o ¹i³ã@s&ddlZddlmZGdd„dƒZdS)éN)Úcached_propertyc@sŒeZdZdZdZdZdd„Zdd„Zedd „ƒZ e d d „ƒZ ed d „ƒZ e dd„ƒZ e dd„ƒZe dd„ƒZe dd„ƒZdd„Zdd„ZdS)ÚFQDNaË From https://tools.ietf.org/html/rfc1035#page-9, RFC 1035 3.1. Name space definitions: Domain names in messages are expressed in terms of a sequence of labels. Each label is represented as a one octet length field followed by that number of octets. Since every domain name ends with the null label of the root, a domain name is terminated by a length byte of zero. The high order two bits of every length octet must be zero, and the remaining six bits of the length field limit the label to 63 octets or less. To simplify implementations, the total length of a domain name (i.e., label octets and label length octets) is restricted to 255 octets or less. Therefore the max length of a domain name is actually 253 ASCII bytes without the trailing null byte or the leading length byte, and the max length of a label is 63 bytes without the leading length byte. z@^((?![-])[-A-Z\d]{1,63}(?s