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# Copyright 2012 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
# either express or implied. See the License for the specific
# language governing permissions and limitations under the License.
"""Base and helper classes for Google RESTful APIs."""
__all__ = ['add_sync_methods']
import random
import time
from . import api_utils
try:
from google.appengine.api import app_identity
from google.appengine.ext import ndb
except ImportError:
from google.appengine.api import app_identity
from google.appengine.ext import ndb
def _make_sync_method(name):
"""Helper to synthesize a synchronous method from an async method name.
Used by the @add_sync_methods class decorator below.
Args:
name: The name of the synchronous method.
Returns:
A method (with first argument 'self') that retrieves and calls
self.<name>, passing its own arguments, expects it to return a
Future, and then waits for and returns that Future's result.
"""
def sync_wrapper(self, *args, **kwds):
method = getattr(self, name)
future = method(*args, **kwds)
return future.get_result()
return sync_wrapper
def add_sync_methods(cls):
"""Class decorator to add synchronous methods corresponding to async methods.
This modifies the class in place, adding additional methods to it.
If a synchronous method of a given name already exists it is not
replaced.
Args:
cls: A class.
Returns:
The same class, modified in place.
"""
for name in cls.__dict__.keys():
if name.endswith('_async'):
sync_name = name[:-6]
if not hasattr(cls, sync_name):
setattr(cls, sync_name, _make_sync_method(name))
return cls
class _AE_TokenStorage_(ndb.Model):
"""Entity to store app_identity tokens in memcache."""
token = ndb.StringProperty()
expires = ndb.FloatProperty()
@ndb.tasklet
def _make_token_async(scopes, service_account_id):
"""Get a fresh authentication token.
Args:
scopes: A list of scopes.
service_account_id: Internal-use only.
Raises:
An ndb.Return with a tuple (token, expiration_time) where expiration_time is
seconds since the epoch.
"""
rpc = app_identity.create_rpc()
app_identity.make_get_access_token_call(rpc, scopes, service_account_id)
token, expires_at = yield rpc
raise ndb.Return((token, expires_at))
class _RestApi(object):
"""Base class for REST-based API wrapper classes.
This class manages authentication tokens and request retries. All
APIs are available as synchronous and async methods; synchronous
methods are synthesized from async ones by the add_sync_methods()
function in this module.
WARNING: Do NOT directly use this api. It's an implementation detail
and is subject to change at any release.
"""
def __init__(self, scopes, service_account_id=None, token_maker=None,
retry_params=None):
"""Constructor.
Args:
scopes: A scope or a list of scopes.
service_account_id: Internal use only.
token_maker: An asynchronous function of the form
(scopes, service_account_id) -> (token, expires).
retry_params: An instance of api_utils.RetryParams. If None, the
default for current thread will be used.
"""
if isinstance(scopes, basestring):
scopes = [scopes]
self.scopes = scopes
self.service_account_id = service_account_id
self.make_token_async = token_maker or _make_token_async
if not retry_params:
retry_params = api_utils._get_default_retry_params()
self.retry_params = retry_params
self.user_agent = {'User-Agent': retry_params._user_agent}
self.expiration_headroom = random.randint(60, 240)
def __getstate__(self):
"""Store state as part of serialization/pickling."""
return {'scopes': self.scopes,
'id': self.service_account_id,
'a_maker': (None if self.make_token_async == _make_token_async
else self.make_token_async),
'retry_params': self.retry_params,
'expiration_headroom': self.expiration_headroom}
def __setstate__(self, state):
"""Restore state as part of deserialization/unpickling."""
self.__init__(state['scopes'],
service_account_id=state['id'],
token_maker=state['a_maker'],
retry_params=state['retry_params'])
self.expiration_headroom = state['expiration_headroom']
@ndb.tasklet
def do_request_async(self, url, method='GET', headers=None, payload=None,
deadline=None, callback=None):
"""Issue one HTTP request.
It performs async retries using tasklets.
Args:
url: the url to fetch.
method: the method in which to fetch.
headers: the http headers.
payload: the data to submit in the fetch.
deadline: the deadline in which to make the call.
callback: the call to make once completed.
Yields:
The async fetch of the url.
"""
retry_wrapper = api_utils._RetryWrapper(
self.retry_params,
retriable_exceptions=api_utils._RETRIABLE_EXCEPTIONS,
should_retry=api_utils._should_retry)
resp = yield retry_wrapper.run(
self.urlfetch_async,
url=url,
method=method,
headers=headers,
payload=payload,
deadline=deadline,
callback=callback,
follow_redirects=False)
raise ndb.Return((resp.status_code, resp.headers, resp.content))
@ndb.tasklet
def get_token_async(self, refresh=False):
"""Get an authentication token.
The token is cached in memcache, keyed by the scopes argument.
Uses a random token expiration headroom value generated in the constructor
to eliminate a burst of GET_ACCESS_TOKEN API requests.
Args:
refresh: If True, ignore a cached token; default False.
Yields:
An authentication token. This token is guaranteed to be non-expired.
"""
key = '%s,%s' % (self.service_account_id, ','.join(self.scopes))
ts = yield _AE_TokenStorage_.get_by_id_async(
key, use_cache=True, use_memcache=True,
use_datastore=self.retry_params.save_access_token)
if refresh or ts is None or ts.expires < (
time.time() + self.expiration_headroom):
token, expires_at = yield self.make_token_async(
self.scopes, self.service_account_id)
timeout = int(expires_at - time.time())
ts = _AE_TokenStorage_(id=key, token=token, expires=expires_at)
if timeout > 0:
yield ts.put_async(memcache_timeout=timeout,
use_datastore=self.retry_params.save_access_token,
use_cache=True, use_memcache=True)
raise ndb.Return(ts.token)
@ndb.tasklet
def urlfetch_async(self, url, method='GET', headers=None,
payload=None, deadline=None, callback=None,
follow_redirects=False):
"""Make an async urlfetch() call.
This is an async wrapper around urlfetch(). It adds an authentication
header.
Args:
url: the url to fetch.
method: the method in which to fetch.
headers: the http headers.
payload: the data to submit in the fetch.
deadline: the deadline in which to make the call.
callback: the call to make once completed.
follow_redirects: whether or not to follow redirects.
Yields:
This returns a Future despite not being decorated with @ndb.tasklet!
"""
headers = {} if headers is None else dict(headers)
headers.update(self.user_agent)
self.token = yield self.get_token_async()
if self.token:
headers['authorization'] = 'OAuth ' + self.token
deadline = deadline or self.retry_params.urlfetch_timeout
ctx = ndb.get_context()
resp = yield ctx.urlfetch(
url, payload=payload, method=method,
headers=headers, follow_redirects=follow_redirects,
deadline=deadline, callback=callback)
raise ndb.Return(resp)
_RestApi = add_sync_methods(_RestApi)
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