2019独角兽企业重金招聘Python工程师标准>>> 
随手记录一下查看nova代码时的笔记
nova.api.openstack.wsgi.ActionDispatcher模块解析:
class ActionDispatcher(object): """ 通过action名将方法名映射到本地方法。 """ def dispatch(self, *args, **kwargs): """ 查找并调用local方法.""" action = kwargs.pop('action', 'default') action_method = getattr(self, str(action), self.default) return action_method(*args, **kwargs) def default(self, data):#子类必须实现的方法 raise NotImplementedError()
nova.api.openstack.wsgi.JSONDeserializer模块解析:
class JSONDeserializer(ActionDispatcher):
def _from_json(self, datastring):
"""将json字符串转为json对象"""
try:
return jsonutils.loads(datastring)
except ValueError:
msg = _("cannot understand JSON")
raise exception.MalformedRequestBody(reason=msg)
def deserialize(self, datastring, action='default'):
return self.dispatch(datastring, action=action)
def default(self, datastring):
return {
'body': self._from_json(datastring)}
nova.api.openstack.wsgi.JSONDictSerializer模块解析:
class JSONDictSerializer(ActionDispatcher):
""" 将JSON请求body体序列化。 """
def serialize(self, data, action='default'):
return self.dispatch(data, action=action)
def default(self, data):
return six.text_type(jsonutils.dumps(data))#调用six模块实现python2与3兼容处理
nova.api.openstack.wsgi.Resource模块解析:
class Resource(wsgi.Application):
""" 处理(反)序列化和控制器分发的WSGI app.
WSGI app读取RoutesMiddleware提供的路由信息，并在其控制器上调用请求的action方法。
所有控制器action方法都必须接受'req'参数，它是传入的wsgi.Request。
如果操作是PUT或POST，控制器方法还必须接受一个“body”参数(反序列化的请求体)。
可能会引发webob.exc异常或返回dict，, 它将被按请求的内容类型序列化。
从webob.exc.HTTPException继承的Exceptions 将自动包装在Fault() 中，以提供API友好的错误响应。
"""
support_api_request_version = False
def __init__(self, controller, inherits=None):
""":param controller: routes库创建的对象
:param inherits: 另一种资源对象，该资源应该继承的扩展extensions. 应用于父资源的任何action extensions也将应用于此资源。
"""
self.controller = controller
self.default_serializers = dict(json=JSONDictSerializer)
# 复制actions字典
self.wsgi_actions = {}
if controller:
self.register_actions(controller)
# 保存插件(extensions)的映射
self.wsgi_extensions = {}
self.wsgi_action_extensions = {}
self.inherits = inherits
def register_actions(self, controller):
""" 使用此资源注册控制器actions。"""
actions = getattr(controller, 'wsgi_actions', {})
for key, method_name in actions.items():
self.wsgi_actions[key] = getattr(controller, method_name)
def register_extensions(self, controller):
""" 使用此资源注册控制器extensions。 """
extensions = getattr(controller, 'wsgi_extensions', [])
for method_name, action_name in extensions:
# 查找extending方法
extension = getattr(controller, method_name)
if action_name:
# action_name还不存在时，初始化列表...
if action_name not in self.wsgi_action_extensions:
self.wsgi_action_extensions[action_name] = []
self.wsgi_action_extensions[action_name].append(extension)
else:
# method_name还不存在时，初始化列表
if method_name not in self.wsgi_extensions:
self.wsgi_extensions[method_name] = []
self.wsgi_extensions[method_name].append(extension)
def get_action_args(self, request_environment):
""" 解析routes创建的字典 ."""
# 检查控制器是否有重写get_action_args()，有就调用重写的方法
if hasattr(self.controller, 'get_action_args'):
return self.controller.get_action_args(request_environment)
try:
args = request_environment['wsgiorg.routing_args'][1].copy()
except (KeyError, IndexError, AttributeError):
return {}
try:
del args['controller']
except KeyError:
pass
try:
del args['format']
except KeyError:
pass
return args
def get_body(self, request):
content_type = request.get_content_type()
return content_type, request.body
def deserialize(self, body):
return JSONDeserializer().deserialize(body)
def process_extensions(self, extensions, resp_obj, request,
action_args):
"""处理插件(extensions)"""
for ext in extensions:
response = None
#常规函数可以得到post-processing...
try:
with ResourceExceptionHandler():
response = ext(req=request, resp_obj=resp_obj,
**action_args)
except exception.VersionNotFoundForAPIMethod:
# 如果附加的方法扩展(@wsgi.extends)名没有版本匹配，则不认为是错误。 跳过代码执行。
continue
except Fault as ex:
response = ex
# response存在返回它，提前退出。 这实际上是代表一种失败模式。 response为None代表成功。
if response:
return response
return None
def _should_have_body(self, request):
return request.method in _METHODS_WITH_BODY #POST和PUT应该包含body内容
@webob.dec.wsgify(RequestClass=Request)
def __call__(self, request):
""" 控制(反)序列化和方法分派的WSGI方法。 """
if self.support_api_request_version:
# 根据报头设置请求的API版本
try:
request.set_api_version_request()
except exception.InvalidAPIVersionString as e:
return Fault(webob.exc.HTTPBadRequest(
explanation=e.format_message()))
except exception.InvalidGlobalAPIVersion as e:
return Fault(webob.exc.HTTPNotAcceptable(
explanation=e.format_message()))
# 标识action, 参数和请求的内容类型
action_args = self.get_action_args(request.environ)
action = action_args.pop('action', None)
# 过滤掉InvalidContentTypes
try:
content_type, body = self.get_body(request)
accept = request.best_match_content_type()
except exception.InvalidContentType:
msg = _("Unsupported Content-Type")
return Fault(webob.exc.HTTPUnsupportedMediaType(explanation=msg))
# 通过这种方式拆分函数，可以通过包装现有函数的外部工具进行审计。
# 由于@webob.dec.wsgify()装饰器的作用， 如果试图审计__call__()，可能会遇到报错
return self._process_stack(request, action, action_args,
content_type, body, accept)
def _process_stack(self, request, action, action_args,
content_type, body, accept):
""" 实现processing stack."""
# 获取实现方法
try:
meth, extensions = self.get_method(request, action,
content_type, body)
except (AttributeError, TypeError):
return Fault(webob.exc.HTTPNotFound())
except KeyError as ex:
msg = _("There is no such action: %s") % ex.args[0]
return Fault(webob.exc.HTTPBadRequest(explanation=msg))
except exception.MalformedRequestBody:
msg = _("Malformed request body")
return Fault(webob.exc.HTTPBadRequest(explanation=msg))
if body:
msg = _("Action: '%(action)s', calling method: %(meth)s, body: "
"%(body)s") % {
'action': action,
'body': six.text_type(body, 'utf-8'),
'meth': str(meth)}
LOG.debug(strutils.mask_password(msg))
else:
LOG.debug("Calling method '%(meth)s'",
{
'meth': str(meth)})
# 反序列化request body...
try:
contents = {}
if self._should_have_body(request):
# 允许请求方法为PUT和POST的body为空
if request.content_length == 0:
contents = {
'body': None}
else:
contents = self.deserialize(body)
except exception.MalformedRequestBody:
msg = _("Malformed request body")
return Fault(webob.exc.HTTPBadRequest(explanation=msg))
# 更新action参数
action_args.update(contents)
#比对project_id
project_id = action_args.pop("project_id", None)
context = request.environ.get('nova.context')
if (context and project_id and (project_id != context.project_id)):
msg = _("Malformed request URL: URL's project_id '%(project_id)s'"
" doesn't match Context's project_id"
" '%(context_project_id)s'") % \
{
'project_id': project_id,
'context_project_id': context.project_id}
return Fault(webob.exc.HTTPBadRequest(explanation=msg))
response = None
try:
with ResourceExceptionHandler():
action_result = self.dispatch(meth, request, action_args)
except Fault as ex:
response = ex
if not response:
# 无异常时; 将action_result转换ResponseObject
resp_obj = None
if type(action_result) is dict or action_result is None:
resp_obj = ResponseObject(action_result)
elif isinstance(action_result, ResponseObject):
resp_obj = action_result
else:
response = action_result
# 运行post-processing插件(extensions)
if resp_obj:
# 预序列化以设置response对象
if hasattr(meth, 'wsgi_code'):
resp_obj._default_code = meth.wsgi_code
# 调用process_extensions
response = self.process_extensions(extensions, resp_obj,
request, action_args)
if resp_obj and not response:
response = resp_obj.serialize(request, accept)
if hasattr(response, 'headers'):
for hdr, val in list(response.headers.items()):
if six.PY2:
# 在Py2.X Headers 必须是字节字符串
response.headers[hdr] = utils.utf8(val)
else:
# 在Py3.X Headers 必须是utf-8符串
response.headers[hdr] = encodeutils.safe_decode(
utils.utf8(val))
if not request.api_version_request.is_null():
response.headers[API_VERSION_REQUEST_HEADER] = \
'compute ' + request.api_version_request.get_string()
response.headers[LEGACY_API_VERSION_REQUEST_HEADER] = \
request.api_version_request.get_string()
response.headers.add('Vary', API_VERSION_REQUEST_HEADER)
response.headers.add('Vary', LEGACY_API_VERSION_REQUEST_HEADER)
return response
def get_method(self, request, action, content_type, body):
meth, extensions = self._get_method(request,
action,
content_type,
body)
if self.inherits:
_meth, parent_ext = self.inherits.get_method(request,
action,
content_type,
body)
extensions.extend(parent_ext)
return meth, extensions
def _get_method(self, request, action, content_type, body):
""" 查找action-specific的方法及其extensions。"""
# 查找方法
try:
if not self.controller:
meth = getattr(self, action)
else:
meth = getattr(self.controller, action)
except AttributeError:
if (not self.wsgi_actions or
action not in _ROUTES_METHODS + ['action']):
# 找不到抛出error
raise
else:
return meth, self.wsgi_extensions.get(action, [])
if action == 'action':
#此方法会从body中找出action_name,此时的body应该是只有一个key的已经被序列化后的json。
action_name = action_peek(body)
else:
action_name = action
# 查找action方法
return (self.wsgi_actions[action_name],
self.wsgi_action_extensions.get(action_name, []))
def dispatch(self, method, request, action_args):
"""分发一个call到action-specific方法."""
try:
return method(req=request, **action_args)
except exception.VersionNotFoundForAPIMethod:
return Fault(webob.exc.HTTPNotFound())