text: from __future__ import absolute_import
  
  import logging
  import os
  import warnings
  
  from ..exceptions import (
      HTTPError,
      HTTPWarning,
      MaxRetryError,
      ProtocolError,
      TimeoutError,
      SSLError
  )
  from ..packages.six import BytesIO
  from ..request import RequestMethods
  from ..response import HTTPResponse
  from ..util.retry import Retry
  from ..util.timeout import Timeout
  
  
  try:
      from google.appengine.api import urlfetch
  except ImportError:
      urlfetch = None
  
  
  log = logging.getLogger(__name__)
  
  
  class AppEnginePlatformWarning(HTTPWarning):
      pass
  
  
  class AppEnginePlatformError(HTTPError):
      pass
  
  
  class AppEngineManager(RequestMethods):
      """
      Connection manager for Google App Engine sandbox applications.
  
      This manager uses the URLFetch service directly instead of using the
      emulated httplib, and is subject to URLFetch limitations as described in
      the App Engine documentation here:
  
          https://cloud.google.com/appengine/docs/python/urlfetch
  
      Notably it will raise an AppEnginePlatformError if:
          * URLFetch is not available.
          * If you attempt to use this on GAEv2 (Managed VMs), as full socket
            support is available.
          * If a request size is more than 10 megabytes.
          * If a response size is more than 32 megabtyes.
          * If you use an unsupported request method such as OPTIONS.
  
      Beyond those cases, it will raise normal urllib3 errors.
      """
  
      def __init__(self, headers=None, retries=None, validate_certificate=True):
          if not urlfetch:
              raise AppEnginePlatformError(
                  "URLFetch is not available in this environment.")
  
          if is_prod_appengine_mvms():
              raise AppEnginePlatformError(
                  "Use normal urllib3.PoolManager instead of AppEngineManager"
                  "on Managed VMs, as using URLFetch is not necessary in "
                  "this environment.")
  
          warnings.warn(
              "urllib3 is using URLFetch on Google App Engine sandbox instead "
              "of sockets. To use sockets directly instead of URLFetch see "
              "https://urllib3.readthedocs.org/en/latest/contrib.html.",
              AppEnginePlatformWarning)
  
          RequestMethods.__init__(self, headers)
          self.validate_certificate = validate_certificate
  
          self.retries = retries or Retry.DEFAULT
  
      def __enter__(self):
          return self
  
      def __exit__(self, exc_type, exc_val, exc_tb):
          # Return False to re-raise any potential exceptions
          return False
  
      def urlopen(self, method, url, body=None, headers=None,
                  retries=None, redirect=True, timeout=Timeout.DEFAULT_TIMEOUT,
                  **response_kw):
  
          retries = self._get_retries(retries, redirect)
  
          try:
              response = urlfetch.fetch(
                  url,
                  payload=body,
                  method=method,
                  headers=headers or {},
                  allow_truncated=False,
                  follow_redirects=(
                      redirect and
                      retries.redirect != 0 and
                      retries.total),
                  deadline=self._get_absolute_timeout(timeout),
                  validate_certificate=self.validate_certificate,
              )
          except urlfetch.DeadlineExceededError as e:
              raise TimeoutError(self, e)
  
          except urlfetch.InvalidURLError as e:
              if 'too large' in str(e):
                  raise AppEnginePlatformError(
                      "URLFetch request too large, URLFetch only "
                      "supports requests up to 10mb in size.", e)
              raise ProtocolError(e)
  
          except urlfetch.DownloadError as e:
              if 'Too many redirects' in str(e):
                  raise MaxRetryError(self, url, reason=e)
              raise ProtocolError(e)
  
          except urlfetch.ResponseTooLargeError as e:
              raise AppEnginePlatformError(
                  "URLFetch response too large, URLFetch only supports"
                  "responses up to 32mb in size.", e)
  
          except urlfetch.SSLCertificateError as e:
              raise SSLError(e)
  
          except urlfetch.InvalidMethodError as e:
              raise AppEnginePlatformError(
                  "URLFetch does not support method: %s" % method, e)
  
          http_response = self._urlfetch_response_to_http_response(
              response, **response_kw)
  
          # Check for redirect response
          if (http_response.get_redirect_location() and
                  retries.raise_on_redirect and redirect):
              raise MaxRetryError(self, url, "too many redirects")
  
          # Check if we should retry the HTTP response.
          if retries.is_forced_retry(method, status_code=http_response.status):
              retries = retries.increment(
                  method, url, response=http_response, _pool=self)
              log.info("Forced retry: %s" % url)
              retries.sleep()
              return self.urlopen(
                  method, url,
                  body=body, headers=headers,
                  retries=retries, redirect=redirect,
                  timeout=timeout, **response_kw)
  
          return http_response
  
      def _urlfetch_response_to_http_response(self, urlfetch_resp, **response_kw):
  
          if is_prod_appengine():
              # Production GAE handles deflate encoding automatically, but does
              # not remove the encoding header.
              content_encoding = urlfetch_resp.headers.get('content-encoding')
  
              if content_encoding == 'deflate':
                  del urlfetch_resp.headers['content-encoding']
  
          return HTTPResponse(
              # In order for decoding to work, we must present the content as
              # a file-like object.
              body=BytesIO(urlfetch_resp.content),
              headers=urlfetch_resp.headers,
              status=urlfetch_resp.status_code,
              **response_kw
          )
  
      def _get_absolute_timeout(self, timeout):
          if timeout is Timeout.DEFAULT_TIMEOUT:
              return 5  # 5s is the default timeout for URLFetch.
          if isinstance(timeout, Timeout):
              if timeout.read is not timeout.connect:
                  warnings.warn(
                      "URLFetch does not support granular timeout settings, "
                      "reverting to total timeout.", AppEnginePlatformWarning)
              return timeout.total
          return timeout
  
      def _get_retries(self, retries, redirect):
          if not isinstance(retries, Retry):
              retries = Retry.from_int(
                  retries, redirect=redirect, default=self.retries)
  
          if retries.connect or retries.read or retries.redirect:
              warnings.warn(
                  "URLFetch only supports total retries and does not "
                  "recognize connect, read, or redirect retry parameters.",
                  AppEnginePlatformWarning)
  
          return retries
  
  
  def is_appengine():
      return (is_local_appengine() or
              is_prod_appengine() or
              is_prod_appengine_mvms())
  
  
  def is_appengine_sandbox():
      return is_appengine() and not is_prod_appengine_mvms()
  
  
  def is_local_appengine():
      return ('APPENGINE_RUNTIME' in os.environ and
              'Development/' in os.environ['SERVER_SOFTWARE'])
  
  
  def is_prod_appengine():
      return ('APPENGINE_RUNTIME' in os.environ and
              'Google App Engine/' in os.environ['SERVER_SOFTWARE'] and
              not is_prod_appengine_mvms())
  
  
  def is_prod_appengine_mvms():
      return os.environ.get('GAE_VM', False) == 'true'
  