MQTT ping-pong

Another way to have fun during confinement.

Objectives

Get to know the Eclipse Paho MQTT library better, by writing two simple client programs which do the following:

The pinger publishes a "ping" message to the topic "ping-ask" on a broker.
This "ping" is received by a listening ponger that responds with "pong" on another topic called "pong-response".
The pinger receives the "pong" response and rejoices much.

So each program:

As an objective, the Quality of Service we strive for is 2.

For additional fun, each program must exist in two versions: synchronous and asynchronous.

Let's use mosquitto's test server as a broker.

I made an extensive use of the examples provided by the Paho MQTT library. Some of this code is weird, though.

// examples/sync_consume.rs
if let Some((server_uri, ver, session_present)) = rsp.connect_response() { ... }

I couldn't find this connect_response() function anywhere in the library.

Open two terminals in the project directory, and run separately:

cargo run --bin sync_pong

and

cargo run --bin sync_ping

Be sure to launch sync_pong first, otherwise it won't catch the single message that sync_ping sends immediatly when starting.

Same with

cargo run --bin async_pong

and

cargo run --bin async_ping