dev/udp/udp-perturb.c - haproxy - Gitiles

 /*
  * Copyright (C) 2010-2022 Willy Tarreau <w@1wt.eu>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
  * "Software"), to deal in the Software without restriction, including
  * without limitation the rights to use, copy, modify, merge, publish,
  * distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to
  * the following conditions:
  *
  * The above copyright notice and this permission notice shall be
  * included in all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  * OTHER DEALINGS IN THE SOFTWARE.
  */

 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
 #include <ctype.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/tcp.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <fcntl.h>
 #include <errno.h>
 #include <getopt.h>
 #include <signal.h>
 #include <stdarg.h>
 #include <sys/stat.h>
 #include <time.h>
 #include <limits.h>
 #include <poll.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>

 #define MAXCONN 1

 const int zero = 0;
 const int one = 1;

 struct conn {
 	struct sockaddr_storage cli_addr;
 	int fd_bck;
 };

 struct errmsg {
 	char *msg;
 	int size;
 	int len;
 };

 struct sockaddr_storage frt_addr; // listen address
 struct sockaddr_storage srv_addr; // server address

 #define MAXPKTSIZE 16384
 #define MAXREORDER 20
 char trash[MAXPKTSIZE];

 /* history buffer, to resend random packets */
 struct {
 	char buf[MAXPKTSIZE];
 	size_t len;
 } history[MAXREORDER];
 int history_idx = 0;
 unsigned int rand_rate = 0;
 unsigned int corr_rate = 0;
 unsigned int corr_span = 1;
 unsigned int corr_base = 0;

 struct conn conns[MAXCONN];        // sole connection for now
 int fd_frt;

 int nbfd = 0;
 int nbconn = MAXCONN;


 /* display the message and exit with the code */
 __attribute__((noreturn)) void die(int code, const char *format, ...)
 {
 	va_list args;

 	va_start(args, format);
 	vfprintf(stderr, format, args);
 	va_end(args);
 	exit(code);
 }

 /* Xorshift RNG */
 unsigned int prng_state = ~0U/3; // half bits set, but any seed will fit
 static inline unsigned int prng(unsigned int range)
 {
 	unsigned int x = prng_state;

 	x ^= x << 13;
 	x ^= x >> 17;
 	x ^= x << 5;
 	prng_state = x;
         return ((unsigned long long)x * (range - 1) + x) >> 32;
 }

 /* converts str in the form [<ipv4>|<ipv6>|<hostname>]:port to struct sockaddr_storage.
  * Returns < 0 with err set in case of error.
  */
 int addr_to_ss(char *str, struct sockaddr_storage *ss, struct errmsg *err)
 {
 	char *port_str;
 	int port;

 	/* look for the addr/port delimiter, it's the last colon. */
 	if ((port_str = strrchr(str, ':')) == NULL)
 		port_str = str;
 	else
 		*port_str++ = 0;

 	port = atoi(port_str);
 	if (port <= 0 || port > 65535) {
 		err->len = snprintf(err->msg, err->size, "Missing/invalid port number: '%s'\n", port_str);
 		return -1;
 	}
 	*port_str = 0; // present an empty address if none was set

 	memset(ss, 0, sizeof(*ss));

 	if (strrchr(str, ':') != NULL) {
 		/* IPv6 address contains ':' */
 		ss->ss_family = AF_INET6;
 		((struct sockaddr_in6 *)ss)->sin6_port = htons(port);

 		if (!inet_pton(ss->ss_family, str, &((struct sockaddr_in6 *)ss)->sin6_addr)) {
 			err->len = snprintf(err->msg, err->size, "Invalid IPv6 server address: '%s'", str);
 			return -1;
 		}
 	}
 	else {
 		ss->ss_family = AF_INET;
 		((struct sockaddr_in *)ss)->sin_port = htons(port);

 		if (*str == '*' || *str == '\0') { /* INADDR_ANY */
 			((struct sockaddr_in *)ss)->sin_addr.s_addr = INADDR_ANY;
 			return 0;
 		}

 		if (!inet_pton(ss->ss_family, str, &((struct sockaddr_in *)ss)->sin_addr)) {
 			struct hostent *he = gethostbyname(str);

 			if (he == NULL) {
 				err->len = snprintf(err->msg, err->size, "Invalid IPv4 server name: '%s'", str);
 				return -1;
 			}
 			((struct sockaddr_in *)ss)->sin_addr = *(struct in_addr *) *(he->h_addr_list);
 		}
 	}
 	return 0;
 }

 /* returns <0 with err in case of error or the front FD */
 int create_udp_listener(struct sockaddr_storage *addr, struct errmsg *err)
 {
 	int fd;

 	if ((fd = socket(addr->ss_family, SOCK_DGRAM, 0)) == -1) {
 		err->len = snprintf(err->msg, err->size, "socket(): '%s'", strerror(errno));
 		goto fail;
 	}

 	if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) {
 		err->len = snprintf(err->msg, err->size, "fcntl(O_NONBLOCK): '%s'", strerror(errno));
 		goto fail;
 	}

 	if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char *) &one, sizeof(one)) == -1) {
 		err->len = snprintf(err->msg, err->size, "setsockopt(SO_REUSEADDR): '%s'", strerror(errno));
 		goto fail;
 	}

 #ifdef SO_REUSEPORT
 	if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, (char *) &one, sizeof(one)) == -1) {
 		err->len = snprintf(err->msg, err->size, "setsockopt(SO_REUSEPORT): '%s'", strerror(errno));
 		goto fail;
 	}
 #endif
 	if (bind(fd, (struct sockaddr *)addr, addr->ss_family == AF_INET6 ?
 		 sizeof(struct sockaddr_in6) : sizeof(struct sockaddr_in)) == -1) {
 		err->len = snprintf(err->msg, err->size, "bind(): '%s'", strerror(errno));
 		goto fail;
 	}

 	/* the socket is ready */
 	return fd;

  fail:
 	if (fd > -1)
 		close(fd);
 	fd = -1;
 	return fd;
 }

 /* recompute pollfds using frt_fd and scanning nbconn connections.
  * Returns the number of FDs in the set.
  */
 int update_pfd(struct pollfd *pfd, int frt_fd, struct conn *conns, int nbconn)
 {
 	int nbfd = 0;
 	int i;

 	pfd[nbfd].fd   = frt_fd;
 	pfd[nbfd].events = POLLIN;
 	nbfd++;

 	for (i = 0; i < nbconn; i++) {
 		if (conns[i].fd_bck < 0)
 			continue;
 		pfd[nbfd].fd = conns[i].fd_bck;
 		pfd[nbfd].events = POLLIN;
 		nbfd++;
 	}
 	return nbfd;
 }

 /* searches a connection using fd <fd> as back connection, returns it if found
  * otherwise NULL.
  */
 struct conn *conn_bck_lookup(struct conn *conns, int nbconn, int fd)
 {
 	int i;

 	for (i = 0; i < nbconn; i++) {
 		if (conns[i].fd_bck < 0)
 			continue;
 		if (conns[i].fd_bck == fd)
 			return &conns[i];
 	}
 	return NULL;
 }

 /* Try to establish a connection to <sa>. Return the fd or -1 in case of error */
 int add_connection(struct sockaddr_storage *ss)
 {
 	int fd;

 	fd = socket(ss->ss_family, SOCK_DGRAM, 0);
 	if (fd < 0)
 		goto fail;

 	if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1)
 		goto fail;

 	if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) == -1)
 		goto fail;

 	if (connect(fd, (struct sockaddr *)ss, ss->ss_family == AF_INET6 ?
 		    sizeof(struct sockaddr_in6) : sizeof(struct sockaddr_in)) == -1) {
 		if (errno != EINPROGRESS)
 			goto fail;
 	}

 	return fd;
  fail:
 	if (fd > -1)
 		close(fd);
 	return -1;
 }

 /* Handle a read operation on an front FD. Will either reuse the existing
  * connection if the source is found, or will allocate a new one, possibly
  * replacing the oldest one. Returns <0 on error or the number of bytes
  * transmitted.
  */
 int handle_frt(int fd, struct pollfd *pfd, struct conn *conns, int nbconn)
 {
 	struct sockaddr_storage addr;
 	socklen_t addrlen;
 	struct conn *conn;
 	char *pktbuf = trash;
 	int ret;
 	int i;

 	if (rand_rate > 0) {
 		/* keep a copy of this packet */
 		history_idx++;
 		if (history_idx >= MAXREORDER)
 			history_idx = 0;
 		pktbuf = history[history_idx].buf;
 	}

 	addrlen = sizeof(addr);
 	ret = recvfrom(fd, pktbuf, MAXPKTSIZE, MSG_DONTWAIT | MSG_NOSIGNAL,
 		       (struct sockaddr *)&addr, &addrlen);

 	if (rand_rate > 0) {
 		history[history_idx].len = ret; // note: we may store -1/EAGAIN
 		if (prng(100) < rand_rate) {
 			/* return a random buffer or nothing */
 			int idx = prng(MAXREORDER + 1) - 1;
 			if (idx < 0) {
 				/* pretend we didn't receive anything */
 				return 0;
 			}
 			pktbuf = history[idx].buf;
 			ret    = history[idx].len;
 			if (ret < 0)
 				errno = EAGAIN;
 		}
 	}

 	if (ret == 0)
 		return 0;

 	if (ret < 0)
 		return errno == EAGAIN ? 0 : -1;

 	if (corr_rate > 0 && prng(100) < corr_rate) {
 		unsigned int rnd = prng(corr_span * 256); // pos and value
 		unsigned int pos = corr_base + (rnd >> 8);

 		if (pos < ret)
 			pktbuf[pos] ^= rnd;
 	}

 	conn = NULL;
 	for (i = 0; i < nbconn; i++) {
 		if (addr.ss_family != conns[i].cli_addr.ss_family)
 			continue;
 		if (memcmp(&conns[i].cli_addr, &addr,
 			   (addr.ss_family == AF_INET6) ?
 			   sizeof(struct sockaddr_in6) :
 			   sizeof(struct sockaddr_in)) != 0)
 			continue;
 		conn = &conns[i];
 		break;
 	}

 	if (!conn) {
 		/* address not found, create a new conn or replace the oldest
 		 * one. For now we support a single one.
 		 */
 		conn = &conns[0];

 		memcpy(&conn->cli_addr, &addr,
 		       (addr.ss_family == AF_INET6) ?
 		       sizeof(struct sockaddr_in6) :
 		       sizeof(struct sockaddr_in));

 		if (conn->fd_bck < 0) {
 			/* try to create a new connection */
 			conn->fd_bck = add_connection(&srv_addr);
 			nbfd = update_pfd(pfd, fd, conns, nbconn); // FIXME: MAXCONN instead ?
 		}
 	}

 	if (conn->fd_bck < 0)
 		return 0;

 	ret = send(conn->fd_bck, pktbuf, ret, MSG_DONTWAIT | MSG_NOSIGNAL);
 	return ret;
 }

 /* Handle a read operation on an FD. Close and return 0 when the read returns zero or an error */
 int handle_bck(int fd, struct pollfd *pfd, struct conn *conns, int nbconn)
 {
 	struct sockaddr_storage addr;
 	socklen_t addrlen;
 	struct conn *conn;
 	char *pktbuf = trash;
 	int ret;

 	if (rand_rate > 0) {
 		/* keep a copy of this packet */
 		history_idx++;
 		if (history_idx >= MAXREORDER)
 			history_idx = 0;
 		pktbuf = history[history_idx].buf;
 	}

 	ret = recvfrom(fd, pktbuf, MAXPKTSIZE, MSG_DONTWAIT | MSG_NOSIGNAL,
 		       (struct sockaddr *)&addr, &addrlen);

 	if (rand_rate > 0) {
 		history[history_idx].len = ret; // note: we may store -1/EAGAIN
 		if (prng(100) < rand_rate) {
 			/* return a random buffer or nothing */
 			int idx = prng(MAXREORDER + 1) - 1;
 			if (idx < 0) {
 				/* pretend we didn't receive anything */
 				return 0;
 			}
 			pktbuf = history[idx].buf;
 			ret    = history[idx].len;
 			if (ret < 0)
 				errno = EAGAIN;
 		}
 	}

 	if (ret == 0)
 		return 0;

 	if (ret < 0)
 		return errno == EAGAIN ? 0 : -1;

 	conn = conn_bck_lookup(conns, nbconn, fd);
 	if (!conn)
 		return 0;

 	ret = sendto(fd_frt, pktbuf, ret, MSG_DONTWAIT | MSG_NOSIGNAL,
 		     (struct sockaddr *)&conn->cli_addr,
 		     conn->cli_addr.ss_family == AF_INET6 ?
 		     sizeof(struct sockaddr_in6) : sizeof(struct sockaddr_in));
 	return ret;
 }

 /* print the usage message for program named <name> and exit with status <status> */
 void usage(int status, const char *name)
 {
 	if (strchr(name, '/'))
 		name = strrchr(name, '/') + 1;
 	die(status,
 	    "Usage: %s [-h] [options] [<laddr>:]<lport> [<saddr>:]<sport>\n"
 	    "Options:\n"
 	    "  -h           display this help\n"
 	    "  -r rate      reorder/duplicate/lose around <rate>%% of packets\n"
 	    "  -s seed      force initial random seed (currently %#x)\n"
 	    "  -c rate      corrupt around <rate>%% of packets\n"
 	    "  -o ofs       start offset of corrupted area (def: 0)\n"
 	    "  -w width     width of the corrupted area (def: 1)\n"
 	    "", name, prng_state);
 }

 int main(int argc, char **argv)
 {
 	struct errmsg err;
 	struct pollfd *pfd;
 	int opt;
 	int i;

 	err.len = 0;
 	err.size = 100;
 	err.msg = malloc(err.size);

 	while ((opt = getopt(argc, argv, "hr:s:c:o:w:")) != -1) {
 		switch (opt) {
 		case 'r': // rand_rate%
 			rand_rate = atoi(optarg);
 			break;
 		case 's': // seed
 			prng_state = atol(optarg);
 			break;
 		case 'c': // corruption rate
 			corr_rate = atol(optarg);
 			break;
 		case 'o': // corruption offset
 			corr_base = atol(optarg);
 			break;
 		case 'w': // corruption width
 			corr_span = atol(optarg);
 			break;
 		default: // help, anything else
 			usage(0, argv[0]);
 		}
 	}

 	if (argc - optind < 2)
 		usage(1, argv[0]);

 	if (addr_to_ss(argv[optind], &frt_addr, &err) < 0)
 		die(1, "parsing listen address: %s\n", err.msg);

 	if (addr_to_ss(argv[optind+1], &srv_addr, &err) < 0)
 		die(1, "parsing server address: %s\n", err.msg);

 	pfd = calloc(sizeof(struct pollfd), MAXCONN + 1);
 	if (!pfd)
 		die(1, "out of memory\n");

 	fd_frt = create_udp_listener(&frt_addr, &err);
 	if (fd_frt < 0)
 		die(1, "binding listener: %s\n", err.msg);


 	for (i = 0; i < MAXCONN; i++)
 		conns[i].fd_bck = -1;

 	nbfd = update_pfd(pfd, fd_frt, conns, MAXCONN);

 	while (1) {
 		/* listen for incoming packets */
 		int ret, i;

 		ret = poll(pfd, nbfd, 1000);
 		if (ret <= 0)
 			continue;

 		for (i = 0; ret; i++) {
 			if (!pfd[i].revents)
 				continue;
 			ret--;

 			if (pfd[i].fd == fd_frt) {
 				handle_frt(pfd[i].fd, pfd, conns, nbconn);
 				continue;
 			}

 			handle_bck(pfd[i].fd, pfd, conns, nbconn);
 		}
 	}
 }
	/*
	* Copyright (C) 2010-2022 Willy Tarreau <w@1wt.eu>
	*
	* Permission is hereby granted, free of charge, to any person obtaining
	* a copy of this software and associated documentation files (the
	* "Software"), to deal in the Software without restriction, including
	* without limitation the rights to use, copy, modify, merge, publish,
	* distribute, sublicense, and/or sell copies of the Software, and to
	* permit persons to whom the Software is furnished to do so, subject to
	* the following conditions:
	*
	* The above copyright notice and this permission notice shall be
	* included in all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
	* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
	* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
	* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
	* OTHER DEALINGS IN THE SOFTWARE.
	*/

	#include <stdio.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <string.h>
	#include <ctype.h>
	#include <sys/time.h>
	#include <sys/types.h>
	#include <sys/socket.h>
	#include <netinet/tcp.h>
	#include <netinet/in.h>
	#include <arpa/inet.h>
	#include <netdb.h>
	#include <fcntl.h>
	#include <errno.h>
	#include <getopt.h>
	#include <signal.h>
	#include <stdarg.h>
	#include <sys/stat.h>
	#include <time.h>
	#include <limits.h>
	#include <poll.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <stdarg.h>

	#define MAXCONN 1

	const int zero = 0;
	const int one = 1;

	struct conn {
	struct sockaddr_storage cli_addr;
	int fd_bck;
	};

	struct errmsg {
	char *msg;
	int size;
	int len;
	};

	struct sockaddr_storage frt_addr; // listen address
	struct sockaddr_storage srv_addr; // server address

	#define MAXPKTSIZE 16384
	#define MAXREORDER 20
	char trash[MAXPKTSIZE];

	/* history buffer, to resend random packets */
	struct {
	char buf[MAXPKTSIZE];
	size_t len;
	} history[MAXREORDER];
	int history_idx = 0;
	unsigned int rand_rate = 0;
	unsigned int corr_rate = 0;
	unsigned int corr_span = 1;
	unsigned int corr_base = 0;

	struct conn conns[MAXCONN]; // sole connection for now
	int fd_frt;

	int nbfd = 0;
	int nbconn = MAXCONN;


	/* display the message and exit with the code */
	__attribute__((noreturn)) void die(int code, const char *format, ...)
	{
	va_list args;

	va_start(args, format);
	vfprintf(stderr, format, args);
	va_end(args);
	exit(code);
	}

	/* Xorshift RNG */
	unsigned int prng_state = ~0U/3; // half bits set, but any seed will fit
	static inline unsigned int prng(unsigned int range)
	{
	unsigned int x = prng_state;

	x ^= x << 13;
	x ^= x >> 17;
	x ^= x << 5;
	prng_state = x;
	return ((unsigned long long)x * (range - 1) + x) >> 32;
	}

	/* converts str in the form [<ipv4>\|<ipv6>\|<hostname>]:port to struct sockaddr_storage.
	* Returns < 0 with err set in case of error.
	*/
	int addr_to_ss(char str, struct sockaddr_storage ss, struct errmsg *err)
	{
	char *port_str;
	int port;

	/* look for the addr/port delimiter, it's the last colon. */
	if ((port_str = strrchr(str, ':')) == NULL)
	port_str = str;
	else
	*port_str++ = 0;

	port = atoi(port_str);
	if (port <= 0 \|\| port > 65535) {
	err->len = snprintf(err->msg, err->size, "Missing/invalid port number: '%s'\n", port_str);
	return -1;
	}
	*port_str = 0; // present an empty address if none was set

	memset(ss, 0, sizeof(*ss));

	if (strrchr(str, ':') != NULL) {
	/* IPv6 address contains ':' */
	ss->ss_family = AF_INET6;
	((struct sockaddr_in6 *)ss)->sin6_port = htons(port);

	if (!inet_pton(ss->ss_family, str, &((struct sockaddr_in6 *)ss)->sin6_addr)) {
	err->len = snprintf(err->msg, err->size, "Invalid IPv6 server address: '%s'", str);
	return -1;
	}
	}
	else {
	ss->ss_family = AF_INET;
	((struct sockaddr_in *)ss)->sin_port = htons(port);

	if (str == '' \|\| str == '\0') { / INADDR_ANY */
	((struct sockaddr_in *)ss)->sin_addr.s_addr = INADDR_ANY;
	return 0;
	}

	if (!inet_pton(ss->ss_family, str, &((struct sockaddr_in *)ss)->sin_addr)) {
	struct hostent *he = gethostbyname(str);

	if (he == NULL) {
	err->len = snprintf(err->msg, err->size, "Invalid IPv4 server name: '%s'", str);
	return -1;
	}
	((struct sockaddr_in )ss)->sin_addr = (struct in_addr ) (he->h_addr_list);
	}
	}
	return 0;
	}

	/* returns <0 with err in case of error or the front FD */
	int create_udp_listener(struct sockaddr_storage addr, struct errmsg err)
	{
	int fd;

	if ((fd = socket(addr->ss_family, SOCK_DGRAM, 0)) == -1) {
	err->len = snprintf(err->msg, err->size, "socket(): '%s'", strerror(errno));
	goto fail;
	}

	if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1) {
	err->len = snprintf(err->msg, err->size, "fcntl(O_NONBLOCK): '%s'", strerror(errno));
	goto fail;
	}

	if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char *) &one, sizeof(one)) == -1) {
	err->len = snprintf(err->msg, err->size, "setsockopt(SO_REUSEADDR): '%s'", strerror(errno));
	goto fail;
	}

	#ifdef SO_REUSEPORT
	if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, (char *) &one, sizeof(one)) == -1) {
	err->len = snprintf(err->msg, err->size, "setsockopt(SO_REUSEPORT): '%s'", strerror(errno));
	goto fail;
	}
	#endif
	if (bind(fd, (struct sockaddr *)addr, addr->ss_family == AF_INET6 ?
	sizeof(struct sockaddr_in6) : sizeof(struct sockaddr_in)) == -1) {
	err->len = snprintf(err->msg, err->size, "bind(): '%s'", strerror(errno));
	goto fail;
	}

	/* the socket is ready */
	return fd;

	fail:
	if (fd > -1)
	close(fd);
	fd = -1;
	return fd;
	}

	/* recompute pollfds using frt_fd and scanning nbconn connections.
	* Returns the number of FDs in the set.
	*/
	int update_pfd(struct pollfd pfd, int frt_fd, struct conn conns, int nbconn)
	{
	int nbfd = 0;
	int i;

	pfd[nbfd].fd = frt_fd;
	pfd[nbfd].events = POLLIN;
	nbfd++;

	for (i = 0; i < nbconn; i++) {
	if (conns[i].fd_bck < 0)
	continue;
	pfd[nbfd].fd = conns[i].fd_bck;
	pfd[nbfd].events = POLLIN;
	nbfd++;
	}
	return nbfd;
	}

	/* searches a connection using fd <fd> as back connection, returns it if found
	* otherwise NULL.
	*/
	struct conn conn_bck_lookup(struct conn conns, int nbconn, int fd)
	{
	int i;

	for (i = 0; i < nbconn; i++) {
	if (conns[i].fd_bck < 0)
	continue;
	if (conns[i].fd_bck == fd)
	return &conns[i];
	}
	return NULL;
	}

	/* Try to establish a connection to <sa>. Return the fd or -1 in case of error */
	int add_connection(struct sockaddr_storage *ss)
	{
	int fd;

	fd = socket(ss->ss_family, SOCK_DGRAM, 0);
	if (fd < 0)
	goto fail;

	if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1)
	goto fail;

	if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) == -1)
	goto fail;

	if (connect(fd, (struct sockaddr *)ss, ss->ss_family == AF_INET6 ?
	sizeof(struct sockaddr_in6) : sizeof(struct sockaddr_in)) == -1) {
	if (errno != EINPROGRESS)
	goto fail;
	}

	return fd;
	fail:
	if (fd > -1)
	close(fd);
	return -1;
	}

	/* Handle a read operation on an front FD. Will either reuse the existing
	* connection if the source is found, or will allocate a new one, possibly
	* replacing the oldest one. Returns <0 on error or the number of bytes
	* transmitted.
	*/
	int handle_frt(int fd, struct pollfd pfd, struct conn conns, int nbconn)
	{
	struct sockaddr_storage addr;
	socklen_t addrlen;
	struct conn *conn;
	char *pktbuf = trash;
	int ret;
	int i;

	if (rand_rate > 0) {
	/* keep a copy of this packet */
	history_idx++;
	if (history_idx >= MAXREORDER)
	history_idx = 0;
	pktbuf = history[history_idx].buf;
	}

	addrlen = sizeof(addr);
	ret = recvfrom(fd, pktbuf, MAXPKTSIZE, MSG_DONTWAIT \| MSG_NOSIGNAL,
	(struct sockaddr *)&addr, &addrlen);

	if (rand_rate > 0) {
	history[history_idx].len = ret; // note: we may store -1/EAGAIN
	if (prng(100) < rand_rate) {
	/* return a random buffer or nothing */
	int idx = prng(MAXREORDER + 1) - 1;
	if (idx < 0) {
	/* pretend we didn't receive anything */
	return 0;
	}
	pktbuf = history[idx].buf;
	ret = history[idx].len;
	if (ret < 0)
	errno = EAGAIN;
	}
	}

	if (ret == 0)
	return 0;

	if (ret < 0)
	return errno == EAGAIN ? 0 : -1;

	if (corr_rate > 0 && prng(100) < corr_rate) {
	unsigned int rnd = prng(corr_span * 256); // pos and value
	unsigned int pos = corr_base + (rnd >> 8);

	if (pos < ret)
	pktbuf[pos] ^= rnd;
	}

	conn = NULL;
	for (i = 0; i < nbconn; i++) {
	if (addr.ss_family != conns[i].cli_addr.ss_family)
	continue;
	if (memcmp(&conns[i].cli_addr, &addr,
	(addr.ss_family == AF_INET6) ?
	sizeof(struct sockaddr_in6) :
	sizeof(struct sockaddr_in)) != 0)
	continue;
	conn = &conns[i];
	break;
	}

	if (!conn) {
	/* address not found, create a new conn or replace the oldest
	* one. For now we support a single one.
	*/
	conn = &conns[0];

	memcpy(&conn->cli_addr, &addr,
	(addr.ss_family == AF_INET6) ?
	sizeof(struct sockaddr_in6) :
	sizeof(struct sockaddr_in));

	if (conn->fd_bck < 0) {
	/* try to create a new connection */
	conn->fd_bck = add_connection(&srv_addr);
	nbfd = update_pfd(pfd, fd, conns, nbconn); // FIXME: MAXCONN instead ?
	}
	}

	if (conn->fd_bck < 0)
	return 0;

	ret = send(conn->fd_bck, pktbuf, ret, MSG_DONTWAIT \| MSG_NOSIGNAL);
	return ret;
	}

	/* Handle a read operation on an FD. Close and return 0 when the read returns zero or an error */
	int handle_bck(int fd, struct pollfd pfd, struct conn conns, int nbconn)
	{
	struct sockaddr_storage addr;
	socklen_t addrlen;
	struct conn *conn;
	char *pktbuf = trash;
	int ret;

	if (rand_rate > 0) {
	/* keep a copy of this packet */
	history_idx++;
	if (history_idx >= MAXREORDER)
	history_idx = 0;
	pktbuf = history[history_idx].buf;
	}

	ret = recvfrom(fd, pktbuf, MAXPKTSIZE, MSG_DONTWAIT \| MSG_NOSIGNAL,
	(struct sockaddr *)&addr, &addrlen);

	if (rand_rate > 0) {
	history[history_idx].len = ret; // note: we may store -1/EAGAIN
	if (prng(100) < rand_rate) {
	/* return a random buffer or nothing */
	int idx = prng(MAXREORDER + 1) - 1;
	if (idx < 0) {
	/* pretend we didn't receive anything */
	return 0;
	}
	pktbuf = history[idx].buf;
	ret = history[idx].len;
	if (ret < 0)
	errno = EAGAIN;
	}
	}

	if (ret == 0)
	return 0;

	if (ret < 0)
	return errno == EAGAIN ? 0 : -1;

	conn = conn_bck_lookup(conns, nbconn, fd);
	if (!conn)
	return 0;

	ret = sendto(fd_frt, pktbuf, ret, MSG_DONTWAIT \| MSG_NOSIGNAL,
	(struct sockaddr *)&conn->cli_addr,
	conn->cli_addr.ss_family == AF_INET6 ?
	sizeof(struct sockaddr_in6) : sizeof(struct sockaddr_in));
	return ret;
	}

	/* print the usage message for program named <name> and exit with status <status> */
	void usage(int status, const char *name)
	{
	if (strchr(name, '/'))
	name = strrchr(name, '/') + 1;
	die(status,
	"Usage: %s [-h] [options] [<laddr>:]<lport> [<saddr>:]<sport>\n"
	"Options:\n"
	" -h display this help\n"
	" -r rate reorder/duplicate/lose around <rate>%% of packets\n"
	" -s seed force initial random seed (currently %#x)\n"
	" -c rate corrupt around <rate>%% of packets\n"
	" -o ofs start offset of corrupted area (def: 0)\n"
	" -w width width of the corrupted area (def: 1)\n"
	"", name, prng_state);
	}

	int main(int argc, char **argv)
	{
	struct errmsg err;
	struct pollfd *pfd;
	int opt;
	int i;

	err.len = 0;
	err.size = 100;
	err.msg = malloc(err.size);

	while ((opt = getopt(argc, argv, "hr:s:c:o:w:")) != -1) {
	switch (opt) {
	case 'r': // rand_rate%
	rand_rate = atoi(optarg);
	break;
	case 's': // seed
	prng_state = atol(optarg);
	break;
	case 'c': // corruption rate
	corr_rate = atol(optarg);
	break;
	case 'o': // corruption offset
	corr_base = atol(optarg);
	break;
	case 'w': // corruption width
	corr_span = atol(optarg);
	break;
	default: // help, anything else
	usage(0, argv[0]);
	}
	}

	if (argc - optind < 2)
	usage(1, argv[0]);

	if (addr_to_ss(argv[optind], &frt_addr, &err) < 0)
	die(1, "parsing listen address: %s\n", err.msg);

	if (addr_to_ss(argv[optind+1], &srv_addr, &err) < 0)
	die(1, "parsing server address: %s\n", err.msg);

	pfd = calloc(sizeof(struct pollfd), MAXCONN + 1);
	if (!pfd)
	die(1, "out of memory\n");

	fd_frt = create_udp_listener(&frt_addr, &err);
	if (fd_frt < 0)
	die(1, "binding listener: %s\n", err.msg);


	for (i = 0; i < MAXCONN; i++)
	conns[i].fd_bck = -1;

	nbfd = update_pfd(pfd, fd_frt, conns, MAXCONN);

	while (1) {
	/* listen for incoming packets */
	int ret, i;

	ret = poll(pfd, nbfd, 1000);
	if (ret <= 0)
	continue;

	for (i = 0; ret; i++) {
	if (!pfd[i].revents)
	continue;
	ret--;

	if (pfd[i].fd == fd_frt) {
	handle_frt(pfd[i].fd, pfd, conns, nbconn);
	continue;
	}

	handle_bck(pfd[i].fd, pfd, conns, nbconn);
	}
	}
	}