From: Robert Klemme <shortcutter@...>
Date: 2008-09-06T17:59:07+09:00
Subject: Re: Question About TCPServer & TCPSocket classes

On 06.09.2008 07:45, Steve Lewis wrote:
> Hello Rubyists,
> 
> I've been messing around with socket programming in Ruby lately, and I've 
> hit a snag with some of my experiments.  My first, (successful), 
> experiment was to create a basic client/server script wherein the client 
> sends a string to the server, and the server responds by simply writing 
> the string back to the client...that code is as follows:
> 
> Server:
> #####################################
> require 'socket'
> 
> class PingServer < TCPServer
> 
>   def start_server
>     loop do
>       Thread.start(self.accept) do |s|
>         p "Connection accepted from server #{s.inspect}"
>         request = s.readline.gsub(/\n$/, '')
>         p "Request was #{request}"
>         s.write "Your request was as follows: #{request}"
>         s.write Time.now if request == 'time'
>         s.close
>         p "Connection #{s} closed"
>       end
>     end
>   end
> 
> end
> 
> PingServer.new('localhost', 3000).start_server
> 
> ###############################################
> 
> 
> 
> The client code is thus:
> ########################################
>   require 'socket'
>   
>   
> 
>   def send_message(message)
>     TCPSocket.open('localhost', 3000) do |client|
>       client.write(message)
>       stuff =  client.read(100)
>       client.close
>       p stuff
>       get_message
>     end
>   end
>   
>   def get_message
>     message = gets
>     send_message(message) unless message.gsub(/\n/, '') == 'quit'
>     exit  
>   end
>   
>   
>   get_message
> 
> ##################################
> 
> As I said, the above code works as expected, I start the server, then run 
> the client program...I can send strings to the server all day long, and 
> the server writes them right back to me.
> 
> The problem occurs when I try to send the following instead of a string:
> 
> Marshal.dump(%w(foo bar baz))
> 
> Sending the resulting string over the wire causes the server to hang...it 
> doesn't return the string back to the client...I'm at a loss to figure 
> out why it seems to have trouble handling the string...
> 
> Ideas would be appreciated!!

Steve, you are mixing #read, #write on one side and #readline on the 
other side.  Since Marshal.dump creates binary data your #readline on 
the server won't properly work.  You should either use a binary 
protocoll *or* a textual (line based) protocol.  Mixing both causes 
problems.

Just an additional note: if you use Marshal, you can directly read to 
and write from the socket without the intermediate String.  This is 
likely more efficient and also you avoid the issue of not knowing how 
long the Marshal sequence is.

And yet another note: just in case you need a solution with 
communicating processes where all of them are Ruby applications you can 
use DRuby.  But I guess at the moment you want to learn about Ruby 
socket programming so this is probably just for keeping in the back of 
your head.

Kind regards

	robert