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            <h1>Node.js v0.6.12 Manual &amp; Documentation</h1>
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            <h2>Table of Contents</h2>
            <ul>
<li><a href="#addons_addons">Addons</a><ul>
<li><a href="#addons_hello_world">Hello world</a></li>
<li><a href="#addons_addon_patterns">Addon patterns</a><ul>
<li><a href="#addons_function_arguments">Function arguments</a></li>
<li><a href="#addons_callbacks">Callbacks</a></li>
<li><a href="#addons_object_factory">Object factory</a></li>
<li><a href="#addons_function_factory">Function factory</a></li>
<li><a href="#addons_wrapping_c_objects">Wrapping C++ objects</a></li>
<li><a href="#addons_factory_of_wrapped_objects">Factory of wrapped objects</a></li>
<li><a href="#addons_passing_wrapped_objects_around">Passing wrapped objects around</a></li>
</ul>
</li>
</ul>
</li>
</ul>

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          <div id="apicontent">
            <h1>Addons<span><a class="mark" href="#addons_addons" id="addons_addons">#</a></span></h1>
<p>Addons are dynamically linked shared objects. They can provide glue to C and
C++ libraries. The API (at the moment) is rather complex, involving
knowledge of several libraries:

</p>
<ul>
<li><p>V8 JavaScript, a C++ library. Used for interfacing with JavaScript:
creating objects, calling functions, etc.  Documented mostly in the
<code>v8.h</code> header file (<code>deps/v8/include/v8.h</code> in the Node source tree),
which is also available <a href="http://izs.me/v8-docs/main.html">online</a>.</p>
</li>
<li><p><a href="https://github.com/joyent/libuv">libuv</a>, C event loop library. Anytime one
needs to wait for a file descriptor to become readable, wait for a timer, or
wait for a signal to received one will need to interface with libuv. That is,
if you perform any I/O, libuv will need to be used.</p>
</li>
<li><p>Internal Node libraries. Most importantly is the <code>node::ObjectWrap</code>
class which you will likely want to derive from.</p>
</li>
<li><p>Others. Look in <code>deps/</code> for what else is available.</p>
</li>
</ul>
<p>Node statically compiles all its dependencies into the executable. When
compiling your module, you don&apos;t need to worry about linking to any of these
libraries.


</p>
<h2>Hello world<span><a class="mark" href="#addons_hello_world" id="addons_hello_world">#</a></span></h2>
<p>To get started let&apos;s make a small Addon which is the C++ equivalent of
the following Javascript code:

</p>
<pre><code>exports.hello = function() { return &apos;world&apos;; };</code></pre>
<p>First we create a file <code>hello.cc</code>:

</p>
<pre><code>#include &lt;node.h&gt;
#include &lt;v8.h&gt;

using namespace v8;

Handle&lt;Value&gt; Method(const Arguments&amp; args) {
  HandleScope scope;
  return scope.Close(String::New(&quot;world&quot;));
}

void init(Handle&lt;Object&gt; target) {
  target-&gt;Set(String::NewSymbol(&quot;hello&quot;),
      FunctionTemplate::New(Method)-&gt;GetFunction());
}
NODE_MODULE(hello, init)</code></pre>
<p>Note that all Node addons must export an initialization function:

</p>
<pre><code>void Initialize (Handle&lt;Object&gt; target);
NODE_MODULE(module_name, Initialize)</code></pre>
<p>There is no semi-colon after <code>NODE_MODULE</code> as it&apos;s not a function (see <code>node.h</code>).

</p>
<p>The <code>module_name</code> needs to match the filename of the final binary (minus the
.node suffix).

</p>
<p>The source code needs to be built into <code>hello.node</code>, the binary Addon. To
do this we create a file called <code>wscript</code> which is python code and looks
like this:

</p>
<pre><code>srcdir = &apos;.&apos;
blddir = &apos;build&apos;
VERSION = &apos;0.0.1&apos;

def set_options(opt):
  opt.tool_options(&apos;compiler_cxx&apos;)

def configure(conf):
  conf.check_tool(&apos;compiler_cxx&apos;)
  conf.check_tool(&apos;node_addon&apos;)

def build(bld):
  obj = bld.new_task_gen(&apos;cxx&apos;, &apos;shlib&apos;, &apos;node_addon&apos;)
  obj.target = &apos;hello&apos;
  obj.source = &apos;hello.cc&apos;</code></pre>
<p>Running <code>node-waf configure build</code> will create a file
<code>build/default/hello.node</code> which is our Addon.

</p>
<p><code>node-waf</code> is just <a href="http://code.google.com/p/waf">WAF</a>, the python-based build system. <code>node-waf</code> is
provided for the ease of users.

</p>
<p>You can now use the binary addon in a Node project <code>hello.js</code> by pointing <code>require</code> to
the recently built module:

</p>
<pre><code>var addon = require(&apos;./build/Release/hello&apos;);

console.log(addon.hello()); // &apos;world&apos;</code></pre>
<p>Please see patterns below for further information or
</p>
<p><a href="https://github.com/pietern/hiredis-node">https://github.com/pietern/hiredis-node</a> for an example in production.


</p>
<h2>Addon patterns<span><a class="mark" href="#addons_addon_patterns" id="addons_addon_patterns">#</a></span></h2>
<p>Below are some addon patterns to help you get started. Consult the online
<a href="http://izs.me/v8-docs/main.html">v8 reference</a> for help with the various v8
calls, and v8&apos;s <a href="http://code.google.com/apis/v8/embed.html">Embedder&apos;s Guide</a>
for an explanation of several concepts used such as handles, scopes,
function templates, etc.

</p>
<p>To compile these examples, create the <code>wscript</code> file below and run
<code>node-waf configure build</code>:

</p>
<pre><code>srcdir = &apos;.&apos;
blddir = &apos;build&apos;
VERSION = &apos;0.0.1&apos;

def set_options(opt):
  opt.tool_options(&apos;compiler_cxx&apos;)

def configure(conf):
  conf.check_tool(&apos;compiler_cxx&apos;)
  conf.check_tool(&apos;node_addon&apos;)

def build(bld):
  obj = bld.new_task_gen(&apos;cxx&apos;, &apos;shlib&apos;, &apos;node_addon&apos;)
  obj.target = &apos;addon&apos;
  obj.source = [&apos;addon.cc&apos;]</code></pre>
<p>In cases where there is more than one <code>.cc</code> file, simply add the file name to the
<code>obj.source</code> array, e.g.:

</p>
<pre><code>obj.source = [&apos;addon.cc&apos;, &apos;myexample.cc&apos;]</code></pre>
<h3>Function arguments<span><a class="mark" href="#addons_function_arguments" id="addons_function_arguments">#</a></span></h3>
<p>The following pattern illustrates how to read arguments from JavaScript
function calls and return a result. This is the main and only needed source
<code>addon.cc</code>:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;

using namespace v8;

Handle&lt;Value&gt; Add(const Arguments&amp; args) {
  HandleScope scope;

  if (args.Length() &lt; 2) {
    ThrowException(Exception::TypeError(String::New(&quot;Wrong number of arguments&quot;)));
    return scope.Close(Undefined());
  }

  if (!args[0]-&gt;IsNumber() || !args[1]-&gt;IsNumber()) {
    ThrowException(Exception::TypeError(String::New(&quot;Wrong arguments&quot;)));
    return scope.Close(Undefined());
  }

  Local&lt;Number&gt; num = Number::New(args[0]-&gt;NumberValue() +
      args[1]-&gt;NumberValue());
  return scope.Close(num);
}

void Init(Handle&lt;Object&gt; target) {
  target-&gt;Set(String::NewSymbol(&quot;add&quot;),
      FunctionTemplate::New(Add)-&gt;GetFunction());
}

NODE_MODULE(addon, Init)</code></pre>
<p>You can test it with the following JavaScript snippet:

</p>
<pre><code>var addon = require(&apos;./build/Release/addon&apos;);

console.log( &apos;This should be eight:&apos;, addon.add(3,5) );</code></pre>
<h3>Callbacks<span><a class="mark" href="#addons_callbacks" id="addons_callbacks">#</a></span></h3>
<p>You can pass JavaScript functions to a C++ function and execute them from
there. Here&apos;s <code>addon.cc</code>:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;

using namespace v8;

Handle&lt;Value&gt; RunCallback(const Arguments&amp; args) {
  HandleScope scope;

  Local&lt;Function&gt; cb = Local&lt;Function&gt;::Cast(args[0]);
  const unsigned argc = 1;
  Local&lt;Value&gt; argv[argc] = { Local&lt;Value&gt;::New(String::New(&quot;hello world&quot;)) };
  cb-&gt;Call(Context::GetCurrent()-&gt;Global(), argc, argv);

  return scope.Close(Undefined());
}

void Init(Handle&lt;Object&gt; target) {
  target-&gt;Set(String::NewSymbol(&quot;runCallback&quot;),
      FunctionTemplate::New(RunCallback)-&gt;GetFunction());
}

NODE_MODULE(addon, Init)</code></pre>
<p>To test it run the following JavaScript snippet:

</p>
<pre><code>var addon = require(&apos;./build/Release/addon&apos;);

addon.runCallback(function(msg){
  console.log(msg); // &apos;hello world&apos;
});</code></pre>
<h3>Object factory<span><a class="mark" href="#addons_object_factory" id="addons_object_factory">#</a></span></h3>
<p>You can create and return new objects from within a C++ function with this
<code>addon.cc</code> pattern, which returns an object with property <code>msg</code> that echoes
the string passed to <code>createObject()</code>:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;

using namespace v8;

Handle&lt;Value&gt; CreateObject(const Arguments&amp; args) {
  HandleScope scope;

  Local&lt;Object&gt; obj = Object::New();
  obj-&gt;Set(String::NewSymbol(&quot;msg&quot;), args[0]-&gt;ToString());

  return scope.Close(obj);
}

void Init(Handle&lt;Object&gt; target) {
  target-&gt;Set(String::NewSymbol(&quot;createObject&quot;),
      FunctionTemplate::New(CreateObject)-&gt;GetFunction());
}

NODE_MODULE(addon, Init)</code></pre>
<p>To test it in JavaScript:

</p>
<pre><code>var addon = require(&apos;./build/Release/addon&apos;);

var obj1 = addon.createObject(&apos;hello&apos;);
var obj2 = addon.createObject(&apos;world&apos;);
console.log(obj1.msg+&apos; &apos;+obj2.msg); // &apos;hello world&apos;</code></pre>
<h3>Function factory<span><a class="mark" href="#addons_function_factory" id="addons_function_factory">#</a></span></h3>
<p>This pattern illustrates how to create and return a JavaScript function that
wraps a C++ function:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;

using namespace v8;

Handle&lt;Value&gt; MyFunction(const Arguments&amp; args) {
  HandleScope scope;
  return scope.Close(String::New(&quot;hello world&quot;));
}

Handle&lt;Value&gt; CreateFunction(const Arguments&amp; args) {
  HandleScope scope;

  Local&lt;FunctionTemplate&gt; tpl = FunctionTemplate::New(MyFunction);
  Local&lt;Function&gt; fn = tpl-&gt;GetFunction();
  fn-&gt;SetName(String::NewSymbol(&quot;theFunction&quot;)); // omit this to make it anonymous

  return scope.Close(fn);
}

void Init(Handle&lt;Object&gt; target) {
  target-&gt;Set(String::NewSymbol(&quot;createFunction&quot;),
      FunctionTemplate::New(CreateFunction)-&gt;GetFunction());
}

NODE_MODULE(addon, Init)</code></pre>
<p>To test:

</p>
<pre><code>var addon = require(&apos;./build/Release/addon&apos;);

var fn = addon.createFunction();
console.log(fn()); // &apos;hello world&apos;</code></pre>
<h3>Wrapping C++ objects<span><a class="mark" href="#addons_wrapping_c_objects" id="addons_wrapping_c_objects">#</a></span></h3>
<p>Here we will create a wrapper for a C++ object/class <code>MyObject</code> that can be
instantiated in JavaScript through the <code>new</code> operator. First prepare the main
module <code>addon.cc</code>:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;
#include &quot;myobject.h&quot;

using namespace v8;

void InitAll(Handle&lt;Object&gt; target) {
  MyObject::Init(target);
}

NODE_MODULE(addon, InitAll)</code></pre>
<p>Then in <code>myobject.h</code> make your wrapper inherit from <code>node::ObjectWrap</code>:

</p>
<pre><code>#ifndef MYOBJECT_H
#define MYOBJECT_H

#include &lt;node.h&gt;

class MyObject : public node::ObjectWrap {
 public:
  static void Init(v8::Handle&lt;v8::Object&gt; target);

 private:
  MyObject();
  ~MyObject();

  static v8::Handle&lt;v8::Value&gt; New(const v8::Arguments&amp; args);
  static v8::Handle&lt;v8::Value&gt; PlusOne(const v8::Arguments&amp; args);
  double counter_;
};

#endif</code></pre>
<p>And in <code>myobject.cc</code> implement the various methods that you want to expose.
Here we expose the method <code>plusOne</code> by adding it to the constructor&apos;s
prototype:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;
#include &quot;myobject.h&quot;

using namespace v8;

MyObject::MyObject() {};
MyObject::~MyObject() {};

void MyObject::Init(Handle&lt;Object&gt; target) {
  // Prepare constructor template
  Local&lt;FunctionTemplate&gt; tpl = FunctionTemplate::New(New);
  tpl-&gt;SetClassName(String::NewSymbol(&quot;MyObject&quot;));
  tpl-&gt;InstanceTemplate()-&gt;SetInternalFieldCount(1);
  // Prototype
  tpl-&gt;PrototypeTemplate()-&gt;Set(String::NewSymbol(&quot;plusOne&quot;),
      FunctionTemplate::New(PlusOne)-&gt;GetFunction());

  Persistent&lt;Function&gt; constructor = Persistent&lt;Function&gt;::New(tpl-&gt;GetFunction());
  target-&gt;Set(String::NewSymbol(&quot;MyObject&quot;), constructor);
}

Handle&lt;Value&gt; MyObject::New(const Arguments&amp; args) {
  HandleScope scope;

  MyObject* obj = new MyObject();
  obj-&gt;counter_ = args[0]-&gt;IsUndefined() ? 0 : args[0]-&gt;NumberValue();
  obj-&gt;Wrap(args.This());

  return args.This();
}

Handle&lt;Value&gt; MyObject::PlusOne(const Arguments&amp; args) {
  HandleScope scope;

  MyObject* obj = ObjectWrap::Unwrap&lt;MyObject&gt;(args.This());
  obj-&gt;counter_ += 1;

  return scope.Close(Number::New(obj-&gt;counter_));
}</code></pre>
<p>Test it with:

</p>
<pre><code>var addon = require(&apos;./build/Release/addon&apos;);

var obj = new addon.MyObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13</code></pre>
<h3>Factory of wrapped objects<span><a class="mark" href="#addons_factory_of_wrapped_objects" id="addons_factory_of_wrapped_objects">#</a></span></h3>
<p>This is useful when you want to be able to create native objects without
explicitly instantiating them with the <code>new</code> operator in JavaScript, e.g.

</p>
<pre><code>var obj = addon.createObject();
// instead of:
// var obj = new addon.Object();</code></pre>
<p>Let&apos;s register our <code>createObject</code> method in <code>addon.cc</code>:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;
#include &quot;myobject.h&quot;

using namespace v8;

Handle&lt;Value&gt; CreateObject(const Arguments&amp; args) {
  HandleScope scope;
  return scope.Close(MyObject::NewInstance(args));
}

void InitAll(Handle&lt;Object&gt; target) {
  MyObject::Init();

  target-&gt;Set(String::NewSymbol(&quot;createObject&quot;),
      FunctionTemplate::New(CreateObject)-&gt;GetFunction());
}

NODE_MODULE(addon, InitAll)</code></pre>
<p>In <code>myobject.h</code> we now introduce the static method <code>NewInstance</code> that takes
care of instantiating the object (i.e. it does the job of <code>new</code> in JavaScript):

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#ifndef MYOBJECT_H
#define MYOBJECT_H

#include &lt;node.h&gt;

class MyObject : public node::ObjectWrap {
 public:
  static void Init();
  static v8::Handle&lt;v8::Value&gt; NewInstance(const v8::Arguments&amp; args);

 private:
  MyObject();
  ~MyObject();

  static v8::Persistent&lt;v8::Function&gt; constructor;
  static v8::Handle&lt;v8::Value&gt; New(const v8::Arguments&amp; args);
  static v8::Handle&lt;v8::Value&gt; PlusOne(const v8::Arguments&amp; args);
  double counter_;
};

#endif</code></pre>
<p>The implementation is similar to the above in <code>myobject.cc</code>:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;
#include &quot;myobject.h&quot;

using namespace v8;

MyObject::MyObject() {};
MyObject::~MyObject() {};

Persistent&lt;Function&gt; MyObject::constructor;

void MyObject::Init() {
  // Prepare constructor template
  Local&lt;FunctionTemplate&gt; tpl = FunctionTemplate::New(New);
  tpl-&gt;SetClassName(String::NewSymbol(&quot;MyObject&quot;));
  tpl-&gt;InstanceTemplate()-&gt;SetInternalFieldCount(1);
  // Prototype
  tpl-&gt;PrototypeTemplate()-&gt;Set(String::NewSymbol(&quot;plusOne&quot;),
      FunctionTemplate::New(PlusOne)-&gt;GetFunction());

  constructor = Persistent&lt;Function&gt;::New(tpl-&gt;GetFunction());
}

Handle&lt;Value&gt; MyObject::New(const Arguments&amp; args) {
  HandleScope scope;

  MyObject* obj = new MyObject();
  obj-&gt;counter_ = args[0]-&gt;IsUndefined() ? 0 : args[0]-&gt;NumberValue();
  obj-&gt;Wrap(args.This());

  return args.This();
}

Handle&lt;Value&gt; MyObject::NewInstance(const Arguments&amp; args) {
  HandleScope scope;

  const unsigned argc = 1;
  Handle&lt;Value&gt; argv[argc] = { args[0] };
  Local&lt;Object&gt; instance = constructor-&gt;NewInstance(argc, argv);

  return scope.Close(instance);
}

Handle&lt;Value&gt; MyObject::PlusOne(const Arguments&amp; args) {
  HandleScope scope;

  MyObject* obj = ObjectWrap::Unwrap&lt;MyObject&gt;(args.This());
  obj-&gt;counter_ += 1;

  return scope.Close(Number::New(obj-&gt;counter_));
}</code></pre>
<p>Test it with:

</p>
<pre><code>var addon = require(&apos;./build/Release/addon&apos;);

var obj = addon.createObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13

var obj2 = addon.createObject(20);
console.log( obj2.plusOne() ); // 21
console.log( obj2.plusOne() ); // 22
console.log( obj2.plusOne() ); // 23</code></pre>
<h3>Passing wrapped objects around<span><a class="mark" href="#addons_passing_wrapped_objects_around" id="addons_passing_wrapped_objects_around">#</a></span></h3>
<p>In addition to wrapping and returning C++ objects, you can pass them around
by unwrapping them with Node&apos;s <code>node::ObjectWrap::Unwrap</code> helper function.
In the following <code>addon.cc</code> we introduce a function <code>add()</code> that can take on two
<code>MyObject</code> objects:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;
#include &quot;myobject.h&quot;

using namespace v8;

Handle&lt;Value&gt; CreateObject(const Arguments&amp; args) {
  HandleScope scope;
  return scope.Close(MyObject::NewInstance(args));
}

Handle&lt;Value&gt; Add(const Arguments&amp; args) {
  HandleScope scope;

  MyObject* obj1 = node::ObjectWrap::Unwrap&lt;MyObject&gt;(
      args[0]-&gt;ToObject());
  MyObject* obj2 = node::ObjectWrap::Unwrap&lt;MyObject&gt;(
      args[1]-&gt;ToObject());

  double sum = obj1-&gt;Val() + obj2-&gt;Val();
  return scope.Close(Number::New(sum));
}

void InitAll(Handle&lt;Object&gt; target) {
  MyObject::Init();

  target-&gt;Set(String::NewSymbol(&quot;createObject&quot;),
      FunctionTemplate::New(CreateObject)-&gt;GetFunction());

  target-&gt;Set(String::NewSymbol(&quot;add&quot;),
      FunctionTemplate::New(Add)-&gt;GetFunction());
}

NODE_MODULE(addon, InitAll)</code></pre>
<p>To make things interesting we introduce a public method in <code>myobject.h</code> so we
can probe private values after unwrapping the object:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#ifndef MYOBJECT_H
#define MYOBJECT_H

#include &lt;node.h&gt;

class MyObject : public node::ObjectWrap {
 public:
  static void Init();
  static v8::Handle&lt;v8::Value&gt; NewInstance(const v8::Arguments&amp; args);
  double Val() const { return val_; }

 private:
  MyObject();
  ~MyObject();

  static v8::Persistent&lt;v8::Function&gt; constructor;
  static v8::Handle&lt;v8::Value&gt; New(const v8::Arguments&amp; args);
  double val_;
};

#endif</code></pre>
<p>The implementation of <code>myobject.cc</code> is similar as before:

</p>
<pre><code>#define BUILDING_NODE_EXTENSION
#include &lt;node.h&gt;
#include &quot;myobject.h&quot;

using namespace v8;

MyObject::MyObject() {};
MyObject::~MyObject() {};

Persistent&lt;Function&gt; MyObject::constructor;

void MyObject::Init() {
  // Prepare constructor template
  Local&lt;FunctionTemplate&gt; tpl = FunctionTemplate::New(New);
  tpl-&gt;SetClassName(String::NewSymbol(&quot;MyObject&quot;));
  tpl-&gt;InstanceTemplate()-&gt;SetInternalFieldCount(1);

  constructor = Persistent&lt;Function&gt;::New(tpl-&gt;GetFunction());
}

Handle&lt;Value&gt; MyObject::New(const Arguments&amp; args) {
  HandleScope scope;

  MyObject* obj = new MyObject();
  obj-&gt;val_ = args[0]-&gt;IsUndefined() ? 0 : args[0]-&gt;NumberValue();
  obj-&gt;Wrap(args.This());

  return args.This();
}

Handle&lt;Value&gt; MyObject::NewInstance(const Arguments&amp; args) {
  HandleScope scope;

  const unsigned argc = 1;
  Handle&lt;Value&gt; argv[argc] = { args[0] };
  Local&lt;Object&gt; instance = constructor-&gt;NewInstance(argc, argv);

  return scope.Close(instance);
}</code></pre>
<p>Test it with:

</p>
<pre><code>var addon = require(&apos;./build/Release/addon&apos;);

var obj1 = addon.createObject(10);
var obj2 = addon.createObject(20);
var result = addon.add(obj1, obj2);

console.log(result); // 30</code></pre>

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nodejs 0.6.12~dfsg1-1ubuntu1 / usr / share / doc / nodejs / api / addons.html
