testing telnet: howto

monteo · 01-31-2008, 01:45 PM

Hello, I'm trying to test a tcp connection using telnet, I can't use expect or perl. I'm running telnet in the background (seeing how it's input oriented) then chekcing netstat for an established connection, and if found killing the telnet process, then displaying results. Any help would be greatly appreciated. Note, if you're going to use my script for testing please change the x.x.x.x with a valid ip address and possibly 1500 with a valid port. Also, these commands work just fine when running from the command line, however I always get a connection unseccessful when running in a script.

Code:

#!/bin/ksh
#variable definitions
  export SERVER_IP=x.x.x.x
  export SERVER_PORT=1500
  export results=./results

  if [[ -e "$results" ]]; then
    cat /dev/null > $results
  else
    touch $results
  fi

  #clear screen
  clear

  #initiate connection
  telnet $SERVER_IP $SERVER_PORT 1> /dev/null 2> $results &


  #check for established connection
  if [[ -n "`netstat -an|grep $SERVER_IP|grep -i $SERVER_PORT|grep -i established`" ]];then
    echo "\tconnection successful
    
    #close connection
    ps -ef|grep "telnet $SERVER_IP $SERVER_PORT"|grep -v grep|awk '{print $2}' | xargs -i kill -9 {}
    rm -f $results
    results=""
  else
    echo "\tconnection unsuccessful"
    echo "\t`cat $results`"
    rm -f $results
    results=""
  fi

raskin · 01-31-2008, 03:12 PM

In your script, telnet goes to background and you check output nearly immediately, before anything useful has time to occur via network. Try putting sleep 1.

monteo · 01-31-2008, 03:40 PM

I've tried sleeping for up to 10 seconds with no change in status. Also, more often then not, the script won't report a successful connection. Though sometimes it does, leaving me to believe it's a timing issue as well...but having it sleep doesn't change anything. And, when running directly from the command line I get established from netstat immediately.

raskin · 02-01-2008, 05:31 AM

Looks like telnet actually uses that its input is a terminal. Because when I wrapped telnet invocation in a simple wrapper

Code:

#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>

int main(int argc, char ** argv, char ** envp)
{
        int fd, fd2, ptn, bit;
        char ptname[100];
        char readbuf[1025], writebuf[1025];
        size_t readc, writec;
        pid_t readpid,writepid,shellpid;
        int exitstatus;

        fd=open("/dev/ptmx", O_RDWR);

        ioctl(fd, TIOCGPTN, &ptn);

        bit=0;
        ioctl(fd, TIOCSPTLCK, &bit);

        snprintf(ptname, 99, "/dev/pts/%d", ptn);

        fd2=open(ptname, O_RDWR);

        if (!(readpid=fork())){
                while(1) {
                        readc=read(0, readbuf, 1024);
                        write(fd, readbuf, readc);
                }
        }

        if (!(writepid=fork())){
                while(1) {
                        writec=read(fd, writebuf, 1024);
                        write(1, writebuf, writec);
                }
        }

        if (!(shellpid=fork())){
                dup2(fd2,0);
                dup2(fd2,1);
                dup2(fd2,2);

                setpgrp();

                execvp(argv[1], argv+1);
        }

        waitpid(shellpid, &exitstatus, 0);

        kill (readpid, SIGTERM);
        kill (writepid, SIGTERM);

        return exitstatus;
}

- basically it does the main thing expect gives - everything works.