在Google App Engine上出现间歇性下载错误2应用程序错误

Question

我们有两个应用程序，它们都在Google App Engine上运行。应用程序1（App1）作为一个经过认证的用户向应用程序2（App2）发送请求。认证的过程是通过向Google的ClientLogin请求一个认证令牌，然后用这个令牌换取一个cookie。之后，这个cookie会被用来处理后续的请求（具体可以参考这里）。App1运行了以下代码：

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

在10%到30%的请求中，会出现一个下载错误（DownloadError）：

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

对于应用程序2（“服务器”）的请求日志来看，一切正常，符合预期（根据文档，只有在没有有效的HTTP响应时才会出现下载错误）。

那么，为什么会出现这个异常呢？

异常处理 google app engine 认证令牌应用程序间通信请求日志客户端认证 http 响应下载错误

在Google App Engine上出现间歇性下载错误2应用程序错误

1 个回答

撰写回答