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quay/util/failover.py

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import logging
from functools import wraps
logger = logging.getLogger(__name__)
class FailoverException(Exception):
""" Exception raised when an operation should be retried by the failover decorator.
Wraps the exception of the initial failure.
"""
def __init__(self, exception):
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super(FailoverException, self).__init__()
self.exception = exception
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def failover(func):
""" Wraps a function such that it can be retried on specified failures.
Raises FailoverException when all failovers are exhausted.
Example:
@failover
def get_google(scheme, use_www=False):
www = 'www.' if use_www else ''
try:
r = requests.get(scheme + '://' + www + 'google.com')
except requests.RequestException as ex:
raise FailoverException(ex)
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return r
def GooglePingTest():
r = get_google(
(('http'), {'use_www': False}),
(('http'), {'use_www': True}),
(('https'), {'use_www': False}),
(('https'), {'use_www': True}),
)
print('Successfully contacted ' + r.url)
"""
@wraps(func)
def wrapper(*args_sets):
for arg_set in args_sets:
try:
return func(*arg_set[0], **arg_set[1])
except FailoverException as ex:
logger.debug('failing over')
exception = ex.exception
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continue
raise exception
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return wrapper