From: Victor Reyes <victor.reyes@...>
Date: 2008-05-29T20:13:20+09:00
Subject: Re: GServer send/receive limit

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On Thu, May 29, 2008 at 1:19 AM, Eleanor McHugh <
eleanor@games-with-brains.com> wrote:

> On 28 May 2008, at 20:08, Victor Reyes wrote:
>
>> Well, as I said earlier, I found these pieces of code in a website named
>> games-with-brains.com, which I think you have something to do with it,
>> and
>> perhaps it has your picture.
>>
>
> That would be me, and my cruddy code as well so I guess I'd better give you
> some help :)
>
>  Attached is the code I lifted from the website:
>>
>> *THE CLIENT
>>
>> client = TimeClient.new
>> (1..2).each do |i|
>>       client.connect("localhost", 12341955)
>>       client.send
>>       client.on_response
>>
>
> The above line is a bug. My TCPClient class defines send so that it
> automatically calls on_response, so calling on_response a second time will
> cause the program to hang because the server is still waiting for a request
> to respond to. Oddly this isn't apparent in the example provided, which goes
> to prove that just because code appears to work doesn't mean it really does.
>
> Thank goodness we put that disclaimer at the front ;)
>
>
>        puts "=========="
>>       client.disconnect
>>       sleep 3
>> end
>>
>>
>> THE SERVER:
>> cat gs2.rb
>> #!/usr/local/ruby-1.8.6/bin/ruby -W0
>> require 'gserver'
>> class TestServer < GServer
>> def serve( io )
>>       begin
>>               io.puts ">> WELCOME <<"
>>               loop do
>>               begin
>>                     telnet_input = io.gets
>>                     puts "The input: #{telnet_input}"
>>                     break if telnet_input =~ /\Aquit\b/
>>                     cmd = `cat /etc/hosts`
>>
>>                     io.puts cmd
>>
>>                     if telnet_input.chomp.include? "shutdown"
>>                        self.stop
>>                     end
>>                     io.puts eval(telnet_input)
>>               rescue Exception
>>                     io.puts "Oops - " + $!
>>           end
>>               log "Rec'd " + telnet_input
>>          end
>>        io.puts ">> GOODBYE <<"
>>        io.close
>>       rescue Exception
>>           puts "OOPS - " + $!
>>           raise
>>         end
>>       end
>> end
>> ts = TestServer.new 12341955
>> ts.start
>> ts.audit = true
>> ts.join
>>
>
> You'll want to do something to restrict the eval, otherwise you have a
> potential security black hole, and you don't need the io.close call as that
> should be taken care of automatically when the serve method returns.
>
>  THE GLUE THAT KEEPS EVERYTHING TOGETHER, I THINK. Although I don't
>> understand it well.
>>
>
> It's basically just an OO wrapper to make writing a TCP client slightly
> less tedious. The example provided in the presentation is pretty lousy due
> to the time constraints of that medium (we always end up packing in too much
> content for a 45 minute session) and a more elegant implementation would
> mirror the block version of IO.open, removing the need to explicitly connect
> and disconnect.
>
>  cat tcpc.rb
>> #!/usr/local/ruby-1.8.6/bin/ruby -W0
>> require 'socket'
>>
>> EndPoint = Struct.new(:host, :port)
>>
>> class TCPClient
>>       attr_reader :remote, :status
>>
>>       def connect remote_host, remote_port
>>               raise if @socket
>>               puts "starting client"
>>               @remote = EndPoint.new(remote_host, remote_port)
>>               @socket = TCPSocket.new(@remote.host, @remote.port)
>>       end
>>
>>       def send message
>>               @socket.puts(message)
>>               on_response
>>       end
>>
>>       def on_response; end
>>
>
> The two methods above define a callback mechanism so that an object can
> override on_response and this will automatically be called when a message is
> sent. Most times this would probably be done by subclassing.
>
>        def receive
>>               raise unless @socket
>>               begin
>>                       response = @socket.gets
>>               end until response
>>               response
>>       end
>>
>
> And the begin...end clause here is unnecessary thanks to gets being a
> blocking call, so:
>
>        def receive
>                raise unless @socket
>                @socket.gets
>        end
>
>        def disconnect
>>               @socket.close
>>               @socket = nil
>>       end
>> end
>>
>
> Anyway, I'll update the presentation to fix the bug and upload a new copy
> so that no one else wastes time over it.
>
>
>
> Ellie
>
> Eleanor McHugh
> Games With Brains
> http://slides.games-with-brains.net
> ----
> raise ArgumentError unless @reality.responds_to? :reason
>
>
>
>
Eleanor,

Thank you for taking the time to explain this to me. I truly appreciate it.
I'll play with the updated version and see how to use it on my own code.

Thanks a bunch!

Victor

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