MQTT for Tcl: Minimal example

For a minimal example, three components are needed:

A publisher to send a message
A server to relay the message
A subscriber to receive the message

Normally, the broker would be started first, followed by the subscriber. Then the publisher can be executed to send the message.

serer.tcl:

    tcl::tm::path add [file dirname [file normalize [info script]]]
    package require broker

    # Show what's happening
    broker log puts

    broker create server ""
    server listen

    vwait forever

subscriber.tcl:

    tcl::tm::path add [file dirname [file normalize [info script]]]
    package require mqtt

    mqtt create mq
    mq connect
    # Receive all messages
    mq subscribe # message

    proc message {topic message args} {
        puts "$topic: $message"
    }

    vwait forever

publisher.tcl:

    tcl::tm::path add [file dirname [file normalize [info script]]]
    package require mqtt

    mqtt create mq
    mq connect
    mq publish minimal/example/topic "Hello, World!"

    # Allow the client to connect and send the message before terminating    
    after 100 exit
    vwait briefly