class PhusionPassenger::MessageChannel

def recv_io(klass = IO, negotiate = true)

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

this only works on Unix sockets.
side must have sent an IO object by calling send_io(). Note that
Receive an IO object (a file descriptor) from the channel. The other 
def recv_io(klass = IO, negotiate = true)
  write("pass IO") if negotiate
  io = @io.recv_io(klass)
  write("got IO") if negotiate
  return io
end