# Read the content of a *fixext* of `len` bytes
	#
	# ~~~
	# var reader = new BytesReader(b"\xC7\x03\x0A\x0B\x0C\x0D")
	# var ext = reader.read_msgpack
	# assert ext isa MsgPackExt
	# assert ext.typ == 0x0a
	# assert ext.data == b"\x0B\x0C\x0D"
	# ~~~
	private fun read_msgpack_fixext_data(len: Int): MsgPackExt
	do
		var exttyp = read_byte
		if exttyp < 0 then exttyp = 0
		var data = read_bytes(len)
		return new MsgPackExt(exttyp, data)
	end