Skip to content

Latest commit

 

History

History
156 lines (116 loc) · 5.69 KB

PART_4.md

File metadata and controls

156 lines (116 loc) · 5.69 KB
Raw

Part 4: Socket programming and network I/O

The article we'll work through in this part of the course is Implementing a minimal HTTP server in Ruby. Reading it carefully should prepare you to work through the questions and exercises for this topic.

Questions

NOTE: Some of these questions can directly be answered by reading the article, but most require you to search the web for answers. External research is not only OK, it's encouraged!

Q1: Briefly describe what a TCP socket is, using as little jargon as possible.

Q2: The Socket, TCPSocket, and TCPServer classes provide functionality that handles network interactions. What base class provides most of the generic stream processing behavior they all have in common?

Q3: Describe the similarities and differences between client-side and server-side sockets.

Q4: Why is it important to explicitly close sockets when you are done using them?

Q5: What might lead to a socket not being properly closed? What constructs does Ruby provide that can be used to avoid these problems?

Q6: After a client-server interaction is completed, who is responsible for closing sockets: the client, the server, or both the client and the server? Explain your answer.

Q7: What strategies could you use for testing code that makes use of sockets? Consider both unit testing and end-to-end system testing in your response.

Q8: Below are two minimal TCPServer examples, both of which accept incoming connections, and then respond with a "Hello World" message after a short delay.

Suppose that three client requests arrive at roughly the same time. How long would you expect it to take for each server implementation to process the three requests?

Implementation #1:

require "socket"

server = TCPServer.new 2000

loop do
  client = server.accept 

  sleep 10

  client.puts "Hello World!"
  client.puts "Time is #{Time.now}"

  client.close
end

Implementation #2:

require "socket"

server = TCPServer.new 2000

loop do
  Thread.start(server.accept) do |client|
    sleep 10

    client.puts "Hello World!"
    client.puts "Time is #{Time.now}"

    client.close
  end
end

You can experimentally verify your answer using a command line tool like telnet. You should only need to establish a connection to test out the server behavior, as in the following example:

$ telnet localhost 2000
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Hello World!
Time is 2014-06-09 12:20:31 -0400
Connection closed by foreign host.

Exercises

In this set of exercises, you will build a minimal Internet Relay Chat (IRC) client, using nothing but basic socket programming.

STEP 1: Read through IRC Over Telnet, and follow along using telnet on your own machine.

You can join any channel you'd like for experimentation, but are welcome to try using #practicing-ruby-testing if you want to encounter other Practicing Rubyists testing their bots.

You may want to also connect using a regular IRC client to see what the effects of your telnet-based experiments are. If you're not familiar with IRC, you can use the following link to access a web client which will randomly generate a nickname for you and connect you to the #practicing-ruby-testing channel:

http://webchat.freenode.net/?randomnick=1&channels=%23practicing-ruby-testing&uio=d4

STEP 2: Using the TCPSocket class, establish a socket connection to irc.freenode.net on port 6667. Once you're connected, set your NICK and USER information using the commands shown in the IRC Over Telnet article, then join a channel and post a "Hello World" message using the PRIVMSG command. Finally, issue a QUIT message and close the socket connection.

STEP 3: Create a loop to process incoming messages from the server. Whenever a PING command is received, respond with an appropriate PONG command to keep your connection from being terminated. Whenever a PRIVMSG command is received, print the message contents to STDOUT.

STEP 4: Choose a special word for your bot to monitor the chat logs for. Whenever this word is mentioned, send a message in response. For example, you might have your bot respond "MINASWAN!" every time someone mentions the word "Matz".

STEP 5: Make your client more robust by handling common error conditions (e.g. when a given nickname is already in use), and make the nickname used by your bot configurable at runtime. Try to cleanly close your socket connections when possible, and make your error messages human readable and clear.

The IRC Over Telnet article combined with the TCPSocket API documention should give you enough information to complete this set of exercises, but if you want much more detailed information on the IRC protocol, you can check out RFC 1459. In particular, look at the following sections:

If you get stuck and have any questions, don't hesitate to file an issue in this repository or ask for help in the Practicing Ruby campfire chat.