class Net::InternetMessageIO

def buffer_filling(buf, src)
  case src
  when String    # for speeding up.
    0.step(src.size - 1, 1024) do |i|
      buf << src[i, 1024]
      yield
    end
  when File    # for speeding up.
    while s = src.read(1024)
      buf << s
      yield
    end
  else    # generic reader
    src.each do |str|
      buf << str
      yield if buf.size > 1024
    end
    yield unless buf.empty?
  end
end

def dot_stuff(s)
  s.sub(/\A\./, '..')
end

def each_crlf_line(src)
  buffer_filling(@wbuf, src) do
    while line = @wbuf.slice!(/\A[^\r\n]*(?:\n|\r(?:\n|(?!\z)))/)
      yield line.chomp("\n") + "\r\n"
    end
  end
end

def each_list_item
  while (str = readuntil("\r\n")) != ".\r\n"
    yield str.chop
  end
end

def each_message_chunk
  LOG 'reading message...'
  LOG_off()
  read_bytes = 0
  while (line = readuntil("\r\n")) != ".\r\n"
    read_bytes += line.size
    yield line.delete_prefix('.')
  end
  LOG_on()
  LOG "read message (#{read_bytes} bytes)"
end

def initialize(*, **)
  super
  @wbuf = nil
end

def using_each_crlf_line
  @wbuf = ''.b
  yield
  if not @wbuf.empty?   # unterminated last line
    write0 dot_stuff(@wbuf.chomp) + "\r\n"
  elsif @written_bytes == 0   # empty src
    write0 "\r\n"
  end
  write0 ".\r\n"
  @wbuf = nil
end

def write_message(src)
  LOG "writing message from #{src.class}"
  LOG_off()
  len = writing {
    using_each_crlf_line {
      write_message_0 src
    }
  }
  LOG_on()
  LOG "wrote #{len} bytes"
  len
end

def write_message_0(src)
  prev = @written_bytes
  each_crlf_line(src) do |line|
    write0 dot_stuff(line)
  end
  @written_bytes - prev
end

def write_message_by_block(&block)
  LOG 'writing message from block'
  LOG_off()
  len = writing {
    using_each_crlf_line {
      begin
        block.call(WriteAdapter.new(self.method(:write_message_0)))
      rescue LocalJumpError
        # allow `break' from writer block
      end
    }
  }
  LOG_on()
  LOG "wrote #{len} bytes"
  len
end