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1{{+bindTo:partials.standard_nacl_article}} 2 3<section id="c-tutorial-getting-started-part-1"> 4<span id="tutorial"></span><h1 id="c-tutorial-getting-started-part-1"><span id="tutorial"></span>C++ Tutorial: Getting Started (Part 1)</h1> 5<div class="contents local" id="contents" style="display: none"> 6<ul class="small-gap"> 7<li><p class="first"><a class="reference internal" href="#overview" id="id1">Overview</a></p> 8<ul class="small-gap"> 9<li><a class="reference internal" href="#what-the-application-in-this-tutorial-does" id="id2">What the application in this tutorial does</a></li> 10<li><a class="reference internal" href="#communication-between-javascript-and-native-client-modules" id="id3">Communication between JavaScript and Native Client modules</a></li> 11</ul> 12</li> 13<li><a class="reference internal" href="#step-1-download-and-install-the-native-client-sdk" id="id4">Step 1: Download and install the Native Client SDK</a></li> 14<li><a class="reference internal" href="#step-2-start-a-local-server" id="id5">Step 2: Start a local server</a></li> 15<li><a class="reference internal" href="#step-3-set-up-the-chrome-browser" id="id6">Step 3: Set up the Chrome browser</a></li> 16<li><a class="reference internal" href="#step-4-stub-code-for-the-tutorial" id="id7">Step 4: Stub code for the tutorial</a></li> 17<li><a class="reference internal" href="#step-5-compile-the-native-client-module-and-run-the-stub-application" id="id8">Step 5: Compile the Native Client module and run the stub application</a></li> 18<li><a class="reference internal" href="#step-6-modify-the-javascript-code-to-send-a-message-to-the-native-client-module" id="id9">Step 6: Modify the JavaScript code to send a message to the Native Client module</a></li> 19<li><a class="reference internal" href="#step-7-implement-a-message-handler-in-the-native-client-module" id="id10">Step 7: Implement a message handler in the Native Client module</a></li> 20<li><a class="reference internal" href="#step-8-compile-the-native-client-module-and-run-the-application-again" id="id11">Step 8: Compile the Native Client module and run the application again</a></li> 21<li><a class="reference internal" href="#troubleshooting" id="id12">Troubleshooting</a></li> 22<li><a class="reference internal" href="#next-steps" id="id13">Next steps</a></li> 23</ul> 24 25</div><section id="overview"> 26<h2 id="overview">Overview</h2> 27<p>This tutorial shows how to build and run a web application using Portable Native 28Client (PNaCl). This is a client-side application that uses HTML, JavaScript and 29a Native Client module written in C++. The PNaCl toolchain is used to enable 30running the Native Client module directly from a web page.</p> 31<p>It’s recommended to read the <a class="reference internal" href="/native-client/overview.html"><em>Native Client Technical Overview</em></a> prior to going through this tutorial.</p> 32<section id="what-the-application-in-this-tutorial-does"> 33<h3 id="what-the-application-in-this-tutorial-does">What the application in this tutorial does</h3> 34<p>The application in this tutorial shows how to load a Native Client module in a 35web page, and how to send messages between JavaScript and the C++ code in the 36Native Client module. In this simple application, the JavaScript code in the web 37page sends a <code>'hello'</code> message to the Native Client module. When the Native 38Client module receives a message, it checks whether the message is equal to the 39string <code>'hello'</code>. If it is, the Native Client module returns a message saying 40<code>'hello from NaCl'</code>. A JavaScript alert panel displays the message received 41from the Native Client module.</p> 42</section><section id="communication-between-javascript-and-native-client-modules"> 43<h3 id="communication-between-javascript-and-native-client-modules">Communication between JavaScript and Native Client modules</h3> 44<p>The Native Client programming model supports bidirectional communication between 45JavaScript and the Native Client module (C/C++ code). Both sides can initiate 46and respond to messages. In all cases, the communication is asynchronous: The 47caller (JavaScript or the Native Client module) sends a message, but the caller 48does not wait for, or may not even expect, a response. This behavior is 49analogous to client/server communication on the web, where the client posts a 50message to the server and returns immediately. The Native Client messaging 51system is part of the Pepper API, and is described in detail in 52<a class="reference internal" href="/native-client/devguide/coding/message-system.html"><em>Developer’s Guide: Messaging System</em></a>. 53It is also similar to the way <a class="reference external" href="http://en.wikipedia.org/wiki/Web_worker">web workers</a> interact with the main document in 54JavaScript.</p> 55</section></section><section id="step-1-download-and-install-the-native-client-sdk"> 56<h2 id="step-1-download-and-install-the-native-client-sdk">Step 1: Download and install the Native Client SDK</h2> 57<p>Follow the instructions on the <a class="reference internal" href="/native-client/sdk/download.html"><em>Download</em></a> page to 58download and install the Native Client SDK.</p> 59</section><section id="step-2-start-a-local-server"> 60<span id="tutorial-step-2"></span><h2 id="step-2-start-a-local-server"><span id="tutorial-step-2"></span>Step 2: Start a local server</h2> 61<p>To simulate a production environment, the SDK provides a simple web server that 62can be used to serve the application on <code>localhost</code>. A convenience Makefile 63rule called <code>serve</code> is the easiest way to invoke it:</p> 64<pre> 65$ cd pepper_$(VERSION)/getting_started 66$ make serve 67</pre> 68<aside class="note"> 69The SDK may consist of several “bundles”, one per Chrome/Pepper version (see 70<a class="reference internal" href="/native-client/version.html"><em>versioning information</em></a>). In the sample invocation above 71<code>pepper_$(VERSION)</code> refers to the specific version you want to use. For 72example, <code>pepper_31</code>. If you don’t know which version you need, use the 73one labeled <code>(stable)</code> by <code>naclsdk list</code>. See <a class="reference internal" href="/native-client/sdk/download.html"><em>Download the Native 74Client SDK</em></a> for more details. 75</aside> 76<p>If no port number is specified, the server defaults to port 5103, and can be 77accessed at <code>http://localhost:5103</code>.</p> 78<p>Any server can be used for the purpose of development. The one provided with the 79SDK is just a convenience, not a requirement.</p> 80</section><section id="step-3-set-up-the-chrome-browser"> 81<span id="tutorial-step-3"></span><h2 id="step-3-set-up-the-chrome-browser"><span id="tutorial-step-3"></span>Step 3: Set up the Chrome browser</h2> 82<p>PNaCl is enabled by default in Chrome version 31 and later. Please make sure 83that you have a suitable version to work through this tutorial. It’s also 84important to use a Chrome version that’s the same or newer than the SDK bundle 85used to build the Native Client modules.</p> 86<aside class="note"> 87To find out the version of Chrome, type <code>about:chrome</code> in the address bar. 88</aside> 89<p>For a better development experience, it’s also recommended to disable the 90Chrome cache. Chrome caches resources aggressively; disabling the cache helps 91make sure that the latest version of the Native Client module is loaded during 92development.</p> 93<ul class="small-gap"> 94<li>Open Chrome’s developer tools by clicking the menu icon <img alt="menu-icon" src="/native-client/images/menu-icon.png" /> and 95choosing <code>Tools > Developer tools</code>.</li> 96<li>Click the gear icon <img alt="gear-icon" src="/native-client/images/gear-icon.png" /> in the bottom right corner of the Chrome 97window.</li> 98<li>Under the “General” settings, check the box next to “Disable cache (while 99DevTools is open)”.</li> 100<li>Keep the Developer Tools pane open while developing Native Client 101applications.</li> 102</ul> 103</section><section id="step-4-stub-code-for-the-tutorial"> 104<h2 id="step-4-stub-code-for-the-tutorial">Step 4: Stub code for the tutorial</h2> 105<p>The stub code for the tutorial is avalable in the SDK, in 106<code>pepper_$(VERSION)/getting_started/part1</code>. It contains the following files:</p> 107<ul class="small-gap"> 108<li><p class="first"><code>index.html</code>: Contains the HTML layout of the page as well as the JavaScript 109code that interacts with the Native Client module.</p> 110<p>The Native Client module is included in the page with an <code><embed></code> tag that 111points to a manifest file.</p> 112</li> 113<li><code>hello_tutorial.nmf</code>: A manifest file that’s used to point the HTML to the 114Native Client module and optionally provide additional commands to the PNaCl 115translator that is part of the Chrome browser.</li> 116<li><code>hello_tutorial.cc</code>: C++ code for a simple Native Client module.</li> 117<li><code>Makefile</code>: Compilation commands to build the <strong>pexe</strong> (portable executable) 118from the C++ code in <code>hello_tutorial.cc</code>.</li> 119</ul> 120<p>It’s a good idea to take a look at these files now—they contain a large amount 121of comments that help explain their structure and contents. For more details 122on the structure of a typical Native Client application, see 123<a class="reference internal" href="/native-client/devguide/coding/application-structure.html"><em>Application Structure</em></a>.</p> 124<p>The stub code is intentionally very minimal. The C++ code does not do anything 125except correctly initialize itself. The JavaScript code waits for the Native 126Client module to load and changes the status text on the web page accordingly.</p> 127</section><section id="step-5-compile-the-native-client-module-and-run-the-stub-application"> 128<span id="tutorial-step-5"></span><h2 id="step-5-compile-the-native-client-module-and-run-the-stub-application"><span id="tutorial-step-5"></span>Step 5: Compile the Native Client module and run the stub application</h2> 129<p>To compile the Native Client module, run <code>make</code>:</p> 130<pre> 131$ cd pepper_$(VERSION)/getting_started/part1 132$ make 133</pre> 134<p>Since the sample is located within the SDK tree, the Makefile knows how to find 135the PNaCl toolchain automatically and use it to build the module. If you’re 136building applications outside the NaCl SDK tree, you should set the 137<code>$NACL_SDK_ROOT</code> environment variable. See <a class="reference internal" href="/native-client/devguide/devcycle/building.html"><em>Building Native Client 138Modules</em></a> for more details.</p> 139<p>Assuming the local server was started according to the instructions in 140<a class="reference internal" href="#tutorial-step-2"><em>Step 2</em></a>, you can now load the sample by pointing Chrome 141to <code>http://localhost:5103/part1</code>. Chrome should load the Native Client module 142successfully and the Status text should change from “LOADING...” to “SUCCESS”. 143If you run into problems, check out the <a class="reference internal" href="#tutorial-troubleshooting"><em>Troubleshooting section</em></a> below.</p> 144</section><section id="step-6-modify-the-javascript-code-to-send-a-message-to-the-native-client-module"> 145<h2 id="step-6-modify-the-javascript-code-to-send-a-message-to-the-native-client-module">Step 6: Modify the JavaScript code to send a message to the Native Client module</h2> 146<p>In this step, you’ll modify the web page (<code>index.html</code>) to send a message to 147the Native Client module after the page loads the module.</p> 148<p>Look for the JavaScript function <code>moduleDidLoad()</code>, and add new code to send 149a ‘hello’ message to the module. The new function should look as follows:</p> 150<pre class="prettyprint"> 151function moduleDidLoad() { 152 HelloTutorialModule = document.getElementById('hello_tutorial'); 153 updateStatus('SUCCESS'); 154 // Send a message to the Native Client module 155 HelloTutorialModule.postMessage('hello'); 156} 157</pre> 158</section><section id="step-7-implement-a-message-handler-in-the-native-client-module"> 159<h2 id="step-7-implement-a-message-handler-in-the-native-client-module">Step 7: Implement a message handler in the Native Client module</h2> 160<p>In this step, you’ll modify the Native Client module (<code>hello_tutorial.cc</code>) to 161respond to the message received from the JavaScript code in the application. 162Specifically, you’ll:</p> 163<ul class="small-gap"> 164<li>Implement the <code>HandleMessage()</code> member function of the module instance.</li> 165<li>Use the <code>PostMessage()</code> member function to send a message from the module to 166the JavaScript code.</li> 167</ul> 168<p>First, add code to define the variables used by the Native Client module (the 169‘hello’ string you’re expecting to receive from JavaScript and the reply string 170you want to return to JavaScript as a response). In the file 171<code>hello_tutorial.cc</code>, add this code after the <code>#include</code> statements:</p> 172<pre class="prettyprint"> 173namespace { 174// The expected string sent by the browser. 175const char* const kHelloString = "hello"; 176// The string sent back to the browser upon receipt of a message 177// containing "hello". 178const char* const kReplyString = "hello from NaCl"; 179} // namespace 180</pre> 181<p>Now, implement the <code>HandleMessage()</code> member function to check for 182<code>kHelloString</code> and return <code>kReplyString.</code> Look for the following line:</p> 183<pre class="prettyprint"> 184// TODO(sdk_user): 1. Make this function handle the incoming message. 185</pre> 186<p>Populate the member function with code, as follows:</p> 187<pre class="prettyprint"> 188virtual void HandleMessage(const pp::Var& var_message) { 189 if (!var_message.is_string()) 190 return; 191 std::string message = var_message.AsString(); 192 pp::Var var_reply; 193 if (message == kHelloString) { 194 var_reply = pp::Var(kReplyString); 195 PostMessage(var_reply); 196 } 197} 198</pre> 199<p>See the Pepper API documentation for additional information about the 200<a class="reference external" href="/native-client/pepper_stable/cpp/classpp_1_1_instance.html#a5dce8c8b36b1df7cfcc12e42397a35e8">pp::Instance.HandleMessage</a> 201and <a class="reference external" href="/native-client/pepper_stable/cpp/classpp_1_1_instance.html#a67e888a4e4e23effe7a09625e73ecae9">pp::Instance.PostMessage</a> 202member functions.</p> 203</section><section id="step-8-compile-the-native-client-module-and-run-the-application-again"> 204<h2 id="step-8-compile-the-native-client-module-and-run-the-application-again">Step 8: Compile the Native Client module and run the application again</h2> 205<p>Compile the Native Client module by running the <code>make</code> command again.</p> 206<p>Re-run the application by reloading <code>http://localhost:5103/part1</code> in Chrome.</p> 207<p>After Chrome loads the Native Client module, you should see an alert panel 208appear with the message sent from the module.</p> 209</section><section id="troubleshooting"> 210<span id="tutorial-troubleshooting"></span><h2 id="troubleshooting"><span id="tutorial-troubleshooting"></span>Troubleshooting</h2> 211<p>If your application doesn’t run, see <a class="reference internal" href="#tutorial-step-3"><em>Step 3</em></a> above to 212verify that you’ve set up your environment correctly, including both the Chrome 213browser and the local server. Make sure that you’re running a correct version of 214Chrome, which is also greater or equal than the SDK bundle version you are 215using.</p> 216<p>Another useful debugging aid is the Chrome JavaScript console (available via the 217<code>Tools</code> menu in Chrome). Examine it for clues about what went wrong. For 218example, if there’s a message saying “NaCl module crashed”, there is a 219possibility that the Native Client module has a bug; <a class="reference internal" href="/native-client/devguide/devcycle/debugging.html"><em>debugging</em></a> may be required.</p> 220<p>There’s more information about troubleshooting in the documentation:</p> 221<ul class="small-gap"> 222<li><a class="reference internal" href="/native-client/faq.html#faq-troubleshooting"><em>FAQ Troubleshooting</em></a>.</li> 223<li>The <a class="reference internal" href="/native-client/devguide/coding/progress-events.html"><em>Progress Events</em></a> document 224contains some useful information about handling error events.</li> 225</ul> 226</section><section id="next-steps"> 227<h2 id="next-steps">Next steps</h2> 228<ul class="small-gap"> 229<li>See the <a class="reference internal" href="/native-client/devguide/coding/application-structure.html"><em>Application Structure</em></a> 230chapter in the Developer’s Guide for information about how to structure a 231Native Client module.</li> 232<li>Check the <a class="reference external" href="/native-client/pepper_stable/cpp">C++ Reference</a> for details 233about how to use the Pepper APIs.</li> 234<li>Browse through the source code of the SDK examples (in the <code>examples</code> 235directory) to learn additional techniques for writing Native Client 236applications and using the Pepper APIs.</li> 237<li>See the <a class="reference internal" href="/native-client/devguide/devcycle/building.html"><em>Building</em></a>, <a class="reference internal" href="/native-client/devguide/devcycle/running.html"><em>Running</em></a>, and <a class="reference internal" href="/native-client/devguide/devcycle/debugging.html"><em>Debugging pages</em></a> for information about how to build, run, and 238debug Native Client applications.</li> 239<li>Check the <a class="reference external" href="http://code.google.com/p/naclports/">naclports</a> project to see 240what libraries have been ported for use with Native Client. If you port an 241open-source library for your own use, we recommend adding it to naclports 242(see <a class="reference external" href="http://code.google.com/p/naclports/wiki/HowTo_Checkin">How to check code into naclports</a>).</li> 243</ul> 244</section></section> 245 246{{/partials.standard_nacl_article}} 247
