Simple MQTTv5 client

gmqtt-client is pure-rust implementation of an mqtt 5.0 protocol.

Main features: - Auto reconnect - Resubscribe topics after reconnect - Message queue supports Message Expiry Interval and Retain flag

Messages queue

When disconnected from mqtt broker, messages are kept in queue on RAM. If client disconnects from MQTT broker, messages will be kept in queue in RAM.

Messages with Message Expiry Interval are counted down and dropped when expired. For example, if message is sent with message_expiry_interval = 60 (seconds) and client reconnects after 15 seconds, the message will be send with message_expiry_interval = 45 to broker.

Messages with Retain flag and the same topic are replaced in queue. Only last retained message is kept and send to broker.

Those two features help to reduce memory usage when client is offline for long time.

Basic Example

```rust,norun use std::time::Duration; use tokio::runtime; use gmqttclient::{MqttClientBuilder, QoS}; use url::Url; use serde::Serialize;

[derive(Serialize)]

struct Event { id: u32, }

fn main() -> anyhow::Result<()> { let (mqttclient, mqttworker) = MqttClientBuilder::new(Url::parse("tcp://localhost:1883")?) .onmessageownedcallback(|message, instant| { println!("Message: {:?} received {} us ago", message, instant.elapsed().asmicros()); }) .subscribe("client/example/receive", QoS::AtLeastOnce) .build();

let worker_runtime = runtime::Builder::new_multi_thread()
    .enable_all()
    .worker_threads(1)
    .build()?;

worker_runtime.spawn(async { mqtt_worker.run().await });

let payload = Event {
    id: 10
};

mqtt_client.publish_json(
    "client/example/publish",
    &payload,
    false,
    QoS::AtLeastOnce,
    Some(Duration::from_secs(10)),
)?;

std::thread::park();
Ok(())

} ```

Run Example

```sh sudo apt-get install mosquitto mosquitto-clients

Run example client

cargo run --example client

Listen to what is being published

mosquitto_sub -t 'client/example/publish' --pretty -F '%J'

Send a message over to the client

mosquitto_pub -t 'client/example/receive' -m "hello" -q 1 -V 5 -r -D publish message-expiry-interval 5

Send 1000 messages

for i in {0..1000}; do mosquitto_pub -t 'client/example/receive' -m "$i" -q 1 -V 5 -r -D publish message-expiry-interval 5; echo "sending $i"; done ```