這篇文章主要介紹了使用Node.js為其他程序編寫擴展的基本方法 ,文中示例是通過Node讓JavaScript代碼與C++應用產生交互,需要的朋友可以參考下
准備開始
首先我們用下面的目錄結構來創建一個節點通知(node-notify)文件夾.
代碼如下:
.
|-- build/ # This is where our 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 # This is our build configuration used by node-waf
這個看起來很漂亮的tree 用通用的 tree 生成.
現在讓我來創建測試腳本demo.js 和決定我們擴展的API前期看起來應該像:
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8// 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");
編寫我們的Node.js擴展
Init方法
為了創建一個Node.js擴展，我們需要編寫一個繼承node::ObjectWrap的C++類。 ObjectWrap 實現了讓我們更容易與Javascript交互的公共方法
我們先來編寫類的基本框架：
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37#include
#include
// We will need the following libraries for our GTK+ notification
#include
#include
#include
using namespace v8;
class Gtknotify : node::ObjectWrap {
private:
public:
Gtknotify() {}
~Gtknotify() {}
static void Init(Handle 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?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
extern "C" { // Cause of name mangling in C++, we use extern C here
static void init(Handle target) {
Gtknotify::Init(target);
}
// @see http://github.com/ry/node/blob/v0.2.0/src/node.h#L101
NODE_MODULE(gtknotify, init);
}
現在，我們必須把下面的代碼編寫到我們的Init()方法中：
聲明構造函數，並將其綁定到我們的目標變量。var n = require("notification");將綁定notification() 到 n:n.notification().
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14// 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
// Make it persistent and assign it to persistent_function_template which is a static attribute of our class.
Gtknotify::persistent_function_template = v8::Persistent
// 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());
聲明屬性:n.title 和n.icon.
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5// 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()
聲明原型方法：n.send()
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3// 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：
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22// Our constructor
static v8::Persistent
static void Init(Handle target) {
v8::HandleScope scope; // used by v8 for garbage collection
// Our constructor
v8::Local
Gtknotify::persistent_function_template = v8::Persistent
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());
}
剩下要做的就是編寫我們在Init方法中用的C++方法：New,GetTitle,SetTitle,GetIcon,SetIcon,Send
構造器方法: New()
New() 方法創建了我們自定義類的新實例(一個 Gtknotify 對象)，並設置一些初始值，然後返回該對象的 JavaScript 處理。這是 JavaScript 使用 new 操作符調用構造函數的期望行為。
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18std::string title;
std::string icon;
// new notification()
static Handle
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代碼，可以歸結為 C++ 和 JavaScript (v8) 之間的值轉換。
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24// this.title
static v8::Handle
// Extract the C++ request object from the JavaScript wrapper.
Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap
return v8::String::New(gtknotify_instance->title.c_str());
}
// this.title=
static void SetTitle(Local
Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap
v8::String::Utf8Value v8str(value);
gtknotify_instance->title = *v8str;
}
// this.icon
static v8::Handle
// Extract the C++ request object from the JavaScript wrapper.
Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap
return v8::String::New(gtknotify_instance->icon.c_str());
}
// this.icon=
static void SetIcon(Local
Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap
v8::String::Utf8Value v8str(value);
gtknotify_instance->icon = *v8str;
}
原型方法: Send()
首先我們抽取 C++ 對象的 this 引用，然後使用對象的屬性來構建通知並顯示。
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18// this.send()
static v8::Handle
v8::HandleScope scope;
// Extract C++ object reference from "this"
Gtknotify* gtknotify_instance = node::ObjectWrap::Unwrap
// 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);
}
編譯擴展
node-waf 是一個構建工具，用來編譯 Node 的擴展，這是 waf 的基本封裝。構建過程可通過名為 wscript 的文件進行配置。
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17def 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']
現在我們已經准備好要開始構建了，在頂級目錄下運行如下命令：
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：
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6$ node
> var notif = require('./build/default/gtknotify.node');
> n = new notif.notification();
{ icon: 'terminal', title: 'Node.js' }
> n.send("Hello World!");
true
上述的代碼將在你的屏幕右上方顯示一個通知信息。
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的擴展包是非常簡單的. 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 :
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35{
// 擴展的名稱 (不要在名稱中包含node 或者 js, 這是隱式關鍵字).
// 這是通過require() 導入擴展的名稱.
"name" : "notify",
// Version should be http://semver.org/ compliant
"version" : "v0.1.0"
// 這些腳本將在調用npm安裝和npm卸載的時候運行.
, "scripts" : {
"preinstall" : "node-waf configure && node-waf build"
, "preuninstall" : "rm -rf build/*"
}
// 這是構建我們擴展的相對路徑.
, "main" : "build/default/gtknotify.node"
// 以下是可選字段:
, "description" : "Description of the extension...."
, "homepage" : "https://github.com/olalonde/node-notify"
, "author" : {
"name" : "Olivier Lalonde"
, "email" : "[email protected]"
, "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, 可以通過 npm help json 獲取文檔. 注意 大多數字段都是可選的.
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 通過這個命令你可以創建一個到你開發目錄的鏈接,當你的代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庫發布到網上. 首先你要先創建一個賬戶:
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下一步, 回到你的根目錄編碼並且運行:
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就是這樣, 你的包現在已經可以被任何人通過npm install 你的包名命令來安裝了.