#!/usr/bin/env python3
"""mdns-browse: one-shot multicast mDNS enumeration from this vantage.

Sends PTR queries for the DNS-SD service-enumeration name plus common
service types, listens briefly, prints every answer record. Stdlib only.
Diagnostic tool for #619 (WiFi-side multicast reachability)."""

import socket
import struct
import sys
import time

MDNS_GROUP = "224.0.0.251"
MDNS_PORT = 5353
LISTEN_SECONDS = float(sys.argv[1]) if len(sys.argv) > 1 else 6.0
TYPES = {
    1: "A", 28: "AAAA", 12: "PTR", 16: "TXT", 33: "SRV", 47: "NONE",
}
QUERIES = [
    "_services._dns-sd._udp.local",
    "_hap._tcp.local",
    "_airplay._tcp.local",
    "_googlecast._tcp.local",
]


def encode_name(name):
    out = b""
    for part in name.split("."):
        out += bytes([len(part)]) + part.encode("latin1")
    return out + b"\x00"


def read_name(data, off):
    parts = []
    seen = set()
    while True:
        if off in seen or len(seen) > 64:
            return ".".join(parts), off
        seen.add(off)
        length = data[off]
        if length == 0:
            off += 1
            break
        if length & 0xC0:
            ptr = struct.unpack(">H", data[off:off + 2])[0] & 0x3FFF
            parts.append(read_name(data, ptr)[0])
            off += 2
            break
        parts.append(data[off + 1:off + 1 + length].decode("latin1"))
        off += 1 + length
    return ".".join(parts), off


def build_query(names):
    packet = struct.pack(">HHHHHH", 0, 0, len(names), 0, 0, 0)
    for name in names:
        packet += encode_name(name) + struct.pack(">HH", 12, 1)
    return packet


def main():
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.bind(("", MDNS_PORT))
    mreq = socket.inet_aton(MDNS_GROUP) + socket.inet_aton("0.0.0.0")
    sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
    sock.settimeout(0.5)
    sock.sendto(build_query(QUERIES), (MDNS_GROUP, MDNS_PORT))
    deadline = time.time() + LISTEN_SECONDS
    found = set()
    while time.time() < deadline:
        try:
            data, addr = sock.recvfrom(16384)
        except socket.timeout:
            continue
        an = struct.unpack(">H", data[6:8])[0]
        off = 12
        qd = struct.unpack(">H", data[4:6])[0]
        try:
            for _ in range(qd):
                _, off = read_name(data, off)
                off += 4
            for _ in range(an):
                name, name_end = read_name(data, off)
                rtype, _rclass, ttl, rlen = struct.unpack(
                    ">HHIH", data[name_end:name_end + 10])
                detail = ""
                if rtype == 12:
                    detail = " -> " + read_name(data, name_end + 10)[0]
                found.add((TYPES.get(rtype, rtype), name, detail, addr[0]))
                off = name_end + 10 + rlen
        except (IndexError, struct.error):
            continue
    for rtype, name, detail, src in sorted(found):
        print(f"{src:15} {rtype:5} {name}{detail}")
    print(f"-- {len(found)} records from {LISTEN_SECONDS}s listen --")


if __name__ == "__main__":
    main()