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3 <section id="technical-overview">
4 <span id="overview"></span><h1 id="technical-overview"><span id="overview"></span>Technical Overview</h1>
5 <div class="contents local" id="contents" style="display: none">
6 <ul class="small-gap">
7 <li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
8 <li><a class="reference internal" href="#why-use-native-client" id="id3">Why use Native Client?</a></li>
9 <li><a class="reference internal" href="#common-use-cases" id="id4">Common use cases</a></li>
10 <li><p class="first"><a class="reference internal" href="#how-native-client-works" id="id5">How Native Client works</a></p>
11 <ul class="small-gap">
12 <li><a class="reference internal" href="#security" id="id6">Security</a></li>
13 <li><a class="reference internal" href="#portability" id="id7">Portability</a></li>
14 <li><a class="reference internal" href="#toolchains" id="id8">Toolchains</a></li>
15 </ul>
16 </li>
17 <li><p class="first"><a class="reference internal" href="#native-client-in-a-web-application" id="id9">Native Client in a web application</a></p>
18 <ul class="small-gap">
19 <li><a class="reference internal" href="#pepper-plugin-api" id="id10">Pepper Plugin API</a></li>
20 </ul>
21 </li>
22 <li><a class="reference internal" href="#versioning" id="id11">Versioning</a></li>
23 <li><a class="reference internal" href="#where-to-start" id="id12">Where to start</a></li>
24 </ul>
26 </div><section id="introduction">
27 <h2 id="introduction">Introduction</h2>
28 <p><strong>Native Client</strong> (NaCl) is an open-source technology for running native
29 compiled code in the browser, with the goal of maintaining the portability
30 and safety that users expect from web applications. Native Client expands web
31 programming beyond JavaScript, enabling developers to enhance their web
32 applications using their preferred language. This document describes some of
33 the key benefits and common use cases of Native Client.</p>
34 <p>Google has implemented the open-source <a class="reference external" href="http://www.chromium.org/nativeclient">Native Client project</a> in the Chrome browser on Windows, Mac,
35 Linux, and Chrome OS. The <a class="reference internal" href="/native-client/sdk/download.html"><em>Native Client Software Development Kit (SDK)</em></a>, itself an open-source project, lets developers create web
36 applications that use NaCl and run in Chrome across multiple platforms.</p>
37 <p>A web application that uses Native Client generally consists of a combination of
38 JavaScript, HTML, CSS, and a NaCl module that is written in a language supported
39 by the SDK. The NaCl SDK currently supports C and C++; as compilers for
40 additional languages are developed, the SDK will be updated to support those
41 languages as well.</p>
42 <img alt="/native-client/images/web-app-with-nacl.png" src="/native-client/images/web-app-with-nacl.png" />
43 </section><section id="why-use-native-client">
44 <h2 id="why-use-native-client">Why use Native Client?</h2>
45 <p>Native Client open-source technology is designed to run compiled code
46 securely inside a browser at near-native speeds. Native Client puts web
47 applications on the same playing field as traditional (locally-run)
48 software&#8212;it provides the means to fully harness the client&#8217;s computational
49 resources for applications such as 3D games, multimedia editors, CAD modeling,
50 client-side data analytics, and interactive simulations.
51 Native Client also aims to give C and C++ (and eventually other languages) the
52 same level of portability and safety that JavaScript provides on the web today.</p>
53 <p>Here are a few of the key benefits that Native Client offers:</p>
54 <ul class="small-gap">
55 <li><strong>Graphics, audio, and much more:</strong> Run native code modules that render 2D
56 and 3D graphics, play audio, respond to mouse and keyboard events, run on
57 multiple threads, and access memory directly&#8212;all without requiring
58 the user to install a plugin.</li>
59 <li><strong>Portability:</strong> Write your applications once and you&#8217;ll be able to run them
60 across operating systems (Windows, Linux, Mac, and Chrome OS) and CPU
61 architectures (x86 and ARM).</li>
62 <li><strong>Easy migration path to the web:</strong> Many developers and companies have years
63 of work invested in existing desktop applications. Native Client makes the
64 transition from the desktop to a web application significantly easier because
65 it supports C and C++.</li>
66 <li><strong>Security:</strong> Native Client uses a double sandbox model designed to protect
67 the user&#8217;s system from malicious or buggy applications. This model offers the
68 safety of traditional web applications without sacrificing performance and
69 without requiring users to install a plugin.</li>
70 <li><strong>Performance:</strong> Native Client allows web applications to run at speeds
71 comparable to desktop applications (within 5-15% of native speed).
72 Native Client also allows applications to harness all available CPU cores via
73 a threading API; this enables demanding applications such as console-quality
74 games to run inside the browser.</li>
75 </ul>
76 </section><section id="common-use-cases">
77 <h2 id="common-use-cases">Common use cases</h2>
78 <p>Typical use cases for Native Client include the following:</p>
79 <ul class="small-gap">
80 <li><strong>Existing software components:</strong> With support for C and C++, Native
81 Client enables you to reuse existing software modules in
82 web applications&#8212;you don&#8217;t need to rewrite and debug code
83 that&#8217;s already proven to work well.</li>
84 <li><strong>Legacy desktop applications:</strong> Native Client provides a smooth migration
85 path from desktop applications to the web. You can port and recompile existing
86 code for the computation engine of your application directly to Native Client,
87 and need repurpose only the user interface and event handling portions to the
88 new browser platform. Native Client allows you to embed existing functionality
89 directly into the browser. At the same time, your application can take
90 advantage of things the browser does well: handling user interaction and
91 processing events, based on the latest developments in HTML5.</li>
92 <li><strong>Heavy computation in enterprise applications:</strong> Native Client can handle the
93 number crunching required by large-scale enterprise applications. To ensure
94 protection of user data, Native Client enables you to build complex
95 cryptographic algorithms directly into the browser so that unencrypted data
96 never goes out over the network.</li>
97 <li><strong>Multimedia applications:</strong> Codecs for processing sounds, images, and movies
98 can be added to the browser in a Native Client module.</li>
99 <li><strong>Games:</strong> Native Client lets web applications run at close to native
100 speed, reuse existing multithreaded/multicore C/C++ code bases, and
101 access low-latency audio, networking APIs, and OpenGL ES with programmable
102 shaders. Native Client is a natural fit for running a physics engine or
103 artificial intelligence module that powers a sophisticated web game.
104 Native Client also enables applications to run unchanged across
105 many platforms.</li>
106 <li><strong>Any application that requires acceleration</strong>: Native Client fits seamlessly
107 into web applications&#8212;it&#8217;s up to you to decide to what extent to use it.
108 Use of Native Client covers the full spectrum from complete applications to
109 small optimized routines that accelerate vital parts of web apps.</li>
110 </ul>
111 </section><section id="how-native-client-works">
112 <span id="link-how-nacl-works"></span><h2 id="how-native-client-works"><span id="link-how-nacl-works"></span>How Native Client works</h2>
113 <p>Native Client is an umbrella name for a set of interrelated software components
114 that work together to provide a way to develop C/C++ applications and run them
115 securely on the web.</p>
116 <p>At a high level, Native Client consists of:</p>
117 <ul class="small-gap">
118 <li><strong>Toolchains</strong>: collections of development tools (compilers, linkers, etc.)
119 that transform C/C++ code to Native Client modules.</li>
120 <li><strong>Runtime components</strong>: components embedded in the browser or other
121 host platforms that allow execution of Native Client modules
122 securely and efficiently.</li>
123 </ul>
124 <p>The following diagram shows how these components interact:</p>
125 <img alt="/native-client/images/nacl-pnacl-component-diagram.png" src="/native-client/images/nacl-pnacl-component-diagram.png" />
126 <p>The left side of the diagram shows how to use Portable Native Client
127 (PNaCl, pronounced &#8220;pinnacle&#8221;). Developers use the PNaCl toolchain
128 to produce a single, portable (<strong>pexe</strong>) module. At runtime, a translator
129 built into the browser translates the pexe into native code for the
130 relevant client architecture.</p>
131 <p>The right side of the diagram shows how to use traditional (non-portable)
132 Native Client. Developers use a nacl-gcc based toolchain to produce multiple
133 architecture-dependent (<strong>nexe</strong>) modules, which are packaged into an
134 application. At runtime, the browser decides which nexe to load based
135 on the architecture of the client machine.</p>
136 <section id="security">
137 <h3 id="security">Security</h3>
138 <p>Since Native Client permits the execution of native code on client machines,
139 special security measures have to be implemented:</p>
140 <ul class="small-gap">
141 <li>The NaCl sandbox ensures that code accesses system resources only through
142 safe, whitelisted APIs, and operates within its limits without attempting to
143 interfere with other code running either within the browser or outside it.</li>
144 <li>The NaCl validator statically analyzes code prior to running it
145 to make sure it only uses code and data patterns that are permitted and safe.</li>
146 </ul>
147 <p>The above security measures are in addition to the existing sandbox in the
148 Chrome browser&#8212;the Native Client module always executes in a process with
149 restricted permissions. The only interaction between this process and the
150 outside world is through sanctioned browser interfaces. Because of the
151 combination of the NaCl sandbox and the Chrome sandbox, we say that
152 Native Client employs a double sandbox design.</p>
153 </section><section id="portability">
154 <h3 id="portability">Portability</h3>
155 <p>Portable Native Client (PNaCl, prounounced &#8220;pinnacle&#8221;) employs state-of-the-art
156 compiler technology to compile C/C++ source code to a portable bitcode
157 executable (<strong>pexe</strong>). PNaCl bitcode is an OS- and architecture-independent
158 format that can be freely distributed on the web and <a class="reference internal" href="#link-nacl-in-web-apps"><em>embedded in web
159 applications</em></a>.</p>
160 <p>The PNaCl translator is a component embedded in the Chrome browser; its task is
161 to run pexe modules. Internally, the translator compiles a pexe to a nexe
162 (a native executable for the client platform&#8217;s architecture), and then executes
163 the nexe within the Native Client sandbox as described above. It also uses
164 intelligent caching to avoid re-compiling the pexe if it was previously compiled
165 on the client&#8217;s browser.</p>
166 <p>Native Client also supports the execution of nexe modules directly in the
167 browser. However, since nexes contain architecture-specific machine code,
168 they are not allowed to be distributed on the open web&#8212;they can only be
169 used as part of applications and extensions that are installed from the
170 Chrome Web Store.</p>
171 <p>For more details on the difference between NaCl and PNaCl, see
172 <a class="reference internal" href="/native-client/nacl-and-pnacl.html"><em>NaCl and PNaCl</em></a>.</p>
173 </section><section id="toolchains">
174 <span id="id1"></span><h3 id="toolchains"><span id="id1"></span>Toolchains</h3>
175 <p>A toolchain is a set of tools used to create an application from a set of
176 source files. In the case of Native Client, a toolchain consists of a compiler,
177 linker, assembler and other tools that are used to convert an
178 application written in C/C++ into a module that is loadable by the browser.</p>
179 <p>The Native Client SDK provides two toolchains:</p>
180 <ul class="small-gap">
181 <li>a <strong>PNaCl toolchain</strong> for generating portable NaCl modules (pexe files)</li>
182 <li>a <strong>gcc-based toolchain (nacl-gcc)</strong> for generating non-portable NaCl modules
183 (nexe files)</li>
184 </ul>
185 <p>The PNaCl toolchain is recommended for most applications. The nacl-gcc
186 toolchain should only be used for applications that will not be distributed
187 on the open web.</p>
188 </section></section><section id="native-client-in-a-web-application">
189 <span id="link-nacl-in-web-apps"></span><h2 id="native-client-in-a-web-application"><span id="link-nacl-in-web-apps"></span>Native Client in a web application</h2>
190 <p id="application-files">A Native Client application consists of a set of files:</p>
191 <ul class="small-gap">
192 <li><strong>HTML</strong>, <strong>CSS</strong>, and <strong>JavaScript</strong> files, as in any modern web
193 application. The JavaScript code is responsible for communicating with the
194 NaCl module.</li>
195 <li>A <strong>pexe</strong> (portable NaCl) file. This module uses the <a class="reference internal" href="#link-pepper"><em>Pepper</em></a> API, which provides the bridge to JavaScript and
196 browser resources.</li>
197 <li>A Native Client <strong>manifest</strong> file that specifies the pexe to load, along with
198 some loading options. This manifest file is embedded into the HTML page
199 through an <code>&lt;embed&gt;</code> tag, as shown in the figure below.</li>
200 </ul>
201 <img alt="/native-client/images/nacl-in-a-web-app.png" src="/native-client/images/nacl-in-a-web-app.png" />
202 <p>For more details, see <a class="reference internal" href="/native-client/devguide/coding/application-structure.html"><em>Application Structure</em></a>.</p>
203 <section id="pepper-plugin-api">
204 <span id="link-pepper"></span><h3 id="pepper-plugin-api"><span id="link-pepper"></span>Pepper Plugin API</h3>
205 <p>The Pepper Plugin API (PPAPI), called <strong>Pepper</strong> for convenience, is an
206 open-source, cross-platform C/C++ API for web browser plugins. From the point
207 of view of Native Client, Pepper allows a C/C++ module to communicate with
208 the hosting browser and get access to system-level functions in a safe and
209 portable way. One of the security constraints in Native Client is that modules
210 cannot make any OS-level calls directly. Pepper provides analogous APIs that
211 modules can target instead.</p>
212 <p>You can use the Pepper APIs to gain access to the full array of browser
213 capabilities, including:</p>
214 <ul class="small-gap">
215 <li><a class="reference internal" href="/native-client/devguide/coding/message-system.html"><em>Talking to the JavaScript code in your application</em></a> from the C++ code in your NaCl module.</li>
216 <li><a class="reference internal" href="/native-client/devguide/coding/file-io.html"><em>Doing file I/O</em></a>.</li>
217 <li><a class="reference internal" href="/native-client/devguide/coding/audio.html"><em>Playing audio</em></a>.</li>
218 <li><a class="reference internal" href="/native-client/devguide/coding/3D-graphics.html"><em>Rendering 3D graphics</em></a>.</li>
219 </ul>
220 <p>Pepper includes both a C API and a C++ API. The C++ API is a set of bindings
221 written on top of the C API. For additional information about Pepper, see
222 <a class="reference external" href="http://code.google.com/p/ppapi/wiki/Concepts">Pepper Concepts</a>.</p>
223 </section></section><section id="versioning">
224 <h2 id="versioning">Versioning</h2>
225 <p>Chrome is released on a six week cycle, and developer versions of Chrome are
226 pushed to the public beta channel three weeks before each release. As with any
227 software, each release of Chrome may include changes to Native Client and the
228 Pepper interfaces that may require modification to existing applications.
229 However, modules compiled for one version of Pepper/Chrome should work with
230 subsequent versions of Pepper/Chrome. The SDK includes multiple versions of the
231 Pepper APIs to help developers make adjustments to API changes and take
232 advantage of new features: <a class="reference external" href="/native-client/pepper_stable">stable</a>, <a class="reference external" href="/native-client/pepper_beta">beta</a> and <a class="reference external" href="/native-client/pepper_dev">dev</a>.</p>
233 </section><section id="where-to-start">
234 <h2 id="where-to-start">Where to start</h2>
235 <p>The <a class="reference internal" href="/native-client/quick-start.html"><em>Quick Start</em></a> document provides links to downloads and
236 documentation that should help you get started with developing and distributing
237 Native Client applications.</p>
238 </section></section>
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