- client------numbers------>server
  server---even numbers---->client

        523,123,6,235,74,234,764
        6,74,234,764

- client------filename------>server
  server---lines of the file---->client

  if the file is not found:
  server---error message---->client

- "webserver"

    1. make a server that prints every line
       that its clients sends to the server's stdout
    1b. point the server at the client
        e.g.  http://localhost:2222/

    2. emulate a browser: send a similar message
       to a webserver (e.g. www.elte.hu)
       and see what text it sends you

    3. change your server so that it returns
       similar text to your browser