Peter Lubbers - Pro HTML 5 Programming

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Download from Wow! eBook 142 CHAPTER 6 ■ USING THE HTML5 WEBSOCKET API Figure 6-2. A JavaScript stock ticker application It all looks great, but a look under the hood reveals there are some serious issues with this application. For example, in Mozilla Firefox with Firebug, you can see that GET requests hammer the server at one-second intervals. Turning on the Live HTTP Headers add-on reveals the shocking amount of header overhead that is associated with each request. Listings 6-3 and 6-4 show the HTTP header data for just a single request and response. Listing 6-3. HTTP request header GET /PollingStock//PollingStock HTTP/1.1 Host: localhost:8080 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: http://www.example.com/PollingStock/ Cookie: showInheritedConstant=false; showInheritedProtectedConstant=false; showInheritedProperty=false; showInheritedProtectedProperty=false; showInheritedMethod=false; showInheritedProtectedMethod=false; showInheritedEvent=false; showInheritedStyle=false; showInheritedEffect=false
Listing 6-4. HTTP response header HTTP/1.x 200 OK X-Powered-By: Servlet/2.5 Server: Sun Java System Application Server 9.1_02 Content-Type: text/html;charset=UTF-8 Content-Length: 21 Date: Sat, 07 Nov 2009 00:32:46 GMT CHAPTER 6 ■ USING THE HTML5 WEBSOCKET API Just for fun (ha!), we can count all the characters. The total HTTP request and response header information overhead contains 871 bytes and that does not even include any data. Of course, this is just an example and you can have less than 871 bytes of header data, but there are also common cases where the header data exceeded 2,000 bytes. In this example application, the data for a typical stock topic message is only about 20 characters long. As you can see, it is effectively drowned out by the excessive header information, which was not even required in the first place. So, what happens when you deploy this application to a large number of users? Let’s take a look at the network overhead for just the HTTP request and response header data associated with this polling application in three different use cases. • Use case A: 1,000 clients polling every second: Network traffic is (871 × 1,000) = 871,000 bytes = 6,968,000 bits per second (6.6 Mbps) • Use case B: 10,000 clients polling every second: Network traffic is (871 × 10,000) = 8,710,000 bytes = 69,680,000 bits per second (66 Mbps) • Use case C: 100,000 clients polling every 1 second: Network traffic is (871 × 100,000) = 87,100,000 bytes = 696,800,000 bits per second (665 Mbps) That’s an enormous amount of unnecessary network overhead. Consider if we rebuilt the application to use HTML5 WebSockets, adding an event handler to the web page to asynchronously listen for stock update messages from the message broker (more on that in just a little bit). Each of these messages is a WebSocket frame that has just two bytes of overhead (instead of 871). Take a look at how that affects the network overhead in our three use cases. • Use case A: 1,000 clients receive 1 message per second: Network traffic is (2 × 1,000) = 2,000 bytes = 16,000 bits per second (0.015 Mbps) • Use case B: 10,000 clients receive 1 message per second: Network traffic is (2 × 10,000) = 20,000 bytes = 160,000 bits per second (0.153 Mbps) • Use case C: 100,000 clients receive 1 message per second: Network traffic is (2 × 100,000) = 200,000 bytes = 1,600,000 bits per second (1.526 Mbps) As you can see in Figure 6-3, HTML5 WebSockets provide a dramatic reduction of unnecessary network traffic compared to the polling solution. 143
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THE EXPERT’S VOICE ® IN WEB DEVE
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■ ■ ■ Pro HTML5 Programming P
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For my beautiful wife, Vittoria, an
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Contents ■Foreword ..............
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■ CONTENTS Implementing Canvas Se
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■ CONTENTS Summary ..............
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■ CONTENTS Setting and Retrieving
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Foreword In June 2004, representati
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About the Technical Reviewer � Pa
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Introduction HTML5 is brand new. In
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C H A P T E R 1 ■ ■ ■ Overvie
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CHAPTER 1 ■ OVERVIEW OF HTML5 wit
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Interoperability Simplification CHA
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Table 1-2. New sectioning HTML5 ele
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CHAPTER 1 ■ OVERVIEW OF HTML5 Wit
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article { background-color: #eee; d
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CHAPTER 1 ■ OVERVIEW OF HTML5 The
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CHAPTER 1 ■ OVERVIEW OF HTML5 All
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C H A P T E R 3 ■ ■ ■ Working
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Audio and Video Codecs CHAPTER 3
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MEDIA FOR EVERYONE CHAPTER 3 ■ WO
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CHAPTER 3 ■ WORKING WITH HTML5 AU
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Table 3-4 shows a few of the read-o
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find the actual frame since the vid
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A device can use any of the followi
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CHAPTER 11 ■ THE FUTURE OF HTML5
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270 ■ INDEX unsupported, 68 using
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Peter Lubbers - Pro HTML 5 Programming

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