retain_fail.js

var mosca = require("mosca");
var mqtt = require("mqtt");

function promiseMosca(){
    var moscaOpts = {
        http:{
            port:3000,
            static:false,
            bundle:false
        },
        onlyHttp:true
    };

    return new Promise(function(resolve, reject){
        var mqttServer = new mosca.Server(moscaOpts);
        mqttServer.on("ready", function(){
            resolve(mqttServer);
        });
    });
}

function promiseMosquitto(){
    return Promise.resolve();
}

function promiseClient(){
    return new Promise(function(resolve, reject){
        var mqttClient = mqtt.connect("ws://localhost:3000");
        mqttClient.on("connect", function(){
            resolve(mqttClient);
        });
    });
}

function promiseReceipt(client){
    return new Promise(function(resolve, reject){
        client.on("message", function(topic, message, packet){
            resolve([topic, message.toString()]);
        });
    });
}

function promiseSubscription(client, topic){
    return new Promise(function(resolve, reject){
        client.subscribe(topic, {qos:1}, function(err, granted){
            var result = Array.prototype.slice.call(arguments);
            resolve(result);
        });
    });
}

function promisePublication(client,topic,message){
    return new Promise(function(resolve, reject){
        client.publish(topic, message, {qos:1, retain:true}, function(){ 
            resolve(Array.prototype.slice.call(arguments)); 
        });
    });
}

var testTopic = "Hello",
    testMessage = "World";

//var serverPromise = promiseMosca();
var serverPromise = promiseMosquitto();

var testPromise = serverPromise
    .then(function() {
        return promiseClient()
    })
    .then(function(receiver) {
        var receivePromise = promiseReceipt(receiver); //initialised before publication so no events are missed

        return Promise.resolve()
            .then(function(){
                return promiseClient();
            })
            .then(function(sender){
                return promisePublication(sender,testTopic,testMessage);
            })
            .then(function(){ //move this clause to first in the list, and Mosca delivers the message!
                return promiseSubscription(receiver, testTopic);
            })
            .then(function(){
                return receivePromise; //promise initialised earlier is passed back
            });
    });

testPromise.then(function(receiveResult){
        console.log("Message Received: " + JSON.stringify(receiveResult));
    });

Thanks for taking the time to look at this!. Providing a configuration like the one below indeed resolves the issue altogether.

Although I previously had a persistence configuration (and removed it to make a more minimal test case) there must have been something wrong with the configuration I provided. This one is minimal but works...

var moscaOpts = {
        http:{
            port:3000,
            static:false,
            bundle:false
        },
        persistence: {
            factory: mosca.persistence.Memory
        },
        onlyHttp:true
    };