toxcore/core/DHT.c

/* DHT.c
 * 
 * An implementation of the DHT as seen in docs/DHT.txt
 *
 *  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"

typedef struct
{
    uint8_t client_id[CLIENT_ID_SIZE];
    IP_Port ip_port;
    uint32_t timestamp;
    uint32_t last_pinged;
    IP_Port ret_ip_port;/* The ip_port returned by this node for the friend 
                           (for nodes in friends_list) or us (for nodes in close_clientlist) */
    uint32_t ret_timestamp;                       
}Client_data;

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

typedef struct
{
    uint8_t client_id[CLIENT_ID_SIZE];
    Client_data client_list[MAX_FRIEND_CLIENTS];
    uint32_t lastgetnode; /* time at which the last get_nodes request was sent. */
    
    /*Symetric NAT hole punching stuff*/
    uint8_t hole_punching; /*0 if not hole punching, 1 if currently hole punching */
    uint32_t punching_index;
    uint32_t punching_timestamp;
    uint64_t NATping_id;
    uint32_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;
    uint32_t timestamp;
    
}Pinged;

/* Our client id/public key */
uint8_t self_public_key[CLIENT_ID_SIZE];
uint8_t self_secret_key[crypto_box_SECRETKEYBYTES];

/* TODO: Move these out of here and put them into the .c file.
   A list of the clients mathematically closest to ours. */
#define LCLIENT_LIST 32
static Client_data close_clientlist[LCLIENT_LIST];

static Friend * friends_list;
static uint16_t num_friends;

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

static Pinged pings[LPING_ARRAY];

#define LSEND_NODES_ARRAY LPING_ARRAY/2

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 */
int id_closest(uint8_t * client_id, uint8_t * client_id1, uint8_t * client_id2) /* tested */
{
    uint32_t i;
    for(i = 0; i < CLIENT_ID_SIZE; ++i) {
        if(abs(client_id[i] ^ client_id1[i]) < abs(client_id[i] ^ client_id2[i])) {
            return 1;
        } else if(abs(client_id[i] ^ client_id1[i]) > abs(client_id[i] ^ client_id2[i])) {
            return 2;
        }
    }
    
    return 0;
    
}

/* check if client with client_id is already in list of length length.
   if it is set it's 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. */
int client_in_list(Client_data * list, uint32_t length, uint8_t * client_id, IP_Port ip_port)
{
    uint32_t i;
    uint32_t temp_time = unix_time();
    
    for(i = 0; i < length; ++i) {
        /*If ip_port is assigned to a different client_id replace it*/
        if(list[i].ip_port.ip.i == ip_port.ip.i &&
        list[i].ip_port.port == ip_port.port) {
            memcpy(list[i].client_id, client_id, CLIENT_ID_SIZE);
        }
        
        if(memcmp(list[i].client_id, client_id, CLIENT_ID_SIZE) == 0) {
            /* 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) */
int client_in_nodelist(Node_format * list, uint32_t length, uint8_t * client_id)
{
    uint32_t i;
    for(i = 0; i < length; ++i) {
        if(memcmp(list[i].client_id, client_id, CLIENT_ID_SIZE) == 0) {

            return 1;
        }
    }
    return 0;
    
}

/*Return the friend number from the client_id
 Return -1 if failure, number of friend if success*/
static int friend_number(uint8_t * client_id)
{
    uint32_t i;
    for(i = 0; i < num_friends; ++i) {
        if(memcmp(friends_list[i].client_id, client_id, CLIENT_ID_SIZE) == 0) /* Equal */
        {
            return i;
        }
    }
    return -1;
}

/* 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

/* 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: Make this function much more efficient. */
int get_close_nodes(uint8_t * client_id, Node_format * nodes_list)
{
    uint32_t i, j, k;
    int num_nodes=0;
    uint32_t temp_time = unix_time();
    for(i = 0; i < LCLIENT_LIST; ++i) {
        if(close_clientlist[i].timestamp + BAD_NODE_TIMEOUT > temp_time && 
        !client_in_nodelist(nodes_list, MAX_SENT_NODES,close_clientlist[i].client_id)) {
        /* if node is good and not already in list. */
            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) {
                if(id_closest(client_id, nodes_list[j].client_id, close_clientlist[i].client_id) == 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) {
            if(friends_list[i].client_list[j].timestamp + BAD_NODE_TIMEOUT > temp_time && 
            !client_in_nodelist(nodes_list, MAX_SENT_NODES,friends_list[i].client_list[j].client_id)) {
            /* if node is good and not already in list. */
                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) {
                    if(id_closest(client_id, nodes_list[k].client_id, friends_list[i].client_list[j].client_id) == 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) */
int replace_bad(Client_data * list, uint32_t length, uint8_t * client_id, IP_Port ip_port) /* tested */
{
    uint32_t i;
    uint32_t temp_time = unix_time();
    for(i = 0; i < length; ++i) {
        if(list[i].timestamp + BAD_NODE_TIMEOUT < temp_time) /* if node is bad. */ {
            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 */
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;
    uint32_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 */
void returnedip_ports(IP_Port ip_port, uint8_t * client_id, uint8_t * nodeclient_id)
{
    uint32_t i, j;
    uint32_t temp_time = unix_time();
    if(memcmp(client_id, self_public_key, CLIENT_ID_SIZE) == 0) {
        for(i = 0; i < LCLIENT_LIST; ++i) {
            if(memcmp(nodeclient_id, close_clientlist[i].client_id, CLIENT_ID_SIZE) == 0) {
                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(memcmp(client_id, friends_list[i].client_id, CLIENT_ID_SIZE) == 0) {
            for(j = 0; j < MAX_FRIEND_CLIENTS; ++j) {
                if(memcmp(nodeclient_id, friends_list[i].client_list[j].client_id, CLIENT_ID_SIZE) == 0) {
                    friends_list[i].client_list[j].ret_ip_port = ip_port;
                    friends_list[i].client_list[j].ret_timestamp = temp_time;
                    return;
                }
            }
        }
    }
}

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

/* check if we are currently pinging an ip_port and/or a ping_id
   variables with values of zero will not be checked.
   if we are already, return 1
   else return 0
TODO: optimize this */
int is_pinging(IP_Port ip_port, uint64_t ping_id)
{
    uint32_t i;
    uint8_t pinging;
    uint32_t temp_time = unix_time();

    for(i = 0; i < LPING_ARRAY; ++i ) {
        if((pings[i].timestamp + PING_TIMEOUT) > temp_time) {
            pinging = 0;
            if(ip_port.ip.i != 0) {
                if(pings[i].ip_port.ip.i == ip_port.ip.i &&
                pings[i].ip_port.port == ip_port.port) {
                        ++pinging;
                }
            }
            if(ping_id != 0) {
                if(pings[i].ping_id == ping_id)
                {
                        ++pinging;
                }
            }
            if(pinging == (ping_id != 0) + (ip_port.ip.i != 0)) {
                    return 1;
            }
            
        }
    }

    return 0;
    
}

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

    for(i = 0; i < LSEND_NODES_ARRAY; ++i ) {
        if((send_nodes[i].timestamp + PING_TIMEOUT) > temp_time) {
            pinging = 0;
            if(ip_port.ip.i != 0) {
                if(send_nodes[i].ip_port.ip.i == ip_port.ip.i &&
                send_nodes[i].ip_port.port == ip_port.port) {
                        ++pinging;
                }
            }
            if(ping_id != 0) {
                if(send_nodes[i].ping_id == ping_id) {
                        ++pinging;
                }
            }
            if(pinging == (ping_id != 0) + (ip_port.ip.i != 0)) {
                    return 1;
            }
            
        }
    }

    return 0;
    
}

/* Add a new ping request to the list of ping requests
   returns the ping_id to put in the ping request
   returns 0 if problem.
   TODO: optimize this */
uint64_t add_pinging(IP_Port ip_port)
{
    uint32_t i, j;
    uint64_t ping_id = ((uint64_t)random_int() << 32) + random_int();
    uint32_t temp_time = unix_time();
    
    for(i = 0; i < PING_TIMEOUT; ++i ) {
        for(j = 0; j < LPING_ARRAY; ++j ) {
            if((pings[j].timestamp + PING_TIMEOUT - i) < temp_time) {
                    pings[j].timestamp = temp_time;
                    pings[j].ip_port = ip_port;
                    pings[j].ping_id = ping_id;
                    return ping_id;
            }
        }
    }
    return 0;
    
}

/* Same but for get node requests */
uint64_t add_gettingnodes(IP_Port ip_port)
{
    uint32_t i, j;
    uint64_t ping_id = ((uint64_t)random_int() << 32) + random_int();
    uint32_t temp_time = unix_time();
    
    for(i = 0; i < PING_TIMEOUT; ++i ) {
        for(j = 0; j < LSEND_NODES_ARRAY; ++j ) {
            if((send_nodes[j].timestamp + PING_TIMEOUT - i) < temp_time) {
                    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 ping request
   Ping request only works if none has been sent to that ip/port in the last 5 seconds. */
static int pingreq(IP_Port ip_port, uint8_t * public_key)
{
    if(memcmp(public_key, self_public_key, CLIENT_ID_SIZE) == 0) /* check if packet is gonna be sent to ourself */ {
        return 1;
    }
    
    if(is_pinging(ip_port, 0)) {
        return 1;
    }
    
    uint64_t ping_id = add_pinging(ip_port);
    if(ping_id == 0) {
        return 1;
    }
    
    uint8_t data[1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES + sizeof(ping_id) + ENCRYPTION_PADDING];
    uint8_t encrypt[sizeof(ping_id) + ENCRYPTION_PADDING];
    uint8_t nonce[crypto_box_NONCEBYTES];
    random_nonce(nonce);
    
    int len = encrypt_data(public_key, self_secret_key, nonce, (uint8_t *)&ping_id, sizeof(ping_id), encrypt);
    if(len != sizeof(ping_id) + ENCRYPTION_PADDING) {
        return -1;
    }
    data[0] = 0;
    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 ping response */
static int pingres(IP_Port ip_port, uint8_t * public_key, uint64_t ping_id)
{
     /* check if packet is gonna be sent to ourself */
    if(memcmp(public_key, self_public_key, CLIENT_ID_SIZE) == 0) {
        return 1;
    }
    
    uint8_t data[1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES + sizeof(ping_id) + ENCRYPTION_PADDING];
    uint8_t encrypt[sizeof(ping_id) + ENCRYPTION_PADDING];
    uint8_t nonce[crypto_box_NONCEBYTES];
    random_nonce(nonce);
    
    int len = encrypt_data(public_key, self_secret_key, nonce, (uint8_t *)&ping_id, sizeof(ping_id), encrypt);
    if(len != sizeof(ping_id) + ENCRYPTION_PADDING) {
        return -1;
    }
    data[0] = 1;
    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 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(memcmp(public_key, self_public_key, CLIENT_ID_SIZE) == 0) {
        return 1;
    }
    
    if(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)
{
    if(memcmp(public_key, self_public_key, CLIENT_ID_SIZE) == 0) /* check if packet is gonna be sent to ourself */ {
        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);
   
}

/* Packet handling functions
   One to handle each types of packets we receive
   return 0 if handled correctly, 1 if packet is bad. */
int handle_pingreq(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) + ENCRYPTION_PADDING) {
        return 1;
    }
	/* check if packet is from ourself. */
    if(memcmp(packet + 1, self_public_key, CLIENT_ID_SIZE) == 0)  {
        return 1;
    }
    
    
    
    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) + ENCRYPTION_PADDING, (uint8_t *)&ping_id);
    if(len != sizeof(ping_id)) {
        return 1;
    }

    
    pingres(source, packet + 1, ping_id);
    
    pingreq(source, packet + 1); /* TODO: make this smarter? */
 
    return 0;
    
}

int handle_pingres(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) + ENCRYPTION_PADDING) {
        return 1;
    }
    if(memcmp(packet + 1, self_public_key, CLIENT_ID_SIZE) == 0) /* check if packet is from ourself. */ {
        return 1;
    }
    
    
    
    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) + ENCRYPTION_PADDING, (uint8_t *)&ping_id);
    if(len != sizeof(ping_id)) {
        return 1;
    }
    
    if(is_pinging(source, ping_id)) {
        addto_lists(source, packet + 1);
        return 0;
    }
    return 1;
    
}

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(memcmp(packet + 1, self_public_key, CLIENT_ID_SIZE) == 0) {
        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);
    
    pingreq(source, packet + 1); /* TODO: make this smarter? */
    
    return 0;
    
}

int handle_sendnodes(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)
                 + sizeof(Node_format) * MAX_SENT_NODES + ENCRYPTION_PADDING) || 
    (length - (1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES + sizeof(ping_id) 
                 + ENCRYPTION_PADDING)) % (sizeof(Node_format)) != 0 ||
     length < 1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES + sizeof(ping_id) 
                                 + sizeof(Node_format) + ENCRYPTION_PADDING) {
        return 1;
    } 
    uint32_t num_nodes = (length - (1 + CLIENT_ID_SIZE + crypto_box_NONCEBYTES 
                         + sizeof(ping_id) + ENCRYPTION_PADDING)) / 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)  {
        pingreq(nodes_list[i].ip_port, 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;
    if(num_friends == 0) {
        temp = malloc(sizeof(Friend));
    } else {
        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(memcmp(friends_list[i].client_id, client_id, CLIENT_ID_SIZE) == 0){
            --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) {
                friends_list = temp;
            }
            return 0;
        }
    }
    return 1;
}

/* TODO: Optimize this. */
IP_Port DHT_getfriendip(uint8_t * client_id)
{
    uint32_t i, j;
    IP_Port empty = {{{0}}, 0};
    uint32_t temp_time = unix_time();
    for(i = 0; i < num_friends; ++i) {
	     /* Equal */
        if(memcmp(friends_list[i].client_id, client_id, CLIENT_ID_SIZE) == 0) {
            for(j = 0; j < MAX_FRIEND_CLIENTS; ++j) {
                if(memcmp(friends_list[i].client_list[j].client_id, client_id, CLIENT_ID_SIZE) == 0 && 
                 friends_list[i].client_list[j].timestamp + BAD_NODE_TIMEOUT > temp_time) {
                    return friends_list[i].client_list[j].ip_port;
                }   
            }        
            return empty;
        }
    }
    empty.ip.i = 1;
    return empty;
    
}

/* 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

/* 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. */
void doDHTFriends()
{
    uint32_t i, j;
    uint32_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(friends_list[i].client_list[j].timestamp + Kill_NODE_TIMEOUT > temp_time) /* if node is not dead. */ {
                if((friends_list[i].client_list[j].last_pinged + PING_INTERVAL) <= temp_time) {
                    pingreq(friends_list[i].client_list[j].ip_port, friends_list[i].client_list[j].client_id);
                    friends_list[i].client_list[j].last_pinged = temp_time;
                }
                if(friends_list[i].client_list[j].timestamp + BAD_NODE_TIMEOUT > temp_time) /* if node is good. */ {
                    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 uint32_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. */
void doClose() /* tested */
{
    uint32_t i;
    uint32_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(close_clientlist[i].timestamp + Kill_NODE_TIMEOUT > temp_time) {
            if((close_clientlist[i].last_pinged + PING_INTERVAL) <= temp_time)
            {
                pingreq(close_clientlist[i].ip_port, close_clientlist[i].client_id);
                close_clientlist[i].last_pinged = temp_time;
            }
			/* if node is good. */
            if(close_clientlist[i].timestamp + BAD_NODE_TIMEOUT > temp_time) {
                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(memcmp(client_id, close_clientlist[i].client_id, CLIENT_ID_SIZE) == 0) {
            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;
    uint32_t temp_time = unix_time();
    if(friend_num >= num_friends) {
        return -1;
    }
    for(i = 0; i < MAX_FRIEND_CLIENTS; ++i)
    {
	    /*If ip is not zero and node is good */
        if(friends_list[friend_num].client_list[i].ret_ip_port.ip.i != 0 && 
            friends_list[friend_num].client_list[i].ret_timestamp + BAD_NODE_TIMEOUT > temp_time) {
            if(memcmp(friends_list[friend_num].client_list[i].client_id, friends_list[friend_num].client_id, CLIENT_ID_SIZE) == 0 ) {
                return 0;
            }
            ip_portlist[num_ips] = friends_list[friend_num].client_list[i].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)
{
    uint32_t i, j;
    uint32_t sent = 0;
    uint32_t temp_time = unix_time();
    for(i = 0; i < num_friends; ++i) {
	    /* Equal */
        if(memcmp(friends_list[i].client_id, friend_id, CLIENT_ID_SIZE) == 0)  {
            for(j = 0; j < MAX_FRIEND_CLIENTS; ++j) {
			     /*If ip is not zero and node is good */
                if(friends_list[i].client_list[j].ret_ip_port.ip.i != 0 && 
                   friends_list[i].client_list[j].ret_timestamp + BAD_NODE_TIMEOUT > temp_time) {
                    if(sendpacket(friends_list[i].client_list[j].ip_port, packet, length) == length) {
                        ++sent;
                    }
                }
            }
            return sent;
        }
    }
    return 0;
}

/* 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 */
int routeone_tofriend(uint8_t * friend_id, uint8_t * packet, uint32_t length)
{
    int num = friend_number(friend_id);
    if(num == -1) {
        return 0;
    }
    
    IP_Port ip_list[MAX_FRIEND_CLIENTS];
    int n = 0;
    uint32_t i;
    uint32_t temp_time = unix_time();
    for(i = 0; i < MAX_FRIEND_CLIENTS; ++i) {
	    /*If ip is not zero and node is good */
        if(friends_list[num].client_list[i].ret_ip_port.ip.i != 0 && 
            friends_list[num].client_list[i].ret_timestamp + BAD_NODE_TIMEOUT > temp_time) {
            ip_list[n] = friends_list[num].client_list[i].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(memcmp(friends_list[i].client_id, friend_id, CLIENT_ID_SIZE) == 0) {
            return friend_iplist(ip_portlist, i);
        }
    }
    return -1;
}

/*BEGINNING OF NAT PUNCHING FUNCTIONS*/

int send_NATping(uint8_t * public_key, uint64_t ping_id, uint8_t type)
{
    uint8_t data[sizeof(uint64_t) + 1];
    data[0] = type;
    memcpy(data + 1, &ping_id, sizeof(uint64_t));
    
    uint8_t packet[MAX_DATA_SIZE];
    int len = create_request(packet, public_key, data, sizeof(uint64_t) + 1, 254); /* 254 is NAT ping request packet id */
    if(len == -1) {
        return -1;
    }
    int num = 0;
    if(type == 0) {
        num = route_tofriend(public_key, packet, len);/*If packet is request use many people to route it*/
    }
    else if(type == 1) {
        num = routeone_tofriend(public_key, packet, len);/*If packet is response use only one person to route it*/
    }
    if(num == 0) {
        return -1;
    }
    return num;
}

/* Handle a recieved ping request for */
int handle_NATping(uint8_t * packet, uint32_t length, IP_Port source)
{
    if(length <= crypto_box_PUBLICKEYBYTES * 2 + crypto_box_NONCEBYTES + 1 + ENCRYPTION_PADDING &&
    length > MAX_DATA_SIZE + ENCRYPTION_PADDING) {
        return 1;
    }
	/* check if request is for us. */
    if(memcmp(packet + 1, self_public_key, crypto_box_PUBLICKEYBYTES) == 0) {
        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;
        }
        
        if(data[0] == 0) {
            send_NATping(public_key, ping_id, 1);/*1 is reply*/
            return 0;
        } else if (data[0] == 1) {
            if(friends_list[friendnumber].NATping_id == ping_id)
            {
                friends_list[friendnumber].NATping_id = ((uint64_t)random_int() << 32) + random_int();
                friends_list[friendnumber].hole_punching = 1;
                return 0;
            }
        }
        return 1;
    }
	/* if request is not for us, try routing it. */
    else {
        if(route_packet(packet + 1, packet, length) == length) {
            return 0;
        }
    }
    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;
}

#define MAX_PUNCHING_PORTS 32

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)};
        pingreq(pinging, friends_list[friend_num].client_id);
    }
    friends_list[friend_num].punching_index = i;
}

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

static void doNAT()
{
    uint32_t i;
    uint32_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 we are connected to friend or if friend is not online don't try to hole punch with him*/
        if(num < MAX_FRIEND_CLIENTS/2) {
            continue;
        }
        if(friends_list[i].hole_punching != 1) {
            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;
            }
        }
        else if(friends_list[i].punching_timestamp + PUNCH_INTERVAL < 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_pingreq(packet, length, source);   
        
    case 1:
        return handle_pingres(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()
{
    doClose();
    doDHTFriends();
    doNAT();
}

/* get the size of the DHT (for saving) */
uint32_t DHT_size()
{
    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)
{
    if(size < sizeof(close_clientlist)) {
        return -1;
    }
    if((size - sizeof(close_clientlist)) % sizeof(Friend) != 0) {
        return -1;
    }
    uint32_t i, j;
    /* uint32_t temp_time = unix_time(); */
    uint16_t temp;
    
    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) {
                if(tempfriends_list[i].client_list[j].timestamp != 0) {                
                    getnodes(tempfriends_list[i].client_list[j].ip_port, 
                             tempfriends_list[i].client_list[j].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()
{
    uint32_t i;
    uint32_t temp_time = unix_time();
    for(i = 0; i < LCLIENT_LIST; ++i) {
        if(close_clientlist[i].timestamp + BAD_NODE_TIMEOUT > temp_time) {
            return 1;
        }
    }
    return 0;
}