/*
 *  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) 2002-2023 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, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */


/**
 * @file
 * Interface functions to the internal and external multiplexers.
 */


#ifndef FORWARD_H
#define FORWARD_H

/* the following macros must be defined before including any other header
 * file
 */

#define TUN_OUT(c)      (BLEN(&(c)->c2.to_tun) > 0)
#define LINK_OUT(c)     (BLEN(&(c)->c2.to_link) > 0)
#define ANY_OUT(c)      (TUN_OUT(c) || LINK_OUT(c))

#ifdef ENABLE_FRAGMENT
#define TO_LINK_FRAG(c) ((c)->c2.fragment && fragment_outgoing_defined((c)->c2.fragment))
#else
#define TO_LINK_FRAG(c) (false)
#endif

#define TO_LINK_DEF(c)  (LINK_OUT(c) || TO_LINK_FRAG(c))

#include "openvpn.h"
#include "occ.h"
#include "ping.h"

#define IOW_TO_TUN          (1<<0)
#define IOW_TO_LINK         (1<<1)
#define IOW_READ_TUN        (1<<2)
#define IOW_READ_LINK       (1<<3)
#define IOW_SHAPER          (1<<4)
#define IOW_CHECK_RESIDUAL  (1<<5)
#define IOW_FRAG            (1<<6)
#define IOW_MBUF            (1<<7)
#define IOW_READ_TUN_FORCE  (1<<8)
#define IOW_WAIT_SIGNAL     (1<<9)

#define IOW_READ            (IOW_READ_TUN|IOW_READ_LINK)

extern counter_type link_read_bytes_global;

extern counter_type link_write_bytes_global;

void io_wait_dowork(struct context *c, const unsigned int flags);

void pre_select(struct context *c);

void process_io(struct context *c);

/**********************************************************************/
/**
 * Process a data channel packet that will be sent through a VPN tunnel.
 * @ingroup data_control
 *
 * This function controls the processing of a data channel packet which
 * will be sent through a VPN tunnel to a remote OpenVPN peer.  It's
 * general structure is as follows:
 * - Check that the client authentication has succeeded; if not, drop the
 *   packet.
 * - If the \a comp_frag argument is true:
 *   - Call \c lzo_compress() of the \link Data Channel Compression
 *     module\endlink to (possibly) compress the packet.
 *   - Call \c fragment_outgoing() of the \link Data Channel Fragmentation
 *     module\endlink to (possibly) fragment the packet.
 * - Activate the \link Data Channel Crypto module\endlink to perform
 *   security operations on the packet.
 *   - Call \c tls_pre_encrypt() to choose the appropriate security
 *     parameters for this packet.
 *   - Call \c openvpn_encrypt() to encrypt and HMAC signed the packet.
 *   - Call \c tls_post_encrypt() to prepend the one-byte OpenVPN header
 *     and do some TLS accounting.
 * - Place the resulting packet in \c c->c2.to_link so that it can be sent
 *   over the external network interface to its remote destination by the
 *   \link external_multiplexer External Multiplexer\endlink.
 *
 * @param c - The context structure of the VPN tunnel associated with this
 *     packet.
 * @param comp_frag - Whether to do packet compression and fragmentation.
 *     This flag is set to true the first time a packet is processed.  If
 *     the packet then gets fragmented, this function will be called again
 *     once for each remaining fragment with this parameter set to false.
 */
void encrypt_sign(struct context *c, bool comp_frag);

int get_server_poll_remaining_time(struct event_timeout *server_poll_timeout);

/**********************************************************************/
/**
 * Read a packet from the external network interface.
 * @ingroup external_multiplexer
 *
 * The packet read from the external network interface is stored in \c
 * c->c2.buf and its source address in \c c->c2.from.  If an error
 * occurred, the length of \c c->c2.buf will be 0.
 *
 * OpenVPN running as client or as UDP server only has a single external
 * network socket, so this function can be called with the single (client
 * mode) or top level (UDP server) context as its argument. OpenVPN
 * running as TCP server, on the other hand, has a network socket for each
 * active VPN tunnel.  In that case this function must be called with the
 * context associated with the appropriate VPN tunnel for which data is
 * available to be read.
 *
 * @param c - The context structure which contains the external
 *     network socket from which to read incoming packets.
 */
void read_incoming_link(struct context *c);

/**
 * Starts processing a packet read from the external network interface.
 * @ingroup external_multiplexer
 *
 * This function starts the processing of a data channel packet which
 * has come out of a VPN tunnel.  It's high-level structure is as follows:
 * - Verify that a nonzero length packet has been received from a valid
 *   source address for the given context \a c.
 * - Call \c tls_pre_decrypt(), which splits data channel and control
 *   channel packets:
 *   - If a data channel packet, the appropriate security parameters are
 *     loaded.
 *   - If a control channel packet, this function process is it and
 *     afterwards sets the packet's buffer length to 0, so that the data
 *     channel processing steps below will ignore it.
 * - Call \c openvpn_decrypt() of the \link data_crypto Data Channel
 *   Crypto module\endlink to authenticate and decrypt the packet using
 *   the security parameters loaded by \c tls_pre_decrypt() above.
 *
 * @param c - The context structure of the VPN tunnel associated with the
 *     packet.
 * @param lsi - link_socket_info obtained from context before processing.
 * @param floated - Flag indicates that peer has floated.
 *
 * @return true if packet is authenticated, false otherwise.
 */
bool process_incoming_link_part1(struct context *c, struct link_socket_info *lsi, bool floated);

/**
 * Continues processing a packet read from the external network interface.
 * @ingroup external_multiplexer
 *
 * This function continues the processing of a data channel packet which
 * has come out of a VPN tunnel. It must be called after
 * \c process_incoming_link_part1() function.
 *
 * It's high-level structure is as follows:
 * - Call \c fragment_incoming() of the \link fragmentation Data Channel
 *   Fragmentation module\endlink to reassemble the packet if it's
 *   fragmented.
 * - Call \c lzo_decompress() of the \link compression Data Channel
 *   Compression module\endlink to decompress the packet if it's
 *   compressed.
 * - Place the resulting packet in \c c->c2.to_tun so that it can be sent
 *   over the virtual tun/tap network interface to its local destination
 *   by the \link internal_multiplexer Internal Multiplexer\endlink.
 *
 * @param c - The context structure of the VPN tunnel associated with the
 *     packet.
 * @param lsi - link_socket_info obtained from context before processing.
 * @param orig_buf - Pointer to a buffer data.
 *
 */
void process_incoming_link_part2(struct context *c, struct link_socket_info *lsi, const uint8_t *orig_buf);

/**
 * Write a packet to the external network interface.
 * @ingroup external_multiplexer
 *
 * This function writes the packet stored in \c c->c2.to_link to the
 * external network device contained within \c c->c1.link_socket.
 *
 * If an error occurs, it is logged and the packet is dropped.
 *
 * @param c - The context structure of the VPN tunnel associated with the
 *     packet.
 */
void process_outgoing_link(struct context *c);


/**************************************************************************/
/**
 * Read a packet from the virtual tun/tap network interface.
 * @ingroup internal_multiplexer
 *
 * This function reads a packet from the virtual tun/tap network device \c
 * c->c1.tuntap and stores it in \c c->c2.buf.
 *
 * If an error occurs, it is logged and the packet is dropped.
 *
 * @param c - The context structure in which to store the received
 *     packet.
 */
void read_incoming_tun(struct context *c);


/**
 * Process a packet read from the virtual tun/tap network interface.
 * @ingroup internal_multiplexer
 *
 * This function calls \c encrypt_sign() of the \link data_control Data
 * Channel Control module\endlink to process the packet.
 *
 * If an error occurs, it is logged and the packet is dropped.
 *
 * @param c - The context structure of the VPN tunnel associated with the
 *     packet.
 */
void process_incoming_tun(struct context *c);


/**
 * Write a packet to the virtual tun/tap network interface.
 * @ingroup internal_multiplexer
 *
 * This function writes the packet stored in \c c->c2.to_tun to the
 * virtual tun/tap network device \c c->c1.tuntap.
 *
 * If an error occurs, it is logged and the packet is dropped.
 *
 * @param c - The context structure of the VPN tunnel associated with
 *     the packet.
 */
void process_outgoing_tun(struct context *c);


/**************************************************************************/

/*
 * Send a string to remote over the TLS control channel.
 * Used for push/pull messages, passing username/password,
 * etc.
 * @param c          - The context structure of the VPN tunnel associated with
 *                     the packet.
 * @param str        - The message to be sent
 * @param msglevel   - Message level to use for logging
 */
bool
send_control_channel_string(struct context *c, const char *str, int msglevel);

/*
 * Send a string to remote over the TLS control channel.
 * Used for push/pull messages, passing username/password,
 * etc.
 *
 * This variant does not schedule the actual sending of the message
 * The caller needs to ensure that it is scheduled or call
 * send_control_channel_string
 *
 * @param multi      - The tls_multi structure of the VPN tunnel associated
 *                     with the packet.
 * @param str        - The message to be sent
 * @param msglevel   - Message level to use for logging
 */

bool
send_control_channel_string_dowork(struct tls_multi *multi,
                                   const char *str, int msglevel);


/**
 * Reschedule tls_multi_process.
 * NOTE: in multi-client mode, usually calling the function is
 * insufficient to reschedule the client instance object unless
 * multi_schedule_context_wakeup(m, mi) is also called.
 */
void reschedule_multi_process(struct context *c);

#define PIPV4_PASSTOS                   (1<<0)
#define PIP_MSSFIX                      (1<<1)         /* v4 and v6 */
#define PIP_OUTGOING                    (1<<2)
#define PIPV4_EXTRACT_DHCP_ROUTER       (1<<3)
#define PIPV4_CLIENT_NAT                (1<<4)
#define PIPV6_IMCP_NOHOST_CLIENT        (1<<5)
#define PIPV6_IMCP_NOHOST_SERVER        (1<<6)

void process_ip_header(struct context *c, unsigned int flags, struct buffer *buf);

void schedule_exit(struct context *c, const int n_seconds, const int signal);

static inline struct link_socket_info *
get_link_socket_info(struct context *c)
{
    if (c->c2.link_socket_info)
    {
        return c->c2.link_socket_info;
    }
    else
    {
        return &c->c2.link_socket->info;
    }
}

static inline void
register_activity(struct context *c, const int size)
{
    if (c->options.inactivity_timeout)
    {
        c->c2.inactivity_bytes += size;
        if (c->c2.inactivity_bytes >= c->options.inactivity_minimum_bytes)
        {
            c->c2.inactivity_bytes = 0;
            event_timeout_reset(&c->c2.inactivity_interval);
        }
    }
}

/*
 * Return the io_wait() flags appropriate for
 * a point-to-point tunnel.
 */
static inline unsigned int
p2p_iow_flags(const struct context *c)
{
    unsigned int flags = (IOW_SHAPER|IOW_CHECK_RESIDUAL|IOW_FRAG|IOW_READ|IOW_WAIT_SIGNAL);
    if (c->c2.to_link.len > 0)
    {
        flags |= IOW_TO_LINK;
    }
    if (c->c2.to_tun.len > 0)
    {
        flags |= IOW_TO_TUN;
    }
#ifdef _WIN32
    if (tuntap_ring_empty(c->c1.tuntap))
    {
        flags &= ~IOW_READ_TUN;
    }
#endif
    return flags;
}

/*
 * This is the core I/O wait function, used for all I/O waits except
 * for TCP in server mode.
 */
static inline void
io_wait(struct context *c, const unsigned int flags)
{
    if (c->c2.fast_io && (flags & (IOW_TO_TUN|IOW_TO_LINK|IOW_MBUF)))
    {
        /* fast path -- only for TUN/TAP/UDP writes */
        unsigned int ret = 0;
        if (flags & IOW_TO_TUN)
        {
            ret |= TUN_WRITE;
        }
        if (flags & (IOW_TO_LINK|IOW_MBUF))
        {
            ret |= SOCKET_WRITE;
        }
        c->c2.event_set_status = ret;
    }
    else
    {
#ifdef _WIN32
        bool skip_iowait = flags & IOW_TO_TUN;
        if (flags & IOW_READ_TUN)
        {
            /*
             * don't read from tun if we have pending write to link,
             * since every tun read overwrites to_link buffer filled
             * by previous tun read
             */
            skip_iowait = !(flags & IOW_TO_LINK);
        }
        if (tuntap_is_wintun(c->c1.tuntap) && skip_iowait)
        {
            unsigned int ret = 0;
            if (flags & IOW_TO_TUN)
            {
                ret |= TUN_WRITE;
            }
            if (flags & IOW_READ_TUN)
            {
                ret |= TUN_READ;
            }
            c->c2.event_set_status = ret;
        }
        else
#endif /* ifdef _WIN32 */
        {
            /* slow path */
            io_wait_dowork(c, flags);
        }
    }
}

static inline bool
connection_established(struct context *c)
{
    if (c->c2.tls_multi)
    {
        return c->c2.tls_multi->multi_state >= CAS_WAITING_OPTIONS_IMPORT;
    }
    else
    {
        return get_link_socket_info(c)->connection_established;
    }
}

#endif /* FORWARD_H */
