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native_client_sdk/doc_generated/devguide/coding/nacl_io.html

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 <section id="the-nacl-io-library">
 <span id="nacl-io"></span><h1 id="the-nacl-io-library"><span id="nacl-io"></span>The nacl_io Library</h1>
 <div class="contents local" id="contents" style="display: none">
 <ul class="small-gap">
 <li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
 <li><a class="reference internal" href="#using-nacl-io" id="id2">Using nacl_io</a></li>
 <li><p class="first"><a class="reference internal" href="#the-nacl-io-demo" id="id3">The nacl_io demo</a></p>
 <ul class="small-gap">
 <li><a class="reference internal" href="#building-and-running-the-demo" id="id4">Building and running the demo</a></li>
 <li><a class="reference internal" href="#a-look-at-the-code" id="id5">A look at the code</a></li>
 </ul>
 </li>
 <li><a class="reference internal" href="#reference-information" id="id6">Reference information</a></li>
 </ul>
 
-</div><section id="introduction">
-<h2 id="introduction">Introduction</h2>
+</div><h2 id="introduction">Introduction</h2>
 <p><code>nacl_io</code> is a utility library that provides implementations of standard
 C APIs such as POSIX I/O (<code>stdio.h</code>) and BSD sockets (<code>sys/socket.h</code>).
 Its primary function is to allow code that uses these standard APIs to be
 compiled and used in a Native Client module. The library is included as part
 of Native Client SDK and is implemented in on top of Pepper API.</p>
 <p>Since Native Client modules cannot access the host machine&#8217;s file system
 directly, nacl_io provides several alternative filesystem types which
 can be used by the application. For example, the Chrome browser supports the
 <a class="reference external" href="http://www.html5rocks.com/en/tutorials/file/filesystem/">HTML5 File System API</a> which provides
 access to a protected area of the local file system. This filesystem can
@@ skipping 21 matching lines @@
 <td>An HTML5 local file system, which can be persistent or temporary</td>
 </tr>
 <tr class="row-even"><td>http</td>
 <td>Maps files on a remote webserver into the local filesystem.</td>
 </tr>
 <tr class="row-odd"><td>dev</td>
 <td>A file system containing special files (e.g.: <code>/dev/null</code>)</td>
 </tr>
 </tbody>
 </table>
-</section><section id="using-nacl-io">
 <h2 id="using-nacl-io">Using nacl_io</h2>
 <p>Using nacl_io is mostly just a matter of using the standard POSIX C library
 functions. However, there are some steps required to initialize the library
 and setup the filesystem mounts. In general the following steps will be needed
 to use nacl_io in a NaCl application:</p>
 <ol class="arabic simple">
 <li>Link the application with the nacl_io library (<code>-lnacl_io</code>)</li>
 <li>Initialize nacl_io at startup using the <code>nacl_io_init_ppapi</code> or
 <code>nacl_io_init</code> functions.</li>
 <li>Mount any desired filesystems using the <code>mount</code> function. The arguments
 to <code>mount</code> for the different filesystem types are detailed in
 <code>include/nacl_io/nacl_io.h</code>.</li>
 <li>If you are going to mount an HTML5 file system, be sure to allocate space
 for it. You can either set the <code>unlimitedStorage</code> permission in the app&#8217;s
 Web Store manifest file, or call the HTML5 QuotaManagement API. These
 options are explained in the <a class="reference internal" href="/native-client/devguide/coding/file-io.html#quota-management"><em>File IO documentation</em></a>.</li>
 <li>Make sure that file and socket API calls are all made from the background
 thread. This is because the main Pepper thread does not support the blocking
 behavior needed by the POSIX I/O operations.</li>
 </ol>
-</section><section id="the-nacl-io-demo">
 <h2 id="the-nacl-io-demo">The nacl_io demo</h2>
-<section id="building-and-running-the-demo">
 <h3 id="building-and-running-the-demo">Building and running the demo</h3>
 <p>The demo application launches a Native Client module that mounts three file
 systems and displays a set of controls that let you work with them:</p>
 <img alt="/native-client/images/nacl_io1.png" src="/native-client/images/nacl_io1.png" />
 <p>Follow these steps to build and run the demo:</p>
 <ul class="small-gap">
 <li><p class="first">Open a terminal in the demo directory:</p>
 <pre class="prettyprint">
 $ cd $NACL_SDK_ROOT/examples/demo/nacl_io_demo
 </pre>
@@ skipping 14 matching lines @@
 menu that appears below on the left</li>
 <li>enter some data and press the fwrite button</li>
 <li>select the fclose command, be sure the file <code>/persistent/test</code> is selected
 in the menu, and press the fclose button</li>
 <li>select the fopen command</li>
 <li>type in the filename <code>/persistent/test</code></li>
 <li>check the fread checkbox and press the fopen button</li>
 <li>select the fread command, be sure the file /persistent/test is selected in
 the menu, enter a byte count, and press the fread button</li>
 </ol>
-</section><section id="a-look-at-the-code">
 <h3 id="a-look-at-the-code">A look at the code</h3>
 <p>The demo is written C and comprises three files.</p>
-<section id="nacl-io-demo-c">
 <h4 id="nacl-io-demo-c">nacl_io_demo.c</h4>
 <p>This is the demo&#8217;s main file. The code here creates and initializes the Native
 Client module instance. The Pepper function <code>Instance_DidCreate</code> initializes
 nacl_io and mounts an HTML5 filesystem at <code>/persistent</code>.</p>
 <pre class="prettyprint">
 static PP_Bool Instance_DidCreate(PP_Instance instance,
                                   uint32_t argc,
                                   const char* argn[],
                                   const char* argv[]) {
   g_instance = instance;
@@ skipping 24 matching lines @@
         common.createNaClModule(name, tc, config, width, height);
         common.attachDefaultListeners();
       },
       function(e) { alert('Failed to allocate space') });
 }
 </pre>
 <p>The <code>Instance_DidCreate</code> function also creates a worker thread that receives
 messages sent from the html page and performs the specified file system
 operations. The logic for the worker thread is encoded in the other two files,
 described below.</p>
-</section><section id="queue-c">
 <h4 id="queue-c">queue.c</h4>
 <p>This file implements a circular queue that is used to receive messages from the
 browser UI to the Native Client module. The file system commands in the
 enqueued messages are executed on the worker thread. This keeps blocking calls
 (like fread) off the main Native Client thread, which is a good thing. The
 queue is initialized in nacl_io_demo.c <code>Instance_DidCreate</code>.</p>
-</section><section id="handlers-c">
 <h4 id="handlers-c">handlers.c</h4>
 <p>This file implements the stdio calls associated with the commands sent from the
 browser. There is a separate <code>Handle*</code> function for each command: fopen,
 fclose, fseek, fread, fwrite. The handlers are called from the
 <code>HandleMessage</code> function in nacl_io_demo.c, which runs in the worker
 thread managing the message queue. The code for the <code>fwrite</code> handler appears
 below. Notice that it does not contain any PPAPI calls and looks like
 &#8220;ordinary&#8221; C code.</p>
 <pre class="prettyprint">
 int HandleFwrite(int num_params, char** params, char** output) {
@@ skipping 19 matching lines @@
     return 2;
   }
 
   bytes_written = fwrite(data, 1, data_len, file);
 
   *output = PrintfToNewString(&quot;fwrite\1%s\1%d&quot;, file_index_string,
                               bytes_written);
   return 0;
 }
 </pre>
-</section></section></section><section id="reference-information">
 <h2 id="reference-information">Reference information</h2>
 <p>The example discussed here is included in the SDK in the directory
 <code>examples/demo/nacl_io_demo</code>.</p>
 <p>The nacl_io library is included in the SDK toolchain and is not a part of the
 Pepper API. For reference information related to the nacl_io interface see
 its header file in the SDK directory, located at
 <code>include/nacl_io/nacl_io.h</code>.</p>
 <p>For more about the HTML5 file system read the <a class="reference external" href="http://dev.w3.org/2009/dap/file-system/pub/FileSystem/">specification</a>.</p>
-</section></section>
+</section>
 
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