xvine:bug fix

[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.
 */


/**
 * FIXME: 
 * 1. check for memory leaks in all the functions, in all the functions
 * you should check that if you malloc a variable you should free it also.
 * 2. make sure you have gnunet_assert for all target friends
 * 3. pay attention to GNUNET_ntohll and endianess
 * 4. In trail setup, check that you are adding entry even if its a friend.
 *    same for trail setup and add_trail.
 * 5. go through whole code
 * 6. make sure make check passes for minimal things i.e. without congestion,
 *    trail threshold, without multiple trails.
 * 7. write test cases for checking trail congestion, trail threshold, multiple
 *    trails.
 * 
 * 8. while going through the code write the comments for malicious peer.
 *    basic - drop packet, ignore message. Not going to check for behaviour 
 *    where a peer changes the value as we handle that case everywhere. s
 */
/**
 * 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_DHT_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_DHT_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. */

};

/**
 * P2P Result message
 */
struct PeerGetResultMessage
{
  /**
   * Type: #GNUNET_MESSAGE_TYPE_DHT_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_DHT_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_DHT_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_DHT_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_DHT_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_DHT_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_DHT_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_DHT_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_DHT_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_DHT_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 vaule. 
   */
  uint64_t destination_finger_value;
  
  /**
   * Is finger value predecessor or any other finge 
   */
  unsigned int is_predecessor;
  
  /**
   * Trail id to reach to peer.
   */
  struct GNUNET_HashCode trail_id;

  /**
   * FIXME: see the usage of this field and write comment. 
   */
  struct GNUNET_PeerIdentity next_hop;

  /**
   * 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;
};

/**
 * FIXME: now I have removed the first_friend_trail_count,
 * Need to update the code to find the count.
 * 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.
 * @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 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_DHT_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 q
 *                        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_DHT_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
 * @param trail_length Total number of peers in trail_peer_list, not including
 *                     @a source_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_DHT_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);
  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_DHT_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;
  }
  
  GNUNET_assert (NULL != (target_friend = 
                GNUNET_CONTAINER_multipeermap_get (friend_peermap, peer)));
  
  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_DHT_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_DHT_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_DHT_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_DHT_P2P_ADD_TRAIL);
  adm->source_peer = source_peer;
  adm->destination_peer = destination_peer;
  adm->trail_id = trail_id;

  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_DHT_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.
 * @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;

  for (i = 0; i < trail_length; i++)
  {
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &trail[i]))
      return i;
  }

  return -1;
}

/**
 * Check if the friend is congested or have reached maximum number of trails
 * it can be part of of. 
 * @param friend Friend to be chechked.
 * @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_YES;
  else
    return GNUNET_NO;
}


/**
 * FIXME: here we should also check if iterator is null or not. It can be NULL
 * only if we insert randomly at locations. But as we are using trails_count
 * as the parameter, it should not happen.
 * 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;

  finger_trail = GNUNET_new (struct Selected_Finger_Trail);
  
  for (i = 0; i < finger->trails_count; i++)
  {
    iterator = &finger->trail_list[i];
    friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                &iterator->trail_head->peer);
    if (GNUNET_YES == is_friend_congested (friend))
      continue;
   
    /* Check if the trail length of this trail is least seen so far. If yes then
     set finger_trail to this trail.*/
    if (finger_trail->trail_length > iterator->trail_length)
    {
      finger_trail->friend = *friend;
      finger_trail->trail_id = iterator->trail_id;
      finger_trail->trail_length = iterator->trail_length;
    }
  }

  /* No trail found. */  
  if (i == finger->trails_count)
    return NULL;
  
  return finger_trail;
}


/**
 * 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?
  // we do it when we get from the network. 
  
  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;
}


/**
 * FIMXE: COMPLETE THE LOGIC.
 * my_id = 0
 * finger = 5
 * key = 3
 * [0,5) → my_id
 * [5,0) → finger
 *
 * 0 <= key < 5, so my_id 0 is the predecessor. 
 * peer1 != peer2 ever.
 * Select closest predecessor 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_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;
}


/* FIXME: select closest peer w.r.t. value. [finger->friend_id, current_successor->id)
     and [current_successor->id, finger->friend_id). Check in which range value lies.
     Also, check for wrap around. But this will give you the immediate predecessor
     For example. if we have 0,1,6 and I am 0 and one of my finger is 6. Then
     for 1, we will have ranges like [0,6) and [6,0) 1 lies in range from [0,6)
     but successor is 6 not 0 as 6 is > than 1. If you are the closest one, 
     then set the values
     in current_successor. Want to write a generic code so that it is used in 
     * finger_table_add also while choosing the closest one among new and existing
     * one. */
/**
 * my_id = 0
 * finger = 5
 * key = 3
 * [0,5) → my_id
 * [5,0) → finger

 * 0 <= key < 5, so key should go to 5. 

 */
/**
 * Select the closest peer among two peers (which should not be same)
 * with respect to value and finger_table_index
 * @param peer1 First peer
 * @param peer2 Second peer
 * @param value Value relative to which we find the closest
 * @param finger_table_index Index in finger map. If equal to PREDECESSOR_FINGER_ID,
 *                         then we use different logic than other
 *                         finger_table_index
 * @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 finger_table_index)
{
  struct GNUNET_PeerIdentity *closest_peer;

  /* FIXME: select closest peer w.r.t. value. [friend_id, current_successor->id)
     and [current_successor->id, friend_id). Check in which range value lies.
     Also, check for wrap around. Set the value of current_successor accordingly.*/
  if (PREDECESSOR_FINGER_ID == finger_table_index)
    closest_peer = select_closest_predecessor (peer1, peer2, value);
  else
    closest_peer = select_closest_finger (peer1, peer2, value);

  return closest_peer;
}


/**
 * FIXME: free every memory allocated using malloc before the function ends
 * i.e. trail.
 * FIXME: better names and more refactoring. 
 * 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 struct Closest_Peer *
compare_finger_and_current_successor (struct Closest_Peer *current_closest_peer)
{
  struct FingerInfo *finger;
  struct FriendInfo *friend;
  struct GNUNET_PeerIdentity *closest_peer;
  int i;
  
  for (i = 0; i < MAX_FINGERS; i++)
  {
    struct Selected_Finger_Trail *finger_trail;
    
    finger = &finger_table[i];
    
    if (GNUNET_NO == finger->is_present)
      continue;

    /* If my identity is same as current closest peer then don't consider me*/
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                              &current_closest_peer->best_known_destination))
      continue;
    
    /* If I am my own finger, then ignore this finger. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                              &my_identity))
      continue;
    
    /* If finger is friend. */
    if (NULL != (friend = GNUNET_CONTAINER_multipeermap_get 
                (friend_peermap, &finger->finger_identity)))
    {
      if (GNUNET_YES == is_friend_congested (friend))
        continue;
      
       /* If not congested then compare it with current_successor. */
      if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                                 &current_closest_peer->best_known_destination))
        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->finger_identity;
      }
      continue;
    }
    
    /* Choose one of the trail to reach to finger. */
    finger_trail = select_finger_trail (finger);
    
    /* In case no trail found, ignore this finger. */
    if (NULL == finger_trail)
      continue;
    
     closest_peer = select_closest_peer (&finger->finger_identity, 
                                         &current_closest_peer->best_known_destination,
                                         current_closest_peer->destination_finger_value,
                                         current_closest_peer->is_predecessor);
     if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger->finger_identity,
                                               closest_peer))
     {
       current_closest_peer->best_known_destination = finger->finger_identity;
       current_closest_peer->next_hop = finger_trail->friend.id;
       current_closest_peer->trail_id = finger_trail->trail_id;
     }
     GNUNET_free (finger_trail);
     continue;
  }
  return current_closest_peer;
}


/**
 * Compare friend entry with current successor. 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 (GNUNET_YES == is_friend_congested (friend))
    return GNUNET_YES;
 
  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);

  /* If friend is 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->destination_finger_value = destination_finger_value;
  current_closest_peer->is_predecessor = is_predecessor;
  current_closest_peer->next_hop = my_identity;
  current_closest_peer->best_known_destination = my_identity;
  
  return current_closest_peer;
}


/**
 * FIXME: first check if the finger == closest_peer then don't do anything. 
 * 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 congested or have crossed the threshold.
 * @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 first friend to reach 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;
  new_intermediate_trail_id = &current_closest_peer->trail_id;
  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));    
    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
      target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop);  
    GNUNET_free (next_hop);
  }
  else
  {
    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_DHT_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));
  
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    get_path_length = 0;
    msize = sizeof (struct PeerPutMessage);
  }
  
  if (msize > GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  /* This is the first time we got request from our own client file. */
  if (NULL == target_peer)
  {
    struct GNUNET_PeerIdentity *next_hop;
    uint64_t key_value;
    
    memcpy (&key_value, key, sizeof (uint64_t)); //FIXME: endianess of key?
    
    /* 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
    {
      target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop);
    }
    GNUNET_free (next_hop);
  }
  else
  {
    local_best_known_dest = *best_known_dest;
    target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, target_peer); 
  }
  
  pending = GNUNET_malloc (sizeof (struct P2PPendingMessage) + msize);
  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_DHT_P2P_GET);
  pgm->get_path_length = htonl (get_path_length);
  pgm->best_known_destination = local_best_known_dest;
  
  if (NULL == intermediate_trail_id)
    memset (&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);
  
  if (get_path_length != 0)
  {
    gp = (struct GNUNET_PeerIdentity *) &pgm[1];
    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,
                                struct GNUNET_PeerIdentity *target_peer,
                                struct GNUNET_PeerIdentity *source_peer,
                                unsigned int put_path_length,
                                const struct GNUNET_PeerIdentity *put_path,
                                unsigned int get_path_length,
                                struct GNUNET_PeerIdentity *get_path,
                                struct GNUNET_TIME_Absolute expiration,
                                const void *data, size_t data_size)
{
  struct PeerGetResultMessage *get_result;
  struct GNUNET_PeerIdentity *get_result_path;
  struct GNUNET_PeerIdentity *pp;
  struct P2PPendingMessage *pending;
  struct FriendInfo *target_friend;
  int current_path_index;
  size_t msize;

  msize = get_path_length * sizeof (struct GNUNET_PeerIdentity) + data_size +
          sizeof (struct PeerPutMessage);
 
  if (msize >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
  {
    GNUNET_break (0);
    return;
  }
  
  current_path_index = -1;
  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->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_DHT_P2P_GET_RESULT);
  get_result->key = *key;
  /* FIXME: check if you are passing the correct querying_peer as described in
   the get_result documentation. */
  memcpy (&(get_result->querying_peer), source_peer, sizeof (struct GNUNET_PeerIdentity));
  get_result->expiration_time = expiration;
  get_result_path = (struct GNUNET_PeerIdentity *)&get_result[1];
  if (get_path_length != 0)
  memcpy (get_result_path, get_path,
            sizeof (struct GNUNET_PeerIdentity) * get_path_length);
  memcpy (&get_result_path[get_path_length], data, data_size);
  
  /* FIXME: Is this correct? */
  if (put_path_length != 0)
  {
    pp = (struct GNUNET_PeerIdentity *)&get_result_path[1];
    memcpy (pp, put_path,sizeof (struct GNUNET_PeerIdentity) * put_path_length);
  }
  
  target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                     &get_result_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);
  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);

  for (j = 0; j < index ; j++)
    GNUNET_assert (GNUNET_YES ==
                   GNUNET_CONTAINER_multipeermap_iterator_next (iter, NULL, NULL));
  do
  {
    if (j == current_size)
    {
      j = 0;
      GNUNET_CONTAINER_multipeermap_iterator_destroy (iter);
      iter = GNUNET_CONTAINER_multipeermap_iterator_create (friend_peermap);

    }
    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);

  /* My own routing table is all full. I can not store any more trails for which 
     I am source. */
  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;
    }
  }

  if (largest_trail_index == (MAXIMUM_TRAILS_PER_FINGER + 1))
  {
    // tear down new trail: it's not better than the existing ones
    return;
  }

  /* Send trail teardown message across the replaced trail. */
  struct Trail *replace_trail = &existing_finger->trail_list[largest_trail_index];

  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. */
  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;

  for (i = 0; i < existing_finger->trails_count; i++)
  {
    trail_list_iterator = &existing_finger->trail_list[i];
    if (trail_list_iterator->trail_length != trail_length)
      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;
        break;
      }
    }
  }
  return trail_unique;
}


/**
 * Add a new trail to existing finger.
 * @param existing_finger
 * @param new_finger_trail
 * @param new_finger_trail_length
 * @param new_finger_trail_id
 */
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;
  }

  // FIXME checking trail_head is NOT a valid way to verify an open slot
  for (i = 0; existing_finger->trail_list[i].trail_head != NULL; i++)
    GNUNET_assert (i < MAXIMUM_TRAILS_PER_FINGER);

  trail_list_iterator = &existing_finger->trail_list[i];

  if (new_trail_length > 0)
    first_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                      &new_trail[0]);
  else
    first_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                      &(existing_finger->finger_identity));
  first_friend->trails_count++;
  /* FIXME; we removed this field but read fixme. */
  //trail_list_iterator->first_friend_trail_count = first_friend->trails_count;
  trail_list_iterator->trail_length = new_trail_length;

  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);
  }
  existing_finger->trails_count++;
}


/**
 * 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)
{
  /* FIXME: Now source also stores a trail entry in its routing table. before
   sending the trail teardown, you should get next_hop from routing table.
   If it is NULL, it means that path is broken, then remove the trail. 
   return a value to calling function so that if all trails are removed,
   then remove finger. */
  /* We should decerement the friend trail count here. */
  struct FriendInfo *friend;
  
  GNUNET_assert (NULL != (friend = 
          GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                             &trail->trail_head->peer)));
  
  friend->trails_count--;
  GDS_NEIGHBOURS_send_trail_teardown (trail->trail_id,
                                      GDS_ROUTING_SRC_TO_DEST,
                                      &trail->trail_head->peer);
}


/**
 * 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)
{
  struct Trail *trail;
  int i;

  for (i = 0; i < finger->trails_count; i++)
  {
    trail = &finger->trail_list[i];
    if (trail->trail_length > 0)
    {
     /* decerement the friend trails count. */
     send_trail_teardown (finger, trail);
    }
  }
}


/**
 * 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;

  for (i = 0; i < finger->trails_count; i++)
  {
    trail = &finger->trail_list[i];
    if (GNUNET_NO == trail->is_present)
      continue;
    
    if (trail->trail_length > 0)
      free_trail (trail);
  }
  
  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 or a friend. */
  if ((0 == GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &finger_identity)) ||
     (NULL != GNUNET_CONTAINER_multipeermap_get (friend_peermap, &finger_identity)))
  {
    new_entry->trails_count = 0;
    finger_table[finger_table_index] = *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;
  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 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)
    {
      target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                         &trail[0]);
      /* FIXME: In case its finger == friend, then may be we send a trail 
       teardown message as it does not make any sense to have any routing e
       entry in your own routing table.*/
      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;

      target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                         &trail[0]);
      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) * 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 found no other friend except the first hop, 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;
  
  /* If successor is a friend. */
  if (successor->trails_count == 0)
  {
    target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                                       &successor->finger_identity);
    memset ((void *)&trail_id, 0 , sizeof (trail_id));
    GDS_NEIGHBOURS_send_verify_successor_message (my_identity,
                                                  successor->finger_identity,
                                                  trail_id, NULL, 0,
                                                  target_friend);
    return;
  }
  
  for (i = 0; i < successor->trails_count; i++)
  {
    struct Trail *trail;
    struct Trail_Element *element;
    unsigned int trail_length;
    int j = 0;
    
    trail = &successor->trail_list[i];
    
    /* No trail stored at this index. */
    if (GNUNET_YES == trail->is_present)
      continue;
    
    /* Only in case of a friend we can have no trail. We have already handled
     * that case. So, now we should never have any such trail. */
    GNUNET_assert (trail->trail_length > 0);
    trail_id = trail->trail_id;
    trail_length = trail->trail_length;
    
    /* Copy the trail into peer list. */
    element = trail->trail_head;
    struct GNUNET_PeerIdentity peer_list[trail_length];
    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);
    
  }
}


/**
 * FIXME" clear abstraction of current search finger index and finger map index.
 * it never goes to 63. I don't know why
 * 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];
  if (GNUNET_NO == successor->is_present)
    GNUNET_break(0);
 
  /* 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
 *                            -1, 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 FriendInfo *friend;
  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;
  }
  
  /* If finger is a friend, then decrement the trail count and free the finger. */
  friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                              &finger->finger_identity);
  if (NULL != friend)
  {
    friend->trails_count--;
    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;
}

#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

/**
 * 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_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 GNUNET_PeerIdentity *updated_trail;
  struct FingerInfo *successor;
  int updated_finger_trail_length; 
  unsigned int finger_table_index;
  
#if 0
  test_friend_peermap_print();
  test_finger_table_print();
#endif
  
  /* 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;
  }
 
   
  /* If the new entry 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))
  {
    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];
  
  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);
  /* No entry present in finger_table for given finger map index. */
  if (GNUNET_NO == existing_finger->is_present)
  {
    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);
    GNUNET_free (updated_trail);
    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, finger_table_index);
    
    /* If the new finger is the closest peer. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&finger_identity, closest_peer))
    {
      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
  {
    /* 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))
    {
      GNUNET_free (updated_trail);
      return;
    }
    /* If the existing finger is not a friend. */
    if (NULL ==
        GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                           &existing_finger->finger_identity))
    {
      /* If there is space to store more trails. */
      if (existing_finger->trails_count < MAXIMUM_TRAILS_PER_FINGER)
        add_new_trail (existing_finger, updated_trail,
                       finger_trail_length, finger_trail_id);
      else
        select_and_replace_trail (existing_finger, updated_trail,
                                  finger_trail_length, finger_trail_id);
    }
  }
  update_current_search_finger_index (finger_identity, finger_table_index);
  GNUNET_free (updated_trail);
  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
  {
    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);
    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 + 1] = *peer;
  get_length = get_length + 1;
  
  memcpy (&key_value, &(get->key), sizeof (uint64_t));
  
  /* 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;
  }
  
  /* 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];
    struct GNUNET_PeerIdentity next_hop;

    memcpy (final_get_path, gp, get_length * sizeof (struct GNUNET_PeerIdentity));
    memcpy (&final_get_path[get_length+1], &my_identity, sizeof (struct GNUNET_PeerIdentity));
    get_length = get_length + 1;
    
    /* Get the next hop to pass the get result message. */
    memcpy (&next_hop, &final_get_path[get_length-2], sizeof (struct GNUNET_PeerIdentity));
    GDS_DATACACHE_handle_get (&(get->key),(get->block_type), NULL, 0, NULL, 0,
                              get_length, final_get_path, &next_hop, &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_non_null (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)
{
  struct PeerGetResultMessage *get_result;
  struct GNUNET_PeerIdentity *get_path;
  struct GNUNET_PeerIdentity *put_path;
  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 = (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;
  }
  
  get_path = (struct GNUNET_PeerIdentity *) &get_result[1];
  payload = &get_path[getlen];
  payload_size = msize - (sizeof (struct PeerGetResultMessage) + 
                          getlen * sizeof (struct GNUNET_PeerIdentity));
  
  
  put_path = &get_path[1];
 
  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 (GNUNET_SYSERR == 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. If @a current_dest is some other peer and not me, then 
 * compare curent_dest and local_dest. 
 * @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.*/
    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 GNUNET_PeerIdentity next_peer;
  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())
  {
    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;
  }

  local_best_known_dest = GNUNET_malloc (sizeof (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);
 
  /* 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)) ||
        (trail_length > 0))
    {
      GDS_ROUTING_add (trail_id, *peer, my_identity);
    }
    if (0 == trail_length)
      memcpy (&next_peer, &source, sizeof (struct GNUNET_PeerIdentity));
    else
      memcpy (&next_peer, &trail_peer_list[trail_length-1], sizeof (struct GNUNET_PeerIdentity));

    target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, &next_peer);
    GDS_NEIGHBOURS_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;
    target_friend = 
            GNUNET_CONTAINER_multipeermap_get (friend_peermap,
                                               next_hop_towards_local_best_known_dest);
    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);
  GNUNET_free (next_hop_towards_local_best_known_dest);
  return GNUNET_OK;
}


/* 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;
}


/**
 * 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 (GNUNET_NO == is_sender_peer_correct (trail_peer_list,
                                           trail_length,
                                           peer, finger_identity, querying_peer))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  
  /* Am I the one who initiated the query? */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&querying_peer,
                                             &my_identity)))
  {
    /* If I am not my own finger identity, then add routing table entry. */
    if (0 != GNUNET_CRYPTO_cmp_peer_identity (&my_identity, &finger_identity))
    {
      GDS_ROUTING_add (trail_id, my_identity, *peer);
    }
    
    finger_table_add (finger_identity, trail_peer_list,
                      trail_length, 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;
  }
  
  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);
  }

  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));
    
  /* Invert the trail from finger to me to get the trail from me to finger. */
  if (trail_length == 0)
    trail_to_new_predecessor = NULL;

  if (trail_length > 0)
  {
    trail_to_new_predecessor = invert_trail (trail, trail_length);
    /* Add an entry in your routing table. */
    GDS_ROUTING_add (trail_to_new_predecessor_id, 
                     trail_to_new_predecessor[trail_length - 1],
                     my_identity);
   
    target_friend = 
            GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                               &trail_to_new_predecessor[trail_length - 1]);
      
    // Before sending the trail may be you need to compress it. And in case
    // it was a friend how did we got the trail. ?? 
    
    /* Add entry in routing table of all peers that are part of trail from me
       to 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;
  
  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;
  }
  
  predecessor_value = compute_finger_identity_value (PREDECESSOR_FINGER_ID);
  closest_peer = select_closest_peer (&finger, 
                                      &current_predecessor->finger_identity,
                                      predecessor_value, PREDECESSOR_FINGER_ID);
  
  /* 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];
  
  //GDS_ROUTING_test_print(); //FIXME REMOVE AFTERWARDS. 
  //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;
    }
    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 my predecessor. */
  if (0 == (GNUNET_CRYPTO_cmp_peer_identity (&current_predecessor->finger_identity,
                                             &source_peer)))
  {
    trail_to_predecessor = NULL;
    trail_to_predecessor_length = 0;
  }
  else
  {
    if (NULL == (GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                    &current_predecessor->finger_identity)))
    {
      /* Only if current predecessor is not a friend, we have a trail to reach
       to it. Only in that case we pass the trail. */
      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;
    }
  }
  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;
  
  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, 0);
  
  /* 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)
  {
    GDS_ROUTING_add (trail_id, my_identity, trail_to_new_successor[0]);
    target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                       &trail_to_new_successor[0]);
  }
  else
  {
    target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, 
                                                       &probable_successor);
  }
  
  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)));
  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))
  {
    /* Add an entry in routing table only if new predecessor is not a friend. */
    if (NULL == GNUNET_CONTAINER_multipeermap_get(friend_peermap, &source))
    {
      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));
  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. */
  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));
    }

    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 
     * 2. If trail length > 0. 
     * NOTE: In case trail length > 0 and source is my friend, then also I add
     *       an entry in routing table,as we will send a trail compression message
     *       later.
     */
    if ((0 != GNUNET_CRYPTO_cmp_peer_identity (&source, &my_identity)) ||
        (trail_length > 0))
      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];
    
    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;

    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)))
  {
    /* Update your prev hop to source of this message. */
    GDS_ROUTING_update_trail_prev_hop (trail_id,
                                       trail_compression->source_peer);
    return GNUNET_OK;
  }
  
  /* Pass the message to next hop to finally reach to new_first_friend. */
  next_hop = GDS_ROUTING_get_next_hop (trail_id, GDS_ROUTING_SRC_TO_DEST);
  if (NULL == next_hop)
  {
    GNUNET_break (0); 
    return GNUNET_OK;
  }
  
  GNUNET_assert (NULL != (target_friend = 
          GNUNET_CONTAINER_multipeermap_get (friend_peermap, next_hop)));
  GDS_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 *prev_hop;
  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. */
  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;
  }
  GNUNET_free_non_null (prev_hop);
  
  next_hop = GDS_ROUTING_get_next_hop (trail_id, trail_direction);
  if (NULL == next_hop)
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  
  GNUNET_assert (GNUNET_YES == GDS_ROUTING_remove_trail (trail_id));
  
  /* If next_hop is my_identity, it means I am the final destination. */
  if (0 == GNUNET_CRYPTO_cmp_peer_identity (next_hop, &my_identity))
    return GNUNET_OK;
  
  /* If not final destination, then send a trail teardown message to next hop.*/
  GDS_NEIGHBOURS_send_trail_teardown (trail_id, trail_direction, next_hop);
  GNUNET_free (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 (GNUNET_SYSERR == my_index)
    {
      GNUNET_break_op (0);
      return GNUNET_SYSERR;
    }

    if (0 == my_index)
      next_hop = source_peer;
    else
      next_hop = trail[trail_length - 1];
    
    /* Add in your routing table. */
    GNUNET_assert (GNUNET_OK == GDS_ROUTING_add (trail_id, next_hop, *peer));
    target_friend = GNUNET_CONTAINER_multipeermap_get (friend_peermap, &next_hop);
    GDS_NEIGHBOURS_send_add_trail (source_peer, destination_peer, trail_id,
                                   trail, trail_length, target_friend);
    return GNUNET_OK;
  }
  
  /* I am the destination. Add an entry in routing table. */
  GNUNET_assert (GNUNET_OK == GDS_ROUTING_add (trail_id, *peer, my_identity));
  return GNUNET_OK;
}


/**
 * Send trail teardown and free the finger trail in which the first
 * friend to reach to a finger is disconnected_friend 
 * @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];
    
    if (GNUNET_NO == trail->is_present)
      continue;
    
    /* First friend to reach to finger is disconnected_peer. */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (&trail->trail_head->peer,
                                              disconnected_friend))
    {
      matching_trails_count++;
      send_trail_teardown (remove_finger, trail);
      if (trail->trail_length > 0)
      free_trail (trail);
    }
  }  
  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 free that entry. Don't send trail
 *    teardown message, as there is no trail to reach to a finger which is a friend. 
 * 2. Check if disconnected_friend is the first friend in the trail to reach to a finger.
 *   2.1 Send trail teardown message across all the trails 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_friend)
{
  struct FingerInfo *remove_finger;
  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 friend a finger? */
    if (0 == GNUNET_CRYPTO_cmp_peer_identity (disconnected_friend,
                                              &remove_finger->finger_identity))
    {
      /* No trail to reach this finger as it is a friend, don't send 
       * trail_teardown message. */
      remove_finger->is_present = GNUNET_NO;
      memset ((void *)&finger_table[i], 0, sizeof (finger_table[i]));
      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_friend, 
                                                   remove_finger);
    
    /* All the finger trails had disconnected_friend as the first friend,
     * so free the finger. */
    if (removed_trails_count == remove_finger->trails_count)
    {
      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. */
  GDS_ROUTING_remove_trail_by_peer (peer);
  
  /* 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 there are no more friends in friend_peermap, then don't schedule
   * find_finger_trail_task. */
  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));
#if 0
   FPRINTF (stderr,_("\nSUPU %s, %s, %d, my_identity = %s"),
   __FILE__, __func__,__LINE__, GNUNET_i2s (&my_identity));
#endif
}


/**
 * Initialize finger table entries.
 */
static void
finger_table_init ()
{
  int i;
  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_DHT_P2P_PUT, 0},
    {&handle_dht_p2p_get, GNUNET_MESSAGE_TYPE_DHT_P2P_GET, 0},
    {&handle_dht_p2p_get_result, GNUNET_MESSAGE_TYPE_DHT_P2P_GET_RESULT, 0},
    {&handle_dht_p2p_trail_setup, GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP, 0},
    {&handle_dht_p2p_trail_setup_result, GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP_RESULT, 0},
    {&handle_dht_p2p_verify_successor, GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR, 0},
    {&handle_dht_p2p_verify_successor_result, GNUNET_MESSAGE_TYPE_DHT_P2P_VERIFY_SUCCESSOR_RESULT, 0},
    {&handle_dht_p2p_notify_new_successor, GNUNET_MESSAGE_TYPE_DHT_P2P_NOTIFY_NEW_SUCCESSOR, 0},
    {&handle_dht_p2p_trail_setup_rejection, GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_SETUP_REJECTION, 0},
    {&handle_dht_p2p_trail_compression, GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_COMPRESSION, 
                                        sizeof (struct PeerTrailCompressionMessage)},
    {&handle_dht_p2p_trail_teardown, GNUNET_MESSAGE_TYPE_DHT_P2P_TRAIL_TEARDOWN, 
                                     sizeof (struct PeerTrailTearDownMessage)},
    {&handle_dht_p2p_add_trail, GNUNET_MESSAGE_TYPE_DHT_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;
}