MQTTier

A Rust MQTT client library providing an abstracted interface around rumqttc.

Features

• Asynchronous: Built on top of tokio for async/await support
• Serialization: Uses serde for JSON serialization of published messages
• Logging: Integrated with the standard Rust logging ecosystem
• Reconnection: Automatic reconnection on connection loss
• Queueing: Messages and subscriptions are queued when disconnected (or before connection is made.)
• Cloneable: Client can be cloned and shared across tasks
• MQTT 5.0: Uses MQTT version 5 protocol

Usage

Add this to your Cargo.toml (use the current crate version):

[dependencies]
mqttier = "0.2"

Basic Example

This example has been abbreviated to focus on library-specific calls.

// Create a new MQTT client
let client = MqttierClient::new("localhost", 1883, Some("mqttier_example".to_string())).unwrap();

// Start the run loop (spawned background tasks). Call once per client.
client.start().await.unwrap();

// Create mpsc channel for receiving messages
let (message_tx, mut message_rx) = mpsc::channel::<ReceivedMessage>(64);

// Subscribe to a topic. We pass the tx-side of the channel that will receive messages
// for this subscription. The function returns a subscription id (`usize`).
let subscription_id = client.subscribe("test/topic".to_string(), 0, message_tx).await.unwrap();

// Start a task to handle incoming messages
tokio::spawn(async move {
    while let Some(message) = message_rx.recv().await {
        if let Ok(test_msg) = serde_json::from_slice::<TestMessage>(&message.payload) {
            println!("Parsed message: {:?}", test_msg);
        }
    }
});

// Publish a serializable structure and wait for its publish completion
let completion_rx = client.publish_structure("test/topic".to_string(), &test_message).await.unwrap();
match completion_rx.await {
    Ok(result) => println!("Publish result: {:?}", result),
    Err(_) => println!("Publish completion channel closed"),
}

API

MqttierClient

new(hostname: &str, port: u16, client_id: Option<String>) -> Result<Self>

Creates a new MQTT client.

• hostname: The MQTT broker hostname
• port: The MQTT broker port
• client_id: Optional client ID. If None, a random UUID is generated

start() -> Result<()>

Starts the background run loop for connections and publishing. This should be called once per client. If already running, this method does nothing.

subscribe(topic: String, qos: u8, message_tx: mpsc::Sender<ReceivedMessage>) -> Result<usize>

Subscribes to a topic and returns a subscription ID (usize).

• topic: The MQTT topic to subscribe to
• qos: The Quality of Service level (0, 1, or 2)
• message_tx: The sender channel for delivering received messages (bounded channel with capacity you choose)
• Returns: The subscription ID (usize)

publish_structure<T: Serialize>(topic: String, payload: T) -> Result<oneshot::Receiver<PublishResult>>

Publishes a serializable struct as JSON to a topic and returns a oneshot::Receiver<PublishResult> which will resolve with the publish outcome.

• topic: The MQTT topic to publish to
• payload: The struct to publish (must implement Serialize)

publish_request<T: Serialize>(topic: String, payload: T, response_topic: String, correlation_id: Vec<u8>) -> Result<oneshot::Receiver<PublishResult>>

Publishes a request message with response topic and correlation ID.

• topic: The MQTT topic to publish to
• payload: The struct to publish
• response_topic: The topic for responses
• correlation_id: Correlation ID for matching responses (Vec<u8>)

publish_response<T: Serialize>(topic: String, payload: T, correlation_id: Vec<u8>) -> Result<oneshot::Receiver<PublishResult>>

Publishes a response message with correlation ID.

• topic: The MQTT topic to publish to
• payload: The struct to publish
• correlation_id: Correlation ID for matching requests

publish_state<T: Serialize>(topic: String, payload: T, state_version: u32) -> Result<oneshot::Receiver<PublishResult>>

Publishes a state message with a version property.

• topic: The MQTT topic to publish to
• payload: The struct to publish
• state_version: Version number for the state

Behavior

Automatic Reconnection

The client automatically reconnects when the connection is lost, with a 5-second delay between attempts.

Message Queueing

When disconnected:

• Subscription requests are queued and processed when reconnected
• Publish requests are queued and sent when reconnected

Logging

The library emits tracing events using the tracing crate. Initialize a tracing subscriber in your application, for example:

tracing_subscriber::fmt().with_env_filter("info").init();

Example

See examples/basic_usage.rs for a complete example.

Run the example with:

cargo run --example basic_usage

License

This project is licensed under the LGPLv2 License. (Not v3!)