mqttrust

A lightweight, #![no_std] async MQTT client for embedded systems.

Features

• Minimal footprint designed for resource-constrained environments
• Fully asynchronous, built on top of the Embassy async ecosystem
• Supports both MQTTv3.1.1 and MQTTv5
• Pluggable transport layer (bring your own TCP/TLS stack)
• Optional embedded-tls integration for secure connections
• QoS 0, 1, and 2 (QoS 2 via feature flag)
• Configurable buffer sizes via compile-time feature flags
• Automatic reconnection with configurable backoff
• Topic filter matching with wildcard support (+ and #)
• defmt and log logging support

Quick start

use embassy_sync::blocking_mutex::raw::NoopRawMutex;
use mqttrust::{
    transport::embedded_nal::NalTransport, Config, IpBroker, Publish, State, Subscribe,
};

// Create state with TX/RX buffer sizes
static STATE: StaticCell<State<NoopRawMutex, 1024, 1024>> = StaticCell::new();
let state = STATE.init(State::new());

// Configure the client
let broker = IpBroker::new(Ipv4Addr::new(192, 168, 1, 100), 1883);
let config = Config::builder()
    .client_id("my-device".try_into().unwrap())
    .keepalive_interval(Duration::from_secs(30))
    .build();

let (mut mqtt_stack, client) = mqttrust::new(state, config);

// Run the stack in a background task
spawner.spawn(mqtt_task(mqtt_stack, broker)).unwrap();

// Subscribe and publish
let topics = ["sensor/temperature".into()];
let mut subscription = client
    .subscribe::<1>(Subscribe::builder().topics(&topics).build())
    .await
    .unwrap();

client
    .publish(Publish::builder().topic_name("sensor/temperature").payload(b"23.5").build())
    .await
    .unwrap();

Feature flags

| Feature | Default | Description | |---------|---------|-------------| | mqttv5 | Yes | Enable MQTTv5 protocol support | | mqttv3 | No | Enable MQTTv3.1.1 protocol support | | embedded-tls | Yes | TLS transport via embedded-tls | | qos2 | No | Enable QoS 2 (Exactly Once) support | | std | No | Enable standard library support | | defmt | No | Logging via defmt | | log | No | Logging via the log crate | | thumbv6 | No | Cortex-M0/M0+ support |

Exactly one of mqttv5 or mqttv3 must be enabled.

Buffer size configuration

Internal buffer sizes are configured via feature flags. Each setting has a default value (shown below) and can be overridden by enabling the corresponding feature:

| Prefix | Default | Options | |--------|---------|---------| | max-client-id-len- | 64 | 16, 32, 64, 128, 256 | | max-topic-len- | 128 | 32, 64, 128, 256 | | max-sub-topics-per-msg- | 8 | 2, 4, 8, 16 | | max-subscribers- | 8 | 2, 4, 8, 16 | | max-inflight- | 8 | 2, 4, 8, 16 | | max-pubsub-messages- | 16 | 8, 16, 32, 64, 128, 256 |

For example, to allow up to 256-byte topic names:

[dependencies]
mqttrust = { version = "1.0", features = ["mqttv5", "max-topic-len-256"] }

Contributing

Contributions are welcome. Please follow these guidelines:

1. Fork the repository.
2. Create a new branch.
3. Make your changes.
4. Submit a pull request.

License

This project is licensed under the MIT License. See the LICENSE file for details.