path: root/ncat/ncat_main.c

/***************************************************************************
 * ncat_main.c -- main function: option parsing and checking, dispatching  *
 * to mode-specific functions.                                             *
 ***********************IMPORTANT NMAP LICENSE TERMS************************
 *
 * The Nmap Security Scanner is (C) 1996-2023 Nmap Software LLC ("The Nmap
 * Project"). Nmap is also a registered trademark of the Nmap Project.
 *
 * This program is distributed under the terms of the Nmap Public Source
 * License (NPSL). The exact license text applying to a particular Nmap
 * release or source code control revision is contained in the LICENSE
 * file distributed with that version of Nmap or source code control
 * revision. More Nmap copyright/legal information is available from
 * https://nmap.org/book/man-legal.html, and further information on the
 * NPSL license itself can be found at https://nmap.org/npsl/ . This
 * header summarizes some key points from the Nmap license, but is no
 * substitute for the actual license text.
 *
 * Nmap is generally free for end users to download and use themselves,
 * including commercial use. It is available from https://nmap.org.
 *
 * The Nmap license generally prohibits companies from using and
 * redistributing Nmap in commercial products, but we sell a special Nmap
 * OEM Edition with a more permissive license and special features for
 * this purpose. See https://nmap.org/oem/
 *
 * If you have received a written Nmap license agreement or contract
 * stating terms other than these (such as an Nmap OEM license), you may
 * choose to use and redistribute Nmap under those terms instead.
 *
 * The official Nmap Windows builds include the Npcap software
 * (https://npcap.com) for packet capture and transmission. It is under
 * separate license terms which forbid redistribution without special
 * permission. So the official Nmap Windows builds may not be redistributed
 * without special permission (such as an Nmap OEM license).
 *
 * Source is provided to this software because we believe users have a
 * right to know exactly what a program is going to do before they run it.
 * This also allows you to audit the software for security holes.
 *
 * Source code also allows you to port Nmap to new platforms, fix bugs, and add
 * new features. You are highly encouraged to submit your changes as a Github PR
 * or by email to the dev@nmap.org mailing list for possible incorporation into
 * the main distribution. Unless you specify otherwise, it is understood that
 * you are offering us very broad rights to use your submissions as described in
 * the Nmap Public Source License Contributor Agreement. This is important
 * because we fund the project by selling licenses with various terms, and also
 * because the inability to relicense code has caused devastating problems for
 * other Free Software projects (such as KDE and NASM).
 *
 * The free version of Nmap 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. Warranties,
 * indemnification and commercial support are all available through the
 * Npcap OEM program--see https://nmap.org/oem/
 *
 ***************************************************************************/

/* $Id$ */

#include "nsock.h"
#include "ncat.h"
#include "util.h"
#include "sys_wrap.h"

#include <getopt.h>

#ifndef WIN32
#include <unistd.h>
#endif
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#ifndef WIN32
#include <netdb.h>
#endif
#include <fcntl.h>

#ifdef HAVE_OPENSSL
#include <openssl/ssl.h>
#include <openssl/err.h>
#endif

#ifdef HAVE_LUA
#include "ncat_lua.h"
#endif

static int ncat_connect_mode(void);
static int ncat_listen_mode(void);

/* Parses a port number */
static unsigned int parseport(char *str, unsigned int maxport, char *msg)
{
    unsigned long port;
    char *next;
    errno = 0;
    port = strtoul(str, &next, 10);
    if (errno || *next || (maxport && port > maxport))
        bye("Invalid %s number \"%s\".", msg, str);
    return (unsigned int) port;
}

/* Parses proxy address/port combo */
static size_t parseproxy(char *str, struct sockaddr_storage *ss,
    size_t *sslen, unsigned short *portno)
{
    char *p = str;
    int rc;

    if (*p == '[') {
        p = strchr(p, ']');
        if (p == NULL)
            bye("Invalid proxy IPv6 address \"%s\".", str);
        ++str;
        *p++ = '\0';
    }

    p = strchr(p, ':');
    if (p != NULL && strchr(p + 1, ':') == NULL) {
        *p++ = '\0';
        *portno = (unsigned short) parseport(p, 0xFFFF, "proxy port");
    }

    rc = resolve(str, *portno, ss, sslen, o.af);
    if (rc != 0) {
        loguser("Could not resolve proxy \"%s\": %s.\n", str, gai_strerror(rc));
        if (o.af == AF_INET6)
            loguser("Did you specify the port number? It's required for IPv6.\n");
        exit(EXIT_FAILURE);
    }

    return *sslen;
}

static int parse_timespec (const char *const tspec, const char *const optname)
{
    const long l = tval2msecs(tspec);
    if (l <= 0 || l > INT_MAX)
        bye("Invalid %s \"%s\" (must be greater than 0 and less than %ds).",
            optname, tspec, INT_MAX / 1000);
    if (l >= 100 * 1000 && tval_unit(tspec) == NULL)
        bye("Since April 2010, the default unit for %s is seconds, so your "
            "time of \"%s\" is %.1f minutes. Use \"%sms\" for %s milliseconds.",
            optname, optarg, l / 1000.0 / 60, optarg, optarg);
    return (int)l;
}

/* These functions implement a simple linked list to hold allow/deny
   specifications until the end of option parsing. */
struct host_list_node {
    /* If false, then spec is the name of a file containing host patterns. */
    int is_filename;
    char *spec;
    struct host_list_node *next;
};

static void host_list_add_spec(struct host_list_node **list, char *spec)
{
    struct host_list_node *node = (struct host_list_node *) safe_malloc(sizeof(*node));
    node->is_filename = 0;
    node->spec = spec;
    node->next = *list;
    *list = node;
}

static void host_list_add_filename(struct host_list_node **list, char *filename)
{
    struct host_list_node *node = (struct host_list_node *) safe_malloc(sizeof(*node));
    node->is_filename = 1;
    node->spec = filename;
    node->next = *list;
    *list = node;
}

static void host_list_free(struct host_list_node *list)
{
    struct host_list_node *next;
    for ( ; list != NULL; list = next) {
        next = list->next;
        free(list);
    }
}

static void host_list_to_set(struct addrset *set, struct host_list_node *list)
{
    struct host_list_node *node;

    for (node = list; node != NULL; node = node->next) {
        if (node->is_filename) {
            FILE *fd;

            fd = fopen(node->spec, "r");
            if (fd == NULL)
                bye("can't open %s: %s.", node->spec, strerror(errno));
            if (!addrset_add_file(set, fd, o.af, !o.nodns))
                bye("error in hosts file %s.", node->spec);
            fclose(fd);
        } else {
            char *spec, *commalist;

            commalist = node->spec;
            while ((spec = strtok(commalist, ",")) != NULL) {
                commalist = NULL;
                if (!addrset_add_spec(set, spec, o.af, !o.nodns))
                    bye("error in host specification \"%s\".", node->spec);
            }
        }
    }
}

static void print_banner(void)
{
    loguser("Version %s ( %s )\n", NCAT_VERSION, NCAT_URL);
}

int main(int argc, char *argv[])
{
    /* We have to buffer the lists of hosts to allow and deny until after option
       parsing is done. Adding hosts to an addrset can require name resolution,
       which may differ as a result of options like -n and -6. */
    struct host_list_node *allow_host_list = NULL;
    struct host_list_node *deny_host_list = NULL;

    unsigned short proxyport;
    /* vsock ports are 32 bits, so port variables must be at least that wide. */
    unsigned int max_port = 65535;
    long long int srcport = -1;
    char *source = NULL;

    struct option long_options[] = {
        {"4",               no_argument,        NULL,         '4'},
        {"6",               no_argument,        NULL,         '6'},
#if HAVE_SYS_UN_H
        {"unixsock",        no_argument,        NULL,         'U'},
#endif
#if HAVE_LINUX_VM_SOCKETS_H
        {"vsock",           no_argument,        NULL,         0},
#endif
        {"crlf",            no_argument,        NULL,         'C'},
        {"g",               required_argument,  NULL,         'g'},
        {"G",               required_argument,  NULL,         'G'},
        {"exec",            required_argument,  NULL,         'e'},
        {"sh-exec",         required_argument,  NULL,         'c'},
#ifdef HAVE_LUA
        {"lua-exec",        required_argument,  NULL,         0},
        {"lua-exec-internal",required_argument, NULL,         0},
#endif
        {"max-conns",       required_argument,  NULL,         'm'},
        {"help",            no_argument,        NULL,         'h'},
        {"delay",           required_argument,  NULL,         'd'},
        {"listen",          no_argument,        NULL,         'l'},
        {"output",          required_argument,  NULL,         'o'},
        {"hex-dump",        required_argument,  NULL,         'x'},
        {"append-output",   no_argument,        NULL,         0},
        {"idle-timeout",    required_argument,  NULL,         'i'},
        {"keep-open",       no_argument,        NULL,         'k'},
        {"recv-only",       no_argument,        &o.recvonly,  1},
        {"source-port",     required_argument,  NULL,         'p'},
        {"source",          required_argument,  NULL,         's'},
        {"send-only",       no_argument,        &o.sendonly,  1},
        {"no-shutdown",     no_argument,        &o.noshutdown,1},
        {"broker",          no_argument,        NULL,         0},
        {"chat",            no_argument,        NULL,         0},
        {"talk",            no_argument,        NULL,         0},
        {"deny",            required_argument,  NULL,         0},
        {"denyfile",        required_argument,  NULL,         0},
        {"allow",           required_argument,  NULL,         0},
        {"allowfile",       required_argument,  NULL,         0},
        {"telnet",          no_argument,        NULL,         't'},
        {"udp",             no_argument,        NULL,         'u'},
        {"sctp",            no_argument,        NULL,         0},
        {"version",         no_argument,        NULL,         0},
        {"verbose",         no_argument,        NULL,         'v'},
        {"wait",            required_argument,  NULL,         'w'},
        {"nodns",           no_argument,        NULL,         'n'},
        {"proxy",           required_argument,  NULL,         0},
        {"proxy-type",      required_argument,  NULL,         0},
        {"proxy-auth",      required_argument,  NULL,         0},
        {"proxy-dns",       required_argument,  NULL,         0},
        {"nsock-engine",    required_argument,  NULL,         0},
        {"test",            no_argument,        NULL,         0},
        {"ssl",             no_argument,        &o.ssl,       1},
#ifdef HAVE_OPENSSL
        {"ssl-cert",        required_argument,  NULL,         0},
        {"ssl-key",         required_argument,  NULL,         0},
        {"ssl-verify",      no_argument,        NULL,         0},
        {"ssl-trustfile",   required_argument,  NULL,         0},
        {"ssl-ciphers",     required_argument,  NULL,         0},
        {"ssl-servername",  required_argument,  NULL,         0},
        {"ssl-alpn",        required_argument,  NULL,         0},
#else
        {"ssl-cert",        optional_argument,  NULL,         0},
        {"ssl-key",         optional_argument,  NULL,         0},
        {"ssl-verify",      no_argument,        NULL,         0},
        {"ssl-trustfile",   optional_argument,  NULL,         0},
        {"ssl-ciphers",     optional_argument,  NULL,         0},
        {"ssl-alpn",        optional_argument,  NULL,         0},
#endif
        {0, 0, 0, 0}
    };

    gettimeofday(&start_time, NULL);
    /* Set default options. */
    options_init();

#ifdef WIN32
    windows_init();
#endif

    while (1) {
        /* handle command line arguments */
        int option_index;
        int c = getopt_long(argc, argv, "46UCc:e:g:G:i:km:hp:d:lo:x:ts:uvw:nz",
                            long_options, &option_index);

        /* That's the end of the options. */
        if (c == -1)
            break;

        switch (c) {
        case '4':
            o.af = AF_INET;
            break;
        case '6':
#ifdef HAVE_IPV6
            o.af = AF_INET6;
#else
            bye("-6 chosen when IPv6 wasn't compiled in.");
#endif
            break;
#if HAVE_SYS_UN_H
        case 'U':
            o.af = AF_UNIX;
            break;
#endif
        case 'C':
            o.crlf = 1;
            break;
        case 'c':
            if (o.cmdexec != NULL)
                bye("Only one of --exec, --sh-exec, and --lua-exec is allowed.");
            o.cmdexec = optarg;
            o.execmode = EXEC_SHELL;
            break;
        case 'e':
            if (o.cmdexec != NULL)
                bye("Only one of --exec, --sh-exec, and --lua-exec is allowed.");
            o.cmdexec = optarg;
            o.execmode = EXEC_PLAIN;
            break;
        case 'g': {
            char *from = optarg;
            char *a = NULL;
            while (o.numsrcrtes < 8 && (a = strtok(from, ",")))
            {
                union sockaddr_u addr;
                size_t sslen;
                int rc;
                from = NULL;

                rc = resolve(a, 0, &addr.storage, &sslen, AF_INET);
                if (rc != 0) {
                    bye("Sorry, could not resolve source route hop \"%s\": %s.",
                    a, gai_strerror(rc));
                }
                o.srcrtes[o.numsrcrtes++] = addr.in.sin_addr;
            }
            if (strtok(from, ","))
                bye("Sorry, you gave too many source route hops.");
            break;
        }
        case 'G':
            o.srcrteptr = atoi(optarg);
            if (o.srcrteptr < 4 || (o.srcrteptr % 4) || o.srcrteptr > 28)
                bye("Invalid source-route hop pointer %d.", o.srcrteptr);
            break;
        case 'k':
            o.keepopen = 1;
            break;
        case 'm':
            o.conn_limit = atoi(optarg);
            break;
        case 'd':
            o.linedelay = parse_timespec(optarg, "-d delay");
            break;
        case 'o':
            o.normlog = optarg;
            break;
        case 'x':
            o.hexlog = optarg;
            break;
        case 'p':
            srcport = parseport(optarg, 0, "source port");
            break;
        case 'i':
            o.idletimeout = parse_timespec(optarg, "-i timeout");
            break;
        case 's':
            source = optarg;
            break;
        case 'l':
            o.listen = 1;
            break;
        case 'u':
            o.proto = IPPROTO_UDP;
            break;
        case 'v':
            /* One -v activates verbose, after that it's debugging. */
            if (o.verbose == 0)
                o.verbose++;
            else
                o.debug++;
            break;
        case 'n':
            o.nodns = 1;
            break;
        case 'w':
            o.conntimeout = parse_timespec(optarg, "-w timeout");
            break;
        case 't':
            o.telnet = 1;
            break;
        case 'z':
            o.zerobyte = 1;
            break;
        case 0:
            if (strcmp(long_options[option_index].name, "version") == 0) {
                print_banner();
                exit(EXIT_SUCCESS);
            } else if (strcmp(long_options[option_index].name, "proxy") == 0) {
                if (o.proxyaddr)
                    bye("You can't specify more than one --proxy.");
                o.proxyaddr = optarg;
            } else if (strcmp(long_options[option_index].name, "proxy-type") == 0) {
                if (o.proxytype)
                    bye("You can't specify more than one --proxy-type.");
                o.proxytype = optarg;
            } else if (strcmp(long_options[option_index].name, "proxy-auth") == 0) {
                if (o.proxy_auth)
                    bye("You can't specify more than one --proxy-auth.");
                o.proxy_auth = optarg;
            } else if (strcmp(long_options[option_index].name, "proxy-dns") == 0) {
                if (strcmp(optarg, "none") == 0)
                    o.proxydns = 0;
                else if (strcmp(optarg, "local") == 0)
                    o.proxydns = PROXYDNS_LOCAL;
                else if (strcmp(optarg, "remote") == 0)
                    o.proxydns = PROXYDNS_REMOTE;
                else if (strcmp(optarg, "both") == 0)
                    o.proxydns = PROXYDNS_LOCAL | PROXYDNS_REMOTE;
                else
                    bye("Invalid proxy DNS type.");
            } else if (strcmp(long_options[option_index].name, "nsock-engine") == 0) {
                if (nsock_set_default_engine(optarg) < 0)
                    bye("Unknown or non-available engine: %s.", optarg);
                o.nsock_engine = 1;
            } else if (strcmp(long_options[option_index].name, "test") == 0) {
                o.test = 1;
            } else if (strcmp(long_options[option_index].name, "broker") == 0) {
                o.broker = 1;
                /* --broker implies --listen. */
                o.listen = 1;
            } else if (strcmp(long_options[option_index].name, "chat") == 0
                       || strcmp(long_options[option_index].name, "talk") == 0) {
                /* --talk is an older name for --chat. */
                o.chat = 1;
                /* --chat implies --broker. */
                o.broker = 1;
            } else if (strcmp(long_options[option_index].name, "allow") == 0) {
                o.allow = 1;
                host_list_add_spec(&allow_host_list, optarg);
            } else if (strcmp(long_options[option_index].name, "allowfile") == 0) {
                o.allow = 1;
                host_list_add_filename(&allow_host_list, optarg);
            } else if (strcmp(long_options[option_index].name, "deny") == 0) {
                host_list_add_spec(&deny_host_list, optarg);
            } else if (strcmp(long_options[option_index].name, "denyfile") == 0) {
                host_list_add_filename(&deny_host_list, optarg);
            } else if (strcmp(long_options[option_index].name, "append-output") == 0) {
                o.append = 1;
            } else if (strcmp(long_options[option_index].name, "sctp") == 0) {
                o.proto = IPPROTO_SCTP;
            }
#ifdef HAVE_OPENSSL
            else if (strcmp(long_options[option_index].name, "ssl-cert") == 0) {
                o.ssl = 1;
                o.sslcert = Strdup(optarg);
            } else if (strcmp(long_options[option_index].name, "ssl-key") == 0) {
                o.ssl = 1;
                o.sslkey = Strdup(optarg);
            } else if (strcmp(long_options[option_index].name, "ssl-verify") == 0) {
                o.sslverify = 1;
                o.ssl = 1;
            } else if (strcmp(long_options[option_index].name, "ssl-trustfile") == 0) {
                o.ssl = 1;
                if (o.ssltrustfile != NULL)
                    bye("The --ssl-trustfile option may be given only once.");
                o.ssltrustfile = Strdup(optarg);
                /* If they list a trustfile assume they want certificate
                   verification. */
                o.sslverify = 1;
            } else if (strcmp(long_options[option_index].name, "ssl-ciphers") == 0) {
                o.ssl = 1;
                o.sslciphers = Strdup(optarg);
            } else if (strcmp(long_options[option_index].name, "ssl-servername") == 0) {
                o.ssl = 1;
                o.sslservername = Strdup(optarg);
            }
#ifdef HAVE_ALPN_SUPPORT
            else if (strcmp(long_options[option_index].name, "ssl-alpn") == 0) {
                o.ssl = 1;
                o.sslalpn = Strdup(optarg);
            }
#else
            else if (strcmp(long_options[option_index].name, "ssl-alpn") == 0) {
                bye("OpenSSL does not have ALPN support compiled in. The --ssl-alpn option cannot be chosen.");
            }
#endif
#else
            else if (strcmp(long_options[option_index].name, "ssl-cert") == 0) {
                bye("OpenSSL isn't compiled in. The --ssl-cert option cannot be chosen.");
            } else if (strcmp(long_options[option_index].name, "ssl-key") == 0) {
                bye("OpenSSL isn't compiled in. The --ssl-key option cannot be chosen.");
            } else if (strcmp(long_options[option_index].name, "ssl-verify") == 0) {
                bye("OpenSSL isn't compiled in. The --ssl-verify option cannot be chosen.");
            } else if (strcmp(long_options[option_index].name, "ssl-trustfile") == 0) {
                bye("OpenSSL isn't compiled in. The --ssl-trustfile option cannot be chosen.");
            } else if (strcmp(long_options[option_index].name, "ssl-ciphers") == 0) {
                bye("OpenSSL isn't compiled in. The --ssl-ciphers option cannot be chosen.");
            } else if (strcmp(long_options[option_index].name, "ssl-servername") == 0) {
                bye("OpenSSL isn't compiled in. The --ssl-servername option cannot be chosen.");
            } else if (strcmp(long_options[option_index].name, "ssl-alpn") == 0) {
                bye("OpenSSL isn't compiled in. The --ssl-alpn option cannot be chosen.");
            }
#endif
#ifdef HAVE_LUA
            else if (strcmp(long_options[option_index].name, "lua-exec") == 0) {
                if (o.cmdexec != NULL)
                    bye("Only one of --exec, --sh-exec, and --lua-exec is allowed.");
                o.cmdexec = optarg;
                o.execmode = EXEC_LUA;
            } else if (strcmp(long_options[option_index].name, "lua-exec-internal") == 0) {
                /* This command-line switch is undocumented on purpose. Do NOT use it
                   explicitly as its behavior might differ between Ncat releases.

                   Its goal is to switch the Ncat process to the Lua interpreter state
                   so that its standard output and input can be redirected to
                   particular connection's streams. Although it is implemented by
                   forking in POSIX builds, Windows does not have the fork() system
                   call and thus requires this workaround. More info here:
                   http://seclists.org/nmap-dev/2013/q2/492 */
#ifdef WIN32
                if (o.debug)
                    logdebug("Enabling binary stdout for the Lua output.\n");
                int result = _setmode(_fileno(stdout), _O_BINARY);
                if (result == -1)
                    perror("Cannot set mode");
#endif
                ncat_assert(argc == 3);
                o.cmdexec = argv[2];
                lua_setup();
                lua_run();
            }
#endif
#if HAVE_LINUX_VM_SOCKETS_H
            else if (strcmp(long_options[option_index].name, "vsock") == 0) {
                o.af = AF_VSOCK;
            }
#endif
            break;
        case 'h':
            printf("%s %s ( %s )\n", NCAT_NAME, NCAT_VERSION, NCAT_URL);
            printf(
"Usage: ncat [options] [hostname] [port]\n"
"\n"
"Options taking a time assume seconds. Append 'ms' for milliseconds,\n"
"'s' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).\n"
"  -4                         Use IPv4 only\n"
"  -6                         Use IPv6 only\n"
#if HAVE_SYS_UN_H
"  -U, --unixsock             Use Unix domain sockets only\n"
#endif
#if HAVE_LINUX_VM_SOCKETS_H
"      --vsock                Use vsock sockets only\n"
#endif
"  -C, --crlf                 Use CRLF for EOL sequence\n"
"  -c, --sh-exec <command>    Executes the given command via /bin/sh\n"
"  -e, --exec <command>       Executes the given command\n"
#ifdef HAVE_LUA
"      --lua-exec <filename>  Executes the given Lua script\n"
#endif
"  -g hop1[,hop2,...]         Loose source routing hop points (8 max)\n"
"  -G <n>                     Loose source routing hop pointer (4, 8, 12, ...)\n"
"  -m, --max-conns <n>        Maximum <n> simultaneous connections\n"
"  -h, --help                 Display this help screen\n"
"  -d, --delay <time>         Wait between read/writes\n"
"  -o, --output <filename>    Dump session data to a file\n"
"  -x, --hex-dump <filename>  Dump session data as hex to a file\n"
"  -i, --idle-timeout <time>  Idle read/write timeout\n"
"  -p, --source-port port     Specify source port to use\n"
"  -s, --source addr          Specify source address to use (doesn't affect -l)\n"
"  -l, --listen               Bind and listen for incoming connections\n"
"  -k, --keep-open            Accept multiple connections in listen mode\n"
"  -n, --nodns                Do not resolve hostnames via DNS\n"
"  -t, --telnet               Answer Telnet negotiations\n"
"  -u, --udp                  Use UDP instead of default TCP\n"
"      --sctp                 Use SCTP instead of default TCP\n"
"  -v, --verbose              Set verbosity level (can be used several times)\n"
"  -w, --wait <time>          Connect timeout\n"
"  -z                         Zero-I/O mode, report connection status only\n"
"      --append-output        Append rather than clobber specified output files\n"
"      --send-only            Only send data, ignoring received; quit on EOF\n"
"      --recv-only            Only receive data, never send anything\n"
"      --no-shutdown          Continue half-duplex when receiving EOF on stdin\n"
"      --allow                Allow only given hosts to connect to Ncat\n"
"      --allowfile            A file of hosts allowed to connect to Ncat\n"
"      --deny                 Deny given hosts from connecting to Ncat\n"
"      --denyfile             A file of hosts denied from connecting to Ncat\n"
"      --broker               Enable Ncat's connection brokering mode\n"
"      --chat                 Start a simple Ncat chat server\n"
"      --proxy <addr[:port]>  Specify address of host to proxy through\n"
"      --proxy-type <type>    Specify proxy type (\"http\", \"socks4\", \"socks5\")\n"
"      --proxy-auth <auth>    Authenticate with HTTP or SOCKS proxy server\n"
"      --proxy-dns <type>     Specify where to resolve proxy destination\n"

#ifdef HAVE_OPENSSL
"      --ssl                  Connect or listen with SSL\n"
"      --ssl-cert             Specify SSL certificate file (PEM) for listening\n"
"      --ssl-key              Specify SSL private key (PEM) for listening\n"
"      --ssl-verify           Verify trust and domain name of certificates\n"
"      --ssl-trustfile        PEM file containing trusted SSL certificates\n"
"      --ssl-ciphers          Cipherlist containing SSL ciphers to use\n"
"      --ssl-servername       Request distinct server name (SNI)\n"
"      --ssl-alpn             ALPN protocol list to use\n"
#endif
"      --version              Display Ncat's version information and exit\n"
"\n"
"See the ncat(1) manpage for full options, descriptions and usage examples\n"
            );
            exit(EXIT_SUCCESS);
        case '?':
            /* Consider unrecognised parameters/arguments as fatal. */
            bye("Try `--help' or man(1) ncat for more information, usage options and help.");
        default:
            /* We consider an unrecognised option fatal. */
            bye("Unrecognised option.");
        }
    }

#if HAVE_LINUX_VM_SOCKETS_H
    if (o.af == AF_VSOCK)
        max_port = UINT32_MAX;
#endif

    if (srcport > max_port)
        bye("Invalid source port %lld.", srcport);

#ifndef HAVE_OPENSSL
    if (o.ssl)
        bye("OpenSSL isn't compiled in. The --ssl option cannot be chosen.");
#endif

    if (o.normlog)
        o.normlogfd = ncat_openlog(o.normlog, o.append);
    if (o.hexlog)
        o.hexlogfd = ncat_openlog(o.hexlog, o.append);

    if (o.verbose)
        print_banner();

    if (o.debug)
        nbase_set_log(loguser, logdebug);
    else
        nbase_set_log(loguser, NULL);

#if HAVE_SYS_UN_H
    /* Using Unix domain sockets, so do the checks now */
    if (o.af == AF_UNIX) {
        if (o.proxyaddr || o.proxytype)
            bye("Proxy option not supported when using Unix domain sockets.");
#ifdef HAVE_OPENSSL
        if (o.ssl)
            bye("SSL option not supported when using Unix domain sockets.");
#endif
        if (o.broker)
            bye("Connection brokering not supported when using Unix domain sockets.");
        if (srcport != -1)
            bye("Specifying source port when using Unix domain sockets doesn't make sense.");
        if (o.numsrcrtes > 0)
            bye("Loose source routing not allowed when using Unix domain sockets.");
    }
#endif  /* HAVE_SYS_UN_H */

#if HAVE_LINUX_VM_SOCKETS_H
    if (o.af == AF_VSOCK) {
        if (o.proxyaddr || o.proxytype)
            bye("Proxy option not supported when using vsock sockets.");
#ifdef HAVE_OPENSSL
        if (o.ssl)
            bye("SSL option not supported when using vsock sockets.");
#endif
        if (o.broker)
            bye("Connection brokering not supported when using vsock sockets.");
        if (o.numsrcrtes > 0)
            bye("Loose source routing not allowed when using vsock sockets.");
    }
#endif  /* HAVE_LINUX_VM_SOCKETS_H */

    /* Create a static target address, because at least one target address must be always allocated */
    targetaddrs = (struct sockaddr_list *)safe_zalloc(sizeof(struct sockaddr_list));

    /* Will be AF_INET or AF_INET6 or AF_UNIX when valid */
    memset(&srcaddr.storage, 0, sizeof(srcaddr.storage));
    srcaddr.storage.ss_family = AF_UNSPEC;
    targetaddrs->addr.storage = srcaddr.storage;

    /* Clear the listenaddrs array */
    int i;
    for (i = 0; i < NUM_LISTEN_ADDRS; i++) {
        listenaddrs[i].storage = srcaddr.storage;
    }

    if (o.proxyaddr) {
        if (!o.proxytype)
            o.proxytype = Strdup("http");

        /* validate proxy type and configure its default port */
        if (!strcmp(o.proxytype, "http"))
            proxyport = DEFAULT_PROXY_PORT;
        else if (!strcmp(o.proxytype, "socks4") || !strcmp(o.proxytype, "4"))
            proxyport = DEFAULT_SOCKS4_PORT;
        else if (!strcmp(o.proxytype, "socks5") || !strcmp(o.proxytype, "5"))
            proxyport = DEFAULT_SOCKS5_PORT;
        else
            bye("Invalid proxy type \"%s\".", o.proxytype);

        /* Parse HTTP/SOCKS proxy address and store it in targetss.
         * If the proxy server is given as an IPv6 address (not hostname),
         * the port number MUST be specified as well or parsing will break
         * (due to the colons in the IPv6 address and host:port separator).
         */

        targetaddrs->addrlen = parseproxy(o.proxyaddr,
            &targetaddrs->addr.storage, &targetaddrs->addrlen, &proxyport);
        if (o.af == AF_INET) {
            targetaddrs->addr.in.sin_port = htons(proxyport);
        } else { // might modify to else if and test AF_{INET6|UNIX|UNSPEC}
            targetaddrs->addr.in6.sin6_port = htons(proxyport);
        }

        if (o.listen)
            bye("Invalid option combination: --proxy and -l.");
    } else {
        if (o.proxytype) {
            if (!o.listen)
                bye("Proxy type (--proxy-type) specified without proxy address (--proxy).");
            if (strcmp(o.proxytype, "http"))
                bye("Invalid proxy type \"%s\"; Ncat proxy server only supports \"http\".", o.proxytype);
        }
    }

    if (!o.proxy_auth)
        o.proxy_auth = getenv("NCAT_PROXY_AUTH");

    if (o.zerobyte) {
      if (o.listen)
        bye("Services designed for LISTENING can't be used with -z");
      if (o.telnet)
        bye("Invalid option combination: -z and -t.");
      if (o.execmode||o.cmdexec)
        bye("Command execution can't be done along with option -z.");
      if (!o.idletimeout && o.proto == IPPROTO_UDP)
        o.idletimeout = 2 * 1000;
    }
    /* Default port */
    if (o.listen && o.proxytype && !o.portno && srcport == -1)
        o.portno = DEFAULT_PROXY_PORT;
    else
        o.portno = DEFAULT_NCAT_PORT;

    /* Resolve the given source address */
    if (source) {
        int rc = 0;

        if (o.listen)
            bye("-l and -s are incompatible.  Specify the address and port to bind to like you would a host to connect to.");

#if HAVE_SYS_UN_H
        /* if using UNIX sockets just copy the path.
         * If it's not valid, it will fail later! */
        if (o.af == AF_UNIX) {
            if (o.proto == IPPROTO_UDP) {
                NCAT_INIT_SUN(&srcaddr, source);
                srcaddrlen = SUN_LEN(&srcaddr.un);
            }
            else
                if (o.verbose)
                    loguser("Specifying source socket for other than DATAGRAM Unix domain sockets have no effect.\n");
        } else
#endif
#if HAVE_LINUX_VM_SOCKETS_H
        if (o.af == AF_VSOCK) {
            long long_cid;

            srcaddr.vm.svm_family = AF_VSOCK;

            errno = 0;
            long_cid = strtol(source, NULL, 10);
            if (errno != 0 || long_cid <= 0 || long_cid > UINT32_MAX)
                bye("Invalid source address CID \"%s\".", source);
            srcaddr.vm.svm_cid = long_cid;

            srcaddrlen = sizeof(srcaddr.vm);
        } else
#endif
            rc = resolve(source, 0, &srcaddr.storage, &srcaddrlen, o.af);
        if (rc != 0)
            bye("Could not resolve source address \"%s\": %s.", source, gai_strerror(rc));
    }

    host_list_to_set(o.allowset, allow_host_list);
    host_list_free(allow_host_list);
    host_list_to_set(o.denyset, deny_host_list);
    host_list_free(deny_host_list);

    int rc;
    int num_ports = 0;
    if (srcport != -1 && o.listen) {
        /* Treat "ncat -l -p <port>" the same as "ncat -l <port>" for nc
           compatibility. */
        o.portno = (unsigned int) srcport;
        num_ports++;
    }
    /* How many arguments are left? */
    ncat_assert(optind <= argc);
    switch (argc - optind) {
      case 2:
#if HAVE_SYS_UN_H
        /* We do not use ports with Unix domain sockets. */
        if (o.af == AF_UNIX) {
            bye("Using Unix domain sockets and specifying port doesn't make sense.");
        }
#endif
        if (num_ports == 0)
          o.portno = parseport(argv[optind + 1], max_port, "port");
        num_ports++;
        /* fall through: */
      case 1:
#if HAVE_SYS_UN_H
        if (o.af == AF_UNIX) {
            NCAT_INIT_SUN(&targetaddrs->addr, argv[optind]);
            targetaddrs->addrlen = SUN_LEN(&targetaddrs->addr.un);
            o.sslservername = o.target = argv[optind];
            break;
        }
#endif
#if HAVE_LINUX_VM_SOCKETS_H
        if (o.af == AF_VSOCK) {
            long long_cid;

            memset(&targetaddrs->addr.storage, 0, sizeof(struct sockaddr_vm));
            targetaddrs->addr.vm.svm_family = AF_VSOCK;

            errno = 0;
            long_cid = strtol(argv[optind], NULL, 10);
            if (errno != 0 || long_cid <= 0 || long_cid > UINT32_MAX)
                bye("Invalid CID \"%s\".", argv[optind]);
            targetaddrs->addr.vm.svm_cid = long_cid;

            targetaddrs->addrlen = sizeof(targetaddrs->addr.vm);
            o.sslservername = o.target = argv[optind];
            break;
        }
#endif
        /* Support ncat -l <port>, but otherwise assume ncat <target> */
        if (num_ports == 0 && o.listen) {
            rc = strspn(argv[optind], "1234567890");
            /* If the last arg is 5 or fewer digits, assume it's a port number */
            if (argv[optind][rc] == '\0' && rc <= 5) {
                o.portno = parseport(argv[optind], max_port, "port");
                num_ports++;
                break;
            }
        }
        o.target = argv[optind];
        /* resolve hostname only if o.proxytype == NULL
         * targetss contains data already and you don't want remove them
         */
        if( !o.proxytype
                && (rc = resolve_multi(o.target, 0, targetaddrs, o.af)) != 0)

            bye("Could not resolve hostname \"%s\": %s.", o.target, gai_strerror(rc));
        if (!o.sslservername)
            o.sslservername = o.target;
        break;
      case 0:
#if HAVE_SYS_UN_H
        if (o.af == AF_UNIX) {
            bye("You must specify a path to a socket to %s.",
                    o.listen ? "listen on" : "connect to");
        }
#endif
        /* Listen defaults to any address and DEFAULT_NCAT_PORT */
        if (!o.listen)
            bye("You must specify a host to connect to.");
        break;
      default:
        if (num_ports == 0)
            o.portno = parseport(argv[optind + 1], max_port, "port");
        num_ports += argc - optind - 1;
        break;
    }

    if (num_ports > 1) {
        loguser("Got more than one port specification: %u", o.portno);
        for (rc = argc - num_ports + 1; rc < argc; rc++)
            loguser_noprefix(" %s", argv[rc]);
        loguser_noprefix(". QUITTING.\n");
        exit(2);
    }

    if (o.proxytype && !o.listen)
        ; /* Do nothing - port is already set to proxyport  */
    else {
        struct sockaddr_list *targetaddrs_item = targetaddrs;
        while (targetaddrs_item != NULL)
        {
            if (targetaddrs_item->addr.storage.ss_family == AF_INET)
                targetaddrs_item->addr.in.sin_port = htons(o.portno);
#ifdef HAVE_IPV6
            else if (targetaddrs_item->addr.storage.ss_family == AF_INET6)
                targetaddrs_item->addr.in6.sin6_port = htons(o.portno);
#endif
#if HAVE_SYS_UN_H
            /* If we use Unix domain sockets, we have to count with them. */
            else if (targetaddrs_item->addr.storage.ss_family == AF_UNIX)
                ; /* Do nothing. */
#endif
#if HAVE_LINUX_VM_SOCKETS_H
            else if (targetaddrs_item->addr.storage.ss_family == AF_VSOCK)
                targetaddrs_item->addr.vm.svm_port = o.portno;
#endif
            else if (targetaddrs_item->addr.storage.ss_family == AF_UNSPEC)
                ; /* Leave unspecified. */
            else
                bye("Unknown address family %d.", targetaddrs_item->addr.storage.ss_family);
            targetaddrs_item = targetaddrs_item->next;
        }
    }

    if (srcport != -1 && !o.listen) {
            if (srcaddr.storage.ss_family == AF_UNSPEC) {
                /* We have a source port but not an explicit source address;
                   fill in an unspecified address of the same family as the
                   target. */
                srcaddr.storage.ss_family = targetaddrs->addr.storage.ss_family;
                if (srcaddr.storage.ss_family == AF_INET)
                    srcaddr.in.sin_addr.s_addr = INADDR_ANY;
                else if (srcaddr.storage.ss_family == AF_INET6)
                    srcaddr.in6.sin6_addr = in6addr_any;
            }
            if (srcaddr.storage.ss_family == AF_INET)
                srcaddr.in.sin_port = htons((unsigned int) srcport);
#ifdef HAVE_IPV6
            else if (srcaddr.storage.ss_family == AF_INET6)
                srcaddr.in6.sin6_port = htons((unsigned int) srcport);
#endif
#ifdef HAVE_LINUX_VM_SOCKETS_H
            else if (srcaddr.storage.ss_family == AF_VSOCK)
                srcaddr.vm.svm_port = (unsigned int) srcport;
#endif
    }

    if (o.proto == IPPROTO_UDP) {

#ifndef HAVE_DTLS_CLIENT_METHOD
        if (o.ssl)
            bye("OpenSSL does not have DTLS support compiled in.");
#endif
    }

    /* Do whatever is necessary to receive \n for line endings on input from
       the console. A no-op on Unix. */
    set_lf_mode();

#ifdef HAVE_LUA
    if (o.execmode == EXEC_LUA)
        lua_setup();
#endif

    if (o.listen)
        return ncat_listen_mode();
    else
        return ncat_connect_mode();
}

/* connect error handling and operations. */
static int ncat_connect_mode(void)
{
    /*
     * allow/deny commands with connect make no sense. If you don't want to
     * connect to a host, don't try to.
     */
    if (o.allow || o.deny)
        bye("Invalid option combination: allow/deny with connect.");

    /* o.conn_limit with 'connect' doesn't make any sense. */
    if (o.conn_limit != -1)
        bye("Invalid option combination: `--max-conns' with connect.");

    if (o.chat)
        bye("Invalid option combination: `--chat' with connect.");

    if (o.keepopen)
        bye("Invalid option combination: `--keep-open' with connect.");

    return ncat_connect();
}

static int ncat_listen_mode(void)
{
    /* Can't 'listen' AND 'connect' to a proxy server at the same time. */
    if (o.proxyaddr != NULL)
        bye("Invalid option combination: --proxy and -l.");

    if (o.broker && o.cmdexec != NULL)
        bye("Invalid option combination: --broker and -e.");

    if (o.proxytype != NULL && o.telnet)
        bye("Invalid option combination: --telnet has no effect with --proxy-type.");

    if (o.conn_limit != -1 && !(o.keepopen || o.broker))
        loguser("Warning: Maximum connections ignored, since it does not take "
                "effect without -k or --broker.\n");

    /* Set the default maximum simultaneous TCP connection limit. */
    if (o.conn_limit == -1)
        o.conn_limit = DEFAULT_MAX_CONNS;

#ifndef WIN32
    /* See if the shell is executable before we get deep into this */
    if (o.execmode == EXEC_SHELL && access("/bin/sh", X_OK) == -1)
        bye("/bin/sh is not executable, so `-c' won't work.");
#endif

    if (targetaddrs->addr.storage.ss_family != AF_UNSPEC) {
        listenaddrs[num_listenaddrs++] = targetaddrs->addr;
    } else {
        size_t ss_len;
        int rc;

        /* No command-line address. Listen on IPv4 or IPv6 or both. */
        /* Try to bind to IPv6 first; on AIX a bound IPv4 socket blocks an IPv6
           socket on the same port, despite IPV6_V6ONLY. */
#ifdef HAVE_IPV6
        if (o.af == AF_INET6 || o.af == AF_UNSPEC) {
            ss_len = sizeof(listenaddrs[num_listenaddrs]);
            rc = resolve("::", o.portno, &listenaddrs[num_listenaddrs].storage, &ss_len, AF_INET6);
            if (rc == 0)
                num_listenaddrs++;
            else if (o.debug > 0)
                logdebug("Failed to resolve default IPv6 address: %s\n", gai_strerror(rc));
        }
#endif
        if (o.af == AF_INET || o.af == AF_UNSPEC) {
            ss_len = sizeof(listenaddrs[num_listenaddrs]);
            rc = resolve("0.0.0.0", o.portno, &listenaddrs[num_listenaddrs].storage, &ss_len, AF_INET);
            if (rc != 0)
                bye("Failed to resolve default IPv4 address: %s.", gai_strerror(rc));
            num_listenaddrs++;
        }
#ifdef HAVE_LINUX_VM_SOCKETS_H
        if (o.af == AF_VSOCK) {
            listenaddrs[num_listenaddrs].vm.svm_family = AF_VSOCK;
            listenaddrs[num_listenaddrs].vm.svm_cid = VMADDR_CID_ANY;
            listenaddrs[num_listenaddrs].vm.svm_port = o.portno;
            num_listenaddrs++;
        }
#endif
    }

    if (o.proxytype) {
        if (strcmp(o.proxytype, "http") == 0)
            o.httpserver = 1;
    }

    /* Fire the listen/select dispatcher for bog-standard listen operations. */
    return ncat_listen();
}