## page was renamed from PyLons/call-cycle
<<TableOfContents>>

= PyLons 请求生命周期 =

本文对 PyLons 内部调用过程的大致轮廓进行了简单的勾勒. 

首先通过命令 {{{paster create --template=PyLons yourproject}}} 创建一个项目. 然后 ==>

" {{{yourproject_dir::command}}} "
{{{
# 读取配置文件并启动服务器和应用程序
paster serve development.ini  ==>
}}}

" {{{yourproject_dir::development.ini}}} "
{{{
#PasteScript 的命令会通过配置文件中指定的 egg 的 entry_points 找到相应的对象
[server:main]
# 指定 paster serve 使用的 web 服务器
use = egg:Paste#http  
[app:main]
use = egg:yourproject  ==>
}}}

" {{{yourproject_dir/setup.py}}} "
{{{#!python
entry_points="""
    [paste.app_factory]
    main=yourproject:make_app  ==>
    ...
"""
}}}

" {{{yourproject.__init__.py}}} "
{{{#!python
from yourproject.config.middleware import make_app  ==>
}}}

" {{{yourproject.config.middleware.py}}} "
{{{#!python
def make_app(...):
    ...
    # 核心 app
    app = PyLons.wsgiapp.PyLonsApp(config)  ==>
    app = ConfigMiddleware(app, ... )
    # YOUR MIDDLEWARE
    # 将 HTTPExceptions 转换成 HTTP responses
    app = httpexceptions.make_middleware(app, ... )
    app = ErrorHandler(app, ... )
    # 处理静态文件
    static_app = StaticURLParser(...)
    # 处理 webhelpers 中使用到的 javascript 文件
    javascripts_app = StaticJavascripts()
    # 该中间件的作用是: 对列表中的 app 一个一个尝试, 如果 app 产生 404 错误则继续试下一个
    app = Cascade([static_app, javascripts_app, app])
    app = ErrorDocuments(app, ... )
    # 
    app = RegistryManager(app)
    return app
}}}

" {{{PyLons.wsgiapp.py}}} "
{{{#!python
class PyLonsApp(object):
    def __init__(self, ...):
        self.app = PyLonsBaseWSGIApp(... ) ==>
    def __call__(self, environ, start_response):
        ...
        return self.app(environ, start_response)
}}}

" {{{PyLons.wsgiapp.py}}} "
{{{#!python
class PyLonsBaseWSGIApp(object):
    def __init__(self ... )
        ...
    def __call__(self, environ, start_response):
        #正常情况下大致执行流程:
        self.setup_app_env(...)
        req = PyLons.request._current_obj()
        # 通过 url dispatcher (routes) 找到相应 controller
        controller = self.resolve(environ, start_response)
        # 执行该 controller
        response = self.dispatch(controller, environ, start_response)
        status, response_headers, content = response.wsgi_response()
        start_response(status, response_headers)
        return content
        ...

    def dispatch(self, controller, environ, start_response):
        # 如果是 class, 则实例化之
        if not hasattr(controller, '__class__') or \
            getattr(controller, '__class__') == type:
            controller = controller()
        
        # 把它当个 wsgi application 调用之
        return controller(environ, start_response) ==>
}}}

" {{{PyLons.controllers.py}}} "
{{{#!python
class Controller(object):
    ...
    def _dispatch_call(self):
        """将请求分发到具体函数"""
        action = self._req.environ['PyLons.routes_dict'].get('action')
        action_method = action.replace('-', '_')
        func = getattr(self, action_method, None)
        if isinstance(func, types.MethodType):
            response = self._inspect_call(func)
        else:
            if asbool(CONFIG['global_conf'].get('debug')):
                raise NotImplementedError('Action %s is not implemented' % action)
            else:
                response = PyLons.Response(code=404)
        return response

class WSGIController(Controller):
    ...
    def __call__(self, environ, start_response):
        self.start_response = start_response
        match = environ['PyLons.routes_dict']
        self._req = PyLons.request._current_obj()
        
        # 不调用私有方法
        if match.get('action').startswith('_'):
            return PyLons.Response(code=404)
        
        if hasattr(self, '__before__'):
            self._inspect_call(self.__before__)
        # 此方法请看上面的 Controller 类
        response = self._dispatch_call()
        if hasattr(self, '__after__'):
            self._inspect_call(self.__after__)
        
        if hasattr(response, 'wsgi_response'):
            # 估计返回的是 paste.wsgiwrappers.WSGIResponse 
            status, response_headers, content = response.wsgi_response()
            start_response(status, response_headers)
        
            # 如果是在测试, 将 response 放到测试环境中去
            if environ.get('paste.testing'):
                environ['paste.testing_variables']['response'] = response
            response = content
        
        # 看来是个 WSGI应用程序 的 Response
        return response

class RPCController(object):
    ...
}}}

= 结论 =

从中我们大致可以看出 PyLons 扩展的潜力:

 * 首先用户代码中通过命令 {{{paster controller controllername}}} 生成的 {{{Controller}}} 都默认继承自 {{{yourproject.lib.base.BaseController}}} ( 后者继承自 {{{PyLons.controllers.WSGIController}}} ), 那么修改 {{{BaseController}}} 可以影响到所有默认生成的 {{{Controller}}}
 * Controller 中有两个特殊的方法 {{{__before__}}} 和 {{{__after__}}}, 这个两个方法的行为可以影响到当前 {{{controller}}} 中所有 {{{action}}}
 * 在 {{{yourproject/config/middleware.py}}} 添加其他 wsgi中间件.
 * 在 {{{Controller}}} 中直接调用标准的 WSGI 应用程序 并返回其结果
 * 而且注意到 {{{PyLonsApp}}} 和 {{{WSGIController}}} 都是 WSGI应用程序, 不过里面通过 {{{environ}}} 依赖到一些其他的东西, 比如 routes, 单独拿出来用的意义似乎不太大  :-(
 ....