text: /*
   * Pscan is a mini port scanner implementation for busybox
   *
   * Copyright 2007 Tito Ragusa <farmatito@tiscali.it>
   *
   * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
   */
  
  #include "libbb.h"
  
  /* debugging */
  #ifdef DEBUG_PSCAN
  #define DMSG(...) bb_error_msg(__VA_ARGS__)
  #define DERR(...) bb_perror_msg(__VA_ARGS__)
  #else
  #define DMSG(...) ((void)0)
  #define DERR(...) ((void)0)
  #endif
  
  static const char *port_name(unsigned port)
  {
  	struct servent *server;
  
  	server = getservbyport(htons(port), NULL);
  	if (server)
  		return server->s_name;
  	return "unknown";
  }
  
  /* We don't expect to see 1000+ seconds delay, unsigned is enough */
  #define MONOTONIC_US() ((unsigned)monotonic_us())
  
  int pscan_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  int pscan_main(int argc, char **argv)
  {
  	const char *opt_max_port = "1024";      /* -P: default max port */
  	const char *opt_min_port = "1";         /* -p: default min port */
  	const char *opt_timeout = "5000";       /* -t: default timeout in msec */
  	/* We estimate rtt and wait rtt*4 before concluding that port is
  	 * totally blocked. min rtt of 5 ms may be too low if you are
  	 * scanning an Internet host behind saturated/traffic shaped link.
  	 * Rule of thumb: with min_rtt of N msec, scanning 1000 ports
  	 * will take N seconds at absolute minimum */
  	const char *opt_min_rtt = "5";          /* -T: default min rtt in msec */
  	len_and_sockaddr *lsap;
  	int s;
  	unsigned port, max_port, nports;
  	unsigned closed_ports = 0;
  	unsigned open_ports = 0;
  	/* all in usec */
  	unsigned timeout;
  	unsigned min_rtt;
  	unsigned rtt_4;
  	unsigned start;
  
  	opt_complementary = "=1"; /* exactly one non-option */
  	getopt32(argv, "p:P:t:T:", &opt_min_port, &opt_max_port, &opt_timeout, &opt_min_rtt);
  	argv += optind;
  	max_port = xatou_range(opt_max_port, 1, 65535);
  	port = xatou_range(opt_min_port, 1, max_port);
  	nports = max_port - port + 1;
  	rtt_4 = timeout = xatou_range(opt_timeout, 1, INT_MAX/1000 / 4) * 1000;
  	min_rtt = xatou_range(opt_min_rtt, 1, INT_MAX/1000 / 4) * 1000;
  
  	DMSG("min_rtt %u timeout %u", min_rtt, timeout);
  
  	lsap = xhost2sockaddr(*argv, port);
  	printf("Scanning %s ports %u to %u\n Port\tProto\tState\tService\n",
  			*argv, port, max_port);
  
  	for (; port <= max_port; port++) {
  		DMSG("rtt %u", rtt_4);
  
  		/* The SOCK_STREAM socket type is implemented on the TCP/IP protocol. */
  		set_nport(lsap, htons(port));
  		s = xsocket(lsap->sa.sa_family, SOCK_STREAM, 0);
  
  		/* We need unblocking socket so we don't need to wait for ETIMEOUT. */
  		/* Nonblocking connect typically "fails" with errno == EINPROGRESS */
  		ndelay_on(s);
  		DMSG("connect to port %u", port);
  		start = MONOTONIC_US();
  		if (connect(s, &lsap->sa, lsap->len) == 0) {
  			/* Unlikely, for me even localhost fails :) */
  			DMSG("connect succeeded");
  			goto open;
  		}
  		/* Check for untypical errors... */
  		if (errno != EAGAIN && errno != EINPROGRESS
  		 && errno != ECONNREFUSED
  		) {
  			bb_perror_nomsg_and_die();
  		}
  
  		while (1) {
  			if (errno == ECONNREFUSED) {
  				DMSG("port %u: ECONNREFUSED", port);
  				closed_ports++;
  				break;
  			}
  			DERR("port %u errno %d @%u", port, errno, MONOTONIC_US() - start);
  			if ((MONOTONIC_US() - start) > rtt_4)
  				break;
  			/* Can sleep (much) longer than specified delay.
  			 * We check rtt BEFORE we usleep, otherwise
  			 * on localhost we'll do zero writes done (!)
  			 * before we exceed (rather small) rtt */
  			usleep(rtt_4/8);
  			DMSG("write to port %u @%u", port, MONOTONIC_US() - start);
  			if (write(s, " ", 1) >= 0) { /* We were able to write to the socket */
   open:
  				open_ports++;
  				printf("%5u\ttcp\topen\t%s\n", port, port_name(port));
  				break;
  			}
  		}
  		DMSG("out of loop @%u", MONOTONIC_US() - start);
  
  		/* Estimate new rtt - we don't want to wait entire timeout
  		 * for each port. *4 allows for rise in net delay.
  		 * We increase rtt quickly (*4), decrease slowly (4/8 == 1/2)
  		 * because we don't want to accidentally miss ports. */
  		rtt_4 = (MONOTONIC_US() - start) * 4;
  		if (rtt_4 < min_rtt)
  			rtt_4 = min_rtt;
  		if (rtt_4 > timeout)
  			rtt_4 = timeout;
  		/* Clean up */
  		close(s);
  	}
  	if (ENABLE_FEATURE_CLEAN_UP) free(lsap);
  
  	printf("%d closed, %d open, %d timed out ports\n",
  					closed_ports,
  					open_ports,
  					nports - (closed_ports + open_ports));
  	return EXIT_SUCCESS;
  }
  