GMail API在随机时刻返回未使用的错误

Question

我在谷歌应用引擎上运行一个Python应用程序，它定期检查多个用户的最新电子邮件。我注意到，在随机时刻，API返回以下错误：

error: An error occured while connecting to the server: Unable to fetch URL: https://www.googleapis.com/discovery/v1/apis/gmail/v1/rest?userIp=0.1.0.2

通常，如果作业再次运行，它就会工作。在我的代码下面。我想了解是什么导致了这种情况，更重要的是，我如何防止错误阻塞进程（例如，当抛出此错误时，如何使用相同的值再次运行作业）。

class getLatest(webapp2.RequestHandler):
  def post(self):
    try:
      email = self.request.get('email')
      g = Credentials.get_by_id(email)
      REFRESH_TOKEN = g.refresh_token
      start_history_id = g.hid
      credentials = OAuth2Credentials(None, settings.CLIENT_ID,
                             settings.CLIENT_SECRET, REFRESH_TOKEN, None,
                             GOOGLE_TOKEN_URI, None,
                             revoke_uri=GOOGLE_REVOKE_URI,
                             id_token=None,
                             token_response=None)
      http = credentials.authorize(httplib2.Http())
      service = discovery.build("gmail", "v1", http=http)
      for n in range(0, 5): 
        try:
          history = service.users().history().list(userId=email, startHistoryId=start_history_id).execute(http=http)
          break
        except errors.HttpError, e:
          if n < 4:
            time.sleep((2 ** n) + random.randint(0, 1000) / 1000)
          else:
            raise
      changes = history['history'] if 'history' in history else []
      while 'nextPageToken' in history:
        page_token = history['nextPageToken']
        for n in range(0, 5): 
          try:
            history = service.users().history().list(userId=email, startHistoryId=start_history_id, pageToken=page_token).execute(http=http)
            break
          except errors.HttpError, e:
            if n < 4:
              time.sleep((2 ** n) + random.randint(0, 1000) / 1000)
            else:
              raise
        changes.extend(history['history'])
    except errors.HttpError, error:
        logging.exception('An error occurred: '+str(error))
        if error.resp.status == 401:
            # Credentials have been revoked.
            # TODO: Redirect the user to the authorization URL.
            raise NotImplementedError()
        else:
            stacktrace = traceback.format_exc()
            logging.exception('%s', stacktrace)

更新

我根据下面的答案更新了代码，但它似乎从未多次运行请求。一旦发生异常，进程就会中止。

Answer 1

此错误可能是由于多种原因造成的，包括您的代理脱机一段时间或超过Gmail API的速率限制。如果出现这些临时问题，您需要以优雅的方式重试。以下是可能有帮助的代码编辑：

class getLatest(webapp2.RequestHandler):
  def post(self):
try:
  email = self.request.get('email')
  g = Credentials.get_by_id(email)
  REFRESH_TOKEN = g.refresh_token
  start_history_id = g.hid
  credentials = OAuth2Credentials(None, settings.CLIENT_ID,
                         settings.CLIENT_SECRET, REFRESH_TOKEN, None,
                         GOOGLE_TOKEN_URI, None,
                         revoke_uri=GOOGLE_REVOKE_URI,
                         id_token=None,
                         token_response=None)
  http = credentials.authorize(httplib2.Http())
  service = discovery.build("gmail", "v1", http=http)
  for n in range(0, 5):  
  try:
      history = service.users().history().list(userId=email, startHistoryId=start_history_id).execute(http=http)
      break
  except Exception as e:
        # Apply exponential backoff.
        time.sleep((2 ** n) + random.randint(0, 1000) / 1000)
  changes = history['history'] if 'history' in history else []
  while 'nextPageToken' in history:
    page_token = history['nextPageToken']
    for n in range(0, 5):  
    try:
       history = service.users().history().list(userId=email, startHistoryId=start_history_id, pageToken=page_token).execute(http=http)
       changes.extend(history['history'])
       break
    except Exception as e:
        # Apply exponential backoff.
        time.sleep((2 ** n) + random.randint(0, 1000) / 1000)
except errors.HttpError, error:
    logging.exception('An error occurred: '+str(error))
    if error.resp.status == 401:
        # Credentials have been revoked.
        # TODO: Redirect the user to the authorization URL.
        raise NotImplementedError()
    else:
        stacktrace = traceback.format_exc()
        logging.exception('%s', stacktrace)

从本质上讲，如果谷歌端从指数后退的同一点发生异常，则此代码会重试。添加您要重试的错误代码。希望这能解决你的问题。

Answer 2

事实证明，这与此处报告的问题相同。我在请求发现文档时达到了速率限制，您每天只需要这样做一次。我通过在我的应用程序上实现建议的解决方案解决了这个问题。代码可以在这个堆栈溢出问题中找到。