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

[Snippet] CSS - Child element overlap parent

I searched from somewhere and found that a lot of people says a basic concept for implementing this feature looks like below: HTML code: <div id="parent"> <div id="child"> </div> </div> And, CSS: #parent{ position: relative; overflow:hidden; } #child{ position: absolute; top: -1; right: -1px; } However, I had a lot of grand-parents in my case and the above code didn't work. Therefore, I needed an alternative. I presumed that my app uses Boostrap and AngularJs, maybe some CSS from them affects mine. I didn't know exactly the problem, but I believed when all CSS is loaded into my browser, I could completely handle it. www.tom-collinson.com I tried to create an example to investigated this problem by Fiddle . Accidentally, I just changed: position: parent; to position: static; for one of parents -> the problem is solved. Look at my code: <div class="modal-body dn-placeholder-parent-positi...

Building a Wizard with Chain of Responsibility Pattern

What is the Idea? We want to create a page that there are some steps and each step has its own business. Users are able to click on a step and its status could be changed. Primefaces owns a component " Wizard " but it it quite hard for us in order to apply our very specific and complicated business domain logic on each step; even we cannot click on a step of this component. We somehow are able to use the component " TabView " works with a strong back-end mechanism. A backend mechanism! what do I mean? Yes, we need it because we want to abstract the behaviors of each step otherwise we will get trouble with many events handling. Obviously, each step has some behaviors such as "next", "back" and "switch' are the same and they are related to each other; but the business of these behaviors can be different totally. That is where the pattern "Chain of Responsibility" can be applied. Step by Step Building It! In this simple pr...

Updates to the Scrum Guide - The 5 Scrum Values

This article is available at blog.scrum.org , here I just quote my favorite points and give my comment at the end of this post. Ken Schwaber and Jeff Sutherland, the creators of Scrum delivered a webinar on their latest update to the Scrum Guide . The update was a simple one, adding the 5 values of Scrum to the Guide: These values sound easy? Well, there are many misunderstandings and common problems when applying these values. Here are some example: Value Misunderstanding Getting the value right Commitment Committing to something that you don’t understand because you are told to by your boss. Committing yourself to the team and Sprint Goal. Focus Focusing on keeping the customer happy Being focused on the sprint and its goal. Openness Telling everyone everything about all your work Highlighting when you have challenges and problems that are stopping you from success Respect Thinking you are helping the team by being a hero Helping peop...

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 to convert time between timezone in Java, Primefaces?

I use the calendar Primefaces component with timeOnly and timeZone attributes for using only hour format (HH:mm). Like this: <p:calendar id="xabsOvertimeTimeFrom" pattern="HH:mm" timeOnly="true" value="#{data.dateFrom}" timeZone="#{data.timeZone}"/> We can convert the value of #{data.dateFrom} from GMT/UTC time zone to local, conversely, from local time zone to GMT/UTC time zone. Here is my functions: package vn.nvanhuong.timezoneconverter; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; import java.util.TimeZone; public class TimeZoneConverter { /** * convert a date with hour format (HH:mm) from local time zone to UTC time zone */ public static Date convertHourToUTCTimeZone(Date inputDate) throws ParseException { if(inputDate == null){ return null; } Calendar calendar = Calendar.getInstance(); calendar.setTime(inputDate); int ...

vhandit

Search This Blog