1 {{+bindTo:partials.standard_nacl_article}} 2 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> 25 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—it provides the means to fully harness the client’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—all without requiring 58 the user to install a plugin.</li> 59 <li><strong>Portability:</strong> Write your applications once and you’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’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—you don’t need to rewrite and debug code 83 that’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—it’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 “pinnacle”). 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—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 “pinnacle”) 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’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’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—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><embed></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> 239 240 {{/partials.standard_nacl_article}} 241
