104 lines
3.0 KiB
Python
Executable File
104 lines
3.0 KiB
Python
Executable File
#!/usr/bin/env python3
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"""
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Resolve hostname.local via mDNS multicast (pure Python, no dependencies).
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Usage: mdns-resolve <hostname.local> [timeout_seconds]
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Returns: IP address on stdout, or exit 1 on failure.
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"""
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import sys
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import socket
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import struct
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import select
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import time
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def build_mdns_query(hostname: str) -> bytes:
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header = struct.pack('>HHHHHH', 0, 0, 1, 0, 0, 0)
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question = b''
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for part in hostname.rstrip('.').split('.'):
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question += bytes([len(part)]) + part.encode()
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question += b'\x00'
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question += struct.pack('>HH', 1, 1) # Type A, Class IN
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return header + question
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def parse_mdns_response(data: bytes) -> str | None:
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if len(data) < 12:
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return None
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qdcount = struct.unpack('>H', data[4:6])[0]
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ancount = struct.unpack('>H', data[6:8])[0]
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if ancount == 0:
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return None
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offset = 12
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for _ in range(qdcount):
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while offset < len(data) and data[offset] != 0:
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if data[offset] & 0xc0 == 0xc0:
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offset += 2
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break
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offset += data[offset] + 1
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else:
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offset += 1
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offset += 4
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for _ in range(ancount):
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while offset < len(data):
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if data[offset] & 0xc0 == 0xc0:
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offset += 2
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break
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elif data[offset] == 0:
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offset += 1
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break
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else:
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offset += data[offset] + 1
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if offset + 10 > len(data):
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break
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rtype, rclass, ttl, rdlength = struct.unpack('>HHIH', data[offset:offset+10])
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offset += 10
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if rtype == 1 and rdlength == 4 and offset + 4 <= len(data):
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return socket.inet_ntoa(data[offset:offset+4])
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offset += rdlength
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return None
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def resolve_mdns(hostname: str, timeout: float = 2.0) -> str | None:
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if not hostname.endswith('.local'):
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hostname += '.local'
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try:
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sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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sock.setblocking(False)
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sock.sendto(build_mdns_query(hostname), ('224.0.0.251', 5353))
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end_time = time.time() + timeout
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while time.time() < end_time:
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ready, _, _ = select.select([sock], [], [], 0.1)
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if ready:
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try:
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data, _ = sock.recvfrom(4096)
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ip = parse_mdns_response(data)
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if ip:
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sock.close()
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return ip
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except Exception:
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pass
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sock.close()
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except Exception:
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pass
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return None
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def main():
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if len(sys.argv) < 2:
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print("Usage: mdns-resolve <hostname.local> [timeout]", file=sys.stderr)
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sys.exit(1)
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hostname = sys.argv[1]
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timeout = float(sys.argv[2]) if len(sys.argv) > 2 else 2.0
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ip = resolve_mdns(hostname, timeout)
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if ip:
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print(ip)
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else:
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sys.exit(1)
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if __name__ == "__main__":
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main()
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