# Read the length as a 64 bits integer, then the content of the block
	#
	# To be used with `Writer::write_block`.
	#
	# Returns a truncated string when an error is pending (`last_error != null`).
	fun read_block: String
	do
		var length = read_int64
		if length == 0 then return ""
		return read_bytes(length).to_s
	end