CMSC 417 Computer Networks Fall 2008
Programming Assignment 2
1 Introduction
In this assignment you will write the server program which will communicate using
sockets with the client program in the previous assignment.
2 The Protocol
Your server will run on a linuxlab machine and will listen on a TCP socket bound to a port as described
below. Note that you cannot bind to a port below 1024 without having super user (root) access.
Given that your class account login id is cs4170xx, the ports you should use are 10xx0-10xx9 (inclusive).
Thus, if your login id is cs417060, you will use port range 10600-10609. Your final project must work with
any port, but when you are testing your project you should only use the ports you have been allocated to
avoid collision with others.
The rest of the protocol is as described in Project 0.
3 The server program
The command line syntax for a minimal server is given below. The server will take the port as argument.
(you can almost re-use the argument parsing code in the client).
server
server server
server [<port>]
[<port>][<port>]
[<port>]
• The cookie should be generated using the formula:
(a + b + c + d) × 13 mod 1111, where a.b.c.d is the IP address of the client, 0 ≤ a, b, c, d ≤ 255.
• After the successful communication, the server MUST print the cookie it generates along with the client’s
login id, first name, IP address and port number. All this information should be in a single line. An example
is:
555 cs417050 Nikolaos from 128.8.126.208:48542
555 cs417050 Nikolaos from 128.8.126.208:48542555 cs417050 Nikolaos from 128.8.126.208:48542
555 cs417050 Nikolaos from 128.8.126.208:48542
Notice that ((128+8+126+208) × 13 mod 1111) is 555
•For project 1 the server only accepted null terminated strings. Your server should work even when the
client sends the string without the terminal ‘\0’ character.
• Note well: your server should not accept spurious input from the clients.
• We will test your server with non-confor ming clients; the server should print out an error message
containing the client’s IP address and port number also in a single line, as such:
**Error** from 128.8.126.133:48522
**Error** from 128.8.126.133:48522**Error** from 128.8.126.133:48522
**Error** from 128.8.126.133:48522
and immediately close the connection when it finds a bad message from the client. It should not
breakdown, but continue operating after servicing misbehaving clients. Bad messages, as per project 0, are
ones that have an incorrect magic string, incorrect message type or too many fields.
Remember, the cookie sent in the STATUS message has to match the cookie in the CLIENT BYE
message for a communication to be successful.
