[paho-dev] Support for Futures and Streams in the Rust Client Library

[Frank Pagliughi <fpagliughi@xxxxxxxxxxxxxx>]

Hello All,

Significant improvements were added to the Paho Rust client over the holiday break. The library now supports Rust Futures and Streams. This allows an MQTT client to be fully integrated into an application using Futures for other asynchronous I/O, such as for data collection, file manipulation, or databases.

Futures allow asynchronous operations to work as simply as blocking calls, while allowing threads to be shared between operations. Chaining futures together lets us write concise code with full error handling, such as this snippet which opens a client connection, waits for it to complete, publishes a message, and then closes the connection:

cli.connect(None)
    .and_then(|_| {
        let msg = mqtt::Message::new("test", "Hello futures world!", 1);
        cli.publish(msg)
    })
    .and_then(|_| cli.disconnect(None))
    .wait().unwrap_or_else(|err| {
        println!("Error: {}", err);
    });

This is mostly compatible with the existing asynchronous API which uses "Token" objects. Now the Tokens simply implement the Futures trait.

The implementation is up on GitHub (https://github.com/eclipse/paho.mqtt.rust). A release should be coming shortly. This is the last major feature for the current version of the library. Next, we'll move on to MQTT v5 support.

Frank