libbacnet

A sans-IO BACnet/IP client library written in Rust with a Python asyncio interface.

Overview

libbacnet implements the BACnet/IP client protocol as a pure state machine (the sans-IO pattern). All protocol logic lives in a Rust Stack type that:

• receives inputs (Received, Tick, Send),
• returns outputs (Transmit, Event, Deadline),
• never touches a socket, spawns a thread, or reads a clock.

A thin Python asyncio layer (BacnetProtocol / BacnetClient) wires the stack to UDP I/O, drives the retry scheduler, and exposes async def methods for each supported service.

Supported services

Service	Direction
ReadProperty	confirmed request
ReadPropertyMultiple	confirmed request
WriteProperty	confirmed request
Who-Is / I-Am	unconfirmed
WhoIsRouterToNetwork / IAmRouterToNetwork	unconfirmed (NPDU)

Segmented responses (ComplexACK with more-follows) are transparently reassembled; large segmented requests are automatically fragmented.

Non-goals (v0.1)

• MS/TP or other physical layers (BACnet/IP only)
• Server / device role
• COV subscriptions, alarms, trend logs
• BBMD / foreign device registration
• IPv6

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Quick start

import asyncio
from libbacnet import BacnetClient, BacnetAddr, ObjectIdentifier, PropertyIdentifier

async def main():
    async with BacnetClient(local_addr=("0.0.0.0", 47808)) as client:
        # Discover devices (3-second collection window)
        devices = await client.who_is(wait=3.0)
        print(f"Found {len(devices)} device(s)")

        for ev in devices:
            addr = BacnetAddr(ev.src.addr, ev.src.port)
            obj = ObjectIdentifier(object_type=8, instance=ev.message.device_id.instance)

            # Read the device object's description — returns a ReadPropertyResult
            result = await client.read_property(
                addr=addr,
                obj_id=obj,
                prop_id=PropertyIdentifier.DESCRIPTION,
            )
            print(f"  {addr} description: {result.value}")

asyncio.run(main())

See examples/discover_read_write.py for a longer example that performs Who-Is discovery, reads the object list, reads and writes present-value on each object, and then reads all values with read_property_multiple.

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Limitations and known constraints

• BACnet/IP only — MS/TP and other data links are not supported.
• Client role only — incoming confirmed requests from other devices are silently ignored.
• IPv4 only — BacnetAddr stores an IPv4 address; IPv6 BVLC is not implemented.
• No BBMD — the library sends Original-Unicast-NPDU (0x0A) and Original-Broadcast-NPDU (0x0B) only. Foreign device registration and broadcast distribution are out of scope.
• Single-threaded — Stack is not Send + Sync; use it from a single asyncio event loop thread.