Peter Lubbers - Pro HTML 5 Programming

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Download from Wow! eBook 92 CHAPTER 4 ■ USING THE HTML5 GEOLOCATION API Table 4-6. Browser support for HTML5 Geolocation Browser Details Chrome Supported in Google Chrome version 2 with Gears Firefox Supported in version 3.5 and greater Internet Explorer Supported via the Gears plugin Opera Planned support version 10, experimental support in nightly builds Safari Supported in version 4 for the iPhone Due to the varying levels of support, it is a good idea to first see whether HTML5 Geolocation is supported before you use the APIs. The section “Checking for Browser Support” later in this chapter will show you how you can programmatically check for browser support. Privacy The HTML5 Geolocation specification mandates that a mechanism is provided to protect the user's privacy. Furthermore, location information should not be made available unless the application’s users grant their express permission. This makes sense and addresses the “big brother” concerns users often raise about HTML5 Geolocation applications. However, as you can see from some of the possible use cases for HTML 5 Geolocation applications, there is usually an incentive for the user to share this information. For example, users might be OK with sharing their location if this could let them know about a rare 50% discount on a pair of running shoes that are ready to be picked up in a store located just a few blocks away from where they happen to be drinking coffee. Let’s take a closer look at the browser and device privacy architecture shown in Figure 4-1.
Figure 4-1. HTML5 Geolocation browser and device privacy architecture CHAPTER 4 ■ USING THE HTML5 GEOLOCATION API The following steps are shown in the diagram: 1. A user navigates to a location-aware application in the browser. 2. The application web page loads and requests coordinates from the browser by making a Geolocation function call. The browser intercepts this and requests user permission. Let's assume that the permission is granted. 3. The browser retrieves coordinate information from the device it is running on. For example, the IP address, Wi-Fi, or GPS coordinates. This is an internal function of the browser. 4. The browser sends these coordinates to a trusted external location service, which returns a detailed location that can now be sent back to the host of the HTML5 Geolocation application. ■ Important: The application does not have direct access to the device; it can only query the browser to access the device on its behalf. Triggering the Privacy Protection Mechanism When you access a web page that uses the HTML5 Geolocation APIs, the privacy protection mechanism should kick in. Figure 4-2 shows what this looks like in Firefox 3.5. 93
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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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• MathML • Microdata • Server
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Figure 1-1. A page rendered in stan
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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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Figure 1-2. An HTML5 page with all
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CHAPTER 1 ■ OVERVIEW OF HTML5 The
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Figure 1-3. Developer Tools view in
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CHAPTER 1 ■ OVERVIEW OF HTML5 All
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26 CHAPTER 2 ■ USING THE HTML5 CA
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Listing 6-4. HTTP response header H
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EXISTING WEBSOCKET SERVERS CHAPTER
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def terminate(self): self.ready_sta
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Basic API Usage CHAPTER 6 ■ USING
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HTML5 WebSocket / Geolocation Track
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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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