Simpliest mock SMTP server

mockmail.rb

require 'socket'
require 'nkf'

DEBUG = false
#KANJI = nil
KANJI = '-s'

def data(sock)
  s = ""

  sock.print "354 End data with <CR><LF>.<CR><LF>\r\n"
  while(line = sock.gets)
    puts line if DEBUG
    break if line =~ /^\.\r?\n?$/
    s += line
  end
  s
end

def parse_message(s)
  (header, body) = s.gsub(/\r\n/,"\n").split(/\n\n/,2)
  headers = {}
  header.gsub(/\n[\s\t]+/, ' ').split(/\n/).each { |line|
    (k,v) = line.split(/: +/,2)
    headers[k] = v
  }
  [headers, body]
end

def write(io, from, to, headers, body)
  io.puts "envelope-from: #{from}"
  io.puts "envelope-to: #{to.join '; '}"
  io.puts "---"
  headers.each { |k,v| io.puts "#{k}: #{v}" }
  io.puts "\n\n"
  io.puts body
  io.puts "==="
end

def session(sock)
  sock.print "220 localhost SMTP mockmail\r\n"
  from = nil
  to = []
  body = nil
  while(line = sock.gets)
    line.chomp!
    puts line if DEBUG
    sock.print case line
      when /HELO/: "250 localhost\r\n"
      when /RSET/: "250 Ok\r\n"
      when /VRFY/:
        /VRFY [^\s]/ =~ line
        "252 #{$1}\r\n"
      when /MAIL FROM/:
        /MAIL FROM:\s*\<?([^\s<>]+)\>?/ =~ line
        from = $1
        puts from if DEBUG
        "250 Ok\r\n"
      when /RCPT TO/:
        /RCPT TO:\s*\<?([^\s\r\n\t\f<>]+)\>?/ =~ line
        to << $1
        puts to if DEBUG
        "250 Ok\r\n"
      when /DATA/:
        message = data(sock)
        "250 Ok\r\n"
      when /QUIT/:
        sock.print "221 Bye\r\n"
        break
      else "500 Err\r\n"
    end
  end
  (headers, body) = parse_message(message)
  if KANJI
    headers.each { |k,v| headers[k] = NKF.nkf(KANJI,v) }
  end
  if headers['Content-Transfer-Encoding'] == 'base64'
    body = body.unpack('m')[0]
    body = NKF.nkf(KANJI,body) if KANJI
  end
  write(STDOUT, from, to, headers, body)
  open("mockmail.txt", "a") { |f|
    write(f, from, to, headers, body)
  }
  sock.close
end

def main
  begin
    server = TCPServer.new('localhost',25)
    Thread.start {
      loop { sleep 1 }
    }
    loop do 
      Thread.start(server.accept) { |sock|
        begin
          session(sock)
        rescue Exception => e
          p e
        end
      }
    end
  rescue Interrupt => i
    puts "ending..."
  end
end

main