Return to netcat.c CVS log

Up to [local] / src / usr.bin / nc

Fix the naming of interfaces and variables for rdomains and rtables
and make it possible to bind sockets (including listening sockets!)
to rtables and not just rdomains.  This changes the name of the
system calls, socket option, and ioctl.  After building with this
you should remove the files /usr/share/man/cat2/[gs]etrdomain.0.

Since this removes the existing [gs]etrdomain() system calls, the
libc major is bumped.

Written by claudio@, criticized^Wcritiqued by me

/* $OpenBSD: netcat.c,v 1.98 2010/07/03 04:44:51 guenther Exp $ */
/*
 * Copyright (c) 2001 Eric Jackson <ericj@monkey.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Re-written nc(1) for OpenBSD. Original implementation by
 * *Hobbit* <hobbit@avian.org>.
 */

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

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/tcp.h>
#include <netinet/ip.h>
#include <arpa/telnet.h>

#include <err.h>
#include <errno.h>
#include <netdb.h>
#include <poll.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>
#include "atomicio.h"

#ifndef SUN_LEN
#define SUN_LEN(su) \
	(sizeof(*(su)) - sizeof((su)->sun_path) + strlen((su)->sun_path))
#endif

#define PORT_MAX	65535
#define PORT_MAX_LEN	6

/* Command Line Options */
int	dflag;					/* detached, no stdin */
unsigned int iflag;				/* Interval Flag */
int	jflag;					/* use jumbo frames if we can */
int	kflag;					/* More than one connect */
int	lflag;					/* Bind to local port */
int	nflag;					/* Don't do name look up */
char   *Pflag;					/* Proxy username */
char   *pflag;					/* Localport flag */
int	rflag;					/* Random ports flag */
char   *sflag;					/* Source Address */
int	tflag;					/* Telnet Emulation */
int	uflag;					/* UDP - Default to TCP */
int	vflag;					/* Verbosity */
int	xflag;					/* Socks proxy */
int	zflag;					/* Port Scan Flag */
int	Dflag;					/* sodebug */
int	Iflag;					/* TCP receive buffer size */
int	Oflag;					/* TCP send buffer size */
int	Sflag;					/* TCP MD5 signature option */
int	Tflag = -1;				/* IP Type of Service */
u_int	rtableid;

int timeout = -1;
int family = AF_UNSPEC;
char *portlist[PORT_MAX+1];

void	atelnet(int, unsigned char *, unsigned int);
void	build_ports(char *);
void	help(void);
int	local_listen(char *, char *, struct addrinfo);
void	readwrite(int);
int	remote_connect(const char *, const char *, struct addrinfo);
int	socks_connect(const char *, const char *, struct addrinfo,
	    const char *, const char *, struct addrinfo, int, const char *);
int	udptest(int);
int	unix_connect(char *);
int	unix_listen(char *);
void	set_common_sockopts(int);
int	parse_iptos(char *);
void	usage(int);

int
main(int argc, char *argv[])
{
	int ch, s, ret, socksv;
	char *host, *uport;
	struct addrinfo hints;
	struct servent *sv;
	socklen_t len;
	struct sockaddr_storage cliaddr;
	char *proxy;
	const char *errstr, *proxyhost = "", *proxyport = NULL;
	struct addrinfo proxyhints;

	ret = 1;
	s = 0;
	socksv = 5;
	host = NULL;
	uport = NULL;
	sv = NULL;

	while ((ch = getopt(argc, argv,
	    "46DdhI:i:jklnO:P:p:rSs:tT:UuV:vw:X:x:z")) != -1) {
		switch (ch) {
		case '4':
			family = AF_INET;
			break;
		case '6':
			family = AF_INET6;
			break;
		case 'U':
			family = AF_UNIX;
			break;
		case 'X':
			if (strcasecmp(optarg, "connect") == 0)
				socksv = -1; /* HTTP proxy CONNECT */
			else if (strcmp(optarg, "4") == 0)
				socksv = 4; /* SOCKS v.4 */
			else if (strcmp(optarg, "5") == 0)
				socksv = 5; /* SOCKS v.5 */
			else
				errx(1, "unsupported proxy protocol");
			break;
		case 'd':
			dflag = 1;
			break;
		case 'h':
			help();
			break;
		case 'i':
			iflag = strtonum(optarg, 0, UINT_MAX, &errstr);
			if (errstr)
				errx(1, "interval %s: %s", errstr, optarg);
			break;
		case 'j':
			jflag = 1;
			break;
		case 'k':
			kflag = 1;
			break;
		case 'l':
			lflag = 1;
			break;
		case 'n':
			nflag = 1;
			break;
		case 'P':
			Pflag = optarg;
			break;
		case 'p':
			pflag = optarg;
			break;
		case 'r':
			rflag = 1;
			break;
		case 's':
			sflag = optarg;
			break;
		case 't':
			tflag = 1;
			break;
		case 'u':
			uflag = 1;
			break;
		case 'V':
			rtableid = (unsigned int)strtonum(optarg, 0,
			    RT_TABLEID_MAX, &errstr);
			if (errstr)
				errx(1, "rtable %s: %s", errstr, optarg);
			break;
		case 'v':
			vflag = 1;
			break;
		case 'w':
			timeout = strtonum(optarg, 0, INT_MAX / 1000, &errstr);
			if (errstr)
				errx(1, "timeout %s: %s", errstr, optarg);
			timeout *= 1000;
			break;
		case 'x':
			xflag = 1;
			if ((proxy = strdup(optarg)) == NULL)
				err(1, NULL);
			break;
		case 'z':
			zflag = 1;
			break;
		case 'D':
			Dflag = 1;
			break;
		case 'I':
			Iflag = strtonum(optarg, 1, 65536 << 14, &errstr);
			if (errstr != NULL)
				errx(1, "TCP receive window %s: %s",
				    errstr, optarg);
			break;
		case 'O':
			Oflag = strtonum(optarg, 1, 65536 << 14, &errstr);
			if (errstr != NULL)
				errx(1, "TCP send window %s: %s",
				    errstr, optarg);
			break;
		case 'S':
			Sflag = 1;
			break;
		case 'T':
			Tflag = parse_iptos(optarg);
			break;
		default:
			usage(1);
		}
	}
	argc -= optind;
	argv += optind;

	/* Cruft to make sure options are clean, and used properly. */
	if (argv[0] && !argv[1] && family == AF_UNIX) {
		if (uflag)
			errx(1, "cannot use -u and -U");
		host = argv[0];
		uport = NULL;
	} else if (argv[0] && !argv[1]) {
		if  (!lflag)
			usage(1);
		uport = argv[0];
		host = NULL;
	} else if (argv[0] && argv[1]) {
		host = argv[0];
		uport = argv[1];
	} else
		usage(1);

	if (lflag && sflag)
		errx(1, "cannot use -s and -l");
	if (lflag && pflag)
		errx(1, "cannot use -p and -l");
	if (lflag && zflag)
		errx(1, "cannot use -z and -l");
	if (!lflag && kflag)
		errx(1, "must use -l with -k");

	/* Initialize addrinfo structure. */
	if (family != AF_UNIX) {
		memset(&hints, 0, sizeof(struct addrinfo));
		hints.ai_family = family;
		hints.ai_socktype = uflag ? SOCK_DGRAM : SOCK_STREAM;
		hints.ai_protocol = uflag ? IPPROTO_UDP : IPPROTO_TCP;
		if (nflag)
			hints.ai_flags |= AI_NUMERICHOST;
	}

	if (xflag) {
		if (uflag)
			errx(1, "no proxy support for UDP mode");

		if (lflag)
			errx(1, "no proxy support for listen");

		if (family == AF_UNIX)
			errx(1, "no proxy support for unix sockets");

		/* XXX IPv6 transport to proxy would probably work */
		if (family == AF_INET6)
			errx(1, "no proxy support for IPv6");

		if (sflag)
			errx(1, "no proxy support for local source address");

		proxyhost = strsep(&proxy, ":");
		proxyport = proxy;

		memset(&proxyhints, 0, sizeof(struct addrinfo));
		proxyhints.ai_family = family;
		proxyhints.ai_socktype = SOCK_STREAM;
		proxyhints.ai_protocol = IPPROTO_TCP;
		if (nflag)
			proxyhints.ai_flags |= AI_NUMERICHOST;
	}

	if (lflag) {
		int connfd;
		ret = 0;

		if (family == AF_UNIX)
			s = unix_listen(host);

		/* Allow only one connection at a time, but stay alive. */
		for (;;) {
			if (family != AF_UNIX)
				s = local_listen(host, uport, hints);
			if (s < 0)
				err(1, NULL);
			/*
			 * For UDP, we will use recvfrom() initially
			 * to wait for a caller, then use the regular
			 * functions to talk to the caller.
			 */
			if (uflag) {
				int rv, plen;
				char buf[16384];
				struct sockaddr_storage z;

				len = sizeof(z);
				plen = jflag ? 16384 : 2048;
				rv = recvfrom(s, buf, plen, MSG_PEEK,
				    (struct sockaddr *)&z, &len);
				if (rv < 0)
					err(1, "recvfrom");

				rv = connect(s, (struct sockaddr *)&z, len);
				if (rv < 0)
					err(1, "connect");

				connfd = s;
			} else {
				len = sizeof(cliaddr);
				connfd = accept(s, (struct sockaddr *)&cliaddr,
				    &len);
			}

			readwrite(connfd);
			close(connfd);
			if (family != AF_UNIX)
				close(s);

			if (!kflag)
				break;
		}
	} else if (family == AF_UNIX) {
		ret = 0;

		if ((s = unix_connect(host)) > 0 && !zflag) {
			readwrite(s);
			close(s);
		} else
			ret = 1;

		exit(ret);

	} else {
		int i = 0;

		/* Construct the portlist[] array. */
		build_ports(uport);

		/* Cycle through portlist, connecting to each port. */
		for (i = 0; portlist[i] != NULL; i++) {
			if (s)
				close(s);

			if (xflag)
				s = socks_connect(host, portlist[i], hints,
				    proxyhost, proxyport, proxyhints, socksv,
				    Pflag);
			else
				s = remote_connect(host, portlist[i], hints);

			if (s < 0)
				continue;

			ret = 0;
			if (vflag || zflag) {
				/* For UDP, make sure we are connected. */
				if (uflag) {
					if (udptest(s) == -1) {
						ret = 1;
						continue;
					}
				}

				/* Don't look up port if -n. */
				if (nflag)
					sv = NULL;
				else {
					sv = getservbyport(
					    ntohs(atoi(portlist[i])),
					    uflag ? "udp" : "tcp");
				}

				fprintf(stderr,
				    "Connection to %s %s port [%s/%s] "
				    "succeeded!\n", host, portlist[i],
				    uflag ? "udp" : "tcp",
				    sv ? sv->s_name : "*");
			}
			if (!zflag)
				readwrite(s);
		}
	}

	if (s)
		close(s);

	exit(ret);
}

/*
 * unix_connect()
 * Returns a socket connected to a local unix socket. Returns -1 on failure.
 */
int
unix_connect(char *path)
{
	struct sockaddr_un sun;
	int s;

	if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
		return (-1);
	(void)fcntl(s, F_SETFD, 1);

	memset(&sun, 0, sizeof(struct sockaddr_un));
	sun.sun_family = AF_UNIX;

	if (strlcpy(sun.sun_path, path, sizeof(sun.sun_path)) >=
	    sizeof(sun.sun_path)) {
		close(s);
		errno = ENAMETOOLONG;
		return (-1);
	}
	if (connect(s, (struct sockaddr *)&sun, SUN_LEN(&sun)) < 0) {
		close(s);
		return (-1);
	}
	return (s);

}

/*
 * unix_listen()
 * Create a unix domain socket, and listen on it.
 */
int
unix_listen(char *path)
{
	struct sockaddr_un sun;
	int s;

	/* Create unix domain socket. */
	if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
		return (-1);

	memset(&sun, 0, sizeof(struct sockaddr_un));
	sun.sun_family = AF_UNIX;

	if (strlcpy(sun.sun_path, path, sizeof(sun.sun_path)) >=
	    sizeof(sun.sun_path)) {
		close(s);
		errno = ENAMETOOLONG;
		return (-1);
	}

	if (bind(s, (struct sockaddr *)&sun, SUN_LEN(&sun)) < 0) {
		close(s);
		return (-1);
	}

	if (listen(s, 5) < 0) {
		close(s);
		return (-1);
	}
	return (s);
}

/*
 * remote_connect()
 * Returns a socket connected to a remote host. Properly binds to a local
 * port or source address if needed. Returns -1 on failure.
 */
int
remote_connect(const char *host, const char *port, struct addrinfo hints)
{
	struct addrinfo *res, *res0;
	int s, error, on = 1;

	if ((error = getaddrinfo(host, port, &hints, &res)))
		errx(1, "getaddrinfo: %s", gai_strerror(error));

	res0 = res;
	do {
		if ((s = socket(res0->ai_family, res0->ai_socktype,
		    res0->ai_protocol)) < 0)
			continue;

		if (rtableid) {
			if (setsockopt(s, IPPROTO_IP, SO_RTABLE, &rtableid,
			    sizeof(rtableid)) == -1)
				err(1, "setsockopt SO_RTABLE");
		}

		/* Bind to a local port or source address if specified. */
		if (sflag || pflag) {
			struct addrinfo ahints, *ares;

			/* try SO_BINDANY, but don't insist */
			setsockopt(s, SOL_SOCKET, SO_BINDANY, &on, sizeof(on));
			memset(&ahints, 0, sizeof(struct addrinfo));
			ahints.ai_family = res0->ai_family;
			ahints.ai_socktype = uflag ? SOCK_DGRAM : SOCK_STREAM;
			ahints.ai_protocol = uflag ? IPPROTO_UDP : IPPROTO_TCP;
			ahints.ai_flags = AI_PASSIVE;
			if ((error = getaddrinfo(sflag, pflag, &ahints, &ares)))
				errx(1, "getaddrinfo: %s", gai_strerror(error));

			if (bind(s, (struct sockaddr *)ares->ai_addr,
			    ares->ai_addrlen) < 0)
				errx(1, "bind failed: %s", strerror(errno));
			freeaddrinfo(ares);
		}

		set_common_sockopts(s);

		if (connect(s, res0->ai_addr, res0->ai_addrlen) == 0)
			break;
		else if (vflag)
			warn("connect to %s port %s (%s) failed", host, port,
			    uflag ? "udp" : "tcp");

		close(s);
		s = -1;
	} while ((res0 = res0->ai_next) != NULL);

	freeaddrinfo(res);

	return (s);
}

/*
 * local_listen()
 * Returns a socket listening on a local port, binds to specified source
 * address. Returns -1 on failure.
 */
int
local_listen(char *host, char *port, struct addrinfo hints)
{
	struct addrinfo *res, *res0;
	int s, ret, x = 1;
	int error;

	/* Allow nodename to be null. */
	hints.ai_flags |= AI_PASSIVE;

	/*
	 * In the case of binding to a wildcard address
	 * default to binding to an ipv4 address.
	 */
	if (host == NULL && hints.ai_family == AF_UNSPEC)
		hints.ai_family = AF_INET;

	if ((error = getaddrinfo(host, port, &hints, &res)))
		errx(1, "getaddrinfo: %s", gai_strerror(error));

	res0 = res;
	do {
		if ((s = socket(res0->ai_family, res0->ai_socktype,
		    res0->ai_protocol)) < 0)
			continue;

		if (rtableid) {
			if (setsockopt(s, IPPROTO_IP, SO_RTABLE, &rtableid,
			    sizeof(rtableid)) == -1)
				err(1, "setsockopt SO_RTABLE");
		}

		ret = setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &x, sizeof(x));
		if (ret == -1)
			err(1, NULL);

		set_common_sockopts(s);

		if (bind(s, (struct sockaddr *)res0->ai_addr,
		    res0->ai_addrlen) == 0)
			break;

		close(s);
		s = -1;
	} while ((res0 = res0->ai_next) != NULL);

	if (!uflag && s != -1) {
		if (listen(s, 1) < 0)
			err(1, "listen");
	}

	freeaddrinfo(res);

	return (s);
}

/*
 * readwrite()
 * Loop that polls on the network file descriptor and stdin.
 */
void
readwrite(int nfd)
{
	struct pollfd pfd[2];
	unsigned char buf[16384];
	int n, wfd = fileno(stdin);
	int lfd = fileno(stdout);
	int plen;

	plen = jflag ? 16384 : 2048;

	/* Setup Network FD */
	pfd[0].fd = nfd;
	pfd[0].events = POLLIN;

	/* Set up STDIN FD. */
	pfd[1].fd = wfd;
	pfd[1].events = POLLIN;

	while (pfd[0].fd != -1) {
		if (iflag)
			sleep(iflag);

		if ((n = poll(pfd, 2 - dflag, timeout)) < 0) {
			close(nfd);
			err(1, "Polling Error");
		}

		if (n == 0)
			return;

		if (pfd[0].revents & POLLIN) {
			if ((n = read(nfd, buf, plen)) < 0)
				return;
			else if (n == 0) {
				shutdown(nfd, SHUT_RD);
				pfd[0].fd = -1;
				pfd[0].events = 0;
			} else {
				if (tflag)
					atelnet(nfd, buf, n);
				if (atomicio(vwrite, lfd, buf, n) != n)
					return;
			}
		}

		if (!dflag && pfd[1].revents & POLLIN) {
			if ((n = read(wfd, buf, plen)) < 0)
				return;
			else if (n == 0) {
				shutdown(nfd, SHUT_WR);
				pfd[1].fd = -1;
				pfd[1].events = 0;
			} else {
				if (atomicio(vwrite, nfd, buf, n) != n)
					return;
			}
		}
	}
}

/* Deal with RFC 854 WILL/WONT DO/DONT negotiation. */
void
atelnet(int nfd, unsigned char *buf, unsigned int size)
{
	unsigned char *p, *end;
	unsigned char obuf[4];

	if (size < 3)
		return;
	end = buf + size - 2;

	for (p = buf; p < end; p++) {
		if (*p != IAC)
			continue;

		obuf[0] = IAC;
		p++;
		if ((*p == WILL) || (*p == WONT))
			obuf[1] = DONT;
		else if ((*p == DO) || (*p == DONT))
			obuf[1] = WONT;
		else
			continue;

		p++;
		obuf[2] = *p;
		if (atomicio(vwrite, nfd, obuf, 3) != 3)
			warn("Write Error!");
	}
}

/*
 * build_ports()
 * Build an array or ports in portlist[], listing each port
 * that we should try to connect to.
 */
void
build_ports(char *p)
{
	const char *errstr;
	char *n;
	int hi, lo, cp;
	int x = 0;

	if ((n = strchr(p, '-')) != NULL) {
		if (lflag)
			errx(1, "Cannot use -l with multiple ports!");

		*n = '\0';
		n++;

		/* Make sure the ports are in order: lowest->highest. */
		hi = strtonum(n, 1, PORT_MAX, &errstr);
		if (errstr)
			errx(1, "port number %s: %s", errstr, n);
		lo = strtonum(p, 1, PORT_MAX, &errstr);
		if (errstr)
			errx(1, "port number %s: %s", errstr, p);

		if (lo > hi) {
			cp = hi;
			hi = lo;
			lo = cp;
		}

		/* Load ports sequentially. */
		for (cp = lo; cp <= hi; cp++) {
			portlist[x] = calloc(1, PORT_MAX_LEN);
			if (portlist[x] == NULL)
				err(1, NULL);
			snprintf(portlist[x], PORT_MAX_LEN, "%d", cp);
			x++;
		}

		/* Randomly swap ports. */
		if (rflag) {
			int y;
			char *c;

			for (x = 0; x <= (hi - lo); x++) {
				y = (arc4random() & 0xFFFF) % (hi - lo);
				c = portlist[x];
				portlist[x] = portlist[y];
				portlist[y] = c;
			}
		}
	} else {
		hi = strtonum(p, 1, PORT_MAX, &errstr);
		if (errstr)
			errx(1, "port number %s: %s", errstr, p);
		portlist[0] = strdup(p);
		if (portlist[0] == NULL)
			err(1, NULL);
	}
}

/*
 * udptest()
 * Do a few writes to see if the UDP port is there.
 * XXX - Better way of doing this? Doesn't work for IPv6.
 * Also fails after around 100 ports checked.
 */
int
udptest(int s)
{
	int i, ret;

	for (i = 0; i <= 3; i++) {
		if (write(s, "X", 1) == 1)
			ret = 1;
		else
			ret = -1;
	}
	return (ret);
}

void
set_common_sockopts(int s)
{
	int x = 1;

	if (Sflag) {
		if (setsockopt(s, IPPROTO_TCP, TCP_MD5SIG,
			&x, sizeof(x)) == -1)
			err(1, NULL);
	}
	if (Dflag) {
		if (setsockopt(s, SOL_SOCKET, SO_DEBUG,
			&x, sizeof(x)) == -1)
			err(1, NULL);
	}
	if (jflag) {
		if (setsockopt(s, SOL_SOCKET, SO_JUMBO,
			&x, sizeof(x)) == -1)
			err(1, NULL);
	}
	if (Tflag != -1) {
		if (setsockopt(s, IPPROTO_IP, IP_TOS,
		    &Tflag, sizeof(Tflag)) == -1)
			err(1, "set IP ToS");
	}
	if (Iflag) {
		if (setsockopt(s, SOL_SOCKET, SO_RCVBUF,
		    &Iflag, sizeof(Iflag)) == -1)
			err(1, "set TCP receive buffer size");
	}
	if (Oflag) {
		if (setsockopt(s, SOL_SOCKET, SO_SNDBUF,
		    &Oflag, sizeof(Oflag)) == -1)
			err(1, "set TCP send buffer size");
	}
}

int
parse_iptos(char *s)
{
	int tos = -1;

	if (strcmp(s, "lowdelay") == 0)
		return (IPTOS_LOWDELAY);
	if (strcmp(s, "throughput") == 0)
		return (IPTOS_THROUGHPUT);
	if (strcmp(s, "reliability") == 0)
		return (IPTOS_RELIABILITY);

	if (sscanf(s, "0x%x", &tos) != 1 || tos < 0 || tos > 0xff)
		errx(1, "invalid IP Type of Service");
	return (tos);
}

void
help(void)
{
	usage(0);
	fprintf(stderr, "\tCommand Summary:\n\
	\t-4		Use IPv4\n\
	\t-6		Use IPv6\n\
	\t-D		Enable the debug socket option\n\
	\t-d		Detach from stdin\n\
	\t-h		This help text\n\
	\t-I length	TCP receive buffer length\n\
	\t-i secs\t	Delay interval for lines sent, ports scanned\n\
	\t-k		Keep inbound sockets open for multiple connects\n\
	\t-l		Listen mode, for inbound connects\n\
	\t-n		Suppress name/port resolutions\n\
	\t-O length	TCP send buffer length\n\
	\t-P proxyuser\tUsername for proxy authentication\n\
	\t-p port\t	Specify local port for remote connects\n\
	\t-r		Randomize remote ports\n\
	\t-S		Enable the TCP MD5 signature option\n\
	\t-s addr\t	Local source address\n\
	\t-T ToS\t	Set IP Type of Service\n\
	\t-t		Answer TELNET negotiation\n\
	\t-U		Use UNIX domain socket\n\
	\t-u		UDP mode\n\
	\t-V rtable	Specify alternate routing table\n\
	\t-v		Verbose\n\
	\t-w secs\t	Timeout for connects and final net reads\n\
	\t-X proto	Proxy protocol: \"4\", \"5\" (SOCKS) or \"connect\"\n\
	\t-x addr[:port]\tSpecify proxy address and port\n\
	\t-z		Zero-I/O mode [used for scanning]\n\
	Port numbers can be individual or ranges: lo-hi [inclusive]\n");
	exit(1);
}

void
usage(int ret)
{
	fprintf(stderr,
	    "usage: nc [-46DdhklnrStUuvz] [-I length] [-i interval] [-O length]\n"
	    "\t  [-P proxy_username] [-p source_port] [-s source_ip_address] [-T ToS]\n"
	    "\t  [-V rtable] [-w timeout] [-X proxy_protocol]\n"
	    "\t  [-x proxy_address[:port]] [hostname] [port]\n");
	if (ret)
		exit(1);
}