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<section id="c-tutorial-getting-started-part-1">
<span id="tutorial"></span><h1 id="c-tutorial-getting-started-part-1"><span id="tutorial"></span>C++ Tutorial: Getting Started (Part 1)</h1>
<div class="contents local" id="contents" style="display: none">
<ul class="small-gap">
<li><p class="first"><a class="reference internal" href="#overview" id="id1">Overview</a></p>
<ul class="small-gap">
<li><a class="reference internal" href="#what-the-application-in-this-tutorial-does" id="id2">What the application in this tutorial does</a></li>
<li><a class="reference internal" href="#communication-between-javascript-and-native-client-modules" id="id3">Communication between JavaScript and Native Client modules</a></li>
</ul>
</li>
<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>
<li><a class="reference internal" href="#step-2-start-a-local-server" id="id5">Step 2: Start a local server</a></li>
<li><a class="reference internal" href="#step-3-set-up-the-chrome-browser" id="id6">Step 3: Set up the Chrome browser</a></li>
<li><a class="reference internal" href="#step-4-stub-code-for-the-tutorial" id="id7">Step 4: Stub code for the tutorial</a></li>
<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>
<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>
<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>
<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>
<li><a class="reference internal" href="#troubleshooting" id="id12">Troubleshooting</a></li>
<li><a class="reference internal" href="#next-steps" id="id13">Next steps</a></li>
</ul>

</div><h2 id="overview">Overview</h2>
<p>This tutorial shows how to build and run a web application using Portable Native
Client (PNaCl). This is a client-side application that uses HTML, JavaScript and
a Native Client module written in C++. The PNaCl toolchain is used to enable
running the Native Client module directly from a web page.</p>
<p>It&#8217;s recommended that you 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>
<h3 id="what-the-application-in-this-tutorial-does">What the application in this tutorial does</h3>
<p>The application in this tutorial shows how to load a Native Client module in a
web page, and how to send messages between JavaScript and the Native Client
module. In this simple application, the JavaScript sends a <code>'hello'</code> message
to the Native Client module. When the Native Client module receives a message,
it checks whether the message is equal to the string <code>'hello'</code>. If it is, the
Native Client module returns a message saying <code>'hello from NaCl'</code>. A
JavaScript alert panel displays the message received from the Native Client
module.</p>
<h3 id="communication-between-javascript-and-native-client-modules">Communication between JavaScript and Native Client modules</h3>
<p>The Native Client programming model supports bidirectional communication between
JavaScript and the Native Client module. Both sides can initiate
and respond to messages. In all cases, the communication is asynchronous: The
caller (JavaScript or the Native Client module) sends a message, but the caller
does not wait for, or may not even expect, a response. This behavior is
analogous to client/server communication on the web, where the client posts a
message to the server and returns immediately. The Native Client messaging
system is part of the Pepper API, and is described in detail in
<a class="reference internal" href="/native-client/devguide/coding/message-system.html"><em>Developer&#8217;s Guide: Messaging System</em></a>.
It 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
JavaScript.</p>
<h2 id="step-1-download-and-install-the-native-client-sdk">Step 1: Download and install the Native Client SDK</h2>
<p>Follow the instructions on the <a class="reference internal" href="/native-client/sdk/download.html"><em>Download</em></a> page to
download and install the Native Client SDK.</p>
<h2 id="step-2-start-a-local-server"><span id="tutorial-step-2"></span>Step 2: Start a local server</h2>
<p>To simulate a production environment, the SDK provides a simple web server that
can be used to serve the application on <code>localhost</code>. A convenience Makefile
rule called <code>serve</code> is the easiest way to invoke it:</p>
<pre>
$ cd pepper_$(VERSION)/getting_started
$ make serve
</pre>
<aside class="note">
The SDK may consist of several &#8220;bundles&#8221;, one per Chrome/Pepper version (see
<a class="reference internal" href="/native-client/version.html"><em>versioning information</em></a>). In the sample invocation above
<code>pepper_$(VERSION)</code> refers to the specific version you want to use. For
example, <code>pepper_37</code>. If you don&#8217;t know which version you need, use the
one labeled <code>(stable)</code> by the <code>naclsdk list</code> command. See
<a class="reference internal" href="/native-client/sdk/download.html"><em>Download the Native Client SDK</em></a> for more details.
</aside>
<p>If no port number is specified, the server defaults to port 5103, and can be
accessed at <code>http://localhost:5103</code>.</p>
<p>Any server can be used for the purpose of development. The one provided with the
SDK is just a convenience, not a requirement.</p>
<h2 id="step-3-set-up-the-chrome-browser"><span id="tutorial-step-3"></span>Step 3: Set up the Chrome browser</h2>
<p>PNaCl is enabled by default in Chrome. We recommend that you use a version of
Chrome that&#8217;s the same or newer than the SDK bundle used to build Native Client
modules. Older PNaCl modules will always work with newer versions of Chrome, but
the converse is not true.</p>
<aside class="note">
To find out the version of Chrome, type <code>about:chrome</code> in the address bar.
</aside>
<p>For a better development experience, it&#8217;s also recommended to disable the
Chrome cache. Chrome caches resources aggressively; disabling the cache helps
make sure that the latest version of the Native Client module is loaded during
development.</p>
<ul class="small-gap">
<li>Open Chrome&#8217;s developer tools by clicking the menu icon <img alt="menu-icon" src="/native-client/images/menu-icon.png" /> and
choosing <code>Tools &gt; Developer tools</code>.</li>
<li>Click the gear icon <img alt="gear-icon" src="/native-client/images/gear-icon.png" /> in the bottom right corner of the Chrome
window.</li>
<li>Under the &#8220;General&#8221; settings, check the box next to &#8220;Disable cache (while
DevTools is open)&#8221;.</li>
<li>Keep the Developer Tools pane open while developing Native Client
applications.</li>
</ul>
<h2 id="step-4-stub-code-for-the-tutorial">Step 4: Stub code for the tutorial</h2>
<p>The stub code for the tutorial is avalable in the SDK, in
<code>pepper_$(VERSION)/getting_started/part1</code>. It contains the following files:</p>
<ul class="small-gap">
<li><p class="first"><code>index.html</code>: Contains the HTML layout of the page as well as the JavaScript
code that interacts with the Native Client module.</p>
<p>The Native Client module is included in the page with an <code>&lt;embed&gt;</code> tag that
points to a manifest file.</p>
</li>
<li><code>hello_tutorial.nmf</code>: A manifest file that&#8217;s used to point the HTML to the
Native Client module and optionally provide additional commands to the PNaCl
translator that is part of the Chrome browser.</li>
<li><code>hello_tutorial.cc</code>: C++ code for a simple Native Client module.</li>
<li><code>Makefile</code>: Compilation commands to build the <strong>pexe</strong> (portable executable)
from the C++ code in <code>hello_tutorial.cc</code>.</li>
</ul>
<p>It&#8217;s a good idea to take a look at these files now&#8212;they contain a large amount
of comments that help explain their structure and contents. For more details
on the structure of a typical Native Client application, see
<a class="reference internal" href="/native-client/devguide/coding/application-structure.html"><em>Application Structure</em></a>.</p>
<p>The stub code is intentionally very minimal. The C++ code does not do anything
except correctly initialize itself. The JavaScript code waits for the Native
Client module to load and changes the status text on the web page accordingly.</p>
<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>
<p>To compile the Native Client module, run <code>make</code>:</p>
<pre>
$ cd pepper_$(VERSION)/getting_started/part1
$ make
</pre>
<p>Since the sample is located within the SDK tree, the Makefile knows how to find
the PNaCl toolchain automatically and use it to build the module. If you&#8217;re
building applications outside the NaCl SDK tree, you should set the
<code>$NACL_SDK_ROOT</code> environment variable. See <a class="reference internal" href="/native-client/devguide/devcycle/building.html"><em>Building Native Client
Modules</em></a> for more details.</p>
<p>Assuming the local server was started according to the instructions in
<a class="reference internal" href="#tutorial-step-2"><em>Step 2</em></a>, you can now load the sample by pointing Chrome
to <code>http://localhost:5103/part1</code>. Chrome should load the Native Client module
successfully and the Status text should change from &#8220;LOADING...&#8221; to &#8220;SUCCESS&#8221;.
If you run into problems, check out the <a class="reference internal" href="#tutorial-troubleshooting"><em>Troubleshooting section</em></a> below.</p>
<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>
<p>In this step, you&#8217;ll modify the web page (<code>index.html</code>) to send a message to
the Native Client module after the page loads the module.</p>
<p>Look for the JavaScript function <code>moduleDidLoad()</code>, and add new code to send
a &#8216;hello&#8217; message to the module. The new function should look as follows:</p>
<pre class="prettyprint">
function moduleDidLoad() {
  HelloTutorialModule = document.getElementById('hello_tutorial');
  updateStatus('SUCCESS');
  // Send a message to the Native Client module
  HelloTutorialModule.postMessage('hello');
}
</pre>
<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>
<p>In this step, you&#8217;ll modify the Native Client module (<code>hello_tutorial.cc</code>) to
respond to the message received from the JavaScript code in the application.
Specifically, you&#8217;ll:</p>
<ul class="small-gap">
<li>Implement the <code>HandleMessage()</code> member function of the module instance.</li>
<li>Use the <code>PostMessage()</code> member function to send a message from the module to
the JavaScript code.</li>
</ul>
<p>First, add code to define the variables used by the Native Client module (the
&#8216;hello&#8217; string you&#8217;re expecting to receive from JavaScript and the reply string
you want to return to JavaScript as a response). In the file
<code>hello_tutorial.cc</code>, add this code after the <code>#include</code> statements:</p>
<pre class="prettyprint">
namespace {
// The expected string sent by the browser.
const char* const kHelloString = &quot;hello&quot;;
// The string sent back to the browser upon receipt of a message
// containing &quot;hello&quot;.
const char* const kReplyString = &quot;hello from NaCl&quot;;
} // namespace
</pre>
<p>Now, implement the <code>HandleMessage()</code> member function to check for
<code>kHelloString</code> and return <code>kReplyString.</code> Look for the following line:</p>
<pre class="prettyprint">
// TODO(sdk_user): 1. Make this function handle the incoming message.
</pre>
<p>Populate the member function with code, as follows:</p>
<pre class="prettyprint">
virtual void HandleMessage(const pp::Var&amp; var_message) {
  if (!var_message.is_string())
    return;
  std::string message = var_message.AsString();
  pp::Var var_reply;
  if (message == kHelloString) {
    var_reply = pp::Var(kReplyString);
    PostMessage(var_reply);
  }
}
</pre>
<p>See the Pepper API documentation for additional information about the
<a class="reference external" href="/native-client/pepper_stable/cpp/classpp_1_1_instance.html#a5dce8c8b36b1df7cfcc12e42397a35e8">pp::Instance.HandleMessage</a>
and <a class="reference external" href="/native-client/pepper_stable/cpp/classpp_1_1_instance.html#a67e888a4e4e23effe7a09625e73ecae9">pp::Instance.PostMessage</a>
member functions.</p>
<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>
<ol class="arabic">
<li><p class="first">Compile the Native Client module by running the <code>make</code> command again.</p>
</li>
<li><p class="first">Start the SDK web server by running <code>make server</code>.</p>
</li>
<li><p class="first">Re-run the application by reloading <code>http://localhost:5103/part1</code> in
Chrome.</p>
<p>After Chrome loads the Native Client module, you should see the message sent
from the module.</p>
</li>
</ol>
<h2 id="troubleshooting"><span id="tutorial-troubleshooting"></span>Troubleshooting</h2>
<p>If your application doesn&#8217;t run, see <a class="reference internal" href="#tutorial-step-3"><em>Step 3</em></a> above to
verify that you&#8217;ve set up your environment correctly, including both the Chrome
browser and the local server. Make sure that you&#8217;re running a correct version of
Chrome, which is also greater or equal than the SDK bundle version you are
using.</p>
<p>Another useful debugging aid is the Chrome JavaScript console (available via the
<code>Tools</code> menu in Chrome). Examine it for clues about what went wrong. For
example, if there&#8217;s a message saying &#8220;NaCl module crashed&#8221;, there is a
possibility 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>
<p>There&#8217;s more information about troubleshooting in the documentation:</p>
<ul class="small-gap">
<li><a class="reference internal" href="/native-client/faq.html#faq-troubleshooting"><em>FAQ Troubleshooting</em></a>.</li>
<li>The <a class="reference internal" href="/native-client/devguide/coding/progress-events.html"><em>Progress Events</em></a> document
contains some useful information about handling error events.</li>
</ul>
<h2 id="next-steps">Next steps</h2>
<ul class="small-gap">
<li>See the <a class="reference internal" href="/native-client/devguide/coding/application-structure.html"><em>Application Structure</em></a>
section in the Developer&#8217;s Guide for information about how to structure a
Native Client module.</li>
<li>Check the <a class="reference external" href="/native-client/pepper_stable/cpp">C++ Reference</a> for details
about how to use the Pepper APIs.</li>
<li>Browse through the source code of the SDK examples (in the <code>examples</code>
directory) to learn additional techniques for writing Native Client
applications and using the Pepper APIs.</li>
<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
debug Native Client applications.</li>
<li>Check the <a class="reference external" href="http://code.google.com/p/naclports/">naclports</a> project to see
what libraries have been ported for use with Native Client. If you port an
open-source library for your own use, we recommend adding it to naclports
(see <a class="reference external" href="http://code.google.com/p/naclports/wiki/HowTo_Checkin">How to check code into naclports</a>).</li>
</ul>
</section>

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