Netscape came up with a scripting language called JavaScript
(originally LiveScript), and another small company called FutureWave Software
started working on an animation software called FutureSplash Animator. Later,
both of them became the cause of Java applets almost disappearing from the Web.
FutureWave was acquired by Macromedia in 1996 and they renamed FutureSplash Animator to Flash. Flash, as we all know, went on to rule the Web as the most widely available platform for creating animations, games, video players, and everything interactive, for the major part of the next decade.
In 1999, Microsoft used its iframe technology and JavaScript to update news and
stock quotes on Internet Explorer's default home page (http://home.microsoft.
com). In the same year, they released a proprietary ActiveX extension for IE, called XMLHTTP. This was the era when XML was the "in" thing and everyone wanted to use XML for anything they were doing.
This XMLHTTP component was originally meant to load XML data in the page asynchronously, using JavaScript. It was soon adopted by Mozilla, Safari, and Opera, as XMLHttpRequest (or XHR, for short). But it was with the launch of Gmail (by Google) that the term AJAX (Asynchronous JavaScript and XML)—coined by Jesse James Garrett in an article titled Ajax: A New Approach to Web Applications—became the buzzword in web development.
There are multiple mechanisms to give the feeling of data being pushed from the server to the client. These included Hidden iframe, XHR polling, XHR long polling, and Script tag long polling (or, JSONP long polling).
XHR polling : The first and the easiest to implement is XHR polling, in which the browser keeps polling for data periodically, and the server keeps responding with an empty response unless it has data to send back to the browser. Following an event, such as receiving a mail, or creating/updating a record in the database, the server responds to the next polling request with new data.
As you can see, there is a problem with this. The browser has to keep making requests to the server even when there is no data. This causes the server to get and process data even when there is nothing to deliver.
One of the solutions to this is to modify the server to piggyback the actual client requests by not only sending the data requested by the client, but also appending additional data that the server has, to send to the browser. The client needs to be modified to understand and act upon the additional incoming data.
As the new data is only sent when there is a client action, it causes delays in the
data reaching the browser. The solution to receiving events quickly while avoiding frequent server queries is long polling.
XHR long polling : In long polling, when the browser sends a request to the server, the server won't respond immediately if it doesn't have data to respond with, and will suspend the request. Once the event occurs, the server closes the suspended request by sending over a response to the client. As soon as the client receives the response, it sends a new request.
HTML5 :
In HTML5,there are two new methods for pushing data from the server to the client. One is Server-Sent Events (SSE) and the other is the full duplex WebSockets.
Server-Sent Events attempts to standardize Comet-like communication across
browsers. In this approach, there is a JavaScript API to create an event source, that is,a stream over which the server can send events. This is a unidirectional protocol. We will still be using the good old XHR. This is a good approach when you don't need full duplex communication; just push updates from the server to client.
The other specification which goes on to implement a full duplex communication protocol for the web applications is WebSockets. In WebSockets, the client initiates a socket connection with the server, which supports this protocol as well. The server and client will send and receive data on this socket connection.
Reference : Socket.IO Real-time Web Application Development
(originally LiveScript), and another small company called FutureWave Software
started working on an animation software called FutureSplash Animator. Later,
both of them became the cause of Java applets almost disappearing from the Web.
FutureWave was acquired by Macromedia in 1996 and they renamed FutureSplash Animator to Flash. Flash, as we all know, went on to rule the Web as the most widely available platform for creating animations, games, video players, and everything interactive, for the major part of the next decade.
In 1999, Microsoft used its iframe technology and JavaScript to update news and
stock quotes on Internet Explorer's default home page (http://home.microsoft.
com). In the same year, they released a proprietary ActiveX extension for IE, called XMLHTTP. This was the era when XML was the "in" thing and everyone wanted to use XML for anything they were doing.
This XMLHTTP component was originally meant to load XML data in the page asynchronously, using JavaScript. It was soon adopted by Mozilla, Safari, and Opera, as XMLHttpRequest (or XHR, for short). But it was with the launch of Gmail (by Google) that the term AJAX (Asynchronous JavaScript and XML)—coined by Jesse James Garrett in an article titled Ajax: A New Approach to Web Applications—became the buzzword in web development.
There are multiple mechanisms to give the feeling of data being pushed from the server to the client. These included Hidden iframe, XHR polling, XHR long polling, and Script tag long polling (or, JSONP long polling).
XHR polling : The first and the easiest to implement is XHR polling, in which the browser keeps polling for data periodically, and the server keeps responding with an empty response unless it has data to send back to the browser. Following an event, such as receiving a mail, or creating/updating a record in the database, the server responds to the next polling request with new data.
As you can see, there is a problem with this. The browser has to keep making requests to the server even when there is no data. This causes the server to get and process data even when there is nothing to deliver.
One of the solutions to this is to modify the server to piggyback the actual client requests by not only sending the data requested by the client, but also appending additional data that the server has, to send to the browser. The client needs to be modified to understand and act upon the additional incoming data.
As the new data is only sent when there is a client action, it causes delays in the
data reaching the browser. The solution to receiving events quickly while avoiding frequent server queries is long polling.
XHR long polling : In long polling, when the browser sends a request to the server, the server won't respond immediately if it doesn't have data to respond with, and will suspend the request. Once the event occurs, the server closes the suspended request by sending over a response to the client. As soon as the client receives the response, it sends a new request.
HTML5 :
In HTML5,there are two new methods for pushing data from the server to the client. One is Server-Sent Events (SSE) and the other is the full duplex WebSockets.
Server-Sent Events attempts to standardize Comet-like communication across
browsers. In this approach, there is a JavaScript API to create an event source, that is,a stream over which the server can send events. This is a unidirectional protocol. We will still be using the good old XHR. This is a good approach when you don't need full duplex communication; just push updates from the server to client.
The other specification which goes on to implement a full duplex communication protocol for the web applications is WebSockets. In WebSockets, the client initiates a socket connection with the server, which supports this protocol as well. The server and client will send and receive data on this socket connection.
Reference : Socket.IO Real-time Web Application Development
No comments:
Post a Comment