net_crypto.c

/* SPDX-License-Identifier: GPL-3.0-or-later
 * Copyright © 2016-2018 The TokTok team.
 * Copyright © 2013 Tox project.
 */

/**
 * Functions for the core network crypto.
 *
 * NOTE: This code has to be perfect. We don't mess around with encryption.
 */
#include "net_crypto.h"

#include <math.h>
#include <stdlib.h>
#include <string.h>

#include "list.h"
#include "mono_time.h"
#include "util.h"

typedef struct Packet_Data {
    uint64_t sent_time;
    uint16_t length;
    uint8_t data[MAX_CRYPTO_DATA_SIZE];
} Packet_Data;

typedef struct Packets_Array {
    Packet_Data *buffer[CRYPTO_PACKET_BUFFER_SIZE];
    uint32_t  buffer_start;
    uint32_t  buffer_end; /* packet numbers in array: `{buffer_start, buffer_end)` */
} Packets_Array;

typedef enum Crypto_Conn_State {
    /* the connection slot is free. This value is 0 so it is valid after
     * `crypto_memzero(...)` of the parent struct
     */
    CRYPTO_CONN_FREE = 0,
    CRYPTO_CONN_NO_CONNECTION,       /* the connection is allocated, but not yet used */
    CRYPTO_CONN_COOKIE_REQUESTING,   /* we are sending cookie request packets */
    CRYPTO_CONN_HANDSHAKE_SENT,      /* we are sending handshake packets */
    /* we are sending handshake packets.
     * we have received one from the other, but no data */
    CRYPTO_CONN_NOT_CONFIRMED,
    CRYPTO_CONN_ESTABLISHED,         /* the connection is established */
} Crypto_Conn_State;

typedef struct Crypto_Connection {
    uint8_t public_key[CRYPTO_PUBLIC_KEY_SIZE]; /* The real public key of the peer. */
    uint8_t recv_nonce[CRYPTO_NONCE_SIZE]; /* Nonce of received packets. */
    uint8_t sent_nonce[CRYPTO_NONCE_SIZE]; /* Nonce of sent packets. */
    uint8_t sessionpublic_key[CRYPTO_PUBLIC_KEY_SIZE]; /* Our public key for this session. */
    uint8_t sessionsecret_key[CRYPTO_SECRET_KEY_SIZE]; /* Our private key for this session. */
    uint8_t peersessionpublic_key[CRYPTO_PUBLIC_KEY_SIZE]; /* The public key of the peer. */
    uint8_t shared_key[CRYPTO_SHARED_KEY_SIZE]; /* The precomputed shared key from encrypt_precompute. */
    Crypto_Conn_State status; /* See Crypto_Conn_State documentation */
    uint64_t cookie_request_number; /* number used in the cookie request packets for this connection */
    uint8_t dht_public_key[CRYPTO_PUBLIC_KEY_SIZE]; /* The dht public key of the peer */

    uint8_t *temp_packet; /* Where the cookie request/handshake packet is stored while it is being sent. */
    uint16_t temp_packet_length;
    uint64_t temp_packet_sent_time; /* The time at which the last temp_packet was sent in ms. */
    uint32_t temp_packet_num_sent;

    IP_Port ip_portv4; /* The ip and port to contact this guy directly.*/
    IP_Port ip_portv6;
    uint64_t direct_lastrecv_timev4; /* The Time at which we last received a direct packet in ms. */
    uint64_t direct_lastrecv_timev6;

    uint64_t last_tcp_sent; /* Time the last TCP packet was sent. */

    Packets_Array send_array;
    Packets_Array recv_array;

    connection_status_cb *connection_status_callback;
    void *connection_status_callback_object;
    int connection_status_callback_id;

    connection_data_cb *connection_data_callback;
    void *connection_data_callback_object;
    int connection_data_callback_id;

    connection_lossy_data_cb *connection_lossy_data_callback;
    void *connection_lossy_data_callback_object;
    int connection_lossy_data_callback_id;

    uint64_t last_request_packet_sent;
    uint64_t direct_send_attempt_time;

    uint32_t packet_counter;
    double packet_recv_rate;
    uint64_t packet_counter_set;

    double packet_send_rate;
    uint32_t packets_left;
    uint64_t last_packets_left_set;
    double last_packets_left_rem;

    double packet_send_rate_requested;
    uint32_t packets_left_requested;
    uint64_t last_packets_left_requested_set;
    double last_packets_left_requested_rem;

    uint32_t last_sendqueue_size[CONGESTION_QUEUE_ARRAY_SIZE];
    uint32_t last_sendqueue_counter;
    long signed int last_num_packets_sent[CONGESTION_LAST_SENT_ARRAY_SIZE];
    long signed int last_num_packets_resent[CONGESTION_LAST_SENT_ARRAY_SIZE];
    uint32_t packets_sent;
    uint32_t packets_resent;
    uint64_t last_congestion_event;
    uint64_t rtt_time;

    /* TCP_connection connection_number */
    unsigned int connection_number_tcp;

    uint8_t maximum_speed_reached;

    /* Must be a pointer, because the struct is moved in memory */
    pthread_mutex_t *mutex;

    dht_pk_cb *dht_pk_callback;
    void *dht_pk_callback_object;
    uint32_t dht_pk_callback_number;
} Crypto_Connection;

static const Crypto_Connection empty_crypto_connection = {{0}};

struct Net_Crypto {
    const Logger *log;
    Mono_Time *mono_time;

    DHT *dht;
    TCP_Connections *tcp_c;

    Crypto_Connection *crypto_connections;
    pthread_mutex_t tcp_mutex;

    pthread_mutex_t connections_mutex;
    unsigned int connection_use_counter;

    uint32_t crypto_connections_length; /* Length of connections array. */

    /* Our public and secret keys. */
    uint8_t self_public_key[CRYPTO_PUBLIC_KEY_SIZE];
    uint8_t self_secret_key[CRYPTO_SECRET_KEY_SIZE];

    /* The secret key used for cookies */
    uint8_t secret_symmetric_key[CRYPTO_SYMMETRIC_KEY_SIZE];

    new_connection_cb *new_connection_callback;
    void *new_connection_callback_object;

    /* The current optimal sleep time */
    uint32_t current_sleep_time;

    BS_List ip_port_list;
};

const uint8_t *nc_get_self_public_key(const Net_Crypto *c)
{
    return c->self_public_key;
}

const uint8_t *nc_get_self_secret_key(const Net_Crypto *c)
{
    return c->self_secret_key;
}

TCP_Connections *nc_get_tcp_c(const Net_Crypto *c)
{
    return c->tcp_c;
}

DHT *nc_get_dht(const Net_Crypto *c)
{
    return c->dht;
}

non_null()
static bool crypt_connection_id_is_valid(const Net_Crypto *c, int crypt_connection_id)
{
    if ((uint32_t)crypt_connection_id >= c->crypto_connections_length) {
        return false;
    }

    if (c->crypto_connections == nullptr) {
        return false;
    }

    const Crypto_Conn_State status = c->crypto_connections[crypt_connection_id].status;

    return status != CRYPTO_CONN_NO_CONNECTION && status != CRYPTO_CONN_FREE;
}

/** cookie timeout in seconds */
#define COOKIE_TIMEOUT 15
#define COOKIE_DATA_LENGTH (uint16_t)(CRYPTO_PUBLIC_KEY_SIZE * 2)
#define COOKIE_CONTENTS_LENGTH (uint16_t)(sizeof(uint64_t) + COOKIE_DATA_LENGTH)
#define COOKIE_LENGTH (uint16_t)(CRYPTO_NONCE_SIZE + COOKIE_CONTENTS_LENGTH + CRYPTO_MAC_SIZE)

#define COOKIE_REQUEST_PLAIN_LENGTH (uint16_t)(COOKIE_DATA_LENGTH + sizeof(uint64_t))
#define COOKIE_REQUEST_LENGTH (uint16_t)(1 + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_NONCE_SIZE + COOKIE_REQUEST_PLAIN_LENGTH + CRYPTO_MAC_SIZE)
#define COOKIE_RESPONSE_LENGTH (uint16_t)(1 + CRYPTO_NONCE_SIZE + COOKIE_LENGTH + sizeof(uint64_t) + CRYPTO_MAC_SIZE)

/** Create a cookie request packet and put it in packet.
 * dht_public_key is the dht public key of the other
 *
 * packet must be of size COOKIE_REQUEST_LENGTH or bigger.
 *
 * return -1 on failure.
 * return COOKIE_REQUEST_LENGTH on success.
 */
non_null()
static int create_cookie_request(const Net_Crypto *c, uint8_t *packet, const uint8_t *dht_public_key,
                                 uint64_t number, uint8_t *shared_key)
{
    uint8_t plain[COOKIE_REQUEST_PLAIN_LENGTH];
    uint8_t padding[CRYPTO_PUBLIC_KEY_SIZE] = {0};

    memcpy(plain, c->self_public_key, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(plain + CRYPTO_PUBLIC_KEY_SIZE, padding, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(plain + (CRYPTO_PUBLIC_KEY_SIZE * 2), &number, sizeof(uint64_t));

    dht_get_shared_key_sent(c->dht, shared_key, dht_public_key);
    uint8_t nonce[CRYPTO_NONCE_SIZE];
    random_nonce(nonce);
    packet[0] = NET_PACKET_COOKIE_REQUEST;
    memcpy(packet + 1, dht_get_self_public_key(c->dht), CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(packet + 1 + CRYPTO_PUBLIC_KEY_SIZE, nonce, CRYPTO_NONCE_SIZE);
    int len = encrypt_data_symmetric(shared_key, nonce, plain, sizeof(plain),
                                     packet + 1 + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_NONCE_SIZE);

    if (len != COOKIE_REQUEST_PLAIN_LENGTH + CRYPTO_MAC_SIZE) {
        return -1;
    }

    return (1 + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_NONCE_SIZE + len);
}

/** Create cookie of length COOKIE_LENGTH from bytes of length COOKIE_DATA_LENGTH using encryption_key
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int create_cookie(const Mono_Time *mono_time, uint8_t *cookie, const uint8_t *bytes,
                         const uint8_t *encryption_key)
{
    uint8_t contents[COOKIE_CONTENTS_LENGTH];
    const uint64_t temp_time = mono_time_get(mono_time);
    memcpy(contents, &temp_time, sizeof(temp_time));
    memcpy(contents + sizeof(temp_time), bytes, COOKIE_DATA_LENGTH);
    random_nonce(cookie);
    int len = encrypt_data_symmetric(encryption_key, cookie, contents, sizeof(contents), cookie + CRYPTO_NONCE_SIZE);

    if (len != COOKIE_LENGTH - CRYPTO_NONCE_SIZE) {
        return -1;
    }

    return 0;
}

/** Open cookie of length COOKIE_LENGTH to bytes of length COOKIE_DATA_LENGTH using encryption_key
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int open_cookie(const Mono_Time *mono_time, uint8_t *bytes, const uint8_t *cookie,
                       const uint8_t *encryption_key)
{
    uint8_t contents[COOKIE_CONTENTS_LENGTH];
    const int len = decrypt_data_symmetric(encryption_key, cookie, cookie + CRYPTO_NONCE_SIZE,
                                           COOKIE_LENGTH - CRYPTO_NONCE_SIZE, contents);

    if (len != sizeof(contents)) {
        return -1;
    }

    uint64_t cookie_time;
    memcpy(&cookie_time, contents, sizeof(cookie_time));
    const uint64_t temp_time = mono_time_get(mono_time);

    if (cookie_time + COOKIE_TIMEOUT < temp_time || temp_time < cookie_time) {
        return -1;
    }

    memcpy(bytes, contents + sizeof(cookie_time), COOKIE_DATA_LENGTH);
    return 0;
}


/** Create a cookie response packet and put it in packet.
 * request_plain must be COOKIE_REQUEST_PLAIN_LENGTH bytes.
 * packet must be of size COOKIE_RESPONSE_LENGTH or bigger.
 *
 * return -1 on failure.
 * return COOKIE_RESPONSE_LENGTH on success.
 */
non_null()
static int create_cookie_response(const Net_Crypto *c, uint8_t *packet, const uint8_t *request_plain,
                                  const uint8_t *shared_key, const uint8_t *dht_public_key)
{
    uint8_t cookie_plain[COOKIE_DATA_LENGTH];
    memcpy(cookie_plain, request_plain, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(cookie_plain + CRYPTO_PUBLIC_KEY_SIZE, dht_public_key, CRYPTO_PUBLIC_KEY_SIZE);
    uint8_t plain[COOKIE_LENGTH + sizeof(uint64_t)];

    if (create_cookie(c->mono_time, plain, cookie_plain, c->secret_symmetric_key) != 0) {
        return -1;
    }

    memcpy(plain + COOKIE_LENGTH, request_plain + COOKIE_DATA_LENGTH, sizeof(uint64_t));
    packet[0] = NET_PACKET_COOKIE_RESPONSE;
    random_nonce(packet + 1);
    int len = encrypt_data_symmetric(shared_key, packet + 1, plain, sizeof(plain), packet + 1 + CRYPTO_NONCE_SIZE);

    if (len != COOKIE_RESPONSE_LENGTH - (1 + CRYPTO_NONCE_SIZE)) {
        return -1;
    }

    return COOKIE_RESPONSE_LENGTH;
}

/** Handle the cookie request packet of length length.
 * Put what was in the request in request_plain (must be of size COOKIE_REQUEST_PLAIN_LENGTH)
 * Put the key used to decrypt the request into shared_key (of size CRYPTO_SHARED_KEY_SIZE) for use in the response.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int handle_cookie_request(const Net_Crypto *c, uint8_t *request_plain, uint8_t *shared_key,
                                 uint8_t *dht_public_key, const uint8_t *packet, uint16_t length)
{
    if (length != COOKIE_REQUEST_LENGTH) {
        return -1;
    }

    memcpy(dht_public_key, packet + 1, CRYPTO_PUBLIC_KEY_SIZE);
    dht_get_shared_key_sent(c->dht, shared_key, dht_public_key);
    int len = decrypt_data_symmetric(shared_key, packet + 1 + CRYPTO_PUBLIC_KEY_SIZE,
                                     packet + 1 + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_NONCE_SIZE, COOKIE_REQUEST_PLAIN_LENGTH + CRYPTO_MAC_SIZE,
                                     request_plain);

    if (len != COOKIE_REQUEST_PLAIN_LENGTH) {
        return -1;
    }

    return 0;
}

/** Handle the cookie request packet (for raw UDP)
 */
non_null(1, 2, 3) nullable(5)
static int udp_handle_cookie_request(void *object, const IP_Port *source, const uint8_t *packet, uint16_t length,
                                     void *userdata)
{
    const Net_Crypto *c = (const Net_Crypto *)object;
    uint8_t request_plain[COOKIE_REQUEST_PLAIN_LENGTH];
    uint8_t shared_key[CRYPTO_SHARED_KEY_SIZE];
    uint8_t dht_public_key[CRYPTO_PUBLIC_KEY_SIZE];

    if (handle_cookie_request(c, request_plain, shared_key, dht_public_key, packet, length) != 0) {
        return 1;
    }

    uint8_t data[COOKIE_RESPONSE_LENGTH];

    if (create_cookie_response(c, data, request_plain, shared_key, dht_public_key) != sizeof(data)) {
        return 1;
    }

    if ((uint32_t)sendpacket(dht_get_net(c->dht), source, data, sizeof(data)) != sizeof(data)) {
        return 1;
    }

    return 0;
}

/** Handle the cookie request packet (for TCP)
 */
non_null()
static int tcp_handle_cookie_request(const Net_Crypto *c, int connections_number, const uint8_t *packet,
                                     uint16_t length)
{
    uint8_t request_plain[COOKIE_REQUEST_PLAIN_LENGTH];
    uint8_t shared_key[CRYPTO_SHARED_KEY_SIZE];
    uint8_t dht_public_key[CRYPTO_PUBLIC_KEY_SIZE];

    if (handle_cookie_request(c, request_plain, shared_key, dht_public_key, packet, length) != 0) {
        return -1;
    }

    uint8_t data[COOKIE_RESPONSE_LENGTH];

    if (create_cookie_response(c, data, request_plain, shared_key, dht_public_key) != sizeof(data)) {
        return -1;
    }

    int ret = send_packet_tcp_connection(c->tcp_c, connections_number, data, sizeof(data));
    return ret;
}

/** Handle the cookie request packet (for TCP oob packets)
 */
non_null()
static int tcp_oob_handle_cookie_request(const Net_Crypto *c, unsigned int tcp_connections_number,
        const uint8_t *dht_public_key, const uint8_t *packet, uint16_t length)
{
    uint8_t request_plain[COOKIE_REQUEST_PLAIN_LENGTH];
    uint8_t shared_key[CRYPTO_SHARED_KEY_SIZE];
    uint8_t dht_public_key_temp[CRYPTO_PUBLIC_KEY_SIZE];

    if (handle_cookie_request(c, request_plain, shared_key, dht_public_key_temp, packet, length) != 0) {
        return -1;
    }

    if (public_key_cmp(dht_public_key, dht_public_key_temp) != 0) {
        return -1;
    }

    uint8_t data[COOKIE_RESPONSE_LENGTH];

    if (create_cookie_response(c, data, request_plain, shared_key, dht_public_key) != sizeof(data)) {
        return -1;
    }

    int ret = tcp_send_oob_packet(c->tcp_c, tcp_connections_number, dht_public_key, data, sizeof(data));
    return ret;
}

/** Handle a cookie response packet of length encrypted with shared_key.
 * put the cookie in the response in cookie
 *
 * cookie must be of length COOKIE_LENGTH.
 *
 * return -1 on failure.
 * return COOKIE_LENGTH on success.
 */
non_null()
static int handle_cookie_response(uint8_t *cookie, uint64_t *number,
                                  const uint8_t *packet, uint16_t length,
                                  const uint8_t *shared_key)
{
    if (length != COOKIE_RESPONSE_LENGTH) {
        return -1;
    }

    uint8_t plain[COOKIE_LENGTH + sizeof(uint64_t)];
    const int len = decrypt_data_symmetric(shared_key, packet + 1, packet + 1 + CRYPTO_NONCE_SIZE,
                                           length - (1 + CRYPTO_NONCE_SIZE), plain);

    if (len != sizeof(plain)) {
        return -1;
    }

    memcpy(cookie, plain, COOKIE_LENGTH);
    memcpy(number, plain + COOKIE_LENGTH, sizeof(uint64_t));
    return COOKIE_LENGTH;
}

#define HANDSHAKE_PACKET_LENGTH (1 + COOKIE_LENGTH + CRYPTO_NONCE_SIZE + CRYPTO_NONCE_SIZE + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_SHA512_SIZE + COOKIE_LENGTH + CRYPTO_MAC_SIZE)

/** Create a handshake packet and put it in packet.
 * cookie must be COOKIE_LENGTH bytes.
 * packet must be of size HANDSHAKE_PACKET_LENGTH or bigger.
 *
 * return -1 on failure.
 * return HANDSHAKE_PACKET_LENGTH on success.
 */
non_null()
static int create_crypto_handshake(const Net_Crypto *c, uint8_t *packet, const uint8_t *cookie, const uint8_t *nonce,
                                   const uint8_t *session_pk, const uint8_t *peer_real_pk, const uint8_t *peer_dht_pubkey)
{
    uint8_t plain[CRYPTO_NONCE_SIZE + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_SHA512_SIZE + COOKIE_LENGTH];
    memcpy(plain, nonce, CRYPTO_NONCE_SIZE);
    memcpy(plain + CRYPTO_NONCE_SIZE, session_pk, CRYPTO_PUBLIC_KEY_SIZE);
    crypto_sha512(plain + CRYPTO_NONCE_SIZE + CRYPTO_PUBLIC_KEY_SIZE, cookie, COOKIE_LENGTH);
    uint8_t cookie_plain[COOKIE_DATA_LENGTH];
    memcpy(cookie_plain, peer_real_pk, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(cookie_plain + CRYPTO_PUBLIC_KEY_SIZE, peer_dht_pubkey, CRYPTO_PUBLIC_KEY_SIZE);

    if (create_cookie(c->mono_time, plain + CRYPTO_NONCE_SIZE + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_SHA512_SIZE,
                      cookie_plain, c->secret_symmetric_key) != 0) {
        return -1;
    }

    random_nonce(packet + 1 + COOKIE_LENGTH);
    int len = encrypt_data(peer_real_pk, c->self_secret_key, packet + 1 + COOKIE_LENGTH, plain, sizeof(plain),
                           packet + 1 + COOKIE_LENGTH + CRYPTO_NONCE_SIZE);

    if (len != HANDSHAKE_PACKET_LENGTH - (1 + COOKIE_LENGTH + CRYPTO_NONCE_SIZE)) {
        return -1;
    }

    packet[0] = NET_PACKET_CRYPTO_HS;
    memcpy(packet + 1, cookie, COOKIE_LENGTH);

    return HANDSHAKE_PACKET_LENGTH;
}

/** Handle a crypto handshake packet of length.
 * put the nonce contained in the packet in nonce,
 * the session public key in session_pk
 * the real public key of the peer in peer_real_pk
 * the dht public key of the peer in dht_public_key and
 * the cookie inside the encrypted part of the packet in cookie.
 *
 * if expected_real_pk isn't NULL it denotes the real public key
 * the packet should be from.
 *
 * nonce must be at least CRYPTO_NONCE_SIZE
 * session_pk must be at least CRYPTO_PUBLIC_KEY_SIZE
 * peer_real_pk must be at least CRYPTO_PUBLIC_KEY_SIZE
 * cookie must be at least COOKIE_LENGTH
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null(1, 2, 3, 4, 5, 6, 7) nullable(9)
static int handle_crypto_handshake(const Net_Crypto *c, uint8_t *nonce, uint8_t *session_pk, uint8_t *peer_real_pk,
                                   uint8_t *dht_public_key, uint8_t *cookie, const uint8_t *packet, uint16_t length, const uint8_t *expected_real_pk)
{
    if (length != HANDSHAKE_PACKET_LENGTH) {
        return -1;
    }

    uint8_t cookie_plain[COOKIE_DATA_LENGTH];

    if (open_cookie(c->mono_time, cookie_plain, packet + 1, c->secret_symmetric_key) != 0) {
        return -1;
    }

    if (expected_real_pk != nullptr && public_key_cmp(cookie_plain, expected_real_pk) != 0) {
        return -1;
    }

    uint8_t cookie_hash[CRYPTO_SHA512_SIZE];
    crypto_sha512(cookie_hash, packet + 1, COOKIE_LENGTH);

    uint8_t plain[CRYPTO_NONCE_SIZE + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_SHA512_SIZE + COOKIE_LENGTH];
    int len = decrypt_data(cookie_plain, c->self_secret_key, packet + 1 + COOKIE_LENGTH,
                           packet + 1 + COOKIE_LENGTH + CRYPTO_NONCE_SIZE,
                           HANDSHAKE_PACKET_LENGTH - (1 + COOKIE_LENGTH + CRYPTO_NONCE_SIZE), plain);

    if (len != sizeof(plain)) {
        return -1;
    }

    if (crypto_sha512_cmp(cookie_hash, plain + CRYPTO_NONCE_SIZE + CRYPTO_PUBLIC_KEY_SIZE) != 0) {
        return -1;
    }

    memcpy(nonce, plain, CRYPTO_NONCE_SIZE);
    memcpy(session_pk, plain + CRYPTO_NONCE_SIZE, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(cookie, plain + CRYPTO_NONCE_SIZE + CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_SHA512_SIZE, COOKIE_LENGTH);
    memcpy(peer_real_pk, cookie_plain, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(dht_public_key, cookie_plain + CRYPTO_PUBLIC_KEY_SIZE, CRYPTO_PUBLIC_KEY_SIZE);
    return 0;
}


non_null()
static Crypto_Connection *get_crypto_connection(const Net_Crypto *c, int crypt_connection_id)
{
    if (!crypt_connection_id_is_valid(c, crypt_connection_id)) {
        return nullptr;
    }

    return &c->crypto_connections[crypt_connection_id];
}


/** Associate an ip_port to a connection.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int add_ip_port_connection(Net_Crypto *c, int crypt_connection_id, const IP_Port *ip_port)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (net_family_is_ipv4(ip_port->ip.family)) {
        if (!ipport_equal(ip_port, &conn->ip_portv4) && !ip_is_lan(&conn->ip_portv4.ip)) {
            if (!bs_list_add(&c->ip_port_list, (const uint8_t *)ip_port, crypt_connection_id)) {
                return -1;
            }

            bs_list_remove(&c->ip_port_list, (uint8_t *)&conn->ip_portv4, crypt_connection_id);
            conn->ip_portv4 = *ip_port;
            return 0;
        }
    } else if (net_family_is_ipv6(ip_port->ip.family)) {
        if (!ipport_equal(ip_port, &conn->ip_portv6)) {
            if (!bs_list_add(&c->ip_port_list, (const uint8_t *)ip_port, crypt_connection_id)) {
                return -1;
            }

            bs_list_remove(&c->ip_port_list, (uint8_t *)&conn->ip_portv6, crypt_connection_id);
            conn->ip_portv6 = *ip_port;
            return 0;
        }
    }

    return -1;
}

/** Return the IP_Port that should be used to send packets to the other peer.
 *
 * return IP_Port with family 0 on failure.
 * return IP_Port on success.
 */
non_null()
static IP_Port return_ip_port_connection(const Net_Crypto *c, int crypt_connection_id)
{
    const IP_Port empty = {{{0}}};

    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return empty;
    }

    const uint64_t current_time = mono_time_get(c->mono_time);
    bool v6 = 0;
    bool v4 = 0;

    if ((UDP_DIRECT_TIMEOUT + conn->direct_lastrecv_timev4) > current_time) {
        v4 = 1;
    }

    if ((UDP_DIRECT_TIMEOUT + conn->direct_lastrecv_timev6) > current_time) {
        v6 = 1;
    }

    /* Prefer IP_Ports which haven't timed out to those which have.
     * To break ties, prefer ipv4 lan, then ipv6, then non-lan ipv4.
     */
    if (v4 && ip_is_lan(&conn->ip_portv4.ip)) {
        return conn->ip_portv4;
    }

    if (v6 && net_family_is_ipv6(conn->ip_portv6.ip.family)) {
        return conn->ip_portv6;
    }

    if (v4 && net_family_is_ipv4(conn->ip_portv4.ip.family)) {
        return conn->ip_portv4;
    }

    if (ip_is_lan(&conn->ip_portv4.ip)) {
        return conn->ip_portv4;
    }

    if (net_family_is_ipv6(conn->ip_portv6.ip.family)) {
        return conn->ip_portv6;
    }

    if (net_family_is_ipv4(conn->ip_portv4.ip.family)) {
        return conn->ip_portv4;
    }

    return empty;
}

/** Sends a packet to the peer using the fastest route.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int send_packet_to(Net_Crypto *c, int crypt_connection_id, const uint8_t *data, uint16_t length)
{
// TODO(irungentoo): TCP, etc...
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    bool direct_send_attempt = false;

    pthread_mutex_lock(conn->mutex);
    IP_Port ip_port = return_ip_port_connection(c, crypt_connection_id);

    // TODO(irungentoo): on bad networks, direct connections might not last indefinitely.
    if (!net_family_is_unspec(ip_port.ip.family)) {
        bool direct_connected = false;

        // FIXME(sudden6): handle return value
        crypto_connection_status(c, crypt_connection_id, &direct_connected, nullptr);

        if (direct_connected) {
            if ((uint32_t)sendpacket(dht_get_net(c->dht), &ip_port, data, length) == length) {
                pthread_mutex_unlock(conn->mutex);
                return 0;
            }

            pthread_mutex_unlock(conn->mutex);
            LOGGER_WARNING(c->log, "sending packet of length %d failed", length);
            return -1;
        }

        // TODO(irungentoo): a better way of sending packets directly to confirm the others ip.
        const uint64_t current_time = mono_time_get(c->mono_time);

        if ((((UDP_DIRECT_TIMEOUT / 2) + conn->direct_send_attempt_time) < current_time && length < 96)
                || data[0] == NET_PACKET_COOKIE_REQUEST || data[0] == NET_PACKET_CRYPTO_HS) {
            if ((uint32_t)sendpacket(dht_get_net(c->dht), &ip_port, data, length) == length) {
                direct_send_attempt = true;
                conn->direct_send_attempt_time = mono_time_get(c->mono_time);
            }
        }
    }

    pthread_mutex_unlock(conn->mutex);
    pthread_mutex_lock(&c->tcp_mutex);
    const int ret = send_packet_tcp_connection(c->tcp_c, conn->connection_number_tcp, data, length);
    pthread_mutex_unlock(&c->tcp_mutex);

    pthread_mutex_lock(conn->mutex);

    if (ret == 0) {
        conn->last_tcp_sent = current_time_monotonic(c->mono_time);
    }

    pthread_mutex_unlock(conn->mutex);

    if (direct_send_attempt) {
        return 0;
    }

    return ret;
}

/*** START: Array Related functions */


/** Return number of packets in array
 * Note that holes are counted too.
 */
non_null()
static uint32_t num_packets_array(const Packets_Array *array)
{
    return array->buffer_end - array->buffer_start;
}

/** Add data with packet number to array.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int add_data_to_buffer(Packets_Array *array, uint32_t number, const Packet_Data *data)
{
    if (number - array->buffer_start >= CRYPTO_PACKET_BUFFER_SIZE) {
        return -1;
    }

    uint32_t num = number % CRYPTO_PACKET_BUFFER_SIZE;

    if (array->buffer[num] != nullptr) {
        return -1;
    }

    Packet_Data *new_d = (Packet_Data *)calloc(1, sizeof(Packet_Data));

    if (new_d == nullptr) {
        return -1;
    }

    *new_d = *data;
    array->buffer[num] = new_d;

    if (number - array->buffer_start >= num_packets_array(array)) {
        array->buffer_end = number + 1;
    }

    return 0;
}

/** Get pointer of data with packet number.
 *
 * return -1 on failure.
 * return 0 if data at number is empty.
 * return 1 if data pointer was put in data.
 */
non_null()
static int get_data_pointer(const Packets_Array *array, Packet_Data **data, uint32_t number)
{
    const uint32_t num_spots = num_packets_array(array);

    if (array->buffer_end - number > num_spots || number - array->buffer_start >= num_spots) {
        return -1;
    }

    uint32_t num = number % CRYPTO_PACKET_BUFFER_SIZE;

    if (array->buffer[num] == nullptr) {
        return 0;
    }

    *data = array->buffer[num];
    return 1;
}

/** Add data to end of array.
 *
 * return -1 on failure.
 * return packet number on success.
 */
non_null()
static int64_t add_data_end_of_buffer(const Logger *logger, Packets_Array *array, const Packet_Data *data)
{
    const uint32_t num_spots = num_packets_array(array);

    if (num_spots >= CRYPTO_PACKET_BUFFER_SIZE) {
        LOGGER_WARNING(logger, "crypto packet buffer size exceeded; rejecting packet of length %d", data->length);
        return -1;
    }

    Packet_Data *new_d = (Packet_Data *)calloc(1, sizeof(Packet_Data));

    if (new_d == nullptr) {
        LOGGER_ERROR(logger, "packet data allocation failed");
        return -1;
    }

    *new_d = *data;
    uint32_t id = array->buffer_end;
    array->buffer[id % CRYPTO_PACKET_BUFFER_SIZE] = new_d;
    ++array->buffer_end;
    return id;
}

/** Read data from beginning of array.
 *
 * return -1 on failure.
 * return packet number on success.
 */
non_null()
static int64_t read_data_beg_buffer(Packets_Array *array, Packet_Data *data)
{
    if (array->buffer_end == array->buffer_start) {
        return -1;
    }

    const uint32_t num = array->buffer_start % CRYPTO_PACKET_BUFFER_SIZE;

    if (array->buffer[num] == nullptr) {
        return -1;
    }

    *data = *array->buffer[num];
    uint32_t id = array->buffer_start;
    ++array->buffer_start;
    free(array->buffer[num]);
    array->buffer[num] = nullptr;
    return id;
}

/** Delete all packets in array before number (but not number)
 *
 * return -1 on failure.
 * return 0 on success
 */
non_null()
static int clear_buffer_until(Packets_Array *array, uint32_t number)
{
    const uint32_t num_spots = num_packets_array(array);

    if (array->buffer_end - number >= num_spots || number - array->buffer_start > num_spots) {
        return -1;
    }

    uint32_t i;

    for (i = array->buffer_start; i != number; ++i) {
        uint32_t num = i % CRYPTO_PACKET_BUFFER_SIZE;

        if (array->buffer[num] != nullptr) {
            free(array->buffer[num]);
            array->buffer[num] = nullptr;
        }
    }

    array->buffer_start = i;
    return 0;
}

non_null()
static int clear_buffer(Packets_Array *array)
{
    uint32_t i;

    for (i = array->buffer_start; i != array->buffer_end; ++i) {
        uint32_t num = i % CRYPTO_PACKET_BUFFER_SIZE;

        if (array->buffer[num] != nullptr) {
            free(array->buffer[num]);
            array->buffer[num] = nullptr;
        }
    }

    array->buffer_start = i;
    return 0;
}

/** Set array buffer end to number.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int set_buffer_end(Packets_Array *array, uint32_t number)
{
    if (number - array->buffer_start > CRYPTO_PACKET_BUFFER_SIZE) {
        return -1;
    }

    if (number - array->buffer_end > CRYPTO_PACKET_BUFFER_SIZE) {
        return -1;
    }

    array->buffer_end = number;
    return 0;
}

/** Create a packet request packet from recv_array and send_buffer_end into
 * data of length.
 *
 * return -1 on failure.
 * return length of packet on success.
 */
non_null()
static int generate_request_packet(uint8_t *data, uint16_t length, const Packets_Array *recv_array)
{
    if (length == 0) {
        return -1;
    }

    data[0] = PACKET_ID_REQUEST;

    uint16_t cur_len = 1;

    if (recv_array->buffer_start == recv_array->buffer_end) {
        return cur_len;
    }

    if (length <= cur_len) {
        return cur_len;
    }

    uint32_t n = 1;

    for (uint32_t i = recv_array->buffer_start; i != recv_array->buffer_end; ++i) {
        uint32_t num = i % CRYPTO_PACKET_BUFFER_SIZE;

        if (recv_array->buffer[num] == nullptr) {
            data[cur_len] = n;
            n = 0;
            ++cur_len;

            if (length <= cur_len) {
                return cur_len;
            }
        } else if (n == 255) {
            data[cur_len] = 0;
            n = 0;
            ++cur_len;

            if (length <= cur_len) {
                return cur_len;
            }
        }

        ++n;
    }

    return cur_len;
}

/** Handle a request data packet.
 * Remove all the packets the other received from the array.
 *
 * return -1 on failure.
 * return number of requested packets on success.
 */
non_null()
static int handle_request_packet(Mono_Time *mono_time, Packets_Array *send_array,
                                 const uint8_t *data, uint16_t length,
                                 uint64_t *latest_send_time, uint64_t rtt_time)
{
    if (length == 0) {
        return -1;
    }

    if (data[0] != PACKET_ID_REQUEST) {
        return -1;
    }

    if (length == 1) {
        return 0;
    }

    ++data;
    --length;

    uint32_t n = 1;
    uint32_t requested = 0;

    const uint64_t temp_time = current_time_monotonic(mono_time);
    uint64_t l_sent_time = -1;

    for (uint32_t i = send_array->buffer_start; i != send_array->buffer_end; ++i) {
        if (length == 0) {
            break;
        }

        uint32_t num = i % CRYPTO_PACKET_BUFFER_SIZE;

        if (n == data[0]) {
            if (send_array->buffer[num] != nullptr) {
                uint64_t sent_time = send_array->buffer[num]->sent_time;

                if ((sent_time + rtt_time) < temp_time) {
                    send_array->buffer[num]->sent_time = 0;
                }
            }

            ++data;
            --length;
            n = 0;
            ++requested;
        } else {
            if (send_array->buffer[num] != nullptr) {
                l_sent_time = max_u64(l_sent_time, send_array->buffer[num]->sent_time);

                free(send_array->buffer[num]);
                send_array->buffer[num] = nullptr;
            }
        }

        if (n == 255) {
            n = 1;

            if (data[0] != 0) {
                return -1;
            }

            ++data;
            --length;
        } else {
            ++n;
        }
    }

    *latest_send_time = max_u64(*latest_send_time, l_sent_time);

    return requested;
}

/** END: Array Related functions */

#define MAX_DATA_DATA_PACKET_SIZE (MAX_CRYPTO_PACKET_SIZE - (1 + sizeof(uint16_t) + CRYPTO_MAC_SIZE))

/** Creates and sends a data packet to the peer using the fastest route.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int send_data_packet(Net_Crypto *c, int crypt_connection_id, const uint8_t *data, uint16_t length)
{
    const uint16_t max_length = MAX_CRYPTO_PACKET_SIZE - (1 + sizeof(uint16_t) + CRYPTO_MAC_SIZE);

    if (length == 0 || length > max_length) {
        LOGGER_ERROR(c->log, "zero-length or too large data packet: %d (max: %d)", length, max_length);
        return -1;
    }

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        LOGGER_ERROR(c->log, "connection id %d not found", crypt_connection_id);
        return -1;
    }

    pthread_mutex_lock(conn->mutex);
    const uint16_t packet_size = 1 + sizeof(uint16_t) + length + CRYPTO_MAC_SIZE;
    VLA(uint8_t, packet, packet_size);
    packet[0] = NET_PACKET_CRYPTO_DATA;
    memcpy(packet + 1, conn->sent_nonce + (CRYPTO_NONCE_SIZE - sizeof(uint16_t)), sizeof(uint16_t));
    const int len = encrypt_data_symmetric(conn->shared_key, conn->sent_nonce, data, length, packet + 1 + sizeof(uint16_t));

    if (len + 1 + sizeof(uint16_t) != packet_size) {
        LOGGER_ERROR(c->log, "encryption failed: %d", len);
        pthread_mutex_unlock(conn->mutex);
        return -1;
    }

    increment_nonce(conn->sent_nonce);
    pthread_mutex_unlock(conn->mutex);

    return send_packet_to(c, crypt_connection_id, packet, SIZEOF_VLA(packet));
}

/** Creates and sends a data packet with buffer_start and num to the peer using the fastest route.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int send_data_packet_helper(Net_Crypto *c, int crypt_connection_id, uint32_t buffer_start, uint32_t num,
                                   const uint8_t *data, uint16_t length)
{
    if (length == 0 || length > MAX_CRYPTO_DATA_SIZE) {
        LOGGER_ERROR(c->log, "zero-length or too large data packet: %d (max: %d)", length, MAX_CRYPTO_PACKET_SIZE);
        return -1;
    }

    num = net_htonl(num);
    buffer_start = net_htonl(buffer_start);
    uint16_t padding_length = (MAX_CRYPTO_DATA_SIZE - length) % CRYPTO_MAX_PADDING;
    VLA(uint8_t, packet, sizeof(uint32_t) + sizeof(uint32_t) + padding_length + length);
    memcpy(packet, &buffer_start, sizeof(uint32_t));
    memcpy(packet + sizeof(uint32_t), &num, sizeof(uint32_t));
    memset(packet + (sizeof(uint32_t) * 2), PACKET_ID_PADDING, padding_length);
    memcpy(packet + (sizeof(uint32_t) * 2) + padding_length, data, length);

    return send_data_packet(c, crypt_connection_id, packet, SIZEOF_VLA(packet));
}

non_null()
static int reset_max_speed_reached(Net_Crypto *c, int crypt_connection_id)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    /* If last packet send failed, try to send packet again.
     * If sending it fails we won't be able to send the new packet. */
    if (conn->maximum_speed_reached) {
        Packet_Data *dt = nullptr;
        const uint32_t packet_num = conn->send_array.buffer_end - 1;
        const int ret = get_data_pointer(&conn->send_array, &dt, packet_num);

        if (ret == 1 && dt->sent_time == 0) {
            if (send_data_packet_helper(c, crypt_connection_id, conn->recv_array.buffer_start, packet_num,
                                        dt->data, dt->length) != 0) {
                return -1;
            }

            dt->sent_time = current_time_monotonic(c->mono_time);
        }

        conn->maximum_speed_reached = 0;
    }

    return 0;
}

/**  return -1 if data could not be put in packet queue.
 *  return positive packet number if data was put into the queue.
 */
non_null()
static int64_t send_lossless_packet(Net_Crypto *c, int crypt_connection_id, const uint8_t *data, uint16_t length,
                                    uint8_t congestion_control)
{
    if (length == 0 || length > MAX_CRYPTO_DATA_SIZE) {
        LOGGER_ERROR(c->log, "rejecting too large (or empty) packet of size %d on crypt connection %d", length,
                     crypt_connection_id);
        return -1;
    }

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    /* If last packet send failed, try to send packet again.
     * If sending it fails we won't be able to send the new packet. */
    reset_max_speed_reached(c, crypt_connection_id);

    if (conn->maximum_speed_reached && congestion_control) {
        LOGGER_INFO(c->log, "congestion control: maximum speed reached on crypt connection %d", crypt_connection_id);
        return -1;
    }

    Packet_Data dt;
    dt.sent_time = 0;
    dt.length = length;
    memcpy(dt.data, data, length);
    pthread_mutex_lock(conn->mutex);
    const int64_t packet_num = add_data_end_of_buffer(c->log, &conn->send_array, &dt);
    pthread_mutex_unlock(conn->mutex);

    if (packet_num == -1) {
        return -1;
    }

    if (!congestion_control && conn->maximum_speed_reached) {
        return packet_num;
    }

    if (send_data_packet_helper(c, crypt_connection_id, conn->recv_array.buffer_start, packet_num, data, length) == 0) {
        Packet_Data *dt1 = nullptr;

        if (get_data_pointer(&conn->send_array, &dt1, packet_num) == 1) {
            dt1->sent_time = current_time_monotonic(c->mono_time);
        }
    } else {
        conn->maximum_speed_reached = 1;
        LOGGER_DEBUG(c->log, "send_data_packet failed (packet_num = %ld)", (long)packet_num);
    }

    return packet_num;
}

/** Get the lowest 2 bytes from the nonce and convert
 * them to host byte format before returning them.
 */
non_null()
static uint16_t get_nonce_uint16(const uint8_t *nonce)
{
    uint16_t num;
    memcpy(&num, nonce + (CRYPTO_NONCE_SIZE - sizeof(uint16_t)), sizeof(uint16_t));
    return net_ntohs(num);
}

#define DATA_NUM_THRESHOLD 21845

/** Handle a data packet.
 * Decrypt packet of length and put it into data.
 * data must be at least MAX_DATA_DATA_PACKET_SIZE big.
 *
 * return -1 on failure.
 * return length of data on success.
 */
non_null()
static int handle_data_packet(const Net_Crypto *c, int crypt_connection_id, uint8_t *data, const uint8_t *packet,
                              uint16_t length)
{
    const uint16_t crypto_packet_overhead = 1 + sizeof(uint16_t) + CRYPTO_MAC_SIZE;

    if (length <= crypto_packet_overhead || length > MAX_CRYPTO_PACKET_SIZE) {
        return -1;
    }

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    uint8_t nonce[CRYPTO_NONCE_SIZE];
    memcpy(nonce, conn->recv_nonce, CRYPTO_NONCE_SIZE);
    uint16_t num_cur_nonce = get_nonce_uint16(nonce);
    uint16_t num;
    net_unpack_u16(packet + 1, &num);
    uint16_t diff = num - num_cur_nonce;
    increment_nonce_number(nonce, diff);
    int len = decrypt_data_symmetric(conn->shared_key, nonce, packet + 1 + sizeof(uint16_t),
                                     length - (1 + sizeof(uint16_t)), data);

    if ((unsigned int)len != length - crypto_packet_overhead) {
        return -1;
    }

    if (diff > DATA_NUM_THRESHOLD * 2) {
        increment_nonce_number(conn->recv_nonce, DATA_NUM_THRESHOLD);
    }

    return len;
}

/** Send a request packet.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int send_request_packet(Net_Crypto *c, int crypt_connection_id)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    uint8_t data[MAX_CRYPTO_DATA_SIZE];
    int len = generate_request_packet(data, sizeof(data), &conn->recv_array);

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

    return send_data_packet_helper(c, crypt_connection_id, conn->recv_array.buffer_start, conn->send_array.buffer_end, data,
                                   len);
}

/** Send up to max num previously requested data packets.
 *
 * return -1 on failure.
 * return number of packets sent on success.
 */
non_null()
static int send_requested_packets(Net_Crypto *c, int crypt_connection_id, uint32_t max_num)
{
    if (max_num == 0) {
        return -1;
    }

    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    const uint64_t temp_time = current_time_monotonic(c->mono_time);
    const uint32_t array_size = num_packets_array(&conn->send_array);
    uint32_t num_sent = 0;

    for (uint32_t i = 0; i < array_size; ++i) {
        Packet_Data *dt;
        const uint32_t packet_num = i + conn->send_array.buffer_start;
        const int ret = get_data_pointer(&conn->send_array, &dt, packet_num);

        if (ret == -1) {
            return -1;
        }

        if (ret == 0) {
            continue;
        }

        if (dt->sent_time) {
            continue;
        }

        if (send_data_packet_helper(c, crypt_connection_id, conn->recv_array.buffer_start, packet_num, dt->data,
                                    dt->length) == 0) {
            dt->sent_time = temp_time;
            ++num_sent;
        }

        if (num_sent >= max_num) {
            break;
        }
    }

    return num_sent;
}


/** Add a new temp packet to send repeatedly.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int new_temp_packet(const Net_Crypto *c, int crypt_connection_id, const uint8_t *packet, uint16_t length)
{
    if (length == 0 || length > MAX_CRYPTO_PACKET_SIZE) {
        return -1;
    }

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    uint8_t *temp_packet = (uint8_t *)malloc(length);

    if (temp_packet == nullptr) {
        return -1;
    }

    if (conn->temp_packet != nullptr) {
        free(conn->temp_packet);
    }

    memcpy(temp_packet, packet, length);
    conn->temp_packet = temp_packet;
    conn->temp_packet_length = length;
    conn->temp_packet_sent_time = 0;
    conn->temp_packet_num_sent = 0;
    return 0;
}

/** Clear the temp packet.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int clear_temp_packet(const Net_Crypto *c, int crypt_connection_id)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (conn->temp_packet != nullptr) {
        free(conn->temp_packet);
    }

    conn->temp_packet = nullptr;
    conn->temp_packet_length = 0;
    conn->temp_packet_sent_time = 0;
    conn->temp_packet_num_sent = 0;
    return 0;
}


/** Send the temp packet.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int send_temp_packet(Net_Crypto *c, int crypt_connection_id)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (conn->temp_packet == nullptr) {
        return -1;
    }

    if (send_packet_to(c, crypt_connection_id, conn->temp_packet, conn->temp_packet_length) != 0) {
        return -1;
    }

    conn->temp_packet_sent_time = current_time_monotonic(c->mono_time);
    ++conn->temp_packet_num_sent;
    return 0;
}

/** Create a handshake packet and set it as a temp packet.
 * cookie must be COOKIE_LENGTH.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int create_send_handshake(Net_Crypto *c, int crypt_connection_id, const uint8_t *cookie,
                                 const uint8_t *dht_public_key)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    uint8_t handshake_packet[HANDSHAKE_PACKET_LENGTH];

    if (create_crypto_handshake(c, handshake_packet, cookie, conn->sent_nonce, conn->sessionpublic_key,
                                conn->public_key, dht_public_key) != sizeof(handshake_packet)) {
        return -1;
    }

    if (new_temp_packet(c, crypt_connection_id, handshake_packet, sizeof(handshake_packet)) != 0) {
        return -1;
    }

    send_temp_packet(c, crypt_connection_id);
    return 0;
}

/** Send a kill packet.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int send_kill_packet(Net_Crypto *c, int crypt_connection_id)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    uint8_t kill_packet = PACKET_ID_KILL;
    return send_data_packet_helper(c, crypt_connection_id, conn->recv_array.buffer_start, conn->send_array.buffer_end,
                                   &kill_packet, sizeof(kill_packet));
}

non_null(1) nullable(3)
static void connection_kill(Net_Crypto *c, int crypt_connection_id, void *userdata)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return;
    }

    if (conn->connection_status_callback != nullptr) {
        conn->connection_status_callback(conn->connection_status_callback_object, conn->connection_status_callback_id, 0,
                                         userdata);
    }

    while (1) { /* TODO(irungentoo): is this really the best way to do this? */
        pthread_mutex_lock(&c->connections_mutex);

        if (c->connection_use_counter == 0) {
            break;
        }

        pthread_mutex_unlock(&c->connections_mutex);
    }

    crypto_kill(c, crypt_connection_id);
    pthread_mutex_unlock(&c->connections_mutex);
}

/** Handle a received data packet.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null(1, 3) nullable(6)
static int handle_data_packet_core(Net_Crypto *c, int crypt_connection_id, const uint8_t *packet, uint16_t length,
                                   bool udp, void *userdata)
{
    if (length > MAX_CRYPTO_PACKET_SIZE || length <= CRYPTO_DATA_PACKET_MIN_SIZE) {
        return -1;
    }

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    uint8_t data[MAX_DATA_DATA_PACKET_SIZE];
    int len = handle_data_packet(c, crypt_connection_id, data, packet, length);

    if (len <= (int)(sizeof(uint32_t) * 2)) {
        return -1;
    }

    uint32_t buffer_start;
    uint32_t num;
    memcpy(&buffer_start, data, sizeof(uint32_t));
    memcpy(&num, data + sizeof(uint32_t), sizeof(uint32_t));
    buffer_start = net_ntohl(buffer_start);
    num = net_ntohl(num);

    uint64_t rtt_calc_time = 0;

    if (buffer_start != conn->send_array.buffer_start) {
        Packet_Data *packet_time;

        if (get_data_pointer(&conn->send_array, &packet_time, conn->send_array.buffer_start) == 1) {
            rtt_calc_time = packet_time->sent_time;
        }

        if (clear_buffer_until(&conn->send_array, buffer_start) != 0) {
            return -1;
        }
    }

    const uint8_t *real_data = data + (sizeof(uint32_t) * 2);
    uint16_t real_length = len - (sizeof(uint32_t) * 2);

    while (real_data[0] == PACKET_ID_PADDING) { /* Remove Padding */
        ++real_data;
        --real_length;

        if (real_length == 0) {
            return -1;
        }
    }

    if (real_data[0] == PACKET_ID_KILL) {
        connection_kill(c, crypt_connection_id, userdata);
        return 0;
    }

    if (conn->status == CRYPTO_CONN_NOT_CONFIRMED) {
        clear_temp_packet(c, crypt_connection_id);
        conn->status = CRYPTO_CONN_ESTABLISHED;

        if (conn->connection_status_callback != nullptr) {
            conn->connection_status_callback(conn->connection_status_callback_object, conn->connection_status_callback_id, 1,
                                             userdata);
        }
    }

    if (real_data[0] == PACKET_ID_REQUEST) {
        uint64_t rtt_time;

        if (udp) {
            rtt_time = conn->rtt_time;
        } else {
            rtt_time = DEFAULT_TCP_PING_CONNECTION;
        }

        int requested = handle_request_packet(c->mono_time, &conn->send_array,
                                              real_data, real_length,
                                              &rtt_calc_time, rtt_time);

        if (requested == -1) {
            return -1;
        }

        set_buffer_end(&conn->recv_array, num);
    } else if (real_data[0] >= PACKET_ID_RANGE_LOSSLESS_START && real_data[0] <= PACKET_ID_RANGE_LOSSLESS_END) {
        Packet_Data dt = {0};
        dt.length = real_length;
        memcpy(dt.data, real_data, real_length);

        if (add_data_to_buffer(&conn->recv_array, num, &dt) != 0) {
            return -1;
        }

        while (1) {
            pthread_mutex_lock(conn->mutex);
            const int ret = read_data_beg_buffer(&conn->recv_array, &dt);
            pthread_mutex_unlock(conn->mutex);

            if (ret == -1) {
                break;
            }

            if (conn->connection_data_callback != nullptr) {
                conn->connection_data_callback(conn->connection_data_callback_object, conn->connection_data_callback_id, dt.data,
                                               dt.length, userdata);
            }

            /* conn might get killed in callback. */
            conn = get_crypto_connection(c, crypt_connection_id);

            if (conn == nullptr) {
                return -1;
            }
        }

        /* Packet counter. */
        ++conn->packet_counter;
    } else if (real_data[0] >= PACKET_ID_RANGE_LOSSY_START && real_data[0] <= PACKET_ID_RANGE_LOSSY_END) {

        set_buffer_end(&conn->recv_array, num);

        if (conn->connection_lossy_data_callback != nullptr) {
            conn->connection_lossy_data_callback(conn->connection_lossy_data_callback_object,
                                                 conn->connection_lossy_data_callback_id, real_data, real_length, userdata);
        }
    } else {
        return -1;
    }

    if (rtt_calc_time != 0) {
        uint64_t rtt_time = current_time_monotonic(c->mono_time) - rtt_calc_time;

        if (rtt_time < conn->rtt_time) {
            conn->rtt_time = rtt_time;
        }
    }

    return 0;
}

non_null()
static int handle_packet_cookie_response(Net_Crypto *c, int crypt_connection_id, const uint8_t *packet, uint16_t length)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (conn->status != CRYPTO_CONN_COOKIE_REQUESTING) {
        return -1;
    }

    uint8_t cookie[COOKIE_LENGTH];
    uint64_t number;

    if (handle_cookie_response(cookie, &number, packet, length, conn->shared_key) != sizeof(cookie)) {
        return -1;
    }

    if (number != conn->cookie_request_number) {
        return -1;
    }

    if (create_send_handshake(c, crypt_connection_id, cookie, conn->dht_public_key) != 0) {
        return -1;
    }

    conn->status = CRYPTO_CONN_HANDSHAKE_SENT;
    return 0;
}

non_null(1, 3) nullable(5)
static int handle_packet_crypto_hs(Net_Crypto *c, int crypt_connection_id, const uint8_t *packet, uint16_t length,
                                   void *userdata)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (conn->status != CRYPTO_CONN_COOKIE_REQUESTING
            && conn->status != CRYPTO_CONN_HANDSHAKE_SENT
            && conn->status != CRYPTO_CONN_NOT_CONFIRMED) {
        return -1;
    }

    uint8_t peer_real_pk[CRYPTO_PUBLIC_KEY_SIZE];
    uint8_t dht_public_key[CRYPTO_PUBLIC_KEY_SIZE];
    uint8_t cookie[COOKIE_LENGTH];

    if (handle_crypto_handshake(c, conn->recv_nonce, conn->peersessionpublic_key, peer_real_pk, dht_public_key, cookie,
                                packet, length, conn->public_key) != 0) {
        return -1;
    }

    if (public_key_cmp(dht_public_key, conn->dht_public_key) == 0) {
        encrypt_precompute(conn->peersessionpublic_key, conn->sessionsecret_key, conn->shared_key);

        if (conn->status == CRYPTO_CONN_COOKIE_REQUESTING) {
            if (create_send_handshake(c, crypt_connection_id, cookie, dht_public_key) != 0) {
                return -1;
            }
        }

        conn->status = CRYPTO_CONN_NOT_CONFIRMED;
    } else {
        if (conn->dht_pk_callback != nullptr) {
            conn->dht_pk_callback(conn->dht_pk_callback_object, conn->dht_pk_callback_number, dht_public_key, userdata);
        }
    }

    return 0;
}

non_null(1, 3) nullable(6)
static int handle_packet_crypto_data(Net_Crypto *c, int crypt_connection_id, const uint8_t *packet, uint16_t length,
                                     bool udp, void *userdata)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (conn->status != CRYPTO_CONN_NOT_CONFIRMED && conn->status != CRYPTO_CONN_ESTABLISHED) {
        return -1;
    }

    return handle_data_packet_core(c, crypt_connection_id, packet, length, udp, userdata);
}

/** Handle a packet that was received for the connection.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null(1, 3) nullable(6)
static int handle_packet_connection(Net_Crypto *c, int crypt_connection_id, const uint8_t *packet, uint16_t length,
                                    bool udp, void *userdata)
{
    if (length == 0 || length > MAX_CRYPTO_PACKET_SIZE) {
        return -1;
    }

    switch (packet[0]) {
        case NET_PACKET_COOKIE_RESPONSE:
            return handle_packet_cookie_response(c, crypt_connection_id, packet, length);

        case NET_PACKET_CRYPTO_HS:
            return handle_packet_crypto_hs(c, crypt_connection_id, packet, length, userdata);

        case NET_PACKET_CRYPTO_DATA:
            return handle_packet_crypto_data(c, crypt_connection_id, packet, length, udp, userdata);

        default:
            return -1;
    }
}

/** Set the size of the friend list to numfriends.
 *
 *  return -1 if realloc fails.
 *  return 0 if it succeeds.
 */
non_null()
static int realloc_cryptoconnection(Net_Crypto *c, uint32_t num)
{
    if (num == 0) {
        free(c->crypto_connections);
        c->crypto_connections = nullptr;
        return 0;
    }

    Crypto_Connection *newcrypto_connections = (Crypto_Connection *)realloc(c->crypto_connections,
            num * sizeof(Crypto_Connection));

    if (newcrypto_connections == nullptr) {
        return -1;
    }

    c->crypto_connections = newcrypto_connections;
    return 0;
}


/** Create a new empty crypto connection.
 *
 * return -1 on failure.
 * return connection id on success.
 */
non_null()
static int create_crypto_connection(Net_Crypto *c)
{
    while (1) { /* TODO(irungentoo): is this really the best way to do this? */
        pthread_mutex_lock(&c->connections_mutex);

        if (c->connection_use_counter == 0) {
            break;
        }

        pthread_mutex_unlock(&c->connections_mutex);
    }

    int id = -1;

    for (uint32_t i = 0; i < c->crypto_connections_length; ++i) {
        if (c->crypto_connections[i].status == CRYPTO_CONN_FREE) {
            id = i;
            break;
        }
    }

    if (id == -1) {
        if (realloc_cryptoconnection(c, c->crypto_connections_length + 1) == 0) {
            id = c->crypto_connections_length;
            ++c->crypto_connections_length;
            c->crypto_connections[id] = empty_crypto_connection;
        }
    }

    if (id != -1) {
        // Memsetting float/double to 0 is non-portable, so we explicitly set them to 0
        c->crypto_connections[id].packet_recv_rate = 0;
        c->crypto_connections[id].packet_send_rate = 0;
        c->crypto_connections[id].last_packets_left_rem = 0;
        c->crypto_connections[id].packet_send_rate_requested = 0;
        c->crypto_connections[id].last_packets_left_requested_rem = 0;
        c->crypto_connections[id].mutex = (pthread_mutex_t *)calloc(1, sizeof(pthread_mutex_t));

        if (c->crypto_connections[id].mutex == nullptr) {
            pthread_mutex_unlock(&c->connections_mutex);
            return -1;
        }

        if (pthread_mutex_init(c->crypto_connections[id].mutex, nullptr) != 0) {
            free(c->crypto_connections[id].mutex);
            pthread_mutex_unlock(&c->connections_mutex);
            return -1;
        }

        c->crypto_connections[id].status = CRYPTO_CONN_NO_CONNECTION;
    }

    pthread_mutex_unlock(&c->connections_mutex);
    return id;
}

/** Wipe a crypto connection.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null()
static int wipe_crypto_connection(Net_Crypto *c, int crypt_connection_id)
{
    if ((uint32_t)crypt_connection_id >= c->crypto_connections_length) {
        return -1;
    }

    if (c->crypto_connections == nullptr) {
        return -1;
    }

    const Crypto_Conn_State status = c->crypto_connections[crypt_connection_id].status;

    if (status == CRYPTO_CONN_FREE) {
        return -1;
    }

    uint32_t i;

    pthread_mutex_destroy(c->crypto_connections[crypt_connection_id].mutex);
    free(c->crypto_connections[crypt_connection_id].mutex);
    crypto_memzero(&c->crypto_connections[crypt_connection_id], sizeof(Crypto_Connection));

    /* check if we can resize the connections array */
    for (i = c->crypto_connections_length; i != 0; --i) {
        if (c->crypto_connections[i - 1].status != CRYPTO_CONN_FREE) {
            break;
        }
    }

    if (c->crypto_connections_length != i) {
        c->crypto_connections_length = i;
        realloc_cryptoconnection(c, c->crypto_connections_length);
    }

    return 0;
}

/** Get crypto connection id from public key of peer.
 *
 *  return -1 if there are no connections like we are looking for.
 *  return id if it found it.
 */
non_null()
static int getcryptconnection_id(const Net_Crypto *c, const uint8_t *public_key)
{
    for (uint32_t i = 0; i < c->crypto_connections_length; ++i) {
        if (!crypt_connection_id_is_valid(c, i)) {
            continue;
        }

        if (public_key_cmp(public_key, c->crypto_connections[i].public_key) == 0) {
            return i;
        }
    }

    return -1;
}

/** Add a source to the crypto connection.
 * This is to be used only when we have received a packet from that source.
 *
 *  return -1 on failure.
 *  return positive number on success.
 *  0 if source was a direct UDP connection.
 */
non_null()
static int crypto_connection_add_source(Net_Crypto *c, int crypt_connection_id, const IP_Port *source)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (net_family_is_ipv4(source->ip.family) || net_family_is_ipv6(source->ip.family)) {
        if (add_ip_port_connection(c, crypt_connection_id, source) != 0) {
            return -1;
        }

        if (net_family_is_ipv4(source->ip.family)) {
            conn->direct_lastrecv_timev4 = mono_time_get(c->mono_time);
        } else {
            conn->direct_lastrecv_timev6 = mono_time_get(c->mono_time);
        }

        return 0;
    }

    if (net_family_is_tcp_family(source->ip.family)) {
        if (add_tcp_number_relay_connection(c->tcp_c, conn->connection_number_tcp, source->ip.ip.v6.uint32[0]) == 0) {
            return 1;
        }
    }

    return -1;
}


/** Set function to be called when someone requests a new connection to us.
 *
 * The set function should return -1 on failure and 0 on success.
 *
 * n_c is only valid for the duration of the function call.
 */
void new_connection_handler(Net_Crypto *c, new_connection_cb *new_connection_callback, void *object)
{
    c->new_connection_callback = new_connection_callback;
    c->new_connection_callback_object = object;
}

/** Handle a handshake packet by someone who wants to initiate a new connection with us.
 * This calls the callback set by new_connection_handler() if the handshake is ok.
 *
 * return -1 on failure.
 * return 0 on success.
 */
non_null(1, 2, 3) nullable(5)
static int handle_new_connection_handshake(Net_Crypto *c, const IP_Port *source, const uint8_t *data, uint16_t length,
        void *userdata)
{
    New_Connection n_c;
    n_c.cookie = (uint8_t *)malloc(COOKIE_LENGTH);

    if (n_c.cookie == nullptr) {
        return -1;
    }

    n_c.source = *source;
    n_c.cookie_length = COOKIE_LENGTH;

    if (handle_crypto_handshake(c, n_c.recv_nonce, n_c.peersessionpublic_key, n_c.public_key, n_c.dht_public_key,
                                n_c.cookie, data, length, nullptr) != 0) {
        free(n_c.cookie);
        return -1;
    }

    const int crypt_connection_id = getcryptconnection_id(c, n_c.public_key);

    if (crypt_connection_id != -1) {
        Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

        if (conn == nullptr) {
            return -1;
        }

        if (public_key_cmp(n_c.dht_public_key, conn->dht_public_key) != 0) {
            connection_kill(c, crypt_connection_id, userdata);
        } else {
            if (conn->status != CRYPTO_CONN_COOKIE_REQUESTING && conn->status != CRYPTO_CONN_HANDSHAKE_SENT) {
                free(n_c.cookie);
                return -1;
            }

            memcpy(conn->recv_nonce, n_c.recv_nonce, CRYPTO_NONCE_SIZE);
            memcpy(conn->peersessionpublic_key, n_c.peersessionpublic_key, CRYPTO_PUBLIC_KEY_SIZE);
            encrypt_precompute(conn->peersessionpublic_key, conn->sessionsecret_key, conn->shared_key);

            crypto_connection_add_source(c, crypt_connection_id, source);

            if (create_send_handshake(c, crypt_connection_id, n_c.cookie, n_c.dht_public_key) != 0) {
                free(n_c.cookie);
                return -1;
            }

            conn->status = CRYPTO_CONN_NOT_CONFIRMED;
            free(n_c.cookie);
            return 0;
        }
    }

    int ret = c->new_connection_callback(c->new_connection_callback_object, &n_c);
    free(n_c.cookie);
    return ret;
}

/** Accept a crypto connection.
 *
 * return -1 on failure.
 * return connection id on success.
 */
int accept_crypto_connection(Net_Crypto *c, const New_Connection *n_c)
{
    if (getcryptconnection_id(c, n_c->public_key) != -1) {
        return -1;
    }

    const int crypt_connection_id = create_crypto_connection(c);

    if (crypt_connection_id == -1) {
        LOGGER_ERROR(c->log, "Could not create new crypto connection");
        return -1;
    }

    Crypto_Connection *conn = &c->crypto_connections[crypt_connection_id];

    if (n_c->cookie_length != COOKIE_LENGTH) {
        wipe_crypto_connection(c, crypt_connection_id);
        return -1;
    }

    pthread_mutex_lock(&c->tcp_mutex);
    const int connection_number_tcp = new_tcp_connection_to(c->tcp_c, n_c->dht_public_key, crypt_connection_id);
    pthread_mutex_unlock(&c->tcp_mutex);

    if (connection_number_tcp == -1) {
        wipe_crypto_connection(c, crypt_connection_id);
        return -1;
    }

    conn->connection_number_tcp = connection_number_tcp;
    memcpy(conn->public_key, n_c->public_key, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(conn->recv_nonce, n_c->recv_nonce, CRYPTO_NONCE_SIZE);
    memcpy(conn->peersessionpublic_key, n_c->peersessionpublic_key, CRYPTO_PUBLIC_KEY_SIZE);
    random_nonce(conn->sent_nonce);
    crypto_new_keypair(conn->sessionpublic_key, conn->sessionsecret_key);
    encrypt_precompute(conn->peersessionpublic_key, conn->sessionsecret_key, conn->shared_key);
    conn->status = CRYPTO_CONN_NOT_CONFIRMED;

    if (create_send_handshake(c, crypt_connection_id, n_c->cookie, n_c->dht_public_key) != 0) {
        pthread_mutex_lock(&c->tcp_mutex);
        kill_tcp_connection_to(c->tcp_c, conn->connection_number_tcp);
        pthread_mutex_unlock(&c->tcp_mutex);
        wipe_crypto_connection(c, crypt_connection_id);
        return -1;
    }

    memcpy(conn->dht_public_key, n_c->dht_public_key, CRYPTO_PUBLIC_KEY_SIZE);
    conn->packet_send_rate = CRYPTO_PACKET_MIN_RATE;
    conn->packet_send_rate_requested = CRYPTO_PACKET_MIN_RATE;
    conn->packets_left = CRYPTO_MIN_QUEUE_LENGTH;
    conn->rtt_time = DEFAULT_PING_CONNECTION;
    crypto_connection_add_source(c, crypt_connection_id, &n_c->source);
    return crypt_connection_id;
}

/** Create a crypto connection.
 * If one to that real public key already exists, return it.
 *
 * return -1 on failure.
 * return connection id on success.
 */
int new_crypto_connection(Net_Crypto *c, const uint8_t *real_public_key, const uint8_t *dht_public_key)
{
    int crypt_connection_id = getcryptconnection_id(c, real_public_key);

    if (crypt_connection_id != -1) {
        return crypt_connection_id;
    }

    crypt_connection_id = create_crypto_connection(c);

    if (crypt_connection_id == -1) {
        return -1;
    }

    Crypto_Connection *conn = &c->crypto_connections[crypt_connection_id];

    pthread_mutex_lock(&c->tcp_mutex);
    const int connection_number_tcp = new_tcp_connection_to(c->tcp_c, dht_public_key, crypt_connection_id);
    pthread_mutex_unlock(&c->tcp_mutex);

    if (connection_number_tcp == -1) {
        wipe_crypto_connection(c, crypt_connection_id);
        return -1;
    }

    conn->connection_number_tcp = connection_number_tcp;
    memcpy(conn->public_key, real_public_key, CRYPTO_PUBLIC_KEY_SIZE);
    random_nonce(conn->sent_nonce);
    crypto_new_keypair(conn->sessionpublic_key, conn->sessionsecret_key);
    conn->status = CRYPTO_CONN_COOKIE_REQUESTING;
    conn->packet_send_rate = CRYPTO_PACKET_MIN_RATE;
    conn->packet_send_rate_requested = CRYPTO_PACKET_MIN_RATE;
    conn->packets_left = CRYPTO_MIN_QUEUE_LENGTH;
    conn->rtt_time = DEFAULT_PING_CONNECTION;
    memcpy(conn->dht_public_key, dht_public_key, CRYPTO_PUBLIC_KEY_SIZE);

    conn->cookie_request_number = random_u64();
    uint8_t cookie_request[COOKIE_REQUEST_LENGTH];

    if (create_cookie_request(c, cookie_request, conn->dht_public_key, conn->cookie_request_number,
                              conn->shared_key) != sizeof(cookie_request)
            || new_temp_packet(c, crypt_connection_id, cookie_request, sizeof(cookie_request)) != 0) {
        pthread_mutex_lock(&c->tcp_mutex);
        kill_tcp_connection_to(c->tcp_c, conn->connection_number_tcp);
        pthread_mutex_unlock(&c->tcp_mutex);
        wipe_crypto_connection(c, crypt_connection_id);
        return -1;
    }

    return crypt_connection_id;
}

/** Set the direct ip of the crypto connection.
 *
 * Connected is 0 if we are not sure we are connected to that person, 1 if we are sure.
 *
 * return -1 on failure.
 * return 0 on success.
 */
int set_direct_ip_port(Net_Crypto *c, int crypt_connection_id, const IP_Port *ip_port, bool connected)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (add_ip_port_connection(c, crypt_connection_id, ip_port) != 0) {
        return -1;
    }

    const uint64_t direct_lastrecv_time = connected ? mono_time_get(c->mono_time) : 0;

    if (net_family_is_ipv4(ip_port->ip.family)) {
        conn->direct_lastrecv_timev4 = direct_lastrecv_time;
    } else {
        conn->direct_lastrecv_timev6 = direct_lastrecv_time;
    }

    return 0;
}


non_null(1, 3) nullable(5)
static int tcp_data_callback(void *object, int crypt_connection_id, const uint8_t *data, uint16_t length,
                             void *userdata)
{
    Net_Crypto *c = (Net_Crypto *)object;

    if (length == 0 || length > MAX_CRYPTO_PACKET_SIZE) {
        return -1;
    }

    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    if (data[0] == NET_PACKET_COOKIE_REQUEST) {
        return tcp_handle_cookie_request(c, conn->connection_number_tcp, data, length);
    }

    // This unlocks the mutex that at this point is locked by do_tcp before
    // calling do_tcp_connections.
    pthread_mutex_unlock(&c->tcp_mutex);
    int ret = handle_packet_connection(c, crypt_connection_id, data, length, 0, userdata);
    pthread_mutex_lock(&c->tcp_mutex);

    if (ret != 0) {
        return -1;
    }

    // TODO(irungentoo): detect and kill bad TCP connections.
    return 0;
}

non_null(1, 2, 4) nullable(6)
static int tcp_oob_callback(void *object, const uint8_t *public_key, unsigned int tcp_connections_number,
                            const uint8_t *data, uint16_t length, void *userdata)
{
    Net_Crypto *c = (Net_Crypto *)object;

    if (length == 0 || length > MAX_CRYPTO_PACKET_SIZE) {
        return -1;
    }

    if (data[0] == NET_PACKET_COOKIE_REQUEST) {
        return tcp_oob_handle_cookie_request(c, tcp_connections_number, public_key, data, length);
    }

    if (data[0] == NET_PACKET_CRYPTO_HS) {
        IP_Port source;
        source.port = 0;
        source.ip.family = net_family_tcp_family;
        source.ip.ip.v6.uint32[0] = tcp_connections_number;

        if (handle_new_connection_handshake(c, &source, data, length, userdata) != 0) {
            return -1;
        }

        return 0;
    }

    return -1;
}

/** Add a tcp relay, associating it to a crypt_connection_id.
 *
 * return 0 if it was added.
 * return -1 if it wasn't.
 */
int add_tcp_relay_peer(Net_Crypto *c, int crypt_connection_id, const IP_Port *ip_port, const uint8_t *public_key)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    pthread_mutex_lock(&c->tcp_mutex);
    int ret = add_tcp_relay_connection(c->tcp_c, conn->connection_number_tcp, ip_port, public_key);
    pthread_mutex_unlock(&c->tcp_mutex);
    return ret;
}

/** Add a tcp relay to the array.
 *
 * return 0 if it was added.
 * return -1 if it wasn't.
 */
int add_tcp_relay(Net_Crypto *c, const IP_Port *ip_port, const uint8_t *public_key)
{
    pthread_mutex_lock(&c->tcp_mutex);
    int ret = add_tcp_relay_global(c->tcp_c, ip_port, public_key);
    pthread_mutex_unlock(&c->tcp_mutex);
    return ret;
}

/** Return a random TCP connection number for use in send_tcp_onion_request.
 *
 * TODO(irungentoo): This number is just the index of an array that the elements can
 * change without warning.
 *
 * return TCP connection number on success.
 * return -1 on failure.
 */
int get_random_tcp_con_number(Net_Crypto *c)
{
    pthread_mutex_lock(&c->tcp_mutex);
    int ret = get_random_tcp_onion_conn_number(c->tcp_c);
    pthread_mutex_unlock(&c->tcp_mutex);

    return ret;
}

/** Send an onion packet via the TCP relay corresponding to tcp_connections_number.
 *
 * return 0 on success.
 * return -1 on failure.
 */
int send_tcp_onion_request(Net_Crypto *c, unsigned int tcp_connections_number, const uint8_t *data, uint16_t length)
{
    pthread_mutex_lock(&c->tcp_mutex);
    int ret = tcp_send_onion_request(c->tcp_c, tcp_connections_number, data, length);
    pthread_mutex_unlock(&c->tcp_mutex);

    return ret;
}

/** Copy a maximum of num random TCP relays we are connected to to tcp_relays.
 * NOTE that the family of the copied ip ports will be set to TCP_INET or TCP_INET6.
 *
 * return number of relays copied to tcp_relays on success.
 * return 0 on failure.
 */
unsigned int copy_connected_tcp_relays(Net_Crypto *c, Node_format *tcp_relays, uint16_t num)
{
    if (num == 0) {
        return 0;
    }

    pthread_mutex_lock(&c->tcp_mutex);
    unsigned int ret = tcp_copy_connected_relays(c->tcp_c, tcp_relays, num);
    pthread_mutex_unlock(&c->tcp_mutex);

    return ret;
}

uint32_t copy_connected_tcp_relays_index(Net_Crypto *c, Node_format *tcp_relays, uint16_t num, uint32_t idx)
{
    if (num == 0) {
        return 0;
    }

    pthread_mutex_lock(&c->tcp_mutex);
    uint32_t ret = tcp_copy_connected_relays_index(c->tcp_c, tcp_relays, num, idx);
    pthread_mutex_unlock(&c->tcp_mutex);

    return ret;
}

non_null()
static void do_tcp(Net_Crypto *c, void *userdata)
{
    pthread_mutex_lock(&c->tcp_mutex);
    do_tcp_connections(c->log, c->tcp_c, userdata);
    pthread_mutex_unlock(&c->tcp_mutex);

    for (uint32_t i = 0; i < c->crypto_connections_length; ++i) {
        const Crypto_Connection *conn = get_crypto_connection(c, i);

        if (conn == nullptr) {
            continue;
        }

        if (conn->status != CRYPTO_CONN_ESTABLISHED) {
            continue;
        }

        bool direct_connected = false;

        if (!crypto_connection_status(c, i, &direct_connected, nullptr)) {
            continue;
        }

        pthread_mutex_lock(&c->tcp_mutex);
        set_tcp_connection_to_status(c->tcp_c, conn->connection_number_tcp, !direct_connected);
        pthread_mutex_unlock(&c->tcp_mutex);
    }
}

/** Set function to be called when connection with crypt_connection_id goes connects/disconnects.
 *
 * The set function should return -1 on failure and 0 on success.
 * Note that if this function is set, the connection will clear itself on disconnect.
 * Object and id will be passed to this function untouched.
 * status is 1 if the connection is going online, 0 if it is going offline.
 *
 * return -1 on failure.
 * return 0 on success.
 */
int connection_status_handler(const Net_Crypto *c, int crypt_connection_id,
                              connection_status_cb *connection_status_callback, void *object, int id)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    conn->connection_status_callback = connection_status_callback;
    conn->connection_status_callback_object = object;
    conn->connection_status_callback_id = id;
    return 0;
}

/** Set function to be called when connection with crypt_connection_id receives a lossless data packet of length.
 *
 * The set function should return -1 on failure and 0 on success.
 * Object and id will be passed to this function untouched.
 *
 * return -1 on failure.
 * return 0 on success.
 */
int connection_data_handler(const Net_Crypto *c, int crypt_connection_id,
                            connection_data_cb *connection_data_callback, void *object, int id)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    conn->connection_data_callback = connection_data_callback;
    conn->connection_data_callback_object = object;
    conn->connection_data_callback_id = id;
    return 0;
}

/** Set function to be called when connection with crypt_connection_id receives a lossy data packet of length.
 *
 * The set function should return -1 on failure and 0 on success.
 * Object and id will be passed to this function untouched.
 *
 * return -1 on failure.
 * return 0 on success.
 */
int connection_lossy_data_handler(const Net_Crypto *c, int crypt_connection_id,
                                  connection_lossy_data_cb *connection_lossy_data_callback,
                                  void *object, int id)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    conn->connection_lossy_data_callback = connection_lossy_data_callback;
    conn->connection_lossy_data_callback_object = object;
    conn->connection_lossy_data_callback_id = id;
    return 0;
}


/** Set the function for this friend that will be callbacked with object and number if
 * the friend sends us a different dht public key than we have associated to him.
 *
 * If this function is called, the connection should be recreated with the new public key.
 *
 * object and number will be passed as argument to this function.
 *
 * return -1 on failure.
 * return 0 on success.
 */
int nc_dht_pk_callback(const Net_Crypto *c, int crypt_connection_id, dht_pk_cb *function, void *object, uint32_t number)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    conn->dht_pk_callback = function;
    conn->dht_pk_callback_object = object;
    conn->dht_pk_callback_number = number;
    return 0;
}

/** Get the crypto connection id from the ip_port.
 *
 * return -1 on failure.
 * return connection id on success.
 */
non_null()
static int crypto_id_ip_port(const Net_Crypto *c, const IP_Port *ip_port)
{
    return bs_list_find(&c->ip_port_list, (const uint8_t *)ip_port);
}

#define CRYPTO_MIN_PACKET_SIZE (1 + sizeof(uint16_t) + CRYPTO_MAC_SIZE)

/** Handle raw UDP packets coming directly from the socket.
 *
 * Handles:
 * Cookie response packets.
 * Crypto handshake packets.
 * Crypto data packets.
 *
 */
non_null(1, 2, 3) nullable(5)
static int udp_handle_packet(void *object, const IP_Port *source, const uint8_t *packet, uint16_t length,
                             void *userdata)
{
    Net_Crypto *c = (Net_Crypto *)object;

    if (length <= CRYPTO_MIN_PACKET_SIZE || length > MAX_CRYPTO_PACKET_SIZE) {
        return 1;
    }

    const int crypt_connection_id = crypto_id_ip_port(c, source);

    if (crypt_connection_id == -1) {
        if (packet[0] != NET_PACKET_CRYPTO_HS) {
            return 1;
        }

        if (handle_new_connection_handshake(c, source, packet, length, userdata) != 0) {
            return 1;
        }

        return 0;
    }

    if (handle_packet_connection(c, crypt_connection_id, packet, length, 1, userdata) != 0) {
        return 1;
    }

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    pthread_mutex_lock(conn->mutex);

    if (net_family_is_ipv4(source->ip.family)) {
        conn->direct_lastrecv_timev4 = mono_time_get(c->mono_time);
    } else {
        conn->direct_lastrecv_timev6 = mono_time_get(c->mono_time);
    }

    pthread_mutex_unlock(conn->mutex);
    return 0;
}

/** The dT for the average packet receiving rate calculations.
 * Also used as the */
#define PACKET_COUNTER_AVERAGE_INTERVAL 50

/** Ratio of recv queue size / recv packet rate (in seconds) times
 * the number of ms between request packets to send at that ratio
 */
#define REQUEST_PACKETS_COMPARE_CONSTANT (0.125 * 100.0)

/** Timeout for increasing speed after congestion event (in ms). */
#define CONGESTION_EVENT_TIMEOUT 1000

/** If the send queue is SEND_QUEUE_RATIO times larger than the
 * calculated link speed the packet send speed will be reduced
 * by a value depending on this number.
 */
#define SEND_QUEUE_RATIO 2.0

non_null()
static void send_crypto_packets(Net_Crypto *c)
{
    const uint64_t temp_time = current_time_monotonic(c->mono_time);
    double total_send_rate = 0;
    uint32_t peak_request_packet_interval = -1;

    for (uint32_t i = 0; i < c->crypto_connections_length; ++i) {
        Crypto_Connection *conn = get_crypto_connection(c, i);

        if (conn == nullptr) {
            continue;
        }

        if ((CRYPTO_SEND_PACKET_INTERVAL + conn->temp_packet_sent_time) < temp_time) {
            send_temp_packet(c, i);
        }

        if ((conn->status == CRYPTO_CONN_NOT_CONFIRMED || conn->status == CRYPTO_CONN_ESTABLISHED)
                && (CRYPTO_SEND_PACKET_INTERVAL + conn->last_request_packet_sent) < temp_time) {
            if (send_request_packet(c, i) == 0) {
                conn->last_request_packet_sent = temp_time;
            }
        }

        if (conn->status == CRYPTO_CONN_ESTABLISHED) {
            if (conn->packet_recv_rate > CRYPTO_PACKET_MIN_RATE) {
                double request_packet_interval = REQUEST_PACKETS_COMPARE_CONSTANT / ((num_packets_array(
                                                     &conn->recv_array) + 1.0) / (conn->packet_recv_rate + 1.0));

                double request_packet_interval2 = ((CRYPTO_PACKET_MIN_RATE / conn->packet_recv_rate) *
                                                   (double)CRYPTO_SEND_PACKET_INTERVAL) + (double)PACKET_COUNTER_AVERAGE_INTERVAL;

                if (request_packet_interval2 < request_packet_interval) {
                    request_packet_interval = request_packet_interval2;
                }

                if (request_packet_interval < PACKET_COUNTER_AVERAGE_INTERVAL) {
                    request_packet_interval = PACKET_COUNTER_AVERAGE_INTERVAL;
                }

                if (request_packet_interval > CRYPTO_SEND_PACKET_INTERVAL) {
                    request_packet_interval = CRYPTO_SEND_PACKET_INTERVAL;
                }

                if (temp_time - conn->last_request_packet_sent > (uint64_t)request_packet_interval) {
                    if (send_request_packet(c, i) == 0) {
                        conn->last_request_packet_sent = temp_time;
                    }
                }

                if (request_packet_interval < peak_request_packet_interval) {
                    peak_request_packet_interval = request_packet_interval;
                }
            }

            if ((PACKET_COUNTER_AVERAGE_INTERVAL + conn->packet_counter_set) < temp_time) {
                const double dt = (double)(temp_time - conn->packet_counter_set);

                conn->packet_recv_rate = (double)conn->packet_counter / (dt / 1000.0);
                conn->packet_counter = 0;
                conn->packet_counter_set = temp_time;

                uint32_t packets_sent = conn->packets_sent;
                conn->packets_sent = 0;

                uint32_t packets_resent = conn->packets_resent;
                conn->packets_resent = 0;

                /* conjestion control
                 *  calculate a new value of conn->packet_send_rate based on some data
                 */

                unsigned int pos = conn->last_sendqueue_counter % CONGESTION_QUEUE_ARRAY_SIZE;
                conn->last_sendqueue_size[pos] = num_packets_array(&conn->send_array);

                long signed int sum = 0;
                sum = (long signed int)conn->last_sendqueue_size[pos] -
                      (long signed int)conn->last_sendqueue_size[(pos + 1) % CONGESTION_QUEUE_ARRAY_SIZE];

                unsigned int n_p_pos = conn->last_sendqueue_counter % CONGESTION_LAST_SENT_ARRAY_SIZE;
                conn->last_num_packets_sent[n_p_pos] = packets_sent;
                conn->last_num_packets_resent[n_p_pos] = packets_resent;

                conn->last_sendqueue_counter = (conn->last_sendqueue_counter + 1) %
                                               (CONGESTION_QUEUE_ARRAY_SIZE * CONGESTION_LAST_SENT_ARRAY_SIZE);

                bool direct_connected = 0;
                /* return value can be ignored since the `if` above ensures the connection is established */
                crypto_connection_status(c, i, &direct_connected, nullptr);

                /* When switching from TCP to UDP, don't change the packet send rate for CONGESTION_EVENT_TIMEOUT ms. */
                if (!(direct_connected && conn->last_tcp_sent + CONGESTION_EVENT_TIMEOUT > temp_time)) {
                    long signed int total_sent = 0;
                    long signed int total_resent = 0;

                    // TODO(irungentoo): use real delay
                    unsigned int delay = (unsigned int)(((double)conn->rtt_time / PACKET_COUNTER_AVERAGE_INTERVAL) + 0.5);
                    unsigned int packets_set_rem_array = CONGESTION_LAST_SENT_ARRAY_SIZE - CONGESTION_QUEUE_ARRAY_SIZE;

                    if (delay > packets_set_rem_array) {
                        delay = packets_set_rem_array;
                    }

                    for (unsigned j = 0; j < CONGESTION_QUEUE_ARRAY_SIZE; ++j) {
                        unsigned int ind = (j + (packets_set_rem_array  - delay) + n_p_pos) % CONGESTION_LAST_SENT_ARRAY_SIZE;
                        total_sent += conn->last_num_packets_sent[ind];
                        total_resent += conn->last_num_packets_resent[ind];
                    }

                    if (sum > 0) {
                        total_sent -= sum;
                    } else {
                        if (total_resent > -sum) {
                            total_resent = -sum;
                        }
                    }

                    /* if queue is too big only allow resending packets. */
                    uint32_t npackets = num_packets_array(&conn->send_array);
                    double min_speed = 1000.0 * (((double)total_sent) / ((double)CONGESTION_QUEUE_ARRAY_SIZE *
                                                 PACKET_COUNTER_AVERAGE_INTERVAL));

                    double min_speed_request = 1000.0 * (((double)(total_sent + total_resent)) / (
                            (double)CONGESTION_QUEUE_ARRAY_SIZE * PACKET_COUNTER_AVERAGE_INTERVAL));

                    if (min_speed < CRYPTO_PACKET_MIN_RATE) {
                        min_speed = CRYPTO_PACKET_MIN_RATE;
                    }

                    double send_array_ratio = (double)npackets / min_speed;

                    // TODO(irungentoo): Improve formula?
                    if (send_array_ratio > SEND_QUEUE_RATIO && CRYPTO_MIN_QUEUE_LENGTH < npackets) {
                        conn->packet_send_rate = min_speed * (1.0 / (send_array_ratio / SEND_QUEUE_RATIO));
                    } else if (conn->last_congestion_event + CONGESTION_EVENT_TIMEOUT < temp_time) {
                        conn->packet_send_rate = min_speed * 1.2;
                    } else {
                        conn->packet_send_rate = min_speed * 0.9;
                    }

                    conn->packet_send_rate_requested = min_speed_request * 1.2;

                    if (conn->packet_send_rate < CRYPTO_PACKET_MIN_RATE) {
                        conn->packet_send_rate = CRYPTO_PACKET_MIN_RATE;
                    }

                    if (conn->packet_send_rate_requested < conn->packet_send_rate) {
                        conn->packet_send_rate_requested = conn->packet_send_rate;
                    }
                }
            }

            if (conn->last_packets_left_set == 0 || conn->last_packets_left_requested_set == 0) {
                conn->last_packets_left_requested_set = temp_time;
                conn->last_packets_left_set = temp_time;
                conn->packets_left_requested = CRYPTO_MIN_QUEUE_LENGTH;
                conn->packets_left = CRYPTO_MIN_QUEUE_LENGTH;
            } else {
                if (((uint64_t)((1000.0 / conn->packet_send_rate) + 0.5) + conn->last_packets_left_set) <= temp_time) {
                    double n_packets = conn->packet_send_rate * (((double)(temp_time - conn->last_packets_left_set)) / 1000.0);
                    n_packets += conn->last_packets_left_rem;

                    uint32_t num_packets = n_packets;
                    double rem = n_packets - (double)num_packets;

                    if (conn->packets_left > num_packets * 4 + CRYPTO_MIN_QUEUE_LENGTH) {
                        conn->packets_left = num_packets * 4 + CRYPTO_MIN_QUEUE_LENGTH;
                    } else {
                        conn->packets_left += num_packets;
                    }

                    conn->last_packets_left_set = temp_time;
                    conn->last_packets_left_rem = rem;
                }

                if (((uint64_t)((1000.0 / conn->packet_send_rate_requested) + 0.5) + conn->last_packets_left_requested_set) <=
                        temp_time) {
                    double n_packets = conn->packet_send_rate_requested * (((double)(temp_time - conn->last_packets_left_requested_set)) /
                                       1000.0);
                    n_packets += conn->last_packets_left_requested_rem;

                    uint32_t num_packets = n_packets;
                    double rem = n_packets - (double)num_packets;
                    conn->packets_left_requested = num_packets;

                    conn->last_packets_left_requested_set = temp_time;
                    conn->last_packets_left_requested_rem = rem;
                }

                if (conn->packets_left > conn->packets_left_requested) {
                    conn->packets_left_requested = conn->packets_left;
                }
            }

            int ret = send_requested_packets(c, i, conn->packets_left_requested);

            if (ret != -1) {
                conn->packets_left_requested -= ret;
                conn->packets_resent += ret;

                if ((unsigned int)ret < conn->packets_left) {
                    conn->packets_left -= ret;
                } else {
                    conn->last_congestion_event = temp_time;
                    conn->packets_left = 0;
                }
            }

            if (conn->packet_send_rate > CRYPTO_PACKET_MIN_RATE * 1.5) {
                total_send_rate += conn->packet_send_rate;
            }
        }
    }

    c->current_sleep_time = -1;
    uint32_t sleep_time = peak_request_packet_interval;

    if (c->current_sleep_time > sleep_time) {
        c->current_sleep_time = sleep_time;
    }

    if (total_send_rate > CRYPTO_PACKET_MIN_RATE) {
        sleep_time = (1000.0 / total_send_rate);

        if (c->current_sleep_time > sleep_time) {
            c->current_sleep_time = sleep_time + 1;
        }
    }

    sleep_time = CRYPTO_SEND_PACKET_INTERVAL;

    if (c->current_sleep_time > sleep_time) {
        c->current_sleep_time = sleep_time;
    }
}

/** Return 1 if max speed was reached for this connection (no more data can be physically through the pipe).
 * Return 0 if it wasn't reached.
 */
bool max_speed_reached(Net_Crypto *c, int crypt_connection_id)
{
    return reset_max_speed_reached(c, crypt_connection_id) != 0;
}

/** returns the number of packet slots left in the sendbuffer.
 * return 0 if failure.
 */
uint32_t crypto_num_free_sendqueue_slots(const Net_Crypto *c, int crypt_connection_id)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return 0;
    }

    uint32_t max_packets = CRYPTO_PACKET_BUFFER_SIZE - num_packets_array(&conn->send_array);

    if (conn->packets_left < max_packets) {
        return conn->packets_left;
    }

    return max_packets;
}

/** Sends a lossless cryptopacket.
 *
 * return -1 if data could not be put in packet queue.
 * return positive packet number if data was put into the queue.
 *
 * The first byte of data must be in the PACKET_ID_RANGE_LOSSLESS.
 *
 * congestion_control: should congestion control apply to this packet?
 */
int64_t write_cryptpacket(Net_Crypto *c, int crypt_connection_id, const uint8_t *data, uint16_t length,
                          uint8_t congestion_control)
{
    if (length == 0) {
        // We need at least a packet id.
        LOGGER_ERROR(c->log, "rejecting empty packet for crypto connection %d", crypt_connection_id);
        return -1;
    }

    if (data[0] < PACKET_ID_RANGE_LOSSLESS_START || data[0] > PACKET_ID_RANGE_LOSSLESS_END) {
        LOGGER_ERROR(c->log, "rejecting lossless packet with out-of-range id %d", data[0]);
        return -1;
    }

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        LOGGER_WARNING(c->log, "invalid crypt connection id %d", crypt_connection_id);
        return -1;
    }

    if (conn->status != CRYPTO_CONN_ESTABLISHED) {
        LOGGER_WARNING(c->log, "attempted to send packet to non-established connection %d", crypt_connection_id);
        return -1;
    }

    if (congestion_control && conn->packets_left == 0) {
        LOGGER_ERROR(c->log, "congestion control: rejecting packet of length %d on crypt connection %d", length,
                     crypt_connection_id);
        return -1;
    }

    const int64_t ret = send_lossless_packet(c, crypt_connection_id, data, length, congestion_control);

    if (ret == -1) {
        return -1;
    }

    if (congestion_control) {
        --conn->packets_left;
        --conn->packets_left_requested;
        ++conn->packets_sent;
    }

    return ret;
}

/** Check if packet_number was received by the other side.
 *
 * packet_number must be a valid packet number of a packet sent on this connection.
 *
 * return -1 on failure.
 * return 0 on success.
 *
 * Note: The condition `buffer_end - buffer_start < packet_number - buffer_start` is
 * a trick which handles situations `buffer_end >= buffer_start` and
 * `buffer_end < buffer_start` (when buffer_end overflowed) both correctly.
 *
 * It CANNOT be simplified to `packet_number < buffer_start`, as it will fail
 * when `buffer_end < buffer_start`.
 */
int cryptpacket_received(const Net_Crypto *c, int crypt_connection_id, uint32_t packet_number)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return -1;
    }

    uint32_t num = num_packets_array(&conn->send_array);
    uint32_t num1 = packet_number - conn->send_array.buffer_start;

    if (num >= num1) {
        return -1;
    }

    return 0;
}

/** Sends a lossy cryptopacket.
 *
 * return -1 on failure.
 * return 0 on success.
 *
 * The first byte of data must be in the PACKET_ID_RANGE_LOSSY.
 */
int send_lossy_cryptpacket(Net_Crypto *c, int crypt_connection_id, const uint8_t *data, uint16_t length)
{
    if (length == 0 || length > MAX_CRYPTO_DATA_SIZE) {
        return -1;
    }

    if (data[0] < PACKET_ID_RANGE_LOSSY_START || data[0] > PACKET_ID_RANGE_LOSSY_END) {
        return -1;
    }

    pthread_mutex_lock(&c->connections_mutex);
    ++c->connection_use_counter;
    pthread_mutex_unlock(&c->connections_mutex);

    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    int ret = -1;

    if (conn != nullptr) {
        pthread_mutex_lock(conn->mutex);
        uint32_t buffer_start = conn->recv_array.buffer_start;
        uint32_t buffer_end = conn->send_array.buffer_end;
        pthread_mutex_unlock(conn->mutex);
        ret = send_data_packet_helper(c, crypt_connection_id, buffer_start, buffer_end, data, length);
    }

    pthread_mutex_lock(&c->connections_mutex);
    --c->connection_use_counter;
    pthread_mutex_unlock(&c->connections_mutex);

    return ret;
}

/** Kill a crypto connection.
 *
 * return -1 on failure.
 * return 0 on success.
 */
int crypto_kill(Net_Crypto *c, int crypt_connection_id)
{
    Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    int ret = -1;

    if (conn != nullptr) {
        if (conn->status == CRYPTO_CONN_ESTABLISHED) {
            send_kill_packet(c, crypt_connection_id);
        }

        pthread_mutex_lock(&c->tcp_mutex);
        kill_tcp_connection_to(c->tcp_c, conn->connection_number_tcp);
        pthread_mutex_unlock(&c->tcp_mutex);

        bs_list_remove(&c->ip_port_list, (uint8_t *)&conn->ip_portv4, crypt_connection_id);
        bs_list_remove(&c->ip_port_list, (uint8_t *)&conn->ip_portv6, crypt_connection_id);
        clear_temp_packet(c, crypt_connection_id);
        clear_buffer(&conn->send_array);
        clear_buffer(&conn->recv_array);
        ret = wipe_crypto_connection(c, crypt_connection_id);
    }

    return ret;
}

bool crypto_connection_status(const Net_Crypto *c, int crypt_connection_id, bool *direct_connected,
                              uint32_t *online_tcp_relays)
{
    const Crypto_Connection *conn = get_crypto_connection(c, crypt_connection_id);

    if (conn == nullptr) {
        return false;
    }

    if (direct_connected != nullptr) {
        *direct_connected = 0;

        const uint64_t current_time = mono_time_get(c->mono_time);

        if ((UDP_DIRECT_TIMEOUT + conn->direct_lastrecv_timev4) > current_time) {
            *direct_connected = 1;
        } else if ((UDP_DIRECT_TIMEOUT + conn->direct_lastrecv_timev6) > current_time) {
            *direct_connected = 1;
        }
    }

    if (online_tcp_relays != nullptr) {
        *online_tcp_relays = tcp_connection_to_online_tcp_relays(c->tcp_c, conn->connection_number_tcp);
    }

    return true;
}

void new_keys(Net_Crypto *c)
{
    crypto_new_keypair(c->self_public_key, c->self_secret_key);
}

/** Save the public and private keys to the keys array.
 *  Length must be CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_SECRET_KEY_SIZE.
 *
 * TODO(irungentoo): Save only secret key.
 */
void save_keys(const Net_Crypto *c, uint8_t *keys)
{
    memcpy(keys, c->self_public_key, CRYPTO_PUBLIC_KEY_SIZE);
    memcpy(keys + CRYPTO_PUBLIC_KEY_SIZE, c->self_secret_key, CRYPTO_SECRET_KEY_SIZE);
}

/** Load the secret key.
 * Length must be CRYPTO_SECRET_KEY_SIZE.
 */
void load_secret_key(Net_Crypto *c, const uint8_t *sk)
{
    memcpy(c->self_secret_key, sk, CRYPTO_SECRET_KEY_SIZE);
    crypto_derive_public_key(c->self_public_key, c->self_secret_key);
}

/** Create new instance of Net_Crypto.
 *  Sets all the global connection variables to their default values.
 */
Net_Crypto *new_net_crypto(const Logger *log, Mono_Time *mono_time, DHT *dht, const TCP_Proxy_Info *proxy_info)
{
    if (dht == nullptr) {
        return nullptr;
    }

    Net_Crypto *temp = (Net_Crypto *)calloc(1, sizeof(Net_Crypto));

    if (temp == nullptr) {
        return nullptr;
    }

    temp->log = log;
    temp->mono_time = mono_time;

    temp->tcp_c = new_tcp_connections(log, mono_time, dht_get_self_secret_key(dht), proxy_info);

    if (temp->tcp_c == nullptr) {
        free(temp);
        return nullptr;
    }

    set_packet_tcp_connection_callback(temp->tcp_c, &tcp_data_callback, temp);
    set_oob_packet_tcp_connection_callback(temp->tcp_c, &tcp_oob_callback, temp);

    if (create_recursive_mutex(&temp->tcp_mutex) != 0 ||
            pthread_mutex_init(&temp->connections_mutex, nullptr) != 0) {
        kill_tcp_connections(temp->tcp_c);
        free(temp);
        return nullptr;
    }

    temp->dht = dht;

    new_keys(temp);
    new_symmetric_key(temp->secret_symmetric_key);

    temp->current_sleep_time = CRYPTO_SEND_PACKET_INTERVAL;

    networking_registerhandler(dht_get_net(dht), NET_PACKET_COOKIE_REQUEST, &udp_handle_cookie_request, temp);
    networking_registerhandler(dht_get_net(dht), NET_PACKET_COOKIE_RESPONSE, &udp_handle_packet, temp);
    networking_registerhandler(dht_get_net(dht), NET_PACKET_CRYPTO_HS, &udp_handle_packet, temp);
    networking_registerhandler(dht_get_net(dht), NET_PACKET_CRYPTO_DATA, &udp_handle_packet, temp);

    bs_list_init(&temp->ip_port_list, sizeof(IP_Port), 8);

    return temp;
}

non_null(1) nullable(2)
static void kill_timedout(Net_Crypto *c, void *userdata)
{
    for (uint32_t i = 0; i < c->crypto_connections_length; ++i) {
        const Crypto_Connection *conn = get_crypto_connection(c, i);

        if (conn == nullptr) {
            continue;
        }

        if (conn->status == CRYPTO_CONN_COOKIE_REQUESTING || conn->status == CRYPTO_CONN_HANDSHAKE_SENT
                || conn->status == CRYPTO_CONN_NOT_CONFIRMED) {
            if (conn->temp_packet_num_sent < MAX_NUM_SENDPACKET_TRIES) {
                continue;
            }

            connection_kill(c, i, userdata);
        }

#if 0

        if (conn->status == CRYPTO_CONN_ESTABLISHED) {
            // TODO(irungentoo): add a timeout here?
            do_timeout_here();
        }

#endif
    }
}

/** return the optimal interval in ms for running do_net_crypto.
 */
uint32_t crypto_run_interval(const Net_Crypto *c)
{
    return c->current_sleep_time;
}

/** Main loop. */
void do_net_crypto(Net_Crypto *c, void *userdata)
{
    kill_timedout(c, userdata);
    do_tcp(c, userdata);
    send_crypto_packets(c);
}

void kill_net_crypto(Net_Crypto *c)
{
    for (uint32_t i = 0; i < c->crypto_connections_length; ++i) {
        crypto_kill(c, i);
    }

    pthread_mutex_destroy(&c->tcp_mutex);
    pthread_mutex_destroy(&c->connections_mutex);

    kill_tcp_connections(c->tcp_c);
    bs_list_free(&c->ip_port_list);
    networking_registerhandler(dht_get_net(c->dht), NET_PACKET_COOKIE_REQUEST, nullptr, nullptr);
    networking_registerhandler(dht_get_net(c->dht), NET_PACKET_COOKIE_RESPONSE, nullptr, nullptr);
    networking_registerhandler(dht_get_net(c->dht), NET_PACKET_CRYPTO_HS, nullptr, nullptr);
    networking_registerhandler(dht_get_net(c->dht), NET_PACKET_CRYPTO_DATA, nullptr, nullptr);
    crypto_memzero(c, sizeof(Net_Crypto));
    free(c);
}