Liberty nova-api load app过程跟踪

来源：互联网发布：唱歌培训软件编辑：程序博客网时间：2024/05/01 12:06

本博客欢迎转载，但请注明出处 http://blog.csdn.net/ringoshen/article/details/51334973

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之前的文章中已经分析了nova-api的整体启动流程，但是其中一些重要的细节并没有深入看，今天这篇文章主要看一下nova-api中的loadapp的过程。至于URLMap、APIRouter以及各个Filter的功能流程之后在解析http请求的时候会做一下分析。
接下来还是直接看一下代码。

# nova/service.pyclass WSGIService(service.Service):    def __init__(self, name, loader=None, use_ssl=False, max_url_len=None):        ... ...        ... ...        # 接下来2步加载app，app的信息在"/etc/nova/api-paste.ini"，        # loader = <nova.wsgi.Loader object at 0x7f6f2b5b1ed0>        self.loader = loader or wsgi.Loader()        # app = <nova.api.openstack.urlmap.URLMap object at 0x7f6f2b541790>        # 这边主要返回一个URLMap对象，从名字上就知道是用来根据url路由到app        self.app = self.loader.load_app(name)        ... ...        ... ...

加载app代码跟踪

这边简单跟踪一下整体的代码调用过程，不做细节的介绍。

# nova/wsgi.pyclass Loader(object):    ... ...    def load_app(self, name):        try:            LOG.debug("Loading app %(name)s from %(path)s",                      {'name': name, 'path': self.config_path})            # deploy.loadapp("config:'/etc/nova/api-paste.ini'", name='osapi_compute')            return deploy.loadapp("config:%s" % self.config_path, name=name)        except LookupError:            LOG.exception(_LE("Couldn't lookup app: %s"), name)            raise exception.PasteAppNotFound(name=name, path=self.config_path)

之后的流程就开始在paste.deploy中执行。

# paste/deploy/loadwsgi.py# uri = 'config:/etc/nova/api-paste.ini'# name = 'osapi_compute'# kw = {}# APP = _App()def loadapp(uri, name=None, **kw):    return loadobj(APP, uri, name=name, **kw)

def loadobj(object_type, uri, name=None, relative_to=None,            global_conf=None):    # object_type = <application protocols=[['paste.app_factory'], ['paste.composite_factory'], ['paste.composit_factory']] prefixes=[['app', 'application'], ['composite', 'composit'], ['pipeline'], ['filter-app']]>    # uri = 'config:/etc/nova/api-paste.ini'    # name = 'osapi_compute'    # relative_to = None    # global_conf = None    # 这一个过程十分漫长    context = loadcontext(        object_type, uri, name=name, relative_to=relative_to,        global_conf=global_conf)    return context.create()

def loadcontext(object_type, uri, name=None, relative_to=None,                global_conf=None):    ... ...    ... ...    # scheme = 'config'    # _loaders['config'] = _loadconfig    return _loaders[scheme](        object_type,        uri, path, name=name, relative_to=relative_to,        global_conf=global_conf)

def _loadconfig(object_type, uri, path, name, relative_to,                global_conf):    ... ...    ... ...    # path = '/etc/nova/api-paste.ini'    path = unquote(path)    # loader = <paste.deploy.loadwsgi.ConfigLoader object at 0x7fe4c77f2e50>    loader = ConfigLoader(path)    if global_conf:        loader.update_defaults(global_conf, overwrite=False)    return loader.get_context(object_type, name, global_conf)

class ConfigLoader(_Loader):    def __init__(self, filename):        # filename = '/etc/nova/api-paste.ini'        self.filename = filename = filename.strip()        # defaults = {'__file__': '/etc/nova/api-paste.ini', 'here': '/etc/nova'}        defaults = {            'here': os.path.dirname(os.path.abspath(filename)),            '__file__': os.path.abspath(filename)            }        self.parser = NicerConfigParser(filename, defaults=defaults)        self.parser.optionxform = str  # Don't lower-case keys        with open(filename) as f:            self.parser.read_file(f)    def get_context(self, object_type, name=None, global_conf=None):        if self.absolute_name(name):            return loadcontext(object_type, name,                               relative_to=os.path.dirname(self.filename),                               global_conf=global_conf)        # section = 'composite:osapi_compute'        section = self.find_config_section(            object_type, name=name)        ... ...        ... ...        # 循环读取section成local_conf和global_conf        for option in self.parser.options(section):            if option.startswith('set '):                name = option[4:].strip()                global_additions[name] = global_conf[name] = (                    self.parser.get(section, option))            elif option.startswith('get '):                name = option[4:].strip()                get_from_globals[name] = self.parser.get(section, option)            else:                if option in defaults:                    continue                local_conf[option] = self.parser.get(section, option)        # local_conf = {'/v2': 'openstack_compute_api_v21_legacy_v2_compatible', '/v2.1': 'openstack_compute_api_v21', 'use': 'call:nova.api.openstack.urlmap:urlmap_factory', '/': 'oscomputeversions'}        # global_conf = {'__file__': '/etc/nova/api-paste.ini', 'here': '/etc/nova'}        ... ...        ... ...        if section.startswith('filter-app:'):            context = self._filter_app_context(                object_type, section, name=name,                global_conf=global_conf, local_conf=local_conf,                global_additions=global_additions)        elif section.startswith('pipeline:'):            context = self._pipeline_app_context(                object_type, section, name=name,                global_conf=global_conf, local_conf=local_conf,                global_additions=global_additions)        elif 'use' in local_conf:            context = self._context_from_use(                object_type, local_conf, global_conf, global_additions,                section)        else:            context = self._context_from_explicit(                object_type, local_conf, global_conf, global_additions,                section)        if filter_with is not None:            filter_with_context = LoaderContext(                obj=None,                object_type=FILTER_WITH,                protocol=None,                global_conf=global_conf, local_conf=local_conf,                loader=self)            filter_with_context.filter_context = self.filter_context(                name=filter_with, global_conf=global_conf)            filter_with_context.next_context = context            return filter_with_context        return context    def _context_from_use(self, object_type, local_conf, global_conf,                          global_additions, section):        # 这边真正取到urlmap_factory        # use = 'call:nova.api.openstack.urlmap:urlmap_factory'        use = local_conf.pop('use')        context = self.get_context(            object_type, name=use, global_conf=global_conf)        context.global_conf.update(global_additions)        context.local_conf.update(local_conf)        if '__file__' in global_conf:            context.global_conf['__file__'] = global_conf['__file__']        context.loader = self        if context.protocol is None:            section_protocol = section.split(':', 1)[0]            if section_protocol in ('application', 'app'):                context.protocol = 'paste.app_factory'            elif section_protocol in ('composit', 'composite'):                context.protocol = 'paste.composit_factory'            else:                context.protocol = 'paste.%s_factory' % section_protocol        return context

之后又调用回loadcontext方法。

def loadcontext(object_type, uri, name=None, relative_to=None,                global_conf=None):    ... ...    ... ...    # 此处开始加载urlmap的步骤    # scheme = 'call'    # _loaders['call'] = _loadfunc    return _loaders[scheme](        object_type,        uri, path, name=name, relative_to=relative_to,        global_conf=global_conf)

def _loadfunc(object_type, uri, spec, name, relative_to,             global_conf):    loader = FuncLoader(spec)    return loader.get_context(object_type, name, global_conf)

class FuncLoader(_Loader):    def __init__(self, spec):        self.spec = spec        if not ':' in spec:            raise LookupError("Configuration not in format module:function")    def get_context(self, object_type, name=None, global_conf=None):        # 从uri -> module的过程主要是通过这个方法实现，实现方式主要是动态加载        # module = __import__(parts)        obj = lookup_object(self.spec)        return LoaderContext(obj, object_type, None, global_conf or {}, {}, self,)

class LoaderContext(object):    def __init__(self, obj, object_type, protocol,                 global_conf, local_conf, loader,                 distribution=None, entry_point_name=None):        self.object = obj        self.object_type = object_type        self.protocol = protocol        self.global_conf = global_conf        self.local_conf = local_conf        self.loader = loader        self.distribution = distribution        self.entry_point_name = entry_point_name    # 之前的create方法的定义在此    def create(self):        return self.object_type.invoke(self)

这是之前APP = _App()的定义

class _App(_ObjectType):    name = 'application'    egg_protocols = ['paste.app_factory', 'paste.composite_factory',                     'paste.composit_factory']    config_prefixes = [['app', 'application'], ['composite', 'composit'],                       'pipeline', 'filter-app']    def invoke(self, context):        if context.protocol in ('paste.composit_factory',                                'paste.composite_factory'):            return fix_call(context.object,                            context.loader, context.global_conf,                            **context.local_conf)        elif context.protocol == 'paste.app_factory':            return fix_call(context.object, context.global_conf, **context.local_conf)        else:            assert 0, "Protocol %r unknown" % context.protocol

之后调用了公共模块

# paste/deploy/util.pydef fix_call(callable, *args, **kw):    """    Call ``callable(*args, **kw)`` fixing any type errors that come out.    """    try:        # ###### 此处真正调用urlmap_factory工厂方法 ######        val = callable(*args, **kw)    except TypeError:        exc_info = fix_type_error(None, callable, args, kw)        reraise(*exc_info)    return val

# nova/api/openstack/urlmap.pydef urlmap_factory(loader, global_conf, **local_conf):    if 'not_found_app' in local_conf:        not_found_app = local_conf.pop('not_found_app')    else:        not_found_app = global_conf.get('not_found_app')    if not_found_app:        not_found_app = loader.get_app(not_found_app, global_conf=global_conf)    urlmap = URLMap(not_found_app=not_found_app)    for path, app_name in local_conf.items():        path = paste.urlmap.parse_path_expression(path)        # 类似的方法加载section里面的各类app        app = loader.get_app(app_name, global_conf=global_conf)        urlmap[path] = app    return urlmap

至此，加载app的方法调用过程就走完一遍了，已经加载到我们需要的urlmap_factory，至于urlmap里面的app的加载方式跟上述方式整体上是大致一样的，这里不继续跟踪，不过可以看一下filter包裹app的过程。

# nova/api/auth.py# 在Liberty版本中采用的openstack compute api是v2.1def pipeline_factory_v21(loader, global_conf, **local_conf):    """A paste pipeline replica that keys off of auth_strategy."""    return _load_pipeline(loader, local_conf[CONF.auth_strategy].split())

# nova/api/auth.pydef _load_pipeline(loader, pipeline):    # 加载pipeline中各个filter    filters = [loader.get_filter(n) for n in pipeline[:-1]]    # 加载app（osapi_compute_app_v21）    app = loader.get_app(pipeline[-1])    # 倒序filter    filters.reverse()    # 反复使用filter包装app    for filter in filters:        app = filter(app)    return app

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