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mqtt-regex

mqtt-regex

Converts an MQTT topic with parameters into a regular expression.

Example

var mqtt_regex = require("mqtt-regex");
 
var pattern = "chat/+id/+user/#path";
 
var room_message_info = mqtt_regex(pattern).exec;
 
var topic = "chat/lobby/bob/text";
 
var message_content = "Hello, World!";
 
var params = room_message_info(topic);
 
if(params && (params.path.indexOf("text") !== -1)) {
    chat.getRoom(params.id).sendFrom(params.user, message_content)
}

Installing

With npm:

$ npm install --save mqtt-regex

To use it in the browser, either compile a package with node run build or use Browserify.

API

The API is super simple and should be easy to integrate with any project

mqtt_regex(topic_pattern)

Takes an MQTT topic pattern, and generates a RegExp object along with a function for parsing params from the result. The results also have an exec function that does both. The return looks like

{
    regex: "RegExp object for matching"
    getParams: function(results){
        // Processes results from RegExp.prototype.exec 
        // Returns an object containing the values for each param 
    },
    exec: function(topic){
        // Performs regex.exec on topic 
        // If there was a match, parses parameters and returns result 
    },
    topic: "Regular MQTT topic with the pattern stuff stripped out"
}

How params work

MQTT defines two types of "wildcards", one for matching a single section of the path (+), and one for zero or more sections of the path (#). Note that the # wildcard can only be used if it's at the end of the topic. This library was inspired by the syntax in the routers for Express and Sinatra, and an attempt was made to have this just as simple to use.

Examples of topic patterns:

user/+id/#path

This would match paths that start with user/, and then extract the next section as the user id. Then it would get all subsequent paths and turn them into an array for the path param. Here is some input/output that you can expect:

user/bob/status/mood: {id: "bob", path:["status","mood"]
user/bob: {id:"bob", path: []}
user/bob/ishungry: {id: "bob", path: ["ishungry"]

device/+/+/component/+type/#path

Not all wildcards need to be associated with a parameter, and it could be useful to just use plain MQTT topics. In this example you might only care about the status of some part of a device, and are willing to ignore a part of the path. Here are some examples of what this might be used with:

device/deviceversion/deviceidhere/component/infrared/status/active: {type:"infrared",path: ["status","active"]}