From: Alexy Khrabrov <deliverable@...>
Date: 2007-11-09T20:45:08+09:00
Subject: background process readling lines and responding

Greetings -- I'm debugging a way to call a command-line executable as a
server.  In normal life it behaves like grep, reading lines from stdin
and printing responses to stdout.  So I'm debugging the Ruby wrapper on
grep, as the original takes a long time to load (thus the whole
exercise).  Here's what I got -- but it swallows the first line of input
and doesn't respond!  Why?

#!/usr/bin/env ruby

require 'optparse'
require 'ostruct'

class Server

  def initialize(cmd_line)
    puts "starting server with the following command line:"
    puts cmd_line
    @pipe = IO.popen cmd_line, "r+"
  end


  def process(sent)
    return nil if sent.nil? or sent =~ /^\s+$/

    puts "sending: [#{sent}]"
    @pipe.write(sent)

    @pipe.readlines
  end
end # class

def main
  o = OpenStruct.new
  files = OptionParser.new do |opt|
    opt.on("-e", "--exe EXE", "server executable basename") { |val|
o.exe = val }
  end.parse(*ARGV)

  ps = Server.new(o.exe)

  STDIN.each_line do |line|
    out = ps.process(line)
    puts out
  end
end

main if $0 == __FILE__

-- Here's what happens when I try to use it:

$ aha-grep-server.rb -e "grep abra"
starting server with the following command line:
grep abra
abracadabra
sending: [abracadabra
]

-- then it just hangs there, @pipe.readlines returning nothing.  What's
the right IO semantics here?

Cheers,
Alexy
-- 
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