log.Printf("%s %x: %v", l.prefix, p[0:n], err)
	} else {
		log.Printf("%s %x", l.prefix, p[0:n])
	}
	return
}

// NewReadLogger returns a reader that behaves like r except
// that it logs (using [log.Printf]) each read to standard error,
// printing the prefix and the hexadecimal data read.
func NewReadLogger(prefix string, r io.Reader) io.Reader {
	return &readLogger{prefix, r}