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Diffstat (limited to 'python/urllib3/util/retry.py')
| -rw-r--r-- | python/urllib3/util/retry.py | 411 |
1 files changed, 411 insertions, 0 deletions
diff --git a/python/urllib3/util/retry.py b/python/urllib3/util/retry.py new file mode 100644 index 0000000..e7d0abd --- /dev/null +++ b/python/urllib3/util/retry.py @@ -0,0 +1,411 @@ +from __future__ import absolute_import +import time +import logging +from collections import namedtuple +from itertools import takewhile +import email +import re + +from ..exceptions import ( + ConnectTimeoutError, + MaxRetryError, + ProtocolError, + ReadTimeoutError, + ResponseError, + InvalidHeader, +) +from ..packages import six + + +log = logging.getLogger(__name__) + + +# Data structure for representing the metadata of requests that result in a retry. +RequestHistory = namedtuple('RequestHistory', ["method", "url", "error", + "status", "redirect_location"]) + + +class Retry(object): + """ Retry configuration. + + Each retry attempt will create a new Retry object with updated values, so + they can be safely reused. + + Retries can be defined as a default for a pool:: + + retries = Retry(connect=5, read=2, redirect=5) + http = PoolManager(retries=retries) + response = http.request('GET', 'http://example.com/') + + Or per-request (which overrides the default for the pool):: + + response = http.request('GET', 'http://example.com/', retries=Retry(10)) + + Retries can be disabled by passing ``False``:: + + response = http.request('GET', 'http://example.com/', retries=False) + + Errors will be wrapped in :class:`~urllib3.exceptions.MaxRetryError` unless + retries are disabled, in which case the causing exception will be raised. + + :param int total: + Total number of retries to allow. Takes precedence over other counts. + + Set to ``None`` to remove this constraint and fall back on other + counts. It's a good idea to set this to some sensibly-high value to + account for unexpected edge cases and avoid infinite retry loops. + + Set to ``0`` to fail on the first retry. + + Set to ``False`` to disable and imply ``raise_on_redirect=False``. + + :param int connect: + How many connection-related errors to retry on. + + These are errors raised before the request is sent to the remote server, + which we assume has not triggered the server to process the request. + + Set to ``0`` to fail on the first retry of this type. + + :param int read: + How many times to retry on read errors. + + These errors are raised after the request was sent to the server, so the + request may have side-effects. + + Set to ``0`` to fail on the first retry of this type. + + :param int redirect: + How many redirects to perform. Limit this to avoid infinite redirect + loops. + + A redirect is a HTTP response with a status code 301, 302, 303, 307 or + 308. + + Set to ``0`` to fail on the first retry of this type. + + Set to ``False`` to disable and imply ``raise_on_redirect=False``. + + :param int status: + How many times to retry on bad status codes. + + These are retries made on responses, where status code matches + ``status_forcelist``. + + Set to ``0`` to fail on the first retry of this type. + + :param iterable method_whitelist: + Set of uppercased HTTP method verbs that we should retry on. + + By default, we only retry on methods which are considered to be + idempotent (multiple requests with the same parameters end with the + same state). See :attr:`Retry.DEFAULT_METHOD_WHITELIST`. + + Set to a ``False`` value to retry on any verb. + + :param iterable status_forcelist: + A set of integer HTTP status codes that we should force a retry on. + A retry is initiated if the request method is in ``method_whitelist`` + and the response status code is in ``status_forcelist``. + + By default, this is disabled with ``None``. + + :param float backoff_factor: + A backoff factor to apply between attempts after the second try + (most errors are resolved immediately by a second try without a + delay). urllib3 will sleep for:: + + {backoff factor} * (2 ** ({number of total retries} - 1)) + + seconds. If the backoff_factor is 0.1, then :func:`.sleep` will sleep + for [0.0s, 0.2s, 0.4s, ...] between retries. It will never be longer + than :attr:`Retry.BACKOFF_MAX`. + + By default, backoff is disabled (set to 0). + + :param bool raise_on_redirect: Whether, if the number of redirects is + exhausted, to raise a MaxRetryError, or to return a response with a + response code in the 3xx range. + + :param bool raise_on_status: Similar meaning to ``raise_on_redirect``: + whether we should raise an exception, or return a response, + if status falls in ``status_forcelist`` range and retries have + been exhausted. + + :param tuple history: The history of the request encountered during + each call to :meth:`~Retry.increment`. The list is in the order + the requests occurred. Each list item is of class :class:`RequestHistory`. + + :param bool respect_retry_after_header: + Whether to respect Retry-After header on status codes defined as + :attr:`Retry.RETRY_AFTER_STATUS_CODES` or not. + + :param iterable remove_headers_on_redirect: + Sequence of headers to remove from the request when a response + indicating a redirect is returned before firing off the redirected + request. + """ + + DEFAULT_METHOD_WHITELIST = frozenset([ + 'HEAD', 'GET', 'PUT', 'DELETE', 'OPTIONS', 'TRACE']) + + RETRY_AFTER_STATUS_CODES = frozenset([413, 429, 503]) + + DEFAULT_REDIRECT_HEADERS_BLACKLIST = frozenset(['Authorization']) + + #: Maximum backoff time. + BACKOFF_MAX = 120 + + def __init__(self, total=10, connect=None, read=None, redirect=None, status=None, + method_whitelist=DEFAULT_METHOD_WHITELIST, status_forcelist=None, + backoff_factor=0, raise_on_redirect=True, raise_on_status=True, + history=None, respect_retry_after_header=True, + remove_headers_on_redirect=DEFAULT_REDIRECT_HEADERS_BLACKLIST): + + self.total = total + self.connect = connect + self.read = read + self.status = status + + if redirect is False or total is False: + redirect = 0 + raise_on_redirect = False + + self.redirect = redirect + self.status_forcelist = status_forcelist or set() + self.method_whitelist = method_whitelist + self.backoff_factor = backoff_factor + self.raise_on_redirect = raise_on_redirect + self.raise_on_status = raise_on_status + self.history = history or tuple() + self.respect_retry_after_header = respect_retry_after_header + self.remove_headers_on_redirect = remove_headers_on_redirect + + def new(self, **kw): + params = dict( + total=self.total, + connect=self.connect, read=self.read, redirect=self.redirect, status=self.status, + method_whitelist=self.method_whitelist, + status_forcelist=self.status_forcelist, + backoff_factor=self.backoff_factor, + raise_on_redirect=self.raise_on_redirect, + raise_on_status=self.raise_on_status, + history=self.history, + remove_headers_on_redirect=self.remove_headers_on_redirect + ) + params.update(kw) + return type(self)(**params) + + @classmethod + def from_int(cls, retries, redirect=True, default=None): + """ Backwards-compatibility for the old retries format.""" + if retries is None: + retries = default if default is not None else cls.DEFAULT + + if isinstance(retries, Retry): + return retries + + redirect = bool(redirect) and None + new_retries = cls(retries, redirect=redirect) + log.debug("Converted retries value: %r -> %r", retries, new_retries) + return new_retries + + def get_backoff_time(self): + """ Formula for computing the current backoff + + :rtype: float + """ + # We want to consider only the last consecutive errors sequence (Ignore redirects). + consecutive_errors_len = len(list(takewhile(lambda x: x.redirect_location is None, + reversed(self.history)))) + if consecutive_errors_len <= 1: + return 0 + + backoff_value = self.backoff_factor * (2 ** (consecutive_errors_len - 1)) + return min(self.BACKOFF_MAX, backoff_value) + + def parse_retry_after(self, retry_after): + # Whitespace: https://tools.ietf.org/html/rfc7230#section-3.2.4 + if re.match(r"^\s*[0-9]+\s*$", retry_after): + seconds = int(retry_after) + else: + retry_date_tuple = email.utils.parsedate(retry_after) + if retry_date_tuple is None: + raise InvalidHeader("Invalid Retry-After header: %s" % retry_after) + retry_date = time.mktime(retry_date_tuple) + seconds = retry_date - time.time() + + if seconds < 0: + seconds = 0 + + return seconds + + def get_retry_after(self, response): + """ Get the value of Retry-After in seconds. """ + + retry_after = response.getheader("Retry-After") + + if retry_after is None: + return None + + return self.parse_retry_after(retry_after) + + def sleep_for_retry(self, response=None): + retry_after = self.get_retry_after(response) + if retry_after: + time.sleep(retry_after) + return True + + return False + + def _sleep_backoff(self): + backoff = self.get_backoff_time() + if backoff <= 0: + return + time.sleep(backoff) + + def sleep(self, response=None): + """ Sleep between retry attempts. + + This method will respect a server's ``Retry-After`` response header + and sleep the duration of the time requested. If that is not present, it + will use an exponential backoff. By default, the backoff factor is 0 and + this method will return immediately. + """ + + if response: + slept = self.sleep_for_retry(response) + if slept: + return + + self._sleep_backoff() + + def _is_connection_error(self, err): + """ Errors when we're fairly sure that the server did not receive the + request, so it should be safe to retry. + """ + return isinstance(err, ConnectTimeoutError) + + def _is_read_error(self, err): + """ Errors that occur after the request has been started, so we should + assume that the server began processing it. + """ + return isinstance(err, (ReadTimeoutError, ProtocolError)) + + def _is_method_retryable(self, method): + """ Checks if a given HTTP method should be retried upon, depending if + it is included on the method whitelist. + """ + if self.method_whitelist and method.upper() not in self.method_whitelist: + return False + + return True + + def is_retry(self, method, status_code, has_retry_after=False): + """ Is this method/status code retryable? (Based on whitelists and control + variables such as the number of total retries to allow, whether to + respect the Retry-After header, whether this header is present, and + whether the returned status code is on the list of status codes to + be retried upon on the presence of the aforementioned header) + """ + if not self._is_method_retryable(method): + return False + + if self.status_forcelist and status_code in self.status_forcelist: + return True + + return (self.total and self.respect_retry_after_header and + has_retry_after and (status_code in self.RETRY_AFTER_STATUS_CODES)) + + def is_exhausted(self): + """ Are we out of retries? """ + retry_counts = (self.total, self.connect, self.read, self.redirect, self.status) + retry_counts = list(filter(None, retry_counts)) + if not retry_counts: + return False + + return min(retry_counts) < 0 + + def increment(self, method=None, url=None, response=None, error=None, + _pool=None, _stacktrace=None): + """ Return a new Retry object with incremented retry counters. + + :param response: A response object, or None, if the server did not + return a response. + :type response: :class:`~urllib3.response.HTTPResponse` + :param Exception error: An error encountered during the request, or + None if the response was received successfully. + + :return: A new ``Retry`` object. + """ + if self.total is False and error: + # Disabled, indicate to re-raise the error. + raise six.reraise(type(error), error, _stacktrace) + + total = self.total + if total is not None: + total -= 1 + + connect = self.connect + read = self.read + redirect = self.redirect + status_count = self.status + cause = 'unknown' + status = None + redirect_location = None + + if error and self._is_connection_error(error): + # Connect retry? + if connect is False: + raise six.reraise(type(error), error, _stacktrace) + elif connect is not None: + connect -= 1 + + elif error and self._is_read_error(error): + # Read retry? + if read is False or not self._is_method_retryable(method): + raise six.reraise(type(error), error, _stacktrace) + elif read is not None: + read -= 1 + + elif response and response.get_redirect_location(): + # Redirect retry? + if redirect is not None: + redirect -= 1 + cause = 'too many redirects' + redirect_location = response.get_redirect_location() + status = response.status + + else: + # Incrementing because of a server error like a 500 in + # status_forcelist and a the given method is in the whitelist + cause = ResponseError.GENERIC_ERROR + if response and response.status: + if status_count is not None: + status_count -= 1 + cause = ResponseError.SPECIFIC_ERROR.format( + status_code=response.status) + status = response.status + + history = self.history + (RequestHistory(method, url, error, status, redirect_location),) + + new_retry = self.new( + total=total, + connect=connect, read=read, redirect=redirect, status=status_count, + history=history) + + if new_retry.is_exhausted(): + raise MaxRetryError(_pool, url, error or ResponseError(cause)) + + log.debug("Incremented Retry for (url='%s'): %r", url, new_retry) + + return new_retry + + def __repr__(self): + return ('{cls.__name__}(total={self.total}, connect={self.connect}, ' + 'read={self.read}, redirect={self.redirect}, status={self.status})').format( + cls=type(self), self=self) + + +# For backwards compatibility (equivalent to pre-v1.9): +Retry.DEFAULT = Retry(3) |