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"""A pure python implementation of multicast DNS service discovery.

Licensed under LGPL-2.1-or-later; see COPYING for details. This file is

part of a continuously modified work; modification dates are recorded

in the project's git history.

"""

from __future__ import annotations

import re

import socket

_BROWSER_TIME = 10000 # ms

_CHECK_TIME = 500 # ms

_LISTENER_TIME = 200 # ms

_REGISTER_TIME = 225 # ms

_UNREGISTER_TIME = 125 # ms

_DUPLICATE_PACKET_SUPPRESSION_INTERVAL = 1000 # ms

# Per-listener bounded recency window. 16 is large enough to defeat

# the alternating-payload bypass (RFC 6762 §6.2, issue #1724 — even a

# rotation of a dozen distinct payloads still dedups), and small

# enough that the dict bookkeeping per miss stays cheap under a

# hostile flood.

_RECENT_PACKETS_MAX = 16

_DUPLICATE_QUESTION_INTERVAL = 999 # ms # Must be 1ms less than _DUPLICATE_PACKET_SUPPRESSION_INTERVAL

_CACHE_CLEANUP_INTERVAL = 10 # s

_LOADED_SYSTEM_TIMEOUT = 10 # s

_STARTUP_TIMEOUT = 9 # s must be lower than _LOADED_SYSTEM_TIMEOUT

_ONE_SECOND = 1000 # ms

# If the system is loaded or the event

# loop was blocked by another task that was doing I/O in the loop

# (shouldn't happen but it does in practice) we need to give

# a buffer timeout to ensure a coroutine can finish before

# the future times out

_MDNS_ADDR = "224.0.0.251"

_MDNS_ADDR6 = "ff02::fb"

_MDNS_PORT = 5353

_DNS_PORT = 53

_DNS_HOST_TTL = 120 # two minute for host records (A, SRV etc) as-per RFC6762

_DNS_OTHER_TTL = 4500 # 75 minutes for non-host records (PTR, TXT etc) as-per RFC6762

# Currently we enforce a minimum TTL for PTR records to avoid

# ServiceBrowsers generating excessive queries refresh queries.

# Apple uses a 15s minimum TTL, however we do not have the same

# level of rate limit and safe guards so we use 1/4 of the recommended value

_DNS_PTR_MIN_TTL = 1125

# Upper bound on the number of records the DNSCache will hold before it

# starts evicting the closest-to-expiration entry to make room for new

# arrivals. Bounds the memory a malicious LAN peer can force the cache

# to retain by multicasting many unique-name records.

_MAX_CACHE_RECORDS = 10000

# Upper bound on the number of entries QuestionHistory will hold between

# the periodic 10s cache-cleanup ticks. Bounds the memory a malicious LAN

# peer can force the duplicate-question-suppression history to retain by

# flooding distinct questions (RFC 6762 §7.3, defense-in-depth).

_MAX_QUESTION_HISTORY_ENTRIES = 10000

# Per-entry cap on the number of known-answer records QuestionHistory

# will retain. Each TC-deferred reassembly can carry up to ~12k records

# (~750 records/packet x _MAX_DEFERRED_PER_ADDR fragments), and the

# resulting set is stored by reference under each non-unicast question

# in the history dict; without a per-entry cap a LAN attacker can pin

# hundreds of MB across the _MAX_QUESTION_HISTORY_ENTRIES dimension.

# 256 is well above any RFC-realistic known-answer list for a single

# question; oversized payloads are dropped from the history (no

# suppression for that one query) rather than truncated, since a

# truncated stored set would over-suppress legitimate follow-up

# queries (`suppresses()` returns True when stored set is a subset of

# the incoming known-answers, so a smaller stored set matches more

# easily).

_MAX_KNOWN_ANSWERS_PER_HISTORY_ENTRY = 256

# Per-addr cap on the number of truncated (TC-bit) packets retained for

# RFC 6762 §18.5 reassembly. The spec anticipates only a handful of

# segments per truncated query; 16 is well above legitimate need and

# keeps the per-arrival dedup scan a constant-time cost under a flood.

_MAX_DEFERRED_PER_ADDR = 16

# Per-listener cap on the number of distinct addrs with in-flight

# TC-deferral state. Each entry can hold up to _MAX_DEFERRED_PER_ADDR

# packets of up to _MAX_MSG_ABSOLUTE bytes; 512 leaves headroom for a

# legitimate burst (LAN-wide power-resume / boot storm where many

# devices announce at once) while bounding worst-case memory at

# ~72 MB even when a peer floods with spoofed source IPs.

_MAX_DEFERRED_ADDRS = 512

_DNS_PACKET_HEADER_LEN = 12

_MAX_MSG_ABSOLUTE = 8966

_MAX_MSG_TYPICAL = 1460

# DNS header flag bits, RFC 1035 section 4.1.1 and RFC 6762 section 18

_FLAGS_AA = 0x0400

_FLAGS_AD = 0x0020

_FLAGS_CD = 0x0010

_FLAGS_QR_MASK = 0x8000

_FLAGS_QR_QUERY = 0x0000

_FLAGS_QR_RESPONSE = 0x8000

_FLAGS_RA = 0x0080

_FLAGS_RD = 0x0100

_FLAGS_TC = 0x0200

_FLAGS_Z = 0x0040

_CLASS_IN = 1

_CLASS_CS = 2

_CLASS_CH = 3

_CLASS_HS = 4

_CLASS_NONE = 254

_CLASS_ANY = 255

_CLASS_MASK = 0x7FFF

_CLASS_UNIQUE = 0x8000

_CLASS_IN_UNIQUE = _CLASS_IN | _CLASS_UNIQUE

_TYPE_A = 1

_TYPE_NS = 2

_TYPE_MD = 3

_TYPE_MF = 4

_TYPE_CNAME = 5

_TYPE_SOA = 6

_TYPE_MB = 7

_TYPE_MG = 8

_TYPE_MR = 9

_TYPE_NULL = 10

_TYPE_WKS = 11

_TYPE_PTR = 12

_TYPE_HINFO = 13

_TYPE_MINFO = 14

_TYPE_MX = 15

_TYPE_TXT = 16

_TYPE_AAAA = 28

_TYPE_SRV = 33

_TYPE_NSEC = 47

_TYPE_ANY = 255

# Wire values mapped to short human readable names, used only for reprs

# and debug logging; _type_label and _class_label in _dns.py supply the

# unknown-value fallback. Sorted by mnemonic.

_CLASSES = {

_CLASS_ANY: "any",

_CLASS_CH: "ch",

_CLASS_CS: "cs",

_CLASS_HS: "hs",

_CLASS_IN: "in",

_CLASS_NONE: "none",

}

_TYPES = {

_TYPE_A: "a",

_TYPE_AAAA: "aaaa",

_TYPE_ANY: "any",

_TYPE_CNAME: "cname",

_TYPE_HINFO: "hinfo",

_TYPE_MB: "mb",

_TYPE_MD: "md",

_TYPE_MF: "mf",

_TYPE_MG: "mg",

_TYPE_MINFO: "minfo",

_TYPE_MR: "mr",

_TYPE_MX: "mx",

_TYPE_NS: "ns",

_TYPE_NSEC: "nsec",

_TYPE_NULL: "null",

_TYPE_PTR: "ptr",

_TYPE_SOA: "soa",

_TYPE_SRV: "srv",

_TYPE_TXT: "txt",

_TYPE_WKS: "wks",

}

_ADDRESS_RECORD_TYPES = {_TYPE_A, _TYPE_AAAA}

_HAS_A_TO_Z = re.compile(r"[A-Za-z]")

_HAS_ONLY_A_TO_Z_NUM_HYPHEN = re.compile(r"^[A-Za-z0-9\-]+$")

_HAS_ONLY_A_TO_Z_NUM_HYPHEN_UNDERSCORE = re.compile(r"^[A-Za-z0-9\-\_]+$")

_HAS_ASCII_CONTROL_CHARS = re.compile(r"[\x00-\x1f\x7f]")

_EXPIRE_REFRESH_TIME_PERCENT = 75

_LOCAL_TRAILER = ".local."

_TCP_PROTOCOL_LOCAL_TRAILER = "._tcp.local."

_NONTCP_PROTOCOL_LOCAL_TRAILER = "._udp.local."

# https://datatracker.ietf.org/doc/html/rfc6763#section-9

_SERVICE_TYPE_ENUMERATION_NAME = "_services._dns-sd._udp.local."

_IPPROTO_IPV6 = socket.IPPROTO_IPV6

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