code: func expire(addrs []DatabaseAddress, now int64) []DatabaseAddress {
  	i := 0
  	for i < len(addrs) {
  		if addrs[i].Expires < now {
  			// This item is expired. Replace it with the last in the list
  			// (noop if we are at the last item).
  			addrs[i] = addrs[len(addrs)-1]
  			// Wipe the last item of the list to release references to
  			// strings and stuff.
  			addrs[len(addrs)-1] = DatabaseAddress{}
  			// Shorten the slice.
  			addrs = addrs[:len(addrs)-1]
  			continue
  		}
  		i++
  	}
  	return addrs
  }
docs: // expire returns the list of addresses after removing expired entries.
  // Expiration happen in place, so the slice given as the parameter is
  // destroyed. Internal order is not preserved.