Homework 2: Simple Network Programming

Due Tuesday, Sep 9th, 12:40pm (at class start).


Section 0: Cleanup

Deal with my comments on the first homework: fix problems, etc.

Section 1: More Iterators and Generators

Implement both a re-entrant non-generator iterator, PrimeIter, and a generator, prime_generator, that calculate prime numbers using Eratosthenes' Sieve. Your code should pass the following tests:

import homework2_primes, types

prime5 = [2, 3, 5, 7, 11]

primer = homework2_primes.PrimeIter()
x = [ (i, j, k) for (i, j, k) in zip(primer, primer, range(5)) ]
assert prime5 == [ i for (i, j, k) in x ]
assert prime5 == [ j for (i, j, k) in x ]

primer = homework2_primes.prime_generator()
assert isinstance(primer, types.GeneratorType)
x = [ i for (i, k) in zip(primer, range(5)) ]
assert prime5 == x

Here is a potentially useful utility function that you should feel free to use in your own code:

def divides(primes, n):
  """
  'primes' is a list of prime numbers, 'n' is a positive integer.
  'divides' returns True if any number in 'primes' divides 'n'.
  """
  for trial in primes:
     if n % trial == 0: return True
  return False

Section 2: Write a spambot

Write a command-line program that connects to a specified server on the SMTP port (port 25) and sends an e-mail from you to a specified address; the e-mail should contain a specified word. The program should be named 'send-email' and be in the 'homework2/' subdirectory of your svn archive. So, for example, the following command

python homework2/send-email teckla.idyll.org titus@cse491.msu.idyll.org blarny

would send an e-mail containing the word 'blarny' to 'titus@cse491.msu.idyll.org' using the mail server 'teckla.idyll.org'.

You don't need to do any error trapping or handling.

Very important: Actually sending spam is a violation of the MSU network policy, and it is also very unfriendly. Stick to using the server 'teckla.idyll.org' and your own username @ cse491.msu.idyll.org, or else you may find your network access cut off or worse. Plus you could get me in trouble, which may sound like fun but won't be - for you. Promise.

Section 3: Write a simple TCP echo server

Create a Python echo server that, when run, binds to the specified port and echoes whatever data is sent to it back to the sender, up until a simple 'n.n' is received, at which point the connection is terminated. This echo server should take two arguments on the command line: the host IP address and the port to which to bind. For example,

python homework2/echo-server localhost 4199

Please do not use any Python network libraries other than 'socket' for this assignment. You can (and should) process connections synchronously; there's no need to handle multiple connections in parallel. (Guess what a future homework is? ;)

The echo server should echo exactly what it receives, with no interpretation or parsing other than the end period.

Hint: you can use the spambot from section 2 to test your echo-server without writing a new Python program; just set the spambot program to print whatever it receives to the console, so you can verify that the echo server is working properly.