func (b *Reader) Buffered() int { return b.w - b.r }

// ReadSlice reads until the first occurrence of delim in the input,
// returning a slice pointing at the bytes in the buffer.
// The bytes stop being valid at the next read.
// If ReadSlice encounters an error before finding a delimiter,
// it returns all the data in the buffer and the error itself (often io.EOF).
// ReadSlice fails with error [ErrBufferFull] if the buffer fills without a delim.

func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) {
	slice, err := b.readSlice(delim)
	// return a copy of slice. The buffer's backing array may
	// be overwritten by later calls.
	line = append(line, slice...)
	return line, err
}

// readSlice is like ReadBytes but returns a reference to internal buffer data.
func (b *Buffer) readSlice(delim byte) (line []byte, err error) {
	i := IndexByte(b.buf[b.off:], delim)

	}
	// Test error after ReadSlice.
	_, _, err = r.ReadRune() // reset state
	if err != nil {
		t.Error("unexpected error on ReadRune (4):", err)
	}
	_, err = r.ReadSlice(0)
	if err != io.EOF {
		t.Error("unexpected error on ReadSlice (4):", err)
	}
	if r.UnreadRune() == nil {
		t.Error("expected error after ReadSlice (4)")
	}
}

func TestUnreadRuneAtEOF(t *testing.T) {

// The returned bytes are owned by the bufio.Reader
// so they are only valid until the next bufio read.
func readChunkLine(b *bufio.Reader) ([]byte, []byte, error) {
	buf, err := b.ReadSlice('\n')
	if err != nil {
		// We always know when EOF is coming.
		// If the caller asked for a line, there should be a line.
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		} else if err == bufio.ErrBufferFull {