From: Steve Lewis <poeticjustice72182@...>
Date: 2008-09-07T09:58:59+09:00
Subject: Re: Question About TCPServer & TCPSocket classes

On Sat, 06 Sep 2008 11:04:43 +0200, Robert Klemme wrote:

> 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

Robert,

Thanks for the help!  You're correct, my curiosity here is mostly 
academic, but DRuby looks like the practical solution to use when I 
decide I'd like to try something more substantial.