BACnet B-SS (Smart Sensor) - Rust example

A minimal, copy-paste-friendly example showing how to implement the BACnet B-SS (Smart Sensor) device profile in Rust, using the CAS BACnet Stack through the stack's own Rust adapter. It listens on BACnet/IP (UDP 47808), answers ReadProperty, and is discoverable via Who-Is / I-Am. Its readings follow a sensor Simulation (labelled below), and it reports a broken sensor the BACnet way.

This is a faithful Rust port of the reworked BACnetProfileExample-B-SS-CPP (v1.3.0): the same Device, objects, properties, Simulation, Failure Modes, test-only hook and command-line options, proven by the same Wire Tests, which cannot tell the two apart on the wire.

TUTORIAL.md - how to extend this example and how to review it for conformance. Read it when you start turning this into your own device.
docs/PICS.md - the Protocol Implementation Conformance Statement: every object, every property, and who answers it.

Versions: this document describes example v1.1.0, built and verified against CAS BACnet Stack 6.0.23 (6.x @ 64b2cfac5, the ReleaseDll shared library built from the submodule, loaded at run time through the stack's Rust adapter compiled in place from the submodule), at Protocol_Revision 30, with the Rust common/ helper at v1.1.0 and wiretest/ at 0.7.0. Running the example prints all three versions - if what it prints disagrees with this line, trust the program and check CHANGELOG.md.

What is the B-SS (Smart Sensor) profile?

B-SS (BACnet Smart Sensor), defined in Annex L of ANSI/ASHRAE 135, is the simplest BACnet device profile - the standard describes it as "a simple sensing device with very limited resources." It is meant for inexpensive, fixed-function sensors (temperature, humidity, occupancy, a contact, ...) that mostly just need to report what they measure when asked.

A B-SS device answers ReadProperty and is discoverable. It does not have to support WriteProperty (a smart sensor is read-only), alarming / event reporting, scheduling, or trending, and this example implements none of them on purpose.

But it is still a full BACnet device. Even the simplest profile must present the standard object model - a Device object, a Network Port object (every device needs one), and its sensor objects - and each object must expose all of its required properties. The CAS BACnet Stack generates most of those automatically (Object_Identifier, Object_Type, Status_Flags, Object_List, Protocol_*, ...); this example supplies the handful that are application-specific. The result is conformant for Protocol_Revision 30. docs/PICS.md lists every property and who answers it.

The device this example creates

Device 389001  "Chipkin Example B-SS"   (Vendor 389 - Chipkin Automation Systems)
    │
    ├── Analog Input 1       "Bronze"      Present_Value  21.5 -> ramps 18.0 .. 26.0  (REAL, degrees Celsius)
    ├── Binary Input 1       "Emerald"     Present_Value  toggles every 3 s     (0 = inactive / 1 = active)
    ├── Multi-State Input 1  "Hot Pink"    Present_Value  1 -> 2 -> 3 every 4 s (state, 1..3)
    └── Network Port 1       "Vermilion"   the BACnet/IP port     (required on every device)

The scenario: a sensor a controller reads

What a B-SS is for, in one sentence, from Annex L.4.5 of ANSI/ASHRAE 135-2024: "Ability to provide values for any of its BACnet objects upon request." A controller or workstation (the Peer - any BACnet client, or the Python client in tests/) reads the sensor and gets what it is measuring now:

The Peer finds the sensor with Who-Is and reads its Object_List.
It reads Analog Input 1 Present_Value - say 22.0 - and again a few seconds later - 23.5. The reading follows the (simulated) room temperature, 0.5 C a second. Binary Input 1 and Multi-State Input 1 change too.
Failure Mode - a broken sensor. When the sensor wire breaks, Analog Input 1 Reliability reads open-loop (4) and the FAULT bit of Status_Flags is TRUE (clause 12.2.7 derives FAULT from Reliability). The reading stops changing. Repair the wire and Reliability returns to no-fault-detected, FAULT clears, and the reading moves again.
Failure Mode - a request it cannot serve. Reading an object or property the sensor does not have, or an array element past the end, gets the error clause 15.5.1.3.1 names (unknown-object, unknown-property, invalid-array-index); a WriteProperty gets a Reject unrecognized-service, because a B-SS is read-only.

The sensor Simulation

A real smart sensor samples a thermistor, a contact and a selector switch. This example has none of them, so it simulates them - non-BACnet scaffolding, outside the BACnet Surface, in section 2 of src/main.rs (sensor_simulation_tick(), called beside BACnetStack_Tick()). Once a second:

the temperature (Analog Input 1) moves 0.5 C, ramping up to 26.0 and back down to 18.0;
the contact (Binary Input 1) toggles every 3 s;
the selector (Multi-State Input 1) steps 1 -> 2 -> 3 -> 1 every 4 s.

The broken wire is a test-only hook, not a feature: if the environment variable CAS_EXAMPLE_TEST_SENSOR_FAULT_FILE names a file, the wire counts as broken for as long as that file exists. The Wire Tests create and delete it. Nothing on the network can break the sensor.

To port the example to hardware, replace sensor_simulation_tick() with your own sampling (on a timer or another thread - never block the BACnet callbacks on slow I/O), and set Reliability from your hardware's own diagnostics.

What this example supports

The example implements exactly the capabilities below - and nothing more, which is the point of a profile example.

BIBBs (BACnet Interoperability Building Blocks)

BIBB	Description	Supported
DS-RP-B	Data Sharing - ReadProperty - B	✅
DM-DDB-B	Device Management - Dynamic Device Binding - B	✅
DM-DOB-B	Device Management - Dynamic Object Binding - B	✅

Services (executed / B-side)

Service	Notes
ReadProperty	Responds to property reads (DS-RP-B).
Who-Is / I-Am	Answers Who-Is with I-Am, and broadcasts an I-Am on start-up (DM-DDB-B).
Who-Has / I-Have	Answers Who-Has with I-Have (DM-DOB-B).

Object types

Object type	Instance	Name
Device	389001	Chipkin Example B-SS
Analog Input	1	Bronze
Binary Input	1	Emerald
Multi-state Input	1	Hot Pink
Network Port	1	Vermilion

Every required property of every object, and who answers it, is in docs/PICS.md.

Requires the CAS BACnet Stack (licensed product)

This example builds against the CAS BACnet Stack, which is a commercial Chipkin product - it is not free or open source, and there is no public/trial build. The stack is referenced here as the private git submodule submodules/cas-bacnet-stack (tracking the 6.x branch). The Rust edition loads the stack as a shared library (CASBACnetStack_x64_Release.dll on Windows / libCASBACnetStack_x64_Release.so on Linux) that you build from that submodule - this repository and its releases never contain it (see Run a release), and never contain the stack's Rust adapter either (it is compiled in place from the submodule). To get the CAS BACnet Stack (and access to build this example), contact Chipkin: https://store.chipkin.com/services/stacks/bacnet-stack or sales@chipkin.com.

What's in this repository

This is a self-contained project. It ships:

src/main.rs - the example device, in the C++ main.cpp's four sections: configuration, the sensor Simulation, the get_property_* callbacks, and main().
src/common/ - the Rust common/ helper (UDP socket, BACnet/IP transport callbacks, IPv4, command line and console, device state, BACnet constants).
tests/ - the Wire Tests (tests/README.md), copied unchanged from the C++ edition; wiretest/ - the series' shared Wiretest Harness 0.7.0, vendored verbatim.
docs/PICS.md - the conformance statement; docs/objects.json - the input to its objects-and-properties generator.
submodules/cas-bacnet-stack/ - the CAS BACnet Stack as a git submodule (private; requires a license - see above). Its Rust adapter, adapters/rust/cas_bacnet_stack_adapters.rs, is compiled into this example in place; its MSVC / g++ build produces the shared library, in its own bin/ folder.

Prerequisites

Rust 1.70 or later with Cargo (verified with rustc 1.99.1, MSVC host on Windows). The crates (libloading, once_cell, ctrlc, if-addrs) come from crates.io on the first build.
To build the stack's shared library: on Windows, Visual Studio Build Tools (MSBuild, C++); on Linux, a C++17 g++.
Python 3 (standard library only) to run the Wire Tests.
Git (to fetch the stack submodule).

Build

git clone --recursive https://github.com/chipkin/BACnetProfileExample-B-SS-Rust.git
cd BACnetProfileExample-B-SS-Rust

Already cloned without --recursive? Run git submodule update --init --recursive.

1. Build the CAS BACnet Stack library from the submodule

The library goes into the submodule's own bin/ folder, and the example loads it from there at run time. Do not copy it into this repository (it is gitignored, and never part of a release).

Windows - the stack's MSVC project has a ReleaseDll|x64 configuration that builds exactly this DLL, under exactly this name (a customer-interface build: no test-tool exports):

& "C:\Program Files (x86)\Microsoft Visual Studio\2022\BuildTools\MSBuild\Current\Bin\amd64\MSBuild.exe" `
  submodules\cas-bacnet-stack\projects\msvs\CASBACnetStack\CASBACnetStack.vcxproj `
  -p:Configuration=ReleaseDll -p:Platform=x64 -m
# -> submodules\cas-bacnet-stack\bin\CASBACnetStack_x64_Release.dll

(Adjust the MSBuild path to your Visual Studio / Build Tools install.)

Linux - build the shared library straight from the stack's sources:

mkdir -p submodules/cas-bacnet-stack/bin
g++ -shared -fPIC -std=c++17 -O2 \
    -I submodules/cas-bacnet-stack/source \
    submodules/cas-bacnet-stack/source/*.cpp \
    -o submodules/cas-bacnet-stack/bin/libCASBACnetStack_x64_Release.so

Only the Release library is used (there is no DebugDll configuration).

2. Build the example

cargo build --release
# -> target/release/BACnetExampleBSS (.exe on Windows)

The build has no warnings. It also compiles the stack's Rust adapter, from submodules/cas-bacnet-stack/adapters/rust/, into the executable.

Run

./target/release/BACnetExampleBSS --port 47821 --deviceID 12345

The executable loads the stack library when it starts, before any other stack call. It looks, in this order:

CAS_BACNET_STACK_LIBRARY_PATH, if it is set (the full path of the library file - the stack's Rust adapter's own override);
the run directory - the folder that holds the executable;
in a development checkout only, submodules/cas-bacnet-stack/bin/, found by walking up from the executable's folder (so target/release/ finds the library the submodule build put there - nothing to copy).

If none of them has the library, the example prints the message shown in Run a release to stderr and exits with code 1. --help and --version work without it.

Expected output:

BACnet B-SS (Smart Sensor) Example - Rust v1.1.0
CAS BACnet Stack version: 6.0.23.0
Common helper (common/) version: 1.1.0
FYI: Listening for BACnet/IP on UDP port 47821 (Network Port 1).
TX 21 bytes to <your-subnet-broadcast>:47821 (broadcast) (Network Port 1) - Unconfirmed: I-Am
FYI: Device 12345 ("Chipkin Example B-SS") ready. Vendor ID 389. Press 'h' for help.

Every BACnet frame in or out then prints one RX / TX line. The device listens on UDP 47808 (BACnet/IP) by default. Allow that port through your firewall. To use a different port, pass --port.

Command-line options

Option	Default	Meaning
`--port <n>`	`47808`	UDP port to listen on (BACnet/IP).
`--deviceID <n>`	`389001`	The device's BACnet instance number (BACnet requires this to be configurable).
`--help`, `-h`	-	Show usage and exit.
`--version`	-	Print the example, stack and `common/` versions, then exit.

An invalid --port or --deviceID prints a warning and the default is used.

Interactive commands

On a terminal, press the key and then Enter (the C++ edition reads single raw key presses - Rust's standard library cannot switch the terminal out of line mode; see TUTORIAL.md):

Key	Action
`h`	Show the version information and this command list.
`q`	Quit.
`u`	Nudge the simulated Analog Input 1 (`Bronze`) reading up by 1.1 (the C++ edition's up arrow).
`d`	Nudge it down by 1.1 (the C++ edition's down arrow).

The Simulation carries on ramping from the nudged value, and a client re-reading it sees the change. Ctrl+C also shuts the device down cleanly. With stdin a pipe (as the Wire Tests run it), each byte is a key: a q written to it quits at once.

Run a release

A GitHub release of this example contains the example only: the BACnetExampleBSS executable for Windows and Linux, metrics-*.json, and the docs. It does not contain the CAS BACnet Stack library - that is a commercially licensed (paid) Chipkin product, and it is never redistributed here. Without it the example cannot start; it says so and exits with code 1:

ERROR: This example cannot run without the CAS BACnet Stack library.

  Missing file: CASBACnetStack_x64_Release.dll
  Looked in:    C:\BACnetExampleBSS

The CAS BACnet Stack is a commercially licensed (paid) library from Chipkin.
It is not included in this release, so the example cannot start without it.

  - To license the CAS BACnet Stack: https://store.chipkin.com/contact-us
  - Licensed customers: build the library from the cas-bacnet-stack submodule
    (see README.md) and place CASBACnetStack_x64_Release.dll next to this executable.

To run a release:

License the CAS BACnet Stack - https://store.chipkin.com/contact-us.
Build the library from the cas-bacnet-stack submodule (Build, step 1): CASBACnetStack_x64_Release.dll on Windows, libCASBACnetStack_x64_Release.so on Linux.
Put it next to the executable (the run directory), or set CAS_BACNET_STACK_LIBRARY_PATH to its full path, and start the example.

CI checks this on every build: it runs the packaged executable without the library and requires the first line above and exit code 1.

Verify

Use a BACnet client such as the CAS BACnet Explorer:

Discover - send a Who-Is. The device replies with I-Am from instance 389001 (vendor 389). It also broadcasts an I-Am at start-up.
Browse the object model - the device shows five objects: the Device (Chipkin Example B-SS), the three sensors, and the Network Port (Vermilion). Reading the Device's Object_List returns all five.
Read the Device - ReadProperty 389001 -> Object_Name returns "Chipkin Example B-SS"; Protocol_Revision returns 30; Description returns the profile description string.
Read a sensor - ReadProperty Analog Input 1 -> Present_Value returns the current simulated temperature (21.5 at start-up, then 0.5 higher each second); read it again and it has moved. Units returns degrees-Celsius; Reliability returns no-fault-detected; Status_Flags returns all FALSE; Out_Of_Service returns false; Object_Name returns "Bronze". Repeat for Binary Input 1 ("Emerald", has Polarity) and Multi-State Input 1 ("Hot Pink", has Number_Of_States = 3). Every required property of every object is readable.
Confirm the profile boundary - a WriteProperty to any object is rejected. That is correct: a B-SS Smart Sensor is read-only.

Wire Tests

The checks above, automated: a Python BACnet client (the Peer) drives the running example over BACnet/IP from outside it. Python 3 standard library only. The scripts are the C++ edition's tests/, unchanged; the Rust build is a single executable, so --exe points them at it.

Script	What it proves
`discovery_test.py`	Who-Is, the Device's `Object_List`, then for every object its `Property_List` and a ReadProperty of every property it lists - every read comes back as a value.
`sensing_test.py`	The Profile Function. Reads the three sensors again and again for 12 s; the readings follow the Simulation (0.5 C steps, a toggle every 3 s, states in order). Fails against a sensor that serves constants.
`failure_modes_test.py`	The Failure Modes. Breaks the simulated sensor wire: `Reliability` `open-loop`, `Status_Flags` FAULT, a frozen reading; repairs it: all clear, the reading moves. Then the errors for an unknown object / property / array index, and the Reject for a WriteProperty.

Run them all after the build:

python tests/run_wire_tests.py --exe target/release/BACnetExampleBSS --port 47821      # Linux
python tests/run_wire_tests.py --exe target\release\BACnetExampleBSS.exe --port 47821  # Windows

(--exe is needed: the tests' default is the C++ edition's build/ folder, and Cargo builds into target/release/. The library is found through the development-checkout fallback, submodules/cas-bacnet-stack/bin/ - no copy next to the executable.) It ends with ALL WIRE TESTS PASSED (exit 0); about 40 seconds. tests/README.md says what each check proves. Verified on Windows only (3 runs in a row, 36/36 checks each, no [RETRY] lines); this port has not been run on Linux. CI (.github/workflows/release.yml) runs them on Linux.

How the Rust binding works

If you have read the C++ edition, the object model and callback shapes are the same; this section is only about what is mechanically different in Rust.

The stack's Rust adapter, in place. src/main.rs compiles submodules/cas-bacnet-stack/adapters/rust/cas_bacnet_stack_adapters.rs as a module (#[path = ...] mod cas_bacnet_stack_adapters;). The stack generates that file from its C header (ci_scripts/generate-rust-adapter.js); nothing from the stack is copied into this repository.
Loaded at run time. The adapter opens the shared library with libloading and looks up each BACnetStack_* symbol at its first call. Every binding returns Result (an Err means the symbol was not found). load_bacnet_functions() in src/main.rs is the Rust edition's LoadBACnetFunctions(): it finds the library (see Run), opens it, points the adapter's CAS_BACNET_STACK_LIBRARY_PATH at that exact file, and only then makes the first call - so a missing library is a message, never a panic.
Plain function pointers. BACnetStack_RegisterCallback*() takes an extern "C" fn, not a closure, so every callback is a free-standing function that reads the device's state from one static (src/common/device_state.rs) instead of the C++ edition's g_* globals.
No panic crosses into C. Every callback body runs inside std::panic::catch_unwind and declines if it panics.
A standard-library transport. src/common/simple_udp.rs owns the UDP socket (std::net::UdpSocket, non-blocking); the stack pulls one datagram per receive callback, as in every edition.

One stack-adapter defect (cas-bacnet-stack#3970) is worked around in this example's own code, marked in place - see TODO.md.

The BACnet profile example series

The CAS BACnet Stack supports every standardized device profile in ASHRAE 135-2024 Annex L, and there is one example repository per profile. Pick the profile your device claims, then the language you build in. "Ask" means the example hasn't been built yet for that language - contact Chipkin if you need one.

Controllers (Annex L.4)

Profile	C++	Node.js	C#	Rust	Python	Go
B-SS Smart Sensor	B-SS-CPP	B-SS-Node	B-SS-CS	B-SS-Rust	B-SS-Python	B-SS-Go
B-SA Smart Actuator	B-SA-CPP	Ask	Ask	Ask	Ask	Ask
B-ASC Application Specific Controller	B-ASC-CPP	B-ASC-Node	Ask	Ask	Ask	Ask
B-AAC Advanced Application Controller	B-AAC-CPP	Ask	Ask	Ask	Ask	Ask
B-BC Building Controller	B-BC-CPP	Ask	Ask	Ask	Ask	Ask

Life safety controllers (Annex L.5)

Profile	C++	Node.js	C#	Rust	Python	Go
B-LSC Life Safety Controller	B-LSC-CPP 🚧	Ask	Ask	Ask	Ask	Ask
B-ALSC Advanced Life Safety Controller	B-ALSC-CPP	Ask	Ask	Ask	Ask	Ask

Access control controllers (Annex L.6)

Profile	C++	Node.js	C#	Rust	Python	Go
B-ACC Access Control Controller	B-ACC-CPP	Ask	Ask	Ask	Ask	Ask
B-AACC Advanced Access Control Controller	B-AACC-CPP	Ask	Ask	Ask	Ask	Ask

Lighting controllers (Annex L.11)

Profile	C++	Node.js	C#	Rust	Python	Go
B-LD Lighting Device	B-LD-CPP	Ask	Ask	Ask	Ask	Ask
B-LS Lighting Supervisor	B-LS-CPP	Ask	Ask	Ask	Ask	Ask

Elevator controllers (Annex L.13)

Profile	C++	Node.js	C#	Rust	Python	Go
B-EM Elevator Monitor	B-EM-CPP	Ask	Ask	Ask	Ask	Ask
B-EC Elevator Controller	B-EC-CPP	Ask	Ask	Ask	Ask	Ask
B-AEC Advanced Elevator Controller	B-AEC-CPP	Ask	Ask	Ask	Ask	Ask

Authentication and authorization (Annex L.14)

Profile	C++	Node.js	C#	Rust	Python	Go
B-AS Authorization Server	B-AS-CPP	Ask	Ask	Ask	Ask	Ask

Miscellaneous (Annex L.7, combinable with any one family)

Profile	C++	Node.js	C#	Rust	Python	Go
B-BBMD Broadcast Management Device	B-BBMD-CPP	Ask	Ask	Ask	Ask	Ask
B-ACDC Access Control Door Controller	B-ACDC-CPP	Ask	Ask	Ask	Ask	Ask
B-ACCR Access Control Credential Reader	B-ACCR-CPP	Ask	Ask	Ask	Ask	Ask
B-RTR Router	B-RTR-CPP	Ask	Ask	Ask	Ask	Ask
B-GW Gateway	B-GW-CPP	Ask	Ask	Ask	Ask	Ask
B-DAP Device Address Proxy	B-DAP-CPP	Ask	Ask	Ask	Ask	Ask
B-SCHUB BACnet/SC Hub	B-SCHUB-CPP	Ask	Ask	Ask	Ask	Ask
B-GENERAL General device (Annex L.8)	(satisfied by every example above)	—	—	—	—	—

Operator interfaces and workstations (Annex L.1–L.3, L.9–L.10, L.12)

Client-side profiles.

Profile	C++	Node.js	C#	Rust	Python	Go
B-OD Operator Display	B-OD-CPP	Ask	Ask	Ask	Ask	Ask
B-OWS Operator Workstation	planned	—	—	—	—	—
B-AWS Advanced Operator Workstation	planned	—	—	—	—	—
B-XAWS Extended Advanced Operator Workstation	planned	—	—	—	—	—
B-LSAP Life Safety Annunciator Panel	planned	—	—	—	—	—
B-LSWS Life Safety Workstation	planned	—	—	—	—	—
B-ALSWS Advanced Life Safety Workstation	planned	—	—	—	—	—
B-ACSD Access Control Security Display	planned	—	—	—	—	—
B-ACWS Access Control Workstation	planned	—	—	—	—	—
B-AACWS Advanced Access Control Workstation	planned	—	—	—	—	—
B-LOD Lighting Operator Display	planned	—	—	—	—	—
B-ALWS Advanced Lighting Workstation	planned	—	—	—	—	—
B-LCS Lighting Control Station	planned	—	—	—	—	—
B-ALCS Advanced Lighting Control Station	planned	—	—	—	—	—
B-ED Elevator Display	planned	—	—	—	—	—
B-EWS Elevator Workstation	planned	—	—	—	—	—
B-AEWS Advanced Elevator Workstation	planned	—	—	—	—	—

🚧 = in progress. "Ask" = not yet built for that language; contact Chipkin if you need it. Profile definitions: ANSI/ASHRAE 135-2024 Annex L. BIBB definitions: Annex K. Get the stack: https://store.chipkin.com/services/stacks/bacnet-stack.

References

ANSI/ASHRAE Standard 135 (BACnet) - the protocol standard. Object model (Clause 12), services (Clause 15), BACnet/IP (Annex J), device profiles (Annex L). Purchase / preview via the ASHRAE store.
What is BACnet? - Chipkin's introduction: https://docs.chipkin.com/protocols/bacnet/.
CAS BACnet Stack - product page and documentation: https://store.chipkin.com/services/stacks/bacnet-stack.
CAS BACnet Explorer - client for testing this device: https://store.chipkin.com/products/tools/cas-bacnet-explorer.
Shared helper used by this example - src/common/README.md.

See also TUTORIAL.md, docs/PICS.md, CHANGELOG.md, TODO.md and AGENTS.md.

Name		Name	Last commit message	Last commit date
.github/workflows		.github/workflows
docs		docs
src		src
submodules		submodules
tests		tests
wiretest		wiretest
.gitignore		.gitignore
.gitmodules		.gitmodules
AGENTS.md		AGENTS.md
CHANGELOG.md		CHANGELOG.md
Cargo.lock		Cargo.lock
Cargo.toml		Cargo.toml
LICENSE		LICENSE
README.md		README.md
TODO.md		TODO.md
TUTORIAL.md		TUTORIAL.md

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