def send_io(io)
      # We read a message before actually calling #send_io
      # in order to prevent the other side from accidentally
      # read()ing past the normal data and reading our file
      # descriptor too.
      #
      # For example suppose that side A looks like this:
      #
      #   read(fd, buf, 1024)
      #   read_io(fd)
      #
      # and side B:
      #
      #   write(fd, buf, 100)
      #   send_io(fd_to_pass)
      #
      # If B completes both write() and send_io(), then A's read() call
      # reads past the 100 bytes that B sent. On some platforms, like
      # Linux, this will cause read_io() to fail. And it just so happens
      # that Ruby's IO#read method slurps more than just the given amount
      # of bytes.
      result = read
      if !result
        raise EOFError, "End of stream"
      elsif result != ["pass IO"]
        raise IOError, "IO passing pre-negotiation header expected"
      else
        @io.send_io(io)
        # Once you've sent the IO you expect to be able to close it on the
        # sender's side, even if the other side hasn't read the IO yet.
        # Not so: on some operating systems (I'm looking at you OS X) this
        # can cause the receiving side to receive a bad file descriptor.
        # The post negotiation protocol ensures that we block until the
        # other side has really received the IO.
        result = read
        if !result
          raise EOFError, "End of stream"
        elsif result != ["got IO"]
          raise IOError, "IO passing post-negotiation header expected"
        end
      end
    end
def send_io(io)
      # We read a message before actually calling #send_io
      # in order to prevent the other side from accidentally
      # read()ing past the normal data and reading our file
      # descriptor too.
      #
      # For example suppose that side A looks like this:
      #
      #   read(fd, buf, 1024)
      #   read_io(fd)
      #
      # and side B:
      #
      #   write(fd, buf, 100)
      #   send_io(fd_to_pass)
      #
      # If B completes both write() and send_io(), then A's read() call
      # reads past the 100 bytes that B sent. On some platforms, like
      # Linux, this will cause read_io() to fail. And it just so happens
      # that Ruby's IO#read method slurps more than just the given amount
      # of bytes.
      result = read
      if !result
        raise EOFError, "End of stream"
      elsif result != ["pass IO"]
        raise IOError, "IO passing pre-negotiation header expected"
      else
        @io.send_io(io)
        # Once you've sent the IO you expect to be able to close it on the
        # sender's side, even if the other side hasn't read the IO yet.
        # Not so: on some operating systems (I'm looking at you OS X) this
        # can cause the receiving side to receive a bad file descriptor.
        # The post negotiation protocol ensures that we block until the
        # other side has really received the IO.
        result = read
        if !result
          raise EOFError, "End of stream"
        elsif result != ["got IO"]
          raise IOError, "IO passing post-negotiation header expected"
        end
      end
    end
Send an IO object (a file descriptor) over the channel. The other
 side must receive the IO object by calling recv_io(). Note that
 this only works on Unix sockets.

 Might raise SystemCallError, IOError or SocketError when something
 goes wrong.