1.. _overview: 2 3################## 4Technical Overview 5################## 6 7.. contents:: 8 :local: 9 :backlinks: none 10 :depth: 2 11 12**Native Client** (NaCl) is an open-source technology for running native 13compiled code in the browser, with the goal of maintaining the portability 14and safety that users expect from web applications. Native Client expands web 15programming beyond JavaScript, enabling you to enhance your web applications 16using your preferred language. This document describes some of the key benefits 17and common use cases of Native Client. 18 19Google has implemented the open-source `Native Client project 20<http://www.chromium.org/nativeclient>`_ in the Chrome browser on Windows, Mac, 21Linux, and Chrome OS. The :doc:`Native Client Software Development Kit (SDK) 22<sdk/download>`, itself an open-source project, lets you create web applications 23that use NaCl and run in Chrome across multiple platforms. 24 25A Native Client web application consists of JavaScript, HTML, CSS, and a NaCl 26module written in a language supported by the SDK. The NaCl SDK currently 27supports C and C++; as compilers for additional languages are developed, the SDK 28will be updated. 29 30.. figure:: /images/web-app-with-nacl.png 31 :alt: A web application with and without Native Client 32 33 A web application with and without Native Client 34 35Native Client comes in two flavors: traditional (NaCl) and portable (PNaCl). 36Traditional, which must be distributed through the Chrome Web Store lets you 37target a specific hardware platform. Portable can run on the open web. A 38bitcode file that can be loaded from any web server is downloaded to a client 39machine and converted to hardware-specific code before any execution. For 40details, see :doc:`NaCl and PNaCl </nacl-and-pnacl>`. 41 42.. _why-use-native-client: 43 44Why use Native Client? 45====================== 46 47Native Client open-source technology is designed to run compiled code 48securely inside a browser at near-native speeds. Native Client gives web 49applications some advantages of desktop software. Specifically, it provides the 50means to fully harness the client's computational resources for applications 51such as: 52 53- 3D games 54- multimedia editors 55- CAD modeling 56- client-side data analytics 57- interactive simulations. 58 59Native Client gives C and C++ (and other languages targeting it) the same level 60of portability and safety as JavaScript. 61 62.. _benefits-of-native-client: 63 64Benefits of Native Client 65========================= 66 67Benefits of Native Client include: 68 69* **Graphics, audio, and much more:** Running native code modules that render 2D 70 and 3D graphics, play audio, respond to mouse and keyboard events, run on 71 multiple threads, and access memory directly---all without requiring the user 72 to install a plug-in. 73* **Portability:** Writing your applications once and running them on multiple 74 operating systems (Windows, Linux, Mac, and Chrome OS) and CPU architectures 75 (x86 and ARM). 76* **Easy migration path to the web:** Leveraging years of work in existing 77 desktop applications. Native Client makes the transition from the desktop to 78 a web application significantly easier because it supports C and C++. 79* **Security:** Protecting the user's system from malicious or buggy 80 applications through Native Client's double sandbox model. This model offers 81 the safety of traditional web applications without sacrificing performance 82 and without requiring users to install a plug-in. 83* **Performance:** Running at speeds within 5% to 15% of a native desktop 84 application. Native Client also allows applications to harness all available 85 CPU cores via a threading API. This enables demanding applications such as 86 console-quality games to run inside the browser. 87 88.. _common-use-cases: 89 90Common use cases 91================ 92 93Typical use cases for Native Client include the following: 94 95* **Existing software components:** Native Client lets you repurpose existing 96 C and C++ software in web applications. You don't need to rewrite and debug 97 code that already works. It also lets your application take advantage of 98 things the browser does well such as handling user interaction and processing 99 events. You can also take advantage of the latest developments in HTML5. 100* **Legacy desktop applications:** Native Client provides a smooth migration 101 path from desktop applications to the web. You can port and recompile existing 102 code for the computation engine of your application directly to Native Client, 103 and need rebuild only the user interface and event handling portions for the 104 browser. 105* **Heavy computation in enterprise applications:** Native Client can handle the 106 number crunching required by large-scale enterprise applications. To ensure 107 protection of user data, Native Client lets you run complex cryptographic 108 algorithms directly in the browser so that unencrypted data never goes out 109 over the network. 110* **Multimedia applications:** Codecs for processing sounds, images, and movies 111 can be added to the browser in a Native Client module. 112* **Games:** Native Client lets web applications run at close to native 113 speed, reuse existing multithreaded/multicore C/C++ code bases, and 114 access low-latency audio, networking APIs, and OpenGL ES with programmable 115 shaders. Native Client is a natural fit for running a physics engine or 116 artificial intelligence module that powers a sophisticated web game. 117 Native Client also enables applications to run unchanged across 118 many platforms. 119* **Any application that requires acceleration:** Native Client fits seamlessly 120 into web applications. It's up to you to decide to what extent to use it. 121 Use of Native Client covers the full spectrum from complete applications to 122 small optimized routines that accelerate vital parts of web applications. 123 124.. _link_how_nacl_works: 125 126How Native Client works 127======================= 128 129Native Client is an umbrella name for a set of related software components for 130developing C/C++ applications and running them securely on the web. At a high 131level, Native Client consists of: 132 133* **Toolchains:** collections of development tools (compilers, linkers, etc.) 134 that transform C/C++ code to Portable Native Client modules or Native Client 135 modules. 136* **Runtime components:** components embedded in the browser or other host 137 platforms that allow execution of Native Client modules securely and 138 efficiently. 139 140The following diagram shows how these components interact: 141 142.. figure:: /images/nacl-pnacl-component-diagram.png 143 :alt: The Native Client toolchains and their outputs 144 145 The Native Client toolchains and their outputs 146 147.. _toolchains: 148 149Toolchains 150---------- 151 152A Native Client toolchain consists of a compiler, a linker, an assembler and 153other tools that are used to convert C/C++ source code into a module that is 154loadable by a browser. 155 156The Native Client SDK provides two toolchains: 157 158* The left side of the diagram shows **Portable Native Client** (PNaCl, 159 pronounced "pinnacle"). An LLVM based toolchain produces a single, portable 160 (**pexe**) module. At runtime an ahead-of-time (AOT) translator, built into 161 the browser, translates the pexe into native code for the relevant client 162 architecture. 163 164* The right side of the diagram shows **(non-portable) Native Client**. A GCC 165 based toolchain produces multiple architecture-dependent (**nexe**) modules, 166 which are packaged into an application. At runtime the browser determines 167 which nexe to load based on the architecture of the client machine. 168 169The PNaCl toolchain is recommended for most applications. The NaCl-GCC 170toolchain should only be used for applications that won't be distributed on the 171open web. 172 173.. _security: 174 175Security 176-------- 177 178Since Native Client permits the execution of native code on client machines, 179special security measures have to be implemented: 180 181* The NaCl sandbox ensures that code accesses system resources only through 182 safe, whitelisted APIs, and operates within its limits without attempting to 183 interfere with other code running either within the browser or outside it. 184* The NaCl validator statically analyzes code before running it to make sure it 185 only uses code and data patterns that are permitted and safe. 186 187These security measures are in addition to the existing sandbox in the 188Chrome browser. The Native Client module always executes in a process with 189restricted permissions. The only interaction between this process and the 190outside world is through defined browser interfaces. Because of the 191combination of the NaCl sandbox and the Chrome sandbox, we say that 192Native Client employs a **double sandbox** design. 193 194.. _portability: 195 196Portability 197----------- 198 199Portable Native Client (PNaCl, prounounced "pinnacle") employs state-of-the-art 200compiler technology to compile C/C++ source code to a portable bitcode 201executable (**pexe**). PNaCl bitcode is an OS- and architecture-independent 202format that can be freely distributed on the web and :ref:`embedded in web 203applications<link_nacl_in_web_apps>`. 204 205The PNaCl translator is a component embedded in the Chrome browser; its task is 206to run pexe modules. Internally, the translator compiles a pexe to a nexe 207(described above), and then executes the nexe within the Native Client sandbox 208as described above. The translator uses intelligent caching to avoid 209re-compiling the pexe if it was previously compiled on the client's browser. 210 211Native Client also supports the execution of nexe modules directly in the 212browser. However, since nexes contain architecture-specific machine code, they 213are not allowed to be distributed on the open web. They can only be used as part 214of applications and extensions that are installed from the Chrome Web Store. 215 216For more details on the difference between NaCl and PNaCl, see 217:doc:`NaCl and PNaCl <nacl-and-pnacl>`. 218 219.. _link_nacl_in_web_apps: 220 221Structure of a web application 222============================== 223 224.. _application_files: 225 226A Native Client application consists of a set of files: 227 228* **HTML and CSS:** The HTML file tells the browser where to find the manifest 229 (nmf file) through the embed tag. 230 231 .. naclcode:: 232 233 <embed name="mygame" src="mygame.nmf" type="application/x-pnacl" /> 234 235* **Manifest:** The manifest identifies the module to load and specifies 236 options. For example, "mygame.nmf" might look like this: 237 238 .. naclcode:: 239 240 {... 241 ... 242 "url": "mygame.pexe", 243 } 244 245* **pexe (portable NaCl file):** A compiled Native Client module. It uses the 246 :ref:`Pepper API <link_pepper>`, which provides a bridge to JavaScript and 247 other browser resources. 248 249.. figure:: /images/nacl-in-a-web-app.png 250 :alt: Structure of a web application 251 252 Structure of a web application 253 254For more details, see :doc:`Application Structure 255<devguide/coding/application-structure>`. 256 257.. _link_pepper: 258 259Pepper plug-in API 260------------------ 261 262The Pepper plug-in API (PPAPI), called **Pepper** for convenience, is an 263open-source, cross-platform C/C++ API for web browser plug-ins. Pepper allows a 264C/C++ module to communicate with the hosting browser and to access system-level 265functions in a safe and portable way. One of the security constraints in Native 266Client is that modules cannot make OS-level calls. Pepper provides analogous 267APIs that modules can use instead. 268 269You can use the Pepper APIs to gain access to the full array of browser 270capabilities, including: 271 272* :doc:`Talking to the JavaScript code in your application 273 <devguide/coding/message-system>` from the C++ code in your NaCl module. 274* :doc:`Doing file I/O <devguide/coding/file-io>`. 275* :doc:`Playing audio <devguide/coding/audio>`. 276* :doc:`Rendering 3D graphics <devguide/coding/3D-graphics>`. 277 278Pepper includes both a :doc:`C API </c-api>` and a :doc:`C++ API </cpp-api>`. 279The C++ API is a set of bindings written on top of the C API. For additional 280information about Pepper, see `Pepper Concepts 281<http://code.google.com/p/ppapi/wiki/Concepts>`_. 282 283Where to start 284============== 285 286The :doc:`Quick Start <quick-start>` document provides links to downloads and 287documentation to help you get started with developing and distributing Native 288Client applications. 289
