"""Utility functions for parsing and converting expiration values"""
from datetime import datetime, timedelta, timezone
from email.utils import parsedate_to_datetime
from fnmatch import fnmatch
from logging import getLogger
from math import ceil
from typing import Optional
from typing import Pattern as RegexPattern
from .._utils import try_int
from . import ExpirationPattern, ExpirationPatterns, ExpirationTime
# Special expiration values that may be set by either headers or keyword args
DO_NOT_CACHE = 0x0D0E0200020704 # Per RFC 4824
EXPIRE_IMMEDIATELY = 0
NEVER_EXPIRE = -1
logger = getLogger(__name__)
[docs]def get_expiration_datetime(
expire_after: ExpirationTime,
start_time: Optional[datetime] = None,
negative_delta: bool = False,
ignore_invalid_httpdate: bool = False,
) -> Optional[datetime]:
"""Convert an expiration value in any supported format to an absolute datetime"""
# Never expire (or do not cache, in which case expiration won't be used)
if expire_after is None or expire_after in [NEVER_EXPIRE, DO_NOT_CACHE]:
return None
# Expire immediately
elif try_int(expire_after) == EXPIRE_IMMEDIATELY:
return start_time or utcnow()
# Already a datetime or httpdate str (allowed for headers only)
if isinstance(expire_after, str):
expire_after_dt = _parse_http_date(expire_after)
if not expire_after_dt and not ignore_invalid_httpdate:
raise ValueError(f'Invalid HTTP date: {expire_after}')
return expire_after_dt
elif isinstance(expire_after, datetime):
return expire_after.astimezone(timezone.utc)
# Otherwise, it must be a timedelta or time in seconds
if not isinstance(expire_after, timedelta):
expire_after = timedelta(seconds=expire_after)
if negative_delta:
expire_after = -expire_after
return (start_time or utcnow()) + expire_after
[docs]def get_expiration_seconds(expire_after: ExpirationTime) -> int:
"""Convert an expiration value in any supported format to an expiration time in seconds"""
if expire_after == DO_NOT_CACHE:
return DO_NOT_CACHE
expires = get_expiration_datetime(expire_after, ignore_invalid_httpdate=True)
return ceil((expires - utcnow()).total_seconds()) if expires else NEVER_EXPIRE
[docs]def get_url_expiration(
url: Optional[str], urls_expire_after: Optional[ExpirationPatterns] = None
) -> ExpirationTime:
"""Check for a matching per-URL expiration, if any"""
if not url:
return None
for pattern, expire_after in (urls_expire_after or {}).items():
if _url_match(url, pattern):
logger.debug(f'URL {url} matched pattern "{pattern}": {expire_after}')
return expire_after
return None
[docs]def add_tzinfo(dt: Optional[datetime]) -> Optional[datetime]:
"""Add a UTC timezone to a datetime object, if it doesn't already have one. This is used mainly
during deserialization for backends that don't store timezone info.
"""
if dt and dt.tzinfo is None:
return dt.replace(tzinfo=timezone.utc)
return dt
[docs]def utcnow() -> datetime:
"""Get the current time in UTC (timezone-aware)"""
return datetime.now(timezone.utc)
def _parse_http_date(value: str) -> Optional[datetime]:
"""Attempt to parse an HTTP (RFC 5322-compatible) timestamp"""
try:
expire_after = parsedate_to_datetime(value)
return expire_after.astimezone(timezone.utc)
except (TypeError, ValueError):
logger.debug(f'Failed to parse timestamp: {value}')
return None
def _url_match(url: str, pattern: ExpirationPattern) -> bool:
"""Determine if a URL matches a pattern
Args:
url: URL to test. Its base URL (without protocol) will be used.
pattern: Glob pattern to match against. A recursive wildcard will be added if not present
Example:
>>> url_match('https://httpbin.org/delay/1', 'httpbin.org/delay')
True
>>> url_match('https://httpbin.org/stream/1', 'httpbin.org/*/1')
True
>>> url_match('https://httpbin.org/stream/2', 'httpbin.org/*/1')
False
>>> url_match('https://httpbin.org/stream/2', re.compile('httpbin.org/*/\\d+'))
True
>>> url_match('https://httpbin.org/stream/x', re.compile('httpbin.org/*/\\d+'))
False
"""
if isinstance(pattern, RegexPattern):
match = pattern.search(url)
return match is not None
else:
url = url.split('://')[-1]
pattern = pattern.split('://')[-1].rstrip('*') + '**'
return fnmatch(url, pattern)