toxcore/core/DHT.c

/* DHT.c
 *
 * An implementation of the DHT as seen in http://wiki.tox.im/index.php/DHT
 *
 *  Copyright (C) 2013 Tox project All Rights Reserved.
 *
 *  This file is part of Tox.
 *
 *  Tox 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 of the License, or
 *  (at your option) any later version.
 *
 *  Tox 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 Tox.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

/*----------------------------------------------------------------------------------*/

#include "DHT.h"
#include "packets.h"
#include "ping.h"

/* maximum number of clients stored per friend. */
#define MAX_FRIEND_CLIENTS 8

/* A list of the clients mathematically closest to ours. */
#define LCLIENT_LIST 32

/* The list of ip ports along with the ping_id of what we sent them and a timestamp */
#define LPING_ARRAY 256

#define LSEND_NODES_ARRAY LPING_ARRAY/2

/* the number of seconds for a non responsive node to become bad. */
#define BAD_NODE_TIMEOUT 70

/* the max number of nodes to send with send nodes. */
#define MAX_SENT_NODES 8

/* ping timeout in seconds */
#define PING_TIMEOUT 5

/* The timeout after which a node is discarded completely. */
#define Kill_NODE_TIMEOUT 300

/* ping interval in seconds for each node in our lists. */
#define PING_INTERVAL 60

/* ping interval in seconds for each random sending of a get nodes request. */
#define GET_NODE_INTERVAL 10

#define MAX_PUNCHING_PORTS 32

/*Interval in seconds between punching attempts*/
#define PUNCH_INTERVAL 10

/*----------------------------------------------------------------------------------*/

typedef struct {
    uint8_t     client_id[CLIENT_ID_SIZE];
    IP_Port     ip_port;
    uint64_t    timestamp;
    uint64_t    last_pinged;

    /* Returned by this node. Either our friend or us */
    IP_Port     ret_ip_port;
    uint64_t    ret_timestamp;
} Client_data;

typedef struct {
    uint8_t     client_id[CLIENT_ID_SIZE];
    Client_data client_list[MAX_FRIEND_CLIENTS];

    /* time at which the last get_nodes request was sent. */
    uint64_t    lastgetnode;

    /* Symetric NAT hole punching stuff */

    /* 1 if currently hole punching, otherwise 0 */
    uint8_t     hole_punching; 
    uint32_t    punching_index;
    uint64_t    punching_timestamp;
    uint64_t    recvNATping_timestamp;
    uint64_t    NATping_id;
    uint64_t    NATping_timestamp;
} Friend;

typedef struct {
    uint8_t     client_id[CLIENT_ID_SIZE];
    IP_Port     ip_port;
} Node_format;

typedef struct {
    IP_Port     ip_port;
    uint64_t    ping_id;
    uint64_t    timestamp;
} Pinged;

/*----------------------------------------------------------------------------------*/

                    /* Our client id/public key */
uint8_t             self_public_key[CLIENT_ID_SIZE];
uint8_t             self_secret_key[crypto_box_SECRETKEYBYTES];
static Client_data  close_clientlist[LCLIENT_LIST];
static Friend *     friends_list;
static uint16_t     num_friends;
static Pinged       send_nodes[LSEND_NODES_ARRAY];

/*----------------------------------------------------------------------------------*/

/* Compares client_id1 and client_id2 with client_id
 * return 0 if both are same distance
 * return 1 if client_id1 is closer
 * return 2 if client_id2 is closer
 */
static int id_closest(uint8_t * id, uint8_t * id1, uint8_t * id2)
{
    size_t   i;
    uint8_t distance1, distance2;

    for(i = 0; i < CLIENT_ID_SIZE; ++i) {

        distance1 = abs(id[i] ^ id1[i]);
        distance2 = abs(id[i] ^ id2[i]);
        
        if(distance1 < distance2)
            return 1;
        if(distance1 > distance2)
            return 2;
    }
    return 0;
}

static int ipport_equal(IP_Port a, IP_Port b)
{
  return (a.ip.i == b.ip.i) && (a.port == b.port);
}

static int id_equal(uint8_t* a, uint8_t* b)
{
  return memcmp(a, b, CLIENT_ID_SIZE) == 0;
}

static int is_timeout(uint64_t time_now, uint64_t timestamp, uint64_t timeout)
{
  return timestamp + timeout <= time_now;
}

/* check if client with client_id is already in list of length length.
 * if it is then set its corresponding timestamp to current time.
 * if the id is already in the list with a different ip_port, update it.
 * return True(1) or False(0)
 *
 * TODO: maybe optimize this.
 */
static int client_in_list(Client_data * list, uint32_t length, uint8_t * client_id, IP_Port ip_port)
{
    uint32_t i;
    uint64_t temp_time = unix_time();

    for(i = 0; i < length; ++i) {
        /*If ip_port is assigned to a different client_id replace it*/
        if(ipport_equal(list[i].ip_port, ip_port)) {
            memcpy(list[i].client_id, client_id, CLIENT_ID_SIZE);
        }

        if(id_equal(list[i].client_id, client_id)) {
            /* Refresh the client timestamp. */
            list[i].timestamp = temp_time;
            list[i].ip_port.ip.i = ip_port.ip.i;
            list[i].ip_port.port = ip_port.port;
            return 1;
        }
    }
    return 0;
}

/* check if client with client_id is already in node format list of length length.
 * return True(1) or False(0)
 */
static int client_in_nodelist(Node_format * list, uint32_t length, uint8_t * client_id)
{
    uint32_t i;

    for(i = 0; i < length; ++i) {
        if(id_equal(list[i].client_id, client_id))
            return 1;
    }

    return 0;
}

/* Returns the friend number from the client_id, or -1 if a failure occurs
 */
static int friend_number(uint8_t * client_id)
{
    uint32_t i;

    for(i = 0; i < num_friends; ++i) {
        if(id_equal(friends_list[i].client_id, client_id))
            return i;
    }

    return -1;
}

/* Find MAX_SENT_NODES nodes closest to the client_id for the send nodes request:
 * put them in the nodes_list and return how many were found.
 *
 * TODO: For the love of based Allah make this function cleaner and much more efficient.
 */
static int get_close_nodes(uint8_t * client_id, Node_format * nodes_list)
{
    uint32_t    i, j, k;
    uint64_t    temp_time = unix_time();
    int         num_nodes = 0, closest, tout, inlist;

    for (i = 0; i < LCLIENT_LIST; ++i) {
        tout = is_timeout(temp_time, close_clientlist[i].timestamp, BAD_NODE_TIMEOUT);
        inlist = client_in_nodelist(nodes_list, MAX_SENT_NODES, close_clientlist[i].client_id);

        /* if node isn't good or is already in list. */
        if(tout || inlist)
            continue;

        if(num_nodes < MAX_SENT_NODES) {

            memcpy( nodes_list[num_nodes].client_id, 
                    close_clientlist[i].client_id, 
                    CLIENT_ID_SIZE );

            nodes_list[num_nodes].ip_port = close_clientlist[i].ip_port;
            num_nodes++;

        } else {

            for(j = 0; j < MAX_SENT_NODES; ++j) {
                closest = id_closest(   client_id, 
                                        nodes_list[j].client_id, 
                                        close_clientlist[i].client_id );
                if(closest == 2) {
                    memcpy( nodes_list[j].client_id, 
                            close_clientlist[i].client_id, 
                            CLIENT_ID_SIZE);

                    nodes_list[j].ip_port = close_clientlist[i].ip_port;
                    break;
                }
            }
        }
    }

    for(i = 0; i < num_friends; ++i) {
        for(j = 0; j < MAX_FRIEND_CLIENTS; ++j) {

            tout = is_timeout(temp_time, friends_list[i].client_list[j].timestamp, BAD_NODE_TIMEOUT);
            inlist = client_in_nodelist(    nodes_list,
                                            MAX_SENT_NODES, 
                                            friends_list[i].client_list[j].client_id);

            /* if node isn't good or is already in list. */
            if(tout || inlist)
                continue;

            if(num_nodes < MAX_SENT_NODES) {

                memcpy( nodes_list[num_nodes].client_id, 
                        friends_list[i].client_list[j].client_id, 
                        CLIENT_ID_SIZE);

                nodes_list[num_nodes].ip_port = friends_list[i].client_list[j].ip_port;
                num_nodes++;
            } else  {
                for(k = 0; k < MAX_SENT_NODES; ++k) {

                    closest = id_closest(   client_id, 
                                            nodes_list[k].client_id, 
                                            friends_list[i].client_list[j].client_id );
                    if(closest == 2) {
                        memcpy( nodes_list[k].client_id, 
                                friends_list[i].client_list[j].client_id, 
                                CLIENT_ID_SIZE );

                        nodes_list[k].ip_port = friends_list[i].client_list[j].ip_port;
                        break;
                    }
                }
            }
        }
    }
    return num_nodes;
}

/* replace first bad (or empty) node with this one
 * return 0 if successful
 * return 1 if not (list contains no bad nodes)
 */
static int replace_bad(    Client_data *   list, 
                    uint32_t        length,  
                    uint8_t *       client_id,   
                    IP_Port         ip_port )
{
    uint32_t i;
    uint64_t temp_time = unix_time();
    for(i = 0; i < length; ++i) {
        /* if node is bad */
        if(is_timeout(temp_time, list[i].timestamp, BAD_NODE_TIMEOUT)) {
            memcpy(list[i].client_id, client_id, CLIENT_ID_SIZE);
            list[i].ip_port = ip_port;
            list[i].timestamp = temp_time;
            list[i].ret_ip_port.ip.i = 0;
            list[i].ret_ip_port.port = 0;
            list[i].ret_timestamp = 0;
            return 0;
        }
    }

    return 1;
}

/* replace the first good node that is further to the comp_client_id than that of the client_id in the list */
static int replace_good(   Client_data *   list,
                    uint32_t        length, 
                    uint8_t *       client_id, 
                    IP_Port         ip_port, 
                    uint8_t *       comp_client_id )
{
    uint32_t i;
    uint64_t temp_time = unix_time();

    for(i = 0; i < length; ++i)
        if(id_closest(comp_client_id, list[i].client_id, client_id) == 2) {
            memcpy(list[i].client_id, client_id, CLIENT_ID_SIZE);
            list[i].ip_port = ip_port;
            list[i].timestamp = temp_time;
            list[i].ret_ip_port.ip.i = 0;
            list[i].ret_ip_port.port = 0;
            list[i].ret_timestamp = 0;
            return 0;
        }

    return 1;
}

/* Attempt to add client with ip_port and client_id to the friends client list 
 * and close_clientlist 
 */
void addto_lists(IP_Port ip_port, uint8_t * client_id)
{
    uint32_t i;

    /* NOTE: current behavior if there are two clients with the same id is
     * to replace the first ip by the second. 
     */
    if (!client_in_list(close_clientlist, LCLIENT_LIST, client_id, ip_port)) {
        if (replace_bad(close_clientlist, LCLIENT_LIST, client_id, ip_port)) {
            /* if we can't replace bad nodes we try replacing good ones */
            replace_good(   close_clientlist, 
                            LCLIENT_LIST, 
                            client_id, 
                            ip_port, 
                            self_public_key );
        }
    }

    for (i = 0; i < num_friends; ++i) {
        if (!client_in_list(    friends_list[i].client_list, 
                                MAX_FRIEND_CLIENTS, 
                                client_id, 
                                ip_port )) {

            if (replace_bad(    friends_list[i].client_list, 
                                MAX_FRIEND_CLIENTS,
                                client_id, 
                                ip_port )) {
                /* if we can't replace bad nodes we try replacing good ones. */
                replace_good(   friends_list[i].client_list, 
                                MAX_FRIEND_CLIENTS, 
                                client_id, 
                                ip_port, 
                                friends_list[i].client_id );
            }
        }
    }
}

/* If client_id is a friend or us, update ret_ip_port
 * nodeclient_id is the id of the node that sent us this info
 */
static void returnedip_ports(IP_Port ip_port, uint8_t * client_id, uint8_t * nodeclient_id)
{
    uint32_t i, j;
    uint64_t temp_time = unix_time();

    if (id_equal(client_id, self_public_key)) {

        for (i = 0; i < LCLIENT_LIST; ++i) {
            if (id_equal(nodeclient_id, close_clientlist[i].client_id)) {
                close_clientlist[i].ret_ip_port = ip_port;
                close_clientlist[i].ret_timestamp = temp_time;
                return;
            }
        }

    } else {

        for (i = 0; i < num_friends; ++i) {
            if (id_equal(client_id, friends_list[i].client_id)) {

                for (j = 0; j < MAX_FRIEND_CLIENTS; ++j) {
                    if (id_equal(nodeclient_id, friends_list[i].client_list[j].client_id)) {
                        friends_list[i].client_list[j].ret_ip_port = ip_port;
                        friends_list[i].client_list[j].ret_timestamp = temp_time;
                        return;
                    }
                }
            }
        }

    }
}

/* Same as last function but for get_node requests. */
static int is_gettingnodes(IP_Port ip_port, uint64_t ping_id)
{
    uint32_t i;
    uint8_t pinging;
    uint64_t temp_time = unix_time();

    for(i = 0; i < LSEND_NODES_ARRAY; ++i ) {
        if(!is_timeout(temp_time, send_nodes[i].timestamp, PING_TIMEOUT)) {
            pinging = 0;

            if(ip_port.ip.i != 0 && ipport_equal(send_nodes[i].ip_port, ip_port))
                    ++pinging;

            if(ping_id != 0 && send_nodes[i].ping_id == ping_id)
                    ++pinging;

            if(pinging == (ping_id != 0) + (ip_port.ip.i != 0))
                return 1;
        }
    }

    return 0;
}

/* Same but for get node requests */
static uint64_t add_gettingnodes(IP_Port ip_port)
{
    uint32_t i, j;
    uint64_t ping_id = ((uint64_t)random_int() << 32) + random_int();
    uint64_t temp_time = unix_time();

    for(i = 0; i < PING_TIMEOUT; ++i ) {
        for(j = 0; j < LSEND_NODES_ARRAY; ++j ) {
            if(is_timeout(temp_time, send_nodes[j].timestamp, PING_TIMEOUT - i)) {
                send_nodes[j].timestamp = temp_time;
                send_nodes[j].ip_port = ip_port;
                send_nodes[j].ping_id = ping_id;
                return ping_id;
            }
        }
    }

    return 0;
}

/* send a getnodes request */
static int getnodes(IP_Port ip_port, uint8_t * public_key, uint8_t * client_id)
{
    /* check if packet is gonna be sent to ourself */
    if(id_equal(public_key, self_public_key) || is_gettingnodes(ip_port, 0))
        return 1;

    uint64_t ping_id = add_gettingnodes(ip_port);

    if(ping_id == 0)
        return 1;

    uint8_t data[1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES + sizeof(ping_id) + CLIENT_ID_SIZE + ENCRYPTION_PADDING];
    uint8_t plain[sizeof(ping_id) + CLIENT_ID_SIZE];
    uint8_t encrypt[sizeof(ping_id) + CLIENT_ID_SIZE + ENCRYPTION_PADDING];
    uint8_t nonce[crypto_box_NONCEBYTES];
    random_nonce(nonce);

    memcpy(plain, &ping_id, sizeof(ping_id));
    memcpy(plain + sizeof(ping_id), client_id, CLIENT_ID_SIZE);

    int len = encrypt_data( public_key, 
                            self_secret_key, 
                            nonce, 
                            plain, 
                            sizeof(ping_id) + CLIENT_ID_SIZE, 
                            encrypt );

    if(len != sizeof(ping_id) + CLIENT_ID_SIZE + ENCRYPTION_PADDING)
        return -1;

    data[0] = 2;
    memcpy(data + 1, self_public_key, CLIENT_ID_SIZE);
    memcpy(data + 1 + CLIENT_ID_SIZE, nonce, crypto_box_NONCEBYTES);
    memcpy(data + 1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES, encrypt, len);

    return sendpacket(ip_port, data, sizeof(data));
}

/* send a send nodes response */
static int sendnodes(IP_Port ip_port, uint8_t * public_key, uint8_t * client_id, uint64_t ping_id)
{
    /* check if packet is gonna be sent to ourself */
    if(id_equal(public_key, self_public_key)) 
        return 1;

    uint8_t data[1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES + sizeof(ping_id)
                 + sizeof(Node_format) * MAX_SENT_NODES + ENCRYPTION_PADDING];

    Node_format nodes_list[MAX_SENT_NODES];
    int num_nodes = get_close_nodes(client_id, nodes_list);

    if(num_nodes == 0)
        return 0;

    uint8_t plain[sizeof(ping_id) + sizeof(Node_format) * MAX_SENT_NODES];
    uint8_t encrypt[sizeof(ping_id) + sizeof(Node_format) * MAX_SENT_NODES + ENCRYPTION_PADDING];
    uint8_t nonce[crypto_box_NONCEBYTES];
    random_nonce(nonce);

    memcpy(plain, &ping_id, sizeof(ping_id));
    memcpy(plain + sizeof(ping_id), nodes_list, num_nodes * sizeof(Node_format));

    int len = encrypt_data( public_key, 
                            self_secret_key, 
                            nonce, 
                            plain,
                            sizeof(ping_id) + num_nodes * sizeof(Node_format), 
                            encrypt );

    if(len != sizeof(ping_id) + num_nodes * sizeof(Node_format) + ENCRYPTION_PADDING)
        return -1;

    data[0] = 3;
    memcpy(data + 1, self_public_key, CLIENT_ID_SIZE);
    memcpy(data + 1 + CLIENT_ID_SIZE, nonce, crypto_box_NONCEBYTES);
    memcpy(data + 1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES, encrypt, len);

    return sendpacket(ip_port, data, 1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES + len);
}

static int handle_getnodes(uint8_t * packet, uint32_t length, IP_Port source)
{
    uint64_t ping_id;

    if (length != ( 1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES 
                    + sizeof(ping_id) + CLIENT_ID_SIZE + ENCRYPTION_PADDING ))
        return 1;

    /* check if packet is from ourself. */
    if (id_equal(packet + 1, self_public_key))
        return 1;

    uint8_t plain[sizeof(ping_id) + CLIENT_ID_SIZE];

    int len = decrypt_data( packet + 1, 
                            self_secret_key, 
                            packet + 1 + CLIENT_ID_SIZE,
                            packet + 1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES,
                            sizeof(ping_id) + CLIENT_ID_SIZE + ENCRYPTION_PADDING, 
                            plain );

    if (len != sizeof(ping_id) + CLIENT_ID_SIZE)
        return 1;

    memcpy(&ping_id, plain, sizeof(ping_id));
    sendnodes(source, packet + 1, plain + sizeof(ping_id), ping_id);

    send_ping_request(source, (clientid_t*) (packet + 1)); /* TODO: make this smarter? */

    return 0;
}

static int handle_sendnodes(uint8_t * packet, uint32_t length, IP_Port source)
{
    uint64_t ping_id;
    uint32_t cid_size = 1 + CLIENT_ID_SIZE;
    cid_size += crypto_box_NONCEBYTES + sizeof(ping_id) + ENCRYPTION_PADDING;

    if (length > (cid_size + sizeof(Node_format) * MAX_SENT_NODES) ||
        ((length - cid_size) % sizeof(Node_format)) != 0 ||
        (length < cid_size + sizeof(Node_format)))
        return 1;

    uint32_t num_nodes = (length - cid_size) / sizeof(Node_format);
    uint8_t plain[sizeof(ping_id) + sizeof(Node_format) * MAX_SENT_NODES];

    int len = decrypt_data( 
            packet + 1, 
            self_secret_key, 
            packet + 1 + CLIENT_ID_SIZE,
            packet + 1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES,
            sizeof(ping_id) + num_nodes * sizeof(Node_format) + ENCRYPTION_PADDING, plain );

    if(len != sizeof(ping_id) + num_nodes * sizeof(Node_format))
        return 1;

    memcpy(&ping_id, plain, sizeof(ping_id));
    if(!is_gettingnodes(source, ping_id))
        return 1;

    Node_format nodes_list[MAX_SENT_NODES];
    memcpy(nodes_list, plain + sizeof(ping_id), num_nodes * sizeof(Node_format));

    addto_lists(source, packet + 1);

    uint32_t i;
    for(i = 0; i < num_nodes; ++i)  {
        send_ping_request(nodes_list[i].ip_port, (clientid_t*) &nodes_list[i].client_id);
        returnedip_ports(nodes_list[i].ip_port, nodes_list[i].client_id, packet + 1);
    }

    return 0;
}

/*----------------------------------------------------------------------------------*/
/*------------------------END of packet handling functions--------------------------*/

int DHT_addfriend(uint8_t * client_id)
{
    Friend * temp;
    temp = realloc(friends_list, sizeof(Friend) * (num_friends + 1));
    if (temp == NULL)
        return 1;

    friends_list = temp;
    memset(&friends_list[num_friends], 0, sizeof(Friend));
    memcpy(friends_list[num_friends].client_id, client_id, CLIENT_ID_SIZE);

    friends_list[num_friends].NATping_id = ((uint64_t)random_int() << 32) + random_int();
    ++num_friends;
    return 0;
}

int DHT_delfriend(uint8_t * client_id)
{
    uint32_t i;
    Friend * temp;
    for (i = 0; i < num_friends; ++i) {
        /* Equal */
        if (id_equal(friends_list[i].client_id, client_id)) {
            --num_friends;

            if (num_friends != i) {
                memcpy( friends_list[i].client_id, 
                        friends_list[num_friends].client_id, 
                        CLIENT_ID_SIZE );
            }

            temp = realloc(friends_list, sizeof(Friend) * (num_friends));
            if (temp == NULL)
                return 1;

            friends_list = temp;
            return 0;
        }
    }

    return 1;
}

/* TODO: Optimize this. */
IP_Port DHT_getfriendip(uint8_t * client_id)
{
    uint32_t i, j;
    uint64_t temp_time = unix_time();
    IP_Port empty = {{{0}}, 0};

    for (i = 0; i < num_friends; ++i) {
        /* Equal */
        if (id_equal(friends_list[i].client_id, client_id)) {
            for (j = 0; j < MAX_FRIEND_CLIENTS; ++j) {
                if (id_equal(friends_list[i].client_list[j].client_id, client_id) && !is_timeout(temp_time, friends_list[i].client_list[j].timestamp, BAD_NODE_TIMEOUT))
                    return friends_list[i].client_list[j].ip_port;
            }
            return empty;
        }
    }
    empty.ip.i = 1;
    return empty;
}

/* Ping each client in the "friends" list every 60 seconds. Send a get nodes request
 * every 20 seconds to a random good node for each "friend" in our "friends" list. 
 */
static void doDHTFriends(void)
{
    uint32_t i, j;
    uint64_t temp_time = unix_time();
    uint32_t rand_node;
    uint32_t index[MAX_FRIEND_CLIENTS];

    for (i = 0; i < num_friends; ++i) {
        uint32_t num_nodes = 0;
        for (j = 0; j < MAX_FRIEND_CLIENTS; ++j) {
            /* if node is not dead. */
          if (!is_timeout(temp_time, friends_list[i].client_list[j].timestamp, Kill_NODE_TIMEOUT)) {
                if ((friends_list[i].client_list[j].last_pinged + PING_INTERVAL) <= temp_time) {
                    send_ping_request( friends_list[i].client_list[j].ip_port, 
                                       (clientid_t*) &friends_list[i].client_list[j].client_id );
                    friends_list[i].client_list[j].last_pinged = temp_time;
                }
                /* if node is good. */
                if (!is_timeout(temp_time, friends_list[i].client_list[j].timestamp, BAD_NODE_TIMEOUT)) { 
                    index[num_nodes] = j;
                    ++num_nodes;
                }
            }
        }
        if(friends_list[i].lastgetnode + GET_NODE_INTERVAL <= temp_time && num_nodes != 0) {
            rand_node = rand() % num_nodes;
            getnodes( friends_list[i].client_list[index[rand_node]].ip_port,
                      friends_list[i].client_list[index[rand_node]].client_id,
                      friends_list[i].client_id );
            friends_list[i].lastgetnode = temp_time;
        }
    }
}

static uint64_t close_lastgetnodes;

/* Ping each client in the close nodes list every 60 seconds.
 * Send a get nodes request every 20 seconds to a random good node in the list.
 */
static void doClose(void)
{
    uint32_t i;
    uint64_t temp_time = unix_time();
    uint32_t num_nodes = 0;
    uint32_t rand_node;
    uint32_t index[LCLIENT_LIST];

    for (i = 0; i < LCLIENT_LIST; ++i) {
        /* if node is not dead. */
        if (!is_timeout(temp_time, close_clientlist[i].timestamp, Kill_NODE_TIMEOUT)) {
            if ((close_clientlist[i].last_pinged + PING_INTERVAL) <= temp_time) {
                send_ping_request( close_clientlist[i].ip_port, 
                                   (clientid_t*) &close_clientlist[i].client_id );
                close_clientlist[i].last_pinged = temp_time;
            }
            /* if node is good. */
            if (!is_timeout(temp_time, close_clientlist[i].timestamp, BAD_NODE_TIMEOUT)) {
                index[num_nodes] = i;
                ++num_nodes;
            }
        }
    }

    if (close_lastgetnodes + GET_NODE_INTERVAL <= temp_time && num_nodes != 0) {
        rand_node = rand() % num_nodes;
        getnodes( close_clientlist[index[rand_node]].ip_port,
                  close_clientlist[index[rand_node]].client_id,
                  self_public_key );
        close_lastgetnodes = temp_time;
    }
}

void DHT_bootstrap(IP_Port ip_port, uint8_t * public_key)
{
    getnodes(ip_port, public_key, self_public_key);
}

/* send the given packet to node with client_id
 * returns -1 if failure 
 */
int route_packet(uint8_t * client_id, uint8_t * packet, uint32_t length)
{
    uint32_t i;

    for (i = 0; i < LCLIENT_LIST; ++i) {
        if (id_equal(client_id, close_clientlist[i].client_id))
            return sendpacket(close_clientlist[i].ip_port, packet, length);
    }

    return -1;
}

/* Puts all the different ips returned by the nodes for a friend_num into array ip_portlist
 * ip_portlist must be at least MAX_FRIEND_CLIENTS big
 * returns the number of ips returned
 * return 0 if we are connected to friend or if no ips were found.
 * returns -1 if no such friend
 */
static int friend_iplist(IP_Port * ip_portlist, uint16_t friend_num)
{
    int num_ips = 0;
    uint32_t i;
    uint64_t temp_time = unix_time();
    
    if (friend_num >= num_friends)
        return -1;

    Friend * friend = &friends_list[friend_num];
    Client_data * client;

    for (i = 0; i < MAX_FRIEND_CLIENTS; ++i) {
        client = &friend->client_list[i];

        /*If ip is not zero and node is good */
        if (client->ret_ip_port.ip.i != 0 && !is_timeout(temp_time, client->ret_timestamp, BAD_NODE_TIMEOUT)) {

            if (id_equal(client->client_id, friend->client_id))
                return 0;

            ip_portlist[num_ips] = client->ret_ip_port;
            ++num_ips;
        }
    }
    return num_ips;
}

/* Send the following packet to everyone who tells us they are connected to friend_id
 * returns the number of nodes it sent the packet to
 */
int route_tofriend(uint8_t * friend_id, uint8_t * packet, uint32_t length)
{
    int num = friend_number(friend_id);
    if (num == -1)
        return 0;

    uint32_t i, sent = 0;
    uint64_t temp_time = unix_time();
    Friend * friend = &friends_list[num];
    Client_data * client;

    for (i = 0; i < MAX_FRIEND_CLIENTS; ++i) {
        client = &friend->client_list[i];

        /*If ip is not zero and node is good */
        if (client->ret_ip_port.ip.i != 0 && !is_timeout(temp_time, client->ret_timestamp, BAD_NODE_TIMEOUT)) {

            if (sendpacket(client->ip_port, packet, length) == length)
                ++sent;
        }
    }
    return sent;
}

/* Send the following packet to one random person who tells us they are connected to friend_id
*  returns the number of nodes it sent the packet to
*/
static int routeone_tofriend(uint8_t * friend_id, uint8_t * packet, uint32_t length)
{
    int num = friend_number(friend_id);
    if (num == -1)
        return 0;

    Friend * friend = &friends_list[num];
    Client_data * client;

    IP_Port ip_list[MAX_FRIEND_CLIENTS];
    int n = 0;
    uint32_t i;
    uint64_t temp_time = unix_time();

    for (i = 0; i < MAX_FRIEND_CLIENTS; ++i) {
        client = &friend->client_list[i];

        /*If ip is not zero and node is good */
        if(client->ret_ip_port.ip.i != 0 && !is_timeout(temp_time, client->ret_timestamp, BAD_NODE_TIMEOUT)) {
            ip_list[n] = client->ip_port;
            ++n;
        }
    }
    if (n < 1)
        return 0;
    if (sendpacket(ip_list[rand() % n], packet, length) == length)
        return 1;
    return 0;
}

/* Puts all the different ips returned by the nodes for a friend_id into array ip_portlist
 * ip_portlist must be at least MAX_FRIEND_CLIENTS big
 * returns the number of ips returned
 * return 0 if we are connected to friend or if no ips were found.
 * returns -1 if no such friend
 */
int friend_ips(IP_Port * ip_portlist, uint8_t * friend_id)
{
    uint32_t i;
    for (i = 0; i < num_friends; ++i) {
        /* Equal */
        if (id_equal(friends_list[i].client_id, friend_id))
            return friend_iplist(ip_portlist, i);
    }
    return -1;
}

/*----------------------------------------------------------------------------------*/
/*---------------------BEGINNING OF NAT PUNCHING FUNCTIONS--------------------------*/

static int send_NATping(uint8_t * public_key, uint64_t ping_id, uint8_t type)
{
    uint8_t data[sizeof(uint64_t) + 1];
    uint8_t packet[MAX_DATA_SIZE];

    int num = 0;

    data[0] = type;
    memcpy(data + 1, &ping_id, sizeof(uint64_t));
    /* 254 is NAT ping request packet id */
    int len = create_request(packet, public_key, data, sizeof(uint64_t) + 1, 254);

    if (len == -1)
        return -1;

    if (type == 0) /*If packet is request use many people to route it*/
        num = route_tofriend(public_key, packet, len);
    else if (type == 1) /*If packet is response use only one person to route it*/
        num = routeone_tofriend(public_key, packet, len);

    if (num == 0)
        return -1;
    return num;
}

/* Handle a received ping request for */
static int handle_NATping(uint8_t * packet, uint32_t length, IP_Port source)
{
    if (length < crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES + ENCRYPTION_PADDING 
            || length > MAX_DATA_SIZE + ENCRYPTION_PADDING)
        return 1;

    /* check if request is for us. */
    if (id_equal(packet + 1, self_public_key)) {
        uint8_t public_key[crypto_box_PUBLICKEYBYTES];
        uint8_t data[MAX_DATA_SIZE];

        int len = handle_request(public_key, data, packet, length);
        if (len != sizeof(uint64_t) + 1)
            return 1;

        uint64_t ping_id;
        memcpy(&ping_id, data + 1, sizeof(uint64_t));

        int friendnumber = friend_number(public_key);
        if (friendnumber == -1)
            return 1;

        Friend * friend = &friends_list[friendnumber];

        if (data[0] == 0) {
            /* 1 is reply */
            send_NATping(public_key, ping_id, 1);
            friend->recvNATping_timestamp = unix_time();
            return 0;
        } else if (data[0] == 1) {
            if (friend->NATping_id == ping_id) {
                friend->NATping_id = ((uint64_t)random_int() << 32) + random_int();
                friend->hole_punching = 1;
                return 0;
            }
        }
        return 1;
    }

    /* if request is not for us, try routing it. */
    route_packet(packet + 1, packet, length);

    return 0;
}

/* Get the most common ip in the ip_portlist
 * Only return ip if it appears in list min_num or more
 * len must not be bigger than MAX_FRIEND_CLIENTS
 * return ip of 0 if failure 
 */
static IP NAT_commonip(IP_Port * ip_portlist, uint16_t len, uint16_t min_num)
{
    IP zero = {{0}};
    if(len > MAX_FRIEND_CLIENTS)
        return zero;

    uint32_t i, j;
    uint16_t numbers[MAX_FRIEND_CLIENTS] = {0};

    for(i = 0; i < len; ++i) {
        for(j = 0; j < len; ++j) {
            if(ip_portlist[i].ip.i == ip_portlist[j].ip.i)
                ++numbers[i];
        }
        if(numbers[i] >= min_num)
            return ip_portlist[i].ip;
    }
    return zero;
}

/* Return all the ports for one ip in a list
 * portlist must be at least len long
 * where len is the length of ip_portlist
 * returns the number of ports and puts the list of ports in portlist
 */
static uint16_t NAT_getports(uint16_t * portlist, IP_Port * ip_portlist, uint16_t len, IP ip)
{
    uint32_t i;
    uint16_t num = 0;

    for(i = 0; i < len; ++i) {
        if(ip_portlist[i].ip.i == ip.i) {
            portlist[num] = ntohs(ip_portlist[i].port);
            ++num;
        }
    }
    return num;
}

static void punch_holes(IP ip, uint16_t * port_list, uint16_t numports, uint16_t friend_num)
{
    if(numports > MAX_FRIEND_CLIENTS || numports == 0)
        return;

    uint32_t i;
    uint32_t top = friends_list[friend_num].punching_index + MAX_PUNCHING_PORTS;

    for(i = friends_list[friend_num].punching_index; i != top; i++) {
        /*TODO: improve port guessing algorithm*/
        uint16_t port = port_list[(i/2) % numports] + (i/(2*numports))*((i % 2) ? -1 : 1);
        IP_Port pinging = {ip, htons(port)};
        send_ping_request(pinging, (clientid_t*) &friends_list[friend_num].client_id);
    }
    friends_list[friend_num].punching_index = i;
}

static void doNAT(void)
{
    uint32_t i;
    uint64_t temp_time = unix_time();

    for (i = 0; i < num_friends; ++i) {
        IP_Port ip_list[MAX_FRIEND_CLIENTS];
        int num = friend_iplist(ip_list, i);

        /*If already connected or friend is not online don't try to hole punch*/
        if (num < MAX_FRIEND_CLIENTS/2)
            continue;

        if (friends_list[i].NATping_timestamp + PUNCH_INTERVAL < temp_time) {
            send_NATping(friends_list[i].client_id, friends_list[i].NATping_id, 0); /*0 is request*/
            friends_list[i].NATping_timestamp = temp_time;
        }
        if (friends_list[i].hole_punching == 1 &&
            friends_list[i].punching_timestamp + PUNCH_INTERVAL < temp_time && 
            friends_list[i].recvNATping_timestamp + PUNCH_INTERVAL*2 >= temp_time) {

            IP ip = NAT_commonip(ip_list, num, MAX_FRIEND_CLIENTS/2);
            if (ip.i == 0)
                continue;

            uint16_t port_list[MAX_FRIEND_CLIENTS];
            uint16_t numports = NAT_getports(port_list, ip_list, num, ip);
            punch_holes(ip, port_list, numports, i);

            friends_list[i].punching_timestamp = temp_time;
            friends_list[i].hole_punching = 0;
        }
    }
}

/*----------------------------------------------------------------------------------*/
/*-----------------------END OF NAT PUNCHING FUNCTIONS------------------------------*/

int DHT_handlepacket(uint8_t * packet, uint32_t length, IP_Port source)
{
    switch (packet[0]) {
    case 0:
        return handle_ping_request(packet, length, source);

    case 1:
        return handle_ping_response(packet, length, source);

    case 2:
        return handle_getnodes(packet, length, source);

    case 3:
        return handle_sendnodes(packet, length, source);

    case 254:
        return handle_NATping(packet, length, source);

    default:
        return 1;

    }

    return 0;
}

void doDHT(void)
{
    doClose();
    doDHTFriends();
    doNAT();
}

/* get the size of the DHT (for saving) */
uint32_t DHT_size(void)
{
    return sizeof(close_clientlist) + sizeof(Friend) * num_friends;
}

/* save the DHT in data where data is an array of size DHT_size() */
void DHT_save(uint8_t * data)
{
    memcpy(data, close_clientlist, sizeof(close_clientlist));
    memcpy(data + sizeof(close_clientlist), friends_list, sizeof(Friend) * num_friends);
}

/* load the DHT from data of size size;
 * return -1 if failure
 * return 0 if success 
 */
int DHT_load(uint8_t * data, uint32_t size)
{
    init_ping();

    if(size < sizeof(close_clientlist))
        return -1;

    if((size - sizeof(close_clientlist)) % sizeof(Friend) != 0)
        return -1;

    uint32_t i, j;
    uint16_t temp;
    /* uint64_t temp_time = unix_time(); */

    Client_data * client;

    temp = (size - sizeof(close_clientlist))/sizeof(Friend);

    if(temp != 0) {
        Friend * tempfriends_list = (Friend *)(data + sizeof(close_clientlist));

        for(i = 0; i < temp; ++i) {
            DHT_addfriend(tempfriends_list[i].client_id);

            for(j = 0; j < MAX_FRIEND_CLIENTS; ++j) {
                client = &tempfriends_list[i].client_list[j];
                if(client->timestamp != 0)
                    getnodes(client->ip_port, client->client_id, tempfriends_list[i].client_id);
            }
        }
    }
    Client_data * tempclose_clientlist = (Client_data *)data;

    for(i = 0; i < LCLIENT_LIST; ++i) {
        if(tempclose_clientlist[i].timestamp != 0)
            DHT_bootstrap(  tempclose_clientlist[i].ip_port, 
                            tempclose_clientlist[i].client_id );
    }
    return 0;
}

/* returns 0 if we are not connected to the DHT
 * returns 1 if we are 
 */
int DHT_isconnected(void)
{
    uint32_t i;
    uint64_t temp_time = unix_time();

    for(i = 0; i < LCLIENT_LIST; ++i) {
      if(!is_timeout(temp_time, close_clientlist[i].timestamp, BAD_NODE_TIMEOUT))
            return 1;
    }
    return 0;
}