使用Node.js為其他程式編寫擴充功能的基本方法_node.js

 準備開始

首先我們用下面的目錄結構來建立一個節點通知(node-notify)資料夾.
 

複製程式碼 程式碼如下:

.
|-- build/                   # extension is built.
|-- demo/
|   `-- demo.js              # This is a demo Node.js script to test our extension.
|-- src/
|   `-- node_gtknotify.cpp   # This is the where we do the mapping from C to Javascript.
`-- wscript                  # 以> our build configuration used by node-waf

這個看起來很漂亮的tree 用通用的 tree 產生.

現在讓我來建立測試腳本demo.js 和決定我們擴充的API前期看起來應該像:
 

// This loads our extension on the notify variable.
// It will only load a constructor function, notify.notification().
var notify = require("../build/default/gtknotify.node"); // path to our extension
 
var notification = new notify.notification();
notification.title = "Notification title";
notification.icon = "emblem-default"; // see /usr/share/icons/gnome/16x16
notification.send("Notification message");

寫我們的Node.js擴充
Init方法

為了建立一個Node.js擴展，我們需要寫一個繼承node::ObjectWrap的C 類別。 ObjectWrap 實作了讓我們更容易與Javascript互動的公共方法

我們先來寫類別的基本架構：
 

#include <v8.h> // v8 is the Javascript engine used by QNode
#include <node.h>
// We will need the following libraries for our GTK+ notification
#include <string>
#include <gtkmm.h>
#include <libnotifymm.h>
 
using namespace v8;
 
class Gtknotify : node::ObjectWrap {
 private:
 public:
  Gtknotify() {}
  ~Gtknotify() {}
  static void Init(Handle<Object> target) {
   // This is what Node will call when we load the extension through require(), see boilerplate code below.
  }
};
 
/*
 * WARNING: Boilerplate code ahead.
 *
 * See https://www.cloudkick.com/blog/2010/aug/23/writing-nodejs-native-extensions/ & http://www.freebsd.org/cgi/man.cgi&#63;query=dlsym
 * 
 * Thats it for actual interfacing with v8, finally we need to let Node.js know how to dynamically load our code.
 * Because a Node.js extension can be loaded at runtime from a shared object, we need a symbol that the dlsym function can find,
 * so we do the following: 
 */
 
v8::Persistent<FunctionTemplate> Gtknotify::persistent_function_template;
extern "C" { // Cause of name mangling in C++, we use extern C here
 static void init(Handle<Object> target) {
  Gtknotify::Init(target);
 }
 // @see http://github.com/ry/node/blob/v0.2.0/src/node.h#L101
 NODE_MODULE(gtknotify, init);
}

現在，我們必須把下面的程式碼寫到我們的Init()方法：

    宣告建構函數，並將其綁定到我們的目標變數。 var n = require("notification");將綁定notification() 到 n:n.notification().

// Wrap our C++ New() method so that it's accessible from Javascript
  // This will be called by the new operator in Javascript, for example: new notification();
  v8::Local<FunctionTemplate> local_function_template = v8::FunctionTemplate::New(New);
   
  // Make it persistent and assign it to persistent_function_template which is a static attribute of our class.
  Gtknotify::persistent_function_template = v8::Persistent<FunctionTemplate>::New(local_function_template);
   
  // Each JavaScript object keeps a reference to the C++ object for which it is a wrapper with an internal field.
  Gtknotify::persistent_function_template->InstanceTemplate()->SetInternalFieldCount(1); // 1 since a constructor function only references 1 object
  // Set a "class" name for objects created with our constructor
  Gtknotify::persistent_function_template->SetClassName(v8::String::NewSymbol("Notification"));
   
  // Set the "notification" property of our target variable and assign it to our constructor function
  target->Set(String::NewSymbol("notification"), Gtknotify::persistent_function_template->GetFunction());

    宣告屬性:n.title 和n.icon.
 

  // Set property accessors
  // SetAccessor arguments: Javascript property name, C++ method that will act as the getter, C++ method that will act as the setter
  Gtknotify::persistent_function_template->InstanceTemplate()->SetAccessor(String::New("title"), GetTitle, SetTitle);
  Gtknotify::persistent_function_template->InstanceTemplate()->SetAccessor(String::New("icon"), GetIcon, SetIcon);
  // For instance, n.title = "foo" will now call SetTitle("foo"), n.title will now call GetTitle()

    宣告原型方法：n.send()
   

  // This is a Node macro to help bind C++ methods to Javascript methods (see https://github.com/joyent/node/blob/v0.2.0/src/node.h#L34)
  // Arguments: our constructor function, Javascript method name, C++ method name
  NODE_SET_PROTOTYPE_METHOD(Gtknotify::persistent_function_template, "send", Send);

現在我們的Init()方法看起來應該是這樣的：
 

// Our constructor
static v8::Persistent<FunctionTemplate> persistent_function_template;
 
static void Init(Handle<Object> target) {
 v8::HandleScope scope; // used by v8 for garbage collection
 
 // Our constructor
 v8::Local<FunctionTemplate> local_function_template = v8::FunctionTemplate::New(New);
 Gtknotify::persistent_function_template = v8::Persistent<FunctionTemplate>::New(local_function_template);
 Gtknotify::persistent_function_template->InstanceTemplate()->SetInternalFieldCount(1); // 1 since this is a constructor function
 Gtknotify::persistent_function_template->SetClassName(v8::String::NewSymbol("Notification"));
 
 // Our getters and setters
 Gtknotify::persistent_function_template->InstanceTemplate()->SetAccessor(String::New("title"), GetTitle, SetTitle);
 Gtknotify::persistent_function_template->InstanceTemplate()->SetAccessor(String::New("icon"), GetIcon, SetIcon);
 
 // Our methods
 NODE_SET_PROTOTYPE_METHOD(Gtknotify::persistent_function_template, "send", Send);
 
 // Binding our constructor function to the target variable
 target->Set(String::NewSymbol("notification"), Gtknotify::persistent_function_template->GetFunction());
}

剩下要做的就是寫我們在Init方法中使用的C 方法：New,GetTitle,SetTitle,GetIcon,SetIcon,Send

構造器方法: New()

New() 方法建立了我們自訂類別的新實例(一個 Gtknotify 物件)，並設定一些初始值，然後傳回該物件的 JavaScript 處理。這是 JavaScript 使用 new 運算子呼叫建構函數的期望行為。

 
std::string title;
std::string icon;
 
// new notification()
static Handle<Value> New(const Arguments& args) {
 HandleScope scope;
 Gtknotify* gtknotify_instance = new Gtknotify();
 // Set some default values
 gtknotify_instance->title = "Node.js";
 gtknotify_instance->icon = "terminal";
 
 // Wrap our C++ object as a Javascript object
 gtknotify_instance->Wrap(args.This());
 
 return args.This();
}
getters 和 setters: GetTitle(), SetTitle(), GetIcon(), SetIcon()

下面主要是一些樣板程式碼，可以歸結為 C 和 JavaScript (v8) 之間的值轉換。
 

// this.title
static v8::Handle<Value> GetTitle(v8::Local<v8::String> property, const v8::AccessorInfo& info) {
 // Extract the C++ request object from the JavaScript wrapper.
 Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap<Gtknotify>(info.Holder());
 return v8::String::New(gtknotify_instance->title.c_str());
}
// this.title=
static void SetTitle(Local<String> property, Local<Value> value, const AccessorInfo& info) {
 Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap<Gtknotify>(info.Holder());
 v8::String::Utf8Value v8str(value);
 gtknotify_instance->title = *v8str;
}
// this.icon
static v8::Handle<Value> GetIcon(v8::Local<v8::String> property, const v8::AccessorInfo& info) {
 // Extract the C++ request object from the JavaScript wrapper.
 Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap<Gtknotify>(info.Holder());
 return v8::String::New(gtknotify_instance->icon.c_str());
}
// this.icon=
static void SetIcon(Local<String> property, Local<Value> value, const AccessorInfo& info) {
 Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap<Gtknotify>(info.Holder());
 v8::String::Utf8Value v8str(value);
 gtknotify_instance->icon = *v8str;
}

原型方法: Send()

首先我們抽取 C 物件的 this 引用，然後使用物件的屬性來建立通知並顯示。
 

// this.send()
static v8::Handle<Value> Send(const Arguments& args) {
 v8::HandleScope scope;
 // Extract C++ object reference from "this"
 Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap<Gtknotify>(args.This());
 
 // Convert first argument to V8 String
 v8::String::Utf8Value v8str(args[0]);
 
 // For more info on the Notify library: http://library.gnome.org/devel/libnotify/0.7/NotifyNotification.html
 Notify::init("Basic");
 // Arguments: title, content, icon
 Notify::Notification n(gtknotify_instance->title.c_str(), *v8str, gtknotify_instance->icon.c_str()); // *v8str points to the C string it wraps
 // Display the notification
 n.show();
 // Return value
 return v8::Boolean::New(true);
}

編譯擴充

node-waf 是一個建置工具，用來編譯 Node 的擴展，這是 waf 的基本封裝。建置過程可透過名為 wscript 的檔案進行設定。
 

def set_options(opt):
 opt.tool_options("compiler_cxx")
 
def configure(conf):
 conf.check_tool("compiler_cxx")
 conf.check_tool("node_addon")
 # This will tell the compiler to link our extension with the gtkmm and libnotifymm libraries.
 conf.check_cfg(package='gtkmm-2.4', args='--cflags --libs', uselib_store='LIBGTKMM')
 conf.check_cfg(package='libnotifymm-1.0', args='--cflags --libs', uselib_store='LIBNOTIFYMM')
 
def build(bld):
 obj = bld.new_task_gen("cxx", "shlib", "node_addon")
 obj.cxxflags = ["-g", "-D_FILE_OFFSET_BITS=64", "-D_LARGEFILE_SOURCE", "-Wall"]
 # This is the name of our extension.
 obj.target = "gtknotify"
 obj.source = "src/node_gtknotify.cpp"
 obj.uselib = ['LIBGTKMM', 'LIBNOTIFYMM']

現在我們已經準備好要開始建置了，在頂層目錄下執行以下指令：

 
node-waf configure && node-waf build

如果一切正常，我們將得到編譯過的擴展，位於：./build/default/gtknotify.node ，來試試：
 

$ node
> var notif = require('./build/default/gtknotify.node');
> n = new notif.notification();
{ icon: 'terminal', title: 'Node.js' }
> n.send("Hello World!");
true

上述的程式碼將在你的螢幕右上方顯示一個通知訊息。

打成npm包

這是非常酷的, 但是怎樣與Node社區分享你的努力的成果呢? 這才是npm主要的用途: 使它更加容易擴展和分發.

打npm的擴充包是非常簡單的. 你所要做的就是在你的頂級目錄中創建一個包含你的擴展信息的文件package.json :
 

{
 // 扩展的名称 (不要在名称中包含node 或者 js, 这是隐式关键字).
 // 这是通过require() 导入扩展的名称.
 
 "name" : "notify",
 
 // Version should be http://semver.org/ compliant
 
 "version" : "v0.1.0"
 
 // 这些脚本将在调用npm安装和npm卸载的时候运行.
 
 , "scripts" : {
   "preinstall" : "node-waf configure && node-waf build"
   , "preuninstall" : "rm -rf build/*"
  }
 
 // 这是构建我们扩展的相对路径.
 
 , "main" : "build/default/gtknotify.node"
 
 // 以下是可选字段:
 
 , "description" : "Description of the extension...."
 , "homepage" : "https://github.com/olalonde/node-notify"
 , "author" : {
   "name" : "Olivier Lalonde"
   , "email" : "olalonde@gmail.com"
   , "url" : "http://www.syskall.com/"
  }
 , "repository" : {
   "type" : "git"
   , "url" : "https://github.com/olalonde/node-notify.git"
  }
}

關於package.json 格式的更多細節, 可以透過 npm help json 取得文件. 注意 大多數欄位都是可選的.

你現在可以在你的頂級目錄中通過運行npm install 來安裝你的新的npm包了. 如果一切順利的話, 應該可以簡單的加載你的擴展var notify = require('你的包名');.另外一個比較有用的命令式npm link 透過這個指令你可以建立一個到你開發目錄的連結,當你的程式碼發生變化時不必每次都去安裝/卸載.

假設你寫了一個很酷的擴展, 你可能想要在中央npm庫發佈到網上. 首先你要先創建一個帳戶:

 

$ npm adduser

下一步, 回到你的根目录编码并且运行:

 
$ npm publish

就是这样, 你的包现在已经可以被任何人通过npm install 你的包名命令来安装了.