MQTT Client

This project provides an implementation of an MQTT client. The client allows you to interact with an MQTT broker, sending and receiving messages in a variety of formats.

Type: MQTT

Represents the MQTT client.

Fields

• host: String: The host address of the MQTT broker. (Supports IPV4 and IPV6)
• port: int: The port number of the MQTT broker.
• topic_name: String: The name of the MQTT topic.
• ssl: bool?: Optional. Indicates if SSL/TLS should be used for the connection. The default value is True.
• format: MQTTFormat?: Optional. The format of the messages in the MQTT topic. (In the current version, this value will be ignored and only plain text is supported)
• on_msg: function?: Only for threaded mode. A user-defined callback function to be invoked by threaded background listeners.
• user: String?: Optional. Username for authentication with the MQTT broker.
• pass: String?: Optional. Password for authentication with the MQTT broker.
• client_id: String?: Optional. Client identifier for the MQTT connection. If not provided, a client ID will be automatically generated by the library.
• qoS: int?: Optional. Quality of Service level for message delivery. (Defined by MQTT protocol, the value is 0, 1 or 2)
• time_out: int?: Optional. Timeout duration for the read/receive operation. The default value is zero which indicates no timeout.

Notes: The client_id must be unique for each client. If a client reboots while the MQTT server remains alive, the client has to use a new client_id.

Methods

Basic IO methods

• write(v: any): Send a message of any type to the MQTT broker.
• read(): any?: Blocking read and return the received message.

Threaded mode configuration

This MQTT library supports background threaded listeners. Each listener can be configured to watch different (or the same) topics and servers. Each listener handles incoming messages by invoking a user-defined callback function. This callback function should always take one unique input argument, which is a String. To configure such listeners, the static fn configure(config: Array<MQTT>); method should be called.

Note: Threaded listeners only work in server mode. The application must be launched with the serve command. Please check the Demo section for a simple example.

Connection management

For a blocking read operation, if the library fails to connect to the server, it will attempt to reconnect every 5 seconds for up to one hour. If the connection cannot be established within this period, it will terminate with an error message indicating the connection failure.

For threaded listeners, if the initial connection to the server fails or if the connection is lost at any point, the library will continuously attempt to reconnect. During the first hour after the disconnection, it will try to reconnect every 5 seconds. If the disconnection persists for more than an hour, the library will try to reconnect every 30 minutes.

Demo

Demo for regular methods

Read operation

@library("mqtt", "0.0.0");



/* Blocking Read (Timeout disabled by time_out: 0) */
fn main() {
    var bst = MQTT{host: "localhost", port: 1883, ssl: false, topic_name: "test", qoS: 0, time_out: 0};
    var msg_in = bst.read();
    if (msg_in != null) {
        println("## Inbound message: " + "${msg_in}");
    }
}

Write operation

@library("mqtt", "0.0.0");



/* Write any */
fn main(){
    var bst = MQTT{host: "localhost", port: 1883, ssl: false, topic_name: "test", qoS: 0, time_out: 0};
    var msg_out = "This is your GreyCat speaking!";
    bst.write(msg_out);
}

Demo for threaded listener

@library("mqtt", "0.0.0");




fn hello(s: String){
   println("## Inbound read message: " + "${s}");
}

fn main(){
    MQTT::configure([MQTT{host: "localhost", port: 1883, ssl: false, topic_name: "test", on_msg: project::hello, client_id: "Echo", qoS: 2}]);
}