code: func MustRead(in []byte) {
  	n, err := Read(in)
  	if err != nil {
  		panic(err)
  	}
  	if n != len(in) {
  		panic("did not read enough random data: only " + strconv.Itoa(n) + " bytes")
  	}
  }
docs: // MustRead fills in entirely with random data, or panics.