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# SPDX-FileCopyrightText: 2015 Eric Larson
#
# SPDX-License-Identifier: Apache-2.0
from __future__ import annotations
import calendar
import time
from datetime import datetime, timedelta, timezone
from email.utils import formatdate, parsedate, parsedate_tz
from typing import TYPE_CHECKING, Any, Mapping
if TYPE_CHECKING:
from pip._vendor.urllib3 import HTTPResponse
TIME_FMT = "%a, %d %b %Y %H:%M:%S GMT"
def expire_after(delta: timedelta, date: datetime | None = None) -> datetime:
date = date or datetime.now(timezone.utc)
return date + delta
def datetime_to_header(dt: datetime) -> str:
return formatdate(calendar.timegm(dt.timetuple()))
class BaseHeuristic:
def warning(self, response: HTTPResponse) -> str | None:
"""
Return a valid 1xx warning header value describing the cache
adjustments.
The response is provided too allow warnings like 113
http://tools.ietf.org/html/rfc7234#section-5.5.4 where we need
to explicitly say response is over 24 hours old.
"""
return '110 - "Response is Stale"'
def update_headers(self, response: HTTPResponse) -> dict[str, str]:
"""Update the response headers with any new headers.
NOTE: This SHOULD always include some Warning header to
signify that the response was cached by the client, not
by way of the provided headers.
"""
return {}
def apply(self, response: HTTPResponse) -> HTTPResponse:
updated_headers = self.update_headers(response)
if updated_headers:
response.headers.update(updated_headers)
warning_header_value = self.warning(response)
if warning_header_value is not None:
response.headers.update({"Warning": warning_header_value})
return response
class OneDayCache(BaseHeuristic):
"""
Cache the response by providing an expires 1 day in the
future.
"""
def update_headers(self, response: HTTPResponse) -> dict[str, str]:
headers = {}
if "expires" not in response.headers:
date = parsedate(response.headers["date"])
expires = expire_after(
timedelta(days=1),
date=datetime(*date[:6], tzinfo=timezone.utc), # type: ignore[index,misc]
)
headers["expires"] = datetime_to_header(expires)
headers["cache-control"] = "public"
return headers
class ExpiresAfter(BaseHeuristic):
"""
Cache **all** requests for a defined time period.
"""
def __init__(self, **kw: Any) -> None:
self.delta = timedelta(**kw)
def update_headers(self, response: HTTPResponse) -> dict[str, str]:
expires = expire_after(self.delta)
return {"expires": datetime_to_header(expires), "cache-control": "public"}
def warning(self, response: HTTPResponse) -> str | None:
tmpl = "110 - Automatically cached for %s. Response might be stale"
return tmpl % self.delta
class LastModified(BaseHeuristic):
"""
If there is no Expires header already, fall back on Last-Modified
using the heuristic from
http://tools.ietf.org/html/rfc7234#section-4.2.2
to calculate a reasonable value.
Firefox also does something like this per
https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching_FAQ
http://lxr.mozilla.org/mozilla-release/source/netwerk/protocol/http/nsHttpResponseHead.cpp#397
Unlike mozilla we limit this to 24-hr.
"""
cacheable_by_default_statuses = {
200,
203,
204,
206,
300,
301,
404,
405,
410,
414,
501,
}
def update_headers(self, resp: HTTPResponse) -> dict[str, str]:
headers: Mapping[str, str] = resp.headers
if "expires" in headers:
return {}
if "cache-control" in headers and headers["cache-control"] != "public":
return {}
if resp.status not in self.cacheable_by_default_statuses:
return {}
if "date" not in headers or "last-modified" not in headers:
return {}
time_tuple = parsedate_tz(headers["date"])
assert time_tuple is not None
date = calendar.timegm(time_tuple[:6])
last_modified = parsedate(headers["last-modified"])
if last_modified is None:
return {}
now = time.time()
current_age = max(0, now - date)
delta = date - calendar.timegm(last_modified)
freshness_lifetime = max(0, min(delta / 10, 24 * 3600))
if freshness_lifetime <= current_age:
return {}
expires = date + freshness_lifetime
return {"expires": time.strftime(TIME_FMT, time.gmtime(expires))}
def warning(self, resp: HTTPResponse) -> str | None:
return None
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