Skip to main content

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:
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
Labels:

Comments

Post a Comment

Popular posts from this blog

Google I/O 2017 Notes

WOW! How meaningful this below video explains about the name of  "I/O". Sundar Pichai talked a lot of Machine Learning Machine Learning is a very hot trend these days. Google uses it for their products. Google Assistant: Easily booking an online meal by talking with Google Assistant like a staff of partners, for example. Google Home: Hands-free calling. Google Photos: sharing suggestion, shared library, photo books and google lens. Youtube: 360 degree video, live stream. Kotlin became an official programming language for Android https://kotlinlang.org I'm on the way to Kotlin! ^^ Reference: [1]. https://www.youtube.com/watch?v=Y2VF8tmLFHw
Post a Comment
Read more

Junit - Test fails on French or German string assertion

In my previous post about building a regex to check a text without special characters but allow German and French . I met a problem that the unit test works fine on my machine using Eclipse, but it was fail when running on Jenkins' build job. Here is my test: @Test public void shouldAllowFrenchAndGermanCharacters(){ String source = "ÄäÖöÜüß áÁàÀâÂéÉèÈêÊîÎçÇ"; assertFalse(SpecialCharactersUtils.isExistSpecialCharater(source)); } Production code: public static boolean isExistNotAllowedCharacters(String source){ Pattern regex = Pattern.compile("^[a-zA-Z_0-9_ÄäÖöÜüß áÁàÀâÂéÉèÈêÊîÎçÇ]*$"); Matcher matcher = regex.matcher(source); return !matcher.matches(); } The result likes the following: Failed tests: SpecialCharactersUtilsTest.shouldAllowFrenchAndGermanCharacters:32 null A guy from stackoverflow.com says: "This is probably due to the default encoding used for your Java source files. The ö in the string literal in the J...
5 comments
Read more

JSF, Primefaces - Invoking Application Code Even When Validation Failed

A use case I have a form which has requirements as follow: - There are some mandatory fields. - Validation is triggered when changing value on each field. - A button "Next" is enable only when all fields are entered. It turns to disabled if any field is empty. My first approach I defined a variable "isDisableNext" at a backend bean "Controller" for dynamically disabling/enabling the "Next" button by performing event "onValueChange", but, it had a problem: <h:form id="personForm"> <p:outputLabel value="First Name" for="firstName"/> <p:inputText id="firstName" value="#{person.firstName}" required="true"> <p:ajax event="change" listener="#{controller.onValueChange}" update="nextButton"/> </p:inputText> <p:outputLabel value="Last Name" for="lastName"/> <p:i...
Post a Comment
Read more

Only allow input number value with autoNumeric.js

autoNumeric is a jQuery plugin that automatically formats currency and numbers as you type on form inputs. I used autoNumeric 1.9.21 for demo code. 1. Dowload autoNumeric.js file from  https://github.com/BobKnothe/autoNumeric 2. Import to project <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script> <script type="text/javascript" src="js/autoNumeric.js"></script> 3. Define a function to use it <script type="text/javascript"> /* only number is accepted */ function txtNumberOnly_Mask() { var inputOrgNumber = $("#numberTxt"); inputOrgNumber.each(function() { $(this).autoNumeric({ aSep : '', aDec: '.', vMin : '0.00' }); }); } </script> 4. Call the function by event <form> <input type="text" value="" id="numberTxt"/>(only number) </form> <script ty...
Post a Comment
Read more