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275 lines
9.3 KiB
Python
275 lines
9.3 KiB
Python
#!/usr/bin/env python3
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"""
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MQTT server (port 1883).
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Parses MQTT CONNECT packets, extracts client_id, etc.
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Responds with CONNACK.
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Supports dynamic topics and retained publishes.
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Logs PUBLISH commands sent by clients.
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"""
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import asyncio
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import json
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import os
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import random
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import struct
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from decnet_logging import syslog_line, write_syslog_file, forward_syslog
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NODE_NAME = os.environ.get("NODE_NAME", "mqtt-broker")
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SERVICE_NAME = "mqtt"
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LOG_TARGET = os.environ.get("LOG_TARGET", "")
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PORT = int(os.environ.get("PORT", "1883"))
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MQTT_ACCEPT_ALL = os.environ.get("MQTT_ACCEPT_ALL", "1") == "1"
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MQTT_PERSONA = os.environ.get("MQTT_PERSONA", "water_plant")
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MQTT_CUSTOM_TOPICS = os.environ.get("MQTT_CUSTOM_TOPICS", "")
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_CONNACK_ACCEPTED = b"\x20\x02\x00\x00"
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_CONNACK_NOT_AUTH = b"\x20\x02\x00\x05"
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def _log(event_type: str, severity: int = 6, **kwargs) -> None:
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line = syslog_line(SERVICE_NAME, NODE_NAME, event_type, severity, **kwargs)
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print(line, flush=True)
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write_syslog_file(line)
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forward_syslog(line, LOG_TARGET)
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def _read_utf8(data: bytes, pos: int):
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"""Read MQTT UTF-8 string (2-byte length prefix). Returns (string, next_pos)."""
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if pos + 2 > len(data):
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return "", pos
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length = struct.unpack(">H", data[pos:pos + 2])[0]
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pos += 2
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return data[pos:pos + length].decode(errors="replace"), pos + length
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def _parse_connect(payload: bytes):
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pos = 0
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proto_name, pos = _read_utf8(payload, pos)
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if pos >= len(payload):
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return {}, pos
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_proto_level = payload[pos]
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pos += 1
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if pos >= len(payload):
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return {}, pos
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flags = payload[pos]
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pos += 1
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pos += 2 # Keep alive
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client_id, pos = _read_utf8(payload, pos)
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result = {"client_id": client_id, "proto": proto_name}
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if flags & 0x04:
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_, pos = _read_utf8(payload, pos)
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_, pos = _read_utf8(payload, pos)
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if flags & 0x80:
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username, pos = _read_utf8(payload, pos)
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result["username"] = username
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if flags & 0x40:
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password, pos = _read_utf8(payload, pos)
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result["password"] = password
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return result
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def _parse_subscribe(payload: bytes):
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"""Returns (packet_id, [(topic, qos), ...])"""
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if len(payload) < 2:
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return 0, []
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pos = 0
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packet_id = struct.unpack(">H", payload[pos:pos+2])[0]
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pos += 2
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topics = []
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while pos < len(payload):
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topic, pos = _read_utf8(payload, pos)
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if pos >= len(payload):
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break
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qos = payload[pos] & 0x03
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pos += 1
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topics.append((topic, qos))
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return packet_id, topics
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def _suback(packet_id: int, granted_qos: list[int]) -> bytes:
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payload = struct.pack(">H", packet_id) + bytes(granted_qos)
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return bytes([0x90, len(payload)]) + payload
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def _publish(topic: str, value: str, retain: bool = True) -> bytes:
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topic_bytes = topic.encode()
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topic_len = struct.pack(">H", len(topic_bytes))
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payload = str(value).encode()
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fixed = 0x31 if retain else 0x30
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remaining = len(topic_len) + len(topic_bytes) + len(payload)
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# variable length encoding
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rem_bytes = []
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while remaining > 0:
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encoded = remaining % 128
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remaining = remaining // 128
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if remaining > 0:
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encoded = encoded | 128
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rem_bytes.append(encoded)
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if not rem_bytes:
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rem_bytes = [0]
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return bytes([fixed]) + bytes(rem_bytes) + topic_len + topic_bytes + payload
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def _parse_publish(payload: bytes, qos: int):
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pos = 0
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topic, pos = _read_utf8(payload, pos)
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packet_id = 0
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if qos > 0:
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if pos + 2 <= len(payload):
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packet_id = struct.unpack(">H", payload[pos:pos+2])[0]
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pos += 2
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data = payload[pos:]
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return topic, packet_id, data
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def _generate_topics() -> dict:
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topics: dict = {}
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if MQTT_CUSTOM_TOPICS:
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try:
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topics = json.loads(MQTT_CUSTOM_TOPICS)
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return topics
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except Exception as e:
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_log("config_error", severity=4, error=str(e))
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if MQTT_PERSONA == "water_plant":
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topics.update({
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"plant/water/tank1/level": f"{random.uniform(60.0, 80.0):.1f}",
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"plant/water/tank1/pressure": f"{random.uniform(2.5, 3.0):.2f}",
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"plant/water/pump1/status": "RUNNING",
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"plant/water/pump1/rpm": f"{int(random.uniform(1400, 1450))}",
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"plant/water/pump2/status": "STANDBY",
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"plant/water/chlorine/dosing": f"{random.uniform(1.1, 1.3):.1f}",
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"plant/water/chlorine/residual": f"{random.uniform(0.7, 0.9):.1f}",
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"plant/water/valve/inlet/state": "OPEN",
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"plant/water/valve/drain/state": "CLOSED",
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"plant/alarm/high_pressure": "0",
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"plant/alarm/low_chlorine": "0",
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"plant/alarm/pump_fault": "0",
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"plant/$SYS/broker/version": "Mosquitto 2.0.15",
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"plant/$SYS/broker/uptime": "2847392",
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})
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elif not topics:
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topics = {
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"device/status": "online",
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"device/uptime": "3600"
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}
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return topics
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class MQTTProtocol(asyncio.Protocol):
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def __init__(self):
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self._transport = None
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self._peer = None
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self._buf = b""
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self._auth = False
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self._topics = _generate_topics()
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def connection_made(self, transport):
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self._transport = transport
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self._peer = transport.get_extra_info("peername", ("?", 0))
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_log("connect", src=self._peer[0], src_port=self._peer[1])
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def data_received(self, data):
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self._buf += data
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try:
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self._process()
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except Exception as e:
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_log("protocol_error", severity=4, error=str(e))
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if self._transport:
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self._transport.close()
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def _process(self):
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while len(self._buf) >= 2:
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pkt_byte = self._buf[0]
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pkt_type = (pkt_byte >> 4) & 0x0f
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flags = pkt_byte & 0x0f
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qos = (flags >> 1) & 0x03
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# Decode remaining length (variable-length encoding)
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pos = 1
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remaining = 0
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multiplier = 1
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while pos < len(self._buf):
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if pos > 4: # MQTT spec: max 4 bytes for remaining length
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self._transport.close()
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self._buf = b""
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return
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byte = self._buf[pos]
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remaining += (byte & 0x7f) * multiplier
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multiplier *= 128
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pos += 1
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if not (byte & 0x80):
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break
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else:
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return # incomplete length
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if len(self._buf) < pos + remaining:
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return # incomplete payload
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payload = self._buf[pos:pos + remaining]
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self._buf = self._buf[pos + remaining:]
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if pkt_type == 1: # CONNECT
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info = _parse_connect(payload)
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_log("auth", **info)
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if MQTT_ACCEPT_ALL:
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self._auth = True
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self._transport.write(_CONNACK_ACCEPTED)
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else:
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self._transport.write(_CONNACK_NOT_AUTH)
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self._transport.close()
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elif pkt_type == 8: # SUBSCRIBE
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if not self._auth:
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self._transport.close()
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continue
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packet_id, subs = _parse_subscribe(payload)
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granted_qos = [1] * len(subs) # grant QoS 1 for all
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self._transport.write(_suback(packet_id, granted_qos))
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# Immediately send retained publishes matching topics
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for sub_topic, _ in subs:
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_log("subscribe", src=self._peer[0], topics=[sub_topic])
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for t, v in self._topics.items():
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# simple match: if topic ends with #, it matches prefix
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if sub_topic.endswith("#"):
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prefix = sub_topic[:-1]
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if t.startswith(prefix):
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self._transport.write(_publish(t, str(v)))
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elif sub_topic == t:
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self._transport.write(_publish(t, str(v)))
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elif pkt_type == 3: # PUBLISH
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if not self._auth:
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self._transport.close()
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continue
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topic, packet_id, data = _parse_publish(payload, qos)
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# Attacker command received!
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_log("publish", src=self._peer[0], topic=topic, payload=data.decode(errors="replace"))
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if qos == 1:
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puback = bytes([0x40, 0x02]) + struct.pack(">H", packet_id)
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self._transport.write(puback)
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elif pkt_type == 12: # PINGREQ
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self._transport.write(b"\xd0\x00") # PINGRESP
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elif pkt_type == 14: # DISCONNECT
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self._transport.close()
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else:
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_log("packet", src=self._peer[0], pkt_type=pkt_type)
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self._transport.close()
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def connection_lost(self, exc):
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_log("disconnect", src=self._peer[0] if self._peer else "?")
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async def main():
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_log("startup", msg=f"MQTT server starting as {NODE_NAME}")
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loop = asyncio.get_running_loop()
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server = await loop.create_server(MQTTProtocol, "0.0.0.0", PORT) # nosec B104
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async with server:
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await server.serve_forever()
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if __name__ == "__main__":
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asyncio.run(main())
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