Lab1 - simple client/server application

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Keywords

client, server, TCP, IP, BSD sockets

Objective

Familiarize yourself with the BSD sockets API by writing a simple server and a client.

Generic requirements

  • The program must rely on the BSD sockets API, not some other library which is an abstraction on top of BSD sockets.
  • TCP must be used at the transport layer.
  • IP must be used at the network layer.

Server requirements

  • The server must print debug information about each incoming connection, indicating the remote address [and other details you think that are relevant].
  • The server must implement 5 special commands that can be received from the client, to which the server will react in a special way:
    • %Hastalavista - if the server receives this command, it will terminate the connection and shut itself down;
    • %Time - the server will react by sending the client the current time of the system on which the server is running
    • The other 3 commands have to be chosen by you
  • If the server receives an unknown command - it must respond with "Can you elaborate on that?"
  • If the server receives an unknown command that ends with a '?' - it must respond with "42"

Bonus features

  • The server must be able to handle multiple client connections at the same time.
  • The server supports an additional special command - %Picsoritdidnthappen. Upon receiving it, the server will send the following image to the client

Terminator2.jpg

Client requirements

  • The client must take its input commands from the keyboard
  • The command will be sent to the server by pressing the Enter key
  • If you implemented the file transfer feature, the client must receive the image and save it to a file in the current directory; i.e. your client does not have to display the image itself.
  • The client will terminate the connection with the server if you try to send the %Close command


Grading policy

Assuming that everything works right,

  • 8 - for implementing all the basic features;
  • 9 - for implementing the basic features + one of the bonus features;
  • 10 - for the basics and both bonus features.

Remark on supporting multiple client connections, there are 2 ways to get that bonus:

  • Describe two different ways in which the feature can be implemented (comparing each approach and discussing the pros and cons of each), or
  • Implement one of the two ways

That's right, the bonus can be yours if you think about it, without actually making it work.


Notes
  • The program does not have to be one with a GUI, a command line application will do.


References

Examples

#Here is a simple example of a server written in Python.
from socket import * 
#note that you could have written import socket
#then you'd have to write "socket." as a prefix to access stuff in this module


response="I am here to serve. I want to talk about it"

#initialize the socket with default settings
listeningSocket = socket()
#bind the socket to an interface
listeningSocket.bind( ("127.0.0.1", 1045) )
print "bind = OK"

#make it listen
listeningSocket.listen(5)
print listeningSocket #print the handle to the socket, so you can see exists

#accept an incoming connection
newAllocatedSocket, address = listeningSocket.accept()
print address, newAllocatedSocket #see some data about the connected client

newAllocatedSocket.send(response) #send a message to the client
data = newAllocatedSocket.recv(10) #read 10 bytes
print data

#newAllocatedSocket.send(gethostname( ))

#close everything and get outta here
newAllocatedSocket.close()
listeningSocket.close()
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