openstack nova源码分析之api(二)

华风

三. nova api中的WSGI application
1. paste.deploy
官方文档：http://pythonpaste.org/deploy/
paste是python的一个WSGI工具包，在WSGI的基础上包装了几层，让应用管理和实现变得方便。
几个概念：
app:WSGI application，实现应用端，响应请求的方法，应当是一个callable object，在被call时传入参数为(env,start_response),app需要完成的任务是响应envrion中的请求，准备好响应头和消息体，然后交给start_response处理，并返回响应消息体。
filter:是一个callable object，其初始化时需要的唯一参数是(app)，在被call时对env进行判断或者说过滤，当满足条件后call自身的app，否则直接链断，给出错误处理。
app_factory:app的工厂方法，参数(global_conf,**kwargs)，其中global_conf对应配置文件中的[DEFAULT]section键值对，kwargs则对应自身setion键值对。该工程方法返回了app的一个实例。
filter_factory:filter的工厂方法，与app_factory比较需要注意的是，该方法返回的是filter类，实例化的过程在pipeline调用。
一个简单的例子：

##################### ##  api-paste.ini  ## #####################   [DEFAULT] #DEFAULT段，下面的键值对将作为global_conf author = zhengtianbao blog = www.zhengtianbao.com   [composite:web] #web是一个符合wsgi的app，不过他是composite类型，下面的use方法将会调用 #Paste包中的urlmap对‘/home’,‘/blog’做初始化，同时在call的时候将会map #到不同的app use = egg:Paste#urlmap /home: home #/blog: blog   [pipeline:home] #pipeline管道，是一个callable对象，具体call的过程为: #faultwarp->logrequest->homeapp #是不是很像linux中的grep命令 #顺便一提home作为一个app的初始化过程顺序为: #faultwarp(logrequest(homeapp())) pipeline = faultwarp logrequest homeapp   [filter:faultwarp] #filter，直接调用factory方法,下面的key=value作为kwargs参数 #相当与: #    import apipaste #    apipaste.FaultWarp(app_from_paste, key=value) paste.filter_factory = apipaste:FaultWarp.factory key = value   [filter:logrequest] paste.filter_factory = apipaste:RequestLogging.factory   [app:homeapp] #app，这里是app最终的实现 #相当与: #    import apipaste #    apipaste.HomeApp(version='1.3') #这里的键值对作为参数传入 paste.app_factory = apipaste:HomeApp.factory version = 1.3

#!/usr/bin/env python #coding=utf8   """apipaste.py"""   import os   import eventlet from eventlet import wsgi from paste import deploy   class HomeApp(object):     """home wsgi application"""           def __init__(self):         print 'In HomeApp init'           def __call__(self, env, start_response):         print 'app:HomeApp is called'         start_response('200 OK', [('Content-Type', 'text/plain')])         return ['welcome to home page, hello world!']           @classmethod     def factory(cls, global_conf, **kwargs):         print 'In HomeApp.factory'         #print 'global_conf: ', global_conf         #print 'kwargs: ', kwargs         return HomeApp()#返回的是HomeApp的一个实例化对象       class FaultWarp(object):     """fault warpper class"""           def __init__(self, app):#init时需要传入一个app对象         print 'In FaultWarp init'         self.app = app           def __call__(self, env, start_response):         #在这里可以对env进行一些判断过滤         print 'filter:FaultWarp is called'         return self.app(env, start_response)           @classmethod     def factory(cls, global_conf, **kwargs):         print 'In FaultWarp factory'         #print 'global_conf: ', global_conf         #print 'kwargs: ', kwargs         return FaultWarp#返回的是FaultWarp类   class RequestLogging(object):     """request log class"""           def __init__(self, app):         print 'In RequestLogging init'         self.app = app               def __call__(self, env, start_response):         #在这里可以对请求进行一些日志操作         print 'filter:RequestLogging is called'         return self.app(env, start_response)           @classmethod     def factory(cls, global_conf, **kwargs):         print 'In RequestLogging factory'         #print 'global_conf: ', global_conf         #print 'kwargs: ', kwargs         return RequestLogging   if __name__ == '__main__':     config_file = 'api-paste.ini'     app = 'web'     #app = 'homeapp'     wsgi_app = deploy.loadapp("config:%s" % os.path.abspath(config_file), app)     wsgi.server(eventlet.listen(('', 8090)), wsgi_app)

我们通过浏览器分别访问
http://localhost:8090/
http://localhost:8090/home/
http://localhost:8090/home/page/id/1
输出结果如下：

[iyunv@localhost 20130801]# python apipaste.py In HomeApp.factory In HomeApp init In FaultWarp factory In RequestLogging factory In RequestLogging init In FaultWarp init (25629) wsgi starting up on http://0.0.0.0:8090/   (25629) accepted ('127.0.0.1', 59121) 127.0.0.1 - - [01/Aug/2013 22:15:48] "GET / HTTP/1.1" 404 448 0.011558 filter:FaultWarp is called filter:RequestLogging is called app:HomeApp is called 127.0.0.1 - - [01/Aug/2013 22:15:53] "GET /home/ HTTP/1.1" 200 160 0.000222 filter:FaultWarp is called filter:RequestLogging is called app:HomeApp is called 127.0.0.1 - - [01/Aug/2013 22:16:01] "GET /home/page/id/1 HTTP/1.1" 200 160 0.000364

发现URL中以/home/开头的地址都分发到了HomeApp，观察打印信息可以跟踪它调用pipeline的过程。
当然,在openstack中的app可不是这么简单的，下面就接着说说webob这个python库。
2. webob
官方文档:http://docs.webob.org/en/latest/
webob是一个Python库，主要是用在WSGI中对请求环境变量request environment（也就是WSGI应用中的参数environ）进行包装（提供wrapper），并提供了一个对象来方便的处理返回response消息。
nova中主要用到了webob中的装饰器，对HTTP请求信息req做了包装判断，对response的处理也做了包装。
基本用法:

#!/usr/bin/env python #coding=utf8   import eventlet from eventlet import wsgi import webob import webob.dec import webob.exc    def hello_world(env, start_response):     start_response('200 OK', [('Content-Type', 'text/plain')])     return ['Hello, World!\r\n']   @webob.dec.wsgify def app(req):     """     webobo.dec.wsgify可以将函数修饰成wsgi app     webob.exc可以生成HTTP的一些错误响应，如404，500等     经过修饰后的WSGI application可以返回以下几种response         #1: 字符串         res = 'hello world!\r\n'         #2: webob错误页信息         res = webob.exc.HTTPForbidden(detail='Error page')         #3: 另外一个wsgi app         res = hello_world     """     #res = 'message\n'     #res = webob.exc.HTTPForbidden(detail='Error page')     #res = hello_world     #在这里可以对req进行操作     req.environ['msg'] = 'welcome to my blog:)'     #这样传递到下一个app的时候就能够做一些判断处理     res = app2     #可以打印查看req的信息     #print dir(req)     #print req     #print req.environ     return res   @webob.dec.wsgify def app2(req):     if req.environ['msg']:         print req.environ['msg']     res = hello_world     return res    #wsgi.server(eventlet.listen(('', 8090)), hello_world) wsgi.server(eventlet.listen(('', 8090)), app)

回过头来，看nova/wsgi.py文件，该文件是nova中wsgi相关的基类，其中定义了下面几个类:
Server –> WSGI server，wsgi api服务基类
Request –> app request, HTTP请求类，继承自webob.Request
Application –> WSGI application基类
Middleware –> WSGI app filter基类，继承自Application
Debug –> debug,继承自Middleware
Router –> WSGI 路由,用到了routes包
Loader –> paste.deploy加载接口类
貌似就剩下Router这个类了，下面就接着讲nova中所用到的routes。
3. routes
官方文档:http://routes.readthedocs.org/en/latest/index.html
Routes 可以方便的定义符合RESTful 标准的 web服务.map.resource可以快速创建出 增/改/删 路由接口.
这里只说明nova中所用到的:

import routes import routes.middleware import webob.dec import webob.exc   mapper = routes.Mapper() #需要对mapper指定controller,这个controller相当于是一个wsgi app,用来做URL路由call的app #1.connect方式创建一条route #mapper.connect(None, '/svrlist', controller=sc, action='list') #2.隐式的创建多条routes #mapper.resource('server', 'servers', controller=sc)   @webob.dec.wsgify def dispatch(req):     match = req.environ['wsgiorg.routing_args'][1]     if not match:         return webob.exc.HTTPNotFound()     app = match['controller']     return app   router = routes.middleware.RoutesMiddleware(dispatch, mapper) #router做为一个wsgi app被call的时候将会对请求URL先在mapper中匹配前面注册的URL route #将匹配到的信息(上面connect或者resource创建的routes)添加到req.environ中 #然后调用dispatch函数,对req.environ['wsgiorg.routing_args']进行判断, #例如id,controller等,然后分发到相应的wsgi app中

下面看从nova中的简化出来的例子:

import eventlet from eventlet import wsgi import routes import routes.middleware import webob import webob.dec import webob.exc    class Router(object):     """wsgi router"""           def __init__(self, mapper):         self.map = mapper         self._router = routes.middleware.RoutesMiddleware(                     self._dispatch,                     self.map)           @webob.dec.wsgify     def __call__(self, req):         return self._router       @staticmethod     @webob.dec.wsgify     def _dispatch(req):         match = req.environ['wsgiorg.routing_args'][1]         print 'match: ', match         #print 'body: ', req.body         if not match:             return webob.exc.HTTPNotFound()         app = match['controller']         #简单的判断方法,nova中是放到了Resource类的call方法中进行判断的         if hasattr(app, match['action']):             fun = getattr(app, match['action'])             return fun(req)         else:             return webob.exc.HTTPNotFound()     class APIRouter(Router):     """"""           def __init__(self):         mapper = routes.Mapper()         self.resources = {}         self._setup_routes(mapper)         super(APIRouter, self).__init__(mapper)       def _setup_routes(self, mapper):         #注册routes,关于下面两个用法请看官方文档说明         self.resources['versions'] = VersionsApp()         self.resources['servers'] = ServersApp()           mapper.connect("version", "/version/",                     controller=self.resources['versions'],                     action='show')         mapper.resource("server", "servers",                     controller=self.resources['servers'],                     collection={'detail': 'GET'},                     member={'action': 'POST'})     class VersionsApp(object):     """wsgi application"""           def __init__(self):         pass           @webob.dec.wsgify     def __call__(self, req):         return 'version called'       @webob.dec.wsgify     def show(self, req):         #对应GET /versions/         return 'in version show fun'             class ServersApp(object):     """wsgi application"""           def __init__(self):         pass       def __call__(self, req):         return 'servers called'       @webob.dec.wsgify       def index(self, req):         #对应GET /servers         return 'welcome to servers app'           @webob.dec.wsgify     def action(self, req):         #对应POST /servers/{id}/action         #这里没有定义id的接口,nova中是在上层route的时候判断定义了接口才能传入id         #例如这个接口定义def action(self, req, id, body)         return 'server action function'   wsgi.server(eventlet.listen(('', 8090)), APIRouter())

请试着发送以下RESTful请求:
GET http://localhost:8090/version/
GET http://localhost:8090/servers
POST http://localhost:8090/servers/2/action Body={‘msg’:’hello world’}
观察返回结果是不是预料的那样.
关于mapper.resource方法的一点说明:
例如创建下面的resource:
map.resource(“message”, “messages”)
则对应为:
GET /messages => messages.index() => url(“messages”)
POST /messages => messages.create() => url(“messages”)
GET /messages/new => messages.new() => url(“new_message”)
PUT /messages/1 => messages.update(id) => url(“message”, id=1)
DELETE /messages/1 => messages.delete(id) => url(“message”, id=1)
GET /messages/1 => messages.show(id) => url(“message”, id=1)
GET /messages/1/edit => messages.edit(id) => url(“edit_message”, id=1)
map.resource(“message”, “messages”, collection={“rss”: “GET”})
GET /messages/rss => messages.rss()
map.resource(“message”, “messages”, member={“mark”:”POST”})
POST /messages/1/mark” => Messages.mark(1)
总结下访问顺序:RESTful请求 -> RoutesMiddleware进行mapper -> wsgi application
大体上nova也是这个流程,不过nova中对Mapper的connect以及resource进行了重写,在router时加了更多的判断,而且最终的wsgi app是包装成Resource(Controller())这种形式的.