What the heck is Meteor DDP?

I was using Meteor for my messenger project. I was so curious about the real time connection. I wanted to know how exactly this mechanism works. In this post, I will go through the DDP Specification, an overview of WebSocket, and a simple demo about how to subscribe a publication of Rocket.Chat (containing a DDP server) from an external webpage.

At a glance, I knew that Meteor invented a protocol called DDP which uses for handling real time connection. So then, what is DDP?

"DDP (Distributed Data Protocol) is the stateful WebSocket protocol that Meteor uses to communicate between the client and the server." [1]

All right! Why does DDP matter?

"DDP is a standard way to solve the biggest problem facing client-side JavaScript developers: querying a server-side database, sending the results down to the client, and then pushing changes to the client whenever anything changes in the database". [2]

In order to understand deeply the protocol, I decided to explore its specification, and then took a look at its implementation.

The Specification

The official specification is easily found here. It is quite simple! I tried to draw a diagram (sequence-liked) to visualize its flow.

The Implementation

As its definition, DDP is a WebSocket protocol. Hence, I needed to understand WebSocket protocol as well. A normative way to learn a protocol is to read it RFC. The WebSocket Protocol is specified under RFC-6455. After that, I followed to implement a WebSocket server with Node.js. I was able to understand how WebSocket protocol works.

Then, I took a look into some implementations of DDP available on the net. Here was an example:

- DDP client

- DDP server

I tried to simplify an implementation of DDP by writing a pseudo code as below:

Practice

Assignment: “Obtaining Active Users of Rocket.Chat instance for a webpage in real time”

As my understanding so far, I needed to use WebSocket with DDP, so that I could:

- Maintain real time connection via WebSocket

- Communicate with Meteor via DDP

With node-ddp-client, I could make a connection with DDP server of Meteor, but the implementation was only in server side. I decided to implement a similar stuff, but in client side, which can be executed in browsers.

Check out my project here

------------

Reference:

[1]. https://github.com/meteor/meteor/tree/devel/packages/ddp

[2]. https://blog.meteor.com/introducing-ddp-6b40c6aff27d?gi=65983e20e448

[3]. https://hackernoon.com/implementing-a-websocket-server-with-node-js-d9b78ec5ffa8

[4]. https://github.com/hharnisc/node-ddp-client

Comments

AngularJS - Build a custom validation directive for using multiple emails in textarea

AngularJS already supports the built-in validation with text input with type email. Something simple likes the following: <input name="input" ng-model="email.text" required="" type="email" /> <span class="error" ng-show="myForm.input.$error.email"> Not valid email!</span> However, I used a text area and I wanted to enter some email addresses that's saparated by a comma (,). I had a short research and it looked like AngualarJS has not supported this functionality so far. Therefore, I needed to build a custom directive that I could add my own validation functions. My validation was done only on client side, so I used the $validators object. Note that, there is the $asyncValidators object which handles asynchronous validation, such as making an $http request to the backend. This is just my implementation on my project. In order to understand that, I supposed you already had experiences with ...

DevOps for Dummies

Everyone talks about it, but not everyone knows what it is. Why DevOps? In general, whenever an organization adopts any new technology, methodology, or approach, that adoption has to be driven by a business need. Any kind of system that need rapid delivery of innovation requires DevOps (development and operations). Why? DevOps requires mechanisms to get fast feedback from all the stakeholders in the software application that's being delivered. DevOps approaches to reduce waste and rework and to shift resources to higher-value activities. DevOps aims to deliver value (of organization or project) faster and more efficiently. DevOps Capabilities The capabilities that make up DevOps are a broad set that span the software delivery life cycle. The following picture is a reference architecture which provides a template of a proven solution by using a set of preferred methods and capabilities. My Remarks Okay, that sounds cool. What does it simply mean, again? The f...

The HelloWorld example of JSF 2.2 with Myfaces

I just did by myself create a very simple app "HelloWorld" of JSF 2.2 with a concrete implementation Myfaces that we can use it later on for our further JSF trying out. I attached the source code link at the end part. Just follow these steps below: 1. Create a Maven project in Eclipse (Kepler) with a simple Java web application archetype "maven-archetype-webapp". Maven should be the best choice for managing the dependencies , so far. JSF is a web framework that is the reason why I chose the mentioned archetype for my example. 2. Import dependencies for JSF implementation - Myfaces (v2.2.10) into file pom.xml . The following code that is easy to find from http://mvnrepository.com/ with key words "myfaces". <dependency> <groupId>org.apache.myfaces.core</groupId> <artifactId>myfaces-api</artifactId> <version>2.2.10</version> </dependency> <dependency> <groupId>org.apache.myfaces.core<...

Styling Sort Icons Using Font Awesome for Primefaces' Data Table

So far, Primefaces has used image sprites for displaying the sort icons. This leads to a problem if we want to make a different style for these icons; for example, I would make the icon "arrow up" more blurry at the first time the table loading because I want to highlight the icon "arrow down". I found a way that I can replace these icons with Font Awesome icons. We will use "CSS Pseudo-classes" to achieve it. The hardest thing here is that we should handle displaying icons in different cases. There is a case both "arrow up" and "arrow down" showing and other case is only one of these icons is shown. .ui-sortable-column-icon.ui-icon.ui-icon-carat-2-n-s { background-image: none; margin-left: 5px; font-size: 1.1666em; position: relative; } .ui-sortable-column-icon.ui-icon.ui-icon-carat-2-n-s:not(.ui-icon-triangle-1-s)::before { content: "\f106"; font-family: "FontAwesome"; position: ...

How I did customize "rasa-nlu-trainer" as my own tool

Check out my implementation here Background I wanted to have a tool for human beings to classify intents and extract entities of texts which were obtained from a raw dataset such as Rocket.chat's conversation, Maluuba Frames or here . Then, the output (labeled texts) could be consumed by an NLU tool such as Rasa NLU. rasa-nlu-trainer was a potential one which I didn't need to build an app from scratch. However, I needed to add more of my own features to fulfill my needs. They were: 1. Loading/displaying raw texts stored by a database such as MongoDB 2. Manually labeling intents and entities for the loaded texts 3. Persisting labeled texts into the database I firstly did look up what rasa-nlu-trainer 's technologies were used in order to see how to implement my mentioned features. At first glance rasa-nlu-trainer was bootstrapped with Create React App. Create React App is a tool to create a React app with no build configuration, as it said. This too...

vhandit

Search This Blog