Use correct key while doing GET. Wait for all PUT and GET requests to complete.

[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"

/**
 * FIXME: 
 * 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.
 * 2. We will keep an entry in routing table even if its a friend for the moment.
 * Because I am not sure if there is a case where it will not work. 
 * Trail id we can keep but actually there is no trail.
 */


/**
 * 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, 30)

/**
 * 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 = 0,
  GDS_FINGER_TYPE_NON_PREDECESSOR = 1
};

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;
};

/**
 * FIXME: removed first_friend_trails_count, need to write a function
 * to calculate each time we need it. Else, keep a pointer to first
 * friend of in the trail. 
 * 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]; 
};


/**
 * Data structure to keep track of closest peer seen so far in find_successor()
 */
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 NULL.
   */
  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;

/**
 * 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;

/**
 * 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;


/**
 * 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);
}


/**
 * Return friend corresponding to peer.
 * @param peer
 * @return  Friend
 */
struct FriendInfo *
GDS_NEIGHBOURS_get_friend (struct GNUNET_PeerIdentity peer)
{
  struct FriendInfo *friend;
  GNUNET_assert (NULL != (friend = 
          GNUNET_CONTAINER_multipeermap_get (friend_peermap, &peer)));
  return friend;
}


/**
 * 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;
  
  if (NULL == intermediate_trail_id)
    memset (&tsm->intermediate_trail_id, 0, sizeof (tsm->intermediate_trail_id));
  else
    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 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_YES if friend is not congested or have not crossed threshold.
 *         #GNUNET_NO if friend is either congested or have crossed threshold 
 */
static int
is_friend_congested (struct FriendInfo *friend)
{
  if ((friend->trails_count < TRAILS_THROUGH_FRIEND_THRESHOLD) && 
      ((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);
  //value = GNUNET_ntohll (value); //FIXME: Is it correct to do it here?
 
  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;
  
  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;
  
  FPRINTF (stderr,_("\nSUPU************  FINGER_TABLE"));
  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);
    
    
    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

/**
 * 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);

  /* It can never happen that we have a finger (which is not a friend or my identity),
     and we don't have a trail to reach to it. */
  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;
    }
    /* This is the first time we enter the loop. Set finger trail length to
     * trail length of this trail. */
    if (!flag)
    {
      flag = 1;
      finger_trail->trail_length = iterator->trail_length;
      finger_trail->friend = *friend;
      finger_trail->trail_id = &iterator->trail_id;   
      //memcmp (finger_trail->trail_id, &iterator->trail_id, sizeof (struct GNUNET_HashCode));
    }
    else if (finger_trail->trail_length > iterator->trail_length)
    {
      /* Check if the trail length of this trail is least seen so far. If yes then
         set finger_trail to this trail.*/
      finger_trail->friend = *friend;
      finger_trail->trail_id = &iterator->trail_id;
      //memcmp (finger_trail->trail_id, &iterator->trail_id, sizeof (struct GNUNET_HashCode));
      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];
    
    /* No valid entry at this index, go to next element.*/
    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;
    }
    /* We have a finger which not a friend, not my identity */
    /* 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;
    }
    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;
  
  /* If friend is either congested or has crossed threshold, then don't consider
   * this friend.*/
  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 current_successor
 */
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;

  current_closest_peer = GNUNET_new (struct Closest_Peer);
  //memset (&current_closest_peer->trail_id, 0, sizeof (current_closest_peer->trail_id)); 
  current_closest_peer->trail_id = NULL;
  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;
}


/**
 * Find the successor for destination_finger_value among my_identity, all my
 * friend and all 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 local_best_known_destination[out] Updated to my_identity if I am the 
 *                                     final destination. Updated to friend 
 *                                     identity in case a friend is successor,
 *                                     updated to finger in case finger is the 
 *                                     destination.
 * @param new_intermediate_trail_id[out] In case a finger is the
 *                                       @a local_best_known_destination,
 *                                       then it is the trail to reach it. Else
 *                                       default set to 0.
 * @param is_predecessor Are we looking for predecessor or finger?
 * @return Next hop to reach to local_best_known_destination. In case my_identity
 *         or a friend is a local_best_known_destination, then 
 *         next_hop = local_best_known_destination. Else
 *         next_hop is the first friend to reach to finger (local_best_known_destination)
 */
static struct GNUNET_PeerIdentity *
find_successor (uint64_t destination_finger_value,
                struct GNUNET_PeerIdentity *local_best_known_destination,
                struct GNUNET_HashCode *new_intermediate_trail_id,
                unsigned int is_predecessor)
{
  struct Closest_Peer *current_closest_peer;
  struct GNUNET_PeerIdentity *next_hop;

   /* 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);
  *local_best_known_destination = current_closest_peer->best_known_destination;
  if (current_closest_peer->trail_id != NULL)
  {
    /* FIXME I was assigning values but if address is NULL, then how do we assing.  */
    memcpy (new_intermediate_trail_id,current_closest_peer->trail_id,sizeof (struct GNUNET_HashCode));
  }

  next_hop = GNUNET_new (struct GNUNET_PeerIdentity);
  *next_hop = current_closest_peer->next_hop;
  return next_hop;
}





/**
 * 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 local_best_known_dest;
  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 GNUNET_PeerIdentity *next_hop;
   
    memcpy (&key_value, key, sizeof (uint64_t));  
    key_value = GNUNET_ntohll (key_value);
    
    next_hop = find_successor (key_value, &local_best_known_dest, 
                               intermediate_trail_id, GDS_FINGER_TYPE_NON_PREDECESSOR);
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&local_best_known_dest, &my_identity)) 
    {
      /* I am the destination but we have already done datacache_put in client file.  */
      return;
    }
    else
      GNUNET_assert (NULL != 
                    (target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop)));  
    GNUNET_free (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);
  if (NULL == best_known_dest)
    ppm->best_known_destination = local_best_known_dest;
  else
    ppm->best_known_destination = *best_known_dest;
  ppm->key = *key;
  if (NULL == intermediate_trail_id)
    memset (&ppm->intermediate_trail_id, 0, sizeof (ppm->intermediate_trail_id));
  else
    ppm->intermediate_trail_id = *intermediate_trail_id;
  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,
                         const 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 local_best_known_dest;
  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;
  }
  //test_friend_peermap_print();
  //test_finger_table_print();
  
  /* This is the first time we got request from our own client file. */
  if (NULL == target_peer)
  {
    struct GNUNET_PeerIdentity *next_hop;
    uint64_t key_value;
    
    memcpy (&key_value, key, sizeof (uint64_t)); 
    key_value = GNUNET_ntohll (key_value);
    
    /* Find the next destination to forward the packet. */
    next_hop = find_successor (key_value, &local_best_known_dest,
                               intermediate_trail_id, GDS_FINGER_TYPE_NON_PREDECESSOR);

    /* I am the destination. I have the data. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity,
                                              &local_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, next_hop)));
    }
    GNUNET_free (next_hop);
  }
  else
  {
    local_best_known_dest = *best_known_dest;
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, target_peer))); 
  }

  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 = local_best_known_dest;
  pgm->key = *key;
  
  if (NULL == intermediate_trail_id)
    memset ((void *)&pgm->intermediate_trail_id, 0, sizeof (pgm->intermediate_trail_id));
  else
    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 friends_peer map
 * @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[i] = 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
    return (my_id64 + (unsigned long) pow (2, finger_index));
}


/*
 * Choose a random friend. Start looking for the trail to reach to
 * finger identity corresponding to current_search_finger_index 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;
  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));
  GDS_NEIGHBOURS_send_trail_setup (my_identity, finger_id_value,
                                   target_friend->id, target_friend, 0, NULL,
                                   is_predecessor, trail_id, NULL);
}


/**
 * 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));
  //GDS_ROUTING_test_print();
  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));
  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;
  
  /* If I am my own finger identity, then we set trail_length = 0.
   Note: Here we don't send trail compression message, as no peer in its
   trail added an entry in its routing table.*/
  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])));
      
      /* Before you send a trail compression, get the routing entry
       from you routing table. update the fields in routing table
       to update your next hop to finger identity. */
      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])));
      GNUNET_assert (NULL != 
                    (GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                        &trail[i])));
      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;
      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;
}


/**
 * Send verify successor message to your current successor over the shortest
 * trail. 
 * @param successor Current successor.
 */
static void
send_verify_successor_message (struct FingerInfo *successor)
{
  /*
   * FIXME: should we send a verify successor message across all the trails
   * in case we send through all friends. It complicates the logic, don't
   * do it at the moment. Write it as optimization and do it later. 
   * 1. Here we can have 3 types of fingers
   * --> my own identity
   *     Assumption that the calling function will not send request for
   *     such successor. Move the logic here. 
   * --> friend is a finger
   *     Need to verify if we keep the trails count for a friend. In case of
   *     friend there is no trail to reach to that friend, so
   *     1. no entry in routing table
   *     2. no trail id
   *     3. no trails count
   *     4. but do we increment the count of trails through the friend? 
   *        Trails count is used only to keep a limit on number of trails
   *        that a friend should be part of. No need to increment the trails
   *        count for a friend which is a finegr also. so, if finger = friend
   *        then don't increment the trails count. But if the same friend 
   *        is the first friend to reach to some other finger then increment
   *        the trails count. Not sure if this design is correct need to verify
   *        again. 
   * --> real finger
   */
  struct FriendInfo *target_friend;
  struct GNUNET_HashCode trail_id;
  int i;
  struct Trail *trail;
  struct Trail_Element *element;
  unsigned int trail_length;
  unsigned int j = 0;
      
  i = 0;
  trail = &successor->trail_list[i];
    
  /* 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 I am not my own successor, then send a verify successor message. */
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &finger_identity))
    {
      send_verify_successor_message (successor);
    }
    return;
  }
  
  current_search_finger_index = current_search_finger_index - 1;
  return;
}


/**
 * 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;
  int 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 = (log10 (diff))/(log10 (2));
  }
  
  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;
}


/**
 * FIXME: Check for memory leaks.
 * 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;
  }
 //test_finger_table_print();
 //s test_friend_peermap_print();
  /* If the new entry for any finger table index other than successor or predecessor
   * is same as successor then don't add it in finger table,
   * reset the current search finger index and exit. */
  if ((0 != finger_table_index) && 
      (PREDECESSOR_FINGER_ID != finger_table_index) &&
      (finger_table_index == current_search_finger_index)) //FIXME; why do I check this cond?
  {
    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_HashCode test_key;
  enum GNUNET_DHT_RouteOption options;
  struct GNUNET_PeerIdentity best_known_dest;
  struct GNUNET_HashCode intermediate_trail_id;
  struct GNUNET_PeerIdentity *next_hop;
  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_YES;
  }
  
  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_YES;
  }
  
  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_YES;
      }
    break;
    case GNUNET_NO:
      GNUNET_break_op (0);
      return GNUNET_YES;
    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);
  }
  else
  {
    key_value = GNUNET_ntohll (key_value);
    next_hop = find_successor (key_value, &best_known_dest, 
                               &intermediate_trail_id, GDS_FINGER_TYPE_NON_PREDECESSOR); 
  }
  
  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;
  }
  
  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);
  
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &best_known_dest)) /* I am the final destination */
  {
    GDS_DATACACHE_handle_put (GNUNET_TIME_absolute_ntoh (put->expiration_time),
                              &(put->key),putlen, pp, ntohl (put->block_type), 
                              payload_size, payload);
    GNUNET_free_non_null (next_hop);
    return GNUNET_YES;
  }
  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_YES;
  }
  return GNUNET_SYSERR;
}


/**
 * 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);
  }
  else
  {
    /* Get the next hop to pass the message to. */
    next_hop = find_successor (key_value, &best_known_dest, 
                               &intermediate_trail_id, GDS_FINGER_TYPE_NON_PREDECESSOR);  
  }
  
  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;
  }
  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;
    /* FIXME: here it may happen that we find our identity closest to key, but
     we don't have the data. then in that case, we should forward the packet
     to the next closest peer. */
    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);
    
    return GNUNET_YES;
  }
  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); 
    GNUNET_free (next_hop);
  }
  return GNUNET_SYSERR;
}


/**
 * 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;
}


/**
 * Get the best known next destination (local_dest) among your fingers, friends 
 * and my identity. In case I was part of trail to reach to some other destination
 * (current_dest), then compare current_dest and local_dest, and choose the
 * closest peer. 
 * @param final_dest_finger_value Peer closest to this value will be
 *                                @a local_best_known_dest
 * @param local_best_known_dest[out] Updated to peer identity which is closest to
 *                                   @a final_dest_finger_value.
 * @param new_intermediate_trail_id In case @a local_best_known_dest is a finger,
 *                                  then the trail id to reach to the finger
 * @param is_predecessor Is source peer trying to setup trail to its predecessor
 *                       or not.
 * @param current_dest Peer which should get this message ultimately according
 *                     to the peer which sent me this message. It could be me
 *                     or some other peer. In case it is not me, then I am a part
 *                     of trail to reach to that peer.
 * @return 
 */
static struct GNUNET_PeerIdentity *
get_local_best_known_next_hop (uint64_t final_dest_finger_value,
                               struct GNUNET_PeerIdentity *local_best_known_dest,
                               struct GNUNET_HashCode *new_intermediate_trail_id,
                               struct GNUNET_HashCode intermediate_trail_id,
                               unsigned int is_predecessor,
                               struct GNUNET_PeerIdentity *current_dest)
{
  struct GNUNET_PeerIdentity *next_hop_to_local_best_known_dest;
  
 /* Choose a local best known hop among your fingers, friends and you.  */
  next_hop_to_local_best_known_dest = find_successor (final_dest_finger_value,
                                                      local_best_known_dest,
                                                      new_intermediate_trail_id,
                                                      is_predecessor);
  
  /* Are we just a part of a trail towards a finger (current_destination)? */
  if (0 != (GNUNET_CRYPTO_cmp_peer_identity (&my_identity, current_dest)))
  {
    struct GNUNET_PeerIdentity *closest_peer;
    
    /* Select best successor among one found locally and current_destination 
     * that we got from network.*/
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (local_best_known_dest, current_dest))
    {  
     // GDS_ROUTING_test_print();
      closest_peer = select_closest_peer (local_best_known_dest,
                                          current_dest,
                                          final_dest_finger_value,
                                          is_predecessor);
    
      /* 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);
        /* FIXME: Here we found next_hop NULL from routing table, but we still 
         * have a next_hop from find_successor should we not break and choose that
         * next_hop. */
        if (NULL == next_hop) 
        {
          GNUNET_break_op (0);
          return NULL;
        }
        next_hop_to_local_best_known_dest = next_hop;
        local_best_known_dest =  current_dest;
        *new_intermediate_trail_id = intermediate_trail_id;
      }
    }
  }
 
  GNUNET_assert (NULL != next_hop_to_local_best_known_dest);
  return next_hop_to_local_best_known_dest;
}


/* 
 * 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 *local_best_known_dest; 
  struct GNUNET_PeerIdentity current_dest;
  struct GNUNET_PeerIdentity *next_hop_towards_local_best_known_dest;
  struct FriendInfo *target_friend;
  struct GNUNET_PeerIdentity source;
  uint64_t final_dest_finger_val;
  struct GNUNET_HashCode *new_intermediate_trail_id;
  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_YES;
  }

  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;
  
  /* Is my routing table full?  */
  if (GNUNET_YES == GDS_ROUTING_threshold_reached())
  {
    /* As my routing table is full, I can no longer handle any more trail
     * through me */
    
    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;
  }

  new_intermediate_trail_id = GNUNET_new (struct GNUNET_HashCode);
  local_best_known_dest = GNUNET_new (struct GNUNET_PeerIdentity);
  
  /* Get the next hop to forward the trail setup request. */
  next_hop_towards_local_best_known_dest = 
          get_local_best_known_next_hop (final_dest_finger_val, 
                                         local_best_known_dest,
                                         new_intermediate_trail_id,
                                         intermediate_trail_id,
                                         is_predecessor,
                                         &current_dest);
 
  GNUNET_assert (NULL != local_best_known_dest);
  GNUNET_assert (NULL != next_hop_towards_local_best_known_dest);
  
  /* Am I the final destination? */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (local_best_known_dest,
                                             &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);
    }
    
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap, peer)));
    GDS_NEIGHBOURS_send_trail_setup_result (source,
                                            my_identity,
                                            target_friend, trail_length,
                                            trail_peer_list,
                                            final_dest_finger_val,
                                            is_predecessor, trail_id);
  }
  else
  {
    /* 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;
    GNUNET_assert (NULL != 
                  (target_friend = 
                   GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                      next_hop_towards_local_best_known_dest)));
    /* FIXME; CHECK IF INTERMEDIATE TRAIL ID is 0 thne pas null. */
    /* URGENT TODO. */
    GDS_NEIGHBOURS_send_trail_setup (source,
                                     final_dest_finger_val,
                                     *local_best_known_dest,
                                     target_friend, trail_length + 1, peer_list,
                                     is_predecessor, trail_id,
                                     new_intermediate_trail_id);
  }
  GNUNET_free (local_best_known_dest);
  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 = htonl (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);
    }
    
    /* FIXME: Remove this assert later. */
    GNUNET_assert (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                              peer));
    finger_table_add (finger_identity, trail_peer_list,
                      trail_length, ulitmate_destination_finger_value,
                      is_predecessor, 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;
  }
  
  /* FIXME: CHECK IF YOU ARE PRESENT MORE THAN ONCE IN THE TRAIL, IF YES
   THEN REMOVE ALL THE ENTRIES AND CHOOSE THE PEER THERE.*/

  if (my_index == 0)
    next_hop = trail_result->querying_peer;
  else
    next_hop = trail_peer_list[my_index - 1];

  /* If the querying_peer is its own finger, then don't add an entry in routing
   * table as querying peer will discard the trail. */
  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--;
  }
  return inverted_trail;
}


/**
 * Return the shortest trail to reach from me to my_predecessor. 
 * @param my_predecessor my current predecessor.
 * @param current_trail Trail from source to me.
 * @param current_trail_length Total number of peers in @a current_trail
 * @param trail_length [out] Total number of peers in selected trail.
 * @return Updated trail from source peer to my_predecessor.
 */
static struct GNUNET_PeerIdentity *
trail_source_to_my_predecessor (const struct GNUNET_PeerIdentity *current_trail,
                                unsigned int current_trail_length,
                                unsigned int *trail_length)
{
  struct GNUNET_PeerIdentity *trail_me_to_predecessor;
  struct Trail *trail;
  struct Trail_Element *trail_element;
  struct FingerInfo *my_predecessor;
  unsigned int i;
  unsigned int shortest_trail_length = 0;
  unsigned int trail_index = 0;
 
  my_predecessor = &finger_table[PREDECESSOR_FINGER_ID];
  
  GNUNET_assert (GNUNET_YES == my_predecessor->is_present);
  
  //if my_predecessor is a friend then don't send back any trail. as
  // there is no trail. 
  *trail_length = 0;
  
  /* Choose the shortest path from me to my predecessor. */
  for (i = 0; i < my_predecessor->trails_count; i++)
  {
    trail = &my_predecessor->trail_list[i];
    if (trail->trail_length > shortest_trail_length)
      continue;
    shortest_trail_length = trail->trail_length;
    trail_index = i;
  }

  *trail_length = shortest_trail_length;
  trail_me_to_predecessor = GNUNET_malloc (sizeof (struct GNUNET_PeerIdentity)
                                          * (*trail_length));
  
  /* Copy the selected trail and send this trail to calling function. */
  i = 0;
  trail = &my_predecessor->trail_list[trail_index];
  trail_element = trail->trail_head;
  while ( i < shortest_trail_length)
  {
    trail_me_to_predecessor[i] = trail_element->peer;
    i++;
    trail_element = trail_element->next;
  }

  return trail_me_to_predecessor;
}


/**
 * FIXME In case predecessor is a friend then do we add it in routing table.
 * if not then check the logic of trail teardown in case we compress the trail
 * such that friend is finger. then do we remove the entry from end points or
 * not. Ideally we should remove the entries from end point. 
 * 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));
  //test_finger_table_print();
  /* Finger is a friend. */
  if (trail_length == 0)
  {
    trail_to_new_predecessor = NULL;
    /* FIXME: check that you always add trail entry even if your finger is 
     friend. */
    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[trail_length - 1]);
   
    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);
}


/* 3. In case you are successor, then 
   *   3.1 check if you have a predecessor
   *   3.2 if no predecessor, then add the source of this message as your
   *       predecessor. To add, first you should generate a new trail id,
   *       invert the trail, send add trail message across new trail, add
   *       an entry in finger table. Now, destination also have routing
   *       table entry so add in your routing table also.
   *   3.3 If its closer than existing one, then do everything in step 1 and
   *       free existing finger. 
   *   3.3 If its same as the old one, then do nothing.
   *   3.4 if its not same as old one, and between source and old one, old one
   *       is the correct predecessor, then construct a trail from source 
   *       to your old successor. scan the trail to remove duplicate entries.
   * 4. send verify successor result, with trail id of trail from source to
   * me. And also send the new trail from source to reach to its probable
   * predecessor. */
 /*
   * 1. this function is called from both verify and notify.
   * 2. so write in a way that it is used in both.
   */
/**
 * Check if you have a predecessor.
 * 1. if no predecessor, then 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.
 * 2. If there is a predecessor, then compare existing one and finger.
 *    2.1 If finger is correct predecessor, then remove current_predecessor. And 
 *        do everything in step 1 to add finger into finger table.
 *    2.2 If current_predecessor is correct predecessor, the construct a trail from
 *        finger to current_predecessor. 
 * @param finger
 * @param trail
 * @param trail_length
 * @return 
 */
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;
  }
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (&current_predecessor->finger_identity,
                                            &finger))
    return;
  
  //test_finger_table_print();
  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;
}


/* 
 * FIXME: if i have no predecessor and I get a new predecessor but the first
 * friend to reach to that hop is congested then?  
 * 1. check if you are the successor or not.
 * 2. if not then get the next hop from routing table, and pass the message,
 * 3. In case you are successor, then 
 *   3.1 check if you have a predecessor
 *   3.2 if no predecessor, then add the source of this message as your
 *       predecessor. To add, first you should generate a new trail id,
 *       invert the trail, send add trail message across new trail, add
 *       an entry in finger table. Now, destination also have routing
 *       table entry so add in your routing table also.
 *   3.3 If its closer than existing one, then do everything in step 1 and
 *       free existing finger. 
 *   3.3 If its same as the old one, then do nothing.
 *   3.4 if its not same as old one, and between source and old one, old one
 *       is the correct predecessor, then choose the shortest path to reach
 *       from you to your predecessor. Pass this trail to source of this message.
 *       It is the responsibility of source peer to scan the trail to reach to
 *       its new probable successor. 
 * 4. send verify successor result, with trail id of trail from source to
 * me. And also send the  trail from me to reach to my predecessor, if
 * my_predecessor != source. 
 *
 * 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 GNUNET_PeerIdentity *trail_to_predecessor;
  struct FingerInfo *current_predecessor;
  struct FriendInfo *target_friend;
  unsigned int trail_to_predecessor_length;
  size_t msize;
  unsigned int trail_length;
  
  msize = ntohs (message->size);
  
  /* Here we pass trail to reach from source to successor, and in case successor
   * does not have any predecessor, then we will add source as my predecessor.
   * So we pass the trail along with trail id. */
  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];
  
  //FIXME: we can have a check if peer is correct peer which should have
  // sent this message. use same function is_sender_peer_correct
  // but specify direction so that the function can be used in other functions
  //also. 
  
  /* 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)))
  {
    /* if current predecessor is not a friend, we have a trail to reach to it*/
    if (NULL == (GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                    &current_predecessor->finger_identity)))
    {
      trail_to_predecessor = 
              trail_source_to_my_predecessor (trail, 
                                              trail_length, 
                                              &trail_to_predecessor_length);
    }
  }
  else
  {
     trail_to_predecessor = NULL;
     trail_to_predecessor_length = 0;
  }
  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_to_predecessor,
                                               trail_to_predecessor_length,
                                               GDS_ROUTING_DEST_TO_SRC,
                                               target_friend);
  GNUNET_free_non_null (trail_to_predecessor);
  return GNUNET_OK;
}


/**
 * Construct the trail from me to probable successor that goes through current 
 * successor. Scan this trail to check if you can shortcut the trail somehow. 
 * In case we can shortcut the trail, don't send trail compression as we don't 
 * have any entry in routing table.
 * @param current_successor
 * @param probable_successor
 * @param trail_from_curr_to_probable_successor
 * @param trail_from_curr_to_probable_successor_length
 * @param trail_to_new_successor_length
 * @return 
 */
static struct GNUNET_PeerIdentity *
get_trail_to_new_successor (struct FingerInfo *current_successor,
                            struct GNUNET_PeerIdentity probable_successor,
                            const struct GNUNET_PeerIdentity *trail,
                            unsigned int trail_length,
                            unsigned int *trail_to_new_successor_length)
{
  struct GNUNET_PeerIdentity *trail_to_new_successor;
  
   /* If the probable successor is a friend, then we don't need to have a trail
    * to reach to it.*/
  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;
  }
  
  /*
   * FIXME: can we some how use the select_finger_trail here?? 
   * complete this logic. 
   * 1. Choose the shortest trail to reach to current successor.
   * 2. append the trail with the current trail
   * 3. scan the trail for duplicate elements
   * 4. scan the trail for friend
   * 5. get the shortest trail. 
   * 6. send back the trail.
   */
  return NULL;
}


/**
 * Compare probable successor and current successor.
 * If the probable successor is the correct successor, then construct the trail
 * from me to probable successor that goes through current successor. Scan this
 * trail to check if you can shortcut the trail somehow. In case we can short
 * cut the trail, don't send trail compression as we don't have any entry in 
 * routing table.
 * Once you have scanned trail, then add an entry in finger table.
 * Add an entry in routing table (Only if new successor is NOT a friend).
 * @param probable_successor Peer which could be our successor
 * @param trail_from_curr_to_probable_successor Trail from current successor 
 *                                               to probable successor, NOT 
 *                                               including them.
 * @param trail_from_curr_to_probable_successor_length Total number of peers
 *                                               in @a trail_from_curr_to_probable_successor
 */
static void
compare_and_update_successor (struct GNUNET_PeerIdentity probable_successor,
                              const struct GNUNET_PeerIdentity *trail_from_curr_to_probable_successor,
                              unsigned int trail_from_curr_to_probable_successor_length)
{
  struct GNUNET_PeerIdentity *closest_peer;
  struct GNUNET_PeerIdentity *trail_to_new_successor;
  struct GNUNET_HashCode trail_id;
  unsigned int trail_to_new_successor_length;
  uint64_t successor_value;
  struct FingerInfo *current_successor;
  struct FriendInfo *target_friend;
  unsigned int is_predecessor = 0;
  //test_finger_table_print();
  current_successor = &finger_table[0];
  GNUNET_assert (GNUNET_YES == current_successor->is_present);

  /* Compute the 64 bit value of successor identity. We need this as we need to
   * find the closest peer w.r.t this value.*/
  successor_value = compute_finger_identity_value (0);
  closest_peer = select_closest_peer (&current_successor->finger_identity,
                                      &probable_successor,
                                      successor_value, is_predecessor);
  
  /* If the current_successor is the closest one, then exit. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (closest_peer,
                                            &current_successor->finger_identity))
    return;
  
  /* probable successor  is the closest_peer. */
  
  /* Get the trail to reach to your new successor. */
  trail_to_new_successor = get_trail_to_new_successor (current_successor,
                                                       probable_successor,
                                                       trail_from_curr_to_probable_successor,
                                                       trail_from_curr_to_probable_successor_length,
                                                       &trail_to_new_successor_length);
  /* 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));
  add_new_finger (probable_successor, trail_to_new_successor, 
                  trail_to_new_successor_length, trail_id, 0);
  
  /* If probable successor is not a friend, then add an entry in your own
   routing table. */
  if (trail_to_new_successor_length > 0)
  {
    /* FIXME: check that you always add trail entry even if your finger is 
     friend. */
    GDS_ROUTING_add (trail_id, my_identity, trail_to_new_successor[0]);
    GNUNET_assert (NULL != 
                   (target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                       &trail_to_new_successor[0])));
  }
  else
  {
    /* FIXME: check that you always add trail entry even if your finger is 
     friend. */
    GDS_ROUTING_add (trail_id, my_identity, probable_successor);
    GNUNET_assert (NULL != 
                  (target_friend = 
                    GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                       &probable_successor)));
  }
  //test_finger_table_print();
  GDS_NEIGHBOURS_send_notify_new_successor (my_identity, probable_successor,
                                            trail_from_curr_to_probable_successor,
                                            trail_from_curr_to_probable_successor_length,
                                            trail_id,
                                            target_friend);
  return;
}


/*
 * 1. If you are not the querying peer then pass on the message,
 * 2. If you are querying peer, then
 *   2.1 is new successor same as old one
 *     2.1.1 if yes then do noting
 *     2.1.2 if no then you need to notify the new one about your existence,
 *     2.1.2,1 also you need to remove the older successor, remove entry
 *             from finger table, send trail teardown message across all the trail
 *             of older successor. Call notify new successor with new trail id 
 *             and new trail to reach it. 
 * 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;
  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;
 
  //FIXME: add a check to ensure that peer from which you got the message is
  //the correct peer.
  /* I am the querying_peer. */
  if(0 == (GNUNET_CRYPTO_cmp_peer_identity (&querying_peer, &my_identity)))
  {
    compare_and_update_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;
}


/* 
 * Add entry in your routing table if source of the message is not a friend.
 * Irrespective if destination peer accepts source peer as predecessor or not, 
 * we need to add an entry. So, that in next round to verify successor, source 
 * is able to reach to its successor.
 * Check if you are the new successor of this message
 * 1. If yes the call function compare_and_update_successor(). This function
 *    checks if source is real predecessor or not and take action accordingly.
 * 2. If not then find the next hop to find the message from the trail that 
 *    you got from the message and pass on the message.
 * 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 PeerTrailRejectionMessage)) % 
      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;
  }
  
  /* 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 == 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;
  
}


/**
 * 1. Set the congestion timeout for the friend which is congested and sent
 * you this message.
 * 2. Check if you were the source of this message
 *   2.1 If yes then exit. find_finger_trail_task is scheduled periodically.
 *       So, we will eventually send a new request to setup trail to finger.
 * 2. Check if you can handle more trails through you. (Routing table space)
 *   2.1 If not then you are congested. Set your congestion time and pass this
 *       message to peer before you in the trail setup so far. 
 *   2.2 If yes, the call find_successor(). It will give you the next hop to 
 *       pass this message.
 *      2.2.1 If you are the final destination, then send back the trail setup 
 *            result.
 *      2.2.2 If you are not the final dest, then send trail setup message to
 *            next_hop.
 * 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_destination;
  struct GNUNET_HashCode new_intermediate_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;
  }

  /* Look for next_hop to pass the trail setup message */
  next_hop = find_successor (ultimate_destination_finger_value,
                             &next_destination,
                             &new_intermediate_trail_id,
                             is_predecessor);
  
  /* Am I the final destination? */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (next_hop, &my_identity)))
  {
    /* Add an entry in routing table only 
     * 1. If I am not the original source which sent the request for trail setup 
      FIXME: check that you always add trail entry even if your finger is 
     friend. */
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (&source, &my_identity)) 
      GNUNET_assert (GNUNET_YES == GDS_ROUTING_add (trail_id, *peer, 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,
                                     next_destination,
                                     target_friend, trail_length + 1, peer_list,
                                     is_predecessor, trail_id,
                                     &new_intermediate_trail_id);
  }

  GNUNET_free (next_hop);
  return GNUNET_OK;
}


/*
 * If you are the new first friend, then update prev hop to source of this message
 * else get the next hop and pass this message forward to ultimately reach
 * new first_friend.
 * 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);
  /* Here we pass only the trail id. */
  if (msize != sizeof (struct PeerTrailCompressionMessage))
  {
    GNUNET_break_op (0);
    return GNUNET_OK;
  }
  
  trail_compression = (const struct PeerTrailCompressionMessage *) message;
  trail_id = trail_compression->trail_id;
  //FIXME: again check if peer is the correct peer. same logic as 
  //trail teardown make a generic function. 
  
  /* 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. */
  /* FIXME THIS FAILS.*/
  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;
}


/**
 * Remove entry from your own routing table and pass the message to next
 * peer in the trail. 
 * 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. */
  /* FIXME: is using negation of trail direction correct. */
#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;
}


/**
 * Add an entry in your routing table. If you are destination of this message
 * then next_hop in routing table should be your own identity. If you are NOT
 * destination, then get the next hop and forward message to it.
 * 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];
    }
    /* FIXME: check that you always add trail entry even if your finger is 
     friend. */
    /* 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;
  }
  /* FIXME: check that you always add trail entry even if your finger is 
     friend. */
  /* 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;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "my_indentity = %s\n",GNUNET_i2s(&my_identity));
}


/**
 * 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;
  }
}


/**
 * 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 */