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136 lines
4.2 KiB
Python
136 lines
4.2 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, username, and password,
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then returns CONNACK with return code 5 (not authorized). Logs all
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interactions as JSON.
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"""
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import asyncio
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import os
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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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# CONNACK: packet type 0x20, remaining length 2, session_present=0, return_code=5
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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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"""Extract client_id, username, password from MQTT CONNECT payload."""
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pos = 0
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# Protocol name
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proto_name, pos = _read_utf8(payload, pos)
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# Protocol level (1 byte)
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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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# Connect flags (1 byte)
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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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# Keep alive (2 bytes)
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pos += 2
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# Client ID
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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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# Will flag
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if flags & 0x04:
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_, pos = _read_utf8(payload, pos) # will topic
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_, pos = _read_utf8(payload, pos) # will message
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# Username flag
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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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# Password flag
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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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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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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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self._process()
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def _process(self):
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while len(self._buf) >= 2:
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pkt_type = (self._buf[0] >> 4) & 0x0f
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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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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", src=self._peer[0], **info)
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self._transport.write(_CONNACK_NOT_AUTH)
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self._transport.close()
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elif pkt_type == 12: # PINGREQ
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self._transport.write(b"\xd0\x00") # PINGRESP
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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", 1883)
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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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