在 api-paste.ini 中有这么一个过滤器
[filter:keystonecontext]
paste.filter_factory = neutron.auth:NeutronKeystoneContext.factory
若是我们的 neutron 走 keystone 认证的话，就会启用这个过滤器。
NeutronKeystoneContext 继承于 oslo_middleware 的 ConfigurableMiddleware 类，重写了 ConfigurableMiddleware 的 __call__ 方法，我们从这里看起。
@classmethod
def factory(cls, global_conf, **local_conf):
"""Factory method for paste.deploy.
:param global_conf: dict of options for all middlewares
(usually the [DEFAULT] section of the paste deploy
configuration file)
:param local_conf: options dedicated to this middleware
(usually the option defined in the middleware
section of the paste deploy configuration file)
"""
conf = global_conf.copy() if global_conf else {}
conf.update(local_conf)
def middleware_filter(app):
return cls(app, conf)
return middleware_filter
- 根据 paste.deploy 的配置文件初始化
ConfigurableMiddleware
def __init__(self, application, conf=None):
"""Base middleware constructor
:param conf: a dict of options or a cfg.ConfigOpts object
"""
self.application = application
# NOTE(sileht): If the configuration come from oslo.config
# just use it.
if isinstance(conf, cfg.ConfigOpts):
self.conf = {}
self.oslo_conf = conf
else:
self.conf = conf or {}
if "oslo_config_project" in self.conf:
if 'oslo_config_file' in self.conf:
default_config_files = [self.conf['oslo_config_file']]
else:
default_config_files = None
if 'oslo_config_program' in self.conf:
program = self.conf['oslo_config_program']
else:
program = None
self.oslo_conf = cfg.ConfigOpts()
self.oslo_conf([],
project=self.conf['oslo_config_project'],
prog=program,
default_config_files=default_config_files,
validate_default_values=True)
else:
# Fallback to global object
self.oslo_conf = cfg.CONF
__init__ 方法主要是做了初始化 oslo_conf 的工作（cfg.ConfigOpts的实例）。
@webob.dec.wsgify
def __call__(self, req):
# Determine the user ID
user_id = req.headers.get('X_USER_ID')
if not user_id:
LOG.debug("X_USER_ID is not found in request")
return webob.exc.HTTPUnauthorized()
# Determine the tenant
tenant_id = req.headers.get('X_PROJECT_ID')
# Suck out the roles
roles = [r.strip() for r in req.headers.get('X_ROLES', '').split(',')]
# Human-friendly names
tenant_name = req.headers.get('X_PROJECT_NAME')
user_name = req.headers.get('X_USER_NAME')
# Use request_id if already set
req_id = req.environ.get(request_id.ENV_REQUEST_ID)
# Get the auth token
auth_token = req.headers.get('X_AUTH_TOKEN',
req.headers.get('X_STORAGE_TOKEN'))
# Create a context with the authentication data
ctx = context.Context(user_id, tenant_id, roles=roles,
user_name=user_name, tenant_name=tenant_name,
request_id=req_id, auth_token=auth_token)
# Inject the context...
req.environ['neutron.context'] = ctx
return self.application
很明显，这里是根据认证的结果来构造一个上下文对象（Context 的实例）。
这个 Context 对象的构造十分的重要这在后面会被很多的地方用到。
看过我之前写的关于 neutron wsgi 实现的文章可以知道，所有的 wsgi 中的 controller 都是在这里实现的：
def Resource(controller, faults=None, deserializers=None, serializers=None,
action_status=None):
"""Represents an API entity resource and the associated serialization and
deserialization logic
"""
default_deserializers = {'application/json': wsgi.JSONDeserializer()}
default_serializers = {'application/json': wsgi.JSONDictSerializer()}
format_types = {'json': 'application/json'}
action_status = action_status or dict(create=201, delete=204)
default_deserializers.update(deserializers or {})
default_serializers.update(serializers or {})
deserializers = default_deserializers
serializers = default_serializers
faults = faults or {}
@webob.dec.wsgify(RequestClass=Request)
def resource(request):
route_args = request.environ.get('wsgiorg.routing_args')
if route_args:
args = route_args[1].copy()
else:
args = {}
# NOTE(jkoelker) by now the controller is already found, remove
# it from the args if it is in the matchdict
args.pop('controller', None)
fmt = args.pop('format', None)
action = args.pop('action', None)
content_type = format_types.get(fmt,
request.best_match_content_type())
language = request.best_match_language()
deserializer = deserializers.get(content_type)
serializer = serializers.get(content_type)
try:
if request.body:
args['body'] = deserializer.deserialize(request.body)['body']
method = getattr(controller, action)
result = method(request=request, **args)
except Exception as e:
mapped_exc = api_common.convert_exception_to_http_exc(e, faults,
language)
if hasattr(mapped_exc, 'code') and 400 <= mapped_exc.code < 500:
LOG.info(_LI('%(action)s failed (client error): %(exc)s'),
{'action': action, 'exc': mapped_exc})
else:
LOG.exception(
_LE('%(action)s failed: %(details)s'),
{
'action': action,
'details': utils.extract_exc_details(e),
}
)
raise mapped_exc
status = action_status.get(action, 200)
body = serializer.serialize(result)
# NOTE(jkoelker) Comply with RFC2616 section 9.7
if status == 204:
content_type = ''
body = None
return webob.Response(request=request, status=status,
content_type=content_type,
body=body)
# NOTE(blogan): this is something that is needed for the transition to
# pecan. This will allow the pecan code to have a handle on the controller
# for an extension so it can reuse the code instead of forcing every
# extension to rewrite the code for use with pecan.
setattr(resource, 'controller', controller)
return resource
这里面有一个关于 Request 的装饰器的使用：
@webob.dec.wsgify(RequestClass=Request)
我们跟踪下去：
class Request(wsgi.Request):
pass
class Request(wsgi.Request):
def best_match_content_type(self):
"""Determine the most acceptable content-type.
Based on:
1) URI extension (.json)
2) Content-type header
3) Accept* headers
"""
# First lookup http request path
parts = self.path.rsplit('.', 1)
if len(parts) > 1:
_format = parts[1]
if _format in ['json']:
return 'application/{0}'.format(_format)
#Then look up content header
type_from_header = self.get_content_type()
if type_from_header:
return type_from_header
ctypes = ['application/json']
#Finally search in Accept-* headers
bm = self.accept.best_match(ctypes)
return bm or 'application/json'
def get_content_type(self):
allowed_types = ("application/json",)
if "Content-Type" not in self.headers:
LOG.debug("Missing Content-Type")
return None
_type = self.content_type
if _type in allowed_types:
return _type
return None
def best_match_language(self):
"""Determines best available locale from the Accept-Language header.
:returns: the best language match or None if the 'Accept-Language'
header was not available in the request.
"""
if not self.accept_language:
return None
all_languages = oslo_i18n.get_available_languages('neutron')
return self.accept_language.best_match(all_languages)
@property
def context(self):
if 'neutron.context' not in self.environ:
self.environ['neutron.context'] = context.get_admin_context()
return self.environ['neutron.context']
我们可以看到这个类中有一个 context 的属性方法，这个就是将刚才我们构造的 Context 实例返回。