examples/ssh_X11_client.c - master - niceSOFT/libssh

examples/ssh_X11_client.c
951 строка23 KB
Jakub Jelen
examples: Fix format string unearthed during macos build
21 янв 2025, 13:35
21 янв 2025, 13:35d545693
/*
 * ssh.c - Simple example of SSH X11 client using libssh
 *
 * Copyright (C) 2022 Marco Fortina
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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.
 *
 *  In addition, as a special exception, the copyright holders give
 *  permission to link the code of portions of this program with the
 *  OpenSSL library under certain conditions as described in each
 *  individual source file, and distribute linked combinations
 *  including the two.
 *  You must obey the GNU General Public License in all respects
 *  for all of the code used other than OpenSSL. *  If you modify
 *  file(s) with this exception, you may extend this exception to your
 *  version of the file(s), but you are not obligated to do so. *  If you
 *  do not wish to do so, delete this exception statement from your
 *  version. *  If you delete this exception statement from all source
 *  files in the program, then also delete it here.
 *
 *
 *
 * ssh_X11_client
 * ==============
 *
 * AUTHOR URL
 * https://gitlab.com/marco.fortina/libssh-x11-client/
 *
 * This is a simple example of SSH X11 client using libssh.
 *
 * Features:
 *
 * - support local display (e.g. :0)
 * - support remote display (e.g. localhost:10.0)
 * - using callbacks and event polling to significantly reduce CPU utilization
 * - use X11 forwarding with authentication spoofing (like openssh)
 *
 * Note:
 *
 * - part of this code was inspired by openssh's one.
 *
 * Dependencies:
 *
 * - gcc >= 7.5.0
 * - libssh >= 0.8.0
 * - libssh-dev >= 0.8.0
 *
 * To Build:
 * gcc -o ssh_X11_client ssh_X11_client.c -lssh -g
 *
 * Donations:
 *
 * If you liked this work and wish to support the developer please donate to:
 * Bitcoin: 1N2rQimKbeUQA8N2LU5vGopYQJmZsBM2d6
 *
 */

#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <poll.h>
#include <pthread.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <time.h>

#include <libssh/libssh.h>
#include <libssh/callbacks.h>

#include <netinet/in.h>
#include <netinet/tcp.h>

#include <sys/un.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>

/*
 * Data Structures and Macros
 */

#define _PATH_UNIX_X 	"/tmp/.X11-unix/X%d"
#define _XAUTH_CMD	"/usr/bin/xauth list %s 2>/dev/null"

typedef struct item {
    ssh_channel channel;
    int fd_in;
    int fd_out;
    int protected;
    struct item *next;
} node_t;

node_t *node = NULL;


/*
 * Mutex
 */

pthread_mutex_t mutex;


/*
 * Function declarations
 */

/* Linked nodes to manage channel/fd tuples */
static int insert_item(ssh_channel channel, int fd_in, int fd_out,
                       int protected);
static void delete_item(ssh_channel channel);
static node_t * search_item(ssh_channel channel);

/* X11 Display */
const char * ssh_gai_strerror(int gaierr);
static int x11_get_proto(const char *display, char **_proto, char **_data);
static void set_nodelay(int fd);
static int connect_local_xsocket_path(const char *pathname);
static int connect_local_xsocket(int display_number);
static int x11_connect_display(void);

/* Send data to channel */
static int copy_fd_to_channel_callback(int fd, int revents, void *userdata);

/* Read data from channel */
static int copy_channel_to_fd_callback(ssh_session session, ssh_channel channel,
                                       void *data, uint32_t len, int is_stderr,
                                       void *userdata);

/* EOF&Close channel */
static void channel_close_callback(ssh_session session, ssh_channel channel,
                                   void *userdata);

/* X11 Request */
static ssh_channel x11_open_request_callback(ssh_session session,
                                             const char *shost, int sport,
                                             void *userdata);

/* Main loop */
static int main_loop(ssh_channel channel);

/* Internals */
int64_t _current_timestamp(void);

/* Global variables */
const char *hostname = NULL;
int enableX11 = 1;

/*
 * Callbacks Data Structures
 */

/* SSH Channel Callbacks */
struct ssh_channel_callbacks_struct channel_cb =
{
    .channel_data_function = copy_channel_to_fd_callback,
    .channel_eof_function = channel_close_callback,
    .channel_close_function = channel_close_callback,
    .userdata = NULL
};

/* SSH Callbacks */
struct ssh_callbacks_struct cb =
{
    .channel_open_request_x11_function = x11_open_request_callback,
    .userdata = NULL
};


/*
 * SSH Event Context
 */

short events = POLLIN | POLLPRI | POLLERR | POLLHUP | POLLNVAL;
ssh_event event;


/*
 * Internal data structures
 */

struct termios _saved_tio;


/*
 * Internal functions
 */

int64_t _current_timestamp(void)
{
    struct timeval tv;
    int64_t milliseconds;

    gettimeofday(&tv, NULL);
    milliseconds = (int64_t)(tv.tv_sec) * 1000 + (tv.tv_usec / 1000);

    return milliseconds;
}

static void _logging_callback(int priority, const char *function,
                              const char *buffer, void *userdata)
{
    FILE *fp = NULL;
    char buf[100];
    int64_t milliseconds;

    time_t now = time(0);

    (void)userdata;

    strftime(buf, 100, "%Y-%m-%d %H:%M:%S", localtime(&now));

    fp = fopen("debug.log","a");
    if (fp == NULL) {
        printf("Error!");
        exit(-11);
    }

    milliseconds = _current_timestamp();

    fprintf(fp, "[%s.%" PRId64 ", %d] %s: %s\n", buf, milliseconds, priority,
            function, buffer);
    fclose(fp);
}

static int _enter_term_raw_mode(void)
{
    struct termios tio;
    int ret = tcgetattr(fileno(stdin), &tio);
    if (ret != -1) {
        _saved_tio = tio;
        tio.c_iflag |= IGNPAR;
        tio.c_iflag &= ~(ISTRIP | INLCR | IGNCR | ICRNL | IXON | IXANY | IXOFF);
#ifdef IUCLC
        tio.c_iflag &= ~IUCLC;
#endif
        tio.c_lflag &= ~(ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHONL);
#ifdef IEXTEN
        tio.c_lflag &= ~IEXTEN;
#endif
        tio.c_oflag &= ~OPOST;
        tio.c_cc[VMIN] = 1;
        tio.c_cc[VTIME] = 0;
        ret = tcsetattr(fileno(stdin), TCSADRAIN, &tio);
    }

    return ret;
}

static int _leave_term_raw_mode(void)
{
    int ret = tcsetattr(fileno(stdin), TCSADRAIN, &_saved_tio);
    return ret;
}


/*
 * Functions
 */

static int insert_item(ssh_channel channel, int fd_in, int fd_out,
                       int protected)
{
    node_t *node_iterator = NULL, *new = NULL;

    pthread_mutex_lock(&mutex);

    if (node == NULL) {
        /* Calloc ensure that node is full of 0 */
        node = (node_t *) calloc(1, sizeof(node_t));
        if (node == NULL) {
            pthread_mutex_unlock(&mutex);
            return -1;
        }
        node->channel = channel;
        node->fd_in = fd_in;
        node->fd_out = fd_out;
        node->protected = protected;
        node->next = NULL;
    } else {
        node_iterator = node;
        while (node_iterator->next != NULL) {
            node_iterator = node_iterator->next;
        }
        /* Create the new node */
        new = (node_t *) malloc(sizeof(node_t));
        if (new == NULL) {
            pthread_mutex_unlock(&mutex);
            return -1;
        }
        new->channel = channel;
        new->fd_in = fd_in;
        new->fd_out = fd_out;
        new->protected = protected;
        new->next = NULL;
        node_iterator->next = new;

    }

    pthread_mutex_unlock(&mutex);
    return 0;
}


static void delete_item(ssh_channel channel)
{
    node_t *current = NULL, *previous = NULL;

    pthread_mutex_lock(&mutex);

    for (current = node; current; previous = current, current = current->next) {
        if (current->channel != channel) {
            continue;
        }

        if (previous == NULL) {
            node = current->next;
        } else {
            previous->next = current->next;
        }

        free(current);
        pthread_mutex_unlock(&mutex);
        return;
    }

    pthread_mutex_unlock(&mutex);
}


static node_t *search_item(ssh_channel channel)
{
    node_t *current = NULL;

    pthread_mutex_lock(&mutex);

    current = node;
    while (current != NULL) {
        if (current->channel == channel) {
            pthread_mutex_unlock(&mutex);
            return current;
        } else {
            current = current->next;
        }
    }

    pthread_mutex_unlock(&mutex);

    return NULL;
}



static void set_nodelay(int fd)
{
    int opt, rc;
    socklen_t optlen;

    optlen = sizeof(opt);

    rc = getsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &opt, &optlen);
    if (rc == -1) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "getsockopt TCP_NODELAY: %.100s",
                 strerror(errno));
        return;
    }
    if (opt == 1) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "fd %d is TCP_NODELAY", fd);
        return;
    }
    opt = 1;
    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "fd %d setting TCP_NODELAY", fd);

    rc = setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt));
    if (rc == -1) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "setsockopt TCP_NODELAY: %.100s",
                 strerror(errno));
    }
}


const char *ssh_gai_strerror(int gaierr)
{
    if (gaierr == EAI_SYSTEM && errno != 0) {
        return strerror(errno);
    }
    return gai_strerror(gaierr);
}



static int x11_get_proto(const char *display, char **_proto, char **_cookie)
{
    char cmd[1024], line[512], xdisplay[512];
    static char proto[512], cookie[512];
    FILE *f = NULL;
    int ret = 0;

    *_proto = proto;
    *_cookie = cookie;

    proto[0] = cookie[0] = '\0';

    if (strncmp(display, "localhost:", 10) == 0) {
        ret = snprintf(xdisplay, sizeof(xdisplay), "unix:%s", display + 10);
        if (ret < 0 || (size_t)ret >= sizeof(xdisplay)) {
            _ssh_log(SSH_LOG_FUNCTIONS, __func__,
                     "display name too long. display: %s", display);
            return -1;
        }
        display = xdisplay;
    }

    snprintf(cmd, sizeof(cmd), _XAUTH_CMD, display);
    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "xauth cmd: %s", cmd);

    f = popen(cmd, "r");
    if (f && fgets(line, sizeof(line), f) &&
        sscanf(line, "%*s %511s %511s", proto, cookie) == 2) {
        ret = 0;
    } else {
        ret = 1;
    }

    if (f) {
        pclose(f);
    }

    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "proto: %s - cookie: %s - ret: %d",
             proto, cookie, ret);

    return ret;
}

static int connect_local_xsocket_path(const char *pathname)
{
    int sock, rc;
    struct sockaddr_un addr;

    sock = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sock == -1) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "socket: %.100s",
                 strerror(errno));
        return -1;
    }

    memset(&addr, 0, sizeof(addr));
    addr.sun_family = AF_UNIX;
    addr.sun_path[0] = '\0';
    /* pathname is guaranteed to be initialized and larger than addr.sun_path[108] */
    memcpy(addr.sun_path + 1, pathname, sizeof(addr.sun_path) - 1);
    rc = connect(sock, (struct sockaddr *)&addr,
                 offsetof(struct sockaddr_un, sun_path) + 1 + strlen(pathname));
    if (rc == 0) {
        return sock;
    }
    close(sock);
    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "connect %.100s: %.100s",
             addr.sun_path, strerror(errno));

    return -1;
}


static int connect_local_xsocket(int display_number)
{
    char buf[1024] = {0};
    snprintf(buf, sizeof(buf), _PATH_UNIX_X, display_number);
    return connect_local_xsocket_path(buf);
}


static int x11_connect_display(void)
{
    int display_number;
    const char *display = NULL;
    char buf[1024], *cp = NULL;
    struct addrinfo hints, *ai = NULL, *aitop = NULL;
    char strport[NI_MAXSERV];
    int gaierr = 0, sock = 0;

    /* Try to open a socket for the local X server. */
    display = getenv("DISPLAY");

    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "display: %s", display);

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

    /* Check if it is a unix domain socket. */
    if (strncmp(display, "unix:", 5) == 0 || display[0] == ':') {
        /* Connect to the unix domain socket. */
        if (sscanf(strrchr(display, ':') + 1, "%d", &display_number) != 1) {
            _ssh_log(SSH_LOG_FUNCTIONS, __func__,
                     "Could not parse display number from DISPLAY: %.100s",
                     display);
            return -1;
        }

        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "display_number: %d",
                 display_number);

        /* Create a socket. */
        sock = connect_local_xsocket(display_number);

        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "socket: %d", sock);

        if (sock < 0) {
            return -1;
        }

        /* OK, we now have a connection to the display. */
        return sock;
    }

    /* Connect to an inet socket. */
    strncpy(buf, display, sizeof(buf) - 1);
    cp = strchr(buf, ':');
    if (cp == 0) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__,
                 "Could not find ':' in DISPLAY: %.100s", display);
        return -1;
    }
    *cp = 0;
    if (sscanf(cp + 1, "%d", &display_number) != 1) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__,
                 "Could not parse display number from DISPLAY: %.100s",
                 display);
        return -1;
    }

    /* Look up the host address */
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    snprintf(strport, sizeof(strport), "%u", 6000 + display_number);
    gaierr = getaddrinfo(buf, strport, &hints, &aitop);
    if (gaierr != 0) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "%.100s: unknown host. (%s)",
                 buf, ssh_gai_strerror(gaierr));
        return -1;
    }
    for (ai = aitop; ai; ai = ai->ai_next) {
        /* Create a socket. */
        sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
        if (sock == -1) {
            _ssh_log(SSH_LOG_FUNCTIONS, __func__, "socket: %.100s",
                     strerror(errno));
            continue;
        }
        /* Connect it to the display. */
        if (connect(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
            _ssh_log(SSH_LOG_FUNCTIONS, __func__,
                     "connect %.100s port %u: %.100s", buf,
                     6000 + display_number, strerror(errno));
            close(sock);
            continue;
        }
        /* Success */
        break;
    }
    freeaddrinfo(aitop);
    if (ai == 0) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "connect %.100s port %u: %.100s",
                 buf, 6000 + display_number, strerror(errno));
        return -1;
    }
    set_nodelay(sock);

    return sock;
}



static int copy_fd_to_channel_callback(int fd, int revents, void *userdata)
{
    ssh_channel channel = (ssh_channel)userdata;
    char buf[2097152];
    int sz = 0, ret = 0;

    node_t *temp_node = search_item(channel);

    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "event: %d - fd: %d", revents, fd);

    if (channel == NULL) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "channel does not exist.");
        if (temp_node->protected == 0) {
            close(fd);
        }
        return -1;
    }

    if (fcntl(fd, F_GETFD) == -1) {
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "fcntl error. fd: %d", fd);
        ssh_channel_close(channel);
        return -1;
    }

    if ((revents & POLLIN) || (revents & POLLPRI)) {
        sz = read(fd, buf, sizeof(buf));
        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "sz: %d", sz);
        if (sz > 0) {
            ret = ssh_channel_write(channel, buf, sz);
            _ssh_log(SSH_LOG_FUNCTIONS, __func__, "channel_write ret: %d", ret);
        } else if (sz < 0) {
            ssh_channel_close(channel);
            return -1;
        } else {
            /* sz = 0. Why the hell I'm here? */
            _ssh_log(SSH_LOG_FUNCTIONS, __func__,
                     "Why the hell am I here?: sz: %d", sz);
            if (temp_node->protected == 0) {
                close(fd);
            }
            return -1;
        }
    }

    if ((revents & POLLHUP) || (revents & POLLNVAL) || (revents & POLLERR)) {
        ssh_channel_close(channel);
        return -1;
    }

    return sz;
}


static int copy_channel_to_fd_callback(ssh_session session, ssh_channel channel,
                                       void *data, uint32_t len, int is_stderr,
                                       void *userdata)
{
    node_t *temp_node = NULL;
    int fd, sz;

    (void)session;
    (void)is_stderr;
    (void)userdata;

    temp_node = search_item(channel);

    fd = temp_node->fd_out;

    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "len: %d - fd: %d - is_stderr: %d",
             len, fd, is_stderr);

    sz = write(fd, data, len);

    return sz;
}


static void channel_close_callback(ssh_session session, ssh_channel channel,
                                   void *userdata)
{
    node_t *temp_node = NULL;

    (void)session;
    (void)userdata;

    temp_node = search_item(channel);

    if (temp_node != NULL) {
        int fd = temp_node->fd_in;

        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "fd: %d", fd);

        delete_item(channel);
        ssh_event_remove_fd(event, fd);

        if (temp_node->protected == 0) {
            close(fd);
        }
    }
}


static ssh_channel x11_open_request_callback(ssh_session session,
                                             const char *shost, int sport,
                                             void *userdata)
{
    ssh_channel channel = NULL;
    int sock, rv;

    (void)shost;
    (void)sport;
    (void)userdata;

    channel	= ssh_channel_new(session);

    sock = x11_connect_display();

    _ssh_log(SSH_LOG_FUNCTIONS, __func__, "sock: %d", sock);

    rv = insert_item(channel, sock, sock, 0);
    if (rv != 0) {
        ssh_channel_free(channel);
        return NULL;
    }

    ssh_event_add_fd(event, sock, events, copy_fd_to_channel_callback, channel);
    ssh_event_add_session(event, session);

    ssh_add_channel_callbacks(channel, &channel_cb);

    return channel;
}



/*
 * MAIN LOOP
 */

static int main_loop(ssh_channel channel)
{
    ssh_session session = ssh_channel_get_session(channel);
    int rv;

    rv = insert_item(channel, fileno(stdin), fileno(stdout), 1);
    if (rv != 0) {
        return -1;
    }

    ssh_callbacks_init(&channel_cb);
    ssh_set_channel_callbacks(channel, &channel_cb);

    event = ssh_event_new();
    if (event == NULL) {
        printf("Couldn't get a event\n");
        return -1;
    }

    rv = ssh_event_add_fd(event, fileno(stdin), events,
                          copy_fd_to_channel_callback, channel);
    if (rv != SSH_OK) {
        printf("Couldn't add an fd to the event\n");
        return -1;
    }

    rv = ssh_event_add_session(event, session);
    if (rv != SSH_OK) {
        printf("Couldn't add the session to the event\n");
        return -1;
    }

    do {
        if (ssh_event_dopoll(event, 1000) == SSH_ERROR) {
            printf("Error : %s\n", ssh_get_error(session));
            /* fall through */
        }
    } while (!ssh_channel_is_closed(channel));

    delete_item(channel);
    ssh_event_remove_fd(event, fileno(stdin));
    ssh_event_remove_session(event, session);
    ssh_event_free(event);

    return 0;
}


/*
 * USAGE
 */

static void usage(void)
{
    fprintf(stderr,
            "Usage : ssh-X11-client [options] [login@]hostname\n"
            "sample X11 client - libssh-%s\n"
            "Options :\n"
            "  -l user : Specifies the user to log in as on the remote "
            "machine.\n"
            "  -p port : Port to connect to on the remote host.\n"
            "  -v      : Verbose mode. Multiple -v options increase the "
            "verbosity. The maximum is 5.\n"
            "  -C      : Requests compression of all data.\n"
            "  -x      : Disables X11 forwarding.\n"
            "\n",
            ssh_version(0));

    exit(0);
}

static int opts(int argc, char **argv)
{
    int i;

    while ((i = getopt(argc,argv,"x")) != -1) {
        switch (i) {
        case 'x':
            enableX11 = 0;
            break;
        default:
            fprintf(stderr, "Unknown option %c\n", optopt);
            return -1;
        }
    }

    if (optind < argc) {
        hostname = argv[optind++];
    }

    if (hostname == NULL) {
        return -1;
    }

    return 0;
}

/*
 * MAIN
 */

int main(int argc, char **argv)
{
    char *password = NULL;

    ssh_session session = NULL;
    ssh_channel channel = NULL;

    int ret;

    const char *display = NULL;
    char *proto = NULL, *cookie = NULL;

    ssh_set_log_callback(_logging_callback);
    ret = ssh_init();
    if (ret != SSH_OK) {
        return ret;
    }

    session = ssh_new();
    if (session == NULL) {
        exit(-1);
    }

    if (ssh_options_getopt(session, &argc, argv) || opts(argc, argv)) {
        fprintf(stderr, "Error parsing command line: %s\n",
                ssh_get_error(session));
        ssh_free(session);
        ssh_finalize();
        usage();
    }

    if (ssh_options_set(session, SSH_OPTIONS_HOST, hostname) < 0) {
        return -1;
    }

    ret = ssh_connect(session);
    if (ret != SSH_OK) {
        fprintf(stderr, "Connection failed : %s\n", ssh_get_error(session));
        exit(-1);
    }

    password = getpass("Password: ");
    ret = ssh_userauth_password(session, NULL, password);
    if (ret != SSH_AUTH_SUCCESS) {
        fprintf(stderr, "Error authenticating with password: %s\n",
                ssh_get_error(session));
        exit(-1);
    }

    channel = ssh_channel_new(session);
    if (channel == NULL) {
        return SSH_ERROR;
    }

    ret = ssh_channel_open_session(channel);
    if (ret != SSH_OK) {
        return ret;
    }

    ret = ssh_channel_request_pty(channel);
    if (ret != SSH_OK) {
        return ret;
    }

    ret = ssh_channel_change_pty_size(channel, 80, 24);
    if (ret != SSH_OK) {
        return ret;
    }

    if (enableX11 == 1) {
        display = getenv("DISPLAY");

        _ssh_log(SSH_LOG_FUNCTIONS, __func__, "display: %s", display);

        if (display) {
            ssh_callbacks_init(&cb);
            ret = ssh_set_callbacks(session, &cb);
            if (ret != SSH_OK) {
                return ret;
            }

            ret = x11_get_proto(display, &proto, &cookie);
            if (ret != 0) {
                _ssh_log(SSH_LOG_FUNCTIONS, __func__,
                         "Using fake authentication data for X11 forwarding");
                proto = NULL;
                cookie = NULL;
            }

            _ssh_log(SSH_LOG_FUNCTIONS, __func__, "proto: %s - cookie: %s",
                     proto, cookie);
            /* See https://gitlab.com/libssh/libssh-mirror/-/blob/master/src/channels.c#L2062 for details. */
            ret = ssh_channel_request_x11(channel, 0, proto, cookie, 0);
            if (ret != SSH_OK) {
                return ret;
            }
        }
    }

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

    ret = ssh_channel_request_shell(channel);
    if (ret != SSH_OK) {
        return ret;
    }

    ret = main_loop(channel);
    if (ret != SSH_OK) {
        return ret;
    }

    _leave_term_raw_mode();

    ssh_channel_close(channel);
    ssh_channel_free(channel);
    ssh_disconnect(session);
    ssh_free(session);
    ssh_finalize();
}