core.io PubSub MQTT

This package is part of the [core.io][https://github.com/goliatone/application-cor] set of libraries, meaning it can be used independently or inside an core.io application.

To install:

$ npm i -S core.io-pubsub-mqtt

Documentation

Request / Response Flow

This module provides a request/response flow that you can leverage to replicate HTTP mechanics. The following illustrates a simple example

• client.js:

pubsub.request('ci/registry/list').then(response => {
    console.log(response.message) //This is my response
}).catch(error => {
    //handle error
});

• server.js:

pubsub.subscribe('ci/registry/list', event => {
    //...perform logic to generate a result object
    let result = { message: 'This is my response' };
    event.respond({ result });
});

If you are using the package as a core.io module and using the dispatch/command flow, you can configure the module to behave use core.io dispatcher handling events with a respondTo function so that your commands do not have to worry about specifically handling the respond call.

Your application setup:

./commands/api.image.get.js

class ApiImageGetCommand {
    execute(event) {
        return {
            success: true,
            message: 'This is my command response'
        };
    }
}

./config/pubsub.js:

module.exports = {
    responseTopicKey: 'responseTopic',
    responseCallerKey: 'respondTo',
    handlers: {
        'mqtt/api/image/get': function handler(topic message) {
            const context = this;
            context.emit('api.image.get', message);
        }
    }
};

Then from your application dispatching the request:

let res = await pubsub.request('api.image.get', {filename});

Response Middleware

You can add response middleware to build the payload of your response object. Note that the middleware will be applied before applying any transformations done in during the payload publish.

In your configuration file:

• config/pubsub.js:

module.exports = {

    /**
     * These functions will be called in the
     * order they are added
     */
    responseMiddleware: [
        function(response, data, error) {

            if(data && !error) {
                response.data = data;
                response.success = true;
            }

            if(error && !data) {
                response.error = error;
                response.success = false;
            }

            return response;
        },

    ]
};

Publish Payload Transformers

You can modify the payload before being published over MQTT. By default we have two transformers, one to add a timestamp and one to add a uuid to the emitted payload.

Ensure UUID

UUID transform to ensure event payloads have a unique ID.

Default implementation will add a field named uuid.

Configuration keypath: pubsub.transforms.ensure.uuid.

You can disable this transformer by setting the value of the configuration keypath to false.

Configuration options:

• fieldName: String representing the payload field name, defaults to uuid.
• getId: function to generate the ID. Default to uuid.v4()

Ensure Timestamp

Timestamp transform to ensure event payloads have a timestamp.

Default implementation will add a field named timestamp.

Configuration keypath: transforms.ensure.timestamp.

You can disable this transformer by setting the value of the configuration keypath to false.

Configuration options:

• fieldName: String representing the payload field name, defaults to timestamp.
• getTimestamp: Function to generate the timestamp. Default to Date.now()

License

® License MIT 2017 by goliatone

TODO:

• [ ] Implement a pin/pong flow so that we can easily build on top of it