Skip to main content
Conventional web applications generate events which are dispatched to the web server. For example a simple click on a link requests a new page from the server.
The type of events which are flowing from web browser to the web server may be called client-sent events.
Along with HTML5, WHATWG Web Applications 1.0 introduces events which flow from web server to the web browsers and they are called Server-Sent Events (SSE). Using SSE you can push DOM events continously from your web server to the visitor's browser.
The event streaming approach opens a persistent connection to the server, sending data to the client when new information is available, eliminating the need for continuous polling.
Server-sent events standardizes how we stream data from the server to the client.

Web Application for SSE

To use Server-Sent Events in a web application, you would need to add an <eventsource> element to the document.
The src attribute of <eventsource> element should point to an URL which should provide a persistent HTTP connection that sends a data stream containing the events.
The URL would point to a PHP, PERL or any Python script which would take care of sending event data consistently. Following is a simple example of web application which would expect server time.
<!DOCTYPE HTML>
<html>
   <head>
   
      <script type="text/javascript">
         /* Define event handling logic here */
      </script>
      
   </head>
   <body>
 
      <div id="sse">
         <eventsource src="/cgi-bin/ticker.cgi" />
      </div>
  
      <div id="ticker">
         <TIME>
      </div>
  
   </body>
</html>

Server Side Script for SSE

A server side script should send Content-type header specifying the type text/event-stream as follows.
print "Content-Type: text/event-stream\n\n";
After setting Content-Type, server side script would send an Event: tag followed by event name. Following example would send Server-Time as event name terminated by a new line character.
print "Event: server-time\n";
Final step is to send event data using Data: tag which would be followed by integer of string value terminated by a new line character as follows −
$time = localtime();
print "Data: $time\n";
Finally, following is complete ticker.cgi written in perl −
#!/usr/bin/perl

print "Content-Type: text/event-stream\n\n";

while(true){
   print "Event: server-time\n";
   $time = localtime();
   print "Data: $time\n";
   sleep(5);
}

Handle Server-Sent Events

Let us modify our web application to handle server-sent events. Following is the final example.
<!DOCTYPE HTML>
<html>
   <head>
 
      <script type="text/javascript">
         document.getElementsByTagName("eventsource")[0].addEventListener("server-time", eventHandler, false);
   
         function eventHandler(event)
         {
            // Alert time sent by the server
            document.querySelector('#ticker').innerHTML = event.data;
         }
      </script>
  
   </head>
   <body>
 
      <div id="sse">
         <eventsource src="/cgi-bin/ticker.cgi" />
      </div>
  
      <div id="ticker" name="ticker">
         [TIME]
      </div>
  
   </body>
</html>
Before testing Server-Sent events, I would suggest to make sure if your web browser supports this concept.

Comments

Post a Comment

Popular posts from this blog

The Windows Firewall with Advanced Security is a firewall that runs on the Windows Server 2012 and is turned on by default. The Firewall settings within Windows Server 2012 are managed from within the  Windows Firewall Microsoft Management Console . To set Firewall settings perform the following steps − Step 1  − Click on the Server Manager from the task bar → Click the Tools menu and select Windows Firewall with Advanced Security. Step 2  − To see the current configuration settings by selecting  Windows Firewall Properties  from the MMC. This  allows access to modify the settings  for each of the three firewall profiles, which are –  Domain, Private and Public  and IPsec settings. Step 3  − Applying custom rules, which will include the following two steps − Select either  Inbound Rules  or  Outbound Rules  under  Windows Firewall with Advanced Security  on the left side of the management console...
Post a Comment
Read more
In this chapter, we will see how to enable remote desktop application. It is important because this enables us to work remotely on the server. To do this, we have the following two options. For the first option, we have to follow the steps given below. Step 1  − Go to Start → right click “This PC” → Properties. Step 2  − On Left side click “Remote Setting”. Step 3  − Check radio button “Allow Remote connection to this computer” and Check box “Allow connection only from computers running Remote Desktop with Network Level Authentication (recommended)” → click “Select Users”. Step 4  − Click Add. Step 5  − Type user that you want to allow access. In my case, it is administrator → click OK. For the  second option , we need to follow the steps given below. Step 1  − Click on “Server Manage” → Local Server → click on “Enable” or Disable, if it is Disabled.
Post a Comment
Read more
In this chapter, we will see how to configure WSUS and tune it. The following steps should be followed for configuring it. Step 1  − When you open it for the first time, you should do it by going to “Server Manager” → Tools → Windows Server Update Services, then a Configuration wizard will be opened and then click → Next. Step 2  − Click “Start Connecting” → Wait until the green bar is full and then → Next. Step 3  − Check the box for which the updates want to be taken, I did for English and then → Next. Step 4  − Check the box for all the products which you want to update. It is just for Microsoft products and it is recommended to include all the products related to Microsoft and then → Next. Step 5  − Choose the classification updated to be downloaded, if you have a very good internet speed, then check all the boxes, otherwise just check “Critical Updates”. Step 6  − Now we should schedule the updates which I will recommend to do it a...
Post a Comment
Read more