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from datetime import timedelta
from typing import Optional
from attr import define, field
from requests.models import CaseInsensitiveDict
from .._utils import decode, get_valid_kwargs, try_int
from ..models import RichMixin
from . import HeaderDict, get_expiration_seconds
@define(repr=False)
class CacheDirectives(RichMixin):
"""Parses Cache-Control directives and other relevant cache settings from either request or
response headers
"""
expires: str = field(default=None)
immutable: bool = field(default=False)
max_age: int = field(default=None, converter=try_int)
max_stale: int = field(default=None, converter=try_int)
min_fresh: int = field(default=None, converter=try_int)
must_revalidate: bool = field(default=False)
no_cache: bool = field(default=False)
no_store: bool = field(default=False)
only_if_cached: bool = field(default=False)
stale_if_error: int = field(default=None, converter=try_int)
stale_while_revalidate: int = field(default=None, converter=try_int)
etag: str = field(default=None)
last_modified: str = field(default=None)
@classmethod
def from_headers(cls, headers: HeaderDict):
"""Parse cache directives and other settings from request or response headers"""
headers = CaseInsensitiveDict(headers)
directives = decode(headers.get('Cache-Control', '')).split(',')
kv_directives = dict(_split_kv_directive(value) for value in directives)
kwargs = get_valid_kwargs(
cls.__init__, {k.replace('-', '_'): v for k, v in kv_directives.items()}
)
kwargs['expires'] = headers.get('Expires')
kwargs['etag'] = headers.get('ETag')
kwargs['last_modified'] = headers.get('Last-Modified')
return cls(**kwargs)
def get_expire_offset(self) -> timedelta:
"""Return the time offset to use for expiration, if either min-fresh or max-stale is set"""
offset_seconds = 0
if self.max_stale:
offset_seconds = self.max_stale
elif self.min_fresh:
offset_seconds = -self.min_fresh
return timedelta(seconds=offset_seconds)
@property
def has_validator(self) -> bool:
return bool(self.etag or self.last_modified)
def _split_kv_directive(directive: str):
"""Split a cache directive into a `(key, value)` pair, or `(key, True)` if value-only"""
directive = directive.strip().lower()
return directive.split('=', 1) if '=' in directive else (directive, True)
def set_request_headers(
headers: Optional[HeaderDict], expire_after, only_if_cached, refresh, force_refresh
):
"""Translate keyword arguments into equivalent request headers"""
headers = CaseInsensitiveDict(headers)
directives = headers['Cache-Control'].split(',') if headers.get('Cache-Control') else []
if expire_after is not None:
directives.append(f'max-age={get_expiration_seconds(expire_after)}')
if only_if_cached:
directives.append('only-if-cached')
if refresh:
directives.append('must-revalidate')
if force_refresh:
directives.append('no-cache')
if directives:
headers['Cache-Control'] = ','.join(directives)
return headers
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