_path_length);
  
  if ((msize <
       sizeof (struct PeerGetResultMessage) +
       getlen * sizeof (struct GNUNET_PeerIdentity) + 
       putlen * sizeof (struct GNUNET_PeerIdentity)) ||
      (getlen >
       GNUNET_SERVER_MAX_MESSAGE_SIZE / sizeof (struct GNUNET_PeerIdentity) ||
      (putlen >
         GNUNET_SERVER_MAX_MESSAGE_SIZE / sizeof (struct GNUNET_PeerIdentity))))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
   
  put_path = (const struct GNUNET_PeerIdentity *) &get_result[1];
  get_path = &put_path[putlen];
  payload = (const void *) &get_path[getlen];
  payload_size = msize - (sizeof (struct PeerGetResultMessage) + 
                         (getlen + putlen) * sizeof (struct GNUNET_PeerIdentity));

  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &(get_path[0]))))
  {
    GDS_CLIENTS_handle_reply (get_result->expiration_time, &(get_result->key), 
                              getlen, get_path, putlen,
                              put_path, get_result->type, payload_size, payload);
    return GNUNET_YES;
  }
  else
  {
    current_path_index = search_my_index (get_path, getlen);
    if (-1 == current_path_index )
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
    GDS_NEIGHBOURS_send_get_result (&(get_result->key), get_result->type,
                                    &get_path[current_path_index - 1],
                                    &(get_result->querying_peer), putlen, put_path,
                                    getlen, get_path, get_result->expiration_time,
                                    payload, payload_size);
    return GNUNET_YES;
  }  
  return GNUNET_SYSERR;
}


/**
 * Find the next hop to pass trail setup message. First find the local best known
 * hop from your own identity, friends and finger. If you were part of trail,
 * then get the next hop from routing table. Compare next_hop from routing table
 * and local best known hop, and return the closest one to final_dest_finger_val
 * @param final_dest_finger_val 64 bit value of finger identity
 * @param intermediate_trail_id If you are part of trail to reach to some other 
 *                              finger, then it is the trail id to reach to
 *                              that finger, else set to 0.
 * @param is_predecessor Are we looking for closest successor or predecessor. 
 * @param current_dest In case you are part of trail, then finger to which 
 *                     we should forward the message. Else my own identity
 * @return Closest Peer for @a final_dest_finger_val
 */
static struct Closest_Peer
get_local_best_known_next_hop (uint64_t final_dest_finger_val, 
                               struct GNUNET_HashCode intermediate_trail_id,
                               unsigned int is_predecessor,
                                struct GNUNET_PeerIdentity prev_hop,
                               struct GNUNET_PeerIdentity source,
                               struct GNUNET_PeerIdentity *current_dest)
{
  struct Closest_Peer peer;
  
  /* Find a local best known peer. */
  peer = find_successor (final_dest_finger_val, is_predecessor);//FIXME: chnage to better name
  
  /* Am I just a part of a trail towards a finger (current_destination)? */
  if (0 != (GNUNET_CRYPTO_cmp_peer_identity (&my_identity, current_dest)))
  {
    /* Select best successor among one found locally and current_destination 
     * that we got from network.*/
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (&peer.best_known_destination,
                                              current_dest))
    { 
      struct GNUNET_PeerIdentity *closest_peer;
      struct GNUNET_PeerIdentity *local_best_known_dest;
      local_best_known_dest = GNUNET_new(struct GNUNET_PeerIdentity);
      memcpy(local_best_known_dest, &peer.best_known_destination, sizeof(struct GNUNET_PeerIdentity));
      
      closest_peer = select_closest_peer (local_best_known_dest,
                                          current_dest,
                                          final_dest_finger_val,
                                          is_predecessor);

      GNUNET_free(local_best_known_dest);
      /* Is current dest (end point of the trail of which I am a part) closest_peer? */
      if (0 == GNUNET_CRYPTO_cmp_peer_identity (current_dest, closest_peer))
      {
        struct GNUNET_PeerIdentity *next_hop;
        next_hop = GDS_ROUTING_get_next_hop (intermediate_trail_id,
                                             GDS_ROUTING_SRC_TO_DEST);
        GNUNET_assert (NULL != next_hop);

        peer.next_hop = *next_hop;
        peer.best_known_destination =  *current_dest;
        peer.trail_id = intermediate_trail_id;
      }
    }  
  }
  return peer;
}


/* 
 * Core handle for 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)
{
  const struct PeerTrailSetupMessage *trail_setup;
  const struct GNUNET_PeerIdentity *trail_peer_list;
  struct GNUNET_PeerIdentity current_dest;
  struct FriendInfo *target_friend;
  struct GNUNET_PeerIdentity source;
  uint64_t final_dest_finger_val;
  struct GNUNET_HashCode intermediate_trail_id;
  struct GNUNET_HashCode trail_id;
  unsigned int is_predecessor;
  uint32_t trail_length;
  size_t msize;

  msize = ntohs (message->size);
  if (msize < sizeof (struct PeerTrailSetupMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }

  trail_setup = (const struct PeerTrailSetupMessage *) message;
  trail_length = (msize - sizeof (struct PeerTrailSetupMessage))/
                  sizeof (struct GNUNET_PeerIdentity);
  if ((msize - sizeof (struct PeerTrailSetupMessage)) % 
      sizeof (struct GNUNET_PeerIdentity) != 0)
  {
    GNUNET_break_op (0);
    return GNUNET_OK;      
  }           
  
  trail_peer_list = (const struct GNUNET_PeerIdentity *)&trail_setup[1];
  current_dest = trail_setup->best_known_destination;
  trail_id = trail_setup->trail_id;
  final_dest_finger_val = 
          GNUNET_ntohll (trail_setup->final_destination_finger_value);
  source = trail_setup->source_peer;
  is_predecessor = ntohl (trail_setup->is_predecessor);
  intermediate_trail_id = trail_setup->intermediate_trail_id;
  
   /* If I was the source and got the message back, then set trail length to 0.*/
  if (0 == GNUNET_CRYPTO_cmp_peer_identity(&my_identity, &source))
  {
   trail_length = 0;  
  }
  
  /* Is my routing table full?  */
  if (GNUNET_YES == GDS_ROUTING_threshold_reached())
  {
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, peer)));
    GDS_NEIGHBOURS_send_trail_rejection (source, final_dest_finger_val,
                                         my_identity, is_predecessor,
                                         trail_peer_list, trail_length,
                                         trail_id, target_friend,
                                         CONGESTION_TIMEOUT);
    return GNUNET_OK;
  }
 
  /* Get the next hop to forward the trail setup request. */
  struct Closest_Peer next_peer = 
          get_local_best_known_next_hop (final_dest_finger_val, 
                                         intermediate_trail_id,
                                         is_predecessor,
                                         *peer,
                                         source,
                                         &current_dest);
 
  /* Am I the final destination? */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&next_peer.best_known_destination,
                                             &my_identity)))
  {
    //
    /* If I was not the source of this message for which now I am destination */
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (&source, &my_identity))
    {
      GDS_ROUTING_add (trail_id, *peer, my_identity);
    }
   
    if(trail_length > 0)
    {
      GNUNET_assert (NULL != 
                    (target_friend = 
                    GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                       &trail_peer_list[trail_length-1])));
    }
    else
    {
      if(0 == GNUNET_CRYPTO_cmp_peer_identity (&source, &my_identity))
      {
        finger_table_add (my_identity, NULL, 0, is_predecessor, 
                          final_dest_finger_val, trail_id);
        return GNUNET_OK;
      }
      GNUNET_assert (NULL != 
                    (target_friend = 
                     GNUNET_CONTAINER_multipeermap_get (friend_peermap, &source)));
    }
   
    GDS_NEIGHBOURS_send_trail_setup_result (source,
                                            my_identity,
                                            target_friend, trail_length,
                                            trail_peer_list,
                                            is_predecessor, 
                                            final_dest_finger_val,trail_id);
  }
  else
  {
    GNUNET_assert (NULL != 
                    (target_friend = 
                      GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                          &next_peer.next_hop)));
    
    if (0 != GNUNET_CRYPTO_cmp_peer_identity(&my_identity, &source))
    {
      /* Add yourself to list of peers. */
      struct GNUNET_PeerIdentity peer_list[trail_length + 1];
 
      memcpy (peer_list, trail_peer_list, 
              trail_length * sizeof (struct GNUNET_PeerIdentity));
      peer_list[trail_length] = my_identity;
     
      GDS_NEIGHBOURS_send_trail_setup (source,
                                       final_dest_finger_val,
                                       next_peer.best_known_destination,
                                       target_friend, trail_length + 1, peer_list,
                                       is_predecessor, trail_id,
                                       next_peer.trail_id);
    }
    else
        GDS_NEIGHBOURS_send_trail_setup (source,
                                         final_dest_finger_val,
                                         next_peer.best_known_destination,
                                         target_friend, 0, NULL,
                                         is_predecessor, trail_id,
                                         next_peer.trail_id);
  }
  return GNUNET_OK;
}

#if 0
/* FIXME: here we are calculating my_index and comparing also in this function.
   And we are doing it again here in this function. Re factor the code. */
/**
 * FIXME: Should we call this function everywhere in all the handle functions
 * where we have a trail to verify from or a trail id. something like
 * if prev hop is not same then drop the message. 
 * Check if sender_peer and peer from which we should receive the message are
 * same or different.
 * @param trail_peer_list List of peers in trail
 * @param trail_length Total number of peers in @a trail_peer_list
 * @param sender_peer Peer from which we got the message. 
 * @param finger_identity Finger to which trail is setup. It is not part of trail.
 * @return #GNUNET_YES if sender_peer and peer from which we should receive the
 *                    message are different.
 *         #GNUNET_NO if sender_peer and peer from which we should receive the
 *                    message are different. 
 */
static int
is_sender_peer_correct (const struct GNUNET_PeerIdentity *trail_peer_list,
                        unsigned int trail_length,
                        const struct GNUNET_PeerIdentity *sender_peer,
                        struct GNUNET_PeerIdentity finger_identity,
                        struct GNUNET_PeerIdentity source_peer)
{
  int my_index;
  
  /* I am the source peer. */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&source_peer,
                                             &my_identity)))
  {
    /* Is the first element of the trail is sender_peer.*/
    if (trail_length > 0)
    {
      if (0 != GNUNET_CRYPTO_cmp_peer_identity (&trail_peer_list[0],
                                                sender_peer))
        return GNUNET_NO;
    }
    else
    {
      /* Is finger the sender peer? */
      if (0 != GNUNET_CRYPTO_cmp_peer_identity (sender_peer,
                                                &finger_identity))
        return GNUNET_NO;
    }
  }
  else
  {
    /* Get my current location in the trail. */
    my_index = search_my_index (trail_peer_list, trail_length);
    if (-1 == my_index)
      return GNUNET_NO;
    
    /* I am the last element in the trail. */
    if ((trail_length - 1) == my_index)
    {
      /* Is finger the sender_peer? */
      if (0 != GNUNET_CRYPTO_cmp_peer_identity (sender_peer,
                                                &finger_identity))
        return GNUNET_NO;
    }
    else
    {
      /* Is peer after me in trail the sender peer? */
      if (0 != GNUNET_CRYPTO_cmp_peer_identity (sender_peer,
                                                &trail_peer_list[my_index + 1]))
        return GNUNET_NO;
    }
  }
  return GNUNET_YES;
}
#endif


/**
 * FIXME: we should also add a case where we search if we are present in the trail
 * twice.
 * Core handle for p2p trail setup result messages.
 * @param closure
 * @param message message
 * @param peer sender of this message. 
 * @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)
{
  const struct PeerTrailSetupResultMessage *trail_result;
  const struct GNUNET_PeerIdentity *trail_peer_list;
  struct GNUNET_PeerIdentity next_hop;
  struct FriendInfo *target_friend;
  struct GNUNET_PeerIdentity querying_peer;
  struct GNUNET_PeerIdentity finger_identity;
  uint32_t trail_length;
  uint64_t ulitmate_destination_finger_value;
  uint32_t is_predecessor;
  struct GNUNET_HashCode trail_id;
  int my_index;
  size_t msize;

  msize = ntohs (message->size);
  if (msize < sizeof (struct PeerTrailSetupResultMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }

  trail_result = (const struct PeerTrailSetupResultMessage *) message;
  trail_length = (msize - sizeof (struct PeerTrailSetupResultMessage))/
                  sizeof (struct GNUNET_PeerIdentity);
  if ((msize - sizeof (struct PeerTrailSetupResultMessage)) % 
      sizeof (struct GNUNET_PeerIdentity) != 0)
  {
    GNUNET_break_op (0);
    return GNUNET_OK;      
  }       

  is_predecessor = ntohl (trail_result->is_predecessor);
  querying_peer = trail_result->querying_peer;
  finger_identity = trail_result->finger_identity;
  trail_id = trail_result->trail_id;
  trail_peer_list = (const struct GNUNET_PeerIdentity *) &trail_result[1];
  ulitmate_destination_finger_value = 
          GNUNET_ntohll (trail_result->ulitmate_destination_finger_value);

  /* FIXME: here we are calculating my_index and comparing also in this function.
   And we are doing it again here in this function. Re factor the code. */
  /* Ensure that sender peer is the peer from which we were expecting the message. */
#if 0
  if (GNUNET_NO == is_sender_peer_correct (trail_peer_list,
                                           trail_length,
                                           peer, finger_identity, querying_peer))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
#endif
  
  /* Am I the one who initiated the query? */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&querying_peer, &my_identity)))
  {
    /* If I am not my own finger identity, then add routing table entry. */
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &finger_identity))
    {
      GDS_ROUTING_add (trail_id, my_identity, *peer);
    }
   
    finger_table_add (finger_identity, trail_peer_list, trail_length,
                      is_predecessor, ulitmate_destination_finger_value, trail_id);
    return GNUNET_YES;
  }
  
  /* Get my location in the trail. */
  my_index = search_my_index (trail_peer_list, trail_length);
  if (-1 == my_index)
  {
    GNUNET_break_op(0);
    return GNUNET_SYSERR;
  }
  
  if (my_index == 0)
    next_hop = trail_result->querying_peer;
  else
    next_hop = trail_peer_list[my_index - 1];
  
  if (0 != (GNUNET_CRYPTO_cmp_peer_identity (&(trail_result->querying_peer),
                                             &(trail_result->finger_identity))))
  {
    GDS_ROUTING_add (trail_id, next_hop, *peer);
  }

  GNUNET_assert (NULL != 
                (target_friend = 
                 GNUNET_CONTAINER_multipeermap_get (friend_peermap, &next_hop)));
  GDS_NEIGHBOURS_send_trail_setup_result (querying_peer, finger_identity,
                                          target_friend, trail_length, trail_peer_list,
                                          is_predecessor, 
                                          ulitmate_destination_finger_value,
                                          trail_id);
  return GNUNET_OK;
}


/**
 * Invert the trail.
 * @param trail Trail to be inverted
 * @param trail_length Total number of peers in the trail.
 * @return Updated trail
 */
static struct GNUNET_PeerIdentity *
invert_trail (const struct GNUNET_PeerIdentity *trail,
              unsigned int trail_length)
{
  int i;
  int j;
  struct GNUNET_PeerIdentity *inverted_trail;

  inverted_trail = GNUNET_malloc (sizeof(struct GNUNET_PeerIdentity) *
                                  trail_length);
  i = 0;
  j = trail_length - 1;
  while (i < trail_length)
  {
    inverted_trail[i] = trail[j];
    i++;
    j--;
  }
  
  GNUNET_assert(NULL != GNUNET_CONTAINER_multipeermap_get(friend_peermap,
                                                          &inverted_trail[0]));
  return inverted_trail;
}


/**
 * Return the shortest trail among all the trails to reach to finger from me.
 * @param finger Finger 
 * @param shortest_trail_length[out] Trail length of shortest trail from me
 *                                   to @a finger
 * @return Shortest trail. 
 */
static struct GNUNET_PeerIdentity *
get_shortest_trail (struct FingerInfo *finger,
                    unsigned int *trail_length)
{
  struct Trail *trail;
  unsigned int flag = 0;
  unsigned int shortest_trail_index = 0;
  int shortest_trail_length = -1;
  struct Trail_Element *trail_element;
  struct GNUNET_PeerIdentity *trail_list;
  unsigned int i;
  
  trail = GNUNET_new (struct Trail);
  
  /* Get the shortest trail to reach to current successor. */
  for (i = 0; i < finger->trails_count; i++)
  {
    trail = &finger->trail_list[i];
   
    if (0 == flag)
    {
      shortest_trail_index = i;
      shortest_trail_length = trail->trail_length; 
      flag = 1;
      continue;
    }
    
    if (shortest_trail_length > trail->trail_length)
    {
      shortest_trail_index = i;
      shortest_trail_length = trail->trail_length;
    }
    continue;
  }
  
  /* Copy the shortest trail and return. */
  trail = &finger->trail_list[shortest_trail_index];
  trail_element = trail->trail_head;
  trail_list = GNUNET_malloc (sizeof(struct GNUNET_PeerIdentity)*
                              shortest_trail_length);
  
  for(i = 0; i < shortest_trail_length; i++,trail_element = trail_element->next)
  {
    trail_list[i] = trail_element->peer; 
  }
  
  GNUNET_assert(shortest_trail_length != -1);
  
  *trail_length = shortest_trail_length;
  return trail_list;
}


/**
 * Return the trail from source to my current predecessor. Check if source
 * is already part of the this trail, if yes then return the shorten trail. 
 * @param current_trail Trail from source to me, NOT including the endpoints.
 * @param current_trail_length Number of peers in @a current_trail.
 * @param trail_src_to_curr_pred_length[out] Number of peers in trail from 
 *                                           source to my predecessor, NOT including
 *                                           the endpoints.
 * @return Trail from source to my predecessor. 
 */
static struct GNUNET_PeerIdentity *
get_trail_src_to_curr_pred (struct GNUNET_PeerIdentity source_peer,
                            const struct GNUNET_PeerIdentity *trail_src_to_me,
                            unsigned int trail_src_to_me_len,
                            unsigned int *trail_src_to_curr_pred_length)
{
  struct GNUNET_PeerIdentity *trail_me_to_curr_pred;
  struct GNUNET_PeerIdentity *trail_src_to_curr_pred;
  unsigned int trail_me_to_curr_pred_length;
  struct FingerInfo *current_predecessor;
  unsigned int i;
  unsigned int j;
  
  current_predecessor = &finger_table[PREDECESSOR_FINGER_ID];
  trail_me_to_curr_pred = get_shortest_trail (current_predecessor,
                                              &trail_me_to_curr_pred_length);
    
  /* Check if trail_me_to_curr_pred contains source. */
  if (trail_me_to_curr_pred_length > 0)
  {
    for(i = trail_me_to_curr_pred_length - 1; i >= 0; i--)
    {
      if(0 != GNUNET_CRYPTO_cmp_peer_identity (&source_peer,
                                               &trail_me_to_curr_pred[i]))
        continue;
       
       i = i+1;
      
      /* Source is the last element in the trail to reach to my pred. 
         Source is direct friend of the pred. */
      if (trail_me_to_curr_pred_length == i)
      {
        *trail_src_to_curr_pred_length = 0;
        return NULL;
      }
      
      *trail_src_to_curr_pred_length = trail_me_to_curr_pred_length - i;
      trail_src_to_curr_pred = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity)*
                                              *trail_src_to_curr_pred_length);
      for(j = 0; j < *trail_src_to_curr_pred_length; i++,j++)
      {
        trail_src_to_curr_pred[j] = trail_me_to_curr_pred[i];
      }
      
      return trail_src_to_curr_pred;
    }
  }
  
  /* Append trail from source to me to my current_predecessor. */
  *trail_src_to_curr_pred_length = trail_src_to_me_len +
                                   trail_me_to_curr_pred_length + 1;

  trail_src_to_curr_pred = GNUNET_malloc (sizeof(struct GNUNET_PeerIdentity)*
                                          *trail_src_to_curr_pred_length);
  
  for (i = 0; i < trail_src_to_me_len; i++)
    trail_src_to_curr_pred[i] = trail_src_to_me[i];
  
  trail_src_to_curr_pred[i] = my_identity;
  i++;
  
  for (j = 0; i < *trail_src_to_curr_pred_length; i++,j++)
    trail_src_to_curr_pred[i] = trail_me_to_curr_pred[j];
 
  return trail_src_to_curr_pred;
}


/**
 * Add finger as your predecessor. To add, first generate a new trail id, invert
 * the trail to get the trail from me to finger, add an entry in your routing 
 * table, send add trail message to peers which are part of trail from me to 
 * finger and add finger in finger table.
 * @param finger
 * @param trail
 * @param trail_length
 */
static void
update_predecessor (struct GNUNET_PeerIdentity finger, 
                    struct GNUNET_PeerIdentity *trail, 
                    unsigned int trail_length)
{
  struct GNUNET_HashCode trail_to_new_predecessor_id;
  struct GNUNET_PeerIdentity *trail_to_new_predecessor;
  struct FriendInfo *target_friend;
  
  /* Generate trail id for trail from me to new predecessor = finger. */
  GNUNET_CRYPTO_random_block (GNUNET_CRYPTO_QUALITY_STRONG,
                              &trail_to_new_predecessor_id, 
                              sizeof (trail_to_new_predecessor_id));
  
  /* Finger is a friend. */
  if (trail_length == 0)
  {
    trail_to_new_predecessor = NULL;
    GDS_ROUTING_add (trail_to_new_predecessor_id, my_identity, finger); 
    GNUNET_assert (NULL != (target_friend = 
                            GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                               &finger)));
  }
  else
  {
    /* Invert the trail to get the trail from me to finger, NOT including the
       endpoints.*/
    trail_to_new_predecessor = invert_trail (trail, trail_length);
  
    /* Add an entry in your routing table. */
    GDS_ROUTING_add (trail_to_new_predecessor_id, 
                     my_identity,
                     trail_to_new_predecessor[0]);
   
    GNUNET_assert (NULL != (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                      &trail_to_new_predecessor[0])));
    GNUNET_assert (NULL != (
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                      &trail[trail_length - 1])));
  }
  
  /* Add entry in routing table of all peers that are part of trail from me
     to finger, including finger. */
  GDS_NEIGHBOURS_send_add_trail (my_identity, 
                                 finger,
                                 trail_to_new_predecessor_id,
                                 trail_to_new_predecessor,
                                 trail_length,
                                 target_friend);

  add_new_finger (finger, trail_to_new_predecessor, trail_length,
                  trail_to_new_predecessor_id, PREDECESSOR_FINGER_ID);
  GNUNET_free_non_null (trail_to_new_predecessor);
}


/* 
 * Check if you already have a predecessor. If not then add finger as your
 * predecessor. If you have predecessor, then compare two peer identites.
 * If finger is correct predecessor, then remove the old entry, add finger in
 * finger table and send add_trail message to add the trail in the routing
 * table of all peers which are part of trail to reach from me to finger. 
 * @param finger New peer which may be our predecessor. 
 * @param trail List of peers to reach from @finger to me. 
 * @param trail_length Total number of peer in @a trail.
 */
static void
compare_and_update_predecessor (struct GNUNET_PeerIdentity finger, 
                                struct GNUNET_PeerIdentity *trail, 
                                unsigned int trail_length)
{
  struct FingerInfo *current_predecessor;
  struct GNUNET_PeerIdentity *closest_peer;
  uint64_t predecessor_value;
  unsigned int is_predecessor = 1;
  
  current_predecessor = &finger_table[PREDECESSOR_FINGER_ID];
  
  GNUNET_assert (0 != GNUNET_CRYPTO_cmp_peer_identity (&finger, &my_identity));
  
  /* No predecessor. Add finger as your predecessor. */
  if (GNUNET_NO == current_predecessor->is_present) 
  {
    update_predecessor (finger, trail, trail_length);
    return;
  }
  /* FIXME: Here we should first call find_successor and get a locally known
   predecessor. If locally known predecessor is closest then current or finger,
   add that as predecessor. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&current_predecessor->finger_identity,
                                            &finger))
  {
    return;
  }
  
  predecessor_value = compute_finger_identity_value (PREDECESSOR_FINGER_ID);
  closest_peer = select_closest_peer (&finger, 
                                      &current_predecessor->finger_identity,
                                      predecessor_value, is_predecessor);
  
  /* Finger is the closest predecessor. Remove the existing one and add the new
     one. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (closest_peer, &finger))
  {
    remove_existing_finger (current_predecessor, PREDECESSOR_FINGER_ID);
    update_predecessor (finger, trail, trail_length);
    return;
  }
  return;
}


/* 
 * Core handle for p2p verify successor 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)
{
  const struct PeerVerifySuccessorMessage *vsm;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_PeerIdentity successor;
  struct GNUNET_PeerIdentity source_peer;
  struct GNUNET_PeerIdentity *trail;
  struct GNUNET_PeerIdentity *next_hop;
  struct FingerInfo *current_predecessor;
  struct FriendInfo *target_friend;
  unsigned int trail_src_to_curr_pred_len = 0;
  struct GNUNET_PeerIdentity *trail_src_to_curr_pred;
  size_t msize;
  unsigned int trail_length;
  
  msize = ntohs (message->size);
  
  if (msize < sizeof (struct PeerVerifySuccessorMessage)) 
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
  
  vsm = (const struct PeerVerifySuccessorMessage *) message;
  trail_length = (msize - sizeof (struct PeerVerifySuccessorMessage))/
                  sizeof (struct GNUNET_PeerIdentity);
  if ((msize - sizeof (struct PeerVerifySuccessorMessage)) % 
      sizeof (struct GNUNET_PeerIdentity) != 0)
  {
    GNUNET_break_op (0);
    return GNUNET_OK;      
  } 
  
  trail_id = vsm->trail_id;
  source_peer = vsm->source_peer;
  successor = vsm->successor;
  trail = (struct GNUNET_PeerIdentity *)&vsm[1];
  
 
  /* I am NOT the successor of source_peer. Pass the message to next_hop on
   * the trail. */
  if(0 != (GNUNET_CRYPTO_cmp_peer_identity (&successor, &my_identity)))
  {
    next_hop = GDS_ROUTING_get_next_hop (trail_id, GDS_ROUTING_SRC_TO_DEST);
    if (NULL == next_hop)
    {
      GNUNET_break (0);
      return GNUNET_SYSERR;
    }
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop)));

    GDS_NEIGHBOURS_send_verify_successor_message (source_peer, successor,
                                                  trail_id, trail, trail_length,
                                                  target_friend);
    return GNUNET_OK;
  }
  
  /* I am the destination of this message. */
  
  /* Check if the source_peer could be our predecessor and if yes then update
   * it.  */
  compare_and_update_predecessor (source_peer, trail, trail_length);
  current_predecessor = &finger_table[PREDECESSOR_FINGER_ID];
  
  /* Is source of this message NOT my predecessor. */
  if (0 != (GNUNET_CRYPTO_cmp_peer_identity (&current_predecessor->finger_identity,
                                             &source_peer)))
  {
    trail_src_to_curr_pred = get_trail_src_to_curr_pred (source_peer,
                                                         trail,
                                                         trail_length,
                                                         &trail_src_to_curr_pred_len);    
  }
  else
  {
    trail_src_to_curr_pred_len = trail_length;
    int i;
    trail_src_to_curr_pred = GNUNET_malloc(sizeof(struct GNUNET_PeerIdentity)*trail_length);
    for(i = 0; i < trail_src_to_curr_pred_len; i++)
    {
      trail_src_to_curr_pred[i] = trail[i];
    }

  }
  
  GNUNET_assert (NULL != 
                (target_friend = 
                 GNUNET_CONTAINER_multipeermap_get (friend_peermap, peer)));
  GDS_NEIGHBOURS_send_verify_successor_result (source_peer, my_identity,
                                               current_predecessor->finger_identity,
                                               trail_id, trail_src_to_curr_pred,
                                               trail_src_to_curr_pred_len,
                                               GDS_ROUTING_DEST_TO_SRC,
                                               target_friend);

  return GNUNET_OK;
}


/**
 * If the trail from me to my probable successor contains a friend not
 * at index 0, then we can shorten the trail.
 * @param probable_successor Peer which is our probable successor
 * @param trail_me_to_probable_successor Peers in path from me to my probable 
 *                                       successor, NOT including the endpoints.
 * @param trail_me_to_probable_successor_len Total number of peers in 
 *                                           @a trail_me_to_probable_succesor.
 * @return Updated trail, if any friend found.
 *         Else the trail_me_to_probable_successor. 
 */
struct GNUNET_PeerIdentity *
check_trail_me_to_probable_succ (struct GNUNET_PeerIdentity probable_successor,
                                 const struct GNUNET_PeerIdentity *trail_me_to_probable_successor,
                                 unsigned int trail_me_to_probable_successor_len,
                                 unsigned int *trail_to_new_successor_length)
{
  unsigned int i;
  unsigned int j;
  struct GNUNET_PeerIdentity *trail_to_new_successor;
    
  /* Probable successor is  a friend */
  if (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                 &probable_successor))
  {
    trail_to_new_successor = NULL;
    *trail_to_new_successor_length = 0;
    return trail_to_new_successor;
  }
  
  /* Is there any friend of yours in this trail. */
  if(trail_me_to_probable_successor_len > 1)
  {
    for (i = trail_me_to_probable_successor_len - 1; i > 0; i--)
    {
      if (NULL == GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                     &trail_me_to_probable_successor[i]))
        continue;
    
      j = 0;
      *trail_to_new_successor_length = (trail_me_to_probable_successor_len - i);
      trail_to_new_successor = GNUNET_malloc (sizeof(struct GNUNET_PeerIdentity)*
                                                *trail_to_new_successor_length);
    
      for(j = 0;i < trail_me_to_probable_successor_len;i++,j++)    
      {
        trail_to_new_successor[j] = trail_me_to_probable_successor[i];
      }
      return trail_to_new_successor;
    }
  }
  
  *trail_to_new_successor_length = trail_me_to_probable_successor_len;
  trail_to_new_successor = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity)*
                                          *trail_to_new_successor_length);
  
  for(i = 0; i < *trail_to_new_successor_length; i++)
    trail_to_new_successor[i] = trail_me_to_probable_successor[i];
  
  return trail_to_new_successor;
}


/**
 * Check if the peer which sent us verify successor result message is still ours
 * successor or not. If not, then compare existing successor and probable successor.
 * In case probable successor is the correct successor, remove the existing
 * successor. Add probable successor as new successor. Send notify new successor
 * message to new successor. 
 * @param curr_succ
 * @param probable_successor
 * @param trail
 * @param trail_length
 */
static void
compare_and_update_successor (struct GNUNET_PeerIdentity curr_succ,
                              struct GNUNET_PeerIdentity probable_successor,
                              const struct GNUNET_PeerIdentity *trail,
                              unsigned int trail_length)
{
  struct FingerInfo *current_successor;
  struct GNUNET_PeerIdentity *closest_peer;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_PeerIdentity *trail_me_to_probable_succ;
  struct FriendInfo *target_friend;
  unsigned int trail_me_to_probable_succ_len;
  unsigned int is_predecessor = GNUNET_NO;
  uint64_t successor_value;
  
  current_successor = &finger_table[0];
  successor_value = compute_finger_identity_value(0);
  
  /* Have we found some other successor, while waiting for verify successor result. */
  if(0 != GNUNET_CRYPTO_cmp_peer_identity(&curr_succ, &current_successor->finger_identity))
  {
    /* We could have added this new successor, only if it was closer the old one. */
    closest_peer = select_closest_peer (&curr_succ,
                                        &current_successor->finger_identity,
                                        successor_value, is_predecessor);
    
    /* FIXME: it may fail in case we have done more number of iterations of
     find _finger_trail_task. */
    /*GNUNET_assert (0 == 
                   GNUNET_CRYPTO_cmp_peer_identity (closest_peer,
                                                    &current_successor->finger_identity));*/
    
  }
  
  closest_peer = select_closest_peer (&probable_successor,
                                      &current_successor->finger_identity,
                                      successor_value, is_predecessor);
  
  /* If the current_successor in the finger table is closest, then do nothing. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (closest_peer,
                                            &current_successor->finger_identity))
    return;
  
  /* Probable successor is the closest peer.*/
  if(trail_length > 0)
    GNUNET_assert(NULL != GNUNET_CONTAINER_multipeermap_get(friend_peermap,
                                                            &trail[0]));
  else
    GNUNET_assert(NULL != GNUNET_CONTAINER_multipeermap_get(friend_peermap,
                                                            &probable_successor));
  
  trail_me_to_probable_succ_len = 0;
  /* TODO: Check if the path to reach to probable successor contains a friend. */
  trail_me_to_probable_succ = 
          check_trail_me_to_probable_succ (probable_successor,
                                           trail, trail_length,
                                           &trail_me_to_probable_succ_len);

  /* Remove the existing successor. */
  remove_existing_finger (current_successor, 0);
  
   /* Generate a new trail id to reach to your new successor. */
  GNUNET_CRYPTO_random_block (GNUNET_CRYPTO_QUALITY_STRONG,
                              &trail_id, sizeof (trail_id));
  
  if (trail_me_to_probable_succ_len > 0)
  {
    GDS_ROUTING_add (trail_id, my_identity, trail_me_to_probable_succ[0]);
    GNUNET_assert (NULL != 
                  (target_friend =
                      GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                        &trail_me_to_probable_succ[0])));
  }
  else
  {
    GDS_ROUTING_add (trail_id, my_identity, probable_successor);
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                       &probable_successor)));
  }
  
  add_new_finger (probable_successor, trail_me_to_probable_succ, 
                  trail_me_to_probable_succ_len, trail_id, 0);
  
  GDS_NEIGHBOURS_send_notify_new_successor (my_identity, probable_successor,
                                            trail_me_to_probable_succ,
                                            trail_me_to_probable_succ_len,
                                            trail_id,
                                            target_friend);
  return;
}


/*
 * Core handle for p2p verify successor 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)
{
  const struct PeerVerifySuccessorResultMessage *vsrm;
  enum GDS_ROUTING_trail_direction trail_direction;
  struct GNUNET_PeerIdentity querying_peer;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_PeerIdentity *next_hop;
  struct FriendInfo *target_friend;
  struct GNUNET_PeerIdentity probable_successor;
  struct GNUNET_PeerIdentity current_successor;
  const struct GNUNET_PeerIdentity *trail;
  unsigned int trail_length;
  size_t msize;

  msize = ntohs (message->size);
  /* We send a trail to reach from old successor to new successor, if
   * old_successor != new_successor.*/
  if (msize < sizeof (struct PeerVerifySuccessorResultMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
  
  vsrm = (const struct PeerVerifySuccessorResultMessage *) message;
  trail_length = (msize - sizeof (struct PeerVerifySuccessorResultMessage))/
                      sizeof (struct GNUNET_PeerIdentity);
  
  if ((msize - sizeof (struct PeerVerifySuccessorResultMessage)) % 
      sizeof (struct GNUNET_PeerIdentity) != 0)
  {
    GNUNET_break_op (0);
    return GNUNET_OK;      
  }  
  
  trail = (const struct GNUNET_PeerIdentity *) &vsrm[1];
  querying_peer = vsrm->querying_peer;
  trail_direction = ntohl (vsrm->trail_direction);
  trail_id = vsrm->trail_id;
  probable_successor = vsrm->probable_successor;
  current_successor = vsrm->current_successor;

  /* I am the querying_peer. */
  if(0 == (GNUNET_CRYPTO_cmp_peer_identity (&querying_peer, &my_identity)))
  {
    compare_and_update_successor (current_successor,
                                  probable_successor, trail, trail_length);
    return GNUNET_OK;
  }
  
  /*If you are not the querying peer then pass on the message */
  GNUNET_assert (NULL != (next_hop =
                         GDS_ROUTING_get_next_hop (trail_id, trail_direction)));
  GNUNET_assert (NULL != 
                (target_friend = 
                 GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop)));
  GDS_NEIGHBOURS_send_verify_successor_result (querying_peer,
                                               vsrm->current_successor,
                                               probable_successor, trail_id,
                                               trail,
                                               trail_length,
                                               trail_direction, target_friend);
  return GNUNET_OK;
}


/* 
 * Core handle for p2p notify new successor 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)
{
  const struct PeerNotifyNewSuccessorMessage *nsm;
  struct GNUNET_PeerIdentity *trail;
  struct GNUNET_PeerIdentity source;
  struct GNUNET_PeerIdentity new_successor;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_PeerIdentity next_hop;
  struct FriendInfo *target_friend;
  int my_index;
  size_t msize;
  uint32_t trail_length;

  msize = ntohs (message->size);
  
  /* We have the trail to reach from source to new successor. */
  if (msize < sizeof (struct PeerNotifyNewSuccessorMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }

  nsm = (const struct PeerNotifyNewSuccessorMessage *) message;
  trail_length = (msize - sizeof (struct PeerNotifyNewSuccessorMessage))/
                  sizeof (struct GNUNET_PeerIdentity);
  if ((msize - sizeof (struct PeerNotifyNewSuccessorMessage)) % 
      sizeof (struct GNUNET_PeerIdentity) != 0)
  {
    GNUNET_break_op (0);
    return GNUNET_OK;      
  }
  
  trail = (struct GNUNET_PeerIdentity *) &nsm[1];
  source  = nsm->source_peer;
  new_successor = nsm->new_successor;
  trail_id = nsm->trail_id;  

  //FIXME: add a check to make sure peer is correct. 
  
  /* I am the new_successor to source_peer. */
  if ( 0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &new_successor))
  {
    GDS_ROUTING_add (trail_id, *peer, my_identity);
    compare_and_update_predecessor (source, trail, trail_length);
    return GNUNET_OK;
  }
  
  GNUNET_assert(trail_length > 0);
  /* I am part of trail to reach to successor. */
  my_index = search_my_index (trail, trail_length);
  if (-1 == my_index) 
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
 
  if ((trail_length-1) == my_index) 
    next_hop = new_successor;
  else
    next_hop = trail[my_index + 1];
 

  /* Add an entry in routing table for trail from source to its new successor. */
  GNUNET_assert (GNUNET_OK == GDS_ROUTING_add (trail_id, *peer, next_hop));

  GNUNET_assert (NULL != 
                (target_friend = 
                 GNUNET_CONTAINER_multipeermap_get (friend_peermap, &next_hop)));
  GDS_NEIGHBOURS_send_notify_new_successor (source, new_successor, trail,
                                            trail_length,
                                            trail_id, target_friend);
  return GNUNET_OK;
  
}


/**
 * Core handler for P2P trail rejection message
 * @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_rejection (void *cls,
                                      const struct GNUNET_PeerIdentity *peer,
                                      const struct GNUNET_MessageHeader *message)
{
  const struct PeerTrailRejectionMessage *trail_rejection;
  unsigned int trail_length;
  const struct GNUNET_PeerIdentity *trail_peer_list;
  struct FriendInfo *target_friend;
  struct GNUNET_TIME_Relative congestion_timeout;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_PeerIdentity next_peer;
  struct GNUNET_PeerIdentity source;
  struct GNUNET_PeerIdentity *next_hop;
  uint64_t ultimate_destination_finger_value;
  unsigned int is_predecessor;
  size_t msize;

  msize = ntohs (message->size);
  /* We are passing the trail setup so far. */
  if (msize < sizeof (struct PeerTrailRejectionMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_YES;
  }
  
  trail_rejection = (const struct PeerTrailRejectionMessage *) message;
  trail_length = (msize - sizeof (struct PeerTrailRejectionMessage))/
                  sizeof (struct GNUNET_PeerIdentity);
  if ((msize - sizeof (struct PeerTrailRejectionMessage)) % 
      sizeof (struct GNUNET_PeerIdentity) != 0)
  {
    GNUNET_break_op (0);
    return GNUNET_OK;      
  }           

  trail_peer_list = (const struct GNUNET_PeerIdentity *)&trail_rejection[1];
  is_predecessor = ntohl (trail_rejection->is_predecessor);
  congestion_timeout = trail_rejection->congestion_time;
  source = trail_rejection->source_peer;
  trail_id = trail_rejection->trail_id;
  ultimate_destination_finger_value = 
          GNUNET_ntohll (trail_rejection->ultimate_destination_finger_value);

  /* First set the congestion time of the friend that sent you this message. */
  GNUNET_assert (NULL != 
                 (target_friend = 
                  GNUNET_CONTAINER_multipeermap_get (friend_peermap, peer)));
  target_friend->congestion_timestamp = 
          GNUNET_TIME_absolute_add (GNUNET_TIME_absolute_get(),
                                    congestion_timeout);

  /* I am the source peer which wants to setup the trail. Do nothing. 
   * send_find_finger_trail_task is scheduled periodically.*/
  if(0 == (GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &source)))
    return GNUNET_OK;

  /* If I am congested then pass this message to peer before me in trail. */
  if(GNUNET_YES == GDS_ROUTING_threshold_reached())
  {
    struct GNUNET_PeerIdentity *new_trail;
    unsigned int new_trail_length;
    
    /* Remove yourself from the trail setup so far. */
    if (trail_length == 1)
    {
      new_trail = NULL;
      new_trail_length = 0;
      next_hop = &source;
    }
    else
    {
      memcpy (&next_hop , &trail_peer_list[trail_length - 2], 
              sizeof (struct GNUNET_PeerIdentity));
      
      /* Remove myself from the trail. */
      new_trail_length = trail_length -1;
      new_trail = GNUNET_malloc (new_trail_length * sizeof (struct GNUNET_PeerIdentity));
      memcpy (new_trail, trail_peer_list, new_trail_length * sizeof (struct GNUNET_PeerIdentity));
    }

    GNUNET_assert (NULL != 
                  (target_friend = 
                    GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop)));
    GDS_NEIGHBOURS_send_trail_rejection (source,
                                         ultimate_destination_finger_value,
                                         my_identity, is_predecessor,
                                         new_trail,new_trail_length,trail_id,
                                         target_friend, CONGESTION_TIMEOUT);
    GNUNET_free (new_trail);
    return GNUNET_OK;
  }
  
  struct Closest_Peer successor;
  successor = find_successor (ultimate_destination_finger_value, is_predecessor);
  
  /* Am I the final destination? */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&successor.best_known_destination, 
                                             &my_identity)))
  {
    if (0 == trail_length)
      next_peer = source;
    else
      next_peer = trail_peer_list[trail_length-1];
    
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, &next_peer)));
    
    GDS_NEIGHBOURS_send_trail_setup_result (source,
                                            my_identity,
                                            target_friend, trail_length,
                                            trail_peer_list,
                                            is_predecessor, 
                                            ultimate_destination_finger_value,
                                            trail_id);
  }
  else
  {
    struct GNUNET_PeerIdentity peer_list[trail_length + 1];

    memcpy (peer_list, trail_peer_list, trail_length * sizeof (struct GNUNET_PeerIdentity));
    peer_list[trail_length] = my_identity;

    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop)));

    GDS_NEIGHBOURS_send_trail_setup (source,
                                     ultimate_destination_finger_value,
                                     successor.best_known_destination,
                                     target_friend, trail_length + 1, peer_list,
                                     is_predecessor, trail_id,
                                     successor.trail_id);
  }
  return GNUNET_OK;
}


/*
 * Core handle for p2p trail tear compression 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_compression (void *cls, const struct GNUNET_PeerIdentity *peer,
                                  const struct GNUNET_MessageHeader *message)
{
  const struct PeerTrailCompressionMessage *trail_compression;
  struct GNUNET_PeerIdentity *next_hop;
  struct FriendInfo *target_friend;
  struct GNUNET_HashCode trail_id;
  size_t msize;

  msize = ntohs (message->size);

  if (msize != sizeof (struct PeerTrailCompressionMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_OK;
  }
  
  trail_compression = (const struct PeerTrailCompressionMessage *) message;
  trail_id = trail_compression->trail_id;
 
  /* Am I the new first friend to reach to finger of this trail. */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&trail_compression->new_first_friend,
                                             &my_identity)))
  {
    GNUNET_assert (NULL != 
                  (GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                      &trail_compression->source_peer)));
    
    /* Update your prev hop to source of this message. */
    GNUNET_assert (GNUNET_SYSERR != 
                  (GDS_ROUTING_update_trail_prev_hop (trail_id,
                                                      trail_compression->source_peer)));
    return GNUNET_OK;
  }
  
  /* Pass the message to next hop to finally reach to new_first_friend. */
  next_hop = GDS_ROUTING_get_next_hop (trail_id, GDS_ROUTING_SRC_TO_DEST);
  
  if (NULL == next_hop) 
  {
    GNUNET_break (0); 
    return GNUNET_OK;
  }
  
  GNUNET_assert (NULL != 
                (target_friend = 
                 GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop)));
  
  GDS_ROUTING_remove_trail (trail_id);
  
  GDS_NEIGHBOURS_send_trail_compression (trail_compression->source_peer,
                                         trail_id,
                                         trail_compression->new_first_friend,
                                         target_friend);
  return GNUNET_OK;
}


/**
 * Core handler for trail teardown message.
 * @param cls closure
 * @param message message
 * @param peer sender of this messsage. 
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
 */
static int
handle_dht_p2p_trail_teardown (void *cls, const struct GNUNET_PeerIdentity *peer,
                               const struct GNUNET_MessageHeader *message)
{
  const struct PeerTrailTearDownMessage *trail_teardown;
  enum GDS_ROUTING_trail_direction trail_direction;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_PeerIdentity *next_hop;
  size_t msize;
  
  msize = ntohs (message->size);
  
  /* Here we pass only the trail id. */
  if (msize != sizeof (struct PeerTrailTearDownMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_OK;
  }
  
  trail_teardown = (const struct PeerTrailTearDownMessage *) message;
  trail_direction = ntohl (trail_teardown->trail_direction);
  trail_id = trail_teardown->trail_id;
  
  /* Check if peer is the real peer from which we should get this message.*/
  /* Get the prev_hop for this trail by getting the next hop in opposite direction. */
#if 0
  GNUNET_assert (NULL != (prev_hop = 
                 GDS_ROUTING_get_next_hop (trail_id, !trail_direction)));
  if (0 != GNUNET_CRYPTO_cmp_peer_identity (prev_hop, peer))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
#endif
  
  next_hop = GDS_ROUTING_get_next_hop (trail_id, trail_direction);
  
  if (NULL == next_hop)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
 
  /* I am the next hop, which means I am the final destination. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (next_hop, &my_identity))
  {
    GNUNET_assert (GNUNET_YES == GDS_ROUTING_remove_trail (trail_id));
    return GNUNET_OK;
  }
  else 
  {
    /* If not final destination, then send a trail teardown message to next hop.*/
    GNUNET_assert (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop));
    GNUNET_assert (GNUNET_YES == GDS_ROUTING_remove_trail (trail_id));
    GDS_NEIGHBOURS_send_trail_teardown (trail_id, trail_direction, *next_hop);
  }
  
  return GNUNET_OK;
}


/**
 * Core handle for p2p add trail message. 
 * @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_add_trail (void *cls, const struct GNUNET_PeerIdentity *peer,
                          const struct GNUNET_MessageHeader *message)
{
  const struct PeerAddTrailMessage *add_trail;
  const struct GNUNET_PeerIdentity *trail;
  struct GNUNET_HashCode trail_id;
  struct GNUNET_PeerIdentity destination_peer;
  struct GNUNET_PeerIdentity source_peer;
  struct GNUNET_PeerIdentity next_hop;
  unsigned int trail_length;
  unsigned int my_index;
  size_t msize;

  msize = ntohs (message->size);
  /* In this message we pass the whole trail from source to destination as we
   * are adding that trail.*/
  if (msize < sizeof (struct PeerAddTrailMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_OK;
  }

  add_trail = (const struct PeerAddTrailMessage *) message;
  trail_length = (msize - sizeof (struct PeerAddTrailMessage))/
                  sizeof (struct GNUNET_PeerIdentity);
  if ((msize - sizeof (struct PeerAddTrailMessage)) % 
      sizeof (struct GNUNET_PeerIdentity) != 0)
  {
    GNUNET_break_op (0);
    return GNUNET_OK;      
  }           

  trail = (const struct GNUNET_PeerIdentity *)&add_trail[1];
  destination_peer = add_trail->destination_peer;
  source_peer = add_trail->source_peer;
  trail_id = add_trail->trail_id;

  //FIXME: add a check that sender peer is not malicious. Make it a generic
  // function so that it can be used in all other functions where we need the
  // same functionality.
  
  /* I am not the destination of the trail. */
  if (0 != GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &destination_peer))
  {
    struct FriendInfo *target_friend;
   
    /* Get my location in the trail. */
    my_index = search_my_index (trail, trail_length);
    if (-1 == my_index)
    {
      
      GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }
    
    
    if ((trail_length - 1) == my_index)
    { 
      next_hop = destination_peer;
    }
    else
    {
      next_hop = trail[my_index + 1];
    }
    
    /* Add in your routing table. */
    GNUNET_assert (GNUNET_OK == GDS_ROUTING_add (trail_id, next_hop, *peer));
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, &next_hop)));
    GDS_NEIGHBOURS_send_add_trail (source_peer, destination_peer, trail_id,
                                   trail, trail_length, target_friend);
    return GNUNET_OK;
  }
  /* I am the destination. Add an entry in routing table. */
  GNUNET_assert (GNUNET_OK == GDS_ROUTING_add (trail_id, *peer, my_identity));
  return GNUNET_OK;
}


/**
 * Free the finger trail in which the first friend to reach to a finger is 
 * disconnected_friend. Also remove entry from routing table for that particular
 * trail id. 
 * @param disconnected_friend PeerIdentity of friend which got disconnected
 * @param remove_finger Finger whose trail we need to check if it has 
 *                      disconnected_friend as the first hop.
 * @return Total number of trails in which disconnected_friend was the first
 *         hop.
 */
static int
remove_matching_trails (const struct GNUNET_PeerIdentity *disconnected_friend,
                        struct FingerInfo *remove_finger)
{
  unsigned int matching_trails_count;
  int i;
  
  /* Number of trails with disconnected_friend as the first hop in the trail
   * to reach from me to remove_finger, NOT including endpoints. */
  matching_trails_count = 0;
  
  /* Iterate over all the trails of finger. */
  for (i = 0; i < remove_finger->trails_count; i++)
  {
    struct Trail *trail;
    trail = &remove_finger->trail_list[i];
    
    /* This assertion is ensure that there are no gaps in the trail list. 
     REMOVE IT AFTERWARDS. */
    GNUNET_assert (GNUNET_YES == trail->is_present);
    
    /* First friend to reach to finger is disconnected_peer. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&trail->trail_head->peer,
                                              disconnected_friend))
    {
      struct GNUNET_PeerIdentity *next_hop;
      struct FriendInfo *remove_friend;
      
      GNUNET_assert (NULL != 
                    (remove_friend = 
                     GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                        disconnected_friend)));
      /* FIXME: removing no but check it. */
      //remove_friend->trails_count--;
      next_hop = GDS_ROUTING_get_next_hop (trail->trail_id, 
                                           GDS_ROUTING_SRC_TO_DEST);
      
      /* Here it may happen that as all the peers got disconnected, the entry in
       routing table for that particular trail has been removed, because the
       previously disconnected peer was either a next hop or prev hop of that
       peer. */
      if (NULL == next_hop)
        continue;
      
      GNUNET_assert (0 == (GNUNET_CRYPTO_cmp_peer_identity (disconnected_friend,
                                                            next_hop)));
      matching_trails_count++;
      GNUNET_assert (GNUNET_YES == GDS_ROUTING_remove_trail (trail->trail_id));
      
      free_trail (trail);
      trail->is_present = GNUNET_NO;
    }
  }  
  return matching_trails_count;
}


/**
 * Iterate over finger_table entries. 
 * 0. Ignore finger which is my_identity or if no valid entry present at 
 *    that finger index. 
 * 1. If disconnected_friend is a finger, then remove the routing entry from
      your own table. Free the trail. 
 * 2. Check if disconnected_friend is the first friend in the trail to reach to a finger.
 *   2.1 Remove all the trails and entry from routing table in which disconnected 
 *       friend is the first friend in the trail. If disconnected_friend is the 
 *       first friend in all the trails to reach finger, then remove the finger. 
 * @param disconnected_friend Peer identity of friend which got disconnected.
 */
static void
remove_matching_fingers (const struct GNUNET_PeerIdentity *disconnected_peer)
{
  struct FingerInfo *remove_finger;
  struct FriendInfo *remove_friend;
  int removed_trails_count;
  int i;
  
  /* Iterate over finger table entries. */
  for (i = 0; i < MAX_FINGERS; i++)
  {
    remove_finger = &finger_table[i];

    /* No finger stored at this trail index. */
    if (GNUNET_NO == remove_finger->is_present)
      continue;
    
    /* I am my own finger, then ignore this finger. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&remove_finger->finger_identity,
                                              &my_identity))
      continue;
    
    /* Is disconnected_peer a finger? */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (disconnected_peer,
                                              &remove_finger->finger_identity))
    {
      struct GNUNET_PeerIdentity *next_hop;
      struct GNUNET_HashCode trail_id;
      
      
      GNUNET_assert (GNUNET_YES == (remove_finger->trail_list[0].is_present));
      trail_id = remove_finger->trail_list[0].trail_id;
     
      if(NULL != 
              (next_hop = 
               GDS_ROUTING_get_next_hop (trail_id, GDS_ROUTING_SRC_TO_DEST)))
      {
        GNUNET_assert (0 ==
                      (GNUNET_CRYPTO_cmp_peer_identity (next_hop,
                                                        &remove_finger->finger_identity)));
        GNUNET_assert (GNUNET_YES == GDS_ROUTING_remove_trail (trail_id));
        GNUNET_assert (NULL !=
                       (remove_friend = 
                        GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                           disconnected_peer)));
      }
      
      remove_finger->trail_list[0].is_present = GNUNET_NO;
      //GNUNET_assert (0 != remove_friend->trails_count);
      //remove_friend->trails_count--; //FIXME; CHECK WHY IT FAILS AND THEN UNCOMMENT.
      remove_finger->is_present = GNUNET_NO;
      memset ((void *)&finger_table[i], 0, sizeof (finger_table[i]));
      continue;
    }
    
    /* If finger is a friend but not disconnected_friend, then continue. */
    if (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                   &remove_finger->finger_identity))
      continue;
    
    /* Iterate over the list of trails to reach remove_finger. Check if 
     * disconnected_friend is the first friend in any of the trail. */
    removed_trails_count = remove_matching_trails (disconnected_peer, 
                                                   remove_finger);
    remove_finger->trails_count = 
            remove_finger->trails_count - removed_trails_count;
    /* All the finger trails had disconnected_friend as the first friend,
     * so free the finger. */
    if (remove_finger->trails_count == 0)
    {
      remove_finger->is_present = GNUNET_NO;
      memset ((void *)&finger_table[i], 0, sizeof (finger_table[i]));
    }      
  }
}


/**
 * 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)
{
  struct FriendInfo *remove_friend;

  /* If disconnected to own identity, then return. */
  if (0 == memcmp (&my_identity, peer, sizeof (struct GNUNET_PeerIdentity)))
    return;

  GNUNET_assert (NULL != (remove_friend =
                          GNUNET_CONTAINER_multipeermap_get (friend_peermap, peer)));

  /* Remove fingers with peer as first friend or if peer is a finger. */
  remove_matching_fingers (peer);
  
  /* Remove any trail from routing table of which peer is a part of. This function
   * internally sends a trail teardown message in the direction of which
   * disconnected peer is not part of. */
  GNUNET_assert (GNUNET_SYSERR != GDS_ROUTING_remove_trail_by_peer (peer));
  
  //GNUNET_assert (0 == remove_friend->trails_count); //FIXME; why should this fai.
  
  /* Remove peer from friend_peermap. */
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CONTAINER_multipeermap_remove (friend_peermap,
                                                       peer,
                                                       remove_friend));
  
  if (0 != GNUNET_CONTAINER_multipeermap_size (friend_peermap))
    return;
  
  if (GNUNET_SCHEDULER_NO_TASK != find_finger_trail_task)
  {
      GNUNET_SCHEDULER_cancel (find_finger_trail_task);
      find_finger_trail_task = GNUNET_SCHEDULER_NO_TASK;
  }
  else
    GNUNET_break (0);

}


/**
 * Method called whenever a peer connects.
 *
 * @param cls closure
 * @param peer_identity peer identity this notification is about
 */
static void
handle_core_connect (void *cls, const struct GNUNET_PeerIdentity *peer_identity)
{
  struct FriendInfo *friend;

  /* Check for connect to self message */
  if (0 == memcmp (&my_identity, peer_identity, sizeof (struct GNUNET_PeerIdentity)))
    return;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Connected to %s\n", GNUNET_i2s (peer_identity));

  /* If peer already exists in our friend_peermap, then exit. */
  if (GNUNET_YES == GNUNET_CONTAINER_multipeermap_contains (friend_peermap, 
                                                            peer_identity))
  {
    GNUNET_break (0);
    return;
  }

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

  friend = GNUNET_new (struct FriendInfo);
  friend->id = *peer_identity;

  GNUNET_assert (GNUNET_OK ==
                 GNUNET_CONTAINER_multipeermap_put (friend_peermap,
                                                    peer_identity, friend,
                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));


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


/**
 * 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;
  
  uint64_t my_id64;
  memcpy (&my_id64, &my_identity, sizeof (uint64_t));
  my_id64 = GNUNET_ntohll (my_id64);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "my_indentity = %s, my_id64=%llu\n",GNUNET_i2s(&my_identity),(unsigned long long)my_id64);

}


/**
 * Initialize finger table entries.
 */
static void
finger_table_init ()
{
  unsigned int i;
  unsigned int j;
 
  for(i = 0; i < MAX_FINGERS; i++)
  {
    finger_table[i].is_present = GNUNET_NO;
    for (j = 0; j < MAXIMUM_TRAILS_PER_FINGER; j++)
      finger_table[i].trail_list[j].is_present = GNUNET_NO;
    memset ((void *)&finger_table[i], 0, sizeof (finger_table[i]));
  }
}


/**
 * Initialize neighbours subsystem.
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
 */
int
GDS_NEIGHBOURS_init (void)
{
  static struct GNUNET_CORE_MessageHandler core_handlers[] = {
    {&handle_dht_p2p_put, GNUNET_MESSAGE_TYPE_XDHT_P2P_PUT, 0},
    {&handle_dht_p2p_get, GNUNET_MESSAGE_TYPE_XDHT_P2P_GET, 0},
    {&handle_dht_p2p_get_result, GNUNET_MESSAGE_TYPE_XDHT_P2P_GET_RESULT, 0},
    {&handle_dht_p2p_trail_setup, GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_SETUP, 0},
    {&handle_dht_p2p_trail_setup_result, GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_SETUP_RESULT, 0},
    {&handle_dht_p2p_verify_successor, GNUNET_MESSAGE_TYPE_XDHT_P2P_VERIFY_SUCCESSOR, 0},
    {&handle_dht_p2p_verify_successor_result, GNUNET_MESSAGE_TYPE_XDHT_P2P_VERIFY_SUCCESSOR_RESULT, 0},
    {&handle_dht_p2p_notify_new_successor, GNUNET_MESSAGE_TYPE_XDHT_P2P_NOTIFY_NEW_SUCCESSOR, 0},
    {&handle_dht_p2p_trail_setup_rejection, GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_SETUP_REJECTION, 0},
    {&handle_dht_p2p_trail_compression, GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_COMPRESSION, 
                                        sizeof (struct PeerTrailCompressionMessage)},
    {&handle_dht_p2p_trail_teardown, GNUNET_MESSAGE_TYPE_XDHT_P2P_TRAIL_TEARDOWN, 
                                     sizeof (struct PeerTrailTearDownMessage)},
    {&handle_dht_p2p_add_trail, GNUNET_MESSAGE_TYPE_XDHT_P2P_ADD_TRAIL, 0},
    {NULL, 0, 0}
  };

  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 (NULL == core_api)
    return GNUNET_SYSERR;

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


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

  GNUNET_CORE_disconnect (core_api);
  core_api = NULL;

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

  if (GNUNET_SCHEDULER_NO_TASK != find_finger_trail_task)
  {
    GNUNET_break (0);
    GNUNET_SCHEDULER_cancel (find_finger_trail_task);
    find_finger_trail_task = GNUNET_SCHEDULER_NO_TASK;
  }
  
  if (GNUNET_SCHEDULER_NO_TASK != send_verify_successor_task)
  {
    GNUNET_SCHEDULER_cancel (send_verify_successor_task);
    send_verify_successor_task = GNUNET_SCHEDULER_NO_TASK;
  }
}


/**
 * Get my identity
 *
 * @return my identity
 */
struct GNUNET_PeerIdentity
GDS_NEIGHBOURS_get_my_id (void)
{
  return my_identity;
}

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