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UNIX NETWORKING PROGRAMMING

Posted on 1998-11-13
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Last Modified: 2013-12-23
I want to write a program in C (under unix) in which a user specifies a remote host name (or ip address) and request a service such as the current time of the remote server. The program should convert the username to an ip address(if username is given), locate the remote host, request the service required by user and display the output(in a user friendly manner) on the user's terminal. Please help!!
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Question by:boosta
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Accepted Solution

by:
davidmwilliams earned 200 total points
ID: 1582608
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

extern int errno;

int TCPdaytime (const char* host, const char *service);
int errexit (const char *format, ...);
int connectTCP (const char *host, const char *service)

#define LINELEN 128

int main (int argc, char *argv [])
{
  char *host = "localhost";
  char *service = "daytime";

  switch (argc)
  {
    case 1:
      host = "localhost";
      break;

    case 3:
      service = argv [2];

    case 2:
      host = argv [1];
      break

    default:
      fprintf (stderr, "usage: TCPdaytime [host [port]]\n");
      exit (1);
  }

  TCPdaytime (host, service);
  exit (0);
}

TCPdaytime (const char *host, const char *service)
{
  char buf [LINELEN + 1];
  int s, n;

  s = connectTCP (host, service);

  while ( (n = read (s, buf, LINELEN)) > 0)
  {
    buf [n] = '\0';
    (void) fputs (buf, stdout);
  }
}

int errexit (const char *format, ...)
{
  va_list args;

  va_start (args, format);
  vfprintf (stderr, format, args);
  va_end (args);
  exit (1);
}

int connectTCP (const char *host, const char *service)
{
  struct hostent *phe;
  struct servent *pse;
  struct protoent *ppe;
  struct sockaddr_in sin;
  int s, type;

  memset (&sin, 0, sizeof (sin));
  sin.sin_family = AF_INET;

  if (pse = getservbyname (service, "tcp"))
    sin.sin_port = pse->s_port;
  else if ( (sin.sin_port = htons ((u_short) atoi (service))) == 0)
    errexit ("Can't get \"%s\" service entry.\n", service);

  if (phe = gethostbyname (host))
    memcpy (&sin.sin_addr, phe->h_addr, phe->h_length);
  else if ((sin.sin_addr.s_addr = inet_addr (host)) == INADDR_NONE)
    errexit ("Can't get \"%s\" host entry.\n", host);

  if ((ppe = getprotobyname ("tcp")) == 0)
    errexit ("Can't get \"tcp\" protocol entry.\n");

  type = SOCK_STREAM;

  s = socket (PF_INET, type, ppe->p_proto);
  if (s < 0)
    errexit ("Can't create socket: %s\n", strerror (errno));

  if (connect (s, (struct sockaddr *) &sin, sizeof (sin)) < 0)
    errexit ("Can't connect to %s.%s: %s\n", host, service, strerror (errno));

  return s;
}
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Author Comment

by:boosta
ID: 1582609
Thanx a lot. Its appropriate and accurate.
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Author Comment

by:boosta
ID: 1582610
Thanx a lot. Its appropriate and accurate.
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LVL 4

Expert Comment

by:davidmwilliams
ID: 1582611
Glad to be able to help !
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