From: Garthy D <garthy_lmkltybr@...>
Date: 2013-03-16T09:57:25+09:00
Subject: Re: IO buffering problem

Hi Andrew,

On 16/03/13 09:04, Andrew Wagner wrote:
> All,
> I'm writing a chess program that has a simple text-based interface. It's
> designed to be run by another program, which has a nice UI. Here's the
> program as it stands now, whittled to the simplest possible use case:
>
> i = 0
> moves = ["a7a6","a6a5","a5a4","a4a3"]
> $stdin.each do |command|
>    if command.start_with?("protover")
>      $stdout.puts "feature ping=0 setboard=1 ics=1 usermove=1"
>    elsif command.start_with?("usermove")
>      $stdout.puts "move #{moves[i]}"
>      i+=1
>    end
>    $stdout.flush
> end
>
> The "protover" thing is needed to tell the UI program how to initialize
> the protocol, and then every time a move is made, the UI program sends
> "usermove <some move>" to my program, which responds with "move <my move>".
>
> If I run this by itself, I can happily enter a few 'usermove' commands
> manually, and get any number of canned moves back. However, when I run
> this under the UI, I get an Interrupt:
>
> bin/winboard.rb:3:in `each': Interrupt
> from bin/winboard.rb:3:in `<main>'
>
> I know that the UI program is pretty reliable, so I'm missing something
> in the way that I'm handling IO buffering or something. If you want the
> nitty gritty details, you can see them at
> http://www.gnu.org/software/xboard/engine-intf.html . I'm running on
> MacOSX. Any suggestions?

Is it possible that you aren't processing one of the commands from the 
program, and the program is terminating your script, perhaps after a 
timeout or incorrect response? I'm wondering what would show up if you 
added this:

else
   $stderr.print "Unknown command: '#{command}'\n"

just before the second-last line. Are you handling every incoming 
command as it expects?

Incidentally, you could always turn those if statements into case/when, 
something like:

case command
when /^protover/
...
when /^usermove/
...
else
   $stderr.print "Unknown command: '#{command}'\n"
end

This might make it easier if there are a lot of commands you need to 
respond to.

Cheers,
Garth