/*
 *  OpenVPN -- An application to securely tunnel IP networks
 *             over a single TCP/UDP port, with support for SSL/TLS-based
 *             session authentication and key exchange,
 *             packet encryption, packet authentication, and
 *             packet compression.
 *
 *  Copyright (C) 2002-2026 OpenVPN Inc <sales@openvpn.net>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, see <https://www.gnu.org/licenses/>.
 */

#ifndef OCC_H
#define OCC_H

#include "forward.h"

/* OCC_STRING_SIZE must be set to sizeof (occ_magic) */
#define OCC_STRING_SIZE 16

/*
 * OCC (OpenVPN Configuration Control) protocol opcodes.
 */

#define OCC_REQUEST 0 /* request options string from peer */
#define OCC_REPLY   1 /* deliver options string to peer */

/*
 * Send an OCC_REQUEST once every OCC_INTERVAL
 * seconds until a reply is received.
 *
 * If we haven't received a reply after
 * OCC_N_TRIES, give up.
 */
#define OCC_INTERVAL_SECONDS 10
#define OCC_N_TRIES          12

/*
 * Other OCC protocol opcodes used to estimate the MTU empirically.
 */
#define OCC_MTU_LOAD_REQUEST 2 /* Ask peer to send a big packet to us */
#define OCC_MTU_LOAD         3 /* Send a big packet to peer */
#define OCC_MTU_REQUEST                                           \
    4                          /* Ask peer to tell us the largest \
                                * packet it has received from us so far */
#define OCC_MTU_REPLY 5        /* Send largest packet size to peer */

/*
 * Process one command from mtu_load_test_sequence
 * once every n seconds, if --mtu-test is specified.
 */
#define OCC_MTU_LOAD_INTERVAL_SECONDS 3

/*
 * Send an exit message to remote.
 */
#define OCC_EXIT 6

/*
 * Used to conduct a load test command sequence
 * of UDP connection for empirical MTU measurement.
 */
struct mtu_load_test
{
    int op;    /* OCC opcode to send to peer */
    int delta; /* determine packet size to send by using
                * this delta against currently
                * configured MTU */
};

extern const uint8_t occ_magic[];

static inline bool
is_occ_msg(const struct buffer *buf)
{
    return buf_string_match_head(buf, occ_magic, OCC_STRING_SIZE);
}

void process_received_occ_msg(struct context *c);

void check_send_occ_req_dowork(struct context *c);

void check_send_occ_load_test_dowork(struct context *c);

void check_send_occ_msg_dowork(struct context *c);

/*
 * Inline functions
 */

static inline int
occ_reset_op(void)
{
    return -1;
}

/*
 * Should we send an OCC_REQUEST message?
 */
static inline void
check_send_occ_req(struct context *c)
{
    if (event_timeout_defined(&c->c2.occ_interval)
        && event_timeout_trigger(&c->c2.occ_interval, &c->c2.timeval,
                                 (!TO_LINK_DEF(c) && c->c2.occ_op < 0) ? ETT_DEFAULT : 0))
    {
        check_send_occ_req_dowork(c);
    }
}

/*
 * Should we send an MTU load test?
 */
static inline void
check_send_occ_load_test(struct context *c)
{
    if (event_timeout_defined(&c->c2.occ_mtu_load_test_interval)
        && event_timeout_trigger(&c->c2.occ_mtu_load_test_interval, &c->c2.timeval,
                                 (!TO_LINK_DEF(c) && c->c2.occ_op < 0) ? ETT_DEFAULT : 0))
    {
        check_send_occ_load_test_dowork(c);
    }
}

/*
 * Should we send an OCC message?
 */
static inline void
check_send_occ_msg(struct context *c)
{
    if (c->c2.occ_op >= 0)
    {
        if (!TO_LINK_DEF(c))
        {
            check_send_occ_msg_dowork(c);
        }
        else
        {
            tv_clear(&c->c2.timeval); /* ZERO-TIMEOUT */
        }
    }
}

/**
 * Small helper function to determine if we should send the exit notification
 * via control channel.
 * @return control channel exit message should be used */
static inline bool
cc_exit_notify_enabled(struct context *c)
{
    /* Check if we have TLS active at all */
    if (!c->c2.tls_multi)
    {
        return false;
    }

    const struct key_state *ks = get_primary_key(c->c2.tls_multi);
    return (ks->crypto_options.flags & CO_USE_CC_EXIT_NOTIFY);
}
#endif /* ifndef OCC_H */
