Swift中的Account Server代码解读

用户的HTTP请求被AccountController、ContainerController与ObjectController分别转发给存储节点上的Account Server、Container Server和Object Server，这三个服务与Proxy Server一样也是WSGI Server，通过run_wsgi()函数启动，通过Paste Deploy加载对应的WSGI ApplicationAccount Server的Paste配置文件位于/etc/swift/account-server/目录下：

[pipeline:main]
pipeline = healthcheck recon account-server
[app:account-server]
use = egg:swift#account

setup.cfg文件配置如下：

[entry_points]
paste.app_factory =
proxy = swift.proxy.server:app_factory
object = swift.obj.server:app_factory
mem_object = swift.obj.mem_server:app_factory
container = swift.container.server:app_factory
account = swift.account.server:app_factory

结合Paste配置文件与setup.cfg文件的设置，Paste Deply最终将使用swift.account.server模块的app_factory()函数加载Account Server的WSGI Application，即swift.account.server. AccountController

#swift/account/server.py
class AccountController(object):
def app_factory(global_conf, **local_conf):
"""paste.deploy app factory for creating WSGI account server apps"""
conf = global_conf.copy()
conf.update(local_conf)
return AccountController(conf)

这里的Controller与上述swift/proxy/controllers目录下的Controller不同，后者的作用是将用户的HTTP请求转发给Account Server，而前者则是对该请求的最终处理。以PUT操作为例，针对Account的PUT操作有两种语义：1 创建一个Account2 创建Account中的Container。它们的区别在于路径参数是否包含Container的信息。

#swift/account/server.py
class AccountController(object):
"""WSGI controller for the account server."""
def PUT(self, req):
"""Handle HTTP PUT request."""
#从请求参数req里面获取drive, part, account, container信息
drive, part, account, container = split_and_validate_path(req, 3, 4)
if self.mount_check and not check_mount(self.root, drive):
return HTTPInsufficientStorage(drive=drive, request=req)
#如果container的信息不为空，则视该请求为创建某个account的container
if container: # put account container
if 'x-timestamp' not in req.headers:
timestamp = Timestamp(time.time())
else:
timestamp = valid_timestamp(req)
pending_timeout = None
container_policy_index = \
req.headers.get('X-Backend-Storage-Policy-Index', 0)
if 'x-trans-id' in req.headers:
pending_timeout = 3
#构建并返回一个AccountBroker类的实例。AccountBroker类继承于
#DatabaseBroker类，其内部包括了针对account数据库文件的操作函数。
#可以把partition理解为一个目录，每一个partition中的accout数据是以这个目录
#中的数据库文件形式存在的。
#该partition中的每一个account都对应一个数据库文件。
#AccountBroker这个类将操作account数据库文件的函数加以封装，
#作为其成员函数来使用
broker = self._get_account_broker(drive, part, account,
pending_timeout=pending_timeout)
if account.startswith(self.auto_create_account_prefix) and \
not os.path.exists(broker.db_file):
try:
#如果该account的数据库文件尚未存在，则调用AccountBroker类的
#initialize（）函数创建该数据文件。
broker.initialize(timestamp.internal)
except DatabaseAlreadyExists:
pass
if req.headers.get('x-account-override-deleted', 'no').lower() != \
'yes' and broker.is_deleted():
return HTTPNotFound(request=req)
#通过调用AccountBroker中的put_container（）函数将container的信息
#写入该account的数据库文件中去。
broker.put_container(container, req.headers['x-put-timestamp'],
req.headers['x-delete-timestamp'],
req.headers['x-object-count'],
req.headers['x-bytes-used'],
container_policy_index)
if req.headers['x-delete-timestamp'] > \
req.headers['x-put-timestamp']:
return HTTPNoContent(request=req)
else:
return HTTPCreated(request=req)
#如果container的信息为空，则视该请求为创建account
else: # put account
timestamp = valid_timestamp(req)
#获取一个AccountBroker的实例
broker = self._get_account_broker(drive, part, account)
#如果该account的数据库文件未存在则创建
if not os.path.exists(broker.db_file):
try:
broker.initialize(timestamp.internal)
created = True
except DatabaseAlreadyExists:
created = False
elif broker.is_status_deleted():
return self._deleted_response(broker, req, HTTPForbidden,
body='Recently deleted')
else:
created = broker.is_deleted()
broker.update_put_timestamp(timestamp.internal)
if broker.is_deleted():
return HTTPConflict(request=req)
metadata = {}
metadata.update((key, (value, timestamp.internal))
for key, value in req.headers.iteritems()
if is_sys_or_user_meta('account', key))
if metadata:
#更新元数据
broker.update_metadata(metadata, validate_metadata=True)
if created:
return HTTPCreated(request=req)
else:
return HTTPAccepted(request=req)