type scriptedReader []func(p []byte) (n int, err error)

func (sr *scriptedReader) Read(p []byte) (n int, err error) {
	if len(*sr) == 0 {
		panic("too many Read calls on scripted Reader. No steps remain.")
	}
	step := (*sr)[0]
	*sr = (*sr)[1:]
	return step(p)
}

func newScriptedReader(steps ...func(p []byte) (n int, err error)) io.Reader {
	sr := scriptedReader(steps)
	return &sr
}