5
我们有两个应用程序都在Google App Engine上运行。 App1向app2发出请求，作为已通过身份验证的用户。该身份验证通过向Google ClientLogin请求用于交换cookie的身份验证令牌起作用。该cookie随后用于后续请求（如描述here）。 APP1运行以下代码：Google App Engine上的间歇性下载错误应用程序错误2
class AuthConnection:
def __init__(self):
self.cookie_jar = cookielib.CookieJar()
self.opener = urllib2.OpenerDirector()
self.opener.add_handler(urllib2.ProxyHandler())
self.opener.add_handler(urllib2.UnknownHandler())
self.opener.add_handler(urllib2.HTTPHandler())
self.opener.add_handler(urllib2.HTTPRedirectHandler())
self.opener.add_handler(urllib2.HTTPDefaultErrorHandler())
self.opener.add_handler(urllib2.HTTPSHandler())
self.opener.add_handler(urllib2.HTTPErrorProcessor())
self.opener.add_handler(urllib2.HTTPCookieProcessor(self.cookie_jar))
self.headers = {'User-Agent': 'Mozilla/5.0 (Windows; U; ' +\
'Windows NT 6.1; en-US; rv:1.9.1.2) ' +\
'Gecko/20090729 Firefox/3.5.2 ' +\
'(.NET CLR 3.5.30729)'
}
def fetch(self, url, method, payload=None):
self.__updateJar(url)
request = urllib2.Request(url)
request.get_method = lambda: method
for key, value in self.headers.iteritems():
request.add_header(key, value)
response = self.opener.open(request)
return response.read()
def __updateJar(self, url):
cache = memcache.Client()
cookie = cache.get('auth_cookie')
if cookie:
self.cookie_jar.set_cookie(cookie)
else:
cookie = self.__retrieveCookie(url=url)
cache.set('auth_cookie', cookie, 5000)
def __getCookie(self, url):
auth_url = 'https://www.google.com/accounts/ClientLogin'
auth_data = urllib.urlencode({'Email': USER_NAME,
'Passwd': PASSPHRASE,
'service': 'ah',
'source': 'app1',
'accountType': 'HOSTED_OR_GOOGLE' })
auth_request = urllib2.Request(auth_url, data=auth_data)
auth_response_body = self.opener.open(auth_request).read()
auth_response_dict = dict(x.split('=')
for x in auth_response_body.split('\n') if x)
cookie_args = {}
cookie_args['continue'] = url
cookie_args['auth'] = auth_response_dict['Auth']
cookie_url = 'https://%s/_ah/login?%s' %\
('app2.appspot.com', (urllib.urlencode(cookie_args)))
cookie_request = urllib2.Request(cookie_url)
for key, value in self.headers.iteritems():
cookie_request.add_header(key, value)
try:
self.opener.open(cookie_request)
except:
pass
for cookie in self.cookie_jar:
if cookie.domain == 'app2domain':
return cookie
对于请求的10- 30％DownloadError升高：
Error fetching https://app2/Resource
Traceback (most recent call last):
File "/base/data/home/apps/app1/5.344034030246386521/source/main/connection/authenticate.py", line 112, in fetch
response = self.opener.open(request)
File "/base/python_runtime/python_dist/lib/python2.5/urllib2.py", line 381, in open
response = self._open(req, data)
File "/base/python_runtime/python_dist/lib/python2.5/urllib2.py", line 399, in _open
'_open', req)
File "/base/python_runtime/python_dist/lib/python2.5/urllib2.py", line 360, in _call_chain
result = func(*args)
File "/base/python_runtime/python_dist/lib/python2.5/urllib2.py", line 1115, in https_open
return self.do_open(httplib.HTTPSConnection, req)
File "/base/python_runtime/python_dist/lib/python2.5/urllib2.py", line 1080, in do_open
r = h.getresponse()
File "/base/python_runtime/python_dist/lib/python2.5/httplib.py", line 197, in getresponse
self._allow_truncated, self._follow_redirects)
File "/base/data/home/apps/app1/5.344034030246386521/source/main/connection/monkeypatch_urlfetch_deadline.py", line 18, in new_fetch
follow_redirects, deadline, *args, **kwargs)
File "/base/python_runtime/python_lib/versions/1/google/appengine/api/urlfetch.py", line 241, in fetch
return rpc.get_result()
File "/base/python_runtime/python_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 501, in get_result
return self.__get_result_hook(self)
File "/base/python_runtime/python_lib/versions/1/google/appengine/api/urlfetch.py", line 325, in _get_fetch_result
raise DownloadError(str(err))
DownloadError: ApplicationError: 2
为APP2（ “服务器”）的请求日志似乎很好，为预期的（根据文档，只有在没有有效的HTTP响应时才会引发DownloadError）。
为什么会引发异常？