return 0, b.err
	}
	n := b.Available()
	if n < utf8.UTFMax {
		if b.Flush(); b.err != nil {
			return 0, b.err
		}
		n = b.Available()
		if n < utf8.UTFMax {
			// Can only happen if buffer is silly small.
			return b.WriteString(string(r))
		}
	}
	size = utf8.EncodeRune(b.buf[b.n:], r)
	b.n += size
	return size, nil
}

// WriteString writes a string.