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# -------------------------------------------------------------------------
# Copyright (c) Microsoft. 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.
# --------------------------------------------------------------------------
from abc import ABCMeta
from math import pow
import random
from .models import LocationMode
class _Retry(object):
'''
The base class for Exponential and Linear retries containing shared code.
'''
__metaclass__ = ABCMeta
def __init__(self, max_attempts, retry_to_secondary):
'''
Constructs a base retry object.
:param int max_attempts:
The maximum number of retry attempts.
:param bool retry_to_secondary:
Whether the request should be retried to secondary, if able. This should
only be enabled of RA-GRS accounts are used and potentially stale data
can be handled.
'''
self.max_attempts = max_attempts
self.retry_to_secondary = retry_to_secondary
def _should_retry(self, context):
'''
A function which determines whether or not to retry.
:param ~azure.storage.models.RetryContext context:
The retry context. This contains the request, response, and other data
which can be used to determine whether or not to retry.
:return:
A boolean indicating whether or not to retry the request.
:rtype: bool
'''
# If max attempts are reached, do not retry.
if context.count >= self.max_attempts:
return False
status = None
if context.response and context.response.status:
status = context.response.status
if status is None:
'''
If status is None, retry as this request triggered an exception. For
example, network issues would trigger this.
'''
return True
elif 200 <= status < 300:
'''
This method is called after a successful response, meaning we failed
during the response body download or parsing. So, success codes should
be retried.
'''
return True
elif 300 <= status < 500:
'''
An exception occured, but in most cases it was expected. Examples could
include a 309 Conflict or 412 Precondition Failed.
'''
if status == 404 and context.location_mode == LocationMode.SECONDARY:
# Response code 404 should be retried if secondary was used.
return True
if status == 408:
# Response code 408 is a timeout and should be retried.
return True
return False
elif status >= 500:
'''
Response codes above 500 with the exception of 501 Not Implemented and
505 Version Not Supported indicate a server issue and should be retried.
'''
if status == 501 or status == 505:
return False
return True
else:
# If something else happened, it's unexpected. Retry.
return True
def _set_next_host_location(self, context):
'''
A function which sets the next host location on the request, if applicable.
:param ~azure.storage.models.RetryContext context:
The retry context containing the previous host location and the request
to evaluate and possibly modify.
'''
if len(context.request.host_locations) > 1:
# If there's more than one possible location, retry to the alternative
if context.location_mode == LocationMode.PRIMARY:
context.location_mode = LocationMode.SECONDARY
else:
context.location_mode = LocationMode.PRIMARY
context.request.host = context.request.host_locations.get(context.location_mode)
def _retry(self, context, backoff):
'''
A function which determines whether and how to retry.
:param ~azure.storage.models.RetryContext context:
The retry context. This contains the request, response, and other data
which can be used to determine whether or not to retry.
:param function() backoff:
A function which returns the backoff time if a retry is to be performed.
:return:
An integer indicating how long to wait before retrying the request,
or None to indicate no retry should be performed.
:rtype: int or None
'''
# If the context does not contain a count parameter, this request has not
# been retried yet. Add the count parameter to track the number of retries.
if not hasattr(context, 'count'):
context.count = 0
# Determine whether to retry, and if so increment the count, modify the
# request as desired, and return the backoff.
if self._should_retry(context):
backoff_interval = backoff(context)
context.count += 1
# If retry to secondary is enabled, attempt to change the host if the
# request allows it
if self.retry_to_secondary:
self._set_next_host_location(context)
return backoff_interval
return None
class ExponentialRetry(_Retry):
'''
Exponential retry.
'''
def __init__(self, initial_backoff=15, increment_power=3, max_attempts=3,
retry_to_secondary=False, random_jitter_range=3):
'''
Constructs an Exponential retry object. The initial_backoff is used for
the first retry. Subsequent retries are retried after initial_backoff +
increment_power^retry_count seconds. For example, by default the first retry
occurs after 15 seconds, the second after (15+3^1) = 18 seconds, and the
third after (15+3^2) = 24 seconds.
:param int initial_backoff:
The initial backoff interval, in seconds, for the first retry.
:param int increment_power:
The base, in seconds, to increment the initial_backoff by after the
first retry.
:param int max_attempts:
The maximum number of retry attempts.
:param bool retry_to_secondary:
Whether the request should be retried to secondary, if able. This should
only be enabled of RA-GRS accounts are used and potentially stale data
can be handled.
:param int random_jitter_range:
A number in seconds which indicates a range to jitter/randomize for the back-off interval.
For example, a random_jitter_range of 3 results in the back-off interval x to vary between x+3 and x-3.
'''
self.initial_backoff = initial_backoff
self.increment_power = increment_power
self.random_jitter_range = random_jitter_range
super(ExponentialRetry, self).__init__(max_attempts, retry_to_secondary)
'''
A function which determines whether and how to retry.
:param ~azure.storage.models.RetryContext context:
The retry context. This contains the request, response, and other data
which can be used to determine whether or not to retry.
:return:
An integer indicating how long to wait before retrying the request,
or None to indicate no retry should be performed.
:rtype: int or None
'''
def retry(self, context):
return self._retry(context, self._backoff)
'''
Calculates how long to sleep before retrying.
:return:
An integer indicating how long to wait before retrying the request,
or None to indicate no retry should be performed.
:rtype: int or None
'''
def _backoff(self, context):
random_generator = random.Random()
backoff = self.initial_backoff + (0 if context.count == 0 else pow(self.increment_power, context.count))
random_range_start = backoff - self.random_jitter_range if backoff > self.random_jitter_range else 0
random_range_end = backoff + self.random_jitter_range
return random_generator.uniform(random_range_start, random_range_end)
class LinearRetry(_Retry):
'''
Linear retry.
'''
def __init__(self, backoff=15, max_attempts=3, retry_to_secondary=False, random_jitter_range=3):
'''
Constructs a Linear retry object.
:param int backoff:
The backoff interval, in seconds, between retries.
:param int max_attempts:
The maximum number of retry attempts.
:param bool retry_to_secondary:
Whether the request should be retried to secondary, if able. This should
only be enabled of RA-GRS accounts are used and potentially stale data
can be handled.
:param int random_jitter_range:
A number in seconds which indicates a range to jitter/randomize for the back-off interval.
For example, a random_jitter_range of 3 results in the back-off interval x to vary between x+3 and x-3.
'''
self.backoff = backoff
self.max_attempts = max_attempts
self.random_jitter_range = random_jitter_range
super(LinearRetry, self).__init__(max_attempts, retry_to_secondary)
'''
A function which determines whether and how to retry.
:param ~azure.storage.models.RetryContext context:
The retry context. This contains the request, response, and other data
which can be used to determine whether or not to retry.
:return:
An integer indicating how long to wait before retrying the request,
or None to indicate no retry should be performed.
:rtype: int or None
'''
def retry(self, context):
return self._retry(context, self._backoff)
'''
Calculates how long to sleep before retrying.
:return:
An integer indicating how long to wait before retrying the request,
or None to indicate no retry should be performed.
:rtype: int or None
'''
def _backoff(self, context):
random_generator = random.Random()
# the backoff interval normally does not change, however there is the possibility
# that it was modified by accessing the property directly after initializing the object
self.random_range_start = self.backoff - self.random_jitter_range if self.backoff > self.random_jitter_range else 0
self.random_range_end = self.backoff + self.random_jitter_range
return random_generator.uniform(self.random_range_start, self.random_range_end)
def no_retry(context):
'''
Specifies never to retry.
:param ~azure.storage.models.RetryContext context:
The retry context.
:return:
Always returns None to indicate never to retry.
:rtype: None
'''
return None
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