CS 742 - Computer Communication Networks - Program 1 - Name:_____________

   DUE: Friday, October 25, 2002

   (100 points)

   o Put your name and add some necessary comments into these code when
     necessary. These are a part of grading in this assignment.

   o Write one page document describing the programs you create and the
     user's guide.

   o Use the handin system to submit all code electronically. The 
     submission ID is 1.


   1. Write a client and server program according to the following
      specifications using C/C++: (50 points)
  
    (1) Client connects to server and sends COMMAND(s) to server.

    (2) Server will listen on some port (must use last 4 digit of SSN # 
        as your port number).

    (3) Client will send hostname along with port number to connect
        in the COMMAND sequence. The COMMAND should look like this:
        CONNECT hostname port-number
        e.g: CONNECT host:kirk.cs.twsu.edu port:80
        (note: CONNECT is in capital)

    (4) Server will read the COMMAND sequence from client, parse it and 
        try to establish connection to (host,port) specified by client. 
        If client issues wrong COMMAND then server will write back
        'Invalid COMMAND' to client, else it will read data from remote 
        host and write it back to client console. If server will be 
        unable to connect to remote host specified by client it will 
        write 'HOST:hostname(port) is not at your service'.

    (5). You must verify that you program is working good for at least 
         these ports (80,25,13).

   2. Write the same program using Java. (50 points)

SAMPLE SESSION:
---------------
> ./server
Server ready to accept connections
wireless.cs.twsu.edu(1222) ==> issued 'COMMAND host:www.google.com port:80'
kirk.cs.twsu.edu(3332)     ==> issued 'COMMAND host:kirk.cs.twsu.edu port:25'
sisko.cs.twsu.edu(1211)    ==> issued 'COMMAND host:www.cisco.com port:13'
web.eecs.mit.edu           ==> issued 'COMMAND host:blah-blah port:11'
156.21.1.1                 ==> issued 'COMMAND host:www.yahoo.id port:1111'

(BONUS)
www.wichita.edu ==> issued 'COMMAND host:wireless port:111 host:yahoo.com port:1111 host:google.com port:1111

> ./client
COMMAND host:kirk.cs.twsu.edu port:13
Wed Sep 25 00:20:06 2002
Connection closed by server
COMMAND host:kirk.cs.twsu.edu port:25
220 kirk.cs.twsu.edu ESMTP Exim 3.35 #1 Wed, 25 Sep 2002 00:21:12 -0500
quit
221 kirk.cs.twsu.edu closing connection
Connection closed by server
CONNECT host:blah-blah port:11
HOST:blah-blah(11) is not at your service

BONUS part:
COMMAND host:kirk.cs.twsu.edu port:25 host:sisko.cs.twsu.edu:13
220 kirk.cs.twsu.edu ESMTP Exim 3.35 #1 Wed, 25 Sep 2002 00:21:12 -0500
quit
221 kirk.cs.twsu.edu closing connection
Connection closed by server
Wed Sep 25 00:20:06 2002
Connection closed by server


EXPLANATION OF SESSION :
-----------------------
We started server by './server', server prints message 'Server ready to
accept connections', now whenever some client connects, it prints client
FQDN(if possible else will print client IP) along with client's remote
port number in (port-number).  Then it prints COMMAND text issued by
client. If you notice, the fourth command(mit one) actually will make
server to send back 'HOST: hostname is not at your service' to client.

We started client by './client', client is ready to accept read from
input and send it to server. we issued several commands , in the first
command 'COMMAND host: kirk.cs.twsu.edu port:13' , we read date from
server , in second we read SMTP server response.

Look at diagram:
  __________                -----------             __________
 |          |   COMMAND    |           |  CONNECT  |          |
 | CLIENT   | <----------> | SERVER    | <-------> | REMOTE   |
 |          |              |           |           |  HOST    |
 |__________|              |___________|           |__________|

COMMAND ==> CONNECT host:kirk.cs.twsu.edu port:25

so remote host is kirk.cs.twsu.edu, your server will attempt to connect
to kirk.cs.twsu.edu on port 25

Please note down, whenever  server <----> remote host connection closes
server inform back to client , and client will display 'Connection closed
by server' on its console

SANITY CHECKS
-------------
 You need to make sure all possible cases that can crash your server
and client , such as :

i) There should be no spaces between host and : and or port and :
i) LIMIT COMMAND Sequence length, else SERVER will not accept that COMMAND
   say COMMAND text can only be of 100 characters.

BONUS POINTS  (20 points)
------------

1- If you will be able to handle COMMAND sequence like this one
   CONNECT host:kirk.cs.twsu.edu port:25 host:sisko.cs.twsu.edu port:13

   Observe, you can specify multiple hosts in one line , in this case
   your server will open connection one by one to remote host(s) at
   specified ports in sequence and gives the output back to client in
   order.

CONNECT host:kirk.cs.twsu.edu port:25 host:sisko.cs.twsu.edu:13

server --> Connection #1 : make connection to kirk port 25.
When Connection #1 is closed, it immediately opens
Connection #2; sisko.cs.twsu.edu at port 13

For each connection, the conditions are same as described above.

2 - If you will be able to handle multiple clients at one time.
    (either through thread of fork()).


OPTIONS:
--------
 - You can use TCP or UDP whatever you want.